Updated on 2024/07/20

写真a

 
SOTA, Takayuki
 
Affiliation
Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Professor
Degree
工学博士 ( 早稲田大学 )
Doctor of Engineering

Research Experience

  • 1990
    -
    1997

    Waseda University, Associate Professor

  • 1988
    -
    1990

    Waseda University, Assistant Professor

  • 1986
    -
    1988

    College of Engineering, Shizuoka University, Assistant Professor

  • 1984
    -
    1986

    Waseda University, Research Assistant

Education Background

  •  
    -
    1986

    Waseda University   Graduate School, Division of Science and Engineering  

Professional Memberships

  •  
     
     

    日本レーザー医学会

  •  
     
     

    応用物理学会

  •  
     
     

    日本物理学会

  •  
     
     

    日本色素細胞学会

  •  
     
     

    日本皮膚悪性腫瘍学会

  •  
     
     

    日本分光学会

▼display all

Research Interests

  • Physical Properties in General(incl. Basic Theories),Solid-State Physics I (Optical Properties, Semiconductor & Dielectrics)

 

Papers

  • Impact of diagenesis and maturation on the survival of eumelanin in the fossil record

    Keely Glass, Shosuke Ito, Philip R. Wilby, Takayuki Sota, Atsushi Nakamura, C. Russell Bowers, Kristen E. Miller, Suryendu Dutta, Roger E. Summons, Derek E. G. Briggs, Kazumasa Wakamatsu, John D. Simon

    ORGANIC GEOCHEMISTRY   64   29 - 37  2013.11

     View Summary

    Melanins are polymeric phenolic pigments classified into two groups based on their chemical structures and molecular precursors: eumelanin (brown-black) and pheomelanin ( yellow-red). Eumelanin is highly resilient and has a proven fossil record, extending back at least similar to 200 Ma. It is widespread in the biological world, occurring in fungi, the ink sacs of cephalopods, the feathers of birds, and the hair, skin, eyes, brain and inner ears of mammals. Although the presence and chemical attributes of fossil eumelanin have been documented, there are few data constraining its long term survival. Here we use a diversity of analytical techniques to compare the chemistry and morphology of fossilized cephalopod ink from three deposits of similar age and lithology, but different maturation histories. We demonstrate that the chemistry of eumelanin begins to alter at the onset of the oil window and is largely independent of age. The decrease in surviving melanin is accompanied by an increase in the relative abundance of organic macromolecular material (kerogen) but, critically for the correct interpretation of fossils, is not accompanied by a consistent change in granule morphology. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI

    Scopus

    44
    Citation
    (Scopus)
  • Hyperspectral screening of melanoma on acral volar skin

    Nagaoka, T, Nakamura, A, Okutani. H, Kiyohara, Y, Koga, H, Saida, T, Sota, T

    Skin Res. Technol.   19 ( 1 ) e290 - e296  2013.01

    DOI

    Scopus

    23
    Citation
    (Scopus)
  • Novel automated screening of age-related macular degeneration

    Yasuyuki Yamauchi, Hiroyuki Kemma, Hiroshi Goto, Atsushi Nakamura, Takashi Nagaoka, Takayuki Sota

    JAPANESE JOURNAL OF OPHTHALMOLOGY   56 ( 6 ) 577 - 583  2012.11

     View Summary

    To determine the objective and quantitative hyperspectral parameters for distinguishing between age-related macular degeneration (AMD) and a normal macula.
    Near-infrared hyperspectral images were taken of 71 eyes of 62 AMD patients with exudative AMD and 21 eyes of 12 control subjects without AMD. The spatial information included a 480 x 321-pixel image in a 50A degrees field located at the ocular fundus and a 720-950-nm-per-pixel reflectance spectrum. Macular vectors were determined as the average spectrum for each macula, and reference vectors were used as average macular vectors for healthy volunteers. Variations in vector length and angle were calculated based on comparison with the reference vector. The AMD differentiation index was a parameter that minimized the plot overlap between AMD patients and controls.
    Statistically significant differences between the AMD patients and controls were noted. Receiver-operating characteristic curve analysis revealed an area under the curve of 0.888. The appropriate threshold values were attained for the proposed discrimination index, including 68 % sensitivity, 95 % specificity and 74 % accuracy.
    This study presents a simplified diagnostic index for the determination of age-related macular degeneration based on near-infrared spectra.

    DOI

    Scopus

    3
    Citation
    (Scopus)
  • First-principles study of spontaneous polarization and band gap bowing in ScxAlyGa1-x-yN alloys lattice-matched to GaN

    Shimada, K, Takouda, M, Hashiguchi, Y, Chichibu, S.F, Hata, M, Sazawa, H, Takada, T, Sota, T

    Semicond. Sci. Technol.   27 ( 10 ) 105014  2012.10

    DOI

  • Signatures of Gamma(1)-Gamma(5) mixed-mode polaritons in polarized reflectance spectra of ZnO

    Ayako Takagi, Atsushi Nakamura, Akira Yoshikaie, So-ichiro Yoshioka, Satoru Adachi, Shigefusa F. Chichibu, Takayuki Sota

    JOURNAL OF PHYSICS-CONDENSED MATTER   24 ( 41 ) 415801  2012.10

     View Summary

    Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Gamma(1) and Gamma(5) excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k perpendicular to a and E parallel to c configurations for an m-plane sample. Theoretical calculations reveal that the mixed-mode polaritons consist of one Gamma(1) transverse mode and two Gamma(5) longitudinal modes. It is also shown that the signatures are sensitive to the valence band ordering.

    DOI

    Scopus

    5
    Citation
    (Scopus)
  • A possible melanoma discrimination index based on hyperspectral data: a pilot study

    Takashi Nagaoka, Atsushi Nakamura, Haruka Okutani, Yoshio Kiyohara, Takayuki Sota

    SKIN RESEARCH AND TECHNOLOGY   18 ( 3 ) 301 - 310  2012.08

     View Summary

    Background Early detection and proper excision of the primary lesions of malignant melanoma (MM) are crucial for reducing melanoma-related deaths. To support the early detection of melanoma, automated melanoma screening systems have been extensively studied and developed. In this article, we present a hyperspectral melanoma screening system and propose a possible melanoma discrimination index derived from the characteristics of the pigment molecules in the skin, both of which have been derived from hyperspectral data (HSD). Methods The index expresses the disordered nature of each lesion including variegation in color based on variation in spectral information obtained from each lesion. Performance of the index in discriminating melanomas from other pigmented skin lesions has been studied in five cases of melanoma (41 HSD sets), one case of Spitz nevus (13 HSD sets), 10 cases of seborrheic keratosis (78 HSD sets), three cases of basal cell carcinoma (16 HSD sets), and nine cases of melanocytic nevus (21 HSD sets), obtained from patients and volunteers, all of whom were Japanese. Results Performance of the index, which reflects the disordered nature of a lesion, discriminates melanomas with a sensitivity of 90%, a specificity of 84%, and an area under the receiver operating characteristic curve of 0.93, on resubstitution. Conclusion An objective melanoma discrimination index at a molecular pigmentary level, derived from HSD, has been proposed, and its performance evaluated. This index was highly successful in discriminating MM from non-melanoma, although the statistical population was small.

    DOI

    Scopus

    40
    Citation
    (Scopus)
  • Direct chemical evidence for eumelanin pigment from the Jurassic period

    Keely Glass, Shosuke Ito, Philip R. Wilby, Takayuki Sota, Atsushi Nakamura, C. Russell Bowers, Jakob Vinther, Suryendu Dutta, Roger Summons, Derek E. G. Briggs, Kazumasa Wakamatsu, John D. Simon

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   109 ( 26 ) 10218 - 10223  2012.06

     View Summary

    Melanin is a ubiquitous biological pigment found in bacteria, fungi, plants, and animals. It has a diverse range of ecological and biochemical functions, including display, evasion, photoprotection, detoxification, and metal scavenging. To date, evidence of melanin in fossil organisms has relied entirely on indirect morphological and chemical analyses. Here, we apply direct chemical techniques to categorically demonstrate the preservation of eumelanin in two >160 Ma Jurassic cephalopod ink sacs and to confirm its chemical similarity to the ink of the modern cephalopod, Sepia officinalis. Identification and characterization of degradation-resistant melanin may provide insights into its diverse roles in ancient organisms.

    DOI

    Scopus

    163
    Citation
    (Scopus)
  • Valence-band-ordering of a strain-free bulk ZnO single crystal identified by four-wave-mixing spectroscopy technique

    K. Hazu, S. F. Chichibu, S. Adachi, T. Sota

    JOURNAL OF APPLIED PHYSICS   111 ( 9 ) 093522  2012.05

     View Summary

    Spectroscopic and temporal four-wave-mixing (FWM) measurements are carried out on a strain-free bulk ZnO single crystal, in order to clarify the valence-band-ordering. Under the collinearly polarized lights with the electric-field component parallel to the c-axis, which can excite dipole-allowed Gamma(1)-excitons, the FWM signal appears only in the energies corresponding to the B-exciton. Under the cross-linear polarization configuration exciting both Gamma(5)- and Gamma(1)-excitons, the FWM signal arising from the two-photon-coherence is absent in the energies corresponding to A-exciton. Both the results indicate that Gamma(1)-exciton state belongs exclusively to B-exciton, meaning that the valence-band ordering is Gamma(9) - Gamma(7) - Gamma(7) in order of decreasing electron energy for the present strain-free ZnO single crystal. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4711103]

    DOI

    Scopus

    8
    Citation
    (Scopus)
  • Mid-infrared vibrational spectroscopic characterization of 5,6-dihydroxyindole and eumelanin derived from it

    Ryosuke Hyogo, Atsushi Nakamura, Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   517 ( 4-6 ) 211 - 216  2011.12  [Refereed]

     View Summary

    Mid-infrared vibrational spectroscopic study has been made on 5,6-dihydroxyindole (DHI) and DHI-derived eumelanin. It has been revealed for DHI monomer that measured infrared absorption spectrum is well reproduced by that predicted from ab initio calculations. Thus, vibrational modes of DHI monomer causing dominant absorption bands have been successfully assigned. It has been also reconfirmed that DHI-derived eumelanin includes indolequinone and/or quinone methide units in addition to DHI units. (C) 2011 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    7
    Citation
    (Scopus)
  • Novel melanoma discrimination index from optical spectra

    Okutani, H, Nakamura, A, Nagaoka, T, Kiyohara, Y, Sota, T

    Skin Cancer   26 ( 1 ) 94 - 97  2011.05

     View Summary

    The ABCD-rule of dermoscopy has increased diagnostic accuracy ; however, some training is required in using it efficiently, and the diagnosis based on morphology is to a large extent subjective as with any clinical diagnosis. Morphology mainly comes from spatial variegation in skin pigmentation, i.e. spatial change in pigment molecular species and their concentration. Optical spectra reflected from the skin carry information about it. An essential feature of melanoma is the variety in morphology of the lesion, which is equivalent to change in spectrum from portion to portion within the lesion. The hyperspectral imaging technique enables one to measure hyperspectral data (HSD) within a short period, which consist of both spatial and spectral information. In this paper, we propose a single melanoma discrimination index derived from HSD using the entropy concept, and demonstrate its usefulness.[Skin Cancer (Japan) 2011 ; 26 : 94-97]

    DOI CiNii

  • Spontaneous polarization and band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaN

    Shimada, K, Zenpuku, A, Fujiwara, K, Hazu, K, Chichibu, S.F, Hata, M, Sazawa, H, Takeda, T, Sota, T

    J. Appl. Phys.   110 ( 074114 )  2011  [Refereed]

    DOI

    Scopus

    10
    Citation
    (Scopus)
  • Photodynamic diagnosis of oral carcinoma using talaporfin sodium and a hyperspectral imaging system: An animal study

    Masashi Migita, Isao Kamiyama, Kenichi Matsuzaka, Atsushi Nakamura, Takayuki Souta, Katsuo Aizawa, Takahiko Shibahara

    Asian Journal of Oral and Maxillofacial Surgery   22 ( 3 ) 126 - 132  2010.09

     View Summary

    The purpose of this study was to examine the efficacy of detecting oral squamous cell carcinoma (SCC) using photodynamic diagnosis (PDD), a highly reliable method for tumor diagnosis, through the use of photosensitizers such as talaporfin sodium. Talaporfin sodium (5mg/kg) was administered to 7 control rats and 43 rats that had ingested the carcinogen 4-nitroquinoline 1-oxide (4NQO). After 8h, tongues were examined by spectral imaging and measurements were made using a hyperspectral imaging system. On each spectral image, macroscopically lesions and normal regions of the tongue were selected. Lesions comprised squamous cell carcinoma (SCC) in 22 cases, carcinoma in situ (CiS) in 9 cases, and dysplasia in 12 cases. The value Δα was determined as the absorbance spectrum of a lesion compared with normal tissue, or as the difference between Δκ at the posterior of the lingual protrusion and Δκ at the anterior of the lingual protrusion in controls. We compared Δα for SCC, CiS, and dysplasia with controls. The value Δα was (2.4±1.78)×10-2 in SCC, (1.2±1.34)×10-2 in CiS, (-0.2±0.49)×10-2 in dysplasia, and (0.21±0.63)×10-2 in controls. Both SCC and CiS showed significant differences from controls (p=0.037 and p=0.021, respectively). Histopathological analysis revealed that proliferating cell nuclear antigen (PCNA) expression increased gradually in the following order: controls, dysplasia, CiS, and SCC. Development of PDD using a hyperspectral imaging system may represent a useful technique for detecting oral SCC. © 2010 Asian Association of Oral and Maxillofacial Surgeons.

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • A melanoma discrimination index based on optical spectra

    Nagaoka, T, Nakamura, A, Aizawa, K, Ohtsubo, S, Kiyohara Y, Sota, T

    Skin Cancer   25 ( 1 ) 81 - 84  2010.05

  • Regioselectivity on the cooxidation of 5,6-dihydroxyindole and its 2-carboxy derivative from the quantum chemical calculations

    Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   490 ( 4-6 ) 226 - 229  2010.04

     View Summary

    We report the heterodimerization of eumelanin precursors from the quantum chemical calculations using a general-purpose reactivity indicator. 5,6-Dihydroxyindole (DHI), its 2-carboxy derivative (DHICA), and related molecules are under consideration. Molecules participating in the reaction have been identified from the electron transfer probability. The heterodimerization has been demonstrated to be the electron-transfer-controlled reaction. The theoretical prediction is in good agreement with the result of the previous cooxidation of DHI and DHICA. (C) 2010 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    6
    Citation
    (Scopus)
  • Identification of extremely radiative nature of AlN by time-resolved photoluminescence

    Onuma, T, Hazu, K, Uedono, A, Sota, T, Chichibu, S.F

    Appl. Phys. Lett.   96(6) Art.No.06906  2010.02

  • Free and bound exciton fine structures in AlN epilayers grown by low-pressure metalorganic vapor phase epitaxy

    Onuma, T, Kosaka, K, Asai, K, Sumiya, S, Shibata, T, Tanaka, M, Sota, T, Uedono, A, Chichibu, S. F

    J. Appl. Phys.   105, Art No.023529  2009.01

  • Possible oxidative polymerization mechanism of 5,6,-didydroxyindole from ab initio calculations

    Okuda, H, Wakamatsu, K, Ito, S, Sota, T

    J. Phys. Chem. A   112(44)   11213 - 11222  2008.11

  • Impact of strain on free-exciton resonance energies in wurtzite AlN

    Ikeda, H, T. Okamura, Matsukawa, K, Sota, T, Sugawara, M, Hoshi, T, Cantu, P, Sharma, R, Kaeding, J.F, Mishra, U. K, Kosaka, K, Asai, K, Sumiya, S, Shibata, T, Tanaka, M, Speck, J.S, DenBarrs, S.P, Nakamura, S, Koyama, T, Onuma, T, Chichibu, S.F

    J.Appl. Phys.   102, artNo.123707  2007.12

  • Atomic distribution in In x Ga 1-x N single-quantum-wells studied by extended X-ray absorption fine structure

    Miyanaga, T, Azuhata, T, Matsuda, S, Ishikawa, Y, Sasaki, S, Uruga, T, Tanida, H, Chichibu, S.F, Sota, T

    Phys. Rev. B/APS   76:Art.No. 035314  2007.07

  • Origin of localized excitons in In-containing three-dimensional bulk (Al, In, Ga)N alloy films probed by time-resolved photoluminescence and monoenergetic positoron annihilation techniques

    Chichibu, S.F, Uedono, A, Onuma, T, Haskell, B.A, Chakraborty, A, Koyama, T, Fini, P.T, Keller, S, DenBaars, S.P, Speck, J.S, Mishra, U.K, Nakamura, S, Yamaguchi, S, Kamiyama, S, Amano, H, Akasaki, I, Han, J, Sota, T

    Philosophical Magazine/Taylor & Francis   87(13), pp.2019-2039  2007.05

  • Mid-infrared absorption spectrum of 5,6-dihydroxyindole-2-carboxylic acid

    Okuda, H, Nakamura, A, Wakamatsu, K, Ito, S, Sota, T

    Chem. Phys. Lett./Elsevier   433(4-6), pp.355-359  2007.01

  • Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors

    Chichibu, S.F, Uedono, A, Onuma, T, Haskell, B.A, Chakraborty, A, Koyama, T, Fini, P.T, Keller, S, DenBaars, S.P, Speck, J.S, Mishra, U.K, Nakamura, S, Yamaguchi, S, Kamiyama, S, Amano, H, Akasaki, I, Han, J, Sota, T

    Nature Material/NPG   5, pp.810-816  2006.10

  • Prospective emission efficiency and in-plane light polarization of nonpolar m-plane InxGa1-xN / GaN blue light emitting diodes fabricated on free-standing GaN substrates

    Koyama, T, Onuma, T, Masui, H, Chakraborty, A, Haskell, B.A, Keller, S, Mishra, U.K, Speck, J., S, Nakamura, S, DenBaars, S. P, Sota, T, Chichibu, S. F

    Appl. Phys. Lett./AIP   89 (9), Art No.091906 1-3  2006.08

  • Improvements in quantum efficiency of excitonic emissions in ZnO epilayers by the elimination of point defects

    Chichibu, S. F, Onuma, T, Kubota, M, Uedono, A, Sota, T, Tsukuazaki, A, Ohtomo, A, Kawasaki, M

    J. Appl. Phys./AIP   99 (9), Art. No. 093505  2006.05

  • Recombination dynamics of a 268 nm emission peak in Al0.53In0.11Ga0.36N/Al0.58In0.02Ga0.40N multiple quantum wells

    Onuma, T, Keller, S, DenBaars, S. P, Speck. J. S, Nakamura, S, Mishra, U. K, Sota. T, Chichibu, S. F

    App. Phys. Lett. /AIP   88, Art. No. 111912  2006.03

  • Conformational properties of and a reorientation triggered by sugar-water vibrational resonance in the hydroxymethyl group in hydrated beta-glucopyranose

    Suzuki T, Kawashima H, Sota T

    J. Phys.Chem. B/ACS   110(5), pp.2405-2418  2006.02

  • Structural fluctuation and dynamics of ribose puckering in aqueous solution from first principles

    Suzuki. T, Kawashima, H, Kotoku, H, Sota, T

    J. Phys. Chem. B/ACS   109(26), pp. 12997-13005  2005.07

  • Circular hydrogen bond networks on the surface of beta-ribofuranose in aqueous solution

    Suzuki, T, Sota, T

    J. Phys. Chem. B/ACS   109(25), pp.12603-12611  2005.06

  • Measurements of exciton-polariton dynamics in ZnO by using nonlinear spectroscopic techniques

    Hazu K, Adachi, S, Sota, T

    J. Luminescence   112;1-4: pp.7-10  2005.04

  • Exciton-polariton spectra and limiting factors for the room-tenperature photoluminescence efficiency in ZnO

    Chichibu, SF, Uedono, A, Tsukazaki, A

    Semicond. Sci. Tech. /IOP   20; 4, pp. S67-S77  2005.04

  • Localized exciton dynamics in nonpolar (1120) InxGa1-xN multiple quantum wells grown on GaN templates prepared by lateral epitaxial overgrowth

    Onuma, T, Chakraborty, A, Haskell, B.A

    Appl. Phys. Lett.   86; 15: Art. No. 151918  2005.04

  • Biexcitons and their dephasing processes in ZnO

    Adachi,S, Hazu, K, Sota, T

    phys. stat. soldi.(c)/Elsevier   2, No.2, pp.890-895  2005.02

  • Limitting factors of room-temperature nonradiative photoluminescence lifetime and nonpolar GaN studied by time-resolved photoluminescence and slow positoron annihilation techniques

    Chichibu, SF, Uedono, A, Onuma, T

    Appl. Phys. Lett./AIP   86 (2), Art. 021914  2005.01

  • Reduced nonradiative defect densities in ZnO epilayers grown on Si substrates by the use of ZnS epitaxial buffer layers

    Onuma, T, Chichibu, SF, Uedono, A

    Appl. Phys. Lett./AIP   85 (23), pp.5586-5588  2004.12

  • Direct comparison of photoluminescence lifetime and defect densities in ZnO epilayers studied by time-resolved photoluminescence and slow positoron annihilation techniques

    Koida, T, Uedono, A, Tsukazaki, A

    Phys. Stat. Solidi A-appl. Res. /Elsevier   201(12), 2841-2845  2004.09

  • Phonon scattering of excitons and biexcitons in ZnO

    Hazu, K, Sota, T, Adachi, S

    J. Appl.. Phys./AIP   96;2,pp.1270-1272  2004.07

  • Improved quantum efficiency in nonpolar (11-20) AlGaN/GaN quantum wells grown on GaN prepared by lateral epitaxial overgrowth

    Koida, T, Chichibu, SF, Sota , T

    Appl. Phys. Lett. /AIP   84;19,pp.3768-3770  2004.05

  • Impact of the k-linear term on nonlinear optical response of the C-exciton manifold in ZnO

    Hazu, K, Torii, K, Sota, T

    J. Appl. Phys./AIP   95;10,pp.5498-5501  2004.05

  • Biexciton formulation and exciton-exciton correlation effects in bulk ZnO

    Adachi, S, Hazu, K, Sota, T

    Semicond. Sci.Technol./IOP   19;4,pp.S276-S278  2004.04

  • Radiative and nonradiative processes in strain-free AlxGa1-xN films studied by time-resolved photoluminescence and positron annihilation techniques

    Onuma, T, Chichibu, SF, Uedono, A

    J. Appl. Phys. /AIP   95;5,pp.2495-2504  2004.03

  • Radiative and nonradiative excitonic transitions in nonpolar (11-20) and polar (000-1) and (0001) ZnO epilayers

    Koida,T, Chichibu, SF, Uedono, A

    Appl. Phys. Lett. /AIP   84;7,pp.1079-1081  2004.02

  • Hydrogen-deuterium exchange effects on beta-endorphin release from AtT20 murine pituitary tumor cells

    Ikeda, M, Suzuki, S, Kishino, M

    Biophysical J./Biophysical Society   86;1, pp.565-575  2004.01

  • Influence of internal electric field on the recombination dynamics of localized excitons in an InGaN double-quantum-well laser diode wafer operated at 450 nm

    Onuma, T, Chichibu, SF, Aoyama, T

    J. Appl. Phys./AIP   42;12,pp.7276-7283  2003.12

  • Exciton-exciton correlation effects on FWM of GaN

    Adachi, S, Sasakura, H, Muto, S

    Phys. Status Solidi/Elsevier   (b)240;2, pp.348-351  2003.11

  • Improving ab initio infrared spectra of glucose-water complexes by considering explicit intermolecular hydrogen bonds

    Suzuki, T, Sota, T

    J. Chem. Phys./AIP   119:19, pp.10133-10137  2003.11

  • Improved Emission Efficiency in InGaN/GaN Quantum Wells with Composition-Graded Walls Studied by Time-Resolved Photoluminescence Spectroscopy

    Onuma,T, Uchinuma, Y, Suh, E-K

    Jpn. J. Appl. Phys./JPSJ   42;11B, pp.L1369 - L1371  2003.11

  • Recombination dynamics of localized excitons in Al1-xInxN epitaxial films on GaN templates grown by metalorganic vapor phase eoutaxy

    Onuma, T, Chichibu, SF, Uchinuma, Y

    J. Appl. Phys./AIP   94;4,pp.2449-2453  2003.08

  • Recombination dynamics of localized excitons in cubic InxGa1-xN/GaN multiple quantum wells grown by rf-MBE on 3C-SiC substrate

    Chichibu, SF, Onuma, T, Aoyama, T

    J. Vac. Sci. Techn. B/AVS   21;4,pp.1856-1862  2003.08

  • Brillouin scattering study of ZnO

    Azuhata, T, Takesada, M, Yagi, T

    J. Appl. Phys./AIP   94;2,pp.968-972  2003.07

  • Strong biexcitonic effects and exciton-exciton correlations in ZnO

    Hazu, K, Sota T, Suzuki, K

    Phys. Rev. B/APS   68;3,Art.No.033205  2003.07

  • Exciton-exciton interaction and hetero-biexciton in GaN

    Adachi, S, Muto, S, Hazu, K

    Phys. Rev. B/APS   67;20,Art.No.205212  2003.05

  • Influence of InN mole fraction on the recombination processes of localized excitons in strained cubic InxGa1-xN/GaN multiple quantum wells

    Chichibu, SF, Onuma, T, Sota, T

    J. Appl. Phys./AIP   93;4,pp.2051-2054  2003.02

  • Polarized photoreflectance spectra of excitonic polaritons in ZnO single crystal

    Chichibu, SF, Sota, T, Cantwell, G

    J. Appl. Phys./AIP   93;1,pp.756-758  2003.01

  • Properties of optical phonons in cubic InxGa1-xN.

    Torii, K, Usukura, N, Nakamura, A

    Appl. Phys. Lett./AIP   82;1,pp.52-54  2003.01

  • Optical properties of Si-, Ge-, and Sn-doped GaN.

    Shikanai, A, Fukahori, H, Kawakami, Y

    Phys. Status Solidi (b)/Elsevier   235;1,pp.26-30  2003.01

  • Correlation between the photoluminescence lifetime and defect density in bulk and epitaxial ZnO

    Koida, T, Chichibu, SF. Uedono, A

    Appl. Phys. Lett./AIP   82;4,pp.532-534  2003.01

  • Recombination dynamics of localized excitons in cubic phase InxGa1-xN/GaN multiple quantum wells on 3C-SiC/Si (001).

    Chichibu, SF, Onuma, T, Kitamura

    Phys. Status Solidi (b)/Elsevier   234;3,pp.746-749  2002.12

  • Orientation and aggregation oc cationic laser dyes in a fluoromica: polarized spectrometric studies

    Iyi, N, Sasai R, Fujita, T

    Appl. Cry Science   22;3,pp.125-136  2002.12

  • Observation of Exciton-Polariton Emissions from ZnO Epitaxial Film on the A-Face of Sapphire Grown by Radical-Source Molecular-Beam-Epitaxy

    Chichibu, SF, Sota, T, Fons, P. J

    Jpn. J. Appl. Phys./IPAP   41;8B,pp.L935-L937  2002.08

  • Excitonic spectra of an AlN epitaxial film on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy

    Onuma, T, Chichibu, S.F, Sota, T

    Appl. Phys. Lett./AIP   81;4,pp.652-654  2002.07

  • Localized exciton dynamics in InGaN quantum well structures

    Chichibu, S. F, Azuhata, T, Okumura, H

    Appl. Surf. Sci.   190;1-4,pp.330-338  2002.05

  • Optical nonlinearities and phase relaxation of excitons in GaN

    Hazu, K, Shikanai, A, Sota, T

    Phys. Rev. B/APS   65;19,Art. No.195202  2002.05

  • Photoreflectance spectra of a ZnO heteroepitaxial film on the nearly lattice-matched ScAlMgO4(0001) substrate grown by laser molecular-beam epitaxy

    Chichibu, S. F, Tsukazaki, A, Kawasaki, M

    Appl. Phys. Lett./AIP   80;16,pp.2860-2862  2002.04

  • Spectroscopic evaluation of glucose concentration in phosphate-buffered saline solution using principal component analysis

    Nakamura, A, Hasegawa, T. Nishijyo, J

    Jpn. J. Appl. Phys./IPAP   41;4B,pp.L440-L442  2002.04

  • Localized exciton dynamics in strained cubic In0.1Ga0.9N/GaN multiple quantum wells

    Chichibu, S. F, Sugiyama, M, Onuma, T

    Appl. Phys. Lett./AIP   79;26,pp.4319-4321  2001.12

  • Band gap bowing and exciton localization in strained cubic InxGa1-xN films grown on 3C-SiC(001) by rf molecular-beam epitaxy.

    Chichibu, S. F, Sugiyama, M, Kuroda, T

    Appl. Phys. Lett./AIP   79;22,pp.3600-3602  2001.11

  • 物性工学

    宗田孝之

    培風館    2001.10

  • Excitonic polariton structures in wurtzite GaN

    Torii, K, Chichibu, S. F, Deguchi, T

    Physica B/Elsevier   302&303;pp.268-276  2001.08

  • Current-modulated electroluminescence spectroscopy and its application to InGaN single-quantum-well blue and green light-emitting diodes

    Azuhata, T, Homma, T, Chichibu, S. F

    Appl. Phys. Lett./AIP   79;8,pp.1100-1102  2001.08

  • Localized excitons in an In0.06Ga0.94N multiple-quantum-well laser diode lased at 400 nm

    Chichibu, S. F, Azuhata, T, Sota, T

    Appl. Phys. Lett./AIP   79;3,pp.341-343  2001.07

  • Impact of internal electric field and localization effect on quantum well excitons in AlGaN/GaN/InGaN light emitting diodes

    Chichibu, S. F, Sota, T, Wada, K

    Phys. Stat. Sol.(a)/Elsevier   183,pp.91-98  2001.01

  • Forward Raman scattering by quasilongitudinal optical phonons in GaN

    Azuhata, T, Ono, M, Torii, K

    J. Appl. Phys/AIP   88;9,pp.5022-5025  2000.11

  • Localized quantum-well excitons in InGaN single-quantum-well amber light emitting diodes

    Chichibu, S. F, Azuhata, T, Sota, T

    J. Appl. Phys/AIP   88;9,pp.5153-5157  2000.11

  • Raman scattering from phonon-polariton in GaN

    Torii, K, Ono, M, Sota, T

    Phys. Rev. B/APS   62;16,pp.10861-10866  2000.10

  • An attenuated total reflection study on surface phonon-polariton in GaN

    Torii, K, Koga, T, Sota, T

    J. Phys.:Condensed Matter/IOP   12;31,pp.7041-7044  2000.08

  • Effective localization of quantum well excitons in InGaN quantum well structures with high InN molar fraction

    Chichibu, S. F, Setoguchi, A, Azuhata, T

    Physica Status Solidi (a) /Elsevier   180;1,pp.321-325  2000.07

  • Application of infrared attenuated total reflection spectroscopy to in situ analysis of atheromatous plaques in aorta

    Nakamura, A, Koga, T, Fujimaki, M

    Jpn. J. Appl. Phys./IPAP   39;6A,ppL.490-492  2000.06

  • Luminescence energy shift and carrier lifetime change dependence on carrier density in In0.12Ga0.88N/In0.03Ga0.97N quantum wells

    Kuroda, T, Tackeuchi, A, Sota, T

    Appl. Phys. Lett./AIP   76;25,pp3753-3755  2000.06

  • No spin polarization of carriers in InGaN

    Tackeuchi, A, Kuroda, T, Shikanai, A

    Physica E./Elsevier   7;3&4,pp1011-1014  2000.05

  • Comparison of optical properties in GaN/AlGaN and InGaN/AlGaN single quantum wells

    Chichibu, S. F, Shikanai, A, Deguchi, T

    Jpn. J. Appl. Phys./IPAP   39;4B,pp.2417-2424  2000.04

  • Chemical bonding properties of cubic III-nitrides semiconductors

    Shimada, K, Sota, T, Suzuki, K

    Progress in Theoretical Physics Supplement/PSJ   138;pp.122-123  2000.04

  • Evidence of localized effects in InGaN single-quantum-well ultraviolet light emitting diodes.

    Chichibu, SF, Wada, K, Mullhauser, J

    Appl.Phys.Lett./AIP   76; 13, pp.1671-1673  2000.03

  • Photoreflectance spectra of excitonic polaritons in GaN substrate prepared by lateral epitaxial overgrowth.

    Chichibu, SF, Torii, K, Deguchi, T

    Appl.Phys.Lett./AIP   76; 12, pp.1576-1578  2000.03

  • Introduction to Nitride Semiconductor Blue Lasers and Light Emitting Diodes

    Taylor & Francis    2000

  • A pump and probe study on photoinduced internal field screening dynamics in an AlGaN.GaN single quantum well structure.

    Shikanai, A, Deguchi, T, Sota, T

    Appl.Phys.Lett./AIP   76; 4, pp.454-456  2000.01

  • Comparison of optical properties in GaN and InGaN quantum well structures.

    SPIE Proceedings Series   3896, pp.98-106  1999.12

  • Properties of quantum well excitons in GaN/AlGaN and InGaN/GaN/AlGaN UV, blue, green, and amber light emitting diode structures.

    Physica Status Solidi (a)/WILLEY-VCH   75; 1, pp.2076-2073  1999.11

  • Optical properties of an InGaN active layer in ultraviolet light emitting diode.

    Jpn.J.Appl.Phys./JJAP   38; 9A/B, pp.L975-L977  1999.09

  • Quantum-confined Stark effect in an AlGaN/GaN single quantum well structure.

    Jpn.J.Appl.Phys./JJAP   38; 8B, pp.L914-L916  1999.08

  • Reflectance and emission spectra of excitonic polaritons in GaN.

    Phys.Rev.B/APS   60; 7, pp.4723-4730  1999.08

  • Structural and vibrational properties of GaN substrate.

    J.Appl.Phys./AIP   86; 4, pp.1860-1866  1999.08

  • Brillouin scattering study of bulk GaN.

    J.Appl.Phys./AIP   85; 12, pp.8502-8504  1999.06

  • Optical properties of InGaN quantum wells.

    Material Sciences and Engineering B/Elsevier   59, pp.298-306  1999.05

  • GaN基板の光学フォノンII

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.421  1999.03

  • InGaN量子井戸における電界効果とエネルギーギャップ不均一性

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.403  1999.03

  • Si添加障壁層を有するInGaN量子井戸の光学的特性

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.406  1999.03

  • LEO-GaN上に成長したGaN単膜、InGaN量子井戸の光学的特性

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.402  1999.03

  • InGaN/AlGaN単一量子井戸のゲインスペクトロスコピー

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1999.03

  • GaN/AlGaN単一量子井戸における量子閉じ込めシュタルク効果

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.398  1999.03

  • GaNのRashba-Sheka-Pikus価電子帯パラメータ

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.399  1999.03

  • InGaNのキャリアのスピン分極

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.406  1999.03

  • Emission mechanisms of GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth.

    Appl. Phys. Lett./AIP   74; 10, pp.1460-1462  1999.03

  • Infrared Lattice Absorption in Wurtzite GaN.

    Jpn J. of Appl. Phys., Part 2/JJAP   38; 2B, pp.L151-L153  1999.02

  • Spectroscopic studies in InGaN quantum wells.

    MRS Internet J.Nitride Semicond. Res./MRS   4S1, G2.7  1999.01

  • First-principles study on piezoelectric constants in strained BN, AlN, and GaN.

    Jpn. J. Appl. Phys., Part 2/JJAP   37; 12A, pp.L1421-L1423  1998.12

  • First-principles study on electronic and elastic properties of BN, AlN,and GaN.

    J. Appl. Phys./AIP   84; 9, pp.4951-4958  1998.11

  • Effective bandgap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures.

    Appl. Phys. Lett./AIP   73; 14, pp.2006-2008  1998.10

  • h-GaNのブリルアン散乱II

    日本物理学会講演概要集/日本物理学会   53; 2-2, p.275  1998.09  [Refereed]

  • GaN基板の光学的特性(1)

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.300  1998.09

  • GaN基板の光学フォノン

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.300  1998.09

  • タンデムファブリ・ペローを用いたGaNのブリルアン散乱II

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.297  1998.09

  • BN, AlN, GaNの圧電定数の歪み依存性

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.297  1998.09

  • Exciton localization in InGaN quantum well devices.

    J. Vac. Sci. Technol. B/AVS   16; 4, pp.2204-2214  1998.07

  • Optical properties of InGaN quantumwells.

    European Materials Research Society, 1998 Spring Meeting   Session L: III-V Nitrides  1998.06

  • Optical properties of InGaN quantumwells.

    European Materials Research Society, 1998 Spring Meeting   Session L: III-V Nitrides  1998.06

  • Luminescence spectra from InGaN multi-quantum wells heavily doped with Si.

    Appl. Phys. Lett./AIP   72; 25, pp.3329-3331  1998.06

  • InGaNの時間分解スペクトロスコピー(1)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.406  1998.03

  • InGaNの光学的特性(10)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1998.03

  • InGaNの光学的特性(9)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1998.03

  • InGaNの光学的特性(8)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1998.03

  • BN, AlN, GaNの圧電定数

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.348  1998.03

  • Gain spectroscopy of continuous wave InGaN multi-quantum well laser diodes.

    Semicond. Sci. Technol./IOP   13;1, pp97-101  1998.01

  • Constant-pressure first-principles molecular dynamics study on BN, AlN, and GaN.

    Mat. Res. Soc. Symp. Proc./MRS    1997.12

  • CuAlSe2の格子力学

    日本物理学会講演概要集/日本物理学会   2, p.259  1997.10

  • CuAlSe2における2フォノン吸収スペクトルと格子力学

    第58回応用物理学会学術講演会講演予稿集/応用物理学会   3, p.1334  1997.10

  • InGaNの光学的特性(7)

    第58回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.256  1997.10

  • InGaNの光学的特性(6)

    第58回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.256  1997.10

  • Gain spectroscopy of continuous wave InGaN multi-quantum well laaser diodes with different degree of compositional fluctuation.

    Proceedings of ICNS'97/ICNS'97   S-8, pp466-467  1997.10

  • Exciton-phonon interaction in wurtzite GaN epilayers.

    Proceedings of ICNS'97/ICNS'97   Th1-6, pp.426-427  1997.10

  • Ab initio study on electronic band structures and related properties of III-nitrides.

    Proceedings of ICNS'97/ICNS'97   P2-34, pp.304-305  1997.10

  • Photoreflectance and photoluminescence spectra of tensile-strained wurtzite GaN epilayers.

    Proceedings of ICNS'97/ICNS'97   P2-33, pp.302-303  1997.10

  • Optical absorption coefficient in wurtzite GaN.

    Proceedings of ICNS'97/ICNS'97   P2-32, pp.300-301  1997.10

  • Bright emission due to recombination of localized excitons in InGaN bulk and quantum well devices.

    Proceedings of ICNS'97/ICNS'97, Tu3-2   pp198-199  1997.10

  • Monochromated Cathodoluminescence Mapping of InGaN Single Quantum Wells.

    Proceedings of ICNS'97/ICNS'97   P1-LN-11, p186  1997.10

  • Gain spectra in cw InGaN/GaN MQW laser diodes.

    Materials Science and Engineering B/Elsevier Science   50, pp.251-255  1997.06

  • Nanosecond pump-and-probe study of wurtzite GaN.

    Materials Science and Engineering B/Elsevier Science   50, pp.180-182  1997.06

  • Urbach-Martienssen tails in a wurtzite GaN epilayer.

    Appl. Phys. Lett. /AIP   70;25, pp.3440-3442  1997.06

  • Luminescences from localized states in InGaN epilayers.

    Appl. Phys. Lett. /AIP   70;21, pp.2822-2824  1997.05

  • Optical properties of tensile-strained wurtzite GaN epitaxial layers.

    Appl. Phys. Lett. /AIP   70;16, pp.2085-2087  1997.04

  • Valence band physics in wurtzite GaN.

    Mat. Res. Soc. Symp. Proc./MRS   468, pp,445-456  1997.04

  • InGaN量子井戸における励起子の局在化

    第44回応用物理学関係連合講演会講演予稿集   第0分冊  1997.03

  • MOCVD成長h-GaN/sapphireの光学的特性VIII-時間分解分光(1)-

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03

  • ワイドギャップ化合物半導体のUrbach's Tail (1)-h-GaN-

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03

  • 引っ張り歪みh-GaNのフォトリフレクタンスおよびフォトルミネッセンス

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03

  • InGaNの光学的特性(5)

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03

  • Exciton Spectra of Cubic and Hexagonal GaN Epitaxial Films

    Jpn. J. Appl. Phys.   36;3B  1997.03

  • Brillouin Scattering Study of Gallium Nitride: Elastic Stiffness Constants

    J. Phys.: Condens. Matter   9;1  1997.01

  • Biaxial Strain Dependence of Exciton Resonance Energies in Wurtzite GaN

    J. Appl. Phys.   81;1  1997.01

  • Recombination of Localized Excitons in InGaN Single- and Multi-Quantum Well Structures

    Proceedings of MRS '96 Fall Meetings   N1.7  1996.12

  • Spontaneous Emission of Localized Excitons in InGaN Single- and Multi-Quantum Well Structures

    Appl. Phys. Lett.   69;27  1996.12

  • BN、AlN、GaNの弾性定数

    日本物理学会1996年秋の分科会講演概要集   第2分冊  1996.10

  • Defect Structure Model of LiNbO<SUB>3</SUB>:Sc<SUB>2</SUB>O<SUB>3</SUB>

    J. Phys.: Condens. Matter   8;37  1996.09

  • MOCVD成長h-GaN/sapphireの光学的特性VII-光吸収スペクトル(2)-

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09

  • InGaNの光学的特性(4)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09

  • InGaNの光学的特性(3)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09

  • InGaNの光学的特性(2)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09

  • InGaNの光学的特性(1)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09

  • Defect Structure Model of LiNbO3:Sc2O3

    J. Phys.: Condens. Matter   8;37  1996.09

  • Effects of Biaxial Strain on Exciton Resonance Energies of Hexagonal GaN

    Appl. Phys. Lett.   68;26  1996.06

  • Optical Phonons in GaN

    Physica   B219&220;1-4  1996.04

  • Elastic Constants of III-V Compound Semiconductors: Modification of Keyes Relation

    J. Phys.: Condens. Matter   8;18  1996.04

  • Brillouin Scattering Study in the GaN Epitaxial Layer

    Physica   B219&220;1-4  1996.04

  • Lattice Dynamics of CuAlS2 and CuAlSe2

    Physica   B219&220;1-4  1996.04

  • Sc2O3添加LiNbO3の欠陥構造モデル

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • ストイキオメトリー組成LiNbO3の光学的特性

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • K2O添加融液によるLiNbO3ストイキオメトリー単結晶の育成と評価

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • CuInSe2薄膜の光吸収スペクトルの解析

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • タンデムファブリ・ペローを用いたGaNのブリルアン散乱

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • MOCVD成長h-GaNのフォトリフレクタンススペクトル

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • MOCVD成長h-GaNのフォトリフレクタンススペクトル (2)

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • Excitonic Emission from Hexagonal GaN Epitaxial Layers

    J. Appl. Phys./American Institute of Physics   79;5  1996.03

  • Contribution of Excitons in the Photoluminescence Spectra of h-GaN Epitaxial Layers Grown on Sapphire Substrates by TF-MOCVD

    Proceedings of the International Symposium on Blue Laser and Light Emitting Diodes/Ohmsha    1996.02

  • GaNのブリルアン散乱

    日本物理学会1995年秋の分科会    1995.09

  • GaPの格子力学-2フォノン状態密度

    日本物理学会1995年秋の分科会    1995.09

  • AlNの格子力学

    日本物理学会1995年秋の分科会    1995.09

  • GaNのブリルアン散乱

    日本物理学会1995年秋の分科会    1995.09

  • MOCVD成長h-GaN/Sapphireの光学特性VI-光吸収スペクトル

    1995年第56回応用物理学会学術講演会    1995.08

  • MOCVD成長h-GaN/Sapphireの光学特性V-フォトルミネッセンススペクトル

    1995年第56回応用物理学会学術講演会    1995.08

  • MOCVD成長h-GaN/Sapphireの光学特性IV-フォトリフレクタンススペクトル (2)

    1995年第56回応用物理学会学術講演会    1995.08

  • CuAlS2エピタキシャル層からの可視・紫外フォトルミネッセンス

    1995年第56回応用物理学会学術講演会    1995.08

  • Defect Structures in LiNbO3

    J. Phys.: Condens. Matter/Institute of Physics   7;18  1995.05

▼display all

Research Projects

  • 古い指紋の顕在化と経時変化メカニズムの解明

    Project Year :

    2017.04
    -
    2020.03
     

     View Summary

    昨年までに、可視ハイパースペクトルイメージャ(HSI)を用いて2重指紋を撮影し、主成分分析(PCA)と多変量波形分解法-繰返し最小二乗法(MCR-ALS)を用いて指紋の分離を行ってきた。本年度は、MCR-ALSと同じく非負のスペクトル分解法である非負値行列因子分解(NMF)を用いて、重畳指紋の分離を行った。その結果、分離の精度はMCR-ALSより若干低かったが、短い時間で収束されることが分かった。実際の指紋検出に使用する際には、状況に応じて使い分けることが望ましいと考えられた。また、二重指紋の分離確率向上、さらには多重指紋の分離を可能とする最適アルゴリズムを探索すべく、スペクトル分離における指導原理や具体的な方法論を多角的に調べ、導入のための検討を行った。昨年度、指紋を構成する物質の一つであるアミノ酸のトリプトファンの経時変化を調べ、1年の時間経過の後に質量数が変化することを示した。本年度は、トリプトファン(Trp)の代謝経路の一つであるキヌレニンの蛍光特性を調べ、1年経過したTrp及び調製直後のTrpと比較した。450nm, 505nmのLED及び532nmのレーザを光源として、HSIを用いて蛍光スペクトルの取得を行った。その結果、調製直後のTrpは長波長側にピークがあり、蛍光強度も低かった。一方、キヌレニンの蛍光特性は、蛍光中心波長、半値幅、蛍光強度ともに、1年経過したTrpと似た傾向を示した。以上のことから、Trpの代謝経路の一つであるキヌレニンが、古い指紋において蛍光が強くなる原因の一つと考えられた。一部ではあるが、指紋成分の経時変化のメカニズムについて知見を得ることができた。昨年度に引き続き2重指紋の分離実験を行った。多変量解析法の一つであり、非負のスペクトル分解法である非負値行列因子分解(NMF)による解析を行い、多変量波形分解法-繰返し最小二乗法(MCR-ALS)や主成分分析法(PCA)による解析と比較した。NMFはMCR-ALSより鮮明度は若干劣っていたが、収束時間が早いという利点があった。実際の指紋検出で使用する際は、状況に応じて使い分けすることが望ましいと考えられた。調査したMCRからNMFに至るスペクトル分離/分解の方法論開発研究論文では、対象混合物を構成する成分のスペクトルと混合割合は既知のものであった。提案手法の有効性を示すには必要な問題設定と考えられる一方で、その汎用性については、常に保証されるものでないと考えられた。潜在指紋のハイパースペクトル・データをスペクトル分解する困難さは、参照スペクトルの欠如にある。定評のあるオープンソースプログラムを単に利用するだけではなく、初期値設定に始まる様々な段階、過程でのアルゴリズム最適化による、プログラムのカスタマイズが必須であると考えられた。指紋の主成分の一つであるアミノ酸のトリプトファンの蛍光特性の経時変化を調べ、時間が経つとトリプトファンの代謝経路の一つであるキヌレニンに変化することが示唆された。空調の故障により温度・湿度を一定に保つことができなくなったため、環境に応じた指紋の経時変化の実験を行うことができなかった。次年度に行う予定である。研究期間を延長したため、経時変化に関する実験を行う。トリプトファンの経時変化について分光光度計により蛍光特性の測定を行う。NMFのオープンソースプログラムを、蓄積している潜在指紋ハイパースペクトルデータの分離/分解に適するようにカスタマイズする。学会等での成果発表および論文作成を行い、研究のまとめを行う

  • Helicon-wave-excited-plasma sputtering epitaxy of polariton laser structures for room temperature operation

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2010.04
    -
    2014.03
     

    CHICHIBU Shigefusa, SOTA Takayuki, UEDONO Akira, HAZU Kouji, FURUSAWA Kentaro

     View Summary

    A cavity-coupled exciton-polariton laser, namely cavity-polariton laser, has been attracting attention as a new generation low-threshold current density coherent light source composed of a semiconductor microcavity. In the present research, a microcavity composed of a ZnO active region sandwiched by pairwise distributed Bragg reflectors (DBRs) that most likely operates at room temperature was fabricated using a uniquely designed Helicon-Wave-Excited Plasma Sputtering (HWPS) method, which enables to grow high quality epitaxial semiconductor films. We eventually observed an enhanced emission peak at around 3.25 eV, which originates from an exciton-polariton emission coupled with a cavity mode. We therefore conclude that a way to fabricate new functional quantum heterostructures and to characterize them was cut open using the growth, fabrication, and characterization methods developed by this research project

  • Helicon-wave-excited-plasma sputtering epitaxy of polariton laser structures for room temperature operation

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2010.04
    -
    2014.03
     

    CHICHIBU Shigefusa, SOTA Takayuki, UEDONO Akira, HAZU Kouji, FURUSAWA Kentaro

     View Summary

    A cavity-coupled exciton-polariton laser, namely cavity-polariton laser, has been attracting attention as a new generation low-threshold current density coherent light source composed of a semiconductor microcavity. In the present research, a microcavity composed of a ZnO active region sandwiched by pairwise distributed Bragg reflectors (DBRs) that most likely operates at room temperature was fabricated using a uniquely designed Helicon-Wave-Excited Plasma Sputtering (HWPS) method, which enables to grow high quality epitaxial semiconductor films. We eventually observed an enhanced emission peak at around 3.25 eV, which originates from an exciton-polariton emission coupled with a cavity mode. We therefore conclude that a way to fabricate new functional quantum heterostructures and to characterize them was cut open using the growth, fabrication, and characterization methods developed by this research project

  • Helicon-wave-excited-plasma sputtering epitaxy of polariton laser structures for room temperature operation

    Project Year :

    2010
    -
    2013
     

     View Summary

    A cavity-coupled exciton-polariton laser, namely cavity-polariton laser, has been attracting attention as a new generation low-threshold current density coherent light source composed of a semiconductor microcavity. In the present research, a microcavity composed of a ZnO active region sandwiched by pairwise distributed Bragg reflectors (DBRs) that most likely operates at room temperature was fabricated using a uniquely designed Helicon-Wave-Excited Plasma Sputtering (HWPS) method, which enables to grow high quality epitaxial semiconductor films. We eventually observed an enhanced emission peak at around 3.25 eV, which originates from an exciton-polariton emission coupled with a cavity mode. We therefore conclude that a way to fabricate new functional quantum heterostructures and to characterize them was cut open using the growth, fabrication, and characterization methods developed by this research project.

  • Dominant factors influencing dielectric properties in several biodegradable polymers

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2008
    -
    2010
     

    OHKI Yoshimichi, TANAKA Toshikatsu, SOTA Takayuki, HIRAI Naoshi

     View Summary

    For typical biodegradable polymers, namely, polyethylene terephthalate succinate, polybutylene succinate, polycaprolactone, polybutylene succinate adipate, polybutylene adipate terephthalate, starch ester, and poly-L-lactic acid, effects of the crystal structure on their dielectric properties were examined by conducting advanced measurements such as photoluminescence using synchrotron radiation, terahertz time domain spectroscopy, and numerical calculations using density functional theory. As a result, much knowledge was obtained on the dominant factors influencing the dielectric properties of biodegradable polymers. This will greatly contribute to the development of eco-friendly dielectric materials.

  • Epitaxial growth and fabrication of microcavities by the helicon-wave-excited-plasma sputtering method

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2007
    -
    2009
     

    CHICHIBU Shigefusa, UEDONO Akira, SOTA Takayuki, SUGIYAMA Mutsumi

     View Summary

    A cavity polariton laser is attracting attention as a new generation coherent light source composed of a semiconductor microcavity. In the present research, epitaxial growth of single crystalline ZnO and MgZnO films exhibiting atomically flat surfaces and abrupt heterointerfaces was carried out using an uniquely designed 'helicon-wave-excited-plasma sputtering epitaxy (HWPSE)' method, in order to assess if ZnO microcavities can be prepared by the method. The epilayer properties resemble those of the films grown using conventional advanced epitaxial growth methods such as molecular beam epitaxy and metalorganic vapor phase epitaxy. In addition, anatase phase Nb-doped TiO_2 films, a new transparent conducting oxide having the refractive index close to GaN, were epitaxially grown. The findings that those new functional semiconductor epilayers can be grown by the inexpensive HWPSE method may cut open the way to fabricate semiconductor heterostructure quantum devices at a low price

  • Active Compensation of the substrate temperature for the growth of high quality II-VI compound films

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2004
    -
    2007
     

    KOBAYASHI Masakazu, HORIKOSHI Yoshiji, UTAKA Katsuyuki, SOUTA Takayuki

     View Summary

    Active compensation of the substrate temperature during the MBE growth of wide bandgap II-VI alloy materials were further applied for various complicated structures, namely superlattices, and delta-doping structures.Different from conventional III-V compound semiconductors such as GaAs, the materials property is significantly affected by the substrate temperature. II-VI wide bandgap compounds were usually grown under lower temperatures than Ga As and related materials, perturbation of the substrate temperature during the growth would cause the deterioration of the film quality of the epitaxial layer. In this research project, heater was introduced to the MBE chamber at the location of source material cells. The substrate temperature perturbation would take place when the cell shutter was opened so that the molecular beam would be introduced toward the substrate since the heat irradiation from the hot cell would take place. The additional heater was to cancel the heat irradiation from the source material cell when those shutters were closed.High quality ternary compound of ZnMgCdS layers were previously grown using this active compensation technique. This technique was also applied for the growth of superlattice structures, namely ZnMgS/ZnCdS, and ZnSe/MgCdS. Uniform layers structure was confirmed by TEM measurement and narrower X-ray diffraction FWHM were obtained by introducing the active compensation technique. This technique was further introduced for the growth of ZnTe homoepitaxial layer where complicated shutter sequence was introduced to form the delta co-doping structure. The PL properties were improved by using this active compensation technique.This active compensation of the substrate is a powerful tool to obtain the high quality II-VI epitaxial layers by MBE

  • Structures and Generation Mechanisms of Defects in High-k Dielectric Films for Silicon ULSIs

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2004
    -
    2006
     

    OHKI Yoshimichi, HAMA Yoshimasa, SOTA Takayuki

     View Summary

    For the coming sub-65 nm complementary metal-oxide-semiconductor (CMOS) technology, high-k materials such as hafnia (HfO_2), hafnium silicate (Hf_xSi_<1-x>O_y), zirconia (ZrO_2), and zirconium silicate (Zr_xSi_<1-x>O_y) are expected to take the place of SiO_2 as the basic material for gate dielectrics. However, there is a high possibility that a lot of localized states due to defects are present in the band gap of these high-k candidates. These localized states are assumed to cause various dielectric malfunctions such as high leakage current, low breakdown voltage, and threshold variation. Therefore, detailed and systematic research on the localized states is indispensable to understand the effects of the defects on electrical properties.
    From this viewpoint, we have carried out basic studies on HfO_2, Hf_xSi_<1-x>O_y, ZrO_2, and ZrxSi_<1-x>O_y, using photoluminescence (PL) as a common tool that can provide fundamental information about the band gap energy and localized states. X-ray photoelectron spectroscopy (XPS) analyses were also carried out to investigate the band profiles. Furthermore, the effects of postannealing on the electrical properties of the high-k materials were also studied.
    Energy band profiles were investigated by XPS for amorphous hafnia and hafnium silicate films sandwiched between an evaporated Au electrode and a Si substrate. Valence band offset and conduction band offset decrease until they become almost constant with an increase in hafnium content at both Si and Au sides. In literature, similar decrease in the valence band offset was reported in zirconium silicate.
    Photoluminescence spectra induced by UV photons were measured for amorphous hafnia and zirconia deposited by plasma-enhanced chemical-vapor deposition, amorphous hafnia deposited by pulse laser deposition, and crystalline yttria-stabilized zirconia (YSZ). A PL peak appears around 2.7 to 2.9 eV similarly in all hafnia and zirconia samples, irrespective of the difference in crystallinity, oxygen deficiency, source alkoxide, deposition method, or the substrate material. The decay profile of the PL is also similar in all the samples. These results indicate that the PL is inherent in hafnia and zirconia, and is not due to impurities, oxygen vacancy, or interface defects between the sample and the substrate. From PL excitation (PLE) and vacuum-ultraviolet (VUV) absorption measurements, the PL was found to be excited by UV photons to tail states at the band edges. When the samples were annealed at 900℃, a new PL peak appears around 4.2 eV in all the samples except YSZ. The PLE and VUV absorption measurements indicate that the 4.2-eV PL is excited due to the interband absorption.
    Mechanisms of PLs induced in hafnium and zirconium silicates were also discussed. A broad PL spectrum was observed from 2.0 to 5.0 eV similarly in both silicates. This PL has two components with peaks around 2.8 to 3.0 eV and 3.8 eV for hafnium silicates and those around 2.7 to 3.0 eV and 3.8 eV for zirconium silicates. Time-resolved PL and PL decay measurements indicate that the origin of the PL component around 2.7(2.8) to 3.0 eV is the same as that of the PL component around 2.7 to 2.9 eV in hafnia and zirconia. Furthermore, PLE and VUV absorption measurements show that both the PL components around 2.7(2.8) to 3.0 eV and 3.8 eV are excited to tail states at the band edges. Through these studies, it is assumed that hafnium silicate, zirconium silicate, hafnia, and zirconia have luminescent centers in their band gaps with their respective upper and lower states that have a certain fixed energy difference irrespective of the hafnium or zirconium content.
    Furthermore, effects of postannealing on the electrical properties of hafnium and zirconium silicates were investigated. When the samples were postannealed in nitrogen monoxide (NO). leakage current and capacitance-voltage (C-V) hysteresis width are decreased drastically. From ESR measurement, it is assumed that paramagnetic defects at the interface between the sample and the Si substrate are responsible for the leakage current and the C-V hysteresis. Furthermore, depth profile by XPS shows that the postnitridation effectively terminates these interface defects and contributes to the improvement in electrical properties.

  • Electron Quantum Correlation in in Semiconductor Quantum-Dot lattice Structures

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2002
    -
    2004
     

    HORIKOSHI Yoshiji, SOTA Takayuki, ONOMITSU Koji, PLOOG Klaus

     View Summary

    Important quantum correlation effects such as quantum Hall effect and fractional quantum Hall effect have been revealed using the semiconductor two-dimensional electron system. In this system, applications to practical devices such as high speed FETs and lasers have also been achieved. In the lower dimensional systems, however, no prominent progress has been achieved in both fundamental research and device applications. A major reason to this lies on their poor geometrical accuracy. In the two-dimensional structures, the thickness of each layer has atomic size accuracy. However, in one- and zero-dimensional structures, side walls are quite rough. Moreover, structures produced by bottom-up.self-assembly process suffer from inhomogeneity and random distribution. In the present research, therefore, we adopted area-selective epitaxy by combining with e-beam lithograph and migration-enhanced epitaxy(MEE). We have succeeded in fabricating high quality one-dimensional electron wires and quantum dot lattices with AlGaAs/GaAs, InAs/GaAs, and InGaAs/GaAs. Atomically flat side walls of nano-structures are formed by utilizing micro-facet structures. To fabricate accurately the structures with designed ones, lateral growth should be minimized. This has been accomplished by optimizing the MEE deposition sequence. One dimensional wires exhibit ballistic transport characteristics. Two dimensional quantum dot lattices show unique transport characteristics. They have proved useful also for two-dimensional photonic crystals

  • 生体・医療光学の基礎的研究

    文部科学省 

    Project Year :

    1999
    -
    2003
     

  • Mechanism of refractive index increase in silica glass for the development of fiber-optic photodevices

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2000
    -
    2002
     

    OHKI Yoshimichi, KATO Hiromitsu, SATO Takayuki, HAMA Yoshimasa

     View Summary

    The refractive index change induced in a transparent material by UV photon or ion irradiation promises direct drawing of a waveguide that can be used as optical gratings. Structural changes in silica glass induced by ion microbeam were evaluated using microscopic photoluminescence and Raman scattering, and optical and atomic force microscopes (AFM) measurements. The AFM measurements on the microbeam irradiated area show the formation of a groove on the surface. In addtion, a cross sectional observation on the surface parallel to the incident plane reveals surface deformation along the ion tracks, which is deepest at the projected range of ions. Taking into account the possible structural changes of silica induced by energy deposition, the measured topological changes at the front and side surfaces result from internal compaction of silica glass. Refractive index changes were estimated from the Lorentz-Lorenz relationship using the distribution of the internal compaction estimated by the AFM measurements. A small refractive index change was observed along the ion tracks besides a much stronger index change at the projected range, suggesting that energy depositions by the ionization as well as by the atomic collision should be taken into account.
    It has also become clear that the refractive index change can be induced by UV photons from a KrF excimer laser in a-SiO_x N_y : H films prepared by PECVD. Fabrication of a diffraction grating was performed using a phase mask made of a high quality fused silica plate. The surface of the fabricated grating observed by scanning electron microscopy (SEM). A clear square-toothed pattern with periodicity of around 1 μm can be observed. Furthermore, from the Fraunhofer diffraction pattern, the periodicity of the grating pattern was estimated to be around 1 μm, which agrees with the SEM image. This simply demonstrates that a-SiO_xN_y : H can be processed by UV photon irradiation.

  • Joint Research on Noninvasive measurement of Blood Glucose

    Project Year :

    2000
     
     
     

  • フォトニクスと先端光子材料開発

    文部科学省 

    Project Year :

    1996
    -
    2000
     

  • Defect detection and structure analysis in silica thin films by use of photoluminescence

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1997
    -
    1999
     

    OHIKI Yoshimichi, SOTA Takayuki, HAMA Yoshimasa

     View Summary

    Amorphous silica, a key material in the modern high-tech society. Is widely used as an insulating layer for a semiconductor device or as an optical fiber. In the present research, the effects of point defects such as impurities or vacaancies in the silica film on the electrical and optical properties have been systematically studied. The point defects were detected by photoluminescence, ESR, FT-IR, visible-VUV absorption, EPMA and SIMS. Electrical properties are examined by high-field conduction. Dielectric breakdown, and C-V measurement. Knowledge on the presence of oxygen vacancy and the estimation of its concentration, structural stabilization by impurity doping, and the relation between the defect concentration and the synthesis method has been obtained. In 1997, we demonstrated tha clear photoluminescence can be obtained in this amorphous SiOィイD22ィエD2 film by using an intense photon source such as an excimer laser or synchrotron radiation. This indicates that photoluminescence can be a strong tool to detect point defects in a-SiOィイD22ィエD2. Using this method, point defects in thermal silicon dioxide and SIMOX buried oxide and those induced in these oxides by ion implantation and heat treatment have been detected. The structures of these defects have also been identified. In 1998, researches were extended to fluorine-doped SiOィイD22ィエD2 film, SIMOX oxide, and silicon nitride film, and the structures of point defects in these materials were clarified. The effect of point defects on the dielectric strength was also examined by measuring the breakdown voltage. In 1999, researches were further extended to a-SiNィイD2xィエD2 a-SiOィイD2xィエD2NィイD2yィエD2, and TaィイD22ィエD2OィイD25ィエD2 films, focusing on the effects of ion implantation and heat treatment on the concentration of point defects. Photochemical reactions responsible for the formation of optical fiber grating in Ge-doped silica glass have been also clarified. Furthermore, stable and high-efficient fabrication method of optical fiber grating by use of ion implantation has bee proposed.

  • Point Defects in Ge-doped SiO_2 Glass-Their Structures and Roles in Nonlinear Optical Effects

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1994
    -
    1995
     

    OHKI Yoshimichi, SOTA T., HAMA Yoshimasa

     View Summary

    (1) The generation mechanism of the absorption changes, which cause a photorefractive change through the Kramers-Kronig relation in Ge-doped SiO_2 glass, has not been clarified yet. In the present paper, we examined the laser-power dependence of the absorption changes around 5 eV,induced by a KrF excimer laser. The induced absorption around 5 eV is composed of three different components, centering at 4.50,5.08, and 5.80 eV.The increasing behavior of each absorption component depends strongly on the energy density. The three absorption components reach different saturation levels, depending on the energy density. Furthermore the absorption induced by a high-power KrF excimer laser is bleached by a laser, the energy density of which is about one-twentieth of the inducing laser. Combining the results of mathematical analysis, it was found that a two-photon process and a one-photon process are, respectively, involved with the induction and the bleach of each absorption. It was also found that the precursor defects, which causes the absorption change, is of an oxygen-deficient type.
    (2) Optical absorption change in the microsecond order in oxygen-deficient Ge-doped silica glass was measured as a function of time just after photon irradiation from a KrF excimer laser. The absorption above 3 eV was found to decay with the same time constant as that of the luminescence at 3.1 eV.From this, it is confirmed that the observed absorption change is due to the excitation of electrons from the lowest excited triplet state to an upper state.
    (3) Defects in buried SiO_2 films in Si formed by implantation of oxygen ions were characterized by photoluminescence (PL) excited by KrF (5.0 eV) excimer laser and synchrotron radiation. Two PL bands were observed at 4.3 and 2.7 eV.The 4.3 eV band has two PL excitation bands at 5.0 and 7.4 eV,and its decay time is 4.0 ns for the 5.0 eV excitation and 2.4 ns for the 7.4 eV excitation. The decay time of the 2.7 eV PL band is found to be 9.7 ms. These results are very similar to those for the 4.3 eV and the 2.7 eV PL bands, which are observed in bulk silica glass of an oxygen-deficient type and attributed to the oxygen vacancy. Through the change in the PL intensity with the film thickness, the buried SiO_2 film is considered to contain the oxygen vacancy defects in a high amount throughout the oxide.

  • Joint Research on Optical Properties of GaN and InGaN

    Project Year :

    1994
     
     
     

  • Excitation states and defect formation in high purity silica glass under gamma-ray or excimer-laser irradiation

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    1991
    -
    1992
     

    OHKI Yoshimichi, NAGASAWA Kaya, SOHTA Takayuki, HAMA Yoshimasa

     View Summary

    The purpose of this study is to clarify the structural and optical properties of point defects in a-SiO_2, and their formation mechanisms under ionizing radiations or laser photons. The emphasis is placed on (i) the characterization of preexisting diamagnetic defects and radiation-induced paramagnetic defects, and (ii) the establishment of the link between the diamagnetic defects and radiation-induced paramagnetic defects. The outline of the present study is as follows.
    1.Defects and optical absorption bands associated with excess oxygen are identified. Two forms of excess oxygen are identified: peroxy linkage and interstitial oxygen. An optical absorption band at 3.8 eV is associated with peroxy linkages.
    2.Characterization of new paramagnetic defects induced by 7.9-eV photons is performed. With the help of computer simulation analyses of the ESR spectra, the paramagnetic defects are identified to be ClO_x radicals (x=2,3).
    3.Time-resolved photoluminescence (PL) measurements are carried out on a series of silicas under 7.9-eV pulsed laser excitation. Correlations of several PL bands with point defects are studied.
    4.Paramagnetic defects induced by 6.4-eV excimer laser are studied on a series of silicas. Effects of the oxygen stoichiometry and hydroxyl content on the defect species and their concentrations are observed. It is shown that precursor transformation dominates in laser-induced defect formation.
    5.Photon-energy dependence of the creation of paramagnetic defects is investigated by means of ESR and uv-vuv optical absorption measurements, using 6.4-eV and 7.9-eV photons, and gamma rays as irradiation sources. Correlations between the preexisting diamagnetic defects and laser-induced paramagnetic defects are investigated.
    6.The effect of hydrogen on the photogeneration of E' centers is studied by means of ESR and uv-vuv absorption measurements. It is found that the creation of E' centers from neutral oxygen vacancies is enhanced in the presence of hydrogen.

  • GaNの光学的非線形性に及ぼす励起子の効果の研究

     View Summary

    本研究の目的はサファイア上に堆積された高品質GaN薄膜、InGaN/GaN単一量子井戸及びInGaN/InGaN多重量子井戸構造における励起子の性質とその光学的非線形性に及ぼす効果を調べることにあった。はじめに、研究コミュニティーからの要請により若干目的に変更が生じたことをお詫びしておく。研究実績は以下の通りである。1.Gan:0.83μm単結晶試料の10K-300Kにおける透過率・反射率の精密測定を行い、基礎吸収端近傍で吸収係数が1×105cm-1であることを見出した。この試料と4μmの試料で、Xeランプとガラスフィルタを組み合わせて得た3.3eV以上の白色スペクトルにより超弱励起PL測定を実施した。A,B励起子の完全分離、均一線幅の同定、A,B励起子第一励起状態からの発光同定ができた。更に膜厚変化に伴う残留歪による励起子発光ピークのシフト、欠陥密度の変化に起因すると思われる束縛励起子発光強度の変化等を見出した。吸収係数の絶対値が大きいことから、基礎吸収端でのポンプ・プローブ(P&P)法による透過率測定は満足のいく結果が得られなかったので、現在測定した吸収係数だけをもとにした光双安定性の計算を実行している最中である。ナノ秒P&P法では、吸収端より長波長側で、光照射後の比較的長い時定数を持つ屈折率変化を見出し、GaNの可変屈折率素子としての可能性を示唆した。2.InGaN単一・多重量子井戸:これら試料における最近の話題はピエゾ電場効果と混晶中のポテンシャル揺動に集中している。観測される電子系は両者の競合で決まっており、個々の効果の分離が難しい。本研究ではSiを高濃度に添加することで前者の効果をほぼゼロに抑制した試料を2つ成長条件を変えて作製し後者の効果の有無を調べた。結果はポテンシャル揺動が明らかに存在することを示した。これが無添加試料において励起子を局在させる一因であると考えられる。これらの試料でのゲインスペクトルを求めた結果、それは電子正孔プラズマモデルで説明できる一方で、如実にポテンシャル揺動を反映している事実を見出した。ポテンシャル揺動が弱い試料でアップ・コンバージョン法により蛍光の立ち上がり時間を測定した結果、それは60fs以下であることを見出した。n型試料でありかつ正孔・LOフォノン散乱が無視できる様にした励起波長での比較的弱励起条件下での結果であることから、実験結果は正孔が電子・正孔散乱により余剰エネルギーを冷たい電子へ移行して速やかに緩和することを反映したものと考えている。InGaN系における光励起正孔の初期緩和に関する研究はこれが始めてであることを付記しておく

  • 微小ディスクレーザー結合による、集積デバイスに関する研究

     View Summary

    固体ソースMBE法では、SiO2マスク上にGa原子が付着しやすいために多結晶が形成されやすく、選択成長は困難とされていたが、これまで我々はMEE法を用いた極めて制御性の良い選択成長法を確立してきた。今年度は、そのMEE法を用いた選択成長により、サブミクロン光導波路の作製に成功した。まず、電子ビームリソグラフィーを用いて、膜厚30nmのSiO2マスクで面を覆ったGaAs(001)基板上の[110]方向に沿った、長さ1μm、幅が200nmのサブミクロンチャネルパターンを作製した。その後、固体ソースMBE装置を使用し、SiドープGaAsの選択成長を行った。基板温度は590℃とし、GaとSiを1.0秒供給後2.0秒のアニール時間を取り入れ、その後As4を2.0秒供給し(成長速度0.2ML/cycle)、選択成長を行った。このチャネル周囲のSiO2マスク幅は約400nmとした。この成長層周囲のサブミクロンマスクにより、SiO2マスク上に供給されるGa原子の拡散による成長層への寄与が小さくなり、チャネル部分と電極との接続部分における膜厚の不均一性が改善された。また、SiO2マスク幅をGa原子の拡散長に近づけることで、完全なる選択性を得ることができ、成長速度の改善がされた。また、従来困難であったAIGaAs選択成長が可能となった。チャネル部分のPL発光強度の二次元パターンを観察したところ、成長層での発光はマスク下の基板からの発光に比べ極めて強く、均質であることが確認され、良質なチャネル構造が形成できたことが分かる。今後、基板面、チャネル方向、チャネルの幅、成長条件等を最適化するとともに光導波路としての特性調べる。さちに低次元の電気伝導特性も検討する。また、ゲート電極で制御することにより、バリスティック伝導および1次元伝導特性の観測が期待され、低消費電力FETへの応用も考えられる

  • 生体分子の一分子検出・機能解析システムの開発と応用

▼display all

Misc

  • Impact of diagenesis and maturation on the survival of eumelanin in the fossil record

    Keely Glass, Shosuke Ito, Philip R. Wilby, Takayuki Sota, Atsushi Nakamura, C. Russell Bowers, Kristen E. Miller, Suryendu Dutta, Roger E. Summons, Derek E. G. Briggs, Kazumasa Wakamatsu, John D. Simon

    ORGANIC GEOCHEMISTRY   64   29 - 37  2013.11  [Refereed]

     View Summary

    Melanins are polymeric phenolic pigments classified into two groups based on their chemical structures and molecular precursors: eumelanin (brown-black) and pheomelanin ( yellow-red). Eumelanin is highly resilient and has a proven fossil record, extending back at least similar to 200 Ma. It is widespread in the biological world, occurring in fungi, the ink sacs of cephalopods, the feathers of birds, and the hair, skin, eyes, brain and inner ears of mammals. Although the presence and chemical attributes of fossil eumelanin have been documented, there are few data constraining its long term survival. Here we use a diversity of analytical techniques to compare the chemistry and morphology of fossilized cephalopod ink from three deposits of similar age and lithology, but different maturation histories. We demonstrate that the chemistry of eumelanin begins to alter at the onset of the oil window and is largely independent of age. The decrease in surviving melanin is accompanied by an increase in the relative abundance of organic macromolecular material (kerogen) but, critically for the correct interpretation of fossils, is not accompanied by a consistent change in granule morphology. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI

  • Impact of diagenesis and maturation on the survival of eumelanin in the fossil record

    Keely Glass, Shosuke Ito, Philip R. Wilby, Takayuki Sota, Atsushi Nakamura, C. Russell Bowers, Kristen E. Miller, Suryendu Dutta, Roger E. Summons, Derek E. G. Briggs, Kazumasa Wakamatsu, John D. Simon

    ORGANIC GEOCHEMISTRY   64   29 - 37  2013.11  [Refereed]

     View Summary

    Melanins are polymeric phenolic pigments classified into two groups based on their chemical structures and molecular precursors: eumelanin (brown-black) and pheomelanin ( yellow-red). Eumelanin is highly resilient and has a proven fossil record, extending back at least similar to 200 Ma. It is widespread in the biological world, occurring in fungi, the ink sacs of cephalopods, the feathers of birds, and the hair, skin, eyes, brain and inner ears of mammals. Although the presence and chemical attributes of fossil eumelanin have been documented, there are few data constraining its long term survival. Here we use a diversity of analytical techniques to compare the chemistry and morphology of fossilized cephalopod ink from three deposits of similar age and lithology, but different maturation histories. We demonstrate that the chemistry of eumelanin begins to alter at the onset of the oil window and is largely independent of age. The decrease in surviving melanin is accompanied by an increase in the relative abundance of organic macromolecular material (kerogen) but, critically for the correct interpretation of fossils, is not accompanied by a consistent change in granule morphology. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI

  • Hyperspectral screening of melanoma on acral volar skin

    Nagaoka, T, Nakamura, A, Okutani. H, Kiyohara, Y, Koga, H, Saida, T, Sota, T

    Skin Res. Technol.   19 ( 1 ) e290 - e296  2013.01  [Refereed]

    DOI

  • Hyperspectral screening of melanoma on acral volar skin

    Nagaoka, T, Nakamura, A, Okutani. H, Kiyohara, Y, Koga, H, Saida, T, Sota, T

    Skin Res. Technol.   19 ( 1 ) e290 - e296  2013.01  [Refereed]

    DOI

  • Novel automated screening of age-related macular degeneration

    Yasuyuki Yamauchi, Hiroyuki Kemma, Hiroshi Goto, Atsushi Nakamura, Takashi Nagaoka, Takayuki Sota

    JAPANESE JOURNAL OF OPHTHALMOLOGY   56 ( 6 ) 577 - 583  2012.11  [Refereed]

     View Summary

    To determine the objective and quantitative hyperspectral parameters for distinguishing between age-related macular degeneration (AMD) and a normal macula.
    Near-infrared hyperspectral images were taken of 71 eyes of 62 AMD patients with exudative AMD and 21 eyes of 12 control subjects without AMD. The spatial information included a 480 x 321-pixel image in a 50A degrees field located at the ocular fundus and a 720-950-nm-per-pixel reflectance spectrum. Macular vectors were determined as the average spectrum for each macula, and reference vectors were used as average macular vectors for healthy volunteers. Variations in vector length and angle were calculated based on comparison with the reference vector. The AMD differentiation index was a parameter that minimized the plot overlap between AMD patients and controls.
    Statistically significant differences between the AMD patients and controls were noted. Receiver-operating characteristic curve analysis revealed an area under the curve of 0.888. The appropriate threshold values were attained for the proposed discrimination index, including 68 % sensitivity, 95 % specificity and 74 % accuracy.
    This study presents a simplified diagnostic index for the determination of age-related macular degeneration based on near-infrared spectra.

    DOI PubMed

  • Novel automated screening of age-related macular degeneration

    Yasuyuki Yamauchi, Hiroyuki Kemma, Hiroshi Goto, Atsushi Nakamura, Takashi Nagaoka, Takayuki Sota

    JAPANESE JOURNAL OF OPHTHALMOLOGY   56 ( 6 ) 577 - 583  2012.11  [Refereed]

     View Summary

    To determine the objective and quantitative hyperspectral parameters for distinguishing between age-related macular degeneration (AMD) and a normal macula.
    Near-infrared hyperspectral images were taken of 71 eyes of 62 AMD patients with exudative AMD and 21 eyes of 12 control subjects without AMD. The spatial information included a 480 x 321-pixel image in a 50A degrees field located at the ocular fundus and a 720-950-nm-per-pixel reflectance spectrum. Macular vectors were determined as the average spectrum for each macula, and reference vectors were used as average macular vectors for healthy volunteers. Variations in vector length and angle were calculated based on comparison with the reference vector. The AMD differentiation index was a parameter that minimized the plot overlap between AMD patients and controls.
    Statistically significant differences between the AMD patients and controls were noted. Receiver-operating characteristic curve analysis revealed an area under the curve of 0.888. The appropriate threshold values were attained for the proposed discrimination index, including 68 % sensitivity, 95 % specificity and 74 % accuracy.
    This study presents a simplified diagnostic index for the determination of age-related macular degeneration based on near-infrared spectra.

    DOI PubMed

  • First-principles study of spontaneous polarization and band gap bowing in ScxAlyGa1-x-yN alloys lattice-matched to GaN

    Shimada, K, Takouda, M, Hashiguchi, Y, Chichibu, S.F, Hata, M, Sazawa, H, Takada, T, Sota, T

    Semicond. Sci. Technol.   27 ( 10 ) 105014  2012.10  [Refereed]

    DOI

  • Signatures of Gamma(1)-Gamma(5) mixed-mode polaritons in polarized reflectance spectra of ZnO

    Ayako Takagi, Atsushi Nakamura, Akira Yoshikaie, So-ichiro Yoshioka, Satoru Adachi, Shigefusa F. Chichibu, Takayuki Sota

    JOURNAL OF PHYSICS-CONDENSED MATTER   24 ( 41 ) 415801  2012.10  [Refereed]

     View Summary

    Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Gamma(1) and Gamma(5) excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k perpendicular to a and E parallel to c configurations for an m-plane sample. Theoretical calculations reveal that the mixed-mode polaritons consist of one Gamma(1) transverse mode and two Gamma(5) longitudinal modes. It is also shown that the signatures are sensitive to the valence band ordering.

    DOI

  • First-principles study of spontaneous polarization and band gap bowing in ScxAlyGa1-x-yN alloys lattice-matched to GaN

    Shimada, K, Takouda, M, Hashiguchi, Y, Chichibu, S.F, Hata, M, Sazawa, H, Takada, T, Sota, T

    Semicond. Sci. Technol.   27 ( 10 ) 105014  2012.10  [Refereed]

    DOI

  • Signatures of Gamma(1)-Gamma(5) mixed-mode polaritons in polarized reflectance spectra of ZnO

    Ayako Takagi, Atsushi Nakamura, Akira Yoshikaie, So-ichiro Yoshioka, Satoru Adachi, Shigefusa F. Chichibu, Takayuki Sota

    JOURNAL OF PHYSICS-CONDENSED MATTER   24 ( 41 ) 415801  2012.10  [Refereed]

     View Summary

    Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Gamma(1) and Gamma(5) excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k perpendicular to a and E parallel to c configurations for an m-plane sample. Theoretical calculations reveal that the mixed-mode polaritons consist of one Gamma(1) transverse mode and two Gamma(5) longitudinal modes. It is also shown that the signatures are sensitive to the valence band ordering.

    DOI

  • A possible melanoma discrimination index based on hyperspectral data: a pilot study

    Takashi Nagaoka, Atsushi Nakamura, Haruka Okutani, Yoshio Kiyohara, Takayuki Sota

    SKIN RESEARCH AND TECHNOLOGY   18 ( 3 ) 301 - 310  2012.08  [Refereed]

     View Summary

    Background Early detection and proper excision of the primary lesions of malignant melanoma (MM) are crucial for reducing melanoma-related deaths. To support the early detection of melanoma, automated melanoma screening systems have been extensively studied and developed. In this article, we present a hyperspectral melanoma screening system and propose a possible melanoma discrimination index derived from the characteristics of the pigment molecules in the skin, both of which have been derived from hyperspectral data (HSD). Methods The index expresses the disordered nature of each lesion including variegation in color based on variation in spectral information obtained from each lesion. Performance of the index in discriminating melanomas from other pigmented skin lesions has been studied in five cases of melanoma (41 HSD sets), one case of Spitz nevus (13 HSD sets), 10 cases of seborrheic keratosis (78 HSD sets), three cases of basal cell carcinoma (16 HSD sets), and nine cases of melanocytic nevus (21 HSD sets), obtained from patients and volunteers, all of whom were Japanese. Results Performance of the index, which reflects the disordered nature of a lesion, discriminates melanomas with a sensitivity of 90%, a specificity of 84%, and an area under the receiver operating characteristic curve of 0.93, on resubstitution. Conclusion An objective melanoma discrimination index at a molecular pigmentary level, derived from HSD, has been proposed, and its performance evaluated. This index was highly successful in discriminating MM from non-melanoma, although the statistical population was small.

    DOI

  • A possible melanoma discrimination index based on hyperspectral data: a pilot study

    Takashi Nagaoka, Atsushi Nakamura, Haruka Okutani, Yoshio Kiyohara, Takayuki Sota

    SKIN RESEARCH AND TECHNOLOGY   18 ( 3 ) 301 - 310  2012.08  [Refereed]

     View Summary

    Background Early detection and proper excision of the primary lesions of malignant melanoma (MM) are crucial for reducing melanoma-related deaths. To support the early detection of melanoma, automated melanoma screening systems have been extensively studied and developed. In this article, we present a hyperspectral melanoma screening system and propose a possible melanoma discrimination index derived from the characteristics of the pigment molecules in the skin, both of which have been derived from hyperspectral data (HSD). Methods The index expresses the disordered nature of each lesion including variegation in color based on variation in spectral information obtained from each lesion. Performance of the index in discriminating melanomas from other pigmented skin lesions has been studied in five cases of melanoma (41 HSD sets), one case of Spitz nevus (13 HSD sets), 10 cases of seborrheic keratosis (78 HSD sets), three cases of basal cell carcinoma (16 HSD sets), and nine cases of melanocytic nevus (21 HSD sets), obtained from patients and volunteers, all of whom were Japanese. Results Performance of the index, which reflects the disordered nature of a lesion, discriminates melanomas with a sensitivity of 90%, a specificity of 84%, and an area under the receiver operating characteristic curve of 0.93, on resubstitution. Conclusion An objective melanoma discrimination index at a molecular pigmentary level, derived from HSD, has been proposed, and its performance evaluated. This index was highly successful in discriminating MM from non-melanoma, although the statistical population was small.

    DOI

  • Direct chemical evidence for eumelanin pigment from the Jurassic period

    Keely Glass, Shosuke Ito, Philip R. Wilby, Takayuki Sota, Atsushi Nakamura, C. Russell Bowers, Jakob Vinther, Suryendu Dutta, Roger Summons, Derek E. G. Briggs, Kazumasa Wakamatsu, John D. Simon

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   109 ( 26 ) 10218 - 10223  2012.06  [Refereed]

     View Summary

    Melanin is a ubiquitous biological pigment found in bacteria, fungi, plants, and animals. It has a diverse range of ecological and biochemical functions, including display, evasion, photoprotection, detoxification, and metal scavenging. To date, evidence of melanin in fossil organisms has relied entirely on indirect morphological and chemical analyses. Here, we apply direct chemical techniques to categorically demonstrate the preservation of eumelanin in two &gt;160 Ma Jurassic cephalopod ink sacs and to confirm its chemical similarity to the ink of the modern cephalopod, Sepia officinalis. Identification and characterization of degradation-resistant melanin may provide insights into its diverse roles in ancient organisms.

    DOI PubMed

  • Direct chemical evidence for eumelanin pigment from the Jurassic period

    Keely Glass, Shosuke Ito, Philip R. Wilby, Takayuki Sota, Atsushi Nakamura, C. Russell Bowers, Jakob Vinther, Suryendu Dutta, Roger Summons, Derek E. G. Briggs, Kazumasa Wakamatsu, John D. Simon

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   109 ( 26 ) 10218 - 10223  2012.06  [Refereed]

     View Summary

    Melanin is a ubiquitous biological pigment found in bacteria, fungi, plants, and animals. It has a diverse range of ecological and biochemical functions, including display, evasion, photoprotection, detoxification, and metal scavenging. To date, evidence of melanin in fossil organisms has relied entirely on indirect morphological and chemical analyses. Here, we apply direct chemical techniques to categorically demonstrate the preservation of eumelanin in two &gt;160 Ma Jurassic cephalopod ink sacs and to confirm its chemical similarity to the ink of the modern cephalopod, Sepia officinalis. Identification and characterization of degradation-resistant melanin may provide insights into its diverse roles in ancient organisms.

    DOI PubMed

  • Valence-band-ordering of a strain-free bulk ZnO single crystal indentified by four-wave-mixing spectroscopy technique

    Hazu, K, Chichibu, S. F, Adachi, S, Sota, T

    J. Appl. Phys.   111 ( 9 ) 093522  2012.05

    DOI

  • Valence-band-ordering of a strain-free bulk ZnO single crystal identified by four-wave-mixing spectroscopy technique

    K. Hazu, S. F. Chichibu, S. Adachi, T. Sota

    JOURNAL OF APPLIED PHYSICS   111 ( 9 ) 093522  2012.05  [Refereed]

     View Summary

    Spectroscopic and temporal four-wave-mixing (FWM) measurements are carried out on a strain-free bulk ZnO single crystal, in order to clarify the valence-band-ordering. Under the collinearly polarized lights with the electric-field component parallel to the c-axis, which can excite dipole-allowed Gamma(1)-excitons, the FWM signal appears only in the energies corresponding to the B-exciton. Under the cross-linear polarization configuration exciting both Gamma(5)- and Gamma(1)-excitons, the FWM signal arising from the two-photon-coherence is absent in the energies corresponding to A-exciton. Both the results indicate that Gamma(1)-exciton state belongs exclusively to B-exciton, meaning that the valence-band ordering is Gamma(9) - Gamma(7) - Gamma(7) in order of decreasing electron energy for the present strain-free ZnO single crystal. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4711103]

    DOI

  • First-principles study of spontaneous polarization and band gap bowing in ScxAlyGa1-x-yN alloys lattice-matched to GaN

    Shimada, K, Takouda, M, Hashiguchi, Y, Chichibu, S.F, Hata, M, Sazawa, H, Takada, T, Sota, T

    Semicond. Sci. Technol.   25 ( 10 ) 105014  2012

    DOI

  • First-principles study of spontaneous polarization and band gap bowing in ScxAlyGa1-x-yN alloys lattice-matched to GaN

    Shimada, K, Takouda, M, Hashiguchi, Y, Chichibu, S.F, Hata, M, Sazawa, H, Takada, T, Sota, T

    Semicond. Sci. Technol.   25 ( 10 ) 105014  2012

    DOI

  • Mid-infrared vibrational spectroscopic characterization of 5,6-dihydroxyindole and eumelanin derived from it

    Ryosuke Hyogo, Atsushi Nakamura, Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   517 ( 4-6 ) 211 - 216  2011.12

     View Summary

    Mid-infrared vibrational spectroscopic study has been made on 5,6-dihydroxyindole (DHI) and DHI-derived eumelanin. It has been revealed for DHI monomer that measured infrared absorption spectrum is well reproduced by that predicted from ab initio calculations. Thus, vibrational modes of DHI monomer causing dominant absorption bands have been successfully assigned. It has been also reconfirmed that DHI-derived eumelanin includes indolequinone and/or quinone methide units in addition to DHI units. (C) 2011 Elsevier B.V. All rights reserved.

    DOI CiNii

  • Mid-infrared vibrational spectroscopic characterization of 5,6-dihydroxyindole and eumelanin derived from it

    Ryosuke Hyogo, Atsushi Nakamura, Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   517 ( 4-6 ) 211 - 216  2011.12

     View Summary

    Mid-infrared vibrational spectroscopic study has been made on 5,6-dihydroxyindole (DHI) and DHI-derived eumelanin. It has been revealed for DHI monomer that measured infrared absorption spectrum is well reproduced by that predicted from ab initio calculations. Thus, vibrational modes of DHI monomer causing dominant absorption bands have been successfully assigned. It has been also reconfirmed that DHI-derived eumelanin includes indolequinone and/or quinone methide units in addition to DHI units. (C) 2011 Elsevier B.V. All rights reserved.

    DOI CiNii

  • Spontaneous polarization and band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaN

    Kazuhiro Shimada, Atsuhito Zenpuku, Kazuya Fujiwara, Kouji Hazu, Shigefusa F. Chichibu, Masahiro Hata, Hiroyuki Sazawa, Tomoyuki Takada, Takayuki Sota

    JOURNAL OF APPLIED PHYSICS   110 ( 7 ) 074114  2011.10

     View Summary

    First-principles calculations are carried out to estimate the spontaneous polarization and the energy band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaN. The ground state properties of alloys are computed by using the pseudopotential-planewave method in conjunction with generalized gradient approximation to density functional theory. We find nonlinear behavior of the spontaneous polarization and the band gap energies in YxAlyGa1-x-yN alloys and the values depend on the atomic geometry in the unit cell, especially on that of yttrium. (C) 2011 American Institute of Physics. [doi:10.1063/1.3651154]

    DOI CiNii

  • Spontaneous polarization and band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaN

    Kazuhiro Shimada, Atsuhito Zenpuku, Kazuya Fujiwara, Kouji Hazu, Shigefusa F. Chichibu, Masahiro Hata, Hiroyuki Sazawa, Tomoyuki Takada, Takayuki Sota

    JOURNAL OF APPLIED PHYSICS   110 ( 7 ) 074114  2011.10

     View Summary

    First-principles calculations are carried out to estimate the spontaneous polarization and the energy band gap bowing in YxAlyGa1-x-yN alloys lattice-matched to GaN. The ground state properties of alloys are computed by using the pseudopotential-planewave method in conjunction with generalized gradient approximation to density functional theory. We find nonlinear behavior of the spontaneous polarization and the band gap energies in YxAlyGa1-x-yN alloys and the values depend on the atomic geometry in the unit cell, especially on that of yttrium. (C) 2011 American Institute of Physics. [doi:10.1063/1.3651154]

    DOI CiNii

  • Novel melanoma discrimination index from optical spectra

    Okutani, H, Nakamura, A, Nagaoka, T, Kiyohara, Y, Sota, T

    Skin Cancer   26 ( 1 ) 94 - 97  2011.05

     View Summary

    The ABCD-rule of dermoscopy has increased diagnostic accuracy ; however, some training is required in using it efficiently, and the diagnosis based on morphology is to a large extent subjective as with any clinical diagnosis. Morphology mainly comes from spatial variegation in skin pigmentation, i.e. spatial change in pigment molecular species and their concentration. Optical spectra reflected from the skin carry information about it. An essential feature of melanoma is the variety in morphology of the lesion, which is equivalent to change in spectrum from portion to portion within the lesion. The hyperspectral imaging technique enables one to measure hyperspectral data (HSD) within a short period, which consist of both spatial and spectral information. In this paper, we propose a single melanoma discrimination index derived from HSD using the entropy concept, and demonstrate its usefulness.[Skin Cancer (Japan) 2011 ; 26 : 94-97]

    DOI CiNii

  • Photodynamic diagnosis of oral carcinoma using talaporfin sodium and a hyperspectral imaging system: An animal study

    Masashi Migita, Isao Kamiyama, Kenichi Matsuzaka, Atsushi Nakamura, Takayuki Souta, Katsuo Aizawa, Takahiko Shibahara

    Asian Journal of Oral and Maxillofacial Surgery   22 ( 3 ) 126 - 132  2010.09

     View Summary

    The purpose of this study was to examine the efficacy of detecting oral squamous cell carcinoma (SCC) using photodynamic diagnosis (PDD), a highly reliable method for tumor diagnosis, through the use of photosensitizers such as talaporfin sodium. Talaporfin sodium (5mg/kg) was administered to 7 control rats and 43 rats that had ingested the carcinogen 4-nitroquinoline 1-oxide (4NQO). After 8h, tongues were examined by spectral imaging and measurements were made using a hyperspectral imaging system. On each spectral image, macroscopically lesions and normal regions of the tongue were selected. Lesions comprised squamous cell carcinoma (SCC) in 22 cases, carcinoma in situ (CiS) in 9 cases, and dysplasia in 12 cases. The value Δα was determined as the absorbance spectrum of a lesion compared with normal tissue, or as the difference between Δκ at the posterior of the lingual protrusion and Δκ at the anterior of the lingual protrusion in controls. We compared Δα for SCC, CiS, and dysplasia with controls. The value Δα was (2.4±1.78)×10-2 in SCC, (1.2±1.34)×10-2 in CiS, (-0.2±0.49)×10-2 in dysplasia, and (0.21±0.63)×10-2 in controls. Both SCC and CiS showed significant differences from controls (p=0.037 and p=0.021, respectively). Histopathological analysis revealed that proliferating cell nuclear antigen (PCNA) expression increased gradually in the following order: controls, dysplasia, CiS, and SCC. Development of PDD using a hyperspectral imaging system may represent a useful technique for detecting oral SCC. © 2010 Asian Association of Oral and Maxillofacial Surgeons.

    DOI

  • Photodynamic diagnosis of oral carcinoma using talaporfin sodium and a hyperspectral imaging system: An animal study

    Masashi Migita, Isao Kamiyama, Kenichi Matsuzaka, Atsushi Nakamura, Takayuki Souta, Katsuo Aizawa, Takahiko Shibahara

    Asian Journal of Oral and Maxillofacial Surgery   22 ( 3 ) 126 - 132  2010.09

     View Summary

    The purpose of this study was to examine the efficacy of detecting oral squamous cell carcinoma (SCC) using photodynamic diagnosis (PDD), a highly reliable method for tumor diagnosis, through the use of photosensitizers such as talaporfin sodium. Talaporfin sodium (5mg/kg) was administered to 7 control rats and 43 rats that had ingested the carcinogen 4-nitroquinoline 1-oxide (4NQO). After 8h, tongues were examined by spectral imaging and measurements were made using a hyperspectral imaging system. On each spectral image, macroscopically lesions and normal regions of the tongue were selected. Lesions comprised squamous cell carcinoma (SCC) in 22 cases, carcinoma in situ (CiS) in 9 cases, and dysplasia in 12 cases. The value Δα was determined as the absorbance spectrum of a lesion compared with normal tissue, or as the difference between Δκ at the posterior of the lingual protrusion and Δκ at the anterior of the lingual protrusion in controls. We compared Δα for SCC, CiS, and dysplasia with controls. The value Δα was (2.4±1.78)×10-2 in SCC, (1.2±1.34)×10-2 in CiS, (-0.2±0.49)×10-2 in dysplasia, and (0.21±0.63)×10-2 in controls. Both SCC and CiS showed significant differences from controls (p=0.037 and p=0.021, respectively). Histopathological analysis revealed that proliferating cell nuclear antigen (PCNA) expression increased gradually in the following order: controls, dysplasia, CiS, and SCC. Development of PDD using a hyperspectral imaging system may represent a useful technique for detecting oral SCC. © 2010 Asian Association of Oral and Maxillofacial Surgeons.

    DOI

  • A melanoma discrimination index based on optical spectra

    Nagaoka, T, Nakamura, A, Aizawa, K, Ohtsubo, S, Kiyohara Y, Sota, T

    Skin Cancer   25 ( 1 ) 81 - 84  2010.05

     View Summary

    The morphology of pigmented skin lesions (PSLs) comes from differences in distribution and in concentration of melanin and hemoglobin pigment molecules. Those differences may be analyzed qualitatively and quantitatively using diffuse reflectance spectra in the visible to near infrared wavelength region. We have expressed differences in concentration distribution of both pigment molecules numerically with the use of diffuse reflectance spectra varying from site to site. Performance of the parameter has been studied on fifteen cases of PSLs : six cases of melanoma, five cases of seborrheic keratosis, and four cases of nevus. It has been demonstrated that the parameter can discriminate melanoma from others with a sensitivity of 85% and a specificity of 91%. It has also been suggested that the parameter reflects both boundary irregularity and variation in colors of PSLs.[Skin Cancer (Japan) 2010 ; 25 : 81-84]

    DOI CiNii

  • Regioselectivity on the cooxidation of 5,6-dihydroxyindole and its 2-carboxy derivative from the quantum chemical calculations

    Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   490 ( 4-6 ) 226 - 229  2010.04  [Refereed]

     View Summary

    We report the heterodimerization of eumelanin precursors from the quantum chemical calculations using a general-purpose reactivity indicator. 5,6-Dihydroxyindole (DHI), its 2-carboxy derivative (DHICA), and related molecules are under consideration. Molecules participating in the reaction have been identified from the electron transfer probability. The heterodimerization has been demonstrated to be the electron-transfer-controlled reaction. The theoretical prediction is in good agreement with the result of the previous cooxidation of DHI and DHICA. (C) 2010 Elsevier B.V. All rights reserved.

    DOI CiNii

  • Regioselectivity on the cooxidation of 5,6-dihydroxyindole and its 2-carboxy derivative from the quantum chemical calculations

    Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   490 ( 4-6 ) 226 - 229  2010.04  [Refereed]

     View Summary

    We report the heterodimerization of eumelanin precursors from the quantum chemical calculations using a general-purpose reactivity indicator. 5,6-Dihydroxyindole (DHI), its 2-carboxy derivative (DHICA), and related molecules are under consideration. Molecules participating in the reaction have been identified from the electron transfer probability. The heterodimerization has been demonstrated to be the electron-transfer-controlled reaction. The theoretical prediction is in good agreement with the result of the previous cooxidation of DHI and DHICA. (C) 2010 Elsevier B.V. All rights reserved.

    DOI CiNii

  • Identification of extremely radiative nature of AlN by time-resolved photoluminescence

    Onuma, T, Hazu, K, Uedono, A, Sota, T, Chichibu, S.F

    Appl. Phys. Lett.   96(6) Art.No.06906 ( 6 ) 061906  2010.02

    DOI CiNii

  • Identification of extremely radiative nature of AlN by time-resolved photoluminescence

    T. Onuma, K. Hazu, A. Uedono, T. Sota, S. F. Chichibu

    APPLIED PHYSICS LETTERS   96 ( 6 ) 061906  2010.02  [Refereed]

     View Summary

    Extremely radiative nature of high-quality AlN single crystalline epilayers was identified by means of far ultraviolet time-resolved photoluminescence using a frequency-quadrupled femtosecond Al(2)O(3):Ti laser. The gross radiative lifetimes of a free excitonic polariton emission as short as 10 ps at 7 K and 180 ps at 300 K were revealed, which are the shortest ever reported for bulk semiconductor materials.

    DOI CiNii

  • Free and bound exciton fine structures in AlN epilayers grown by low-pressure metalorganic vapor phase epitaxy

    Onuma, T, Kosaka, K, Asai, K, Sumiya, S, Shibata, T, Tanaka, M, Sota, T, Uedono, A, Chichibu, S. F

    J. Appl. Phys.   105, Art No.023529 ( 2 ) 023529  2009.01  [Refereed]

    DOI CiNii

  • Free and bound exciton fine structures in AlN epilayers grown by low-pressure metalorganic vapor phase epitaxy

    Onuma, T, Kosaka, K, Asai, K, Sumiya, S, Shibata, T, Tanaka, M, Sota, T, Uedono, A, Chichibu, S. F

    J. Appl. Phys.   105, Art No.023529 ( 2 ) 023529  2009.01  [Refereed]

    DOI CiNii

  • Possible Oxidative Polymerization Mechanism of 5,6-Dihydroxyindole from A Initio Calculations

    Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    JOURNAL OF PHYSICAL CHEMISTRY A   112 ( 44 ) 11213 - 11222  2008.11

     View Summary

    The reactivity of 5,6-dihydroxyindole and its major dimers has been studied with the use of a recently proposed general-purpose reactive indicator (Anderson et al. J. Chem. Theory Comput. 2007, 3, 358-374) from ab initio density-functional theory calculations. Theoretical prediction has reasonably explained previously isolated oligomers up to tetramers. The oxidative polymerization is governed by the electron-transfer-control led reaction. The electrostatic interaction plays a regioselective role in the reactant complex and/or intermediates. A monomer-dimer coupling is able to form trimers, while a part of it is prevented by the exchange repulsion, i.e., steric hindrance. Therefore, a dimer-dimer coupling is also able to form tetramers.

    DOI PubMed CiNii

  • Possible Oxidative Polymerization Mechanism of 5,6-Dihydroxyindole from A Initio Calculations

    Hidekazu Okuda, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    JOURNAL OF PHYSICAL CHEMISTRY A   112 ( 44 ) 11213 - 11222  2008.11  [Refereed]

     View Summary

    The reactivity of 5,6-dihydroxyindole and its major dimers has been studied with the use of a recently proposed general-purpose reactive indicator (Anderson et al. J. Chem. Theory Comput. 2007, 3, 358-374) from ab initio density-functional theory calculations. Theoretical prediction has reasonably explained previously isolated oligomers up to tetramers. The oxidative polymerization is governed by the electron-transfer-control led reaction. The electrostatic interaction plays a regioselective role in the reactant complex and/or intermediates. A monomer-dimer coupling is able to form trimers, while a part of it is prevented by the exchange repulsion, i.e., steric hindrance. Therefore, a dimer-dimer coupling is also able to form tetramers.

    DOI PubMed CiNii

  • Impact of strain on free-exciton resonance energies in wurtzite AlN

    Ikeda, H, T. Okamura, Matsukawa, K, Sota, T, Sugawara, M, Hoshi, T, Cantu, P, Sharma, R, Kaeding, J.F, Mishra, U. K, Kosaka, K, Asai, K, Sumiya, S, Shibata, T, Tanaka, M, Speck, J.S, DenBarrs, S.P, Nakamura, S, Koyama, T, Onuma, T, Chichibu, S.F

    J.Appl. Phys.   102, artNo.123707 ( 12 ) 123707  2007.12  [Refereed]

    DOI

  • Impact of strain on free-exciton resonance energies in wurtzite AlN

    Ikeda, H, T. Okamura, Matsukawa, K, Sota, T, Sugawara, M, Hoshi, T, Cantu, P, Sharma, R, Kaeding, J.F, Mishra, U. K, Kosaka, K, Asai, K, Sumiya, S, Shibata, T, Tanaka, M, Speck, J.S, DenBarrs, S.P, Nakamura, S, Koyama, T, Onuma, T, Chichibu, S.F

    J.Appl. Phys.   102, artNo.123707 ( 12 ) 123707  2007.12  [Refereed]

    DOI

  • Atomic distribution in In x Ga 1-x N single-quantum-wells studied by extended X-ray absorption fine structure

    Miyanaga, T, Azuhata, T, Matsuda, S, Ishikawa, Y, Sasaki, S, Uruga, T, Tanida, H, Chichibu, S.F, Sota, T

    Phys. Rev. B/APS   76:Art.No. 035314  2007.07  [Refereed]

  • Atomic distribution in In x Ga 1-x N single-quantum-wells studied by extended X-ray absorption fine structure

    Miyanaga, T, Azuhata, T, Matsuda, S, Ishikawa, Y, Sasaki, S, Uruga, T, Tanida, H, Chichibu, S.F, Sota, T

    Phys. Rev. B/APS   76:Art.No. 035314  2007.07  [Refereed]

  • Mid-infrared absorption spectrum of 5,6-dihydroxyindole-2-carboxylic acid

    Hidekazu Okuda, Atsushi Nakamura, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   433 ( 4-6 ) 355 - 359  2007.01  [Refereed]

     View Summary

    We report the mid-infrared absorption spectrum of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) solid samples in the wavenumber region ranging from 1000 cm(-1) to 4000 cm(-1) with resolution of 4 cm(-1). Vibrational modes for observed dominant absorption bands of DHICA have been successfully assigned with ab initio density-functional theory calculations. The experimental data also suggest the existence of intermolecular hydrogen bonds. (c) 2006 Elsevier B.V. All rights reserved.

    DOI CiNii

  • Origin of localized excitons in In-containing three-dimensional bulk (Al,In,Ga)N alloy films probed by time-resolved photoluminescence and monoenergetic positron annihilation techniques

    S. F. Chichibu, A. Uedono, T. Onuma, B. A. Haskell, A. Chakraborty, T. Koyama, P. T. Fini, S. Keller, S. P. Denbaars, J. S. Speck, U. K. Mishra, S. Nakamura, S. Yamaguchi, S. Kamiyama, H. Amano, I. Akasaki, J. Han, T. Sota

    PHILOSOPHICAL MAGAZINE   87 ( 13 ) 2019 - 2039  2007  [Refereed]

     View Summary

    A principal origin of the defect-insensitive emission probability of In-containing three-dimensional ( 3-D) bulk ( Al, In, Ga) N alloy films, such as InGaN, AlInN and AlInGaN, is proposed. In contrast to In-free GaN or AlGaN, In-containing films grown on sapphire substrates show significant emission probabilities, although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional ( Al, In, Ga)( As, P) light-emitting-diode films. According to the extremely short diffusion lengths of positrons ( &lt; 4 nm) and short radiative lifetimes of excitonic emissions, we conclude that capturing of holes by localized valence states associated with atomic condensates of In-N outrun the trapping by non-radiative recombination centres, which are defect complexes associated with group III vacancies, because holes and positrons have the same positive charge. The captured holes are considered to form localized excitons with surrounding electrons to emit the light. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.

    DOI

  • Mid-infrared absorption spectrum of 5,6-dihydroxyindole-2-carboxylic acid

    Hidekazu Okuda, Atsushi Nakamura, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

    CHEMICAL PHYSICS LETTERS   433 ( 4-6 ) 355 - 359  2007.01  [Refereed]

     View Summary

    We report the mid-infrared absorption spectrum of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) solid samples in the wavenumber region ranging from 1000 cm(-1) to 4000 cm(-1) with resolution of 4 cm(-1). Vibrational modes for observed dominant absorption bands of DHICA have been successfully assigned with ab initio density-functional theory calculations. The experimental data also suggest the existence of intermolecular hydrogen bonds. (c) 2006 Elsevier B.V. All rights reserved.

    DOI CiNii

  • Origin of localized excitons in In-containing three-dimensional bulk (Al,In,Ga)N alloy films probed by time-resolved photoluminescence and monoenergetic positron annihilation techniques

    S. F. Chichibu, A. Uedono, T. Onuma, B. A. Haskell, A. Chakraborty, T. Koyama, P. T. Fini, S. Keller, S. P. Denbaars, J. S. Speck, U. K. Mishra, S. Nakamura, S. Yamaguchi, S. Kamiyama, H. Amano, I. Akasaki, J. Han, T. Sota

    PHILOSOPHICAL MAGAZINE   87 ( 13 ) 2019 - 2039  2007  [Refereed]

     View Summary

    A principal origin of the defect-insensitive emission probability of In-containing three-dimensional ( 3-D) bulk ( Al, In, Ga) N alloy films, such as InGaN, AlInN and AlInGaN, is proposed. In contrast to In-free GaN or AlGaN, In-containing films grown on sapphire substrates show significant emission probabilities, although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional ( Al, In, Ga)( As, P) light-emitting-diode films. According to the extremely short diffusion lengths of positrons ( &lt; 4 nm) and short radiative lifetimes of excitonic emissions, we conclude that capturing of holes by localized valence states associated with atomic condensates of In-N outrun the trapping by non-radiative recombination centres, which are defect complexes associated with group III vacancies, because holes and positrons have the same positive charge. The captured holes are considered to form localized excitons with surrounding electrons to emit the light. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.

    DOI

  • Origin of defect-insensitive emission probability in In-containing (Al, In, Ga) N alloy semiconductors

    Shigefusa F. Chichibu, Akira Uedono, Takeyoshi Onuma, Benjamin A. Haskell, Arpan Chakraborty, Takahiro Koyama, Paul T. Fini, Stacia Keller, Steven P. Denbaars, James S. Speck, Umesh K. Mishra, Shuji Nakamura, Shigeo Yamaguchi, Satoshi Kamiyama, Hiroshi Amano, Isamu Akasaki, Jung Han, Takayuki Sota

    NATURE MATERIALS   5 ( 10 ) 810 - 816  2006.10  [Refereed]

     View Summary

    Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional LEDs. Here we explain why In-containing (Al, In, Ga) N bulk films exhibit a defect-insensitive emission probability. From the extremely short positron diffusion lengths (&lt; 4nm) and short radiative lifetimes of excitonic emissions, we conclude that localizing valence states associated with atomic condensates of In-N preferentially capture holes, which have a positive charge similar to positrons. The holes form localized excitons to emit the light, although some of the excitons recombine at non-radiative centres. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.

    DOI PubMed

  • Origin of defect-insensitive emission probability in In-containing (Al, In, Ga) N alloy semiconductors

    Shigefusa F. Chichibu, Akira Uedono, Takeyoshi Onuma, Benjamin A. Haskell, Arpan Chakraborty, Takahiro Koyama, Paul T. Fini, Stacia Keller, Steven P. Denbaars, James S. Speck, Umesh K. Mishra, Shuji Nakamura, Shigeo Yamaguchi, Satoshi Kamiyama, Hiroshi Amano, Isamu Akasaki, Jung Han, Takayuki Sota

    NATURE MATERIALS   5 ( 10 ) 810 - 816  2006.10  [Refereed]

     View Summary

    Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional LEDs. Here we explain why In-containing (Al, In, Ga) N bulk films exhibit a defect-insensitive emission probability. From the extremely short positron diffusion lengths (&lt; 4nm) and short radiative lifetimes of excitonic emissions, we conclude that localizing valence states associated with atomic condensates of In-N preferentially capture holes, which have a positive charge similar to positrons. The holes form localized excitons to emit the light, although some of the excitons recombine at non-radiative centres. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.

    DOI PubMed

  • Prospective emission efficiency and in-plane light polarization of nonpolar m-plane InxGa1-xN/GaN blue light emitting diodes fabricated on freestanding GaN substrates

    T. Koyama, T. Onuma, H. Masui, A. Chakraborty, B. A. Haskell, S. Keller, U. K. Mishra, J. S. Speck, S. Nakamura, S. P. DenBaars, T. Sota, S. F. Chichibu

    APPLIED PHYSICS LETTERS   89 ( 9 )  2006.08  [Refereed]

     View Summary

    Prospective equivalent internal quantum efficiency (eta(int)) of approximately 34% at 300 K was demonstrated for the blue emission peak of nonpolar m-plane (1 (1) over bar 00) InxGa1-xN/GaN multiple quantum well light emitting diodes (LEDs) fabricated on freestanding m-plane GaN substrates. Although the eta(int) value is yet lower than that of conventional c-plane blue LEDs (&gt; 70%), the results encourage one to realize high performance green, amber, and red LEDs by reducing the concentration of nonradiative defects, according to the absence of the quantum-confined Stark effects due to the polarization fields parallel to the quantum well normal. The electric field component of the blue surface emission was polarized perpendicular to the c axis with the in-plane polarization ratio of 0.58 at 300 K. (c) 2006 American Institute of Physics.

    DOI

  • Prospective emission efficiency and in-plane light polarization of nonpolar m-plane InxGa1-xN/GaN blue light emitting diodes fabricated on freestanding GaN substrates

    T. Koyama, T. Onuma, H. Masui, A. Chakraborty, B. A. Haskell, S. Keller, U. K. Mishra, J. S. Speck, S. Nakamura, S. P. DenBaars, T. Sota, S. F. Chichibu

    APPLIED PHYSICS LETTERS   89 ( 9 )  2006.08  [Refereed]

     View Summary

    Prospective equivalent internal quantum efficiency (eta(int)) of approximately 34% at 300 K was demonstrated for the blue emission peak of nonpolar m-plane (1 (1) over bar 00) InxGa1-xN/GaN multiple quantum well light emitting diodes (LEDs) fabricated on freestanding m-plane GaN substrates. Although the eta(int) value is yet lower than that of conventional c-plane blue LEDs (&gt; 70%), the results encourage one to realize high performance green, amber, and red LEDs by reducing the concentration of nonradiative defects, according to the absence of the quantum-confined Stark effects due to the polarization fields parallel to the quantum well normal. The electric field component of the blue surface emission was polarized perpendicular to the c axis with the in-plane polarization ratio of 0.58 at 300 K. (c) 2006 American Institute of Physics.

    DOI

  • Improvements in quantum efficiency of excitonic emissions in ZnO epilayers by the elimination of point defects

    S. F. Chichibu, T. Onuma, M. Kubota, A. Uedono, T. Sota, A. Tsukazaki, A. Ohtomo, M. Kawasaki

    Journal of Applied Physics   99 ( 9 )  2006.05  [Refereed]

     View Summary

    The internal quantum efficiency (ηint) of the near-band-edge (NBE) excitonic photoluminescence (PL) in ZnO epilayers was significantly improved by eliminating point defects, as well as by the use of ZnO high-temperature- annealed self-buffer layer (HITAB) on a ScAlMg O4 substrate as epitaxial templates. Negatively charged Zn vacancy (VZn) concentration was greatly reduced by high-temperature growth, and slower postgrowth cooling (annealing) under minimum oxygen pressure further reduced the gross concentration of positively and negatively charged and neutral point defects, according to the suppression of nonequilibrium defect quenching. The nonradiative PL lifetime (τnr) at room temperature was increased by decreasing the gross concentration of point defects, as well as by decreasing the concentration of VZn. Accordingly, certain point defect complexes incorporated with VZn (VZn -X complexes) are assigned to the dominant nonradiative recombination centers. As a result of the elimination of point defects, a record long τnr (3.8 ns) at 300 K was demonstrated. Because the radiative lifetime (τr) is in principle constant in bulk and epitaxial ZnO, the increase in τnr gave rise to the increase in ηint. Rich structures originating from exciton-polaritons and excited states of excitons were eventually observed in the low-temperature PL spectrum of the improved ZnO epilayer on HITAB, of which ηint of the NBE emission was 6.3% at 300 K. © 2006 American Institute of Physics.

    DOI

  • Improvements in quantum efficiency of excitonic emissions in ZnO epilayers by the elimination of point defects

    Chichibu, S. F, Onuma, T, Kubota, M, Uedono, A, Sota, T, Tsukuazaki, A, Ohtomo, A, Kawasaki, M

    J. Appl. Phys./AIP   99 (9), Art. No. 093505  2006.05

    DOI

  • Recombination dynamics of a 268 nm emission peak in Al0.53In0.11Ga0.36N/Al0.58In0.02Ga0.40N multiple quantum wells

    T Onuma, S Keller, SP DenBaars, JS Speck, S Nakamura, UK Mishra, T Sota, SF Chichibu

    APPLIED PHYSICS LETTERS   88 ( 11 )  2006.03  [Refereed]

     View Summary

    Recombination dynamics of the 268 nm photoluminescence (PL) peak in a quaternary Al0.53In0.11Ga0.36N/Al0.58In0.02Ga0.40N multiple quantum well (MQW) grown on relaxed AlGaN templates were studied. Although the polarization field in the compressively strained Al0.53In0.11Ga0.36N wells was as high as 1.6 MV/cm, the value of integrated PL intensity at 300 K divided by that at 8 K (eta(int)) was as high as 1.2%. The value was similar to that obtained for the 285 nm PL peak in an Al0.30Ga0.70N/Al0.70Ga0.30N MQW (1.3%), though the A1N molar fraction in the wells was higher by a factor of 1.7. According to these results and the fact that time-resolved PL signal exhibited a stretched exponential decay shape, the improved eta(int) of the AlInGaN wells was attributed to a beneficial effect of the exciton localization as is the case with InGaN alloys; doping or alloying with InN was confirmed to work also on AlGaN in improving eta(int) to realize deep UV optoelectronic devices.

    DOI

  • Recombination dynamics of a 268 nm emission peak in Al0.53In0.11Ga0.36N/Al0.58In0.02Ga0.40N multiple quantum wells

    T Onuma, S Keller, SP DenBaars, JS Speck, S Nakamura, UK Mishra, T Sota, SF Chichibu

    APPLIED PHYSICS LETTERS   88 ( 11 )  2006.03  [Refereed]

     View Summary

    Recombination dynamics of the 268 nm photoluminescence (PL) peak in a quaternary Al0.53In0.11Ga0.36N/Al0.58In0.02Ga0.40N multiple quantum well (MQW) grown on relaxed AlGaN templates were studied. Although the polarization field in the compressively strained Al0.53In0.11Ga0.36N wells was as high as 1.6 MV/cm, the value of integrated PL intensity at 300 K divided by that at 8 K (eta(int)) was as high as 1.2%. The value was similar to that obtained for the 285 nm PL peak in an Al0.30Ga0.70N/Al0.70Ga0.30N MQW (1.3%), though the A1N molar fraction in the wells was higher by a factor of 1.7. According to these results and the fact that time-resolved PL signal exhibited a stretched exponential decay shape, the improved eta(int) of the AlInGaN wells was attributed to a beneficial effect of the exciton localization as is the case with InGaN alloys; doping or alloying with InN was confirmed to work also on AlGaN in improving eta(int) to realize deep UV optoelectronic devices.

    DOI

  • Conformational properties of and a reorientation triggered by sugar-water vibrational resonance in the hydroxymethyl group in hydrated beta-glucopyranose

    T Suzuki, H Kawashima, T Sota

    JOURNAL OF PHYSICAL CHEMISTRY B   110 ( 5 ) 2405 - 2418  2006.02  [Refereed]

     View Summary

    In this paper, we discuss the conformational properties of the hydroxymethyl group of beta-glucopyranose in aqueous solution and its reorientation mechanism. First, using the values for the hydroxymethyl torsion (O5-C5-C6-06) angle obtained by our ab initio simulations, we reestimate the experimental ratio of the hydroxymethyl rotamer populations. The reestimated ratio is found to be in agreement with those previously reported in several computational studies, which probably partly explains the discrepancies between theoretical and experimental studies that have been discussed in the literature. Second, our time-frequency analysis on a reorientation in the hydroxymethyl group in an ab initio molecular dynamics trajectory suggests that, before the reorientation, the O6-H6 stretching mode is vibrationally coupled with a proton-accepting first-hydration-shell water molecule, whereas the C6-O6 stretching mode is vibrationally coupled with a proton-donating one. The amount of the total vibrational energy induced by these vibrational couplings is estimated to be comparable to typical values for the potential barriers between hydroxymethyl rotamers. To elucidate the vibrational couplings, we investigate the hydrogen-bonding properties around the hydroxymethyl group during the pretransition period. The implications, validity, and limitation of a possible reorientation mechanism based on these findings are also discussed.

    DOI PubMed CiNii

  • Conformational properties of and a reorientation triggered by sugar-water vibrational resonance in the hydroxymethyl group in hydrated beta-glucopyranose

    T Suzuki, H Kawashima, T Sota

    JOURNAL OF PHYSICAL CHEMISTRY B   110 ( 5 ) 2405 - 2418  2006.02  [Refereed]

     View Summary

    In this paper, we discuss the conformational properties of the hydroxymethyl group of beta-glucopyranose in aqueous solution and its reorientation mechanism. First, using the values for the hydroxymethyl torsion (O5-C5-C6-06) angle obtained by our ab initio simulations, we reestimate the experimental ratio of the hydroxymethyl rotamer populations. The reestimated ratio is found to be in agreement with those previously reported in several computational studies, which probably partly explains the discrepancies between theoretical and experimental studies that have been discussed in the literature. Second, our time-frequency analysis on a reorientation in the hydroxymethyl group in an ab initio molecular dynamics trajectory suggests that, before the reorientation, the O6-H6 stretching mode is vibrationally coupled with a proton-accepting first-hydration-shell water molecule, whereas the C6-O6 stretching mode is vibrationally coupled with a proton-donating one. The amount of the total vibrational energy induced by these vibrational couplings is estimated to be comparable to typical values for the potential barriers between hydroxymethyl rotamers. To elucidate the vibrational couplings, we investigate the hydrogen-bonding properties around the hydroxymethyl group during the pretransition period. The implications, validity, and limitation of a possible reorientation mechanism based on these findings are also discussed.

    DOI PubMed CiNii

  • Structural fluctuation and dynamics of ribose puckering in aqueous solution from first principles

    T Suzuki, H Kawashima, H Kotoku, T Sota

    JOURNAL OF PHYSICAL CHEMISTRY B   109 ( 26 ) 12997 - 13005  2005.07  [Refereed]

     View Summary

    Using the method of ab initio molecular dynamics, we examine the structural fluctuation and the low-frequency dynamics of beta-ribofuranose puckering in aqueous solution. Our analysis suggests that the distance between the anomeric and hydroxymethyl oxygens is a simple relevant geometrical parameter that dynamically correlates with the phase angle in the north region. The time-frequency analysis using the Hilbert-Huang transform also confirms the correlation, and most of the instantaneous frequencies for the phase angle and the above distance are found to be concentrated on the region below about 100 cm(-1). Our analysis of ab initio molecular dynamics trajectories suggests that the molecular origin of the hydration effects on the low-frequency dynamics of beta-ribofuranose puckering is closely related to this correlation and thus primarily attributed to the relatively local interactions among the anomeric and hydroxymethyl oxygens and the surrounding water molecules near them. Additionally, we discuss the difference in the low-frequency dynamics of P-ribofuranose puckering between two hydroxymethyl rotarners.

    DOI CiNii

  • Structural fluctuation and dynamics of ribose puckering in aqueous solution from first principles

    T Suzuki, H Kawashima, H Kotoku, T Sota

    JOURNAL OF PHYSICAL CHEMISTRY B   109 ( 26 ) 12997 - 13005  2005.07  [Refereed]

     View Summary

    Using the method of ab initio molecular dynamics, we examine the structural fluctuation and the low-frequency dynamics of beta-ribofuranose puckering in aqueous solution. Our analysis suggests that the distance between the anomeric and hydroxymethyl oxygens is a simple relevant geometrical parameter that dynamically correlates with the phase angle in the north region. The time-frequency analysis using the Hilbert-Huang transform also confirms the correlation, and most of the instantaneous frequencies for the phase angle and the above distance are found to be concentrated on the region below about 100 cm(-1). Our analysis of ab initio molecular dynamics trajectories suggests that the molecular origin of the hydration effects on the low-frequency dynamics of beta-ribofuranose puckering is closely related to this correlation and thus primarily attributed to the relatively local interactions among the anomeric and hydroxymethyl oxygens and the surrounding water molecules near them. Additionally, we discuss the difference in the low-frequency dynamics of P-ribofuranose puckering between two hydroxymethyl rotarners.

    DOI CiNii

  • Circular hydrogen bond networks on the surface of beta-ribofuranose in aqueous solution

    T Suzuki, T Sota

    JOURNAL OF PHYSICAL CHEMISTRY B   109 ( 25 ) 12603 - 12611  2005.06  [Refereed]

    Book review, literature introduction, etc.  

     View Summary

    This paper examines the hydration structure on the surface of beta-ribofuranose in aqueous solution, using the ab initio molecular dynamics method. In particular, we focus on circular hydrogen bond networks involving two ribofuranose oxygens and three water molecules. In our simulations, the circular hydrogen bond networks near the ring oxygen of beta-ribofuranose are found to be significantly influenced by the orientation of the hydroxymethyl group. The arrangements of hydrogen bonds observed in the circular hydrogen bond networks are both homodromic and antidromic. To explain these observations, we analyze the electronic properties of the first-hydration-shell water molecules and the OH groups of beta-ribofuranose, using the centers of their maximally localized Wannier functions. The dipole moments of the proton-accepting first-hydration-shell water molecules in our well-defined circular hydrogen bond networks are found to increase by about 0.3 D compared with that of liquid water, indicating the relatively strong polarization effects created by the interactions between the OH groups of the solute and the surrounding water molecules. Our analysis also implies that circular H-bond networks cannot be fully explained from a simple geometrical point of view.

    DOI CiNii

  • Circular hydrogen bond networks on the surface of beta-ribofuranose in aqueous solution

    T Suzuki, T Sota

    JOURNAL OF PHYSICAL CHEMISTRY B   109 ( 25 ) 12603 - 12611  2005.06  [Refereed]

    Book review, literature introduction, etc.  

     View Summary

    This paper examines the hydration structure on the surface of beta-ribofuranose in aqueous solution, using the ab initio molecular dynamics method. In particular, we focus on circular hydrogen bond networks involving two ribofuranose oxygens and three water molecules. In our simulations, the circular hydrogen bond networks near the ring oxygen of beta-ribofuranose are found to be significantly influenced by the orientation of the hydroxymethyl group. The arrangements of hydrogen bonds observed in the circular hydrogen bond networks are both homodromic and antidromic. To explain these observations, we analyze the electronic properties of the first-hydration-shell water molecules and the OH groups of beta-ribofuranose, using the centers of their maximally localized Wannier functions. The dipole moments of the proton-accepting first-hydration-shell water molecules in our well-defined circular hydrogen bond networks are found to increase by about 0.3 D compared with that of liquid water, indicating the relatively strong polarization effects created by the interactions between the OH groups of the solute and the surrounding water molecules. Our analysis also implies that circular H-bond networks cannot be fully explained from a simple geometrical point of view.

    DOI CiNii

  • Measurements of exciton-polariton dynamics in ZnO by using nonlinear spectroscopic techniques

    K Hazu, S Adachi, T Sota, SF Chichibu

    JOURNAL OF LUMINESCENCE   112 ( 1-4 ) 7 - 10  2005.04  [Refereed]

     View Summary

    We have studied the exciton-polariton dynamics in a c-face bulk ZnO crystal grown by the seeded vapor transport method. We have performed two-pulse spectrally resolved four-wave mixing (SR-FWM) and three-pulse SR-FWM at T = 10 K. In two-pulse FWM experiment, obtained FWM signals showed the fast dephasing which has been attributed to the strong polariton dispersion of the upper polariton of B exciton. On the other hand, in three-pulse FWM experiment, the signal decay shows the free exciton population relaxation. Observed FWM signal has decayed with time constant similar to 12 ps which may represent exciton-polariton lifetime. (c) 2004 Elsevier B.V. All rights reserved.

    DOI

  • Exciton-polariton spectra and limiting factors for the room-temperature photoluminescence efficiency in ZnO

    SF Chichibu, A Uedono, A Tsukazaki, T Onuma, M Zamfirescu, A Ohtomo, A Kavokin, G Cantwell, CW Litton, T Sota, M Kawasaki

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   20 ( 4 ) S67 - S77  2005.04  [Refereed]

     View Summary

    Static and dynamic responses of excitons in state-of-the-art bulk and epitaxial ZnO are reviewed to support the possible realization of polariton lasers, which are coherent and monochromatic light sources due to Bose condensation of exciton-polaritons in semiconductor microcavities (MCs). To grasp the current problems and to pave the way for obtaining ZnO epilayers of improved quality, the following four principal subjects are treated: (i) polarized optical reflectance (OR), photoreflectance (PR) and photoluminescence (PL) spectra of the bulk and epitaxial ZnO were recorded at 8 K. Energies of PR resonances corresponded to those of upper and lower exciton-polariton branches, where A-, B- and C-excitons couple simultaneously to an electromagnetic wave. PL peaks due to the corresponding polariton branches were observed. Longitudinal-transverse splittings (omega(LT)) of the corresponding excitons were 1.5, 11.1 and 13.1 meV, respectively. The latter two values are more than two orders of magnitude greater than that of GaAs being 0.08 meV. (ii) Using these values and material parameters, corresponding vacuum-field Rabi splitting of exciton-polaritons coupled to a model MC mode was calculated to be 191 meV, which is the highest value ever reported for semiconductor MCs and satisfies the requirements to observe the strong exciton-light coupling regime necessary for polariton lasing above room temperature. (iii) Polarized OR and PR spectra of an out-plane nonpolar (1120) ZnO epilayer grown by laser-assisted molecular beam epitaxy (L-MBE) were measured, since ZnO quantum wells (QWs) grown in nonpolar orientations are expected to show higher emission efficiencies due to the elimination of spontaneous and piezoelectric polarization fields normal to the QW plane. They exhibited in-plane anisotropic exciton resonances according to the polarization selection rules for anisotropically-strained wurzite material. (iv) Impacts of point defects on the nonradiative processes in L-MBE ZnO were studied using time-resolved PL making a connection with the results of positron annihilation measurement. Free excitonic PL intensity at room temperature naturally increased with the increase in nonradiative lifetime (tau(nr)). The value of tau(nr) increased and density or size of Zn vacancies (V-Zn) decreased with increasing growth temperature (T-g) in heteroepitaxial films grown on a ScAlMgO4 substrate, and the use of homoepitaxial substrates further reduced VZn density. The value Of tau(nr) was shown to increase with the decrease in gross density of positively and negatively charged and neutral point defects including complexes rather than with the decrease in V-Zn density. The results indicate that the nonradiative recombination process is governed not by single point defects, but by certain defects introduced with the incorporation Of V-Zn, such as V-Zn-defect complexes. As a result of defect elimination by growing the films at high T I followed by subsequent post-growth in situ annealing, combined with the use of high-temperature-annealed ZnO self-buffer layer, a record long tau(nr) for spontaneous emission of 3.8 ns was obtained at room temperature. By using progressively improving epitaxial growth methods, the polariton laser effect is expected to be observed at room temperature in the near future.

    DOI

  • Localized exciton dynamics in nonpolar (1120) InxGa1-xN multiple quantum wells grown on GaN templates prepared by lateral epitaxial overgrowth

    T Onuma, A Chakraborty, BA Haskell, S Keller, SP DenBaars, JS Speck, S Nakamura, UK Mishra, T Sota, SF Chichibu

    APPLIED PHYSICS LETTERS   86 ( 15 )  2005.04  [Refereed]

     View Summary

    Beneficial effects of the localized excitons were confirmed in nonpolar (11(2) over bar 0) InxGa1-xN multiple quantum wells (QWs) grown on GaN templates prepared by lateral epitaxial overgrowth. Due to the absence of the polarization fields normal to the QW plane, the photoluminescence (PL) peak energy moderately shifted to the higher energy and the radiative lifetime did not change remarkably with the decrease in the well thickness. Similar to the case for polar InGaN QWs, time-resolved PL signals exhibited the nonexponential decay shape, which can be explained by thermalization and subsequent localization of excitons. Although the growth conditions were not fully optimized, values of the PL intensity at 300 K divided by that at 8 K were 25% and 17% for the peaks at 2.92 and 2.60 eV, respectively. (C) 2005 American Institute of Physics.

    DOI

  • Measurements of exciton-polariton dynamics in ZnO by using nonlinear spectroscopic techniques

    K Hazu, S Adachi, T Sota, SF Chichibu

    JOURNAL OF LUMINESCENCE   112 ( 1-4 ) 7 - 10  2005.04  [Refereed]

     View Summary

    We have studied the exciton-polariton dynamics in a c-face bulk ZnO crystal grown by the seeded vapor transport method. We have performed two-pulse spectrally resolved four-wave mixing (SR-FWM) and three-pulse SR-FWM at T = 10 K. In two-pulse FWM experiment, obtained FWM signals showed the fast dephasing which has been attributed to the strong polariton dispersion of the upper polariton of B exciton. On the other hand, in three-pulse FWM experiment, the signal decay shows the free exciton population relaxation. Observed FWM signal has decayed with time constant similar to 12 ps which may represent exciton-polariton lifetime. (c) 2004 Elsevier B.V. All rights reserved.

    DOI

  • Exciton-polariton spectra and limiting factors for the room-temperature photoluminescence efficiency in ZnO

    SF Chichibu, A Uedono, A Tsukazaki, T Onuma, M Zamfirescu, A Ohtomo, A Kavokin, G Cantwell, CW Litton, T Sota, M Kawasaki

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   20 ( 4 ) S67 - S77  2005.04  [Refereed]

     View Summary

    Static and dynamic responses of excitons in state-of-the-art bulk and epitaxial ZnO are reviewed to support the possible realization of polariton lasers, which are coherent and monochromatic light sources due to Bose condensation of exciton-polaritons in semiconductor microcavities (MCs). To grasp the current problems and to pave the way for obtaining ZnO epilayers of improved quality, the following four principal subjects are treated: (i) polarized optical reflectance (OR), photoreflectance (PR) and photoluminescence (PL) spectra of the bulk and epitaxial ZnO were recorded at 8 K. Energies of PR resonances corresponded to those of upper and lower exciton-polariton branches, where A-, B- and C-excitons couple simultaneously to an electromagnetic wave. PL peaks due to the corresponding polariton branches were observed. Longitudinal-transverse splittings (omega(LT)) of the corresponding excitons were 1.5, 11.1 and 13.1 meV, respectively. The latter two values are more than two orders of magnitude greater than that of GaAs being 0.08 meV. (ii) Using these values and material parameters, corresponding vacuum-field Rabi splitting of exciton-polaritons coupled to a model MC mode was calculated to be 191 meV, which is the highest value ever reported for semiconductor MCs and satisfies the requirements to observe the strong exciton-light coupling regime necessary for polariton lasing above room temperature. (iii) Polarized OR and PR spectra of an out-plane nonpolar (1120) ZnO epilayer grown by laser-assisted molecular beam epitaxy (L-MBE) were measured, since ZnO quantum wells (QWs) grown in nonpolar orientations are expected to show higher emission efficiencies due to the elimination of spontaneous and piezoelectric polarization fields normal to the QW plane. They exhibited in-plane anisotropic exciton resonances according to the polarization selection rules for anisotropically-strained wurzite material. (iv) Impacts of point defects on the nonradiative processes in L-MBE ZnO were studied using time-resolved PL making a connection with the results of positron annihilation measurement. Free excitonic PL intensity at room temperature naturally increased with the increase in nonradiative lifetime (tau(nr)). The value of tau(nr) increased and density or size of Zn vacancies (V-Zn) decreased with increasing growth temperature (T-g) in heteroepitaxial films grown on a ScAlMgO4 substrate, and the use of homoepitaxial substrates further reduced VZn density. The value Of tau(nr) was shown to increase with the decrease in gross density of positively and negatively charged and neutral point defects including complexes rather than with the decrease in V-Zn density. The results indicate that the nonradiative recombination process is governed not by single point defects, but by certain defects introduced with the incorporation Of V-Zn, such as V-Zn-defect complexes. As a result of defect elimination by growing the films at high T I followed by subsequent post-growth in situ annealing, combined with the use of high-temperature-annealed ZnO self-buffer layer, a record long tau(nr) for spontaneous emission of 3.8 ns was obtained at room temperature. By using progressively improving epitaxial growth methods, the polariton laser effect is expected to be observed at room temperature in the near future.

    DOI

  • Localized exciton dynamics in nonpolar (1120) InxGa1-xN multiple quantum wells grown on GaN templates prepared by lateral epitaxial overgrowth

    T Onuma, A Chakraborty, BA Haskell, S Keller, SP DenBaars, JS Speck, S Nakamura, UK Mishra, T Sota, SF Chichibu

    APPLIED PHYSICS LETTERS   86 ( 15 )  2005.04  [Refereed]

     View Summary

    Beneficial effects of the localized excitons were confirmed in nonpolar (11(2) over bar 0) InxGa1-xN multiple quantum wells (QWs) grown on GaN templates prepared by lateral epitaxial overgrowth. Due to the absence of the polarization fields normal to the QW plane, the photoluminescence (PL) peak energy moderately shifted to the higher energy and the radiative lifetime did not change remarkably with the decrease in the well thickness. Similar to the case for polar InGaN QWs, time-resolved PL signals exhibited the nonexponential decay shape, which can be explained by thermalization and subsequent localization of excitons. Although the growth conditions were not fully optimized, values of the PL intensity at 300 K divided by that at 8 K were 25% and 17% for the peaks at 2.92 and 2.60 eV, respectively. (C) 2005 American Institute of Physics.

    DOI

  • Limiting factors of room-temperature nonradiative photoluminescence lifetime in polar and nonpolar GaN studied by time-resolved photoluminescence and slow positron annihilation techniques

    SF Chichibu, A Uedono, T Onuma, T Sota, BA Haskell, SP DenBaars, JS Speck, S Nakamura

    APPLIED PHYSICS LETTERS   86 ( 2 )  2005.01  [Refereed]

     View Summary

    Room-temperature nonradiative lifetime (tau(nr)) of the near-band-edge excitonic photoluminescence (PL) peak in {0001} polar, (11 (2) over bar0), (1 (1) over bar 00), and (001) nonpolar GaN was shown to increase with the decrease in density or size of Ga vacancies (V-Ga) and with the decrease in gross density of point defects including complexes, leading to the increase in the PL intensity. As the edge threading dislocation density decreased, density or size of V-Ga tended to decrease and tau(nr) tended to increase. However, there existed remarkable exceptions. The results indicate that nonradiative recombination process is governed not by single point defects, but by certain defects introduced with the incorporation of V-Ga, such as V-Ga-defect complexes. (C) 2005 American Institute of Physics.

    DOI

  • Biexcitons and their dephasing processes in ZnO

    S Adachi, K Hazu, T Sota, S Chichibu, G Cantwell, DC Reynolds, CW Litton

    FOURTH INTERNATIONAL CONFERENCE ON PHYSICS OF LIGHT-MATTER COUPLING IN NANOSTRUCTURES (PLMCN4)   2 ( 2 ) 890 - 895  2005  [Refereed]

     View Summary

    We have investigated free excitons and biexcitons of bulk ZnO by time-integrated and spectrally-resolved four-wave mixing. The polarization- and wave-vector-dependent FWM signals for A and B excitons demonstrate clearly that the valence-band ordering is A - Gamma(9), B - Gamma(7), and C - Gamma(7). Next, we gave qualitative explanation of the FWM signals induced by excitons and biexcitons in ZnO. For negative delay times, bound and unbound AB-biexcitons (A exciton-B exciton correlation), which have been considered to play a minor role in GaAs heterostructures, was found to play an important role and give a significant qualitative impact to the optical response of ZnO. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI

  • Limiting factors of room-temperature nonradiative photoluminescence lifetime in polar and nonpolar GaN studied by time-resolved photoluminescence and slow positron annihilation techniques

    SF Chichibu, A Uedono, T Onuma, T Sota, BA Haskell, SP DenBaars, JS Speck, S Nakamura

    APPLIED PHYSICS LETTERS   86 ( 2 )  2005.01  [Refereed]

     View Summary

    Room-temperature nonradiative lifetime (tau(nr)) of the near-band-edge excitonic photoluminescence (PL) peak in {0001} polar, (11 (2) over bar0), (1 (1) over bar 00), and (001) nonpolar GaN was shown to increase with the decrease in density or size of Ga vacancies (V-Ga) and with the decrease in gross density of point defects including complexes, leading to the increase in the PL intensity. As the edge threading dislocation density decreased, density or size of V-Ga tended to decrease and tau(nr) tended to increase. However, there existed remarkable exceptions. The results indicate that nonradiative recombination process is governed not by single point defects, but by certain defects introduced with the incorporation of V-Ga, such as V-Ga-defect complexes. (C) 2005 American Institute of Physics.

    DOI

  • Biexcitons and their dephasing processes in ZnO

    S Adachi, K Hazu, T Sota, S Chichibu, G Cantwell, DC Reynolds, CW Litton

    FOURTH INTERNATIONAL CONFERENCE ON PHYSICS OF LIGHT-MATTER COUPLING IN NANOSTRUCTURES (PLMCN4)   2 ( 2 ) 890 - 895  2005  [Refereed]

     View Summary

    We have investigated free excitons and biexcitons of bulk ZnO by time-integrated and spectrally-resolved four-wave mixing. The polarization- and wave-vector-dependent FWM signals for A and B excitons demonstrate clearly that the valence-band ordering is A - Gamma(9), B - Gamma(7), and C - Gamma(7). Next, we gave qualitative explanation of the FWM signals induced by excitons and biexcitons in ZnO. For negative delay times, bound and unbound AB-biexcitons (A exciton-B exciton correlation), which have been considered to play a minor role in GaAs heterostructures, was found to play an important role and give a significant qualitative impact to the optical response of ZnO. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

    DOI

  • Reduced nonradiative defect densities in ZnO epilayers grown on Si substrates by the use of ZnS epitaxial buffer layers

    Onuma, T, Chichibu, SF, Uedono, A

    Appl. Phys. Lett./AIP   85 (23), pp.5586-5588  2004.12

    DOI

  • Reduced nonradiative defect densities in ZnO epilayers grown on Si substrates by the use of ZnS epitaxial buffer layers

    Onuma, T, Chichibu, SF, Uedono, A

    Appl. Phys. Lett./AIP   85 (23), pp.5586-5588  2004.12

    DOI

  • Direct comparison of photoluminescence lifetime and defect densities in ZnO epilayers studied by time-resolved photoluminescence and slow positoron annihilation techniques

    Koida, T, Uedono, A, Tsukazaki, A

    Phys. Stat. Solidi A-appl. Res. /Elsevier   201(12), 2841-2845  2004.09

    DOI

  • Direct comparison of photoluminescence lifetime and defect densities in ZnO epilayers studied by time-resolved photoluminescence and slow positron annihilation techniques

    T Koida, A Uedono, A Tsukazaki, T Sota, M Kawasaki, SF Chichibu

    PHYSICA STATUS SOLIDI A-APPLIED RESEARCH   201 ( 12 ) 2841 - 2845  2004.09  [Refereed]

     View Summary

    The roles of point defects and defect complexes governing nonradiative processes in ZnO epilayers were studied using time-resolved photoluminescence (PL) and slow positron annihilation measurements. The density or size of Zn vacancies (V-Zn) decreased and the nonradiative PL lifetime (tau(nr)) increased with higher growth temperature for epilayers grown on a ScAlMgO4 substrate. Accordingly, the steady-state free excitonic PL intensity increased with increase in tau(nr) at room temperature. The use of a homoepitaxial substrate further decreased the V-Zn concentration. However, no perfect relation between tau(nr) and the density or size of V-Zn or other positron scattering centers was found. The results indicated that nonradiative recombination processes are governed not solely by single point defects, but by certain defect species introduced by the presence of V-Zn such as vacancy complexes.

    DOI

  • Phonon scattering of excitons and biexcitons in ZnO

    K Hazu, T Sota, S Adachi, S Chichibu, G Cantwell, DC Reynolds, CW Litton

    JOURNAL OF APPLIED PHYSICS   96 ( 2 ) 1270 - 1272  2004.07  [Refereed]

     View Summary

    The phase relaxation time of biexcitons T-2(bi) and that of excitons T-2(ex) in a bulk ZnO have been measured by the use of femtosecond four-wave mixing as functions of excitation wavelength, excitation power, and temperature. The biexciton-acoustic phonon interaction coefficient has been determined to be beta(ac)(bi)approximate to53 mueV/K as an average value. For A excitons, the interaction coefficients with acoustic and optical phonons have been determined to be beta(ac)(ex)approximate to8.4 mueV/K and beta(opt)(ex)approximate to14 meV, respectively. (C) 2004 American Institute of Physics.

    DOI

  • Phonon scattering of excitons and biexcitons in ZnO

    K Hazu, T Sota, S Adachi, S Chichibu, G Cantwell, DC Reynolds, CW Litton

    JOURNAL OF APPLIED PHYSICS   96 ( 2 ) 1270 - 1272  2004.07  [Refereed]

     View Summary

    The phase relaxation time of biexcitons T-2(bi) and that of excitons T-2(ex) in a bulk ZnO have been measured by the use of femtosecond four-wave mixing as functions of excitation wavelength, excitation power, and temperature. The biexciton-acoustic phonon interaction coefficient has been determined to be beta(ac)(bi)approximate to53 mueV/K as an average value. For A excitons, the interaction coefficients with acoustic and optical phonons have been determined to be beta(ac)(ex)approximate to8.4 mueV/K and beta(opt)(ex)approximate to14 meV, respectively. (C) 2004 American Institute of Physics.

    DOI

  • Improved quantum efficiency in nonpolar (11(2)over-bar0) AlGaN/GaN quantum wells grown on GaN prepared by lateral epitaxial overgrowth

    T Koida, SF Chichibu, T Sota, MD Craven, BA Haskell, JS Speck, SP DenBaars, S Nakamura

    APPLIED PHYSICS LETTERS   84 ( 19 ) 3768 - 3770  2004.05  [Refereed]

     View Summary

    Radiative and nonradiative excitonic transitions in nonpolar (11 (2) over bar0) AlxGa1-xN/GaN multiple quantum wells (MQWs) grown on the GaN template prepared by lateral epitaxial overgrowth (LEO-GaN) were investigated. The structural advantages of using nonpolar orientations were confirmed by a moderate shift of the photoluminescence (PL) peak energy and negligible change in low-temperature PL lifetime with decreasing GaN well width, both of which are the results of eliminating quantum-confined Stark effects due to the polarization fields that exist in polar (0001) MQWs. Appearance of the correct in-plane light polarization and improved internal quantum efficiency for the PL peak in the MQWs on LEO-GaN were attributed to the reduction in densities of nonradiative defects and bound states. (C) 2004 American Institute of Physics.

    DOI

  • Impact of the k-linear term on nonlinear optical response of the C-exciton manifold in ZnO

    K Hazu, K Torii, T Sota, S Adachi, SF Chichibu, G Cantwell, DC Reynolds, CW Litton

    JOURNAL OF APPLIED PHYSICS   95 ( 10 ) 5498 - 5501  2004.05  [Refereed]

     View Summary

    Time-integrated and spectrally resolved four-wave mixing (FWM) has been applied to study the impact of the k-linear term on nonlinear optical response of the C-exciton manifold in ZnO. From the excitation wavelength dependence of the FWM signal, we have found possible evidence that the mixing of the Gamma(1) and Gamma(5L) states leads to a three-branch excitonic polariton dispersion but the oscillator strength transfer is small. The energy separation between the lower polariton branch and the extra branch due to the k-linear term has been found to be 3.5 meV. In addition, a binding energy of biexcitons consisting of two C excitons of 1.4 meV has been obtained. (C) 2004 American Institute of Physics.

    DOI

  • Improved quantum efficiency in nonpolar (11(2)over-bar0) AlGaN/GaN quantum wells grown on GaN prepared by lateral epitaxial overgrowth

    T Koida, SF Chichibu, T Sota, MD Craven, BA Haskell, JS Speck, SP DenBaars, S Nakamura

    APPLIED PHYSICS LETTERS   84 ( 19 ) 3768 - 3770  2004.05  [Refereed]

     View Summary

    Radiative and nonradiative excitonic transitions in nonpolar (11 (2) over bar0) AlxGa1-xN/GaN multiple quantum wells (MQWs) grown on the GaN template prepared by lateral epitaxial overgrowth (LEO-GaN) were investigated. The structural advantages of using nonpolar orientations were confirmed by a moderate shift of the photoluminescence (PL) peak energy and negligible change in low-temperature PL lifetime with decreasing GaN well width, both of which are the results of eliminating quantum-confined Stark effects due to the polarization fields that exist in polar (0001) MQWs. Appearance of the correct in-plane light polarization and improved internal quantum efficiency for the PL peak in the MQWs on LEO-GaN were attributed to the reduction in densities of nonradiative defects and bound states. (C) 2004 American Institute of Physics.

    DOI

  • Impact of the k-linear term on nonlinear optical response of the C-exciton manifold in ZnO

    K Hazu, K Torii, T Sota, S Adachi, SF Chichibu, G Cantwell, DC Reynolds, CW Litton

    JOURNAL OF APPLIED PHYSICS   95 ( 10 ) 5498 - 5501  2004.05  [Refereed]

     View Summary

    Time-integrated and spectrally resolved four-wave mixing (FWM) has been applied to study the impact of the k-linear term on nonlinear optical response of the C-exciton manifold in ZnO. From the excitation wavelength dependence of the FWM signal, we have found possible evidence that the mixing of the Gamma(1) and Gamma(5L) states leads to a three-branch excitonic polariton dispersion but the oscillator strength transfer is small. The energy separation between the lower polariton branch and the extra branch due to the k-linear term has been found to be 3.5 meV. In addition, a binding energy of biexcitons consisting of two C excitons of 1.4 meV has been obtained. (C) 2004 American Institute of Physics.

    DOI

  • Biexciton formation and exciton-exciton correlation effects in bulk ZnO

    S Adachi, K Hazu, T Sota, SF Chichibu, G Cantwell, DB Eason, DC Reynolds, CW Litton

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   19 ( 4 ) S276 - S278  2004.04  [Refereed]

     View Summary

    We demonstrate that exciton-exciton correlations strongly affect FWM signals. In particular, A exciton-B exciton correlation (bound and unbound A B-biexcitons), which can be generated even in co-circular polarizations, has a significant qualitative impact on the optical response of bulk ZnO.

    DOI

  • Biexciton formation and exciton-exciton correlation effects in bulk ZnO

    S Adachi, K Hazu, T Sota, SF Chichibu, G Cantwell, DB Eason, DC Reynolds, CW Litton

    SEMICONDUCTOR SCIENCE AND TECHNOLOGY   19 ( 4 ) S276 - S278  2004.04  [Refereed]

     View Summary

    We demonstrate that exciton-exciton correlations strongly affect FWM signals. In particular, A exciton-B exciton correlation (bound and unbound A B-biexcitons), which can be generated even in co-circular polarizations, has a significant qualitative impact on the optical response of bulk ZnO.

    DOI

  • Radiative and nonradiative processes in strain-free AlxGa1-xN films studied by time-resolved photoluminescence and positron annihilation techniques

    T Onuma, SF Chichibu, A Uedono, T Sota, P Cantu, TM Katona, JF Keading, S Keller, UK Mishra, S Nakamura, SP DenBaars

    JOURNAL OF APPLIED PHYSICS   95 ( 5 ) 2495 - 2504  2004.03  [Refereed]

     View Summary

    Radiative and nonradiative processes in nearly strain-free AlxGa1-xN alloys were studied by means of steady-state and time-resolved (TR) photoluminescence (PL) spectroscopy, and the results were connected with that of positron annihilation measurement. The results of steady-state optical reflectance and PL measurements gave the bowing parameter b of approximately -0.82 eV. Values of the full width at half maximum (FWHM) of the near-band-edge PL peak nearly agreed with those predicted by the classical alloy broadening model. However, the Stokes-type shifts (SS) were as large as 100-250 meV and both SS and FWHM of the PL increased with the increase in x for xless than or equal to0.7. Simultaneously, the luminescence redshift due to the increase in temperature T from 8 to 300 K decreased with increasing x and approached zero for x=0.5. These results indicated the presence of compositional fluctuation forming weakly bound states in the alloys, and the localized excitons tended to delocalize with the increase in T. The TRPL signals showed a biexponential decay at low temperature, and the slower component became longer with the increase in x (over 40 ns for x=0.49). Simultaneously, density or size of cation vacancies (V-III) and relative intensity of the deep-level emission over that of the near-band-edge one at 300 K increased as x increased to x=0.7. Consequently, certain trapping mechanisms associated with V-III where suggested, and excitons were then detrapped and transferred to the localized states before the radiative decay at low temperature; the increase in the slower lifetime and its dominance over the entire TRPL signal intensity with increasing x may reflect the increase of the depth and concentration of the trapping level. As the temperature was increased, the TRPL signal became single exponential due to the increasing dominance of nonradiative recombination processes in the free states, resulting in lower internal quantum efficiency (eta(int)) with increasing x for xless than or equal to0.7. Therefore, realization of AlGaN-based efficient deep-UV light emitters requires further reduction of the nonradiative defect density as well as the V-III-related trap density. (C) 2004 American Institute of Physics.

    DOI

  • Radiative and nonradiative processes in strain-free AlxGa1-xN films studied by time-resolved photoluminescence and positron annihilation techniques

    T Onuma, SF Chichibu, A Uedono, T Sota, P Cantu, TM Katona, JF Keading, S Keller, UK Mishra, S Nakamura, SP DenBaars

    JOURNAL OF APPLIED PHYSICS   95 ( 5 ) 2495 - 2504  2004.03  [Refereed]

     View Summary

    Radiative and nonradiative processes in nearly strain-free AlxGa1-xN alloys were studied by means of steady-state and time-resolved (TR) photoluminescence (PL) spectroscopy, and the results were connected with that of positron annihilation measurement. The results of steady-state optical reflectance and PL measurements gave the bowing parameter b of approximately -0.82 eV. Values of the full width at half maximum (FWHM) of the near-band-edge PL peak nearly agreed with those predicted by the classical alloy broadening model. However, the Stokes-type shifts (SS) were as large as 100-250 meV and both SS and FWHM of the PL increased with the increase in x for xless than or equal to0.7. Simultaneously, the luminescence redshift due to the increase in temperature T from 8 to 300 K decreased with increasing x and approached zero for x=0.5. These results indicated the presence of compositional fluctuation forming weakly bound states in the alloys, and the localized excitons tended to delocalize with the increase in T. The TRPL signals showed a biexponential decay at low temperature, and the slower component became longer with the increase in x (over 40 ns for x=0.49). Simultaneously, density or size of cation vacancies (V-III) and relative intensity of the deep-level emission over that of the near-band-edge one at 300 K increased as x increased to x=0.7. Consequently, certain trapping mechanisms associated with V-III where suggested, and excitons were then detrapped and transferred to the localized states before the radiative decay at low temperature; the increase in the slower lifetime and its dominance over the entire TRPL signal intensity with increasing x may reflect the increase of the depth and concentration of the trapping level. As the temperature was increased, the TRPL signal became single exponential due to the increasing dominance of nonradiative recombination processes in the free states, resulting in lower internal quantum efficiency (eta(int)) with increasing x for xless than or equal to0.7. Therefore, realization of AlGaN-based efficient deep-UV light emitters requires further reduction of the nonradiative defect density as well as the V-III-related trap density. (C) 2004 American Institute of Physics.

    DOI

  • Radiative and nonradiative excitonic transitions in nonpolar (112̄0) and polar (0001̄) and (0001) Zno epilayers

    J. Koida, S. F. Chichibu, A. Uedono, T. Sota, A. Tsukazaki, M. Kawasaki

    Applied Physics Letters   84 ( 7 ) 1079 - 1081  2004.02

     View Summary

    The polarized optical reflectance and photoreflectance spectra of an out-plane nonpolar ZnO epilayer grown by laser molecular-beam epitaxy was studied. The electric field component of its excitonic photoluminescence peak was polarized perpendicular to the [0001] axis. The monoenergetic positron beam line was used to determine the parameters in the ZnO epilayers. The negligible impact of growth direction on the defect incorporation suggests a potential use of epitaxial ZnO as polarization-sensitive optoelectronic devices operating in ultraviolet spectral regions.

    DOI

  • Radiative and nonradiative excitonic transitions in nonpolar (11(2)over-bar-0) and polar (000(1)over-bar) and (0001) ZnO epilayers

    T Koida, SF Chichibu, A Uedono, T Sota, A Tsukazaki, M Kawasaki

    APPLIED PHYSICS LETTERS   84 ( 7 ) 1079 - 1081  2004.02  [Refereed]

     View Summary

    Polarized optical reflectance and photoreflectance spectra of an out-plane nonpolar (11(2) over bar 0) ZnO epilayer grown by laser molecular-beam epitaxy exhibited anisotropic exciton resonance structures according to the polarization selection rules for anisotropically strained hexagonal material. Consistently, the electric field component of its excitonic photoluminescence (PL) peak was polarized perpendicular to the [0001] axis. Different from the case for GaN, nonradiative PL lifetime at 293 K and the S parameter, which is a measure of Zn vacancy-related defect density obtained by positron annihilation spectroscopy, of the (11(2) over bar 0) ZnO were comparable to those of state-of-the-art polar (000(1) over bar) and (0001) epilayers. Since the polar epilayers exhibited pronounced exciton-polariton emissions, the negligible impact of growth direction on the defect incorporation suggests a potential use of epitaxial (11(2) over bar 0) ZnO as polarization-sensitive optoelectronic devices operating in ultraviolet spectral regions. (C) 2004 American Institute of Physics.

    DOI

  • Hydrogen-deuterium exchange effects on beta-endorphin release from AtT20 murine pituitary tumor cells

    Ikeda, M, Suzuki, S, Kishino, M

    Biophysical J./Biophysical Society   86;1, pp.565-575  2004.01  [Refereed]

  • Hydrogen-deuterium exchange effects on beta-endorphin release from AtT20 murine pituitary tumor cells

    Ikeda, M, Suzuki, S, Kishino, M

    Biophysical J./Biophysical Society   86;1, pp.565-575  2004.01  [Refereed]

  • Influence of internal electric field on the recombination dynamics of localized excitons in an InGaN double-quantum-well laser diode wafer operated at 450 nm

    T Onuma, SF Chichibu, T Aoyama, K Nakajima, P Ahmet, T Azuhata, T Chikyow, T Sota, S Nagahama, T Mukai

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   42 ( 12 ) 7276 - 7283  2003.12  [Refereed]

     View Summary

    Optical and structural properties of an InGaN double-quantum-well (DQW) laser diode (LD) wafer that lased at 450 nm were investigated to discuss an enormous impact of a polarization-induced electric field on the recombination dynamics in InGaN quantum structures. The quantum-well (QW) structure was shown to have the well thickness as thin as approximately I nm and InN molar fraction x of approximately 14%. The gross effective electric field in the QW (F-QW) was estimated to be 490kV/cm from the Franz-Keldysh oscillation (FKO) period in the electroreflectance (ER) spectrum, implying that an internal piezoelectric field (F-piz) of approximately 1.4MV/cm was cancelled by the pn junction built-in field (F-bi) and Coulomb screening due to carriers in the DQW. The magnitude of F-QW can be further weakened by applying reverse bias (V-R) on the junction; the decrease in the photoluminescence (PL) lifetime at low temperature measured under VR was explained to be due to a recovery of electron-hole wavefunction overlap for small VR (\V-R\&lt;4 V), and due mainly to the tunneling escape of carriers through the barriers for larger VR. By applying an appropriate VR smaller than 4V, electron-hole wavefunction overlap, which had been separated vertically along the c-axis due to quantum-confined Stark effect, could be partially recovered, and then the time-resolved PL signals exhibited a less-pronounced stretched exponential decay, giving a scaling parameter (beta) of 0.85 and effective in-plane localization depth (E-0) of 40-50 meV for the spontaneous emission. These values were closer to those of much homogeneous QWs compared to those reported previously for InGaN QWs having similar InN molar fractions. The use of very thin QWs is considered to bring easier Coulomb screening of F-QW and population inversion under high excitation conditions.

    DOI

  • Influence of internal electric field on the recombination dynamics of localized excitons in an InGaN double-quantum-well laser diode wafer operated at 450 nm

    T Onuma, SF Chichibu, T Aoyama, K Nakajima, P Ahmet, T Azuhata, T Chikyow, T Sota, S Nagahama, T Mukai

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   42 ( 12 ) 7276 - 7283  2003.12  [Refereed]

     View Summary

    Optical and structural properties of an InGaN double-quantum-well (DQW) laser diode (LD) wafer that lased at 450 nm were investigated to discuss an enormous impact of a polarization-induced electric field on the recombination dynamics in InGaN quantum structures. The quantum-well (QW) structure was shown to have the well thickness as thin as approximately I nm and InN molar fraction x of approximately 14%. The gross effective electric field in the QW (F-QW) was estimated to be 490kV/cm from the Franz-Keldysh oscillation (FKO) period in the electroreflectance (ER) spectrum, implying that an internal piezoelectric field (F-piz) of approximately 1.4MV/cm was cancelled by the pn junction built-in field (F-bi) and Coulomb screening due to carriers in the DQW. The magnitude of F-QW can be further weakened by applying reverse bias (V-R) on the junction; the decrease in the photoluminescence (PL) lifetime at low temperature measured under VR was explained to be due to a recovery of electron-hole wavefunction overlap for small VR (\V-R\&lt;4 V), and due mainly to the tunneling escape of carriers through the barriers for larger VR. By applying an appropriate VR smaller than 4V, electron-hole wavefunction overlap, which had been separated vertically along the c-axis due to quantum-confined Stark effect, could be partially recovered, and then the time-resolved PL signals exhibited a less-pronounced stretched exponential decay, giving a scaling parameter (beta) of 0.85 and effective in-plane localization depth (E-0) of 40-50 meV for the spontaneous emission. These values were closer to those of much homogeneous QWs compared to those reported previously for InGaN QWs having similar InN molar fractions. The use of very thin QWs is considered to bring easier Coulomb screening of F-QW and population inversion under high excitation conditions.

    DOI

  • Exciton-exciton correlation effects on FWM of GaN

    Adachi, S, Sasakura, H, Muto, S

    Phys. Status Solidi/Elsevier   (b)240;2, pp.348-351  2003.11  [Refereed]

    DOI

  • Improving ab initio infrared spectra of glucose-water complexes by considering explicit intermolecular hydrogen bonds

    T Suzuki, T Sota

    JOURNAL OF CHEMICAL PHYSICS   119 ( 19 ) 10133 - 10137  2003.11  [Refereed]

     View Summary

    In this paper, using density functional theory, we show the effects of explicit intermolecular hydrogen bonds on infrared spectra of glucose-water complexes. The number of explicit water molecules ranges from four to nine, and we approximate the rest of other water molecules as a continuum medium. When eight or nine water molecules are considered explicitly, our computed spectra are in good agreement with the main features of the experimental one. However, in the cases of explicit water molecules less than eight, our computed spectra are not improved successfully. This suggests that in predicting infrared spectrum of glucose in water the effects of explicit water molecules around the glucose molecule are not negligible. We also discuss the numbers of intermolecular hydrogen bonds, spectral differences between alpha and beta anomers, and the main features of normal modes in the 1000-1200 cm(-1) region. (C) 2003 American Institute of Physics.

    DOI CiNii

  • Improved Emission Efficiency in InGaN/GaN Quantum Wells with Composition-Graded Walls Studied by Time-Resolved Photoluminescence Spectroscopy

    Onuma,T, Uchinuma, Y, Suh, E-K

    Jpn. J. Appl. Phys./JPSJ   42;11B, pp.L1369 - L1371  2003.11  [Refereed]

    DOI

  • Exciton-exciton correlation effects on FWM of GaN

    Adachi, S, Sasakura, H, Muto, S

    Phys. Status Solidi/Elsevier   (b)240;2, pp.348-351  2003.11  [Refereed]

    DOI

  • Improving ab initio infrared spectra of glucose-water complexes by considering explicit intermolecular hydrogen bonds

    T Suzuki, T Sota

    JOURNAL OF CHEMICAL PHYSICS   119 ( 19 ) 10133 - 10137  2003.11  [Refereed]

     View Summary

    In this paper, using density functional theory, we show the effects of explicit intermolecular hydrogen bonds on infrared spectra of glucose-water complexes. The number of explicit water molecules ranges from four to nine, and we approximate the rest of other water molecules as a continuum medium. When eight or nine water molecules are considered explicitly, our computed spectra are in good agreement with the main features of the experimental one. However, in the cases of explicit water molecules less than eight, our computed spectra are not improved successfully. This suggests that in predicting infrared spectrum of glucose in water the effects of explicit water molecules around the glucose molecule are not negligible. We also discuss the numbers of intermolecular hydrogen bonds, spectral differences between alpha and beta anomers, and the main features of normal modes in the 1000-1200 cm(-1) region. (C) 2003 American Institute of Physics.

    DOI CiNii

  • Improved Emission Efficiency in InGaN/GaN Quantum Wells with Composition-Graded Walls Studied by Time-Resolved Photoluminescence Spectroscopy

    Onuma,T, Uchinuma, Y, Suh, E-K

    Jpn. J. Appl. Phys./JPSJ   42;11B, pp.L1369 - L1371  2003.11  [Refereed]

    DOI

  • Recombination dynamics of localized excitons in Al1-xInxN epitaxial films on GaN templates grown by metalorganic vapor phase epitaxy

    T Onuma, S Chichibu, Y Uchinuma, T Sota, S Yamaguchi, S Kamiyama, H Amano, Akasaki, I

    JOURNAL OF APPLIED PHYSICS   94 ( 4 ) 2449 - 2453  2003.08  [Refereed]

     View Summary

    Recombination dynamics of excitons in nearly strain-free Al1-xInxN alloys on the GaN template were studied. Their band-gap energy showed a nonlinear dependence on the InN molar fraction x, and the bowing parameter was determined to be approximately -3.1 eV. Most of the alloys exhibited an extremely diffused band-edge, and consequently exhibited huge Stokes-type shifts up to 1-2 eV and full width at half maximum of the luminescence peaks up to 0.5 eV. The results suggested enhanced material inhomogeneity in AlInN compared to InGaN alloys. Since the time-resolved photoluminescence signal showed a pronounced stretched exponential decay, the spontaneous emission was assigned as being due to the radiative recombination of excitons localized in disordered quantum nanostructures. The integrated PL intensity at 300 K was as strong as 29% of that at low temperature, showing a potential use of AlInN alloys as infrared-to-UV light emitters. (C) 2003 American Institute of Physics.

    DOI

  • Recombination dynamics of localized excitons in cubic InxGa1-xN/GaN multiple quantum wells grown by rf-MBE on 3C-SiC substrate

    Chichibu, SF, Onuma, T, Aoyama, T

    J. Vac. Sci. Techn. B/AVS   21;4,pp.1856-1862  2003.08  [Refereed]

    DOI

  • Recombination dynamics of localized excitons in Al1-xInxN epitaxial films on GaN templates grown by metalorganic vapor phase epitaxy

    T Onuma, S Chichibu, Y Uchinuma, T Sota, S Yamaguchi, S Kamiyama, H Amano, Akasaki, I

    JOURNAL OF APPLIED PHYSICS   94 ( 4 ) 2449 - 2453  2003.08  [Refereed]

     View Summary

    Recombination dynamics of excitons in nearly strain-free Al1-xInxN alloys on the GaN template were studied. Their band-gap energy showed a nonlinear dependence on the InN molar fraction x, and the bowing parameter was determined to be approximately -3.1 eV. Most of the alloys exhibited an extremely diffused band-edge, and consequently exhibited huge Stokes-type shifts up to 1-2 eV and full width at half maximum of the luminescence peaks up to 0.5 eV. The results suggested enhanced material inhomogeneity in AlInN compared to InGaN alloys. Since the time-resolved photoluminescence signal showed a pronounced stretched exponential decay, the spontaneous emission was assigned as being due to the radiative recombination of excitons localized in disordered quantum nanostructures. The integrated PL intensity at 300 K was as strong as 29% of that at low temperature, showing a potential use of AlInN alloys as infrared-to-UV light emitters. (C) 2003 American Institute of Physics.

    DOI

  • Recombination dynamics of localized excitons in cubic InxGa1-xN/GaN multiple quantum wells grown by rf-MBE on 3C-SiC substrate

    Chichibu, SF, Onuma, T, Aoyama, T

    J. Vac. Sci. Techn. B/AVS   21;4,pp.1856-1862  2003.08  [Refereed]

    DOI

  • Brillouin scattering study of ZnO

    T Azuhata, M Takesada, T Yagi, A Shikanai, S Chichibu, K Torii, A Nakamura, T Sota, G Cantwell, DB Eason, CW Litton

    JOURNAL OF APPLIED PHYSICS   94 ( 2 ) 968 - 972  2003.07  [Refereed]

     View Summary

    Polarized Brillouin scattering measurements were carried out for a bulk ZnO single crystal. The whole set of elastic stiffness constants was determined to be c(11)=19.0, c(12)=11.0, c(13)=9.0, c(33)=19.6, c(44)=3.9, and c(66)=4.0 in units of 10(11) dyn/cm(2). The relationships between photoelastic constants at wavelength of 514.5 nm were also obtained: p(11), p(13), p(44), and p(66)=1.8, 2.3, 0.50, and 0.38, respectively, relative to p(12). (C) 2003 American Institute of Physics.

    DOI

  • Strong biexcitonic effects and exciton-exciton correlations in ZnO

    Hazu, K, Sota T, Suzuki, K

    Phys. Rev. B/APS   68;3,Art.No.033205  2003.07  [Refereed]

  • Brillouin scattering study of ZnO

    T Azuhata, M Takesada, T Yagi, A Shikanai, S Chichibu, K Torii, A Nakamura, T Sota, G Cantwell, DB Eason, CW Litton

    JOURNAL OF APPLIED PHYSICS   94 ( 2 ) 968 - 972  2003.07  [Refereed]

     View Summary

    Polarized Brillouin scattering measurements were carried out for a bulk ZnO single crystal. The whole set of elastic stiffness constants was determined to be c(11)=19.0, c(12)=11.0, c(13)=9.0, c(33)=19.6, c(44)=3.9, and c(66)=4.0 in units of 10(11) dyn/cm(2). The relationships between photoelastic constants at wavelength of 514.5 nm were also obtained: p(11), p(13), p(44), and p(66)=1.8, 2.3, 0.50, and 0.38, respectively, relative to p(12). (C) 2003 American Institute of Physics.

    DOI

  • Strong biexcitonic effects and exciton-exciton correlations in ZnO

    Hazu, K, Sota T, Suzuki, K

    Phys. Rev. B/APS   68;3,Art.No.033205  2003.07  [Refereed]

  • Exciton-exciton interaction and hetero-biexciton in GaN

    Adachi, S, Muto, S, Hazu, K

    Phys. Rev. B/APS   67;20,Art.No.205212  2003.05  [Refereed]

  • Exciton-exciton interaction and hetero-biexciton in GaN

    Adachi, S, Muto, S, Hazu, K

    Phys. Rev. B/APS   67;20,Art.No.205212  2003.05  [Refereed]

  • Influence of InN mole fraction on the recombination processes of localized excitons in strained cubic InxGa1-xN/GaN multiple quantum wells

    S Chichibu, T Onuma, T Sota, SP DenBaars, S Nakamura, T Kitamura, Y Ishida, H Okumura

    JOURNAL OF APPLIED PHYSICS   93 ( 4 ) 2051 - 2054  2003.02  [Refereed]

     View Summary

    Recombination dynamics of localized excitons in the best quality strained cubic InxGa1-xN/GaN multiple quantum wells (MQWs) grown on 3C-SiC (001) were studied as functions of InN mole fraction x and temperature T. The MQWs exhibited large Stokes-type shifts although the full width at half maximum of the photoluminescence (PL) peaks being 80-120 meV is 100-300 meV smaller than those reported previously. Time-resolved PL signal showed stretched exponential decay and spectral redshift with time after excitation up to 300 K. These results are fingerprints that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures forming extended and localized states. Effective localization depth increased with the increase in x, which gave rise to fast exciton localization. However, nonradiative lifetime in the free states decreased more rapidly with the increase in x and T, giving the emission efficiency maximum at particular x around 0.1. (C) 2003 American Institute of Physics.

    DOI

  • Influence of InN mole fraction on the recombination processes of localized excitons in strained cubic InxGa1-xN/GaN multiple quantum wells

    S Chichibu, T Onuma, T Sota, SP DenBaars, S Nakamura, T Kitamura, Y Ishida, H Okumura

    JOURNAL OF APPLIED PHYSICS   93 ( 4 ) 2051 - 2054  2003.02  [Refereed]

     View Summary

    Recombination dynamics of localized excitons in the best quality strained cubic InxGa1-xN/GaN multiple quantum wells (MQWs) grown on 3C-SiC (001) were studied as functions of InN mole fraction x and temperature T. The MQWs exhibited large Stokes-type shifts although the full width at half maximum of the photoluminescence (PL) peaks being 80-120 meV is 100-300 meV smaller than those reported previously. Time-resolved PL signal showed stretched exponential decay and spectral redshift with time after excitation up to 300 K. These results are fingerprints that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures forming extended and localized states. Effective localization depth increased with the increase in x, which gave rise to fast exciton localization. However, nonradiative lifetime in the free states decreased more rapidly with the increase in x and T, giving the emission efficiency maximum at particular x around 0.1. (C) 2003 American Institute of Physics.

    DOI

  • Polarized photoreflectance spectra of excitonic polaritons in a ZnO single crystal

    SF Chichibu, T Sota, G Cantwell, DB Eason, CW Litton

    JOURNAL OF APPLIED PHYSICS   93 ( 1 ) 756 - 758  2003.01  [Refereed]

     View Summary

    Exciton-polariton structures in a high-quality bulk ZnO single crystal were resolved at 8 K by means of polarized photoreflectance (PR) and photoluminescence measurements. The energies of the PR resonances corresponded to those of the upper and lower exciton-polariton branches, where A, B, and C excitons couple simultaneously to an electromagnetic wave. Longitudinal-transverse splitting of ground-state exciton polaritons and resonances due to the first excited states of respective excitons were observed due to the large oscillator strength. Photoluminescence peaks due to the corresponding polarion branches were clearly resolved. The valence-band ordering was confirmed to be A-Gamma(9v), B-Gamma(7v)(u), and C-Gamma(7v)(l). (C) 2003 American Institute of Physics.

    DOI

  • Properties of optical phonons in cubic InxGa1-xN

    K Torii, N Usukura, A Nakamura, T Sota, SF Chichibu, T Kitamura, H Okumura

    APPLIED PHYSICS LETTERS   82 ( 1 ) 52 - 54  2003.01  [Refereed]

     View Summary

    Infrared reflectance spectroscopy was carried out to study the properties of zone center optical phonons in ternary cubic InxGa1-xN free from phase separation. Raman spectra were also measured as auxiliary measures. Optical phonon behavior was confirmed to be type I. It is demonstrated that the behavior arises from both the small mass ratio of Ga to In atoms and the rather strong ionicity of Ga-N and In-N bonds. (C) 2003 American Institute of Physics.

    DOI

  • Optical properties of Si-, Ge-, and Sn-doped GaN.

    Shikanai, A, Fukahori, H, Kawakami, Y

    Phys. Status Solidi (b)/Elsevier   235;1,pp.26-30  2003.01  [Refereed]

    DOI

  • Correlation between the photoluminescence lifetime and defect density in bulk and epitaxial ZnO

    T Koida, SF Chichibu, A Uedono, A Tsukazaki, M Kawasaki, T Sota, Y Segawa, H Koinuma

    APPLIED PHYSICS LETTERS   82 ( 4 ) 532 - 534  2003.01  [Refereed]

     View Summary

    Influences of point defects on the nonradiative processes in ZnO were studied using steady-state and time-resolved photoluminescence (PL) spectroscopy making a connection with the results of positron annihilation measurement. Free excitonic PL intensity naturally increased with the increase in the nonradiative PL lifetime (tau(nr)). Density or size of Zn vacancies (V-Zn) decreased and tau(nr) increased with increasing growth temperature in heteroepitaxial films grown on a ScAlMgO4 substrate. Use of homoepitaxial substrate further decreased the V-Zn density. However, tau(nr) was the shortest for the homoepitaxial film; i.e., no clear dependence was found between tau(nr) and density / size of V-Zn or positron scattering centers. The results indicated that nonradiative recombination processes are not solely governed by single point defects, but by certain defect species introduced by the presence of V-Zn such as vacancy complexes. (C) 2003 American Institute of Physics.

    DOI

  • Polarized photoreflectance spectra of excitonic polaritons in a ZnO single crystal

    SF Chichibu, T Sota, G Cantwell, DB Eason, CW Litton

    JOURNAL OF APPLIED PHYSICS   93 ( 1 ) 756 - 758  2003.01  [Refereed]

     View Summary

    Exciton-polariton structures in a high-quality bulk ZnO single crystal were resolved at 8 K by means of polarized photoreflectance (PR) and photoluminescence measurements. The energies of the PR resonances corresponded to those of the upper and lower exciton-polariton branches, where A, B, and C excitons couple simultaneously to an electromagnetic wave. Longitudinal-transverse splitting of ground-state exciton polaritons and resonances due to the first excited states of respective excitons were observed due to the large oscillator strength. Photoluminescence peaks due to the corresponding polarion branches were clearly resolved. The valence-band ordering was confirmed to be A-Gamma(9v), B-Gamma(7v)(u), and C-Gamma(7v)(l). (C) 2003 American Institute of Physics.

    DOI

  • Properties of optical phonons in cubic InxGa1-xN

    K Torii, N Usukura, A Nakamura, T Sota, SF Chichibu, T Kitamura, H Okumura

    APPLIED PHYSICS LETTERS   82 ( 1 ) 52 - 54  2003.01  [Refereed]

     View Summary

    Infrared reflectance spectroscopy was carried out to study the properties of zone center optical phonons in ternary cubic InxGa1-xN free from phase separation. Raman spectra were also measured as auxiliary measures. Optical phonon behavior was confirmed to be type I. It is demonstrated that the behavior arises from both the small mass ratio of Ga to In atoms and the rather strong ionicity of Ga-N and In-N bonds. (C) 2003 American Institute of Physics.

    DOI

  • Optical properties of Si-, Ge-, and Sn-doped GaN.

    Shikanai, A, Fukahori, H, Kawakami, Y

    Phys. Status Solidi (b)/Elsevier   235;1,pp.26-30  2003.01  [Refereed]

    DOI

  • Correlation between the photoluminescence lifetime and defect density in bulk and epitaxial ZnO

    Koida, T, Chichibu, SF. Uedono, A

    Appl. Phys. Lett./AIP   82;4,pp.532-534  2003.01

    DOI

  • Recombination dynamics of localized excitons in cubic phase InxGa1-xN/GaN multiple quantum wells on 3C-SiC/Si (001).

    Chichibu, SF, Onuma, T, Kitamura

    Phys. Status Solidi (b)/Elsevier   234;3,pp.746-749  2002.12  [Refereed]

    DOI

  • Orientation and aggregation oc cationic laser dyes in a fluoromica: polarized spectrometric studies

    Iyi, N, Sasai R, Fujita, T

    Appl. Cry Science   22;3,pp.125-136  2002.12  [Refereed]

    DOI

  • Recombination dynamics of localized excitons in cubic phase InxGa1-xN/GaN multiple quantum wells on 3C-SiC/Si (001).

    Chichibu, SF, Onuma, T, Kitamura

    Phys. Status Solidi (b)/Elsevier   234;3,pp.746-749  2002.12  [Refereed]

    DOI

  • Orientation and aggregation oc cationic laser dyes in a fluoromica: polarized spectrometric studies

    Iyi, N, Sasai R, Fujita, T

    Appl. Cry Science   22;3,pp.125-136  2002.12  [Refereed]

    DOI

  • Observation of exciton-polariton emissions from a ZnO epitaxial film on the a-face of sapphire grown by radical-source molecular-beam-epitaxy

    SF Chichibu, T Sota, PJ Fons, K Ivata, A Yamada, K Matsubara, S Niki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   41 ( 8B ) L935 - L937  2002.08  [Refereed]

     View Summary

    Exciton-polariton emissions were observed at 8 K in the photoluminescence spectrum of a ZnO epitaxial film on the a-face of sapphire grown by radical-source molecular-beam-epitaxy. The resonance energies of corresponding photoreflectance structures agreed with those of longitudinal and transverse excitons, i.e. upper and lower polariton branches, where A, B and C-excitons couple simultaneously to an electromagnetic wave. In contrast to the results obtained for GaN, longitudinal-transverse splitting of the B-excitonic polariton was resolved, which is due to the large oscillator strength.

    DOI

  • Observation of exciton-polariton emissions from a ZnO epitaxial film on the a-face of sapphire grown by radical-source molecular-beam-epitaxy

    SF Chichibu, T Sota, PJ Fons, K Ivata, A Yamada, K Matsubara, S Niki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   41 ( 8B ) L935 - L937  2002.08  [Refereed]

     View Summary

    Exciton-polariton emissions were observed at 8 K in the photoluminescence spectrum of a ZnO epitaxial film on the a-face of sapphire grown by radical-source molecular-beam-epitaxy. The resonance energies of corresponding photoreflectance structures agreed with those of longitudinal and transverse excitons, i.e. upper and lower polariton branches, where A, B and C-excitons couple simultaneously to an electromagnetic wave. In contrast to the results obtained for GaN, longitudinal-transverse splitting of the B-excitonic polariton was resolved, which is due to the large oscillator strength.

    DOI

  • Exciton spectra of an AlN epitaxial film on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy

    T Onuma, SF Chichibu, T Sota, K Asai, S Sumiya, T Shibata, M Tanaka

    APPLIED PHYSICS LETTERS   81 ( 4 ) 652 - 654  2002.07  [Refereed]

     View Summary

    Exciton resonance energies in an AlN epilayer on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy were determined as a function of temperature by means of optical reflectance (OR) and cathodoluminescence measurements. The OR spectra exhibited distinct reflectance anomalies at the photon energies just above the multiple internal reflection fringes, and the spectral line shape was fitted considering A (Gamma(7v)(u)--&gt;Gamma(7c)) and BC (Gamma(9v),Gamma(7v)(l)--&gt;Gamma(7c)) exciton transitions. The fitting gave the values of them at 0 K to be 6.211 and 6.266 eV, giving the crystal- field splitting (Delta(cr)) of approximately 55 meV. The AlN film exhibited an excitonic emission even at 300 K, which is due to the small Bohr radius of excitons and large longitudinal optical phonon energies. The Einstein characteristic temperature Theta(E) was estimated to be 580 K. (C) 2002 American Institute of Physics.

    DOI

  • Exciton spectra of an AlN epitaxial film on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy

    T Onuma, SF Chichibu, T Sota, K Asai, S Sumiya, T Shibata, M Tanaka

    APPLIED PHYSICS LETTERS   81 ( 4 ) 652 - 654  2002.07  [Refereed]

     View Summary

    Exciton resonance energies in an AlN epilayer on (0001) sapphire substrate grown by low-pressure metalorganic vapor phase epitaxy were determined as a function of temperature by means of optical reflectance (OR) and cathodoluminescence measurements. The OR spectra exhibited distinct reflectance anomalies at the photon energies just above the multiple internal reflection fringes, and the spectral line shape was fitted considering A (Gamma(7v)(u)--&gt;Gamma(7c)) and BC (Gamma(9v),Gamma(7v)(l)--&gt;Gamma(7c)) exciton transitions. The fitting gave the values of them at 0 K to be 6.211 and 6.266 eV, giving the crystal- field splitting (Delta(cr)) of approximately 55 meV. The AlN film exhibited an excitonic emission even at 300 K, which is due to the small Bohr radius of excitons and large longitudinal optical phonon energies. The Einstein characteristic temperature Theta(E) was estimated to be 580 K. (C) 2002 American Institute of Physics.

    DOI

  • Localized exciton dynamics in InGaN quantum well structures

    Chichibu, S. F, Azuhata, T, Okumura, H

    Appl. Surf. Sci.   190;1-4,pp.330-338  2002.05  [Refereed]

    DOI

  • Optical nonlinearities and phase relaxation of excitons in GaN

    K Hazu, A Shikanai, T Sota, K Suzuki, S Adachi, SF Chichibu, T Mukai

    PHYSICAL REVIEW B   65 ( 19 )  2002.05  [Refereed]

     View Summary

    We have studied the properties of coherent exciton states in a free standing wurtzite GaN using the degenerate four-wave-mixing (FWM) technique with subpicosecond time resolution. The polarization dependence of spectrally resolved FWM signals has demonstrated that excitation-induced dephasing is the dominant FWM process. The exciton energy renormalization has been found to dependent on the polarization configuration. FWM signals due to local field effect have been successfully discriminated from those due to other effects. These reveal an importance of four-particle correlations in two-exciton continuum states even for the low excitation power limit where no bound biexciton signal is detected. The temperature dependence of the homogeneous broadening of excitons has also been studied up to 60 K, to obtain the exciton-acoustic phonon interaction coefficient of 9 mueV/K.

    DOI

  • Localized exciton dynamics in InGaN quantum well structures

    Chichibu, S. F, Azuhata, T, Okumura, H

    Appl. Surf. Sci.   190;1-4,pp.330-338  2002.05  [Refereed]

    DOI

  • Optical nonlinearities and phase relaxation of excitons in GaN

    K Hazu, A Shikanai, T Sota, K Suzuki, S Adachi, SF Chichibu, T Mukai

    PHYSICAL REVIEW B   65 ( 19 )  2002.05  [Refereed]

     View Summary

    We have studied the properties of coherent exciton states in a free standing wurtzite GaN using the degenerate four-wave-mixing (FWM) technique with subpicosecond time resolution. The polarization dependence of spectrally resolved FWM signals has demonstrated that excitation-induced dephasing is the dominant FWM process. The exciton energy renormalization has been found to dependent on the polarization configuration. FWM signals due to local field effect have been successfully discriminated from those due to other effects. These reveal an importance of four-particle correlations in two-exciton continuum states even for the low excitation power limit where no bound biexciton signal is detected. The temperature dependence of the homogeneous broadening of excitons has also been studied up to 60 K, to obtain the exciton-acoustic phonon interaction coefficient of 9 mueV/K.

    DOI

  • Photoreflectance spectra of a ZnO heteroepitaxial film on the nearly lattice-matched ScAlMgO4 (0001) substrate grown by laser molecular-beam epitaxy

    S. F. Chichibu, A. Tsukazaki, M. Kawasaki, K. Tamura, Y. Segawa, T. Sota, H. Koinuma

    Applied Physics Letters   80 ( 16 ) 2860 - 2862  2002.04

     View Summary

    Photoreflectance spectra of a high-quality ZnO epilayer on the ScAlMgO 4 (0001) substrate grown by laser molecular-beam epitaxy exhibited clear excitonic resonances due to three excitons associated with uppermost valence bands (A, B, and C excitons). The oscillator strengths of the B and C excitons are larger than that of the A exciton. Their broadening was interpreted to be due to the contribution by exciton-polaritons in terms of large longitudinal-transverse splitting of respective excitons. Dependence of the exciton energy on temperature was well fitted assuming the Bose-Einstein statistics giving the Einstein characteristic temperature E of 380 K (33 meV). © 2002 American Institute of Physics.

    DOI

  • Photoreflectance spectra of a ZnO heteroepitaxial film on the nearly lattice-matched ScAlMgO4 (0001) substrate grown by laser molecular-beam epitaxy

    SF Chichibu, A Tsukazaki, M Kawasaki, K Tamura, Y Segawa, T Sota, H Koinuma

    APPLIED PHYSICS LETTERS   80 ( 16 ) 2860 - 2862  2002.04  [Refereed]

     View Summary

    Photoreflectance spectra of a high-quality ZnO epilayer on the ScAlMgO4 (0001) substrate grown by laser molecular-beam epitaxy exhibited clear excitonic resonances due to three excitons associated with uppermost valence bands (A, B, and C excitons). The oscillator strengths of the B and C excitons are larger than that of the A exciton. Their broadening was interpreted to be due to the contribution by exciton-polaritons in terms of large longitudinal-transverse splitting of respective excitons. Dependence of the exciton energy on temperature was well fitted assuming the Bose-Einstein statistics giving the Einstein characteristic temperature Theta(E) of 380 K (33 meV). (C) 2002 American Institute of Physics.

    DOI

  • Spectroscopic evaluation of glucose concentration in phosphate-buffered saline solution using principal component analysis

    A Nakamura, T Hasegawa, J Nishijo, M Kanazawa, K Aizawa, T Sota

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   41 ( 4B ) L440 - L442  2002.04  [Refereed]

     View Summary

    Principal component analysis (PCA) has been used for quantitative analysis of infrared attenuated total reflection (ATR) spectra of chemical mixtures, so that the minute concentration of glucose in the chemical mixture would be evaluated. Spectroscopic calibration of chemical concentration has been, thus far, believed to require multidimensional least-squares methods, such as classical least squares (CLS) and partial least-squares (PLS) regression techniques. In the present study, however, the analysis of the infrared ATR spectra only by PCA has been found to be useful for the evaluation of concentration of specific minute species in a chemical mixture. The prediction accuracy by PCA only has proved to be comparable to that of PLS. The novel technique would enable us to measure the concentration of glucose in human blood with no invasion.

    DOI

  • Spectroscopic evaluation of glucose concentration in phosphate-buffered saline solution using principal component analysis

    A Nakamura, T Hasegawa, J Nishijo, M Kanazawa, K Aizawa, T Sota

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   41 ( 4B ) L440 - L442  2002.04  [Refereed]

     View Summary

    Principal component analysis (PCA) has been used for quantitative analysis of infrared attenuated total reflection (ATR) spectra of chemical mixtures, so that the minute concentration of glucose in the chemical mixture would be evaluated. Spectroscopic calibration of chemical concentration has been, thus far, believed to require multidimensional least-squares methods, such as classical least squares (CLS) and partial least-squares (PLS) regression techniques. In the present study, however, the analysis of the infrared ATR spectra only by PCA has been found to be useful for the evaluation of concentration of specific minute species in a chemical mixture. The prediction accuracy by PCA only has proved to be comparable to that of PLS. The novel technique would enable us to measure the concentration of glucose in human blood with no invasion.

    DOI

  • Localized exciton dynamics in strained cubic In0.1Ga0.9N/GaN multiple quantum wells

    Chichibu, S. F, Sugiyama, M, Onuma, T

    Appl. Phys. Lett./AIP   79;26,pp.4319-4321  2001.12  [Refereed]

    DOI

  • Localized exciton dynamics in strained cubic In0.1Ga0.9N/GaN multiple quantum wells

    Chichibu, S. F, Sugiyama, M, Onuma, T

    Appl. Phys. Lett./AIP   79;26,pp.4319-4321  2001.12  [Refereed]

    DOI

  • Band gap bowing and exciton localization in strained cubic InxGa1-xN films grown on 3C-SiC(001) by rf molecular-beam epitaxy.

    Chichibu, S. F, Sugiyama, M, Kuroda, T

    Appl. Phys. Lett./AIP   79;22,pp.3600-3602  2001.11  [Refereed]

    DOI

  • Band gap bowing and exciton localization in strained cubic InxGa1-xN films grown on 3C-SiC(001) by rf molecular-beam epitaxy.

    Chichibu, S. F, Sugiyama, M, Kuroda, T

    Appl. Phys. Lett./AIP   79;22,pp.3600-3602  2001.11  [Refereed]

    DOI

  • 物性工学

    宗田孝之

    培風館    2001.10  [Refereed]

  • Excitonic polariton structures in wurtzite GaN

    Torii, K, Chichibu, S. F, Deguchi, T

    Physica B/Elsevier   302&amp;303;pp.268-276  2001.08  [Refereed]

    DOI

  • Current-modulated electroluminescence spectroscopy and its application to InGaN single-quantum-well blue and green light-emitting diodes

    Azuhata, T, Homma, T, Chichibu, S. F

    Appl. Phys. Lett./AIP   79;8,pp.1100-1102  2001.08  [Refereed]

    DOI

  • Excitonic polariton structures in wurtzite GaN

    Torii, K, Chichibu, S. F, Deguchi, T

    Physica B/Elsevier   302&amp;303;pp.268-276  2001.08  [Refereed]

    DOI

  • Current-modulated electroluminescence spectroscopy and its application to InGaN single-quantum-well blue and green light-emitting diodes

    Azuhata, T, Homma, T, Chichibu, S. F

    Appl. Phys. Lett./AIP   79;8,pp.1100-1102  2001.08  [Refereed]

    DOI

  • Localized excitons in an In0.06Ga0.94N multiple-quantum-well laser diode lased at 400 nm

    Chichibu, S. F, Azuhata, T, Sota, T

    Appl. Phys. Lett./AIP   79;3,pp.341-343  2001.07  [Refereed]

    DOI

  • Localized excitons in an In0.06Ga0.94N multiple-quantum-well laser diode lased at 400 nm

    Chichibu, S. F, Azuhata, T, Sota, T

    Appl. Phys. Lett./AIP   79;3,pp.341-343  2001.07  [Refereed]

    DOI

  • Impact of internal electric field and localization effect on quantum well excitons in AlGaN/GaN/InGaN light emitting diodes

    Chichibu, S. F, Sota, T, Wada, K

    Phys. Stat. Sol.(a)/Elsevier   183,pp.91-98  2001.01  [Refereed]

    DOI

  • Impact of internal electric field and localization effect on quantum well excitons in AlGaN/GaN/InGaN light emitting diodes

    Chichibu, S. F, Sota, T, Wada, K

    Phys. Stat. Sol.(a)/Elsevier   183,pp.91-98  2001.01  [Refereed]

    DOI

  • Forward Raman scattering by quasilongitudinal optical phonons in GaN

    Azuhata, T, Ono, M, Torii, K

    J. Appl. Phys/AIP   88;9,pp.5022-5025  2000.11  [Refereed]

    DOI

  • Localized quantum-well excitons in InGaN single-quantum-well amber light emitting diodes

    Chichibu, S. F, Azuhata, T, Sota, T

    J. Appl. Phys/AIP   88;9,pp.5153-5157  2000.11  [Refereed]

    DOI

  • Forward Raman scattering by quasilongitudinal optical phonons in GaN

    Azuhata, T, Ono, M, Torii, K

    J. Appl. Phys/AIP   88;9,pp.5022-5025  2000.11  [Refereed]

    DOI

  • Localized quantum-well excitons in InGaN single-quantum-well amber light emitting diodes

    Chichibu, S. F, Azuhata, T, Sota, T

    J. Appl. Phys/AIP   88;9,pp.5153-5157  2000.11  [Refereed]

    DOI

  • Raman scattering from phonon-polariton in GaN

    Torii, K, Ono, M, Sota, T

    Phys. Rev. B/APS   62;16,pp.10861-10866  2000.10  [Refereed]

    DOI

  • Raman scattering from phonon-polariton in GaN

    Torii, K, Ono, M, Sota, T

    Phys. Rev. B/APS   62;16,pp.10861-10866  2000.10  [Refereed]

    DOI

  • An attenuated total reflection study on surface phonon-polariton in GaN

    Torii, K, Koga, T, Sota, T

    J. Phys.:Condensed Matter/IOP   12;31,pp.7041-7044  2000.08  [Refereed]

    DOI

  • An attenuated total reflection study on surface phonon-polariton in GaN

    Torii, K, Koga, T, Sota, T

    J. Phys.:Condensed Matter/IOP   12;31,pp.7041-7044  2000.08  [Refereed]

    DOI

  • Effective localization of quantum well excitons in InGaN quantum well structures with high InN molar fraction

    Chichibu, S. F, Setoguchi, A, Azuhata, T

    Physica Status Solidi (a) /Elsevier   180;1,pp.321-325  2000.07  [Refereed]

    DOI

  • Effective localization of quantum well excitons in InGaN quantum well structures with high InN molar fraction

    Chichibu, S. F, Setoguchi, A, Azuhata, T

    Physica Status Solidi (a) /Elsevier   180;1,pp.321-325  2000.07  [Refereed]

    DOI

  • Application of infrared attenuated total reflection spectroscopy to in situ analysis of atheromatous plaques in aorta

    Nakamura, A, Koga, T, Fujimaki, M

    Jpn. J. Appl. Phys./IPAP   39;6A,ppL.490-492  2000.06  [Refereed]

    DOI

  • Luminescence energy shift and carrier lifetime change dependence on carrier density in In0.12Ga0.88N/In0.03Ga0.97N quantum wells

    Kuroda, T, Tackeuchi, A, Sota, T

    Appl. Phys. Lett./AIP   76;25,pp3753-3755 ( 25 ) 3753 - 3755  2000.06  [Refereed]

    DOI CiNii

  • Application of infrared attenuated total reflection spectroscopy to in situ analysis of atheromatous plaques in aorta

    Nakamura, A, Koga, T, Fujimaki, M

    Jpn. J. Appl. Phys./IPAP   39;6A,ppL.490-492  2000.06  [Refereed]

    DOI

  • Luminescence energy shift and carrier lifetime change dependence on carrier density in In0.12Ga0.88N/In0.03Ga0.97N quantum wells

    Kuroda, T, Tackeuchi, A, Sota, T

    Appl. Phys. Lett./AIP   76;25,pp3753-3755 ( 25 ) 3753 - 3755  2000.06  [Refereed]

    DOI CiNii

  • No spin polarization of carriers in InGaN

    Tackeuchi, A, Kuroda, T, Shikanai, A

    Physica E./Elsevier   7;3&amp;4,pp1011-1014  2000.05  [Refereed]

    DOI

  • No spin polarization of carriers in InGaN

    Tackeuchi, A, Kuroda, T, Shikanai, A

    Physica E./Elsevier   7;3&amp;4,pp1011-1014  2000.05  [Refereed]

    DOI

  • Comparison of optical properties in GaN/AlGaN and InGaN/AlGaN single quantum wells

    Chichibu, S. F, Shikanai, A, Deguchi, T

    Jpn. J. Appl. Phys./IPAP   39;4B,pp.2417-2424  2000.04  [Refereed]

    DOI

  • Chemical bonding properties of cubic III-nitrides semiconductors

    Shimada, K, Sota, T, Suzuki, K

    Progress in Theoretical Physics Supplement/PSJ   138;pp.122-123  2000.04  [Refereed]

  • Comparison of optical properties in GaN/AlGaN and InGaN/AlGaN single quantum wells

    Chichibu, S. F, Shikanai, A, Deguchi, T

    Jpn. J. Appl. Phys./IPAP   39;4B,pp.2417-2424  2000.04  [Refereed]

    DOI

  • Chemical bonding properties of cubic III-nitrides semiconductors

    Shimada, K, Sota, T, Suzuki, K

    Progress in Theoretical Physics Supplement/PSJ   138;pp.122-123  2000.04  [Refereed]

  • Evidence of localized effects in InGaN single-quantum-well ultraviolet light emitting diodes.

    Chichibu, SF, Wada, K, Mullhauser, J

    Appl.Phys.Lett./AIP   76; 13, pp.1671-1673  2000.03  [Refereed]

    DOI

  • Photoreflectance spectra of excitonic polaritons in GaN substrate prepared by lateral epitaxial overgrowth.

    Chichibu, SF, Torii, K, Deguchi, T

    Appl.Phys.Lett./AIP   76; 12, pp.1576-1578  2000.03  [Refereed]

    DOI

  • Evidence of localized effects in InGaN single-quantum-well ultraviolet light emitting diodes.

    Chichibu, SF, Wada, K, Mullhauser, J

    Appl.Phys.Lett./AIP   76; 13, pp.1671-1673  2000.03  [Refereed]

    DOI

  • Photoreflectance spectra of excitonic polaritons in GaN substrate prepared by lateral epitaxial overgrowth.

    Chichibu, SF, Torii, K, Deguchi, T

    Appl.Phys.Lett./AIP   76; 12, pp.1576-1578  2000.03  [Refereed]

    DOI

  • Introduction to Nitride Semiconductor Blue Lasers and Light Emitting Diodes

    Taylor & Francis    2000

  • A pump and probe study on photoinduced internal field screening dynamics in an AlGaN.GaN single quantum well structure.

    Shikanai, A, Deguchi, T, Sota, T

    Appl.Phys.Lett./AIP   76; 4, pp.454-456  2000.01  [Refereed]

    DOI

  • Introduction to Nitride Semiconductor Blue Lasers and Light Emitting Diodes

    Taylor & Francis    2000

  • A pump and probe study on photoinduced internal field screening dynamics in an AlGaN.GaN single quantum well structure.

    Shikanai, A, Deguchi, T, Sota, T

    Appl.Phys.Lett./AIP   76; 4, pp.454-456  2000.01  [Refereed]

    DOI

  • Comparison of optical properties in GaN and InGaN quantum well structures.

    SPIE Proceedings Series   3896, pp.98-106  1999.12  [Refereed]

  • Comparison of optical properties in GaN and InGaN quantum well structures.

    SPIE Proceedings Series   3896, pp.98-106  1999.12  [Refereed]

  • Properties of quantum well excitons in GaN/AlGaN and InGaN/GaN/AlGaN UV, blue, green, and amber light emitting diode structures.

    Physica Status Solidi (a)/WILLEY-VCH   75; 1, pp.2076-2073  1999.11  [Refereed]

  • Properties of quantum well excitons in GaN/AlGaN and InGaN/GaN/AlGaN UV, blue, green, and amber light emitting diode structures.

    Physica Status Solidi (a)/WILLEY-VCH   75; 1, pp.2076-2073  1999.11  [Refereed]

  • Optical properties of an InGaN active layer in ultraviolet light emitting diode.

    Jpn.J.Appl.Phys./JJAP   38; 9A/B, pp.L975-L977  1999.09  [Refereed]

    DOI

  • Optical properties of an InGaN active layer in ultraviolet light emitting diode.

    Jpn.J.Appl.Phys./JJAP   38; 9A/B, pp.L975-L977  1999.09  [Refereed]

    DOI

  • Quantum-confined Stark effect in an AlGaN/GaN single quantum well structure.

    Jpn.J.Appl.Phys./JJAP   38; 8B, pp.L914-L916  1999.08  [Refereed]

    DOI

  • Reflectance and emission spectra of excitonic polaritons in GaN.

    Phys.Rev.B/APS   60; 7, pp.4723-4730  1999.08  [Refereed]

    DOI

  • Structural and vibrational properties of GaN substrate.

    J.Appl.Phys./AIP   86; 4, pp.1860-1866  1999.08  [Refereed]

    DOI

  • Quantum-confined Stark effect in an AlGaN/GaN single quantum well structure.

    Jpn.J.Appl.Phys./JJAP   38; 8B, pp.L914-L916  1999.08  [Refereed]

    DOI

  • Reflectance and emission spectra of excitonic polaritons in GaN.

    Phys.Rev.B/APS   60; 7, pp.4723-4730  1999.08  [Refereed]

    DOI

  • Structural and vibrational properties of GaN substrate.

    J.Appl.Phys./AIP   86; 4, pp.1860-1866  1999.08  [Refereed]

    DOI

  • Brillouin scattering study of bulk GaN.

    J.Appl.Phys./AIP   85; 12, pp.8502-8504  1999.06  [Refereed]

    DOI

  • Brillouin scattering study of bulk GaN.

    J.Appl.Phys./AIP   85; 12, pp.8502-8504  1999.06  [Refereed]

    DOI

  • Optical properties of InGaN quantum wells.

    Material Sciences and Engineering B/Elsevier   59, pp.298-306  1999.05  [Refereed]

    DOI

  • Optical properties of InGaN quantum wells.

    Material Sciences and Engineering B/Elsevier   59, pp.298-306  1999.05  [Refereed]

    DOI

  • GaN基板の光学フォノンII

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.421  1999.03

  • InGaN量子井戸における電界効果とエネルギーギャップ不均一性

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.403  1999.03  [Refereed]

  • Si添加障壁層を有するInGaN量子井戸の光学的特性

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.406  1999.03  [Refereed]

  • LEO-GaN上に成長したGaN単膜、InGaN量子井戸の光学的特性

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.402  1999.03  [Refereed]

  • InGaN/AlGaN単一量子井戸のゲインスペクトロスコピー

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1999.03  [Refereed]

  • GaN/AlGaN単一量子井戸における量子閉じ込めシュタルク効果

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.398  1999.03

  • GaNのRashba-Sheka-Pikus価電子帯パラメータ

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.399  1999.03  [Refereed]

  • InGaNのキャリアのスピン分極

    第46回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.406  1999.03  [Refereed]

  • Emission mechanisms of GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth.

    Appl. Phys. Lett./AIP   74; 10, pp.1460-1462  1999.03  [Refereed]

    DOI

  • Emission mechanisms of GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth.

    Appl. Phys. Lett./AIP   74; 10, pp.1460-1462  1999.03  [Refereed]

    DOI

  • Infrared Lattice Absorption in Wurtzite GaN.

    Jpn J. of Appl. Phys., Part 2/JJAP   38; 2B, pp.L151-L153  1999.02  [Refereed]

    DOI

  • Infrared Lattice Absorption in Wurtzite GaN.

    Jpn J. of Appl. Phys., Part 2/JJAP   38; 2B, pp.L151-L153  1999.02  [Refereed]

    DOI

  • Spectroscopic studies in InGaN quantum wells.

    MRS Internet J.Nitride Semicond. Res./MRS   4S1, G2.7  1999.01  [Refereed]

  • Spectroscopic studies in InGaN quantum wells.

    MRS Internet J.Nitride Semicond. Res./MRS   4S1, G2.7  1999.01  [Refereed]

  • First-principles study on piezoelectric constants in strained BN, AlN, and GaN.

    Jpn. J. Appl. Phys., Part 2/JJAP   37; 12A, pp.L1421-L1423  1998.12  [Refereed]

    DOI

  • First-principles study on piezoelectric constants in strained BN, AlN, and GaN.

    Jpn. J. Appl. Phys., Part 2/JJAP   37; 12A, pp.L1421-L1423  1998.12  [Refereed]

    DOI

  • First-principles study on electronic and elastic properties of BN, AlN,and GaN.

    J. Appl. Phys./AIP   84; 9, pp.4951-4958  1998.11  [Refereed]

    DOI

  • First-principles study on electronic and elastic properties of BN, AlN,and GaN.

    J. Appl. Phys./AIP   84; 9, pp.4951-4958  1998.11  [Refereed]

    DOI

  • Effective bandgap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures.

    Appl. Phys. Lett./AIP   73; 14, pp.2006-2008  1998.10  [Refereed]

    DOI

  • Effective bandgap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures.

    Appl. Phys. Lett./AIP   73; 14, pp.2006-2008  1998.10  [Refereed]

    DOI

  • h-GaNのブリルアン散乱II

    日本物理学会講演概要集/日本物理学会   53; 2-2, p.275  1998.09

  • GaN基板の光学的特性(1)

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.300  1998.09  [Refereed]

  • GaN基板の光学フォノン

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.300  1998.09

  • タンデムファブリ・ペローを用いたGaNのブリルアン散乱II

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.297  1998.09

  • BN, AlN, GaNの圧電定数の歪み依存性

    第59回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.297  1998.09  [Refereed]

  • Exciton localization in InGaN quantum well devices.

    J. Vac. Sci. Technol. B/AVS   16; 4, pp.2204-2214  1998.07  [Refereed]

    DOI

  • Exciton localization in InGaN quantum well devices.

    J. Vac. Sci. Technol. B/AVS   16; 4, pp.2204-2214  1998.07  [Refereed]

    DOI

  • Optical properties of InGaN quantumwells.

    European Materials Research Society, 1998 Spring Meeting   Session L: III-V Nitrides  1998.06  [Refereed]

  • Luminescence spectra from InGaN multi-quantum wells heavily doped with Si.

    Appl. Phys. Lett./AIP   72; 25, pp.3329-3331  1998.06  [Refereed]

    DOI

  • Optical properties of InGaN quantumwells.

    European Materials Research Society, 1998 Spring Meeting   Session L: III-V Nitrides  1998.06  [Refereed]

  • Luminescence spectra from InGaN multi-quantum wells heavily doped with Si.

    Appl. Phys. Lett./AIP   72; 25, pp.3329-3331  1998.06  [Refereed]

    DOI

  • InGaNの時間分解スペクトロスコピー(1)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.406  1998.03  [Refereed]

  • InGaNの光学的特性(10)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1998.03  [Refereed]

  • InGaNの光学的特性(9)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1998.03  [Refereed]

  • InGaNの光学的特性(8)

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.405  1998.03  [Refereed]

  • BN, AlN, GaNの圧電定数

    第45回応用物理学関係連合講演会講演予稿集/応用物理学会   1, p.348  1998.03  [Refereed]

  • Gain spectroscopy of continuous wave InGaN multi-quantum well laser diodes.

    Semicond. Sci. Technol./IOP   13;1, pp97-101  1998.01  [Refereed]

    DOI

  • Gain spectroscopy of continuous wave InGaN multi-quantum well laser diodes.

    Semicond. Sci. Technol./IOP   13;1, pp97-101  1998.01  [Refereed]

    DOI

  • Constant-pressure first-principles molecular dynamics study on BN, AlN, and GaN.

    Mat. Res. Soc. Symp. Proc./MRS    1997.12

  • Constant-pressure first-principles molecular dynamics study on BN, AlN, and GaN.

    Mat. Res. Soc. Symp. Proc./MRS    1997.12

  • CuAlSe&lt;SUB&gt;2&lt;/SUB&gt;の格子力学

    日本物理学会講演概要集/日本物理学会   2, p.259  1997.10

  • CuAlSe&lt;SUB&gt;2&lt;/SUB&gt;における2フォノン吸収スペクトルと格子力学

    第58回応用物理学会学術講演会講演予稿集/応用物理学会   3, p.1334  1997.10

  • InGaNの光学的特性(7)

    第58回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.256  1997.10  [Refereed]

  • InGaNの光学的特性(6)

    第58回応用物理学会学術講演会講演予稿集/応用物理学会   1, p.256  1997.10  [Refereed]

  • Gain spectroscopy of continuous wave InGaN multi-quantum well laaser diodes with different degree of compositional fluctuation.

    Proceedings of ICNS'97/ICNS'97   S-8, pp466-467  1997.10

  • Exciton-phonon interaction in wurtzite GaN epilayers.

    Proceedings of ICNS'97/ICNS'97   Th1-6, pp.426-427  1997.10

  • Ab initio study on electronic band structures and related properties of III-nitrides.

    Proceedings of ICNS'97/ICNS'97   P2-34, pp.304-305  1997.10

  • Photoreflectance and photoluminescence spectra of tensile-strained wurtzite GaN epilayers.

    Proceedings of ICNS'97/ICNS'97   P2-33, pp.302-303  1997.10

  • Optical absorption coefficient in wurtzite GaN.

    Proceedings of ICNS'97/ICNS'97   P2-32, pp.300-301  1997.10  [Refereed]

  • Bright emission due to recombination of localized excitons in InGaN bulk and quantum well devices.

    Proceedings of ICNS'97/ICNS'97, Tu3-2   pp198-199  1997.10

  • Monochromated Cathodoluminescence Mapping of InGaN Single Quantum Wells.

    Proceedings of ICNS'97/ICNS'97   P1-LN-11, p186  1997.10

  • Gain spectroscopy of continuous wave InGaN multi-quantum well laaser diodes with different degree of compositional fluctuation.

    Proceedings of ICNS'97/ICNS'97   S-8, pp466-467  1997.10  [Refereed]

  • Exciton-phonon interaction in wurtzite GaN epilayers.

    Proceedings of ICNS'97/ICNS'97   Th1-6, pp.426-427  1997.10  [Refereed]

  • Ab initio study on electronic band structures and related properties of III-nitrides.

    Proceedings of ICNS'97/ICNS'97   P2-34, pp.304-305  1997.10

  • Photoreflectance and photoluminescence spectra of tensile-strained wurtzite GaN epilayers.

    Proceedings of ICNS'97/ICNS'97   P2-33, pp.302-303  1997.10

  • Optical absorption coefficient in wurtzite GaN.

    Proceedings of ICNS'97/ICNS'97   P2-32, pp.300-301  1997.10

  • Bright emission due to recombination of localized excitons in InGaN bulk and quantum well devices.

    Proceedings of ICNS'97/ICNS'97, Tu3-2   pp198-199  1997.10

  • Monochromated Cathodoluminescence Mapping of InGaN Single Quantum Wells.

    Proceedings of ICNS'97/ICNS'97   P1-LN-11, p186  1997.10  [Refereed]

  • Gain spectra in cw InGaN/GaN MQW laser diodes.

    Materials Science and Engineering B/Elsevier Science   50, pp.251-255  1997.06  [Refereed]

  • Nanosecond pump-and-probe study of wurtzite GaN.

    Materials Science and Engineering B/Elsevier Science   50, pp.180-182  1997.06  [Refereed]

  • Urbach-Martienssen tails in a wurtzite GaN epilayer.

    Appl. Phys. Lett. /AIP   70;25, pp.3440-3442  1997.06  [Refereed]

    DOI

  • Gain spectra in cw InGaN/GaN MQW laser diodes.

    Materials Science and Engineering B/Elsevier Science   50, pp.251-255  1997.06

  • Nanosecond pump-and-probe study of wurtzite GaN.

    Materials Science and Engineering B/Elsevier Science   50, pp.180-182  1997.06

  • Urbach-Martienssen tails in a wurtzite GaN epilayer.

    Appl. Phys. Lett. /AIP   70;25, pp.3440-3442  1997.06  [Refereed]

    DOI

  • Luminescences from localized states in InGaN epilayers.

    Appl. Phys. Lett. /AIP   70;21, pp.2822-2824  1997.05  [Refereed]

    DOI

  • Luminescences from localized states in InGaN epilayers.

    Appl. Phys. Lett. /AIP   70;21, pp.2822-2824  1997.05  [Refereed]

    DOI

  • Optical properties of tensile-strained wurtzite GaN epitaxial layers.

    Appl. Phys. Lett. /AIP   70;16, pp.2085-2087  1997.04  [Refereed]

    DOI

  • Valence band physics in wurtzite GaN.

    Mat. Res. Soc. Symp. Proc./MRS   468, pp,445-456  1997.04  [Refereed]

  • Optical properties of tensile-strained wurtzite GaN epitaxial layers.

    Appl. Phys. Lett. /AIP   70;16, pp.2085-2087  1997.04  [Refereed]

    DOI

  • Valence band physics in wurtzite GaN.

    Mat. Res. Soc. Symp. Proc./MRS   468, pp,445-456  1997.04  [Refereed]

  • InGaN量子井戸における励起子の局在化

    第44回応用物理学関係連合講演会講演予稿集   第0分冊  1997.03  [Refereed]

  • MOCVD成長h-GaN/sapphireの光学的特性VIII-時間分解分光(1)-

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03  [Refereed]

  • ワイドギャップ化合物半導体のUrbach's Tail (1)-h-GaN-

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03  [Refereed]

  • 引っ張り歪みh-GaNのフォトリフレクタンスおよびフォトルミネッセンス

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03

  • InGaNの光学的特性(5)

    第44回応用物理学関係連合講演会講演予稿集   第1分冊  1997.03  [Refereed]

  • Exciton Spectra of Cubic and Hexagonal GaN Epitaxial Films

    Jpn. J. Appl. Phys.   36;3B  1997.03  [Refereed]

    DOI

  • Exciton Spectra of Cubic and Hexagonal GaN Epitaxial Films

    Jpn. J. Appl. Phys.   36;3B  1997.03  [Refereed]

    DOI

  • Brillouin Scattering Study of Gallium Nitride: Elastic Stiffness Constants

    J. Phys.: Condens. Matter   9;1  1997.01  [Refereed]

    DOI

  • Biaxial Strain Dependence of Exciton Resonance Energies in Wurtzite GaN

    J. Appl. Phys.   81;1  1997.01  [Refereed]

    DOI

  • Brillouin Scattering Study of Gallium Nitride: Elastic Stiffness Constants

    J. Phys.: Condens. Matter   9;1  1997.01  [Refereed]

    DOI

  • Biaxial Strain Dependence of Exciton Resonance Energies in Wurtzite GaN

    J. Appl. Phys.   81;1  1997.01  [Refereed]

    DOI

  • Recombination of Localized Excitons in InGaN Single- and Multi-Quantum Well Structures

    Proceedings of MRS '96 Fall Meetings   N1.7  1996.12

  • Spontaneous Emission of Localized Excitons in InGaN Single- and Multi-Quantum Well Structures

    Appl. Phys. Lett.   69;27  1996.12  [Refereed]

    DOI

  • Recombination of Localized Excitons in InGaN Single- and Multi-Quantum Well Structures

    Proceedings of MRS '96 Fall Meetings   N1.7  1996.12

  • Spontaneous Emission of Localized Excitons in InGaN Single- and Multi-Quantum Well Structures

    Appl. Phys. Lett.   69;27  1996.12  [Refereed]

    DOI

  • BN、AlN、GaNの弾性定数

    日本物理学会1996年秋の分科会講演概要集   第2分冊  1996.10  [Refereed]

  • MOCVD成長h-GaN/sapphireの光学的特性VII-光吸収スペクトル(2)-

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09  [Refereed]

  • InGaNの光学的特性(4)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09  [Refereed]

  • InGaNの光学的特性(3)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09  [Refereed]

  • InGaNの光学的特性(2)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09  [Refereed]

  • InGaNの光学的特性(1)

    第57回応用物理学会学術講演会講演予稿集   第1分冊  1996.09  [Refereed]

  • Effects of Biaxial Strain on Exciton Resonance Energies of Hexagonal GaN

    Appl. Phys. Lett.   68;26  1996.06  [Refereed]

    DOI

  • Effects of Biaxial Strain on Exciton Resonance Energies of Hexagonal GaN

    Appl. Phys. Lett.   68;26  1996.06  [Refereed]

    DOI

  • Optical Phonons in GaN

    Physica   B219&amp;220;1-4  1996.04  [Refereed]

  • Elastic Constants of III-V Compound Semiconductors: Modification of Keyes Relation

    J. Phys.: Condens. Matter   8;18  1996.04  [Refereed]

    DOI

  • Brillouin Scattering Study in the GaN Epitaxial Layer

    Physica   B219&amp;220;1-4  1996.04  [Refereed]

  • Lattice Dynamics of CuAlS&lt;SUB&gt;2&lt;/SUB&gt; and CuAlSe&lt;SUB&gt;2&lt;/SUB&gt;

    Physica   B219&amp;220;1-4  1996.04

  • Optical Phonons in GaN

    Physica   B219&amp;220;1-4  1996.04  [Refereed]

  • Elastic Constants of III-V Compound Semiconductors: Modification of Keyes Relation

    J. Phys.: Condens. Matter   8;18  1996.04  [Refereed]

    DOI

  • Brillouin Scattering Study in the GaN Epitaxial Layer

    Physica   B219&amp;220;1-4  1996.04  [Refereed]

  • h-GaNのブリルアン散乱

    日本物理学会第51回年会    1996.03  [Refereed]

  • Sc&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;添加LiNbO&lt;SUB&gt;3&lt;/SUB&gt;の欠陥構造モデル

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • ストイキオメトリー組成LiNbO&lt;SUB&gt;3&lt;/SUB&gt;の光学的特性

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • K&lt;SUB&gt;2&lt;/SUB&gt;O添加融液によるLiNbO&lt;SUB&gt;3&lt;/SUB&gt;ストイキオメトリー単結晶の育成と評価

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • CuInSe&lt;SUB&gt;2&lt;/SUB&gt;薄膜の光吸収スペクトルの解析

    1996年春季第43回応用物理学関係連合講演会    1996.03

  • タンデムファブリ・ペローを用いたGaNのブリルアン散乱

    1996年春季第43回応用物理学関係連合講演会    1996.03  [Refereed]

  • MOCVD成長h-GaNのフォトリフレクタンススペクトル

    1996年春季第43回応用物理学関係連合講演会    1996.03  [Refereed]

  • MOCVD成長h-GaNのフォトリフレクタンススペクトル (2)

    1996年春季第43回応用物理学関係連合講演会    1996.03  [Refereed]

  • h-GaNのブリルアン散乱

    日本物理学会第51回年会    1996.03

  • Excitonic Emission from Hexagonal GaN Epitaxial Layers

    J. Appl. Phys./American Institute of Physics   79;5  1996.03  [Refereed]

    DOI

  • Excitonic Emission from Hexagonal GaN Epitaxial Layers

    J. Appl. Phys./American Institute of Physics   79;5  1996.03  [Refereed]

    DOI

  • Contribution of Excitons in the Photoluminescence Spectra of h-GaN Epitaxial Layers Grown on Sapphire Substrates by TF-MOCVD

    Proceedings of the International Symposium on Blue Laser and Light Emitting Diodes/Ohmsha    1996.02  [Refereed]

  • Contribution of Excitons in the Photoluminescence Spectra of h-GaN Epitaxial Layers Grown on Sapphire Substrates by TF-MOCVD

    Proceedings of the International Symposium on Blue Laser and Light Emitting Diodes/Ohmsha    1996.02  [Refereed]

  • Defect Structure Model of LiNbO3:Sc2O3

    J. Phys.: Condens. Matter   8;37  1996

    DOI

  • Defect Structure Model of LiNbO3:Sc2O3

    J. Phys.: Condens. Matter   8;37  1996

    DOI

  • Lattice Dynamics of CuAlS2 and CuAlSe2

    Physica   B219&220;1-4  1996

  • GaPの格子力学-2フォノン状態密度

    日本物理学会1995年秋の分科会    1995.09

  • AlNの格子力学

    日本物理学会1995年秋の分科会    1995.09  [Refereed]

  • MOCVD成長h-GaN/Sapphireの光学特性VI-光吸収スペクトル

    1995年第56回応用物理学会学術講演会    1995.08  [Refereed]

  • MOCVD成長h-GaN/Sapphireの光学特性V-フォトルミネッセンススペクトル

    1995年第56回応用物理学会学術講演会    1995.08  [Refereed]

  • MOCVD成長h-GaN/Sapphireの光学特性IV-フォトリフレクタンススペクトル (2)

    1995年第56回応用物理学会学術講演会    1995.08  [Refereed]

  • CuAlS&lt;SUB&gt;2&lt;/SUB&gt;エピタキシャル層からの可視・紫外フォトルミネッセンス

    1995年第56回応用物理学会学術講演会    1995.08

  • Defect Structures in LiNbO&lt;SUB&gt;3&lt;/SUB&gt;

    J. Phys.: Condens. Matter/Institute of Physics   7;18  1995.05

    DOI

  • Defect Structures in LiNbO3

    J. Phys.: Condens. Matter/Institute of Physics   7;18  1995

    DOI

  • Hyperspectral screening of melanoma on acral volar skin

    Nagaoka, T, Nakamura, A, Okutani. H, Kiyohara, Y, Koga, H, Saida, T, Sota, T

    Skin Res. Technol.  

    DOI

  • Hyperspectral screening of melanoma on acral volar skin

    Nagaoka, T, Nakamura, A, Okutani. H, Kiyohara, Y, Koga, H, Saida, T, Sota, T

    Skin Res. Technol.  

    DOI

▼display all

Industrial Property Rights

  • 解析装置、分析装置、分析方法およびプログラム

    宗田 孝之, 野口 遼介, 中村 厚

    Patent

  • 解析装置、解析方法、及びプログラム

    宗田 孝之, 中村 厚

    Patent

  • 皮膚疾患の診断のための爪甲色素線状または皮膚の色相の解析方法、診断装置およびコンピュータプログラム

    宗田 孝之, 中村 厚

    Patent

  • メラノーマ鑑別指標の導出方法

    5565765

    宗田 孝之, 中村 厚, 會沢 勝夫, 大坪 真也

    Patent

  • メラノーマ診断用画像の作成方法

    5408527

    宗田 孝之, 中村 厚, 大坪 真也, 會沢 勝夫

    Patent

  • 非侵襲ヒト皮膚メラニン計測法及びその装置

    宗田 孝之, 中村 厚, 大坪 真也, 會沢 勝夫

    Patent

  • 紫外線窒化物半導体発光素子およびその製造方法

    池田 大勝, 宗田 孝之

    Patent

  • 点光源撮影画像の補正装置および補正方法

    川合 健太郎, 宗田 孝之, 會沢 勝夫, 中村 厚

    Patent

  • ラマン分光装置、及び分光装置

    4565119

    宗田 孝之, 會沢 勝夫

    Patent

  • 眼底分光像撮影装置

    4505852

    宗田 孝之, 會沢 勝夫, 中村 厚, 大坪 真也, 高須 正行

    Patent

  • 測定方法および測定装置

    4721144

    宗田 孝之, 會沢 勝夫, 中村 厚, 影山 智, 大坪 真也, 市川 文彦

    Patent

  • 分光分析装置及び分光分析法

    宗田 孝之, 會沢 勝夫, 中村 厚, 池田 照樹

    Patent

  • リアルタイム分光画像分析装置及び分析方法

    宗田 孝之, 會沢 勝夫, 林 仲信, 大坪 真也

    Patent

  • グルコース濃度測定装置

    宗田 孝之, 中村 厚, 會沢 勝夫, 金澤 眞雄, 長谷川 健

    Patent

▼display all

 

Syllabus

▼display all

 

Sub-affiliation

  • Faculty of Science and Engineering   Graduate School of Advanced Science and Engineering

  • Affiliated organization   Global Education Center

Research Institute

  • 2022
    -
    2024

    Kagami Memorial Research Institute for Materials Science and Technology   Concurrent Researcher

  • 2022
    -
    2024

    Waseda Research Institute for Science and Engineering   Concurrent Researcher

Internal Special Research Projects

  • 単糖の水和構造と生物学的役割の関連性についての第一原理分子動力学を用いた研究

    2004  

     View Summary

    水が生体分子の物理・化学的性質にもたらす影響を検証することは、生命の諸現の本質を理解する上で重要な課題である。現時点ではタンパク質やDNA等の水溶液中の第一原理分子動力学シミュレーションは困難だが、分子量が比較的小さくかつ生物学的に重要な単糖ならば、近年の計算機技術の発展により、水和の第一原理分子動力学シミュレーションが可能となった。そこで本研究は、第一原理分子動力学を用い、グルコースやリボースの物理・化学的性質に、水和が与える影響を詳細に検証することを目的とする。この研究は、将来において予想されるRNA等の大規模な第一原理分子動力学シミュレーションを行う上で、必要不可欠な知見を与えるものと期待される。 まず、リボフラノースのヒドロキシメチル基の回転異性体に対して、それぞれ水和構造を調べ、水和構造は回転異性体に比較的強く影響を受けることを確認した。さらに、第一水和層の水分子に属するワニエ関数中心と原子核の座標を用いて水分子が持つ双極子モーメントの分布を求めた。その結果、数ピコ秒間リボフラノースにアクセプターとして水素結合している水分子の双極子モーメントは約0.3デバイ増加することを確認した。この結果は、単糖と第一水和層との間の比較的強い局所的分極相互作用を示している。[1] 次に、水和構造と生物学的に重要であるリボフラノース五員環のパッカリングの関係を調べるため、その構造的な揺らぎおよび低周波数領域のダイナミクスを、近年注目され始めた時間-周波数解析法の一つであるヒルベルト・ファン変換を用いて解析した。その結果、ヒドロキシメチル基回転異性体によって、低周波数領域のダイナミクスが異なっていることを確認した。また、パッカリング位相角が、アノメリック酸素とヒドロキシメチル基の酸素との距離と動的な相関を持ち、その相関性を用いて水和構造がパッカリングのダイナミクスに及ぼすメカニズムを説明することに成功した。この結果は、パッカリングの二つの状態間(S領域とN領域)の遷移、ならびにRNAの水溶液中におけるダイナミクスの理解に重要な意義を持っている。[2]

  • III族窒化物における光励起キャリアの冷却過程に関する研究

    1998  

     View Summary

     ウルツ鉱構造III族窒化物およびその三元混晶は、赤色から紫外域の発光・受光デバイス材料として、また耐環境性に優れた、あるいは高周波用の電子デバイス材料として注目を集めている。これら材料系は難合成材料として知られていたが、合成技術の進歩により一部発光デバイスは実用化され、電子デバイスも試作され動作確認が行われるまでになってきている。しかし、基本的な物性については未だ明らかになっていない部分も多い。 この材料系の特徴のひとつは、立方晶の典型的なIII-VおよびII-VI族化合物半導体とは異なり、LOフォノンのエネルギーが室温の温度エネルギーよりも大きい事であり、このため光励起されたキャリアの初期緩和過程(初期冷却過程)がこれまで知られている典型的な立方晶化合物半導体のそれとは異なったものになっている可能性があることである。本研究は、アップ・コンバージョン蛍光寿命測定法を用いて光励起されたキャリアの発光過程を100 fs程度の時間分解能で調べることにより、初期冷却過程に対する知見を得る事を目的に実施された。具体的には、測定法の欠点を補うため、発光効率の良いSi を添加したInGaN三元混晶の多重量子井戸構造の試料を用い、まず、正孔の緩和(冷却)過程を調べた。実験はすべて室温で行った。 得られた知見は以下のとおりである。時間積算した発光スペクトルはInGaN三元混晶に特有のエネルギー・ギャップ不均一性を反映した2つのピークを示した。いずれのピークも発光の立ちあがりは遅くとも1ps以内であり、発光の減衰は高エネルギー側のピークの方が早いことがわかった。発光の立ちあがり時間が速いのは正孔の緩和(冷却)が速いこととSi添加に起因すると解釈される。このとき正孔の過剰エネルギーは理論計算ではLOフォノンのエネルギーより小さいため、正孔の冷却は添加Siにより供給された冷たい電子あるいは音響フォノンとの散乱が支配しているものと考えられる。これらの散乱確率が大きい理由は正孔の有効質量が大きい事に帰せられる。 現在、電子の冷却過程と発光の減衰の物理を詳しく調べるため、本研究で使用した測定法以外にポンプ・プローブ法を用いて研究を継続している。

  • GaNの光学的非線形性に及ぼす励起子の効果の研究

    1997   鈴木 克生

     View Summary

    本研究の目的はサファイア上に堆積された高品質GaN薄膜、InGaN/GaN単一量子井戸及びInGaN/InGaN多重量子井戸構造における励起子の性質とその光学的非線形性に及ぼす効果を調べることにあった。はじめに、研究コミュニティーからの要請により若干目的に変更が生じたことをお詫びしておく。研究実績は以下の通りである。1. GaN:0.83μm単結晶試料の10K-300Kにおける透過率・反射率の精密測定を行い、基礎吸収端近傍で吸収係数が1&#215; 105cm-1であることを見出した。この試料と4μmの試料でXeランプとガラスフィルタを組み合わせて得た3.3Ev以上の白色スペクトルにより超弱励起PL測定を実施した。A, B励起子の完全分離、均一線幅の同定、A, B励起子第一励起状態からの発行同定ができた。更に膜厚変化に伴う残留歪による励起子発光ピークのシフト、欠陥密度の変化に起因すると思われる束縛励起子発光強度の変化等を見出した。吸収係数の絶対値が大きいことから、基礎吸収端でのポンプ・プローブ(P&P)法による透過率測定は満足のいく結果が得られなかったので、現在測定した吸収係数だけをもとにした光照射後の比較的長い時定数を持つ屈折率変化を見出し、GaNの可変屈折率素子としての可能性を示唆した。2. InGaN単一・多重量子井戸:これら試料における最近の話題はピエゾ電場効果と混晶中のポテンシャル揺動に集中している。観測される電子系は両者の競合で決まっており、個々の効果の分離が難しい。本研究ではSiを高濃度に添加することで前者の効果をほぼゼロに抑制した試料を2つ成長条件を変えて作製し後者の効果の有無を調べた。結果はポテンシャル揺動が明らかに存在することを示した。これが無添加試料において励起子を局在させる一因であると考えられる。これらの試料でのゲインスペクトルを求めた結果、それは電子正孔プラズマモデルで説明できる一方で、如実にポテンシャル揺動を反映している事実を見出した。ポテンシャル揺動が弱い試料でアップ・コンバージョン法により蛍光の立ち上がり時間を測定した結果、それは60fs以下であることを見出した。N型試料でありかつ正孔・LOフォノン散乱が無視できる様にした励起波長での比較的弱励起条件下での結果であることから、実験結果は正孔が電子・正孔散乱により余剰エネルギーを冷たい電子へ移行して速やかに緩和することを反映したものと考えている。InGaN系における光励起正孔の初期緩和に関する研究はこれが始めてであることを付記しておく。研究成果の発表小豆畑他1997年4月“Valence band physics in wurtzite GaN”, in Mat. Res. Soc. Symp. Proc. Vol, 468, 445-456 (1997).宗田他1997年4月“Optical properties of tensile-stained wurtzite GaN epitaxial layers”, Appl. Phys. Lett. 70, 2085 (1997).1997年5月“Luminescences from localized states in InGaN epilayers”, Appl. Phys. Lett. 70, 2822 (1997).1997年6月“Nanosecond pump-and-probe study of wurtzite GaN”, Materials Science and Engineering B 50, 180-182 (1997).1997年6月“Gain spectra in cw InGaN/GaN MQW laser diodes”, Materials Science and Engineering B50, 251-255 (1997).1997年6月“Urbach-Martienssen tails in a wurtzite GaN epilayer”, Appl. Phys. Lett.70, 3440 (1997).1997年10月“Gain spectroscopy of continuous wave InGaN multi-quantum well laaser diodes with different degree of compositional fluctuation” in Proc. of ICNS '97, S-8, Tokushima, Japan, 1997.1997年10月“Optical absorption coefficient in wurtzite GaN”, in Proc. of ICNS '97, P2-34, Tokushima, Japan, 1997鈴木他1997年10月“Ab initio study on eletronic band structures and related properties of III-nitrides”, in Proc. of ICNS '97, P-2-34, Tokushima, Japan, 1997.宗田他1997年10月“Bright emission due to recombination of localized excitons in InGaN bulk and quantum well devices”, in Proc. of ICNS '97, Tu-3-2, Tokushima, Japan, 1997.1997年10月“Excition-phonon interaction in wurtzite GaN epilayers”, in Proc. of ICNS '97,Th1-6, Tokushima, Japan, 19971997年10月“Photoreflectance and photoluminescence spectra of tensile-strained wurtzite GaN epilayers”, in Proc. of ICNS '97, P2-33, Tokushima, Japan, 1997.1997年10月“Monochromated Cathodoluminescence Mapping of InGaN Single Quantum Wells” in Proc. of INCS '97, P1-LN-11, Tokushima, Japan, 1997.1998年1月“Gain spectroscopy of continuous wave InGaN multi-quantum well laser diodes”, Semicond. Sci. Technol. 13, 97-101 (1998).鈴木他1998年“Constant-pressure first-principles molecular dynamics study on BN, AIN, and GaN”, To be published in Proc of MRS 1997 Fall Meeting, Boston, December 3, 1997.他1996年度発表論文数11編