β-Ga2O3 is gaining increasing attention from power device engineers owing to its wide bandgap and fabrication potential of low-cost, large-diameter substrates. Atomic-layer-deposited (ALD) Al2O3 has application potential for the gate insulation and surface passivation of β-Ga2O3 devices, which cannot incorporate a well-established SiO2/Si system. To improve the device performance and reliability, the effect of postdeposition annealing (PDA) on the gate insulation characteristics of Al/ALD-Al2O3/(001) β-Ga2O3 capacitors was comprehensively investigated. As in previous studies, PDA at 700 °C and higher sharply reduced the capacitor leakage current by three orders of magnitude. This threshold temperature was 100 °C lower than that for GaN devices. Space-charge-controlled field emission analysis revealed that the current reduction was achieved via conduction-band-offset enhancement from 1.45 to 2.2 eV. These changes were caused by Al2O3 crystallization, which started at 650 °C according to an x-ray diffraction analysis. Selective-area electron diffraction (SAED) patterns showed that the crystallized films comprised twinned γ-Al2O3, wherein the (111) planes are parallel to the sawtooth β-Ga2O3 (101) planes with epitaxial relations of γ-Al2O3 [0 1 ¯ 1] || β-Ga2O3 [010] and γ-Al2O3 [01 1 ¯] || β-Ga2O3 [010]. This epitaxy was realized by three-dimensional oxygen sublattice matching with relatively small misfits of less than 1%, 1%, and 8% along the γ-Al2O3 [2 1 ¯ 1 ¯], [111], and [01 1 ¯] directions, respectively. Furthermore, the SAED patterns displayed diffraction spots specific to triaxially tripled γ-Al2O3. This is yet to be identified as δ-Al2O3. Contrary to expectations, PDA magnified the bias instability of β-Ga2O3 capacitors, supposedly owing to the Al2O3 and Ga2O3 solid-solution reaction, which contrasts with the previous significant improvement in GaN capacitors. However, PDA negligibly affected the β-Ga2O3 capacitor interface characteristics. This result also contrasts sharply with the previous results obtained for GaN capacitors that experienced a PDA-induced increase in both interface states and flat-band voltage. This apparent thermal stability of Al2O3/(001) β-Ga2O3 interface can be ascribed to the aforementioned small lattice misfit at the γ-Al2O3/(101) β-Ga2O3 interface, which contrasts with the 12% misfit at the γ-Al2O3/(0001) GaN interface. These findings form the foundation for developing technologies to enhance the performance and reliability of ALD-Al2O3/β-Ga2O3 devices. Specifically, based on them, a guideline for reducing the bias instability is proposed.

This article reports on the high operation voltage large-signal performance of two-dimensional hole gas diamond metal-oxide semiconductor field-effect transistors (MOSFETs) with thick atomic-layer-deposition (ALD)-Al2O3 formed on high purity polycrystalline diamond with a (110) preferential orientation. MOSFETs with a 1-μ m gate-length having a gate oxide layer of 200-nm-thick Al2O3, formed by ALD and asymmetric structures, to withstand high-voltage operations. The large-signal performances were evaluated at a quiescent drain voltage of greater than-60 V for the first time in diamond field-effect transistor (FET). As a result, an output power density of 2.5 W/mm under class-A operation at 1 GHz, which is higher than that of diamond FETs fabricated by a self-aligned gate process, was obtained. Moreover, an output power density of 1.5 W/mm was exhibited by the MOSFET when biased at a quiescent drain voltage of-40 V under class-AB operation at 3.6 GHz using an active load-pull system. This is the highest recorded value for diamond FETs at a frequency greater than 2 GHz, owing to the high-voltage operation. These results indicate that diamond p-FETs under high-voltage operations are the most suitable for high-power amplifiers with complementary circuits.

The nitrogen vacancy (NV) center in diamond is fascinating and has a long spin coherence time. It is applied to magnetic sensors with high sensitivity (similar to fT). To achieve a high sensitivity, an aligned NV ensemble is required. This paper presents a new methodology for the fabrication of two-dimensional (2D) aligned NV ensembles by using nitrogen-terminated (111) surface. To realize this, pure diamond growth and high nitrogen coverage on (111) surface were performed. As a result, we have succeeded in producing 2D NV ensembles, with 1 x 10(9) cm(-2). Coherence time T-2 was 2.45 mu s. Also, Using dynamical decoupling, the decoherence sources were revealed. The alignment ratio along [111] axis was archived 60%. Thermal annealing of the nitrogen termination was introduced to improve the alignment ratio. After that, the alignment rate was up to 73%. This report shows that the aligned 2D NV ensemble has possibility to be applied for multiple quantum devices. (C) 2021 Elsevier Ltd. All rights reserved.

We report two-dimensional hole gas (2DHG) diamond field-effect transistors (FETs) with microwave plasma chemical vapor deposition (MPCVD)-regrown p+-diamond (B concentration ∼ 1 × 1022 /cm3) ohmic contacts. The heavily doped p+-diamond shows low ohmic contact resistance of 1.1 Ω mm, which is the lowest value reported in diamond to date. In addition, the p+-diamond with a TiC also offers much stronger metal adhesion when compared with previous Au/hydrogen-terminated diamond surfaces and is suitable for industrial use. Benefiting from the low contact resistance of the p+-diamond layer, a maximum drain current density of 1170 mA/mm and an ON-resistance of 8.9 Ω mm were demonstrated in a 2DHG diamond metal-oxide-semiconductor FET with a 1 μm gate length. These results indicate that the regrown p+-diamond ohmic contacts will make it possible to realize further improvements in the maximum drain current density of 2DHG diamond FETs.

Substrate heating effects on the microstructure and magnetic properties of MnAlGe films grown on Si/SiO2 substrate by sputtering system were investigated. The MnAlGe film fabricated by low-temperature substrate heating demonstrated amorphous phase and paramagnetic property. The film of c-axis orientation associated with the Cu2Sb-type structure was obtained by sputtering at a substrate heating temperature of 270°C and it exhibited perpendicular magnetic anisotropy. From the magnetization curves measured at room temperature, the uniaxial magnetic anisotropy energy, Ku, was evaluated to be in the order of 106 erg/cm3, which is consistent with the literature, although the heating processing and temperature are slightly different. Microstructural observation indicated that the c-axis oriented grains were isolated in the matrix of the amorphous phase. The film lost the c-axis orientation at elevated substrate heating temperature, resulting in loss of the anisotropic magnetic property.

A dynamic space-charge-controlled field emission (SCC-FE) model that considers temporal insulator charge variations caused by voltage stress is developed for analyzing the current conduction in insulators in the entire voltage range of measurement, yielding good agreement between experiments and simulations. The usage of prestressed samples in this analysis is essential for accurately estimating the electron affinities of insulators, yielding 1.65 and 1.93 eV as the estimates for Al2O3 films formed on GaN by atomic-layer deposition (ALD) at 200 and 450 °C, respectively, and 1.65 and 1.83 eV for those on SiO2/Si, respectively. Through the bias instability analysis using the method developed here, the voltage-stress tolerance of both Si and GaN metal-insulator-semiconductor (MIS) capacitors with ALD Al2O3 films was found to be enhanced by the high-temperature (450 °C) ALD. The analysis also revealed the fact that the voltage-stress-induced flatband voltage shift of GaN capacitors with the high-temperature Al2O3 films is mainly caused by the Al2O3 charges near the substrate, hence providing a clue to even better bias stability of the GaN capacitors. With possible applications to other wide-bandgap semiconductor (WBGS) capacitors, the dynamic SCC-FE analysis developed here will play an essential role in analyzing not only gate insulator characteristics but also many reliability issues of various WBGS MIS field-effect transistors.

Superconducting quantum interference devices (SQUIDs) are currently used as magnetic flux detectors with ultra-high sensitivity for various applications such as medical diagnostics and magnetic material microstructure analysis. Single-crystalline superconducting boron-doped diamond is an excellent candidate for fabricating high-performance SQUIDs because of its robustness and high transition temperature, critical current density, and critical field. Here, we propose a fabrication process for a single-crystalline boron-doped diamond Josephson junction with regrowth-induced step edge structure and demonstrate the first operation of a single-crystalline boron-doped diamond SQUID above 2 K. We demonstrate that the step angle is a significant parameter for forming the Josephson junction and that the step angle can be controlled by adjusting the microwave plasma-enhanced chemical vapour deposition conditions of the regrowth layer. The fabricated junction exhibits superconductor-weak superconductor-superconductor-type behaviour without hysteresis and a high critical current density of 5800A/cm(2).

Electric dipoles at a metal-gate/Al2O3 interface are found to control the current conduction in negatively biased Al2O3 metal-insulator-semiconductor (MIS) capacitors by effectively increasing the Al2O3 electron affinity near the gate and thereby reducing the barrier height against electron field emission from the gate. By carrying out space-charge-controlled field emission analysis, the Al2O3 effective electron affinity in Al-gate capacitors was found to be larger than that for the Au gate by 0.38 eV, and the value for the Ni gate was similar to that for the Au gate. The cross-sectional transmission-electron-microscope images of the samples revealed the presence of an approximately 3-nm-thick layer intervening between the Al gate and the Al2O3 film. This layer is likely to have formed Al/Al2O3 interfacial dipoles that caused the aforementioned shift of the Al2O3 effective electron affinity. It was also confirmed that the conventional Fowler-Nordheim tunneling analysis yields remarkably erroneous results under the presence of these dipoles. These findings not only form the basis for investigating the band alignment of metal-gate MIS capacitors, but also alert us to a possibility of unexpectedly large leakage currents in negatively biased metal-gate MIS field-effect transistors.

Quantum information processing requires quantum registers based on coherently interacting quantum bits. The dipolar couplings between nitrogen vacancy (NV) centres with nanometre separation makes them a potential platform for room-temperature quantum registers. The fabrication of quantum registers that consist of NV centre arrays has not advanced beyond NV pairs for several years. Further scaling up of coupled NV centres by using nitrogen implantation through nanoholes has been hampered because the shortening of the separation distance is limited by the nanohole size and ion straggling. Here, we demonstrate the implantation of C5N4Hn from an adenine ion source to achieve further scaling. Because the C5N4Hn ion may be regarded as an ideal point source, the separation distance is solely determined by straggling. We successfully demonstrate the fabrication of strongly coupled triple NV centres. Our method may be extended to fabricate small quantum registers that can perform quantum information processing at room temperature.

Diamond is a promising material for power applications owing to its excellent physical properties. Two-dimensional hole gas (2DHG) diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with hydrogen-terminated (C-H) channel have high current densities and high breakdown fields but often show normally-ON operation. From the viewpoint of safety, normally-OFF operation is required for power applications. In this letter, we used ion implantation to form a shallow and thin nitrogen-doped layer below the C-H channel region, which realized normally OFF operation. Nitrogen-ion implanted length is fixed at 5 or 10 mu m. Nitrogen is a deep donor (1.7 eV) and the nitrogen-doped layer prevents hole accumulation near the surface. The threshold voltage was as high as -2.5 V and no obvious dependence on the threshold voltage of nitrogenion implanted length is observed. The breakdown field was 2.7 MV/cm at room temperature. Of 64 devices with a common gate length, 75% showed normally-OFF operation. We confirmed the threshold voltage shift by a thin and shallow nitrogen-doped layer formed by ion implantation.

To accurately analyze the deep states at the insulator/wide-bandgap semiconductor interface, this study reassessed and improved the conventional photoassisted capacitance-voltage (PACV) method. First, as previously pointed out, the illumination time under depletion should be long enough that the voltage shift caused by interface-state depopulation (in n-type semiconductors) saturates. Excessive illumination, however, causes insulator charging, thereby apparently increasing estimated values. To solve this problem, this study proposes to measure reference characteristics just after postillumination ones. Secondly, the postillumination measurements should be started without delay after turning off the light or may be carried out with the samples being illuminated. Thirdly, the depletion should be deep enough that the magnitude of band bending in the substrate at the beginning of the postillumination measurements is larger than 1 V. This guideline considerably relaxes a previous one that required a band bending of bandgap or larger. Furthermore, this study developed a method for compensating the interface-state depopulation (in n-type) during the reference measurements, in which the depopulation causes the so-called stretch-out. The results thus obtained from an Al/Al2O3/GaN capacitor agreed fairly well with those by a recently developed transient photoassisted capacitance method, supporting the validity of both methods. Being less sensitive to the gate-insulator charging, the advanced PACV method developed here has an advantage over the transient method and, therefore, will help advance the technology for fabricating high-performance, high-reliability insulator/wide-bandgap semiconductor insulators.

© 2019 Elsevier B.V. Key factors in C 1s photoelectron spectroscopy for realistic samples of single crystal diamonds are remarked. Basic equations for angle-dependent photoelectron spectroscopy applied to single crystal diamond samples are described in Appendix A. Carbon 1s photoelectron spectroscopic works so far reported for hydrogen-terminated and oxygen-terminated diamond (001) and (111) samples were reviewed placing special attention on surface C 1s components with reference to the key factors. The results showed diversity in C 1s photoelectron spectra so far reported. We had three specific subjects of the study in C 1s XPS; the first is that we have reconfirmed the phenomenon that surface conductive layers resumed when smooth non-doped CVD C(111)-O samples were annealed in vacuum [Diam.Rela.Mate.18(2009)206]. A single C 1s XPS surface component was found for a smooth C(111)-O sample before the vacuum-anneal, which was attributed to surface carbon atoms in C–O–H bonding. The second subject is that dependence of C 1s XPS spectra on surface sensitivity has been measured for all the samples with different surface roughness of C(001)-O, C(111)-O, C(001)-H, and C(111)-H. The results were converted to the energy difference between the Fermi-level (Ef) and valence band maximum (Ev) on the probing depth from the surface. All the samples showed downward bending of Ev toward the surface. For the C(001)-H samples, this was a reconfirmation of previous work [Surf.Sci.604(2010)1148]. For the C(001)-H and C(111)-H samples, various degrees of downward band bending toward surface were observed and analyzed with two-dimensional band simulation. It was concluded that another source of holes such as shallow acceptors is present in a deeper region of the surface in addition to holes very close to surface caused by the charge-transfer-doping. The third subject is that C 1s XPS spectra for superconducting C(111)-O samples showed a lattice distortion of ~9 monolayers near the surface.

The nitrogen-vacancy (NV) center in diamond is the most promising candidate for quantum sensing because of its beneficial properties. For quantum-sensing applications, a shallow NV center is critical for approximating the sensing target on a diamond surface. Such shallow NV centers are strongly affected by the diamond surface termination. The properties of shallow NV centers in hydrogen-, oxygen-, and fluorine-terminated diamond have been well studied. In recent years, silicon-terminated diamond has also been investigated; however, the effect of silicon-terminated diamond on the properties of shallow NV centers remains unclear. Recently, the suitability of nitrogen-terminated diamond for shallow NV centers has been theoretically and experimentally examined; however, quantum sensing has not yet been performed. In this work, we evaluated the effect of silicon and nitrogen termination on shallow NV centers. The negatively charged state of shallow NV centers was unstable below silicon termination. In contrast, the properties of shallow NV centers in nitrogen-terminated diamond were satisfactory for quantum sensing and enabled H-1 NMR detection. Our results are in good agreement with previous reports on silicon and nitrogen terminations and provide the perspective that the stability of shallow NV centers highly depends on the polarity of electron affinity of the diamond surface.

This letter reports the small-signal and large-signal performances at high drain voltage (V-DS) ranging up to 60 V for a 0.5 mu m gate length two-dimensional hole gas diamond metal-oxide-semiconductor field-effect transistor with a 100-nm-thick atomic-layer-deposited Al2O3 film on a IIa-type polycrystalline diamond substrate with (110) preferential surfaces. This diamond FET demonstrated a cutoff frequency (f(T)) of 31 GHz, indicating that its carrier velocity was reaching 1.0 x 10(7) cm/s for the first time in diamond. In addition, a f(T) of 24 GHz was obtained at V-DS = -60 V, thus giving a f(T) x V-DS product of 1.44 THz.V. This diamond FET is promising for use as a high-frequency transistor under high voltage conditions. Under application of a high voltage, a maximum output power density of 3.8W/mm (the highest in diamond) with an associated gain and power added efficiency were 11.6 dB and 23.1% was obtained when biased at V-DS = -50 V using a load-pull system at 1 GHz.

This paper describes a deoxyribonucleic-acid-sensitive electrolyte solution-gate field-effect transistor (SGFET) sensor utilizing a partial carboxyl-terminated boron-doped polycrystalline diamond surface as a linker to connect a deoxyribonucleic acid (DNA) probe. A high density of carboxyl termination on the polycrystalline diamond surface that was employed as a FET channel was achieved using a vacuum ultraviolet system with oxygen gas. A single-stranded DNA probe was immobilized on the polycrystalline diamond channel via amino coupling. The current-voltage characteristics of the polycrystalline diamond SGFET sensor was examined with bias voltages within its potential voltage window. The characteristics of the drain-source current verses the drain-source voltage showed a pinch-off, a shift voltage of up to 40 mV with a coefficient of variation of 4 - 11% was obtained between hybridization and denaturation. In addition, a single nucleotide mutation of DNA sequence was selectively recognized by the shift voltage up to ca. 10 mV.

The ionic-liquid-gating technique can be applied to the search for novel physical phenomena at low temperatures because of its wide controllability of the charge carrier density. Ionic-liquid-gated field-effect transistors are often fragile upon cooling, however, because of the large difference between the thermal expansion coefficients of frozen ionic liquids and solid target materials. In this paper, we provide a practical technique for setting up ionic-liquid-gated field-effect transistors for low-temperature measurements. It allows stable measurements and reduces the electronic inhomogeneity by reducing the shear strain generated in frozen ionic liquid. Published by AIP Publishing.

We demonstrate nano- and micro-size patterning processes for high quality single crystal superconducting boron-doped diamond films with low damage using selective microwave plasma chemical vapour deposition and selective oxygen plasma etching. The offset critical temperature Tc(offset) of the micro strip is 10.2 K even if the strip width is 1 mu m. However, we show that the critical temperature at zero resistivity Tc(zero) of several narrow strips is decreased owing to the unexpected defects induced by polishing damage and natural nanoscale scratch injury. These defects will induce a two-step superconducting transition. The probability of this tendency increases with decreasing the strip width. We also reveal that the critical current density Jc increases with decreasing the strip width, especially below 30 mu m. By using a transport measurement, the maximum Jc is estimated to be 917,000 A/cm(2) at 2.0 K with a strip width of 2 mu m, which is the highest value reported for a superconducting diamond film. The upper critical field is estimated to be 11.5 T by the WHH approximation and 9.3 T by BCS fitting. Such high values mean superconducting diamond wiring can be used under a high magnetic field. We also attempt to fabricate nano-patterning and reveal that the transition temperature suddenly decreases below 400 nm, and superconductivity is not observed below 300 nm. This work contributes to the future development of superconducting nano- and micro-electro mechanical systems by exploiting the excellent properties of robustness, processability, high transition temperature, critical current density, and critical field associated with diamond.

The exceptional performance of diamond-based field-effect transistor technology is not restricted to devices that use single crystalline diamond alone. This letter explores the full potential of the heteroepitaxial diamond field-effect transistor (HED-FET). HED-FET devices were fabricated with a long gate-drain length ( LGD) configuration using C-H bonded channels, and a high maximum current density of 80 mA/mm and a high I ON/I OFF ratio of 109 were achieved. Additionally, the HED-FETs showed an average breakdown voltage of ≥500 V and comparatively high breakdown voltage of more than 1 kV. This letter represents a significant step toward the realization of the potential of widely available heteroepitaxial diamond for use in FET applications.

We have investigated the length-dependence of the in-plane electrical resistivity of vertically aligned and highly dense carbon nanotube (CNT) films that were dense enough to conduct electrons. The in-plane conductivity is well accounted for by a combination of inter-tube hopping (variable range hopping, VRH) and graphitic conduction. VRH conduction was dominant in the thinner CNT films, and the films showed negative temperature dependence of resistivity. The dimension of the VRH component varied depending on the CNT length. In the thicker CNT films, the graphitic conduction appeared, and then, the localization length spread, leading to the positive temperature dependence of resistivity. This behavior can be explained by the presence of a labyrinthine arrangement of graphene walls among aligned CNTs, which was confirmed by transmission electron microscopy observations.

Atomic-layer-deposited (ALD) Al2O3 films are the most promising surface passivation and gate insulation layers in non-Si semiconductor devices. Here, we carried out an extensive study on the time-dependent dielectric breakdown characteristics of ALD-Al2O3 films formed on homo-epitaxial GaN substrates using two different oxidants at two different ALD temperatures. The breakdown times were approximated by Weibull distributions with average shape parameters of 8 or larger. These values are reasonably consistent with percolation theory predictions and are sufficiently large to neglect the wear-out lifetime distribution in assessing the long-term reliability of the Al2O3 films. The 63% lifetime of the Al2O3 films increases exponentially with a decreasing field, as observed in thermally grown SiO2 films at low fields. This exponential relationship disproves the correlation between the lifetime and the leakage current. Additionally, the lifetime decreases with measurement temperature with the most remarkable reduction observed in high-temperature (450 °C) O3-grown films. This result agrees with that from a previous study, thereby ruling out high-temperature O3 ALD as a gate insulation process. When compared at 200 °C under an equivalent SiO2 field of 4 MV/cm, which is a design guideline for thermal SiO2 on Si, high-temperature H2O-grown Al2O3 films have the longest lifetimes, uniquely achieving the reliability target of 20 years. However, this target is accomplished by a relatively narrow margin and, therefore, improvements in the lifetime are expected to be made, along with efforts to decrease the density of extrinsic Al2O3 defects, if any, to promote the practical use of ALD Al2O3 films.

Understanding the electrical contact properties of carbon nanotube (CNT) ends is important to use the high conductance of CNTs in the CNT on-axis direction in applications such as through-silicon via structures. In this study, we experimentally evaluated the contact resistivity between single-/multi-walled CNT ends and a metal nanoprobe using conductive atomic force microscopy (C-AFM). To validate the measured end contact resistivity, we compared our experimentally determined value with that obtained from numerical calculations and reported values for side contact resistivity. The contact resistivity normalized by the length of the CNT ends was 0.6-2.4 x 10(6) Omega nm for single-walled CNTs. This range is 1-2 orders of magnitude higher than that determined theoretically. The contact resistivity of a single-walled CNT end with metal normalized by the contact area was 2-3 orders of magnitude lower than that reported for the resistivity of a CNT sidewall/metal contact. For multi-walled CNTs, the measured contact resistivity was one order of magnitude higher than that of a CNT forest grown by remote plasma-enhanced chemical vapor deposition, whereas the contact resistivity of a top metal electrode was similar to that obtained for a single-walled CNT forest. Published by AIP Publishing.

Power semiconductor devices require low on-resistivity and high breakdown voltages simultaneously. Vertical-type metal-oxide-semiconductor field-effect transistors (MOSFETs) meet these requirements, but have been incompleteness in diamond. Here we show vertical-type p-channel diamond MOSFETs with trench structures and drain current densities equivalent to those of n-channel wide bandgap devices for complementary inverters. We use two-dimensional hole gases induced by atomic layer deposited Al2O3 for the channel and drift layers, irrespective of their crystal orientations. The source and gate are on the planar surface, the drift layer is mainly on the sidewall and the drain is the p(+) substrate. The maximum drain current density exceeds 200 mA mm(-1) at a 12 mu m source-drain distance. On/off ratios of over eight orders of magnitude are demonstrated and the drain current reaches the lower measurement limit in the off-state at room temperature using a nitrogen-doped n-type blocking layer formed using ion implantation and epitaxial growth.

The sheet resistance (R-sk) underneath ohmic Au-electrodes on hydrogen-terminated surface-conductive diamond (001) surfaces was examined by a special current-voltage measurement. It has been found that R-sk is about similar to 200 times larger than the sheet resistance, R-sh, in the open areas without Au-electrodes. The specific contact resistance, R-c, of ohmic Au-electrodes on H-terminated surface-conductive diamonds as determined by linear transmission line models must be corrected accordingly. As the results of this, R-c is suggested to be of the order of 1 x 10(-3)-1 X 10(-4) Omega CM2.

The controlled design of biosensors based on the photo-electrochemical technique with high selectivity, sensitivity, and rapid response for monitoring of mono-bioactive molecules, particularly dopamine (DA) levels in neuronal cells is highly necessary for clinical diagnosis. Hierarchical carbon-, nitrogen-doped (CN) nickel oxide spear thistle (ST) flowers associated in single-heads (S), and symmetric and asymmetric-double heads (D and A, respectively) that are tightly connected through a micrometric dipole-like rod or trunk were fabricated by using a simple synthetic protocol. The CN-ST flower heads were decorated with dense nanotubular like hedgehog needle skins in vertical alignments. These designated architectures are key features for creating biosensor surface electrodes for photo-electrochemical, ultrasensitive screening of mono-bioactive molecules. The exceptional electrode designs produced numerous catalytically active sites, large surface area, and high electron-transfer mobility. The active coating of carbon-nitrogen nanospheres significantly enhanced the photo-electrocatalytic activity of the prepared biosensor electrodes and prevented leakage of photocatalytic activity under long-term exposure to irradiation. Among all photo-electrochemical assays, the biosensors showed significant sensitivity and selectivity for DA in the presence of interfering molecules such as ascorbic acid (AA), uric acid (UA), adrenaline (A), and noradrenaline (NA). The photo-electrochemical property of the CN-SST-{110} crystal surface electrode showed significant sensing performance for DA in terms of unimpeded diffusion pathways, a wide concentration-detection range, and a low detection limit, even in the presence of potentially interfering molecules compared with other electrode-modified CN-DST-{111} and CN-AST-{101} crystal surfaces. Furthermore, the CN-SST photo-biosensor electrode shows potential in the selective and sensitive determination of DA in real samples, such as human serum and secreted DA from living cells. This finding indicates that the hierarchical ST biosensor may enable analytical discrimination and monitoring of DA and can be employed for clinical diagnosis application.

A polycrystalline diamond electrolyte-solution-gate field-effect transistor (BDD-SGFET) was successfully applied to the analysis of water content in ethanol. Due to the use of a no-gate-insulator FET, the developed sensor showed a four-times-faster response than the conventional Si-FET, and a ten-times-faster response than a glass electrode. The output voltage showed good linearity with respect to the water content. This result is of practical importance because the traditional water content measurement methods are impractical due to their slow response.

A vertical edge graphite layer (VEG) fabricated on a diamond (001) substrate and the recovery of the crystallinity of the diamond substrate following high-dose ion implantation and high-temperature annealing (HTA) was investigated. The Al ions were implanted into the diamond (001) surface at 773K (500 degrees C), followed by HTA at 1973 K (1700 degrees C). The graphite edges were vertically oriented, but each domain was randomly rotated in the in-plane direction, which was confirmed via multiple cross-sectional transmission electron microscopy images obtained from different directions rotated 2, 5, 10, and 158 around the [001] axis. The Raman and photoluminescence exhibited no significant peaks. The initial sp(2) structure state of the VEG was nucleated in an early stage of the HTA and the surface diamond was subsequently reconstructed, which was confirmed using stopping-and-range-of-ions-in-matter calculations and Rutherford backscattering/channeling (RBS-C) measurements. The RBS-C spectra indicate that the crystal is maintained after hot implantation and is recovered by HTA. This VEG structure may be useful for ohmic contact with diamond electrical devices. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Diamond electrolyte solution-gate-field effect transistors (SGFETs) are suitable for applications as chemical ion sensors because of their wide potential window and good physical and chemical stabilities. In this study, we fabricated an anodically oxidized diamond SGFET from a full hydrogen-terminated diamond SGFET and demonstrated control of the device threshold voltage by irreversible anodic oxidation. The applied anodic bias voltage (V-AO) was varied gradually from low to high (1.1-1.7 V). As the anodic oxidation proceeded, the threshold voltage shifted to more negative values with no degradation of hole mobility. Thus, anodic oxidation is a useful method for controlling the threshold voltage of diamond SGFETs. Published by AIP Publishing.

Here, we propose simple diamond functionalization by carboxyl termination for adenosine triphosphate (ATP) detection by an aptamer. The high-sensitivity label-free aptamer sensor for ATP detection was fabricated on nanocrystalline diamond (NCD). Carboxyl termination of the NCD surface by vacuum ultraviolet excimer laser and fluorine termination of the background region as a passivated layer were investigated by X-ray photoelectron spectroscopy. Single strand DNA (amide modification) was used as the supporting biomolecule to immobilize into the diamond surface via carboxyl termination and become a double strand with aptamer. ATP detection by aptamer was observed as a 66% fluorescence signal intensity decrease of the hybridization intensity signal. The sensor operation was also investigated by the field-effect characteristics. The shift of the drain current-drain voltage characteristics was used as the indicator for detection of ATP. From the field-effect characteristics, the shift of the drain current-drain voltage was observed in the negative direction. The negative charge direction shows that the aptamer is capable of detecting ATP. The ability of the sensor to detect ATP was investigated by fabricating a field-effect transistor on the modified NCD surface.

A transparent polycrystalline diamond field-effect transistor (FET) was fabricated and measured in room temperature measurements, which reveals comparatively high maximum current density and high breakdown voltage of more than 1000V. A harsh stress environment is proposed for simple and time-effective reliability stress measurement of the FET using a method of 50 continuous cycles of 500-V voltage stress. A 400-nm-thick Al2O3 counter-destructive passivation layer was implemented on the FET for the stress measurements. Devices with wide gate-drain length (L-GD) retain their FET characteristics after the harsh stress measurements by only 50% reductions maximum current density.

A nitridation process of a diamond surface with nitrogen radical exposure far from the radio-frequency plasma for the stabilization of a negatively charged nitrogen-vacancy (NV%) centers near the surface is presented. At a nitrogen coverage of as high as 0.9 monolayers, high average Rabi contrasts of 0.40 +/- 0.06 and 0.46 +/- 0.03 have been obtained for single NV% centers formed by shallow nitrogen implantation with acceleration voltages of 1 and 2 keV, respectively. This indicates that nitrogen termination by a radical exposure process produces an electric charge state suitable for single NV- centers near the surface compared with the states obtained for alternatively terminated surfaces. (C) 2017 The Japan Society of Applied Physics

A fluorine-terminated polycrystalline boron-doped diamond surface is successfully employed as a pH-insensitive SGFET (solution-gate field-effect transistor) for an all-solid-state pH sensor. The fluorinated polycrystalline boron-doped diamond (BDD) channel possesses a pH-insensitivity of less than 3mV/pH compared with a pH-sensitive oxygenated channel. With differential FET (field-effect transistor) sensing, a sensitivity of 27 mv/pH was obtained in the pH range of 2-10; therefore, it demonstrated excellent performance for an all-solid-state pH sensor with a pH-sensitive oxygen-terminated polycrystalline BDD SGFET and a platinum quasi-reference electrode, respectively.

We investigated the charge state stability and coherence properties of near-surface single nitrogen vacancy (NV) centers in 12C-enriched diamond for potential use in nanoscale magnetic field sensing applications. The stability of charge states in negatively charged NV centers (NV-) was evaluated using one of the pulsed optically detected magnetic resonance measurements, Rabi oscillation measurements. During the accumulation of Rabi oscillations, an unstable shallow NV- was converted to a neutral state. As a result, the contrast of Rabi oscillations degraded, depending on charge state stability. We stabilized the NV- state of very shallow NV centers (∼2.6 ± 1.1nm from the surface) created by 1.2 keV nitrogen ion implantation by diamond surface modification, UV/ozone exposure, and oxygen annealing. This improvement indicates that we can suppress the upward surface band bending and surface potential fluctuations through Fermi level pinning originating from oxygen-terminated diamond surfaces.

Diamond has unique physical properties, which show great promise for applications in the next generation power devices. Hydrogen-terminated (C-H) diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) often have normally-on operation in devices, because the C-H channel features a p-type inversion layer; however, normally-off devices are preferable in power MOSFETs from the viewpoint of fail safety. We fabricated hydrogen-terminated (C-H) diamond MOSFETs using a partially oxidized ( partial C-O) channel. The fabricated MOSFETs showed a high breakdown voltage of over 2 kV at room temperature and normally-off characteristics with a gate threshold voltage V-th of -2.5-- 4 V.

We evaluate and compare the performance and potential of GaAs and of wide and extreme bandgap semiconductors (SiC, GaN, Ga2O3, and diamond), relative to silicon, for power electronics applications. We examine their device structures and associated materials/process technologies and selectively reviewthe recent experimental demonstrations of high voltage power devices and IC structures of these semiconductors. We discuss the technical obstacles that still need to be addressed and overcome before large-scale commercialization commences.

Atomic-layer-deposition (ALD) Al2O3 films are promising as gate insulators of non-Si semiconductor devices. Although they allow relatively small leakage currents just after deposition, ALD Al2O3 films formed at low temperatures are subject to high temperature during fabrication or operation of devices. Therefore, the effect of post-deposition annealing (PDA) on the properties of Al2O3 films is investigated in this study. ALD Al2O3 films formed using H2O oxidant at low temperatures are compacted by PDA, but their mass density and dielectric constant remain approximately unchanged or slightly decrease owing to the desorption of methyl groups contained in the films as impurities. In accordance with these results, the wet etching rate of Al2O3 films is not much reduced by PDA. The conduction current in ALD Al2O3 films formed on Si is reduced by PDA and becomes smaller than that in films formed at the same ALD temperatures as those of PDA. The conduction current for PDA temperatures above 250 degrees C, however, increases and, accordingly, spoils the merit of low-temperature ALD. Therefore, given that the dielectric constant of annealed films remains low, high-temperature ALD is practically more significant than applying PDA to low-temperature ALD Al2O3 films from the viewpoint of leakage current under the same thermal budget. Space-charge-controlled field emission analysis revealed that, at the aforementioned threshold temperature, PDA abruptly increases the Al2O3/SiO2 interfacial dipoles and simultaneously reduces the amount of the positive charge near the interface. The so-called negative-charge buildup by PDA might be caused by this decrease in the positive charge. Published by AIP Publishing.

Complementary power field effect transistors (FETs) based on wide bandgap materials not only provide high-voltage switching capability with the reduction of on-resistance and switching losses, but also enable a smart inverter system by the dramatic simplification of external circuits. However, p-channel power FETs with equivalent performance to those of n-channel FETs are not obtained in any wide bandgap material other than diamond. Here we show that a breakdown voltage of more than 1600 V has been obtained in a diamond metal-oxide-semiconductor (MOS) FET with a p-channel based on a two-dimensional hole gas (2DHG). Atomic layer deposited (ALD) Al2O3 induces the 2DHG ubiquitously on a hydrogen-terminated (C-H) diamond surface and also acts as both gate insulator and passivation layer. The high voltage performance is equivalent to that of state-of-the-art SiC planar n-channel FETs and AlGaN/GaN FETs. The drain current density in the on-state is also comparable to that of these two FETs with similar device size and V-B.

Here, we report a novel method for micropatterning oligonucleotides on the diamond surface via forming amine groups on the diamond surface by nitrogen/hydrogen radical treatment. The covalent bonding of the supporting oligonucleotide and characterization of an immobilized hybridized oligonucleotide with Cy5 modification were investigated by fluorescence microscopy. To investigate the effectiveness of nitrogen/hydrogen radical treatment for amine termination, two types of radical treatment were used: hydrogen/nitrogen radical treatment and pure nitrogen radical treatment. From the results, hydrogen/nitrogen radical treatment produces amine (NH2) termination on the diamond surface. The effect of amine termination was investigated by immobilization of single-stranded DNA via amide bonding between surface NH2 groups and COOH groups terminating the DNA. The immobilized single-stranded DNA (supporting DNA), which has a complementary relationship with the adenosine triphosphate (ATP) aptamer (DNA), hybridizes with the aptamer with attached fluorescence dye. When ATP molecules approach the double-stranded DNA, the aptamer forms a close relationship with the supporting DNA and combines with ATP. ATP detection was effectively carried out by reduction of fluorescence. Published by AIP Publishing.

We fabricated and characterized black polycrystalline diamond field effect transistors. By implementing a C-H bonded channel with a wide gate-drain length up to 20 mu m, a breakdown voltage of 1.8 kV was achieved, which is the highest value reported for a diamond field effect transistor ( FET) to date. Several of our devices achieved a breakdown voltage/wide gate-drain length ratio > 100V/mu m. This is comparable to the performance of lateral SiC and GaN FETs. We investigated the effects of voltage stress up to 2.0 kV, and showed that the maximum current density fell to 26% of its initial value of 2.42mA/mm before the device eventually broke down at 1.1 kV. Published by AIP Publishing.

We report magnetoresistance measurements of hydrogen-terminated (100)-oriented diamond surfaces wherein an ionic-liquid-gated field-effect-transistor technique was used to make hole carriers accumulate. Unexpectedly, the observed magnetoresistance is positive within the range of 2<T<10 K and -7<B<7 T, in striking contrast to the negative magnetoresistance previously detected for similar devices with (111)-oriented diamond surfaces. Furthermore, we find that (1) the magnetoresistance is orders of magnitude larger than that of the classical orbital magnetoresistance; (2) the magnetoresistance is nearly independent of the direction of the applied magnetic field; and (3) for the in-plane field, the magnetoresistance ratio, defined as [rho(B) - rho(0)]/rho(0), follows a universal function of B/T. These results indicate that the spin degree of freedom of hole carriers plays an important role in the surface conductivity of hydrogen-terminated (100) diamond.

A polycrystalline boron-doped diamond (BDD) electrolyte solution-gate field effect transistor (SGFET) for use as a pH sensorwas developed. The polycrystalline diamond films with a boron-doped layer possessed semiconducting properties that were comparable to hydrogen-terminated non-doped diamond. The hydrogen-terminated BDD surface was successfully transferred to a partially oxygen-terminated surface by ozone exposure, and its SGFET current-voltage (I-V) characteristics were evaluated with bias voltages within the potential window of diamond. The drain-source current(Ids)-drain-source voltage(Vds) characteristics showed pinch-off and saturation. In addition, they stably operated in electrolyte solutions with pH values from 2 to 12. The transfer characteristics exhibited a pH sensitivity of approximately 30 mV/ pH, which is comparable with the pH sensitivity of the conventional oxygen-terminated nondoped SGFET and the single-crystal BDD SGFET investigated in our previous work. Furthermore, the BDD SGFET exhibited improved long-term stability, and the coefficient of variation (CV) of Ids for 10 months was up to 10%. (C) 2016 Elsevier Ltd. All rights reserved.

To develop high-performance, high-reliability gate insulation and surface passivation technologies for wide-bandgap semiconductor devices, the effect of atomic layer deposition (ALD) temperature on current conduction in Al2O3 films is investigated based on the recently proposed space-charge-controlled field emission model. Leakage current measurement shows that Al2O3 metal-insulator-semiconductor capacitors formed on the Si substrates underperform thermally grown SiO2 capacitors at the same average field. However, using equivalent oxide field as a more practical measure, the Al2O3 capacitors are found to outperform the SiO2 capacitors in the cases where the capacitors are negatively biased and the gate material is adequately selected to reduce virtual dipoles at the gate/Al2O3 interface. The Al2O3 electron affinity increases with the increasing ALD temperature, but the gate-side virtual dipoles are not affected. Therefore, the leakage current of negatively biased Al2O3 capacitors is approximately independent of the ALD temperature because of the compensation of the opposite effects of increased electron affinity and permittivity in Al2O3. By contrast, the substrate-side sheet of charge increases with increasing ALD temperature above 210 degrees C and hence enhances the current of positively biased Al2O3 capacitors more significantly at high temperatures. Additionally, an anomalous oscillatory shift of the current-voltage characteristics with ALD temperature was observed in positively biased capacitors formed by low-temperature (<= 210 degrees C) ALD. This shift is caused by dipoles at the Al2O3/underlying SiO2 interface. Although they have a minimal positive-bias leakage current, the low-temperature-grown Al2O3 films cause the so-called blisters problem when heated above 400 degrees C. Therefore, because of the absence of blistering, a 450 degrees C ALD process is presently the most promising technology for growing high-reliability Al2O3 films. Published by AIP Publishing.

The hydrogen-terminated diamond surface (C-H diamond) has a two-dimensional hole gas (2DHG) layer independent of the crystal orientation. A 2DHG layer is ubiquitously formed on the C-H diamond surface covered by atomic-layer-deposited-Al2O3. Using Al2O3 as a gate oxide, C-H diamond metal oxide semiconductor field-effect transistors (MOSFETs) operate in a trench gate structure where the diamond side-wall acts as a channel. MOSFETs with a side-wall channel exhibit equivalent performance to the lateral C-H diamond MOSFET without a side-wall channel. Here, a vertical-type MOSFET with a drain on the bottom is demonstrated in diamond with channel current modulation by the gate and pinch off. Published by AIP Publishing.

Understanding of the contact conductivity of carbon nanotubes (CNTs) will contribute to the further application of CNTs for electronic devices, such as thin film transistors whose channel or electrode is made of dispersed CNTs. In this study, we estimated the contact conductivity of a CNT/CNT interface from the in-plane conductivity of an uncapped CNT forest on SiC. Investigation of the electrical properties of dense CNT forests is also important to enable their electrical application. The in-plane conductivity of a dense CNT forest on silicon carbide normalized by its thickness was measured to be SO S/cm, which is two to three orders of magnitude lower than the conductivity of a CNT yarn. It was also found that both the CNT cap region and the CNT bulk region exhibit in-plane conductivity. The contact conductivity of CNTs was estimated from the in-plane conductivity in the bulk region. Dense and uncapped CNT forest can be approximated by a conductive mesh, in which each conductive branch corresponds to the CNT/CNT contact conductance. The evaluated contact conductivity was in good agreement with that calculated from the tunneling effect.

Architecture of nanoscale electrochemical sensors for ultra-trace detection of glucose in blood is important in real-life sampling and analysis. To broaden the application of electrochemical sensing of glucose, we fabricated, for the first time, a glucose sensor electrode based on radially oriented NiO nanostrands (NSTs) onto 3D porous Ni foam substrate for monitoring, as well as selective and sensitive sensing of glucose in mammalian blood. The simple, scalable one-pot fabrication of this NST-Ni sensor design enabled control of the pattern of radially oriented NSTs onto 3D porous Ni foam substrate. The radial orientation of NST-Ni electrode onto the interior of the 3D porous substrate with controlled crystal structure size and atomic arrangement along the axis of the strands, intrinsic surface defects, and superior surface properties, such as hydrophilicity, high surface energy, and high density led to highly exposed catalytic active sites. The hierarchical NST-Ni electrode was used to develop a sensitive and selective sensor over a wide range of glucose concentrations among actively competitive ions, chemical species and molecular agents, and multi-cyclic sensing assays. The NST-Ni electrode shows significant glucose sensing performance in terms of unimpeded diffusion pathways, a wide range of concentration detection, and lower limit of detection (0.186 mu M) than NiO nanosheet (NS)-Ni foam electrode pattern, indicating the effectiveness of the shape-dependent structural architecture of NST-Ni electrode. In this study, the NST-Ni electrode is fabricated to develop a simple, selective method for detecting glucose in physiological fluids (e.g., mammalian blood). (C) 2015 Elsevier B.V. All rights reserved.

This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 x 10(13) cm(-2) in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4V and 1.1V in the Au-and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen in order to achieve a low leakage current by suppressing the current enhancement. Although the current conduction in this study is essentially limited by FE, neither the Fowler-Nordheim (FN) nor Poole-Frenkel (PF) plots of the I-V characteristics are fitted by a linear function. The failures of the FN and PF plot methods alert us to the inaccuracies of basing the investigation of current conduction on these traditional plots. Hence, the methodology of a current conduction analysis and the knowledge of Al2O3 charging in this study provide a solid foundation for investigating the current conduction in MIS capacitors. (C) 2016 AIP Publishing LLC.

The electrical contact properties of silicon carbide (SiC) and carbon nanotubes (CNTs) were measured by conductive atomic force microscopy (C-AFM). A CNT forest was synthesized by SiC surface decomposition. Trenches, which electrically separate the conduction area, were fabricated using a focused ion beam (FIB) without a cover layer, and the resistance of each island was measured by C-AFM. From the dependence of the resistance on the CNT forest island size, the contact resistance between the CNTs and the SiC substrate was measured. By varying the dopant density in the SiC substrate, the Schottky barrier height was evaluated to be ~0.5 eV. This is slightly higher than a previously reported result obtained from a similar setup with a metal covering the CNT forest. We assumed that the damaged region existed in the islands, which is due to the trench formation by the FIB. The commensurate barrier height was obtained with the length of the damaged region assumed to be ~3 μm. Here, we could estimate the resistivity of a CNT/SiC interface without a cover layer. This indicates that a CNT forest on SiC is useful as a brief contact electrode.

More than 1600V breakdown voltages have been obtained in hydrogen terminated (C-H) diamond planar p-channel MOSFETs with gate-drain distance of 16-22 mu m. The drain current density exceeds 100mA/mm in the FETs. The blocking voltage and drain current characteristics are comparable to those of n-channel AlGaN/GaN FETs and planar SiC MOSFETs in a similar device size. Atomic layer deposited Al2O3 works as gate insulator and passivation layer. It also induces the 2 dimensional hole gas ubiquitously on C-H diamond surface not only in planar, but in a trench gate structure. The first diamond vertical MOSFET has also operated using the trench structure.

Selective and sensitive glucose sensors with fast response for screening diabetic blood level are demanded. In this paper, the one-pot nanoarchitecture of dendritic NiO@carbon-nitrogen (C-N) dots (designated as NCD) sphere-wrapping Ni foam electrodes are reported as an effective and sensitive glucose sensor in blood samples. In this construction design, the NCD sphere electrode with excessive surface defects, large fractions of catalytic active sites, high surface area, and mobility of electron transfer through the actively surface NCD sphere can massively enhance the electrocatalytic activity for nonenzymatic glucose detection in diabetic blood. This portable sensor enables highly sensitive recognition of glucose detection (approximate to 0.01 x 10(-6) M) over a wider linear range (approximate to 0.005-12 x 10(-3) M) with rapid response time of a few seconds. The key result is that the engineered NCD sphere electrodes function as simple, easy-to-use electrochemical sensing assays of glucose levels in diabetic blood patients with a wide range of precision or linearity, recyclability, and excellent selectivity, even in the presence of potentially interfering organic (ascorbic acid, uric acid, dopamine, lactose, maltose, and sucrose) and inorganic (NaCl, Na2SO4, KCl, and K2SO4) species. The results demonstrate the potential for the electrochemical sensors to be used in preventing serious health problems associated with diabetes mismanagement.

Fast and simple methods with high sensitivity and selectivity for H2O2 assessment are important in biological and medical fields. In this study, we explored the effect of nano-object hemeproteins (denoted as N-HP) with various bio-functionalities on the electrochemical sensing performance of working electrodes toward H2O2 molecules by affecting interfacial electron transport and surface properties of N-HP. We successfully constructed three enzyme-free H2O2 sensors by coating a three-dimensional open-pore nickel (3D-Ni) foam electrode with similar concentrations of three different N-HP namely, hemoglobin (Hb
68.000 kDa, 7.0 nm), myoglobin (Mb, 16,950 kDa, 4.0 nm), and cytochrome c (Cyt.c, 12,327 kDa, 3.0 nm). The N-HP-modified Ni foam can be directly used as electrodes, thereby simplifying the electrode fabrication process and offering advantages, such as enhanced electrode-electrolyte contact area and minimum diffusion resistance. N-HP can function as redox mediators for shuttling electrons on the electrode-electrolyte interface and for engaging sufficient electro-active species exposed on the surface of the Ni foam for Faradaic redox reactions. The electrocatalytic activities of the Ni foam electrodes modified with different N-HP (i.e., Hb, Mb, and Cyt.c) in the selective oxidation of H2O2 were investigated. Among the N-HP-modified Ni foam electrodes, Cyt.c modified Ni foam electrode showed the highest sensitivity with reduced hysteresis between cathodic and anodic sweep and low detection limit (0.20μM, with signal to noise ratio of 3). This diversity in sensing performance originates from the versatility of the heme group with different bio-functionalities, different sizes and interactions at the surface of the immobilized Ni foam substrate. In addition, the N-HP-modified Ni foam electrodes exhibited no effects on major interferences, such as ascorbic, uric acids, dopamine, L-Cysteine (L. Cyst), vitamin A, L-glutathione. Hence, these electrodes can be applied in analyzing biological systems, such as lemon juice. Immobilization of different N-HP with different bio-functionalities and sizes onto Ni foam electrodes may facilitate the design and fabrication of novel biosensors.

The Al2O3 film formed using an atomic layer deposition (ALD) method with trimethylaluminum as Al precursor and H2O as oxidant at a high temperature (450 degrees C) effectively passivates the p- type surface conduction (SC) layer specific to a hydrogen- terminated diamond surface, leading to a successful operation of diamond SC field- effect transistors at 400 degrees C. In order to investigate this excellent passivation effect, we carried out an isotope analysis using D2O instead of H2O in the ALD and found that the Al2O3 film formed at a conventional temperature (100 degrees C) incorporates 50 times more CH3 groups than the high- temperature film. This CH3 is supposed to dissociate from the film when heated afterwards at a higher temperature (550 degrees C) and causes peeling patterns on the H- terminated surface. The high- temperature film is free from this problem and has the largest mass density and dielectric constant among those investigated in this study. The isotope analysis also unveiled a relatively active H- exchange reaction between the diamond H- termination and H2O oxidant during the high- temperature ALD, the SC still being kept intact. This dynamic and yet steady H termination is realized by the suppressed oxidation due to the endothermic reaction with H2O. Additionally, we not only observed the kinetic isotope effect in the form of reduced growth rate of D2O-oxidant ALD but found that the mass density and dielectric constant of D2O-grown Al2O3 films are smaller than those of H2O-grown films. This is a new type of isotope effect, which is not caused by the presence of isotopes in the films unlike the traditional isotope effects that originate from the presence of isotopes itself. Hence, the high-temperature ALD is very effective in forming Al2O3 films as a passivation and/or gate-insulation layer of high-temperature-operation diamond SC devices, and the knowledge of the aforementioned new isotope effect will be a basis for further enhancing ALD technologies in general. (C) 2015 AIP Publishing LLC.

Large-current-controllable carbon nanotube field-effect transistors (CNT-FETs) were fabricated with mm-long CNT sheets. The sheets, synthesized by remote-plasma-enhanced CVD, contained both single-and double-walled CNTs. Titanium was deposited on the sheet as source and drain electrodes, and an electrolyte solution was used as a gate electrode (solution gate) to apply a gate voltage to the CNTs through electric double layers formed around the CNTs. The drain current came to be well modulated as electrolyte solution penetrated into the sheets, and one of the solution gate CNT-FETs was able to control a large current of over 2.5 A. In addition, we determined the transconductance parameter per tube and compared it with values for other CNT-FETs. The potential of CNT sheets for applications requiring the control of large current is exhibited in this study. (C) 2015 AIP Publishing LLC.

We accurately project the blocking capability of diamond junctions with a punch-through design, carrying out the ionization integration that adopts our previous ionization coefficients and hence explicitly giving the breakdown voltage and field as a function of the doping concentration and length of drift layers. Comparing to this result, we assess the blocking capability of various junctions reported in the literature and find that most of these results fall short of our projections more than a little but that a few of them fit closely or approximately with ours and outperform the theoretical projections of others that are based on ionization coefficients other than ours. Albeit thus being most plausible, the ionization coefficient of this study is still empirical in any way. Accordingly, theoretical and experimental efforts are both further needed in order to pursue the ultimate blocking capability of diamond. (C) 2015 AIP Publishing LLC.

Electrical contacts to silicon carbide with low contact resistivity and high current durability are crucial for future SiC power devices, especially miniaturized vertical-type devices. A carbon nanotube (CNT) forest formed by silicon carbide (SiC) decomposition is a densely packed forest, and is ideal for use as a heat-dissipative ohmic contact in SiC power transistors. The contact resistivity and Schottky barrier height in a Ti/CNT/SiC system with various SiC dopant concentrations were evaluated in this study. Contact resistivity was evaluated in relation to contact area. The Schottky barrier height was calculated from the contact resistivity. As a result, the Ti/CNT/SiC contact resistivity at a dopant concentration of 3 x 10(18) cm(-3) was estimated to be similar to 1.3 x 10(-4) Omega cm(2) and the Schottky barrier height of the CNT/SiC contact was in the range of 0.40-0.45 eV. The resistivity is relatively low for SiC contacts, showing that CNTs have the potential to be a good ohmic contact material for SiC power electronic devices. (C) 2015 AIP Publishing LLC.

The repulsive effect of hydrophobic diamond thin film on biomolecule detection, such as single-nucleotide polymorphisms and human immunodeficiency virus type 1 trans-activator of transcription peptide protein detection, was investigated using a mixture of a fluorine-, amine-, and hydrogen-terminated diamond surfaces. These chemical modifications lead to the formation of a surface that effectively resists the nonspecific adsorption of proteins and other biomolecules. The effect of fluorine plasma treatment on elemental composition was also investigated via X-ray photoelectron spectroscopy (XPS). XPS results revealed a fluorocarbon layer on the diamond thin films. The contact angle measurement results indicated that the fluorine-treated diamond thin films were highly hydrophobic with a surface energy value of similar to 25 mN/m. (C) 2014 Elsevier B.V. All rights reserved.

The realization of room-temperature macroscopic field effect transistors (FETs) will lead to new epoch-making possibilities for electronic applications. The I-d-V-g characteristics of the millimeter-sized aluminum-oxide amorphous alloy (Ni0.36Nb0.24Zr0.40)(90)H-10 FETs were measured at a gate-drain bias voltage of 0-60 mu V in nonmagnetic conditions and under a magnetic fields at room temperature. Application of dc voltages to the gate electrode resulted in the transistor exhibiting one-electron Coulomb oscillation with a period of 0.28 mV, Fabry-Perot interference with a period of 2.35 mu V under nonmagnetic conditions, and a Fano effect with a period of 0.26mV for Vg and 0.2 T under a magnetic field. The realization of a low-energy controllable device made from millimeter-sized Ni-Nb-Zr-H amorphous alloy throws new light on cluster electronics. (C) 2015 AIP Publishing LLC.

We have observed zero resistivity above 10K and an onset of resistivity reduction at 25.2K in a heavily B-doped diamond film. However, the effective carrier concentration is similar to that of superconducting diamond with a lower T-c. We found that the carrier has a longer mean free path and lifetime than in the previous report, indicating that this highest T-c diamond has better crystallinity compared to that of other superconducting diamond films. In addition, the susceptibility shows a small transition above 20K in the high quality diamond, suggesting a signature of superconductivity above 20 K. These results strongly suggest that heavier carrier doped defect-free crystalline diamond could give rise to high T-c diamond. (C) 2015 AIP Publishing LLC.

The detection of HIV disease at an early stage has significant clinical implications. We report the detection of HIV-TAT peptide on a functionalized three-dimensional carbon micropillar array platform. The sensor showed a linear relationship between HIV-TAT concentration and fluorescence intensity in the sub-nanomolar range with a detection limit of 50 pmol.

Immobilization is an important process of biosensor application. The simplest functionalize diamond surface was done by attached biomolecule on diamond surface with chemical linker compound modification. Carboxyl treatment is one choice for diamond functionalization. Methane gas was diluted with hydrogen gas for CH3 termination as an initial functionalization of diamond to transform to carboxyl termination. Diamond and biomolecule is a couple of highly functionally collaboration for biosensor even with low coverage for carboxyl terminated. This work shows that low coverage of carboxyl (similar to 1%) as the great data with high stability for biosensor applications.

Structure, lattice parameters, spontaneous magnetization (I-s), and the Curie temperature (T-C) of MnAlGe and MnGaGe compounds with the Cu-2 Sb-type structure and their substituted compounds were investigated. Cr substitution for Mn enhanced I-s and T-C, whereas Fe substitution for Mn degraded them. These behaviors are in accord with the previously reported results, and are also common to the MnGaGe compound series. For MnAlGe, lattice parameter a increases by 0.2% and 0.4% for Cr and Fe substitution, while c changes by +0.1% and -1.3%, respectively. For MnGaGe, a decreases by 0.08% for Cr and increases by 0.2% for Fe substitution, while c changes by + 0.5% and -1.0%, respectively. T-C tended to increase with increasing length of c, suggesting that the interlayer distance between Mn layers is a key factor related to the height of T-C, i.e., the strength of the magnetic exchange interaction.

By forming a highly stable Al2O3 gate oxide on a C-H bonded channel of diamond, high-temperature, and high-voltage metal-oxide-semiconductor field-effect transistor (MOSFET) has been realized. From room temperature to 400 degrees C (673K), the variation of maximum drain-current is within 30% at a given gate bias. The maximum breakdown voltage (V-B) of the MOSFET without a field plate is 600 V at a gate-drain distance (L-GD) of 7 mu m. We fabricated some MOSFETs for which V-B/L-GD > 100 V/mu m. These values are comparable to those of lateral SiC or GaN FETs. The Al2O3 was deposited on the C-H surface by atomic layer deposition (ALD) at 450 degrees C using H2O as an oxidant. The ALD at relatively high temperature results in stable p-type conduction and FET operation at 400 degrees C in vacuum. The drain current density and transconductance normalized by the gate width are almost constant from room temperature to 400 degrees C in vacuum and are about 10 times higher than those of boron-doped diamond FETs. (C) 2014 AIP Publishing LLC.

Although the two-dimensional hole gas (2DHG) of a hydrogen-terminated diamond surface provides a unique p-type conducting layer for high-performance transistors, the conductivity is highly sensitive to its environment. Therefore, the surface must be passivated to preserve the 2DHG, especially at high temperature. We passivated the surface at high temperature (450 degrees C) without the loss of C-H surface bonds by atomic layer deposition (ALD) and investigated the thermal reliability of the Al2O3 film. As a result, C-H bonds were preserved, and the hole accumulation effect appeared after the Al2O3 deposition by ALD with H2O as an oxidant. The sheet resistivity and hole density were almost constant between room temperature and 500 degrees C by the passivation with thick Al2O3 film thicker than 38 nm deposited by ALD at 450 degrees C. After the annealing at 550 degrees C in air The sheet resistivity and hole density were preserved. These results indicate the possibility of high-temperature application of the C-H surface diamond device in air. In the case of lower deposition temperatures, the sheet resistivity increased after air annealing, suggesting an insufficient protection capability of these films. Given the result of sheet resistivity after annealing, the increase in the sheet resistivity of these samples was not greatly significant. However, bubble like patterns were observed in the Al2O3 films formed from 200 to 400 degrees C by air annealing at 550 degrees C for 1 h. On the other hand, the patterns were no longer observed at 450 degrees C deposition. Thus, this 450 degrees C deposition is the sole solution to enabling power device application, which requires high reliability at high temperatures. (C) 2014 AIP Publishing LLC.

Hydrogen termination of diamond lowers its ionization energy, driving electron transfer from the valence band into an adsorbed water layer or to a strong molecular acceptor. This gives rise to p-type surface conductivity with holes confined to a subsurface layer of a few nanometers thickness. The transfer doping mechanism, the electronic behavior of the resulting hole accumulation layer, and the development of robust field-effect transistor (FED devices using this platform are reviewed. An alternative method of modulating the hole carrier density has been developed based upon an electrolyte-gate architecture. The operation of the resulting "solution-gated" FET architecture in two contemporary applications will be described: the charge state control of nitrogen-vacancy centers in diamond and biosensing. Despite 25 years of work in this area, our knowledge of surface conductivity of diamond continues to develop.

Shubnikov-de Haas oscillations are observed in atomically flat hydrogen-terminated diamond surfaces with high-density hole carriers introduced by the electric field effect using an ionic liquid. The Shubnikov-de Haas oscillations depend only on the magnetic field component perpendicular to the diamond surface, thus providing evidence of two-dimensional Fermi surfaces. The effective masses estimated from the temperature dependence of the oscillations are close to the cyclotron effective masses of the valence band maxima in diamond. The estimated quantum scattering time is one order of magnitude longer than the transport scattering time and indicates that the carrier mobility is locally as high as several thousand cm(2)/V s at low temperature.

By forming a highly stable Al2O3 gate oxide on a C-H bonded channel of diamond, high-temperature and high-voltage metal-oxide-semiconductor field-effect transistor (MOSFET) has been realized. From -263 degrees C (10K) to 400 degrees C (673K), the variation of maximum drain-current is within 50% at a given gate bias. The maximum breakdown voltage (VB.,) of the MOSFET without a field plate is 996V at a gate-drain distance (LGD) of 9 mu m. We fabricated some MOSFETs satisfying VB,inaAGD > 200V/[tm (2MV/cm). This value is superior to those of lateral SiC or GaN FETs.

The surface conductivity of (111)- and (100)-oriented hydrogen-terminated diamonds was investigated at low temperatures for different carrier densities. The carrier density was controlled in a wide range in an electric double-layer transistor configuration using ionic liquids. As the carrier density was increased, the temperature dependences of sheet resistance and mobility changed from semiconducting to metallic ones: the sheet resistance and mobility for the (111) surface were nearly independent of temperature for a sheet carrier density of approximate to 4 x 10(13) cm(-2), indicating metallic carrier transport. It was also found that the interface capacitance, determined from the gate voltage dependence of the Hall carrier density, depended significantly on the crystal orientation.

We have clarified the reason that aluminum (Al) buffer layers prepared by sputtering on catalytic substrates are stable for single-walled carbon nanotube forest synthesis on chemical vapor deposition. We have focused on the difference between thermal evaporation and sputtering as the method for the preparation of the buffer layers and have analyzed the Al layers using X-ray photoelectron spectroscopy and transmission electron microscopy. Al layers produced by sputtering strongly suggest the formation of gamma-alumina by aluminum hydroxides while those from thermal evaporation contain metallic Al. As a result a drastic structural change occurs during thermal annealing, making the buffer layer unstable. (C) 2013 Elsevier Ltd. All rights reserved.

The effect of titanium (Ti) added to the top layer of an aluminum (Al)/iron (Fe)/Al (bottom) sandwich catalytic substrate was studied. The Ti caused a significant lengthening in the single-wall carbon nanotube forest produced by chemical vapor deposition (CVD). In general, particles of iron oxide on the Al/Fe/Al catalytic substrate are formed by exposure to the atmosphere during deposition process of the substrate. The particles of iron oxide are metalized during pretreatment under a reductive gas before the growth of the nanotubes with nano-sized dispersion stabilized. On this process, the metallization and the stabilization of nano-sized iron oxide particles occur on the basis of the oxygen affinity in the top aluminum oxide layer, with the ionization tendency Al &gt
Fe. It is thought that the addition of Ti increases the oxygen affinity of the catalytic substrate, since Ti has a stronger ionization tendency than Al. After optimizing the quantity of Ti added to the top layer, we successfully fabricated a millimeter-long, small-diameter, single-wall carbon nanotube forest. © 2013 Elsevier Ltd. All rights reserved.

We report on scanning tunneling microscopy/spectroscopy (STM/STS) experiments on boron-doped diamond films. The tunneling conductance dI/dV spectra measured on the (111)-oriented surface show spatial variations which distribute irrespective of the surface morphology. The spatial variations are discussed in terms of characteristic features of the superconductivity under the condition of the considerable disorder by the boron doping.

Diamond is a promising material for merging solid-state and biological systems owing to its chemical stability, low background current, wide potential window and biocompatibility. The effects of surface charge density on human immunodeficiency virus type 1 Trans-activator transcription (HIV-1 Tat) protein binding have been investigated on a diamond field-effect transistor (FET) using ribonucleic acid (RNA) aptamers as a sensing element on a solid surface. A change in the gate potential of 91.6 mV was observed, whereby a shift in the negative direction was observed at a source-drain current of -8 mu A in the presence of HIV-1 Tat protein bound to the RNA aptamers. Moreover, the reversible change in gate potential caused by the binding and regeneration cycles was very stable throughout cyclical detections. The stable immobilization is achieved via RNA aptamers covalently bonded to the carboxyl-terminated terephtalic acids on amine sites, thereby increasing the sensitivity of the HIV-1 Tat protein sensor. The reliable use of a real sample of HIV-1 Tat protein by an aptamer-FET was demonstrated for the first time, which showed the potential of diamond biointerfaces in clinical biosensor applications. (C) 2012 Elsevier B.V. All rights reserved.

The effects of hydrogen content and cluster morphology on the electronic transport behavior of (Ni0.36Nb0.24Zr0.40)(100-x)H-x (0 < x < 20) glassy alloys containing distorted nanostructural icosahedral Zr5Nb5Ni3 clusters have been studied. When the hydrogen content is less than 7 at%, the hydrogen atom is localized between Ni atoms of neighboring distorted icosahedral Zr5Ni5Nb3 clusters. The I-d-V-g-B characteristics of the (Ni0.36Nb0.4Zr0.40)(90)H-10 glassy alloy field-effect transistor (GAFET) showed room-temperature three-dimensional Coulomb oscillation and the Fano effect, which arises from interference of electrons traveling through two different cluster configurations, namely a localized discrete state inside the quantum dot and a continuum in the arm.

The potential of aptamers as ligand binding molecule has opened new avenues in the development of biosensors for cancer oncoproteins. In this paper, a label-free detection strategy using signaling aptamer/protein binding complex for platelet-derived growth factor (PDGF-BB) oncoprotein detection is reported. The detection mechanism is based on the release of fluorophore (TOTO intercalating dye) from the target binding aptamer's stem structure when it captures PDGF. Amino-terminated three-dimensional carbon microarrays fabricated by pyrolyzing patterned photoresist were used as a detection platform. The sensor showed near linear relationship between the relative fluorescence difference and protein concentration even in the sub-nanomolar range with an excellent detection limit of 5 pmol. This detection strategy is promising in a wide range of applications in the detection of cancer biomarkers and other proteins. (C) 2012 Elsevier B.V. All rights reserved.

A label-free detection strategy for the detection of platelet-derived growth factor (PDGF-BB) oncoprotein detection using signaling aptamer/protein binding complex is reported. The 3D carbon microarrays detection platform was fabricated by pyrolyzing patterned photoresist and surface functionalized using directamination technique. The detection strategy is based on the release of TOTO intercalating dye from the target binding aptamer's stem structure when it captures PDGF. The sensor showed near linear relationship between the relative fluorescence difference and protein concentration with a very good detection limit of 5 pmol. This detection strategy is promising for the potential detection of different cancer biomarkers and proteins.

Electrical resistivity measurements in the temperature range from 6 to 300K were carried out in order to investigate the effects of the hydrogen absorption on the transport properties of Ni36Nb24Zr40 amorphous alloy ribbon. The electrical resistivity basically behaved negative temperature dependence in all prepared specimens of (Ni0.36Nb 0.24Zr0.40)100-xHx with 0 ≤ x &lt
15. The absolute value of temperature coefficient of the resistivity, TCR, increased with increasing the amount of the absorbed hydrogen. In addition, it was also clear that the electrical resistivity gradually increased with the time just after electrochemically charging, and tended to saturate after about 800 ks at 300 K. The behavior of the gradual increase in the electrical resistivity with the time was explained by the model including two kinds of the relaxation times, being associated with the migration of the hydrogen from the sample surface. © 2013 The Japan Institute of Metals and Materials.

Various insulators are used as gate dielectrics and passivation layers in wide-bandgap (WBG) semiconductor devices as well as in advanced Si devices, and the understanding of their current conduction mechanism is essential to achieve their high performance and high reliability. Because these insulators are more or less charged, the conduction current is mostly caused by the Fowler-Nordheim (FN) tunneling into charged insulators, ruling out the conventional analytic FN formula. In order to facilitate the analysis of these currents, we focused on the method, named sheet-charge approximation (SCA), of approximating the charge distribution in the insulators by a charge sheet that has the same areal density and centroid as those of the original. Using, as references, the results obtained exactly calculating the tunneling current in the framework of the Wentzel-Kramers-Brillouin approximation, we confirmed the advantage of SCA over the previous method using a tunneling-endpoint field, the error of SCA-estimated areal charge densities being at most 30% for rectangular charge distributions of which charge centroids are known as in stacked films. In a more general case where the centroid is unknown, the SCA usually provides only a charge moment with reference to the insulator/anode interface, being unable to decompose the moment into the areal charge density and centroid. However, this demerit of SCA can be overcome through a reverse-biased current-voltage measurement using a capacitor formed on a heavily doped substrate or a capacitor with a diffusion layer attached, which measurement provides a charge moment with reference to the original cathode/insulator interface. Using these two kinds of charge moments, we can separately extract the areal charge density and centroid. Hence, the SCA has practical significance as a tool for analyzing conduction currents through charged insulators, especially through stacked films, and accordingly will play an important role in improving the performance and reliability of gate dielectrics and passivation layers for various WBG semiconductor devices as well as of high-k gate stacks for advanced Si devices. © 2013 AIP Publishing LLC.

Use of two-dimensional hole gas (2DHG), induced on a hydrogenated diamond surface, is a solution to overcoming one of demerits of diamond, i.e., deep energy levels of impurities. This 2DHG is affected by its environment and accordingly needs a passivation film to get a stable device operation especially at high temperature. In response to this requirement, we achieved the high-reliability passivation forming an Al2O3 film on the diamond surface using an atomic-layer-deposition (ALD) method with an H2O oxidant at 450 degrees C. The 2DHG thus protected survived air annealing at 550 degrees C for an hour, establishing a stable high-temperature operation of 2DHG devices in air. In part, this achievement is based on high stability of C-H bonds up to 870 degrees C in vacuum and above 450 degrees C in an H2O-containing environment as in the ALD. Chemically, this stability is supported by the fact that both the thermal decomposition of C-H bonds and reaction between C-H bonds and H2O are endothermic processes. It makes a stark contrast to the instability of Si-H bonds, which decompose even at room temperature being exposed to atomic hydrogen. In this respect, the diamond 2DHG devices are also promising as power devices expectedly being free from many instability phenomena, such as hot carrier effect and negative-bias temperature instability, associated with Si devices. As to adsorbate, which is the other prerequisite for 2DHG, it desorbed in vacuum below 250 degrees C, and accordingly some new adsorbates should have adsorbed during the ALD at 450 degrees C. As a clue to this question, we certainly confirmed that some adsorbates, other than those at room temperature, adsorbed in air above 100 degrees C and remained at least up to 290 degrees C. The identification of these adsorbates is open for further investigation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769404]

The development of a sustainable catalyst could potentially provide a long-term solution to industrial processes, especial those in the chemical industry, that require the production of a large quantity of raw materials manufactured from renewable resources. Therefore, establishing a proper design for a highly efficient and long-term reusable catalyst is one of the crucial environmental issues facing humanity. In this study, we developed a simple control for hierarchal mesoporous nickel oxide (NiO) nanomagnets (NMs) with flower- and sphere-like morphology and large mesocage cavities. In the fabrication of super-nanostructure NiO, features that were affected by the shape, surface, and size of particles exhibit high catalytic activities of chemical agents, such as o-aminophenol. Our findings shows that the NiO NM with flower-like morphology NFs has higher catalytic activity toward the oxidation of organic contaminates than that of nanospheres NSs or even other magnetic nanoparticles (NPs) such as Fe3O4 NPs. Furthermore, the NiO NMs are capable of the high-gradient magnetic separation of organic contaminants from aquatic life with excellent reusability even after several cycles, which may help in wastewater management and supply. To understand the effectiveness of NiO NM functionalities in terms of hierarchical mesocage parameters, as well as in terms of shape- and size-morphologies in such chemical reactions, surface interaction and magnetic separation with chemical agents and theoretical calculations were performed. (C) 2012 Elsevier B.V. All rights reserved.

Here we report the performance of surface functionalized diamond surfaces as biosensing platform for human immunodeficiency virus transactivator of transcription (HIV-Tat) peptide detection. Comparative investigations were conducted on nanocrystalline diamond (NCD) and polycrystalline diamond (PCD) films. Scanning electron microscopy (SEM) images revealed the morphology differences between NCD and PCD films. X-ray photoelectron spectroscopy (XPS) data showed that functional components and corresponding coverages, demonstrating denser carboxyl acid groups and fluorinated groups on NCD than that PCD films after UV/ozone and fluorine plasma treatment respectively. Contact angle results showed the differences in surface wettability and free energy between functionalized NCD and PCD biosensors. Fluorescence observations confirmed that higher biosensing performance can be obtained on NCD biosensors with high sensitivity selectivity, and stability. The NCD films with denser surface coverages of functionalizations made NCD films much more priority as an effective biosensing candidate than PCD films. (C) 2012 The Japan Society of Applied Physics

The design of multidirectional porous metal oxide catalysts has attracted extensive attention because such materials have potential for environmental applications. To satisfy the requirements of these applications, large-scale production, low-cost manufacturing, and efficient transformation reactions are needed. The present paper reports the fabrication of hierarchical nickel oxide nanocrystals (NiO NCs) with hexagonal nanoplatelets and micro-, meso-, and macropore cavities through an eco-friendly method. The controlled size and shape of the NiO platelets in condensed orientation sequence "tesserae blocks" led to the formation of a hexagonal mosaic-like morphology. The NiO NCs could be recovered and reused without lost of activity over a number of batch reactions. In addition, theoretical models to predict the molecular structures of both the intermediate and transition states within the chemical transformation reactions were developed. The theoretical findings in the current study provide insight into the key factors that control the changes in the molecular structure throughout the transformation mechanism of the phenolic pollutants using NiO platelet nanocatalysts. (C) 2012 Elsevier B.V. All rights reserved.

The design of multidirectional porous metal oxide catalysts has attracted extensive attention because such materials have potential for environmental applications. To satisfy the requirements of these applications, large-scale production, low-cost manufacturing, and efficient transformation reactions are needed. The present paper reports the fabrication of hierarchical nickel oxide nanocrystals (NiO NCs) with hexagonal nanoplatelets and micro-, meso-, and macropore cavities through an eco-friendly method. The controlled size and shape of the NiO platelets in condensed orientation sequence "tesserae blocks" led to the formation of a hexagonal mosaic-like morphology. The NiO NCs could be recovered and reused without lost of activity over a number of batch reactions. In addition, theoretical models to predict the molecular structures of both the intermediate and transition states within the chemical transformation reactions were developed. The theoretical findings in the current study provide insight into the key factors that control the changes in the molecular structure throughout the transformation mechanism of the phenolic pollutants using NiO platelet nanocatalysts. (C) 2012 Elsevier B.V. All rights reserved.

An aptasensor was designed on a nanocrystalline diamond (NCD) surface that combined with biological recognition elements, PDGF-binding aptamers, which inherently possess high affinity to PDGF-BB proteins. Functional components such as carboxylic acids (-COOH) and amines (-NH2) were directly introduced onto the NCD surface and used as probing units for immobilization of PDGF-binding aptamers. The surface coverage of different components on the NCD was analyzed by X-ray photoelectron spectroscopy (XPS) measurements, and the effects of various functionalizations on the NCD biosensor performance were investigated via fluorescence observations. The coverages of carboxyl and amine groups achieved were 12 and 23%, respectively, for the directly aminated and carboxylated NCD; however, the lower density of carboxyl groups on the functionalized surface did not deteriorate the performance of the COOH-NCD biosensor. Fluorescence investigations demonstrated comparable performance in sensitivity and selectivity for PDGF protein detection on COOH-NCD and NH2-NCD biosensors. Multiple regeneration tests clearly showed that the COOH-NCD biosensor as well as the NH2-NCD biosensor retained a high performance without exhibiting any noticeable degradation.

A vertical superconductor/normal conductor/superconductor (SNS) weak-link Josephson junction has been successfully fabricated from only homoepitaxial diamond films. Superconducting diamond, normal-state diamond, and superconducting diamond are homoepitaxially grown in a sequence. The temperature dependence of the critical superconducting current was fitted using Likharev's theory of SNS weak-link junctions. When the normal-state-diamond thickness L is much larger than the coherent length in the normal-state-diamond xi(n), an exponential temperature dependence of normalized critical current was observed, indicating a proximity effect. Shapiro steps in the current-voltage characteristics under microwave irradiation were observed in the junction with L >>xi(n).

Capacitance distribution of {(Ni0.6Nb0.4)(1-x)Zr-x}(100-y)-H-y (x = 0.30, 0.35, 0.40, 0.45 and 0.50, 0 <= y <= 20) glassy alloy ribbons was carried out by ac impedance analysis at frequency of 1 kHz, in terms of a distributed constant equivalent circuit. The capacitance can be represented by oblique contour lines. The highest capacitance (1-11 mu F) could be found near the point when x = 0.40, y = 10, which is a composition occurring room-temperature Coulomb oscillation, while capacitance of the composition (x = 0.35, y = 4) occurring ballistic transport was around 0.8 mu F. The capacitance difference would be explained by an effect of hydrogen localization derived from morphology of distorted Zr-centered icosahedral Zr5Ni5Nb3 clusters and ideal Ni-centered clusters. The electrocapillarity equation showed that the specific capacitance between two electrodes increases parabolic with decreasing the distance, as a polarized glutinous liquid.

Single-walled carbon nanotube (SWNT) forest synthesis using antenna-type remote plasma chemical vapor deposition (ARPCVD) is presented. A series of synthesis using carbon monoxide gas as carbon feedstock reveals that the remote conditions, in other words, distance between an antenna and a substrate affects the quality of nanotube significantly. That is, far distance geometry on ARPCVD creates high-quality SWNTs. It motivates us to use same methodology for the synthesis using CH4/H-2 previously proven to make long SWNT forests. Finally, along the methodology, we achieve to make SWNT forest with high-quality and small diameter successfully. This study offers an important suggestion to embody SWNT forests with both length and quality using remote plasma CVD. (C) 2012 Elsevier B.V. All rights reserved.

UV/ozone irradiation was designed for controllable oxidation of nanodiamond films with distinctive chemical species. XPS investigation revealed that various kinds of oxygen-related chemical components would be functionalized onto nanodiamond surface covered by selective liquids for UV/ozone treatment. And the results of contact angle tests were in good accordance with the oxygen contents revealed from the deconvoluted C 1 s peaks. The covered solution on the nanodiamond film was found to be one significant factor besides Uv/ozone illumination. Surface chemical components and the wettability were proved to be closely dependent on the covered liquids on the UV/ozone treated nanodiamond surface. Without any cover solution, heavy defects would be induced on nanodiamond via direct UV/ozone irradiation. However, basic solution rich with OH anions would be taken as an effective way for controllable oxidation, achieving high percentage of COOH but less defects on the nanocrystalline diamond surface. This controllable oxidation strategy would be widely applied for controllable surface modification of nanodiamond films in the device field. (C) 2011 Elsevier B.V. All rights reserved.

A solution gate field effect transistor (SGFET) using an oxidised boron delta-doped channel on (1 1 1)diamond is presented for the first time. Employing an optimised plasma chemical vapour deposition (PECVD) recipe to deposit delta-layers, SGFETs show improved current-voltage (I-V) characteristics in comparison to previous similar devices fabricated on (1 0 0) and polycrystalline diamond, where the device is shown to operate in the enhancement mode of operation, achieving channel pinch-off and drain-source current saturation within the electrochemical window of diamond. A maximum gain and transconductance of 3 and 200 mu S/mm are extracted, showing comparable figures of merit to hydrogen-based SGFET. The oxidised device shows a site-binding model pH sensitivity of 36 mV/pH, displaying fast temporal responses. Considering the biocompatibility of diamond towards cells, the device's highly mutable transistor characteristics, pH sensitivity and stability against anodic oxidation common to hydrogen terminated diamond SGFET, oxidised boron delta-doped diamond SGFETs show promise for the recording of action potentials from electrogenic cells. (C) 2011 Elsevier B.V. All rights reserved.

A plasma enhanced chemical vapor deposition protocol for the growth of (delta-doping of boron in diamond is presented, using the (111) diamond plane as a substrate for diamond growth. AC Hall effect measurements have been performed on oxygen terminated delta-layers and desirable sheet carrier densities (similar to 10(13) cm(-2)) for field-effect transistor application are reported with mobilities in excess of what would expected for equivalent but thicker heavily boron-doped diamond films. Temperature-dependent impedance spectroscopy and secondary ion mass spectroscopy measurements show that the grown layers have metallic-like electrical properties with high cut-off frequencies and low thermal impedance activation energies with estimated boron concentrations of approximately 10(20) cm(-3). (C) 2012 American Institute of Physics. [doi:10.1063/1.3682760]

Aptamer-based fluorescence detection of platelet-derived growth factor (PDGF) on a functionalized diamond surface was demonstrated. In this work, a sandwich design based on the ability of PDGF to bind with aptamers at its two available binding sites was employed. It was found that this sandwich design approach significantly increases the fluorescence signal intensity, and thereby a very low detection limit of 4 pM was achieved. The effect of the ionic strength of MgCl2 buffer solution was also investigated, and the most favourable binding for PDGF-BB occurred at a Mg2+ concentration of 5.5 mM. Since the aptamers bind to the target PDGF with high affinity, fluorescence detection exhibited high selectivity towards different biomolecules. The high reproducibility of detection was confirmed by performing three cycles of measurements over a period of three days.

Metal semiconductor field-effect transistors (MESFETs) or metal oxide semiconductor FETs (MOSFETs) can be fabricated on hydrogen-terminated diamond without losing the surface hydrogen--carbon bonds and the surface adsorbates responsible for the surface carrier generation. Those FETs show their best performance in diamond transistors. The maximum drain current density is above 1 A/mm and the highest transconductance is 400 mS/mm. These values are comparable to those of modern FETs made of Si or III--V semiconductors. Regarding RF performance, the highest cutoff frequency reaches nearly 50 GHz. The power handling capability exceeds those of Si and GaAs at 1 GHz. The function of surface adsorbates and their stabilization are crucial for the application of diamond FETs.

An aminated diamond-based aptasensor is presented for adenosine triphosphate (ATP) and platelet-derived growth factor (PDGF) detection. In this work, a signal-off detection method was employed to provide a sensitive, selective and reusable platform for the simple detection of PDGF and ATP. The detection limit of 0.2 nM and 0.2 mu M of PDGF and ATP were achieved, respectively. It was also demonstrated in this study that the aptasensor is selective for PDGF and ATP over other biomolecules. In addition, the reusability of the aptasensor was confirmed by performing multiple cycles, which shows that diamond is a promising candidate as a material for biosensor applications. Moreover, this detection system does not require a target label and it is unaffected by non-specific binding. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.083205jes]

The effects of crystal orientation to the surface chemistry of single crystal diamond (001) and (111) were investigated after wet chemical oxidation. Direct carboxylation has been successfully achieved via wet chemical oxidation on native diamond (001) and (111) surface with distinguished portions of carboxylic acid groups (-COOH). High resolution X-ray photoelectron spectroscopy (XPS) analysis revealed that various kinds of chemical groups including both single and double oxygen-related components were covalently functionalized onto the single crystal diamond. The percentages of -COOH are approximately 9.2% and 4.7% on (001) and (111) surface respectively, showing evidently that the density of -COOH groups on (001) surface is surprisingly higher than that of (111) surface. Comprehensive comparison revealed that oxygen-related groups is higher on (001) compared with that of (111) surface. The conversion mechanism was supposed to explain the evolution from hydrogenated to oxygenated functionalizations on diamond with differently oriented crystal facets, and the crystal orientation was the significant factor in controlling the surface reactivity and hence the oxidization process. (C) 2011 Elsevier B.V. All rights reserved.

The potential of ribonucleic acid (RNA) as both informational and ligand binding molecule have opened a scenario in the development of biosensors. An aminated diamond-based RNA aptasensor is presented for human immunodeficiency virus (HIV) trans-activator of transcription (Tat) peptide protein detection that not only gives a labeled or label-free detection method but also provides a reusable platform for a simple, sensitive, and selective detection of proteins. The immobilized procedure was based on the binding interaction between positively charged amine terminated diamond and the RNA aptamer probe molecules with the negatively charged surface carboxylic compound linker molecule such as terephthalic acid. (C) 2011 American Institute of Physics. [doi:10.1063/1.3643067]

For DNA and protein detection, we have analyzed DNA/RNA immobilized biosensors based on diamond field effect transistors (FETs), where several types of atomic or molecule termination have been realized on their surfaces. Amine termination and carboxyl termination necessary for biomolecule immobilization can be formed directly on the diamond surfaces resulting in the immobilization of short DNA/RNA within 5 nm from the surface. Owing to the high areal capacitance of a liquid electric double layer capacitor and a solid channel capacitor, the change in the surface charge caused by the hybridization of DNA/RNA and the protein binding to DNA/RNA aptamers can be efficiently detected. The charge of surface termination groups such as NH3+, O-, COO- affects the suppression of nonspecific binding. The detection of biomolecules such as one-base mismatch of DNA and proteins that is unaffected by nonspecific binding can be realized as a result. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We studied the electronic structure evolution of heavily B-doped diamond films across the metal-insulator transition (MIT) using ultraviolet photoemission spectroscopy (UPS). From high-temperature UPS, through which electronic states near the Fermi level (E(F)) up to similar to 5k(B)T can be observed (k(B) is the Boltzmann constant and T the temperature), we observed the carrier concentration dependence of spectral shapes near E(F). Using another carrier concentration dependent UPS, we found that the change in energy position of sp-band of the diamond valence band, which corresponds to the shift of E(F), can be explained by the degenerate semiconductor model, indicating that the diamond valence band is responsible for the metallic states for samples with concentrations above MIT. We discuss a possible electronic structure evolution across MIT. (C) 2010 Elsevier Ltd. All rights reserved.

A H-terminated surface conductive layer of B-doped diamond on a (111) surface was used to fabricate a metal-oxide-semiconductor field-effect transistor (MOSFET) using an electron beam evaporated SiO2 or Al2O3 gate insulator and a Cu-metal stacked gate. When the bulk carrier concentration was approximately 10(15)/cm(3) and the B-doped diamond layer was 1.5 mu m thick, the surface carrier mobility of the H-terminated surface on the (111) diamond before FET processing was 35 cm(2)/Vs and the surface carrier concentration was 1.5 9 10(13)/cm(2). For the SiO2 gate (0.76 mu m long and 50 mu m wide), the maximum measured drain current at a gate voltage of -3.0 V was -75 mA/mm and the maximum transconductance was 24 mS/mm, and for the Al2O3 gate (0.64 mu m long and 50 mu m wide), these features were -86 mA/mm and 15 mS/mm, respectively. These values are among the highest reported direct-current (DC) characteristics for a diamond homoepitaxial (111) MOSFET.

The highly sensitive detection of platelet-derived growth factor (PDGF) has been realized using aptamers immobilized on a diamond surface. The detection mechanism of PDGF is based on the release of an intercalating dye from the aptamer's stem structure during deformation when the aptamer captures PDGF. The detection by fluorescence reduction (signal-off method) does not require a target label and is unaffected by nonspecific binding. The high reproducibility of detection was confirmed. Since aptamers bind to their target PDGF with high affinity, the sensor exhibited high selectivity and sensitivity. The quantitation limit was determined to be 1 pM. (C) 2011 The Japan Society of Applied Physics

Four B-2p in-gap components are observed in B-K XAS spectra using single crystalline boron-doped diamond (BDD) sample. From the polarization dependence of the spectra, the weak peak labeled 1 near the Fermi level is assigned to the hybridized state with C-2p hole state. For the BDD sample grown along < 111 > direction, B-2 dimer is easily created along the growth direction and compensate carriers. A considerable amount of B-H complex and/or B-n cluster is also present. A growth of the peak-1 area intensity is most important to rise the superconducting transition temperature of BDD. (C) 2010 Elsevier B.V. All rights reserved.

It is important for a new superconducting device application to demonstrate Josephson effect by homoepitaxial all diamond junction. Using only CVD diamond, we have fabricated stacked SNS (superconductor-normal conductor superconductor) Josephson junction where normal state diamond film is sandwiched by superconducting diamond films. The current-voltage (I-V) characteristics of the junction showed clear Josephson properties at 2K. (C) 2009 Elsevier B.V. All rights reserved.

The film thickness dependence of Tc in heavily B-doped diamond (1 1 1) and (0 0 1) films was investigated and cross-sectional transmission electron microscope observation was employed to investigate the crystalline structure of heavily B-doped diamond. (1 1 1) films with 5 nm or more and (0 0 1) films with 40 nm or more show superconducting transition. Few dislocations are observed in 500 nm from the interface between the substrate and B-doped homoepitaxial layer in (1 1 1) film and defective structure observed in (0 0 1) film. (C) 2010 Elsevier B.V. All rights reserved.

The superconducting transition temperatures (T(C)) of (1 1 1) and (0 0 1) boron-doped diamond films deposited by microwave plasma assisted chemical vapor deposition (MPCVD) are investigated in the wide boron concentration range of 1 x 10(20) - 1 x 10(22) cm(-3). The critical boron concentrations of superconductor to insulator transition in (1 1 1) and (0 0 1) films are 3 x 10(20) cm(-3). T(C) in (1 1 1) films does not have the tendency to saturate up to 1 x 10(22) cm(-3), while T(C) in (0 0 1) films saturates. (C) 2010 Elsevier B.V. All rights reserved.

The detection of platelet-derived growth factor (PDGF) via a solution-gate field-effect transistor (SGFET) has been demonstrated for the first time using aptamers immobilized on a diamond surface. Upon introduction of PDGF to the immobilized aptamer, a shift of 31.7 mV in the negative direction is observed at a source-drain current of -50 mu A. A shift of 32.3 mV in the positive direction is detected after regeneration by SDS solution, indicating that the static measurement returns to its original value. These SGFETs operate stably within the large potential window of diamond (&gt;3.0 V), and hence the surface channel does not need passivating with a thick insulating layer. Thereof, the immobilized aptamer channels have been exposed directly to the electrolyte solution without a gate insulator. Immobilization is achieved via aptamers covalently bonding to amine sites, thereby increasing the sensitivity of the biosensors. Diamond SGFETs have potential for the detection of PDGF and show durability against biological degradation after repeated usage and regeneration. (C) 2010 Elsevier B.V. All rights reserved.

We have developed calcium (Ca(2+)) ion sensitive solution-gate field effect transistors (SGFETs) on polycrystalline diamond by using partial amination and immobilization of calmodulin (CaM), a specific protein to calcium ions. The CaM is covalently immobilized on functionalized diamond surface, and the functionalized surface was analyzed by X-ray photoelectron spectroscopy, respectively. Also, the high performance of the CaM-immobilized diamond SGFET for detecting Ca(2+) were studied with respect to high selectivity and sensitivity in various concentrations and pH. (C) 2010 Elsevier B.V. All rights reserved.

We have investigated drift and hysteresis characteristics on an electrolyte-solution-gate field-effect transistor (SGFET) with a unique structure using polycrystalline diamond and verified the possibility as chemical sensors and biosensors. Silicon-based ion-sensitive field effect transistors (ISFETs) have not yet solved such time-related issues due to the chemical instability of the passivation layer covering on SiO2 and that is why the Si-ISFET is not wide spread. First of all, we have confirmed that the pH sensitivities of oxygen-and amine-terminated diamond surfaces are 20 mV/pH and 48 mV/pH, respectively, whereas that of hydrogen-terminated surface is only 7 mV/pH. Drift characteristics measurement on diamond SGFET reveals that diamond SGFETs with any surface termination are more stable in electrolyte solution than Si-ISFETs with typical passivation membranes. Hysteresis width, which is known to be a more serious cause of measurement error than drift, proves to be 0.39 mV on amine-terminated SGFET. This is less than 1/10 compared with common Si3N4-ISFET. These results can be explained by high tolerance of diamond against ions in solution due to intrinsic chemical stability and densely packed structure of diamond itself. In this work, we bear out that diamond SGFET is a promising platform for highly sensitive biosensor application owing to the superiority in terms of time response and resulting measurement accuracy.

The critical concentration of superconductor-to-insulator transition in boron-doped diamond is determined in two ways, namely, the actual doping concentration of boron and the Hall carrier concentration. Hall carrier concentrations in (111) and (001) films exceed the actual doping concentration owing to the distortion of the Fermi surface. The high critical boron concentration in (110) films is owing to the effect of the high concentration of interstitial boron atoms. A boron concentration of 3 X 10(20) cm(-3) in substitutional site is required for inducing superconductivity in diamond.

Applying the hydrogen (H) radical exposure at the last step of MOSFET fabrication process, an oxygen (O)-terminated channel was converted to a H-terminated one to obtain subsurface hole accumulation for field-effect transistor operation. Low-resistive titanium carbide (TiC) source/drain and alumina gate oxide were resistant to the hydrogenation process. The shallow TiC side contacts (similar to 3 nm in depth) to the hole accumulation layer (channel) showed good ohmic contacts with a specific contact resistance of 2 x 10(-7) -7 x 10(-7) Omega.cm(2). For diamond MOSFETs with the TiC ohmic layer, the saturated maximum drain current and maximum transconductance reached 160 mA/mm and 45 mS/mm, respectively. An f(T) of 6.2 GHz and an f(max) of 12.6 GHz were obtained. The hydrogenation-last approach is a nondestructive method for the fabrication of diamond MOSFET with high production yield.

Multiwalled carbon nanotubes (MWCNTs) were synthesized at 390 degrees C in a hydrogen-free atmosphere by graphite antenna chemical vapor deposition, which provides carbon radicals by the etching of the antenna itself in a He- or Ar-based noble gas plasma. An increase in the number of defects in the graphite layers of the CNTs was observed with increasing hydrogen partial pressure. The results of X-ray photoelectron spectroscopy analysis suggested that these defects were caused by the transformation from an sp(2) to an sp(3) structure in the graphite layers of CNTs due to hydrogen radicals. (C) 2009 Elsevier Ltd. All rights reserved.

Chemical trends of Schottky barrier heights of ten kinds of metal contacts on hydrogen-terminated diamond (001) surfaces are estimated from the temperature dependence of their current-voltage characteristics. In addition to the measurements, the interface of the metal/hydrogen-terminated diamond is theoretically modeled including the carrier density of the surface conductive layer and the electron-affinity variation from the clean surface of the hydrogen-terminated diamond. Based on the model, a relation among the carrier density, the electron affinity variation, and the barrier heights are derived. The relation explains well experimental results of and other than the present work.

Through the enhancement of hole accumulated density near hydrogen-terminated (111) diamond surfaces, low sheet resistance (similar to 5 k Omega/sq) has been obtained compared with widely used (001) diamond surfaces (similar to 10 k Omega/sq). Using the hole accumulation layer channel, a high drain current density of -850 mA/mm was obtained in p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). This drain current density is the highest value for diamond FETs. The high drain current on the (111) surface is attributed to two factors: The low source and drain resistances owing to the high hole carrier density and the high channel mobility at a high gate-source voltage on the (111) surface. (C) 2010 The Japan Society of Applied Physics

We have performed high-resolution soft x-ray B 1s core-level photoemission spectroscopy of heavily boron-doped diamond films in order to study the chemical sites of doped-boron atoms and their relation to the superconducting transition temperature (T-c). We find that B 1s core-level spectra exhibit several fine structures and three bulk components can he resolved from photon energy dependent studies and spectral fittings. These results indicate existence of several chemical environments of doped-boron atoms. One of the bulk components having the lowest binding energy can be assigned to a signal from substitutionally doped-boron atoms. Comparisons of bulk components with T-c suggest spectroscopic evidence for the importance of substitutionally doped-boron atoms for effective carrier and superconductivity.

We have performed scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (111)oriented epitaxial films of heavily boron-doped diamond (T-c similar to 5.4 K). We present that tunneling conductance spectra show temperature-dependent spatial variations. In the low-temperature region (T = 0.47K), the tunneling spectra do not show strong spatial dependence and a superconducting energy gap is observed independent of the surface morphology. In the high-temperature region (T = 4.2 K), on the other hand, the tunneling conductance spectra show significant spatial dependence, indicating the inhomogeneous distribution of the superconducting property due to the distribution of boron atoms. (C) 2008 Elsevier Ltd. All rights reserved.

B-11 static/magic-angle spinning (MAS) NMR experiments are applied to four different B-doped diamond samples prepared by either high-pressure and high-temperature (HPHT) or CVD methods with various starting materials. Application of MAS enhances the spectral resolution appreciably and differences of the four B-doped diamond samples are well reflected in the corresponding MAS spectra. From the comparison among the MAS spectra, and also their dependences on the magnetic-field and the pulse-flip angle. it is suggested that at least four kinds of boron including two kinds of impurities exist in B-doped diamond. We further examine B-11 spin-lattice relaxation times (T-1) for the four components and find that one of them is extremely short (ca. 500 ms) while others are in the range of several seconds. Relation between the component having the short T, and the super conducting transition temperature (T-c) value is suggested. (C) 2008 Elsevier B.V. All rights reserved.

Using diamond field-effect transistors (FETs) operated in electrolyte solution (solution-gate FETs; SGFETs), a label-free charge detection method between complementary and single mismatched target oligonucleotides is proposed. The probe oligonucleotides immobilized at the activated carboxyl groups of carboxylic aromatic compounds (CACs) on the previously formed amino groups of the diamond surface. The high performance of the diamond surface for oligonucleotides detection was studied with respect to selectivity, sensitivity, and reproducibility of the diamond SGFETs. (C) 2008 The Japan Society of Applied Physics

Vertically aligned double-walled carbon nanotube (VA-DWCNT) arrays were synthesized by point-arc microwave plasma chemical vapor deposition on Cr/n-Si and SiO2/n-Si substrates. The outer tube diameters of VA-DWCNTs are in the range of 2.5 -3.8 nm, and the average interlayer spacing is approximately 0.42 nm. The field emission properties of these VA-DWCNTs were studied. It was found that a VA-DWCNT array grown on a Cr/n-Si substrate had better field emission properties as compared with a VA-DWCNT array grown on a SiO2/n-Si substrate and randomly oriented DWCNTs, showing a turn-on field of about 0.85 V mu m(-1) at the emission current density of 0.1 mu A cm(-2) and a threshold field of 1.67 V mu m(-1) at the emission current density of 1.0 mA cm(-2). The better field emission performance of the VA-DWCNT array was mainly attributed to the vertical alignment of DWCNTs on the Cr/n-Si substrate and the low contact resistance between CNTs and the Cr/n-Si substrate.

The effects of surface charge density on DNA hybridization have been investigated on a mixture of hydrogen-, oxygen-, and amine-terminated diamond surfaces. A difference in the hybridization efficiencies of complementary and mismatched DNA was clearly observed by fluorescence and potentiometric observations at a particular coverage of oxygen. In the fluorescence observation, singly mismatched DNA was detected with high contrast after appropriate hybridization on the surface with 10-20% oxygen coverage. The amount of oxygen in the form of C-O- (deprotonated C-OH) producing the surface negative-charge density was estimated by X-ray photoelectron spectroscopy. Electrolyte solution gate field-effect transistors (SGFETs) were used for potentiometric observations. The signal difference (change in gate potential) on the SGFET, which was as large as similar to 20 mV, was caused by the difference in the hybridization efficiencies of complementary target DNA (cDNA) and singly mismatched (1 MM) target DNA with a common probe DNA immobilized on the same SGFET. The reversible change in gate potential caused by the hybridization and denaturation cycles and discriminating between the complementary and 1 MM DNA targets was very stable throughout the cyclical detections. Moreover, the ratio of signals caused by hybridization of the cDNA and 1 MM DNA targets with the probe DNA immobilized on the SGFET was determined to be 3:1 when hybridization had occurred (after 15 min on SGFET), as determined by real-time measurements. From the viewpoint of hybridization kinetics, the rate constant for hybridization of singly mismatched DNA was a factor of similar to 3 smaller than that of cDNA on this functionalized (oxidized and arninated) diamond surface.

Vertically aligned carbon nanotubes (CNTs) were synthesized from Ni nanoparticles prepared by ion implantation. Ni ions were implanted at 30 keV into thermally grown SiO2 Substrates using a focused-ion-beam. High-density nanoparticle formation was investigated with high doses up to 5.0 x 10(17) ions/cm(2). Dense Ni nanoparticles in the order of 10(11)-10(12) cm(-2) were obtained on a SiO2 substrate, and the particle density and diameter were controlled by post-implantation annealing. Particles annealed at 700 degrees C led to vertically aligned CNTs. Interestingly, catalysts were longer along the vertical axis and the lower half of the Ni particle was buried in SiO2. (c) 2008 Elsevier B.V. All rights reserved.

In this work, the channel mobility (mu(ch)) of diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with hole accumulation layer channels was evaluated from the gate-to-channel capacitance and drain conductance for the first time. The FET structure was utilized for the capacitance-voltage (C-V) measurement, and the gate-to-channel capacitance (C-GC) under the forward bias condition was proportional to the gate area, as in the case of Si MOSFETs. For the accurate evaluation of the drain conductance, diamond MOSFETs were fabricated on IIa-type diamond films with low boron concentrations (&lt; 10(14) cm(-3)). In a 60-mu m gate-length diamond MOSFET, a mu(ch) of 145cm(2)/Vs was obtained, which is comparable to that of a SiC inversion layer. (C) 2008 Elsevier B.V. All rights reserved.

Carbon- and boron-2p states of superconducting and non-superconducting boron-doped diamond (BDD) samples are measured using soft X-ray emission and absorption spectroscopy (XES and XAS) near C- and B-K edges. The electronic structure of B 2p does not show a marked boron-doping dependence, except that a. considerable amount of in-gap state in empty states is observed. In C-K XAS spectra, two peaks H and I are observed around the Fermi level. The H peak is attributed to 2p state of carbon first-nearest neighboring to the dopant boron atoms (INN-C), and the I peak to 2p state of carbon further than INN-C from an impurity boron. Incoherent (normal-excitation) XES spectra do not show a large chemical shift by B-doping, but its intensity just below the valence band maximum (VBM) decreases with B-doping. It cannot be interpreted within a simple rigid band model. An elastic peak of I-excited C-K XES spectrum and the width of I-peak of C-K XAS spectrum suggest that impurity state is localized in non-superconducting BDD but is not in superconducting BDD. Namely impurity state of superconducting BDD is merged with the valence band, and holes in the merged state play an important role in the occurrence of superconductivity of BDD.

Laser-excited photoemission spectroscopy is used to show that the doped carriers in metallic or superconducting diamond couple strongly to the lattice via high-energy (_150__meV) optical phonons, with direct observations of localized Franck-Condon multiphonon sidebands appearing as Fermi-edge replicas. It exhibits a temperature-dependent spectral weight transfer from higher to lower energy sidebands and zero-phonon Fermi-edge states. The quantified coupling strength shows a systematic increase on lowering temperature, implicating its relation to the normal state transport and superconductivity.

We measured the electrical properties of vertically aligned carbon nanotubes (CNTs) synthesized from via holes by radical chemical vapor deposition at a low temperature of 390 degrees C, which meets the requirements of the Si large scale integration (LSI) process. To use the CNTs could be used for LSI wiring, we applied chemical mechanical polishing (CMP) to the CNTs and successfully reduced the via resistance by a factor of ten. In addition, the resistance of the CNTs was reduced further to 0.6 Omega for 2-mu m-diameter vias by annealing at 400 degrees C. Although the temperature dependence of the resistance of the CNTs grown in vias (CNT-vias) did not indicate ballistic transport, which is one of the expected properties of CNTs, we found that CMP and annealing are effective for reducing the via resistance of CNTs.

Diamond metal-oxide-semiconductor field-effect transistors (FETs) have been fabricated on IIa-type large-grain diamond substrates with a (110) preferential surface. The drain current and cutoff frequency are -790 mA/mm and 45 GHz, respectively, which are higher than those of single-crystal diamond FETs fabricated on (001) homoepitaxial diamond films. The hole carrier density of the hole accumulation layer depends on the orientation of the hydrogen-terminated diamond surface, for which (110) preferentially oriented films show 50%-70% lower sheet resistance than a (001) substrate. We propose that the hole density of the surface accumulation layer is proportional to the C-H bond density on the surface. (c) 2008 American Institute of Physics.

We investigated the growth mechanism of layered single-walled carbon nanotube (SWNT) mats by a cutting method. Transmission electron microscope observations revealed that new SWNTs grown below first grown SWNTs also have caps at their tips. Raman spectroscopy suggests that the SWNTs in each layer have the same chirality distribution. This growth method might be a way to prove a factor of chirality selection of SWNTs.

Vertically aligned double-walled carbon nanotubes (DWCNTs) with the highest selectivity of 90% were synthesized by a controlled heating method and their electric double-layer capacitor characteristics were evaluated. DWCNT arrays had a specific capacitance of 83 F/g, which is one of the highest values among CNT arrays in a nonaqueous solution and is almost equivalent to that for single-walled CNT (SWCNT) arrays reported previously. At the same specific capacitance, DWCNTs with superior structural properties are more promising for practical capacitors than SWCNTs. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Functionalization of nanoparticles and immobilization of biomolecules on nanoparticles are important techniques for various applications in biotechnology. For application in the biomedical field, the surface of ultradispersed diamond (UDD) is immobilized with amino-terminated DNA after functionalizing carboxylic or amino group on the UDD surface. The characterized surface of UDD, carboxylated UDD, and aminated UDD were analyzed by DRIFT spectroscopy. In addition, hybridization with Cy-5 labeled target DNA was clearly observed on functionalized UDD by fluorescence microscopy.

The assignment of boron not contributing to conductivity in boron-doped diamond to boron-hydrogen complex is reexamined using a new B-11 two-dimensional NMR technique, which is developed to detect H-1-B-11 dipolar broadening. It is shown that the amount of boron-hydrogen complex is not substantial and the previous assignment is thus less plausible. Possible mechanisms of linebroadening are discussed.

Vertically aligned multiwalled carbon nanotubes (MWCNTs) were synthesized by remote plasma chemical vapor deposition at a low temperature of 390 degrees C, which meets the requirement of the large scale integration (LSI) process. For wiring application, we measured the electrical properties of MWCNT-via structures with and without chemical mechanical polishing (CMP). The via resistances were reduced using inner shells of MWCNTs whose caps were opened due to CMP. The improved resistance after annealing at 400 degrees C was 0.6 Omega for 2 mu m vias. Our process is suitable for LSI because the temperature never exceeds the allowable temperature of 400 degrees C in the Si LSI process. (c) 2007 American Institute of Physics.

Hard x-ray photoemission spectroscopy has been used to study intrinsic core-level electronic structure evolution of heavily boron-doped superconducting diamond films made with a microwave plasma-assisted chemical-vapor deposition method. The boron concentration dependent C 1s core-level spectra show systematic changes in the shift of the main peak and in the evolution of an additional feature at 1.1-1.3 eV lower binding energy than the main peak. In comparison to a low boron concentration nonsuperconducting diamond, the higher boron concentration doped diamond films show formation of several additional features in the B 1s core levels. Based on the present results, the local chemical environments around the doped boron atoms, the efficiency of hole doping by boron doping, and the implications for a recent x-ray absorption study are discussed.

Superconductivity was achieved above 10 K in heavily boron-doped diamond thin films deposited by the microwave plasma-assisted chemical vapor deposition (CVD) method. Advantages of the CVD method are the controllability of boron concentration in a wide range, and a high boron concentration, compared to those obtained using the high-pressure high-temperature method. The superconducting transition temperatures of homoepitaxial (111) films are determined to be 11.4 K for Tc onset and 8.4 K for zero resistance from transport measurements. In contrast, the superconducting transition temperatures of (100) films T-C onset=6.3 K and T-C zero=3.2 K were significantly suppressed. (C) 2007 Elsevier B.V. All rights reserved.

We observe strong softening of optical-phonon modes in superconducting (T-c=4.2 K) boron-doped diamond near the Brillouin-zone center using inelastic x-ray scattering from a chemical vapor deposition grown highly oriented sample. The magnitude of the softening, and our observation that it becomes stronger approaching zone center, supports theoretical models suggesting a phonon-mediated pairing mechanism via coupling of optical-phonon modes to Fermi surfaces around the zone center. The electron-phonon coupling parameter is determined as approximately lambda=0.33.

Half-centimeter-high mats of vertically aligned single-walled carbon nanotubes were grown at 600 degrees C by point-arc microwave plasma chemical vapor deposition. The mats were produced from 0.5 nm of an Fe catalyst layer, thus showing one of the highest catalytic yields of similar to 10(5) times. The growth process shows a lack of poisoning of the catalyst, in contrast to other reports. The experimental results confirm that the growth rate is ultimately limited by the gas phase diffusion of hydrocarbon radicals.

The authors fabricated diamond solution-gate field-effect transistors (SGFETs) with miniaturization of the channel length to 5 mu m by photolithography. The channel surface was directly functionalized with amine by ultraviolet irradiation in an ammonia gas for 4 h and aminated diamond SGFETs were sensitive to pH by 40 mV/pH. Urease was immobilized on the amine-modified channel surface, which was sensitive to urea by 27 mu A/decade from 10(-5)M to 10(-2)M. The authors fabricated submicron-sized (500 nm) diamond SGFETs using electron-beam lithography. The transconductance (g(m)) was 56 mS/mm, which was 930-fold greater than that of the 500 mu m channel length. (c) 2007 American Institute of Physics.

The introduction of a high concentration of boron into polycrystalline diamond films is realized by the chemical vapor deposition of the films. The growth parameter a, which is determined as the growth direction, depends on growth conditions such as the methane concentrations and B/C ratio. With an increase in methane concentration or B/C ratio, 〈111〉-faceted growth is frequently observed. From X-ray diffraction measurement, the 〈111〉-textured growth of the film is confirmed under high-α conditions. The diamond film grown, which has an extremely low resistivity (1.23 mΩ·cm), shows a transition to superconductivity at 5.6 K. For films grown under high-α conditions, for which the surface energy of the {111} face is low, a higher Tc is observed.

We investigate the temperature (T)-dependent low-energy electronic structure of a boron-doped diamond thin film using ultrahigh resolution laser-excited photoemission spectroscopy. We observe a clear shift of the leading edge below T=11 K, indicative of a superconducting gap opening (Delta similar to 0.78 meV at T=4.5 K). The gap feature is significantly broad and a well-defined quasiparticle peak is lacking even at the lowest temperature of measurement (=4.5 K). We discuss our results in terms of disorder effects on the normal state transport and superconductivity in this system.

We have investigated the superconductivity discovered in boron-doped diamonds by means of B-11-NMR on heteroepitaxially grown (111) and (100) films. B-11-NMR spectra for all of the films are identified to arise from the substitutional B(1) site as single occupation and lower symmetric B(2) site substituted as boron+hydrogen (B+H) complex, respectively. Clear evidence is presented that the effective carriers introduced by B(1) substitution are responsible for the superconductivity, whereas the charge neutral B(2) sites does not offer the carriers effectively. The result is also corroborated by the density of states deduced by 1/T1T measurement, indicating that the evolution of superconductivity is driven by the effective carrier introduced by substitution at B(1) site.

Here, we report a novel method of micropatterning oligonucleotides via aromatic groups as linkers on partially amino-terminated diamond and the inherence on subsequent hybridization. The covalent immobilization of probe oligonucleotides and characterization of immobilized probe oligonucleotides with carboxylic compounds were investigated by X-ray photoelectron spectroscopy (XPS). To confirm the effects of linker flexibility in a low amino group on diamond for probe oligonucleotides, three kinds of dicarboxylic compounds-adipic acid, terephthalic acid, and trimesic acidswere used for immobilization of probe oligonucleotides, like linkers; and these oligonucleotides were hybridized with target oligonucleotides labeled with Cy 5 on the micropatterned diamond surface. The hybridization intensities determined by epifluorescence microscopy were compared and analyzed.

Here, we report a novel method of micropatterning oligonucleotides via aromatic groups as linkers on partially amino-terminated diamond and the inherence on subsequent hybridization. The covalent immobilization of probe oligonucleotides and characterization of immobilized probe oligonucleotides with carboxylic compounds were investigated by X-ray photoelectron spectroscopy (XPS). To confirm the effects of linker flexibility in a low amino group on diamond for probe oligonucleotides, three kinds of dicarboxylic compounds-adipic acid, terephthalic acid, and trimesic acidswere used for immobilization of probe oligonucleotides, like linkers; and these oligonucleotides were hybridized with target oligonucleotides labeled with Cy 5 on the micropatterned diamond surface. The hybridization intensities determined by epifluorescence microscopy were compared and analyzed.

Mechanisms of the hole trap and detrap on the oxygen-terminated diamond surfaces measured by diamond in-plane-gated field-effect transistors (FETs) have been investigated. Reproducible hysteresis characteristics are observed in the I-DS-V-GS characteristics of the diamond in-plane-gated FETs. They are caused by carrier trapping in the oxidized diamond surface and detrapping under a light irradiation, the wavelength of which affects the hysteresis width. Carriers are trapped by continuous surface states deeper than 2.0 eV from the valence band maximum in the oxidized diamond surface, where the position of the highest occupied level (Fermi level) is located between 2.0 and 2.4 eV. (c) 2006 American Institute of Physics.

Amino groups were functionalized directly on the diamond surface after treating 0.5 monolayer of oxidation for detection of DNAs. Also, immobilization of probe DNAs was carried out directly on the partially aminated diamond without linker molecules. Specific hybridization with 21-mer DNA at a concentration of 100 nM could be clearly detected by two methods, fluorescence microscopy and diamond solution-gate field-effect transistors (SGFETs). DNA hybridization was confirmed using Cy-5-labeled target DNA on a micropatterned diamond surface. The changes in gate potential by the negative charge of immobilized or hybridized DNA were measured on SGFETs and hybridization efficiency on the functionalized diamond surface was estimated as about 40%.

Charge detection biosensors have recently become the focal point of biosensor research, especially field-effect-transistors (FETs) that combine compactness, low cost, high input, and low output impedances, to realize simple and stable in vivo diagnostic systems. However, critical evaluation of the possibility and limitations of charge detection of label-free DNA hybridization using silicon-based ion-sensitive FETs (ISFETs) has been introduced recently. The channel surface of these devices must be covered by relatively thick insulating layers (SiO2, Si3N4, Al2O3, or Ta2O5) to protect against the invasion of ions from solution. These thick insulating layers are not suitable for charge detection of DNA and miniaturization, as the small capacitance of thick insulating layers restricts translation of the negative DNA charge from the electrolyte to the channel surface. To overcome these difficulties, thin-gate-insulator FET sensors should be developed. Here, we report diamond solution-gate FETs (SGFETs), where the DNA-immobilized channels are exposed directly to the electrolyte solution without gate insulator. These SGFETs operate stably within the large potential window of diamond (&gt; 3.0 V). Thus, the channel surface does not need to be covered by thick insulating layers, and DNA is immobilized directly through amine sites, which is a factor of 30 more sensitive than existing Si-ISFET DNA sensors. Diamond SGFETs can rapidly detect complementary, 3-mer mismatched (10 pM) and has a potential for the detection of single-base mismatched oligonucleotide DNA, without biological degradation by cyclically repeated hybridization and denature.

Heavily boron-doped, diamond films can become superconducting with critical temperatures T-c well above 4 K. Here we first measure the reflectivity of such a film down to 5 cm(-1), by also using coherent synchrotron radiation. We thus determine the optical gap 2 Delta, the field penetration depth lambda, the range of action of the Ferrell-Glover-Tinkham sum rule, and the electron-phonon spectral function alpha F-2(omega). We conclude that diamond behaves as a dirty BCS superconductor.

This paper presents, for the first time, a semi-quantitative study on the production of densely packed and vertically aligned (DPVA) single-walled carbon nanotubes (SWNTs) from ultra-thin catalytic films. An up-to-date highest volume density (60-70 kg m(-3)) and the corresponding high surface density on the order of 10(16) m(-2) of DPVA-SWNTs have been achieved by point-arc microwave plasma chemical vapor deposition. The precise thickness control of the sandwich-like catalytic nanostructure of 0.5 nm Al2O3/0.5 nm Fell &gt; 5 nm Al2O3, developed by the authors, and a short-time (5 min) heat pretreatment of substrates at a temperature as low as 600 degrees C play the very key role in the process of fabricating DPVA-SWNTs. (c) 2006 Elsevier Ltd. All rights reserved.

We have introduced pH sensors fabricated on diamond thin films through modification of the surface-terminated atom. We directly modified the diamond surface from hydrogen to amine or oxygen with ultraviolet (UV) irradiation under ammonia gas. The quantified amine site based on the spectra obtained by X-ray photoelectron spectroscopy (XPS) is 26% (2.6 x 10(14) cm(-2)) with UV irradiation for 8 h and its coverage is dependent on the UV irradiation time. This directly aminated diamond surface is stable with long-term exposure in air and electrolyte solution. We fabricated diamond solution-gate field-effect transistors (SGFETs) without insulating layers on the channel surface. These diamond SGFETs with amine modified by direct amination are sensitive to pH (45 mV/pH) over a wide range from pH 2 to 12 and their sensitivity is dependent on the density of binding sites corresponding to UV irradiation time on the channel surface. (c) 2006 Elsevier B.V. All rights reserved.

We have introduced pH sensors fabricated on diamond thin films through modification of the surface-terminated atom. We directly modified the diamond surface from hydrogen to amine or oxygen with ultraviolet (UV) irradiation under ammonia gas. The quantified amine site based on the spectra obtained by X-ray photoelectron spectroscopy (XPS) is 26% (2.6 x 10(14) cm(-2)) with UV irradiation for 8 h and its coverage is dependent on the UV irradiation time. This directly aminated diamond surface is stable with long-term exposure in air and electrolyte solution. We fabricated diamond solution-gate field-effect transistors (SGFETs) without insulating layers on the channel surface. These diamond SGFETs with amine modified by direct amination are sensitive to pH (45 mV/pH) over a wide range from pH 2 to 12 and their sensitivity is dependent on the density of binding sites corresponding to UV irradiation time on the channel surface. (c) 2006 Elsevier B.V. All rights reserved.

Diamond metal-insulator-semiconductor field effect transistors (MISFETs) with gates of 0.2-0.9 mu m length and T-shape were realized by trilayer resist electron-beam lithography. FETs show a cut-off frequency (f(T)) of 11 GHz and maximum oscillation frequency (f(max)) of 22 GHz. The f(max)/f(T) ratio of this FET was more than double that of FETs with a conventional gate structure and the same gate length. The f(T) of 11 GHz was half the maximum for diamond FETs due to parasitic capacitance at the gate-drain and gate-source electrodes. The T-shaped gate structure and the source-to-drain spacing must be optimized to reduce parasitic capacitance between each electrode.

We report a novel method of one-step direct amination oil polycrystalline diamond to produce functionalized surfaces for DNA micropatterning by photolithography. Polycrystalline diamond was exposed to UV irradiation in ammonia gas to generate amine groups directly. After patterning, optical microscopy confirmed that micropatterns covered with an Au mask were regular in size and shape. The regions outside the micropatterns were passivated with fluorine termination by C3F8 plasma, and the chemical changes on the two different surfaces-the amine groups inside the patterned regions by one-step direct amination and fluorine termination outside the patterned regions-were characterized by spatially resolved X-ray photoelectron spectroscopy (XPS). The patterned areas terminated with active amine groups were then immobilized with probe DNA via a bifunctional molecule. The sequence specificity was conducted by hybridizing fluorescently labeled target DNA to both complementary and noncomplementary probe DNA attached inside the micropatterns. The fluorescence micropatterns observed by epifluorescence microscopy corresponded to those imaged by optical microscopy. DNA hybridization and denaturation experiments on a DNA-modified diamond show that the diamond surfaces reveal superior stability. The influence of a different amination time oil fluorescence intensity was compared. Different terminations as passivated layers were investigated, and as a result, fluorine termination points to the greatest signal-to-noise ratio.

Metal-insulator-semiconductor field-effect transistors (MISFETs) with aluminum oxide as a gate insulator have been fabricated on a hydrogen-terminated diamond surface using its surface conductive layer. The aluminum oxide gate insulator was deposited on the diamond surface by the pulsed laser deposition method. The on-off ratio measured by dc was greater than five orders of magnitude, one of the best results reported for diamond FETs. The gate leak current of aluminum oxide MISFETs is three orders of magnitude less than that of conventional CaF2 MISFETs. These characteristics indicate that aluminum oxide gate insulators are suitable for high reliability power device applications of diamond MISFETs. (c) 2006 American Institute of Physics.

Diamond metal-insulator-semiconductor field-effect-transistors (MISFETs) utilizing a hole accumulation layer have been fabricated on a hydrogen-terminated (H-terminated) diamond surface. The highest cut-off frequency (fT) of 30 GHz and the maximum frequency of oscillation (fmax) of 60 GHz were obtained in the 0.35 μm gate diamond MISFET. RF power operations of diamond MISFETs were demonstrated for the first time. In RF power operation, the high power density of 2.14 W/mm was obtained at 1 GHz. © 2006 IEEE.

Vertically aligned single-walled carbon nanotubes (SWNTs) were synthesized at a low temperature of 600°C by radical chemical vapor deposition (CVD). For applying this technique to electronic devices, we synthesized SWNTs in nano-sized SiO2 holes to fabricate SWNT-vias, which is expected to be used for multi-layer interconnects and vertically aligned field effect transistors (FET). SWNTs were grown in holes with various sizes and shapes patterned by electron beam lithography. We also show the concept of large area deposition of vertically aligned SWNTs by improved radical CVD system.

An H-terminated-surface conductive layer of B-doped diamond on a (I 11) surface was used to fabricate a metal insulator semiconductor field effect transistor (MISFET) using CaF2, SiO2 or Al2O3 gate insulators and a Cu-metal stacked gate. For a CaF2 gate, the maximum measured drain current (I-dmax) was 240 mA/mm and the maximum transconductance (g(m)) was 70 mS/mm, and the cut-off frequency of 4 GHz was obtained. For a SiO2 gate, I-dmax and g(m) were 75 mA/mm and 24 mS/mm, respectively, and for an Al2O3 gate, these characteristics were 86 mA/mm and 15 mS/mm, respectively. These values are among the highest reported DC and RF characteristics for a diamond homoepitaxial (I 11) MISFET.

We have performed soft X-ray angle-resolved photoemission spectroscopy (SXARPES) of microwave plasma-assisted chemical vapor deposition diamond films with different B concentrations in order to study the origin of the metallic behavior of superconducting diamond. SXARPES results clearly show valence band dispersions with a bandwidth of similar to 23 eV and with a top of the valence band at gamma point in the Brillouin zone, which are consistent with the calculated valence band dispersions of pure diamond. Boron concentration-dependent band dispersions near the Fermi level (E-F) exhibit a systematic shift of E-F, indicating depopulation of electrons due to hole doping. These SXARPES results indicate that diamond bands retain for heavy boron doping and holes in the diamond band are responsible for the metallic states leading to superconductivity at low temperature. A high-resolution photoemission spectroscopy spectrum near E-F of a heavily boron-doped diamond superconductor is also presented. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

We report on scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (111)-oriented epitaxial films of heavily boron-doped diamond grown by using the microwave plasma-assisted chemical vapor deposition method. STM/STS measurements were performed by He-3-refrigerator based STM under ultra-high vacuum. The STM topography on the film surface shows a corrugation (with a typical size of similar to 1 mu m) and grain-like microstructures (similar to 5-20 nm). The tunneling conductance spectra do not show large spatial dependence and superconductivity is observed independent of the surface structures. The tunneling spectra are analyzed by the Dynes function and the superconducting energy gap is estimated to be Delta = 0.87 meV at T = 0.47 K, corresponding to 2 Delta/k(B)T(c) = 3.7. The relatively large value of the broadening parameter Gamma = 0.38 meV is discussed in terms of the inelastic electron scattering processes. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

We have investigated the low-energy electronic state of boron-doped diamond thin film by the laser-excited photoemission spectroscopy. A clear Fermi-edge is observed for samples doped above the semiconductor-metal boundary, together with the characteristic structures at 150 x n meV possibly due to the strong electron-lattice coupling effect. In addition, for the superconducting sample, we observed a shift of the leading edge below T-c indicative of a superconducting gap opening. We discuss the electron-lattice coupling and the superconductivity in doped diamond. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

We have investigated an origin of the superconductivity discovered in boron (B)-doped diamonds by means of B-11-NMR on heteroepitaxially grown (111) and (100) films and polycrystalline film. The characteristic difference of B-NMR spectral shape for the (111) and (100) thin films is demonstrated as arising from the difference in the concentration (n(B(1))) of boron substituted for carbon. It is revealed from a scaling between a superconducting transition temperature T-c and n(B(1)) that the holes doped into diamond via the substitution of boron for carbon are responsible for the onset of superconductivity. The result suggests that the superconductivity in boron-doped diamond is mediated by the electron-phonon interaction brought about a high Debye temperature similar to 1860 K characteristic for the diamond structure. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

The dispersion of acoustic and optical phonons in highly boron-doped diamond has been measured by inelastic X-ray scattering at an energy resolution of 6.4 meV. The sample is doped in the metallic regime and shows superconductivity below 4.2 K (midpoint). The data are compared to pure and nitrogen-doped diamond that represent the non-metallic state. No difference is found for the acoustic phonons in the three samples, while the optical phonons show a shift of the dispersion (softening) in qualitative agreement with earlier results from Raman spectroscopy. The presence of boron and nitrogen incorporated into the diamond lattice leads to structural disorder. Evidence for this is found both in the observation of otherwise symmetry-forbidded Bragg intensity at (002) and intensity from acoustic phonon modes in the vicinity of (002). (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

Very dense and vertically aligned single-walled carbon nanotubes (SWNTs) were synthesized using a radical CVD apparatus at a low temperature of 600 degrees C. A high density of catalytic particles, which is necessary for the growth of vertically aligned SWNTs, was prepared by heat treatment of a sandwich-like catalyst structure of Al2O3/Fe/Al2O3. In our CVD apparatus, a sphere-shaped microwave plasma ball was fixed at the antenna in the chamber and was 50 mm away from the substrate, which indicates that ions cannot contribute to the growth of SWNTs. The radical CVD system produced a very long catalyst lifetime of over 30 h, because catalysts were not damaged and etched by ions. Using the catalysts with the long lifetime, lengths of SWNTs increased to millimeter order. Root growth mode of SWNTs was clarified by marker growth, which synthesized two vertically aligned SWNT layers on a substrate at different growth times.

We present a simple method for improving the field emission performance of tungsten-tip electron sources based on single-walled carbon nanotube (SWCNT) modification. By coating a sandwich-like thin film of Al-Fe-Al (with Fe as a catalyst) on a tungsten tip, SWCNTs were synthesized at 600 degrees C in a chemical vapor deposition (CVD) reactor. The influence of CNT modification on the electron emission characteristics of the emitters was investigated by means of a triode structure. We have found that CNT-modified tungsten tips exhibit low threshold-voltage for electron emission, and improved emission-current stability, compared with nonmodified and Al-Fe-Al-coated needles. (c) 2006 American Institute of Physics.

The physical properties of lightly doped semiconductors are well described by electronic band- structure calculations and impurity energy levels(1). Such properties form the basis of present- day semiconductor technology. If the doping concentration n exceeds a critical value n(c), the system passes through an insulator- to- metal transition and exhibits metallic behaviour; this is widely accepted to occur as a consequence of the impurity levels merging to form energy bands(2). However, the electronic structure of semiconductors doped beyond nc have not been explored in detail. Therefore, the recent observation of superconductivity emerging near the insulator- to- metal transition(3) in heavily boron- doped diamond(4,5) has stimulated a discussion on the fundamental origin of the metallic states responsible for the superconductivity. Two approaches have been adopted for describing this metallic state: the introduction of charge carriers into either the impurity bands(6) or the intrinsic diamond bands(7-9). Here we show experimentally that the doping- dependent occupied electronic structures are consistent with the diamond bands, indicating that holes in the diamond bands play an essential part in determining the metallic nature of the heavily boron- doped diamond superconductor. This supports the diamond band approach and related predictions, including the possibility of achieving dopant- induced superconductivity in silicon and germanium(7). It should also provide a foundation for the possible development of diamond- based devices(10).

It is very important to control the growth orientation of carbon nanotubes (CNTs) on substrates for applications such as field emission devices and CNT-based FETs. Although chemical vapor deposition (CVD) is the most reliable means to this end, there have been few reports on the synthesis of vertically aligned single-walled carbon nanotubes (SWNTs) using the CVD method. In this study, we demonstrate the low temperature synthesis of extremelydense and vertically aligned SWNTs deposited by point-arc microwave plasma CVD.

The surface potential difference between an H-terminated surface and a locally oxidized diamond surface produced by an atomic force microprobe was investigated using a Kelvin probe force microscope. The potential of the H-terminated diamond surface was observed to be similar to 0.1 V higher than that of the oxidized diamond surface. The surface potential difference can be interpreted in terms of the positions of the vacuum level, the Fermi level, and the conduction and valence band edges, when negative electron affinity and p-type surface conduction are assumed on the H-terminated diamond surface. The surface dipole induced by the electronegativity differences between the surface atoms of the diamond affects the difference in the surface potential between the two surfaces. (c) 2005 Elsevier B.V. All rights reserved.

A novel point-arc microwave plasma chemical vapor deposition (CVD) apparatus was employed to grow single-walled carbon nanotubes (SWNTs) on Si substrates coated with a sandwich-like nano-layer structure of 0.7 nm Al2O3 (top)/0.5 nm Fe/ 5-70nm Al2O3 by conventional high frequency sputtering. The growth of extremely dense and vertically aligned SWNTs with an almost constant growth rate of 270 mu m/h within 40 min at a temperature as low as 600 degrees C was demonstrated for the first time. The volume density of the as-grown SWNT films is as higher as 66 kg/m(3).

Three diamond (001) samples were made by CVD growth on synthetic diamond substrates in a same batch of growth, for which sheet resistance in atmospheric environment was confirmed, A simple two-point probe method has been applied to the samples to measure sheet resistance in UHV of 0.2-50 M Omega/square. Soft X-ray-induced secondary electron spectroscopy has been used to determine the Fermi level position in UHV of the samples for which in-UHV sheet resistance values were known. The Fermi level as measured turned out to be 1.1 +/- 0.2 eV above the valence band top and stayed at the same position within similar to 0.1 eV with the sheet resistance change of an order of 2. On the basis of these findings, a plausible model of surface conductivity of CVD diamond is suggested. (c) 2004 Elsevier B.V. All rights reserved.

ZnTe thin films were electrochemically deposited onto Au-coated Cu substrates from an electrolytic solution containing ZnSO4, TeO2, citric acid and sodium citrate. Effects of deposition potentials and solution's Zn concentrations on the structure, chemical composition and electrical property were investigated. The resistivity, conduction type, carrier density, and carrier mobility were evaluated with a Hall effect measurement apparatus. A film with nearly stoichiometric composition was deposited at -0.80 V vs. Ag/AgCl at 353 K from a solution containing 2.0 x 10(-2) kmol m(-3)-ZnSO4, 1.0 X 10(-4) kmol m(-3)-TeO2, 9.0 X 10(-2) kmol m(-3)-Citric acid and 2.1 x 10(-1) kmol m(-3)-Sodium citrate and was well crystallized with cubic preferential orientation along the (111) plane. A resistivity, the carrier density and the carrier mobility were 4.1 X 10(2) Omega m, 2.9 x 10(19) m(-3) and 5.3 x 10(-4) m(2) V-1 s(-1), respectively.

RF diamond transistors have been developed on a hydrogen-terminated surface conductive layer. $ f_{\text{T } }$ and $ f_{\text{max } }$ of 23 and 25 GHz, respectively, have been achieved in a diamond MISFET with a 0.2 μm gate length. Utilizing de-embedding and small-signal equivalent circuit analysis, parasitic components are extracted. The intrinsic $ f_{\text{T } }$ and $ f_{\text{max } }$ of the 0.2-μm-gate diamond MISFET are estimated to be 26 and 36 GHz, respectively. In this report, some of the challenging steps in device fabrication processes such as the development of a low-resistivity ohmic layer, a high-quality gate insulator and acceptor density control technology, toward high-power and high-frequency diamond transistors with high reliability, are introduced.

DNA micropatterns have been for the first time fabricated on a single-crystal diamond surface in conjunction with the photolithography technique. A new chemical modification process for producing amine groups inside patterned regions and a passivation layer terminated with fluorine outside patterned regions is demonstrated. The resulting amine groups within patterned areas and fluorine termination outside patterned areas on the single-crystal diamond surface were characterized by spatially resolved X-ray photoelectron spectroscopy. Amine-terminated oligonucleotides were then linked to the amine patterned regions using a crosslinker. It was revealed that hybridization on DNA-patterned diamond is specific and selective, with a low background outside the patterns and strong binding to complementary probe DNA immobilized inside the patterns but no binding to noncomplementary probe DNA similarly immobilized inside the patterns. These results suggest that DNA micropatteming on a single-crystal diamond may serve as an ideal platform for future biochips and biosensors.

A diamond electrolyte solution-gate FET (SGFET) for use in electrolyte solutions has been fabricated for the first time. Perfect device characteristics (pinch-off and saturation in I(DS)-V(DS)) have been obtained with bias voltages within the potential window of diamond. The hydrogen-terminated (H-terminated) diamond surface was sensitive to halogen ions at approximately 30 mV/decade. We modified the H-terminated diamond surface with oxygen by treatment with ozone. Partially oxygen-terminated sites were insulating and insensitive to halogen ions. The H-terminated channel surface was modified to be partially amine-oxygen-terminated (H-A-O-terminated) to achieve pH sensitivity when irradiated with UV light in an ammonia solution. The pH sensitivity of a diamond surface modified was about 50 mV/pH unit from pH 2 to 10. We immobilized specific enzymes (urease and glucose oxidase) on the modified channel surface. The sensitivities to urea and glucose were approximately 30 mV/decade and 20 mV/decade, respectively.

Conical carbon nanofibers (CCNFs) have been synthesized on Si substrates coated with a Fe thin film of a few nanometers in thickness by a DC bias-enhanced microwave plasma chemical vapor deposition (CVD) method using H-2 and CH4 as reactant gases under a chamber pressure of about 230 Pa. Without DC bias, only catalytic nanoparticles could be observed by field emission scanning electron microscopy (FE-SEM) on substrate surface after growth. Highly oriented and dense CCNFs could be deposited when a negative DC bias in the range of 150-230 V was applied to the substrate holder during growth. The average density of CCNFs was measured as being of the order of 10(10) cm(-2), while the average length was of the order of 10(2) nm, and the conical angle was in the range of 10-15degrees. The relationships between the density, the root diameter and the length of CCNFs are discussed. (C) 2004 Elsevier B.V. All rights reserved.

We report unambiguous evidence for superconductivity in a heavily boron-doped diamond thin film grown by microwave plasma-assisted chemical vapor deposition (MPCVD). An advantage of the MPCVD-deposited diamond is that it can contain boron at high concentration, especially in (111)-oriented films. Superconducting transition temperatures are determined by transport measurements to be 7.4 K for T-C onset and 4.2 K for zero resistance. The upper critical field is estimated to be 7 T. Magnetization as a function of magnetic fields shows typical type-II superconducting properties. (C) 2004 American Institute of Physics.

Submicrometer-gate (0.2-0.5-mum) diamond metal-insulator-semiconductor field-effect transistors (MISFETs) were fabricated on an H-terminated diamond surface. The maximum transconductance in dc mode reaches 165 mS/mm, while the average transconductance is 70 mS/mm in submicrometer-gate diamond MISFETs. The highest cutoff frequency of 23 GHz and the maximum frequency of oscillation of 25 GHz are realized in the 0.2-mum-gate diamond MISFET. From the intrinsic transconductances or the cutoff frequencies, the saturation velocities are estimated to be 4 x 10(6) cm/s in the submicrometer-gate FETs. They are reduced by gate-drain capacitance and source resistance.

A memory effect of in-plane-gated field-effect transistors (IPGFETs) has been observed on hydrogen-terminated and oxygen-terminated diamond surfaces. The hysteresis characteristics are achieved by the hole traps in the oxygen-terminated surface of the IPGFETs where the threshold voltage shift by the gate voltage sweep is confirmed in the I-d-V-g characteristics. This feature is observed under light illumination, and depends on the radiant flux density. The hysteresis characteristics become very small under the condition of no light irradiation at room temperature. It is assumed that carrier trap sites on the insulating part of IPGFET cause the hysteresis characteristics. Radiant flux enhances carrier migration. (C) 2004 American Institute of Physics.

Communication: Novel antenna edge microwave plasma CVD (AE-MPCVD) is used for the first time to grow CNFs (carbon nanofibers). The synthesis of CNFs on large-area substrates with high growth reproducibility is reported at low microwave power input and with remote deposition. A Growth area ten times as large as the plasma size generated is achieved by AE-MPCVD. Because of its structural simplicity, AE-MPCVD systems can easily be scaled up by applying multi-antenna edge arrays without considering complex microwave geometry or cavity and the total growth area and quality of CNFs are thus expected to be greatly improved.

The enzyme sensors using electrolyte-solution-gate diamond field effect transistors (SGFETs) have been developed for the first time. The hydrogen-terminated surface channel of the FETs was modified into partially aminated and oxygen-terminated (H-A-O-terminated) with irradiation of ultraviolet in an ammonia environment. The pH response of that is obtained about 50 mV/pH at pH 2-10. The concentration of substrates (urea or glucose) in the electrolyte solution has been detected by the pH change due to the bio-catalyzed effect of enzyme (urease or glucose oxidase), which is immobilized on the channel of SGFETs. The sensitivity of urea and glucose is approximately 30 mV/decade and 20 mV/decade respectively.

The electrolyte-solution-gate diamond field effect transistors (SGFETs) have been fabricated on polycrystalline diamond surface and which are used biosensors worked in electrolyte solution. The hydrogen-terminated diamond surface is sensitive to halogen ions about 30mV/decade, which can be applied to cell biological reaction. The hydrogen-terminated surface channel of the SGFETs was modified into partially aminated and oxygen-terminated (H-A-O-terminated) with irradiation of ultraviolet in an ammonia environment to get pH sensitivity and immobilize enzyme. The pH response of that is obtained about 50mV/pH at pH 2-10. The concentration of substrates (urea or glucose) in the electrolyte solution has been detected by the pH change due to the bio-catalyzed effect of enzyme (urease or glucose oxidase), which is immobilized on the channel of SGFETs. The sensitivity of urea and glucose is approximately 30mV/decade and 20mV/decade respectively.

We have investigated the electrolyte-solution-gate field effect transisitors (SGFETs) used hydrogen terminated (H-terminated) or partially oxygen terminated (O-terminated) polycrystalline diamond surface in the Cl- and Br- ionic solutions. The H-terminated channel SGFETs are insensitive to pH values in electrolyte solutions. The threshold voltages of the diamond SGFETs shift according to the density of Cl(-)and Br- ions about 30 mV/decade. One of the attractive biomedical applications for the Cl- sensitive SGFETs is the detection of chloride density in blood or in sweat especially in the case of cystic fibrosis. The sensitivities of Cl- and Br- ions have been lost on the partially O-terminated diamond surface. These phenomena can be explained by the polarity of surface change on the H-terminated and the O-terminated surface. (C) 2003 Elsevier B.V. All rights reserved.

RF diamond FETs have been realized on a hydrogen-terminated diamond surface conductive layer. By utilizing the self-aligned gate fabrication process which is effective for the reduction of the parasitic resistance, the transconductance of diamond FETs has been greatly improved. Consequently, the high frequency operation of 22 GHz has been realized in 0.2 mum gate diamond MISFETs with a CaF2 gate insulator. This value is the highest in diamond FETs and is comparable to the maximum value of SiC MESFETs at present.

Diamond field-effect transistors (FETs) whose channel is partially oxidized and highly resistive are fabricated by ozone treatment. These FETs are operated in electrolyte solutions. From XPS analyses, it is evident that hydrogen-terminated (H-terminated) diamond is partially oxygen-terminated (O-terminated) by ozone treatment. The quantification of surface oxygen in ozone-treated diamond is carried out. The quantification shows that the surface oxygen increases with an increase in ozone treatment time indicating the control of oxygen coverage. The partially O-terminated diamond surface channel is much less conductive compared with the H-terminated diamond. The ozone-treated FETs were operated stably even though the channel of the FETs becomes highly resistive. For the sensing of particular ions or molecules by the immobilization of sensing components, the control of surface termination is necessary. (C) 2003 Elsevier Science B.V. All rights reserved.

Free-exciton emissions increase non-linearly by cathodoluminescence (CL) above the threshold probe current of 30 muA in high-pressure high-temperature synthetic type-IIa diamond. A droplet of electron-hole liquid (EHL) is also observed by CL for the first time. Furthermore, boron acceptor bound-exciton emission as well as free-exciton emission also increases super-linearly in an unintentionally boron-contaminated area. The threshold probe current of non-linear increase of excitonic emission is in accordance with the emergence of the EHL peak. It is considered that the non-linear increase of excitonic emissions is due to the increase in the radiative recombination rate of free excitons under high exciton density. (C) 2003 Elsevier Science B.V. All rights reserved.

The basic characteristics of the short channel FETs have been investigated for the high-frequency performance of the diamond MISFETs. The deep sub-micron gate (0.23-0.5 mum) diamond MISFETs were fabricated on an H-terminated diamond surface. The short channel effect is well suppressed utilizing thin gate insulator. Accordingly, the transconductance is improved by reduction of gate length down to 0.2 mum. This tendency is observed in diamond MISFETs for the first time. Maximum transconductance reaches 71 mS/mm in DC mode and 51 mS/mm in AC mode. The f(T) of 40 GHz is expected in 0.2 mum gate MISFETs as a result. (C) 2003 Elsevier B.V. All rights reserved.

Cryogenic operation of field-effect transistors (FETs) fabricated on hydrogen-terminated (H-terminated) diamond surface conductive layers is investigated. 5-mum gate-length metal-insulator-semiconductor FETs (MISFETs) is fabricated using CaF2 film as a gate insulator. The MISFETs operate successfully even at 4.4 K. At low temperature, the contact between source/drain electrode and H-terminated diamond surface cannot maintain ohmic characteristics, because the thermal activation energy of the carriers is not high enough to overcome the barrier height at the interfaces between the source electrode and the H-terminated diamond. Estimated channel mobility increases from 63 cm(2)/V-s to 137 cm(2)/V-s and the maximum transconductance increases from 10.5 mS/mm to 14.5 mS/mm, as the temperature decreases from 300 K to 4.4 K, indicating reduced phonon scattering of the channel. (C) 2003 Elsevier Science B.V. All rights reserved.

Surface potential of the H-terminated and locally oxidized diamond surfaces is investigated by Kelvin probe force microscope. Potential of H-terminated diamond surface is observed to be similar to0.1 V higher than that of oxidized diamond surface. Surface potential difference is attributed to the surface charge induced by the electronegativity differences of the terminated atoms. The difference of DNA physisorption on the H- and O-terminated diamond surfaces due to the surface charging effect is also observed. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A chemical vapor deposition as-grown diamond (0 0 1) single-domain 2 x 1 surface was studied by electron-spectroscopy and electron-diffraction in ultrahigh vacuum (UHV). In order to change the surface conductivity (SC) of the diamond in UHV, three annealing stages were used; without annealing, annealing at 300 degreesC and annealing at 550 degreesC. From low energy electron diffraction and X-ray photoelectron spectroscopic (XPS) studies, an existence of SC was suggested for the first two stages of annealing and an absence of SC was suggested for the last stage of annealing. Changes in C KVV Auger electron spectroscopic spectra, C KVV Auger electron diffraction (AED) patterns and C 1s XPS peak positions were noticed between the annealing stages at 300 and 550 degreesC. These changes are interpreted as such that the state of hydrogen involvement in a subsurface of diamond (001)2 x 1 changes as SC changes. In particular, the presence of local disorder in diamond configuration in SC subsurface is pointed out from C KVV AED. From C Is XPS peak shifts, a lower bound for the Fermi-level for SC layers from the valence band top is presented to be similar to0.5 eV. (C) 2003 Elsevier Science B.V. All rights reserved.

A chemical vapor deposition as-grown diamond (0 0 1) single-domain 2 x 1 surface was studied by electron-spectroscopy and electron-diffraction in ultrahigh vacuum (UHV). In order to change the surface conductivity (SC) of the diamond in UHV, three annealing stages were used; without annealing, annealing at 300 degreesC and annealing at 550 degreesC. From low energy electron diffraction and X-ray photoelectron spectroscopic (XPS) studies, an existence of SC was suggested for the first two stages of annealing and an absence of SC was suggested for the last stage of annealing. Changes in C KVV Auger electron spectroscopic spectra, C KVV Auger electron diffraction (AED) patterns and C 1s XPS peak positions were noticed between the annealing stages at 300 and 550 degreesC. These changes are interpreted as such that the state of hydrogen involvement in a subsurface of diamond (001)2 x 1 changes as SC changes. In particular, the presence of local disorder in diamond configuration in SC subsurface is pointed out from C KVV AED. From C Is XPS peak shifts, a lower bound for the Fermi-level for SC layers from the valence band top is presented to be similar to0.5 eV. (C) 2003 Elsevier Science B.V. All rights reserved.

Initial growth of heteroepitaxial diamond on Ir (0 0 1)/MgO (0 0 1) was investigated by scanning electron microscopy, reflection high-energy electron diffraction (RHEED) and atornic force microscopy. Bias-enhanced nucleation (BEN) was performed by antenna-edge-type microwave plasma assisted chemical vapor deposition. In BEN, diamond crystallites nucleated and grew along the [ - I 10] and [1 10] directions of iridium. Diamond was likely to nucleate on protruded iridium areas. After BEN, in addition to the diamond diffraction spots, iridium bulk diffraction spots, which were not observed before BEN, were observed by RHEED. The iridium. surface appeared to be protruded and changed by the high ion current density in BEN. Under [0 0 1] selective growth conditions, diamond crystallites, which were less than 10 run in diameter, were etched by H-2 plasma. Diamond nucleated areas corresponded to the surface ridges of iridium along the 1 101 and [ 1 10] directions at 10-40 run intervals before BEN. (C) 2003 Elsevier Science B.V. All rights reserved.

A cut-off frequency of 15 GHz and a maximum frequency of oscillation of 20 GHz are realized in a 0.4-mum gate diamond metal-insulator-semiconductor field-effect transistor (MISFET). The cut-off frequency is the highest value for diamond FETs ever reported. The RF characteristics of the MISFETs are higher than those of metal-semiconductor FETs at the same gate lengths. The CaF2 gate insulator improves the carrier mobility according to the Hall measurement system. The mobility increases in the surface conductive layer result in high RF performance. The source-gate passivation of CaF2 results in the high DC transconductance because of the reduction of series resistances. A cut-off frequency of more than 30 GHz is expected with the gate minimization and the CaF2 passivation of source-gate and gate-drain spacings. (C) 2003 Elsevier Science B.V. All rights reserved.

Diamond dual in-plane-gated field effect transistors with very low gate leakage current have been fabricated on an undoped hydrogen-terminated diamond p-type surface using oxygen plasma etching. Adjusting the threshold voltage optimally by one side gate, lateral electric field from the other side gate modulates the channel conductance. The oxygen plasma etching of 60 nm in depth fully isolated the channel of the hydrogen-terminated diamond surface conductive layer from the side gates resulting very low gate leakage current (&lt; 1 pA at -60 V) at room temperature. This feature provides a necessary condition for the fabrication of diamond single-hole transistors operated at room temperature. (C) 2003 Elsevier Science B.V. All rights reserved.

The effect of I- ions on the threshold voltages of the electrolyte-solution-gate diamond field-effect transistors (SGFETs) in KI solution is investigated. The threshold voltages of hydrogen-terminated (H-terminated) diamond SGFETs shift in the KI concentration range of 10(-6)-10(-1) M in aqueous solutions. The sensitivity of the H-ten-ninated diamond surface to I- ions is higher than that to Cl- or Br- ions. However, the sensitivity to I- ions of the partially oxygen-terminated (O-terminated) diamond surface drastically decreases with ozone treatment. The mechanisms of these phenomena can be explained by the surface charge and the adsorbability of I- ions on the H-terminated and O-terminated diamond surfaces. (C) 2003 Elsevier Science B.V. All rights reserved.

The force-distance curve indicates the difference in wettability between the hydrogen-terininated (H-terminated) diamond surface and the AYM-field-assisted local oxidized (O-terminated) area. Using a hydrophilic (silicon with native oxide) tip and a hydrophobic (coated with gold) tip as AFM tips, the adhesion force mapping measurement shows that the H-terminated surface is hydrophobic and that the O-terminated surface is hydrophilic. After heating in vacuum, the difference in the adhesion force between two surfaces decreased. This means that water adsorbed on the tip and sample surfaces affects the adhesion force. As an alternative measurement, the contact angle measurement of the H-terminated surface and the chemically oxidized surface was performed. It is proved that the oxidized surface is more hydrophilic than the H-terminated surface and that its surface energy is derived from surface polarity such as that involved in hydrogen bonding and electric dipole which is twofold that the H-terminated surface. (C) 2003 Elsevier Science B.V All rights reserved.

Dominant n-type conductivity in sulfur-doped chemical-vapor-deposited diamond is observed by Hall-effect measurement. The activation energy is estimated at 0.5-0.75 eV above 600 K. Below 600 K, the carrier concentration deviates from the activation energy, and Hall mobility decreases in comparison with that above 600 K. It is considered that hopping conduction takes place. By cathodoluminescence measurement, free-exciton recombination radiation is observed in spite of a very high sulfur doping level of 2.5% during deposition, where boron is not detected by secondary ion mass spectroscopy. Therefore, the n-type conductivity of sulfur-doped diamond is caused by a sulfur-related mechanism. (C) 2003 American Institute of Physics.

The origin of surface conductivity (SC) of a CVD diamond (001) single-domain 2x1 surface was studied by electron spectroscopy and electron diffraction in UHV. In order to change SC of the diamond in UHV, two annealing stages were used: annealing at 300 degreesC and annealing at 550 degreesC. From the results of LEED and XPS, the existence of SC was suggested for the first stage of annealing and the absence of SC was suggested for the last stage of annealing. Changes in C KVV AES spectra, C KVV AED patterns and C 1s XPS peak positions were noted between the annealing stages at 300 and 550 degreesC. These changes are interpreted in that the state of hydrogen involvement on a subsurface of diamond (001)2x1 changes as SC changes. From C 1s XPS peak shifts, a lower bound for the Fermi level for SC layers from the valence band top is presented to be similar to0.5 eV.

Nanofabrication of electron devices based on the stability of hydrogen- and oxygen-terminated diamond surfaces is performed using an atomic force microscope modification technology. A nanotechnology involving the separation of C-H and C-O bonded surfaces has been applied to realize the single-hole transistors. The single-hole transistors operate at liquid-nitrogen temperature (77 K), where the Coulomb oscillation characteristics are clearly observed. (C) 2002 American Institute of Physics.

Local insulation on the hydrogen-terminated homoepitaxial diamond (001) surface was performed using an atomic force microscope (AFM). The mechanism is analogous to electrochemical anodic oxidation in which the sample acts as an anode while the AFM tip acts as a cathode and the water layer from the atmosphere between the tip and the sample surface works as the electrolyte. The current measured during insulation indicates the anodization characteristics of the process. The surface modification has been found to be strongly dependent on the electric field between the sample and the tip. We also demonstrate the modification with the alternating current (AC) voltage bias. This method prevents buildup of space charge during modification and leads to the increase of the modified line width compared with the static voltage bias. Under proper conditions, such as suitable writing speed and bias voltage, the minimum line width reaches 35 nm in the case of AC bias.

The current-voltage characteristic of the atomic force microscope (AFM) field-assisted local oxidized region on an undoped hydrogen-terminated (H-terminated) diamond surface is investigated. The barrier height on the top of the valence band between the undoped H-terminated diamond surface and the AFM oxidized surface is estimated by Fowler-Nordheim (F-N) tunneling current analysis. By fitting the parameter of the slope in the F-N plot, the barrier height is estimated to be 61 meV in the electrically isolated conductive island structure. On the other hand, the barrier height is also estimated to be 72 meV in the lateral tunneling diode.

The microwave performance of diamond metal semiconductor field-effect transistors (MESFET) and metal insulator semiconductor field-effect transistors (MISFET) fabricated on hydrogen-terminated diamond surface is investigated. A cut-off frequency of 2.2 GHz is obtained on a 2 mum Cu gate MESFET with a transconductance of 70 mS/mm. A cut-off frequency of 11 GHz is obtained on a 0.7 mum gate MISFET with a transconductance of 40 mS/mm. Despite the lower transconductance, the cut-off frequency of MISFET is higher than that of MESFET due to not only gate minimization but also increased carrier mobility due to the use of CaF2 as the gate insulator, High-frequency equivalent circuits are derived from S-parameters for MISFET with various gate lengths, Reduction of gate-source parasitic resistance and capacitance in MISFET by the improvement of device structure yield high frequency performance.

Heteroepitaxial (0 0 1) diamond films are successfully grown on high-quality (0 0 1)Ir/(0 0 1)MgO substrates. To enhance the epitaxial nucleation and growth of the diamond, antenna-edge microwave plasma chemical vapor deposition (MPCVD) has been used as a bias enhanced nucleation step. Subsequently, the diamond growth step is performed using conventional MPCVD in a &lt;0 0 1&gt; fast growth mode. Scanning electron microscope (SEM) observation and reflection high-energy electron diffraction (RHEED) reveals the epitaxial ordering of deposited film in several millimeters square area. (C) 2002 Elsevier Science B.V. All rights reserved.

The RF device potential of surface-channel polycrystalline diamond metal-insulator-semiconductor field-effect transistors (MISFETs) is demonstrated for the first time, Utilizing a self-aligned gate field-effect transistor (FET) fabrication process, effective transconductance of 70 mS/mm is realized at 0.7 mum gate length. This FET also shows high f(T) and f(max) of 2.7 and 3.8 GHz, respectively. However, the breakdown voltage and f(max)/f(T) ratio are lower than those for the homoepitaxial layer because of the parasitic capacitance at the grain boundaries in the drain region. Because of the fluctuation of channel mobility, the fluctuation of g(m) and f(T) is observed. In order to realize high-power operation at high frequency, the fabrication of the FET on a single grain to reduce the parasitic capacitance is required.

Diamond field-effect transistors (FETs) operate in electrolyte solutions having a wide pH range of 1-13. The FETs have been fabricated using a p-type surface conductive layer, where the diamond surface is exposed directly to the electrolyte solutions. From the drain current-gate voltage (I-ds-V-gs) characteristics of the FETs, it appears that the threshold voltages of the FETs are independent of the pH value of the solution. In Cl- ionic solutions, however, the threshold voltages shift approximately 30mV with a one-order-of-magnitude change of molar concentration of Cl- ions. This sensitivity of the FET to Cl- ion's concrentration is observed in the 10(-1)-10(-6) M range of potassium chloride (KCI) solutions.

A cutoff frequency (f(T)) of 11 GHz is realized in the hydrogen-terminated surface channel diamond metal-insulator-semiconductor field-effect transistor (MISFET) with 0.7 mum gate length. This value is five times higher than that of 2 mum gate metal-semiconductor (MES) FETs and the maximum value in diamond FETs at present. Utilizing CaF2 as an insulator in the MIS structure, the gate-source capacitance is reduced to half that of diamond MESFET because of the gate insulator capacitance being in series to the surface-channel capacitance. This FET also exhibits the highest f(max) of 18 GHz and 15 dB of power gain at 2 GHz. The high-frequency equivalent circuits of diamond MISFET are deduced from the S-parameters obtained from RF measurement.

enhanced nucleation, antenna-edge-type microwave plasma-assisted chemical vapor deposition (MPCVD) was used. Subsequently, the &lt;001&gt; selective and smoothing growth processes were conducted by conventional MPCVD. Reconstructed (2 X I) structure patterns have been observed by reflection high-energy electron diffraction (RHEED), which indicated that the surface of the diamond film is very smooth. The mean roughness is less than 2 nm in a 10-mum(2) area, as revealed by atomic force microscopy observations. (C) 2002 Elsevier Science B.V. All rights reserved.

By the field-assisted local anodization technique using an atomic force microscope (AFM), a single-hole transistor has been fabricated on an undoped hydrogen-terniinated diamond surface where p-type conduction occurs on the subsurface region. A dual side-gated FET structure has been applied to modulate the island potential in the single-hole transistor. The island size is 230 nmx230 nm, and the width of the barrier is approximately 100 nm. Measurements of the current-gate voltage characteristic at a temperature of 4.6 K show significant non-linearities including a current oscillation suggestive of single-hole transistor behavior. The oscillation that is significantly affected by the application of the side gate potential is explained by the shrinkage of the conductive island with the expansion of the depletion region. (C) 2002 Elsevier Science B.V. All rights reserved.

A 0.7-mum-gate-length metal-insulator-semiconductor field effect transistor (MISFET) was fabricated on a hydrogen-terminated diamond surface conductive layer. The maximum transconductance of 100 mS/mm was obtained by DC measurement. The cutoff frequency of 11 GRz and the maximum frequency of oscillation of 18 GHz were achieved for the fabricated MISFET biased at V-GS = 0 V and V-DS = -12 V. These are the highest values for diamond MISFETs ever reported. In the MISFET, high-frequency small-signal equivalent circuit analysis is carried out at V-GS = 0 V and V-DS = -3, -5, -8, -10 and -12 V The analysis indicates that the reduction of parasitic resistance between the source and gate is necessary for realizing higher output power. (C) 2002 Elsevier Science B.V. All rights reserved.

Cryogenic operation of the diamond surface-channel field-effect transistors (FETs) is investigated. Metal-insulator-semiconductor FETs (MISFETs) are fabricated using CaF2 as a gate insulator. MISFETs operate successfully even at 4.4 K. At low temperature, field-effect enhances the drain current, even if the surface holes become almost frozen-out. Channel mobility increases as temperature decreases to 4.4 K, which indicates the reduced phonon scattering.

Free-exciton and bound-exciton recombination radiations are observed reproducibly at different doping levels using cathodoluminescence in phosphorus-doped chemical-vapor-deposited (CVD) diamond thin films. The films are grown by microwave-plasma-assisted CVD, and are doped with phosphine during deposition. From the energy difference between free- and bound-exciton recombination radiation,, the binding energy of free excitons to neutral donors is found to be 90 meV. The intensity of bound-exciton recombination radiation decreases as the temperature increases. On the other hand. the intensity of free-exciton recombination radiation increases apparently from 80 to 150 K in samples with phosphorus-carbon concentration ratios of 200, 500, and 1000 ppm. Using the rate equation for transfer processes among free and bound excitons, the radiative process with increasing temperature is explained. The dissociated bound excitons are directly transferred to free excitons with increasing temperature.

The microwave performance of a diamond metal-semiconductor held-effect transistor (MESFET) is reported for the first time. MESFETs with a gate length of 2-3 mum and a source-gate spacing of 0.1 mum were fabricated on the hydrogen-terminated surface of an undoped diamond film grown by microwave plasma chemical vapor deposition (CVD) utilizing a self-aligned gate fabrication process, A maximum transconductance of 70 mS/mm was obtained on a 2 mum gate MESFET at V-GS = -1.5 V and V-DS = -5 V for which a cutoff frequency f(T) and a maximum oscillating frequency f(max) of 2.2 GHz and 7 GHz were obtained, respectively.

Diamond deposition on a large area silicon wafer substrate (phi 100 mm) is achieved with a methane/hydrogen plasma induced by an antenna-type coaxial microwave plasma generator. Deposition of diamond is observed over the entire substrate. Diamond precursors arc emitted radially onto a silicon substrate from the plasma sphere generated at the tip of the antenna. The possibility of diamond deposition outside the plasma sphere is discussed using a semi-empirical equation.

Diamond field effect transistors have operated in electrolyte solution for the first time. Since the hydrogen-terminated diamond surfaces are stable enough for the use as an electrochemical electrode, the diamond surface channels are exposed to the electrolyte in the transistor structure. A perfect pinch-off and saturated current-voltage characteristics have been obtained for bias voltages within the potential window. The threshold voltages are almost constant in electrolytes with different pH values of 7-13, indicating pH insensitiveness of the hydrogen-terminated diamond surface. Based on this pH insensitive: surface, ion selective regions can be fabricated to form transistor-based biosensors.

The DC operation of surface-channel metal-semiconductor field-effect transistors (MESFETs) using p-type conductive layers on hydrogen-terminated diamond surfaces is investigated by two-dimensional device simulation. As a result, a model to describe the surface semiconducting layer, in which acceptors are distributed two-dimensionally on the surface, is found to reproduce actual device characteristics well. Based on the model, the carrier (hole) concentration at a depth of 10 nm is determined to be three orders less than that at the surface. This thin channel realizes complete channel pinch-off and drain-current saturation with high transconductance, observed in the actual diamond surface-channel MESFETs. In the simulation, the transconductance of diamond surface-channel MESFETs with a self-aligned I mum gate exceeds 100 mS/mm. This result agrees well with a recent experimental result. The transconductance over 100 mS/mm can compete with that of Si metal-oxide-semiconductor field-effect transistors (MOSFETs) of the same gate length. The hydrogen-terminated diaomond surface is naturally equipped with the silicon-on-insulator-like (SOI-like) thin channel and shallow junction depth required for a nanoscale FET, such as one with a gate length of less than 50 nm.

High frequency operations of diamond field-effect transistors (FETs) on the hydrogen-terminated surface channel are realized for the first time. The cut-off frequency (f(T)) and maximum oscillation frequency (f(max)) of surface-channel diamond metal-sen-ii conductor (MES) FET with 2 mum gate length are 2.2 and 7 GHz respectively. Due to the effect of gate insulator insertion, the source-gate capacitance (C-GS) of surface-channel diamond (MIS) FET is reduced as half as that of diamond MESFETs. The 1 mum gate MISFET shows higher f(T) of 4.8 GHz and f(max) of 11 GHz in spite of comparatively low transconductance. The f(T) Of More than 20 GHz is expected at 0.5 mum gate MISFET, because transconductance of 90 mS/mm diamond MISFET with 1 mum gate length has been already demonstrated.

High transconductance and high channel mobility diamond field-effect transistors (FETs) utilizing self-aligned Sate FET fabrication process have been operated. The 2 mum gate metal-semiconductor (MES) FET shows the high frequency operation for the first time. The obtained cut off frequency f(T) and maximum frequency of oscillation f(max) are 2.2 and 7 GHz, respectively. It is expected that the diamond MESFET with 0.5 mum gate length fabricated by self-aligned gate process shows 8 GHz of f(T) and 30 GHz of f(max).

High-performance metal-insulator-semiconductor field-effect transistors (MIS FET) on hydrogen-terminated homoepitaxial diamond films are demonstrated. The gate insulator is evaporated CaF2 which does not cause interface stales. This is the first study of a CaF2/diamond MISFET fabricated by a self-aligned gate fabrication process by which the gate length and the source gate spacing are effectively reduced. The maximum transconductance is 86 mS/mm, which is the highest value in diamond MISFETs at present.

The surface order of a heteroepitaxial diamond (001) film frown on an inclined beta-SiC(001) has been evaluated with a microelectron beam in ultra-high-vacuum. It was determined that the range of order of surface dimer-rows of the heteroepitaxial diamond film is similar to 15 Angstrom.

Field-assisted local oxidation on a hydrogen-terminated (001) diamond surface was performed using an atomic force microscope (AFM). Anodic oxidation by a surface water meniscus layer is suggested to account for this oxidation process. Through the oxygenated al ca, Fowler-Nordheim (F-N) tunneling current was observed. The difference in electron affinity between the hydrogen-terminated surface and the oxygenated area was confirmed by scanning electron microscopic (SEM) observations.

Nanofabrication on a hydrogen-terminated diamond surface is performed by controlling surface adsorbates, using a scanning probe microscope (SPM) technique. Insulated areas are successfully obtained by changing hydrogen termination to oxygen termination. The Auger electron spectrum (AES) indicated the presence of oxygen adsorbed on the modified surface area. A small isolated conductive area is fabricated. and using this structure, a metal-insulator-metal (MIM) diode-like I-V characteristic is observed. Anodic oxidation using the surface water is also suggested for our experimental results. (C) 2000 Elsevier Science B.V. All rights reserved.

High-performance metal-semiconductor held-effect transistors (MESFETs) using the p-type surface conductive layer on homoepitaxial diamond are demonstrated. The maximum transconductance is 110 mS/mm, which is the highest value ever reported in diamond FETs. This value exceeds the normal transconductance of a Si-metal-oxide semiconductor field-effect transistors (MOSFET) with equivalent gate length: The transconductance of the present diamond FETs is proportional to the reciprocal of gate length. Accordingly, the characteristics can be improved by the refinement of gate length. By using an appropriate FET fabrication process, it is expected that the transconductance of a diamond MESFET exceeds 500 mS/mm at gate lengths less than 0.2 mu m.

Metal-oxide-semiconductor field effect transistors (MOSFETs) with a surface p-channel have been fabricated on hydrogen-terminated diamond (001) surfaces without doping. The maximum transconductance of the device with the gate length of 6 μm is 16 mS/mm, which is the highest in diamond MOSFETs and comparable to that of silicon n-channel MOSFET with the same gate length. The relatively high transconductance is due to the low density of surface states on hydrogen-terminated diamond. The diamond MOSFETs operate at the temperatures of up to 330°C in air without any passivation of the device surfaces.

MOSFETs on polished polycrystalline diamond surfaces have been fabricated. The best transconductance is 1.0mS/mm. The breakdown voltages of these FETs are over 200V, comparable to those reported in homoepitaxial diamond MESFETs. A polycrystalline diamond FET is a candidate for sensors in hard environment, due to its feasibility in large-area wafers. © 1999 Elsevier Science S.A.

Hydrogen-terminated diamond surfaces exhibit p-type conduction without doping impurities. The surface conductive layers possess a suitable thickness of similar to 10 nm for FET channels. The present work describes the fabrication of high-performance MESFETs and MOSFETs using the surface conductive layers on hydrogen-terminated homoepitaxial CVD diamond films. In the case of MESFETs, both enhancement-mode (normally off) and depletion-mode (normally on) operations are realized by selecting the gate metals. In the case of MOSFETs, depletion-mode operation is realized at present. The best transconductances in diamond are obtained in both MESFETs and MOSFETs. In addition, the de operation of the diamond surface-channel FETs has been evaluated with device simulations using several models for the surface conductive layer. Consequently, a model with accepters distributed two-dimensionally on the surface reproduces the actual I-V characteristics. Moreover, based on the model, the de performance of self-aligned 1-mu m-gate MESFETs not realized in diamond has been simulated. As a result, their transconductances exceed 100 mS-mm(-1). (C) 1998 Scripta Technica.

The effect of an inclined substrate on heteroepitaxial diamond has been investigated on 4 degrees off beta-SiC(001) tilted around the [&lt;(1)over bar10&gt;] axis. Homogeneous macro steps with (001) terraces are observed in the [&lt;(1)over bar10&gt;] direction forming, a vicinal angle of 3 degrees-4 degrees from the (001) surface reflecting the substrate inclination. The selective growth is effective even if the dominant orientation is inclined by several degrees from the surface normal, The tilt deviation is less than 1 degrees in the heteroepitaxial film. p-channel field effect transistors have been fabricated on these heteroepitaxial films. The device performance is as good as that on homoepitaxial films. (C) 1998 American Institute of Physics.

High-performance MESFETs and MOSFETs have been fabricated on hydrogen-terminated surfaces of homoepitaxial diamond films prepared by chemical vapor deposition (CVD). Both enhancement and depletion-mode MESFETs have been obtained with the best transconductances of 10mS/mm in enhancement mode and 12mS/mm in depletion mode. Depletion-mode MOSFETs have been also realized with the best transconductance of 16mS/mm utilizing evaporated SiOx as gate insulator. The de performance of the devices using the hydrogen-terminated diamond surfaces has been evaluated by two-dimensional drift-diffusion device simulations using several models of surface channels on the hydrogen-terminated surfaces. Consequently, a realistic surface-channel model has been obtained. Based on the model, the simulations for self-aligned-1 mu m-gate devices have been also carried out to predict the operation of smaller diamond devices not realized in diamond at present. Their transconductances exceed 100mS/mm.

High-performance metal-semiconductor field-effect transistors (MESFETs) have been fabricated using p-type surface semiconductive layers on hydrogen-terminated surfaces of homoepitaxial CVD diamond films. In addition, their de operation has been evaluated by device simulations to investigate the device operation mechanism. The fabricated MESFETs have been operated in both enhancement and depletion modes by selecting the electronegativity of the gate metal. The MESFETs exhibit complete channel pinch-off and drain-current saturation. The best transconductance for each mode of MESFETs exceeds 10 mS/mm with a gate length of 3-7 mu m. In the device simulations, a model of the surface semiconductive layer in which accepters are distributed two-dimensionally on the surface reproduces well the actual de characteristics. Based on this model, the simulations for a gate length of 1 mu m have also been carried out to predict the operation of smaller devices. It was found that their transconductances exceed 100 mS/mm.

Using the p-type surface-conductive layer of diamond film, enhancement mode and depletion mode metal-semiconductor field effect transistors were fabricated on the same surface by changing the metals of the gate electrode. The threshold voltages of p-type metal semiconductor field effect transistors (MESFETs) can be controlled from negative (enhancement mode) to positive (depletion mode) as the electronegativities of gate metals increase. By the realization of high transconductance and the fabrication of enhancement and depletion mode MESFETs; the E/D-type logic circuits such as inverter; NAND and NOR circuits were fabricated for the first time.

The operation of high-performance diamond MESFETs using thin p-type surface semiconductive layers of undoped hydrogent-erminated CVD diamond films has been simulated. We have used diffusion profiles of shallow accepters to describe the surface conductive layer. In order to describe metal/hydrogen/diamond interfaces, we have assumed an incomplete contact model where an atomic scale gap (similar to 0.5 nm) is inserted between the metal and the diamond. The results of this model have been compared with those obtained from direct metal/diamond contact model. The experimental I-V characteristics have been realized with acceptor density of 1 x 10(13) cm(-2), and the transconductance per unit gate width of diamond MESFETs with 1 mu m gate length is predicted to be nearly 50 mS mm(-1) by using both complete and incomplete contact models. (C) 1997 Elsevier Science S.A.

We have deposited epitaxial diamond films with very low angular spread on epitaxial beta-phase silicon carbide layers on silicon (001) substrates. From x-ray rocking curve measurements, half-widths of the angular spread of the crystal orientation as low as 0.6 degrees have been determined, which is the smallest value ever reported in heteroepitaxial diamond films and appears to be smaller than those of the beta-phase silicon carbide underlayers. The him surface exhibits a roughness of about 100 nm with very few discernible boundaries due to misorientation. The optimization of the bias-enhanced nucleation process and the control of selective growth are the main factors for the improvement of the crystallinity. (C) 1997 American Institute of Physics.

Surface morphology of continuous heteroepitaxial diamond layers on beta-SiC (001) has been characterized by various methods. From surface normal SEM images, the surface was so smooth that crystal boundaries were not clearly observed, but in AFM and Normarski optical microscope images, shallow gaps supposed to be remnant boundaries and wrinkles on the surfaces were observed. On the other hand, isolated (001) surfaces before coalescence had no wrinkles and were smoother than the surface of continuous heteroepitaxial films. The wrinkles observed only on the continuous heteroepitaxial film are considered to be formed by strain caused by coalescence, and raise the new problem of heteroepitaxy when the degree of orientation is improved. (C) 1997 Elsevier Science S.A.

Using the p-type surface-conductive layer of diamond film, enhancement mode and depletion mode MESFETs have been fabricated by changing the metals of the gate electrode. The threshold voltages of MESFETs depend on the electronegativity of the metals. A MESFET with a Cr gate was operated in depletion mode and exhibited a peak transconductance of 12.3 mS mm(-1), which is the highest in diamond FETs. This high performance can be obtained by a self-aligned gate fabrication process, which minimizes the spacing between the ohmic contacts and the Schottky contact. By utilizing an E-MESFET for the driver and a D-MESFET for the active load, E/D-type logic circuits such as NOT, NAND and NOR circuits have been fabricated for the first time. (C) 1997 Elsevier Science S.A.

The change in electron affinity and the se-ordering of the diamond surface upon annealing of a homoepitaxially grown diamond (100) thin film were investigated by ultraviolet photoemission spectroscopy, low energy electron diffraction (LEED), and Auger electron spectroscopy. When the sample was heated to similar to 1250 degrees C, the electron affinity of the sample changed from negative to positive and the LEED pattern changed from (2 x 1/1 x 2) to (1 x 1). When the sample was further annealed at similar to 900 degrees C, the electron affinity and the LEED pattern reverted to negative and (2 x 1/1 x 2) respectively. The sample was then heated to similar to 1100 degrees C, followed by annealing at similar to 900 degrees C again, and the same phenomenon was observed. These observations were considered to be associated with the disordering/re-ordering behavior of the diamond surface upon annealing.

Isolated metal-semiconductor field effect transistors (MESFETs) have been fabricated on homoepitaxial diamonds grown by microwave plasma chemical vapor deposition. Source, drain and channel regions are fabricated using the surface p-type semiconductive layer unique to hydrogen-terminated diamond surfaces. Other areas are irradiated by an argon beam to obtain highly resistive regions. The maximum transconductance of the isolated MESFETs with 7 mu m gate length is 4.5 mS/mm, which is comparable to that of silicon MOSFET with the same gate length. NOT, NAND, NOR, and R-S flip-flop circuits have been fabricated for the first time on diamond using enhancement-mode active loads.

STM with STS has been employed to acquire the information on the electronic structure of H-terminated homoepitaxial diamond (001) and (111) surfaces. The STS spectra for (001) and (111) surfaces reveal the existence of surface state near the top of valence-band states. It is suggested that this surface state is responsible for the formation of p-type surface semiconductive layers.

In this study, we have observed dominant free-exciton (FE) recombination radiation from chamber frame (CF) diamond. Since CF diamond is extremely purr, in the Ct. spectra of the edge emission we have observed the FELO emission rarely observed in diamond grown by means of a conventional microwave plasma-assisted CVD method. The intensity ratio of the FETO over the band A is 58.5. This high crystallinity of CF diamond is hardly destroyed by the electron beam. In the CF method, when the reaction pressure is a little larger than atmospheric pressure. pure crystals can be obtained.

Metal-semiconductor field-effect transistors (MESFETs) have been fabricated using the p-type surface-conductive layer of diamond film. The surface-conductive layers have been employed as the channel of MESFETs. Since that surface-conductive layer is ultrathin, these MESFETs exhibit the enhancement mode in the gate metal with high Schottky barrier hight. These MESFETs exhibit channel pinch-off, complete current saturation, and the highest transconductance in diamond FETs. The device isolation has been carried out by insulating surface-conductive layer except for channel with exporsure of Ar+. With this technique, the fabrications of diamond logic circuits and memories (NAND, NOR, NOT, and RS flipflop) are demonstrated for the first time.

Undoped hydrogen-terminated CVD diamond films are known to have thin p-type surface semiconductive layers. Enhancement mode MESFETs were fabricated utilizing these layers. In this simulation, we estimated the hole concentration and the channel depth of the surface layer We have evaluated that the channel depth of the surface semiconductive layer is approximately 22nm (the diffusion length, 11nm), and the surface acceptor concentration is 1.0 x 10(10)/cm(3). By evaluating the more accurate hole concentration of the thin p-type semiconductive layer, we may predict the performance of diamond electronic devices having submicron-gate.

Surfaces and interfaces of hydrogen-terminated diamonds are reviewed. The control and preparation of diamond surfaces have been greatly advanced by the recent progress in epitaxial growth, which is discussed in Section 2. In Section 3, the hydrogen-terminated surfaces of (111) and (001) are explained in terms of types of hydrides, surface reconstructions, stability of surface C-H bonds, and surface p-type conduction. In Section 4, metal/diamond contacts are reviewed. Schottky and ohmic properties are discussed on the basis of hydrogen termination, surface treatment, metal electronegativity, interfacial reaction, and surface states. The first application of hydrogen-terminated surfaces as electron devices is presented for the metal-semiconductor field effect transistor.

The 2X1/1X2 surface reconstruction of a homoepitaxial diamond (001) surface has been examined using a scanning tunneling microscope at an atomic scale and reflection electron microscopy at a macroscopic scale. The monohydride dimer, which is a unit of the surface reconstruction, has a symmetric structure. These monohydride structures contribute to the surface p-type conduction in undoped films. The surface is composed of elongated dimer rows. Antiphase boundaries have been observed, which is indicative of low-temperature epitaxy where surface migration is limited. Macroscopic surface flatness has been improved during the growth stage in the presence of oxygen and boron which enhance migration.

Negative substrate-bias effects on diamond heteroepitaxial nucleation have been investigated using microwave plasma-assisted chemical vapor deposition. The density and the percentage of azimuthally ordered particles grown on carburized Si(001) or on high-quality beta-SiC(001) have been estimated by varying the bias-treatment conditions (reaction pressure, microwave power and bias voltage). The percentage of azimuthally ordered particles increases under the following conditions: pressure of 50 Torr, substrate temperature of similar to 900 degrees C and bias voltage of -50 V. Smooth heteroepitaxial diamond films of similar to 4 mu m thickness have been successfully synthesized on high-quality beta-SiC(001) by the bias treatment under the above conditions followed by a two-step growth process: [001] fast growth and [111] fast growth. The initial growth of these films has been governed by the Volmer-Weber mode, where [($) over bar 110]- or [110]-directed protrusions have been formed on beta-SiC(001). Diamond islands grew along the grooves between the beta-SiC protrusions in the initial stage.

Metal-semiconductor field-effect transistors (MESFETs) have been fabricated using the p-type surface-conductive layer of undoped homoepitaxial diamond film on the surface. The layers have been employed as tile channel of MESFETs. Since the surface-conductive layer is ultrathin, the depletion region has already closed the surface-conductive channel at the gate voltage of 0 V i.e., these MESFETs exhibit the enhancement mode (normally off-mode). The threshold voltages are -1.6V and -0.7V in the case of Al and Pb gate respectively. These MESFETs also exhibit channel pinch-off and complete saturation of drain current, and high transconductance of 2.5 mS/mm at room temperature. This value is the highest of all diamond FETs at present. enhancement/resistor (E/R) inverters with the enhancement mode transistor and resistor, and direct coupled enhancement/enhancement (E/E) inverters with the two enhancement mode transistors have been also fabricated. This E/R inverter exhibits high voltage gain. For a E/E inverter, the voltage gain has also been measured as a function of frequency. The high 3-dB frequency (f(H)) is above 2 MHz. The voltage gain at frequency =f(H) (Hz) is equal to 1/root 2 the voltage gain at freyuency=0(Hz).

Tungsten carbide (WC) layers have been grown epitaxially on tungsten single crystals for the first time by using microwave plasma and electron cyclotron resonance plasma carburization of single-crystalline tungsten. WC on tungsten is grown epitaxially as (0001)WC//(110)W in the alignment [1 (2) over bar 10]WC//[(1) over bar 11]W.

Both positive and negative bias effects on the nucleation of chemical vapor deposition (CVD) diamond have been investigated thoroughly in microwave plasma. Prior to the conventional microwave plasma CVD growth of diamond, positive or negative biasing pretreatment has been performed. The pretreatment conditions were varied in terms of substrate bias voltage ( -100∼+100 V), pretreatment pressure ( 0.2∼15 Torr), and methane fraction ( 2∼40%) in hydrogen source gas. It is found that the positive substrate bias as well as the negative bias are effective for the nucleation of diamond.

As-grown homoepitaxial diamond surfaces fabricated by chemical vapor deposition are terminated by hydrogen, and are expected to have a low density of surface states. On such diamond surfaces, high-quality Schottky contacts have been obtained utilizing metals with low electronegativities, such as Al or Pb. The ideality factors of those point contacts to diamond are less than 1.1, which is the nearest value to unity ever reported in diamonds. Quantitative measurements of Schottky barrier heights at various metal contacts have also been performed. A strong correlation between the barrier heights and the metal electronegativities is observed. Even an ohmic property is obtained when metals with higher electronegativities were used. The effect of Fermi level pinning is reduced at the interfaces between metals and hydrogen-terminated diamonds.

Dominant free-exciton (FE) recombination radiation has been obtained from high-purity Chemical vapor deposition (CVD) diamond synthesized on Cu substrates by means of microwave plasma CVD using CH₄+O₂ diluted with H₂. The intensity of FE emission is almost constant between 80 K and 170 K, and is reduced by two orders of magnitude at room temperature. The emission increases in proportion to the incident beam current from 1× 10^-9A to 2× 10^-6A. The spectrum shapes between 200 nm and 600 nm do not depend on the beam current. In addition, the isotopic effect on the FE emission peak shift has been observed in the spectrum from ¹³C-enriched (96.6%) CVD diamond for the first time.

Scanning tunneling microscopy (STM) has been employed in the observations of chemical vapor deposited (CVD) homoepitaxial diamond (111) surfaces. The surfaces are composed of an H-terminated $1\times 1$ structure. Single-atom height steps on the surfaces are observed to be very straight and form a downward slope in the [$11\bar{2}$] direction. Some adsorbates different from the H-terminated monohydride structure have been found on each terrace. We speculate that these adsorbates are CH3.

We present a new technique for providing nuclei for diamond formation on nondiamond substrates and its application to the growth of diamond on a Cu substrate by chemical vapor deposition (CVD). This is a predeposition process in which the substrate is immersed in a CH4/H2 plasma formed by electron cyclotron resonance at a low pressure (0.1 Torr). The technique provides possibilities of nucleation over an increased area at temperatures lower (about 500°C) than usual, as well as improved process controllability. The grown diamonds on Cu exhibit a morphology significantly different from that of diamonds grown on Si.

At the low pressure of 0.1 Torr, we have controlled the plasma potential during diamond deposition for the first time using a magneto-microwave plasma chemical vapor deposition (CVD) system. The potential difference between plasma and substrate is an important factor for fabrication of diamond at this pressure. By lowering the plasma potential, high-quality diamond films have been formed. The films were evaluated by scanning electron microscope (SM) imaging, electron diffraction and Raman spectroscopy.

The effect of 20 MeV electron and neutron irradiation on the cathodoluminescence (CL) spectra of nitrogen-doped CVD diamond has been investigated. The center called 5RL and the center with a zero-phonon line at 3.19 eV (389 nm) are induced by irradiation alone. The center with a zero-phonon line at 2.16 eV (575 nm) has been formed by annealing at 900°C subsequent to the irradiation. The distributions of these centers have been revealed by CL imaging.

At a low temperature of 500°C, we have formed diamond films on Al substrates at 0.1 Torr using a magneto-microwave plasma CVD system. Since diamond can be formed at the low pressure of 0.1 Torr, the important parameters for diamond formation such as the plasma density during the diamond deposition can be measured and is found to be the highest ($2.1\times 10^{11}$ cm-3) at ECR condition. Above $1\times 10^{11}$ cm-3, using a (CH$_{4}+$CO2)/H2 mixture, which is a suitable reaction gas for low-temperature diamond formation, high-quality diamond films have been obtained at temperatures as low as 500°C and at low pressure (0.1 Torr) on Al.

Diamond films have been obtained using magneto-microwave plasma assisted CVD at 0.1 Torr. The reaction gas is a CO/H2 mixture. By setting the ECR condition at the deposition area, a high density plasma ($1\times 10^{11}$ cm-3) is obtained around the substrate. The discharge area is quite uniform in the pressure. Diamond films are obtained on positively biased substrates. As the reaction pressure becomes lower, the substrate temperature for the diamond formation tends to decrease. The films were evaluated by SEM imaging, electron diffraction and Raman spectroscopy.

Large area chemical vapour deposition of diamond has been obtained using magneto-microwave plasma. The important point of the developed system is to set the electron cyclotron resonance condition (875 G), where the highest plasma density is expected, at the deposition area by controlling the distribution of an applied magnetic field. Even in 10 Torr where complete electron gyrations cannot be expected, the size of the discharge area controlled by the magnetic field is 70–80 mm in diameter. This value is the largest of all plasma deposition systems of diamond. The crystallinity obtained by the above-mentioned plasma compares favourably with those of the best ones by previous methods.

The properties of diamond are ascribed to C-C sp³ bondings from the point of chemical bonding. Diamond-like carbon (DLC) thin film is defined as a carbon film which is composed of chiefly C-C sp³ bondings. The characteristics of DLC films are approaching those of diamond crystals. DLC films have been formed in non-equilibrium states such as plasma processes, because sp² bondings are stable under atomospheric pressure and ordinary temperature.<BR>Among plasma processes, we have concentrated on reactive sputtering which is distinguished from usual physical sputtering. In reactive sputtering deposition, H radicals are thought to sputter graphite target chemically and deposit sp³ rich thin films selectively on substrates. We have also discussed characterization techniques which are applied to distinguish the chemical bondings and the micro structures in DLC thin films.

Structures and defects of heterogeneous interfaces have been discussed using the concept of "coherency"which has been applied to interphase boundaries. Interfacial structures have been classified into three kinds, coherent, semicoherent and incoherent interfaces, depending on lattice mismatch. As a case study of the interface with great mismatch of about 10%, the structure of PtSi/ (111) Si interface has been discussed in detail on the basis of HRTEM images. The interface has been found to be atomically abrupt and has atomic steps which increases local coherency between PtSi and Si. (J. Cryst. Soc. Jpn. 28, 151 (1986) ) .

The effect of Pt concentration in Pd thin films on the nucleation and growth of PdSi and PdxPt1-xSi (ternary monosilicide) has been investigated by transmission electron microscopy (TEM). Low concentration of Pt (10 at. %) in Pd film enhances PdSi formation at lower temperature than previously reported. It has been proposed that PdSi formation is governed by its slow nucleation. However, in our studies, the nucleation of PtSi, which is substituted for that of PdSi, triggers the subsequent PdSi growth at low temperatures. High concentration of Pt (55 at. %) in Pd-Pt alloy film lowers the temperature of the phase transformation from metal-rich silicide to monosilicide (PdxPt1-xSi). The temperature is the same as that of PtSi formation. In both cases, the monosilicide layers (about 20 nm) have an epitaxial relationship with (111) Si substrates.

The interface structure between PtSi and (111)Si has been clarified on an atomic scale for the first time, using a 1 mv high-resolution electron microscope. At the interface the transition from the PtSi lattice to the Si lattice is abrupt without the formation of any extra phase. Lattice fringe images show that the interface is heavily undulated and has atomic steps. Large lattice mismatch between PtSi and Si generates these atomic steps and extra half planes of PtSi. The observed relationship between the slope of the interface and the number of extra half planes can be explained by a simple model. © 1984 The Japan Society of Applied Physics.