Kazuo Higuchi

SnS thin film solar cells with Zn1−xMgxO buffer layers

The conduction band offset (CBO) of SnS as the light absorbing layer and Zn1−xMgxO as the buffer layer in SnS thin film solar cells has been optimized to improve the solar cell conversion efficiency. We controlled the CBO experimentally by varying the Mg content (x) of the Zn1−xMgxO layer. The optimum CBO value range for improved solar cell performance was determined to be from −0.1 to 0 eV. A SnS thin film solar cell sample with the optimum CBO value exhibited conversion efficiency of approximately 2.1%.

Tribological characteristics of polycrystalline diamond films produced by chemical vapor deposition

Effects of surface roughness and crystallinity of polycrystalline diamond films on their tribological characteristics, as well as the effects of test environment, have been investigated. Friction and wear characteristics of the diamond films deposited on sintered SiC disks have been examined with a ball-on-disk tester in the absence of any lubricant. The friction coefficients of polished diamond films against SiC and Si 3 N 4 balls were below 0.10 at room temperature while those of as-deposited films were around 0.20. The specific wear of counterparts on the polished film was five orders of magnitude smaller than on the as-deposited film. The friction coefficient between the polished diamond film and a AISI 52100 steel ball was about 0.20. Transfer of a small amount of AISI 52100 material to the diamond film was observed along the wear track of the polished diamond surface. Diamond films of high quality were more resistant to wear than the ones of low quality. On the other hand, the friction coefficients were not affected by the crystallinity of the diamond films in the present study. Tribological characteristics of the diamond films deteriorated with increasing sliding speed and ambient temperature. At 600 °C in dry N 2 , the friction coefficient of diamond films against a SiC ball was about 0.8, which was about ten times higher than that at room temperature in air.

Selected area diamond deposition by control of the nucleation sites

Abstract In the present study, it has been demonstrated that the critical nucleus size of hot-filament chemical vapour deposition diamond is less than 5 nm, by depositing diamond on ultra-fine diamond particles with a mean particle size of 5 nm. Diamond nucleation sites were also investigated by means of deposition on several Si substrates pre-treated in different ways; sonication with diamond powders of different sizes and ion implantation onto the substrates. The nucleation sites were thought to be micro-flaws and/or the residual “diamond dust” on the substrate. An adequate ion implantation has been found to destroy the nucleation sites. It has been further demonstrated that diamond deposition on selected areas is possible by control of the nucleation sites; selected area diamond seeding or ion implantation onto selected areas of the substrate pre-treated with diamond powders.

Large-area diamond deposition and brazing of the diamond films on steel substrates for tribological applications

Abstract Diamond films were successfully deposited on molybdenum substrates as large as 100 mm in diameter at a high deposition rate of 30 μm h −1 by the r.f. induction thermal plasma chemical vapour deposition (CVD) method. Besides the uniformity of the film thickness, the surface morphology and the film quality were confirmed to be homogeneous over the deposited area by scanning electron microscopy and Raman spectroscopy. Self-standing diamond films of 30 mm diameter were obtained when the films were deposited on mirror-finished molybdenum substrates by the r.f. thermal plasma CVD method. One of the self-standing diamond film surfaces (originally substrate side) was as smooth as the mirror-finished substrate surface. The self-standing diamond films were brazed in vacuum on steel substrates so that the smooth surface of the film became the top of the brazed materials. The adhesive strength of the brazed diamond film on the steel substrate was found to be rather high, and the as-brazed diamond film with the smooth surface had a low friction coefficient of 0.1 against steel and a high wear resistance without oil lubrication in an ambient atmosphere.

Frictional properties of chemical vapor deposited diamond thin films

Abstract Diamond thin films deposited on sintered SiC by the hot filament CVD method were subjected to ball-on-disk friction and wear test with a SiC ball in an ambient atmosphere. The friction coefficient of the diamond film with smooth surface was about 0.09 and effectively no wear was detected.

Improved Performance of Solid-State Dye-Sensitized Solar Cells with CuI: Structure Control of Porous TiO2 Films

By increasing the pore and particle size of porous TiO2 films, the photovoltaic properties of solid-state dye-sensitized solar cells were dramatically improved. We analyzed the relation between the photovoltaic property and the microstructure of TiO2/Dye/CuI measured by scanning electron microscopy of the cross section of the cells. The larger pore size of the TiO2 films improved the CuI filling and the high degree of filling improved the short-circuit current density. Multilayered TiO2 films consisting of a TiO2 layer with small TiO2 particles and a second layer with larger TiO2 particles gave a power conversion efficiency under 1 sun of 6.0%.

Large-Area High-Speed Diamond Deposition by Rf Induction Thermal Plasma Chemical Vapor Deposition Method

By introducing methane as a sheath gas and by reducing the reactor chamber pressure to 150 Torr in an rf induction thermal plasma chemical vapor deposition (CVD) method, a large volume of the thermal plasma was stabilized and elongated to reach far into the reactor chamber where a molybdenum substrate was placed. This made it possible to deposit diamond films uniformly on a substrate as large as 100 mm in diameter at a high deposition rate of 30 µm/h. This deposition area is the largest one of diamond films ever deposited by the rf induction thermal plasma CVD method.

In situ process monitoring during multistage coevaporation of Cu2ZnSnS4 thin films

A multistage coevaporation process for the direct growth of Cu2ZnSnS4 (CZTS) thin films without additional atmospheric sulfurization was investigated. To obtain reproducible CZTS films, in situ process monitoring of the film growth was developed by measuring the apparent substrate temperature (Tpyro) using a pyrometer. After CZTS depositions terminated at various endpoints, ex situ characterization of the film properties was performed to clarify the growth mechanism of the films. The results provided clear evidence that CZTS phase formation was significantly delayed via re-evaporation of Sn–S-based compounds in the early part of the first stage, leading to the initial formation of a dominant (CuS + ZnS) structure that coexisted with a small amount of CZTS. CZTS phase formation was then facilitated by the (CuS + ZnS) precursor via a Cu-rich to Cu-poor sequence with an apparent variation in Tpyro during the second stage, and the slightly segregated CuS phase was nearly consumed under (Zn + Sn + S) fluxes. C...

Determination of Elastic Constants of Pentaerythritol Crystal by Ultrasonic Method

The seven elastic constants, Cij, and the elastic compliances, Sij, of the tetragonal pentaerythritol single crystal are determined from the sound velocity measurements by the ultrasonic pulse method at room temperature. The elastic constants obtained are; C11=40.5, C12=26.6, C13=10.5, C16=3.13, C33=13.9, C44=2.74 and C66=2.52 (in unit of 1010 dyn/cm2). The linear compressibilities of the pentaerythritol crystal are calculated from these elastic constants. The compressibility along (001), β(001), is 6.48×10-12 cm2/dyn, and also β(010)=β(100) are 0.48×10-12 cm2/dyn.

Control of interfacial charge-transfer interaction of dye and p-CuI in solid-state dye-sensitized solar cells

We systematically investigated the photovoltaic and absorption characteristics of solid-state dye-sensitized solar cells with CuI to elucidate the impact of the interaction between the dye and CuI. For the ruthenium complex N719, the incident photon-to-current conversion efficiency (IPCE) on the longer-wavelength side decreased owing to the change of the metal-to-ligand charge transfer (CT) of N719 due to the interaction between the thiocyanate groups of N719 and CuI. In contrast, when D149 — which included rhodanine groups — was used, the interaction with CuI and the resultant CT increased the IPCE. The results provide a new strategy for improving the photovoltaic performance by controlling the interfacial CT between the dye and CuI.