Katsuki Kusakabe

Heteroepitaxial growth of diamond on an iridium (100) substrate using microwave plasma-assisted chemical vapor deposition

Abstract An iridium (100) layer was epitaxially coated on a MgO (100) plate by sputtering at 1123 K, and was then utilized in the formation of diamond by microwave plasma-assisted chemical vapor deposition (MPCVD) using methane as the carbon source. The electric contact between the substrate and holder was confirmed by coating the entire MgO surface with iridium. The iridium substrate was then treated by bias-enhanced nucleation under optimized conditions. It was found that diamond particles formed by MPCVD were essentially oriented to the iridium substrate. The diamond particles were then grown to the 〈100〉 and further to the 〈111〉, and a smooth diamond film was obtained. The full width at half maximum of the (400) rocking curve of the diamond film was 0.16°, which was close to that of a diamond single crystal.

Development of a Microchannel Catalytic Reactor System

The purpose of this article is to demonstrate the applicability of microreactors for use in catalytic reactions at elevated temperatures. Microchannels were fabricated on both sides of a silicon wafer by wet chemical etching after pattern transfer using a negative photoresist. The walls of the reactor channel were coated with a platinum layer, for use as a sample catalyst, by sputtering. A heating element was installed in the channel on the opposite surface of the reactor channel. The reactor channel was sealed gas-tight with a glass plate by using an anodic bonding technique. A small-scale palladium membrane was also prepared on the surface of a 50-Μm thick copper film. In the membrane preparation, a negative photoresist was spin-coated and solidified to serve as a protective film. A palladium layer was then electrodeposited on the other uncovered surface. After the protective film was removed, the resist was again spin-coated on the copper surface, and a pattern of microslits was transferred by photolithography. After development, the microslits were electrolitically etched away, resulting in the formation of a palladium membrane as an assemblage of thin layers formed in the microslits. The integration of the microreactor and the membrane is currently under way.

Surface morphology and electrical properties of boron-doped diamond films synthesized by microwave-assisted chemical vapor deposition using trimethylboron on diamond (100) substrate

Prime novelty: The smoothness of the synthesized boron-doped diamond was improved by the pre-treatment of a hydrogen plasma. Moreover, the Hall mobility also increased with this pre-treatment. n nSurface morphology and electrical properties, such as electrical conductivity, hole concentration and Hall mobility, were investigated for boron-doped diamond films, which were synthesized by microwave-assisted chemical vapor deposition (MPCVD) on a (100) diamond substrate. Trimethylboron (TMB) was used as a dopant source and methane (CH4) was used as a carbon source. The morphology of the synthesized diamond surface depended on the MPCVD conditions such as TMB and CH4 concentrations in the gas phase, and lower concentrations of TMB and CH4 lead to a smoother surface. When the substrate was treated in a hydrogen plasma, the electrical properties of the boron-doped diamond films, as well as the smoothness of the surface, were improved. After optimizing the synthesis conditions, Hall mobility reached to 2020 cm2 V−1 s−1 at 243 K for a diamond film with a hole concentration of 5×1012 cm−3.

Electrical properties of boron-doped diamond films synthesized by MPCVD on an iridium substrate

Abstract Boron-doped diamond films were synthesized on an iridium substrate by microwave plasma-assisted chemical vapor deposition, using trimethylboron as the dopant source. The Ir substrate was bias-treated by the constant-current mode to permit the formation of oriented diamond nuclei. In order to isolate the B-doped diamond layer electrically from the Ir substrate, the non-doped diamond particles that were formed were grown in the 〈1xa00xa00〉 and then 〈1xa01xa01〉 directions and finally, a B-doped layer was synthesized to give a B/C ratio of 100–400 ppm. Surface morphology, Hall mobility and hole concentration were investigated for the resulting B-doped diamond films. The Hall mobility was closely related to the surface morphology of the diamond films. After optimizing the synthesis conditions, a Hall mobility of 340 cm−2xa0V−1xa0s−1 and hole concentration of 2×1010 at 250 K was obtained for a heteroepitaxial B-doped diamond film synthesized at a B/C ratio of 200 ppm. These values are smaller than previously reported values for homoepitaxial B-doped diamond film.

Development of a Self-Heating Catalytic Microreactor

Microchannels were fabricated on the both sides of a (100) silicon wafer by wet chemical etching, after pattern transfer using a negative photoresist. The channel (upper width = 600 μm, lower width = 515 μm, depth = 60 μm, and length = 78 mm) on one side was used as a reactor. A heating element (Pt wire) was installed in the channel on the opposite surface of the reactor channel, and a thermocouple was installed in a channel adjacent to the reactor. A thin platinum layer was coated as a catalyst on the walls of the reactor channel by sputtering. In order to increase the surface of the catalyst, a γ-alumina support layer was formed in the reactor channel by a sol-gel process. The reactor channel, as well as the heating channel on the reverse side, was then sealed so as to be gas-tight with glass plates by an anodic bonding technique. A solution of H2PtCl6 was introduced into the reactor channel with the γ-alumina layer, and platinum was loaded on the support. Both platinum catalysts, prepared by sputtering and impregnation techniques, were activated in a flow of hydrogen at 773 K. The self-heating microreactor was then used for the hydrogenation of benzene as a model reaction. The reaction rate of the supported catalyst was one order of magnitude higher than that of the sputtered catalyst.

Preparation of MicroChannel Palladium Membranes by Electrolysis

A negative resist was spin-coated on the surface of a 50-μm thick copper plate and solidified as a protective film. A palladium layer was then electrodeposited on the other uncovered surface. After removing the protection film, the resist was again spin-coated on the copper surface, and a pattern of microslits was transferred. After development, the microslits were anodically etched out. The final result was a palladium membrane, formed as an assemblage of thin layers in the microslits. The H2/N2 separation factor through the palladium membranes was dependent on the electrodeposition conditions employed. The flux of H2 through the palladium membrane formed with a current density of 40 mA cm-2 at an electrolysis temperature of 45°C was 0.06 molm-2 s-1 (H2 pressure on the feed side = 0.1 MPa), and a H2/N2 ideal separation factor was 2000 at a permeation temperature of 300°C