Jun Shioya

Properties of AsF5-intercalated vapor-grown graphite

Abstract Vapor-grown carbon fibers prepared from benzene were heat treated at high temperature (over 3000 °C). Their electrical conductivities consequently increased one order of magnitude and became comparable to those of HOPG and natural graphite. Furthermore, graphite compounds with very high electrical conductivity (9 × 10 5 S/cm) were produced by intercalation of AsF 5 . High electrical conductivities above 1 × 10 5 S/cm were reproducibly obtained by both high-temperature treatment and AsF 5 -intercalation of vapor-grown carbon fibers. AsF 5 -intercalated vapor-grown graphite fibers were relatively stable in air. It was found that AsF 5 predominantly entered these fibers from their ends.

Electronic structure of polysilole and related compounds

The electronic structures, in the optimized geometries, of polysilacyclopentadiene (polysilole), polygermacyclopentadiene, and silole-thiophene alternating copolymer, have been studied theoretically using the one-dimensional tight-binding self-consistent field crystal orbital (SCF-CO) method. It has been found that the band gap values of these polymers are slightly smaller than those of the ordinary five-membered polyheterocycles such as polythiophene. The larger σ-polarized nature between the Group IV atom and the carbon atom might be expected to exhibit a different behaviour, compared with polythiophene, when they are doped with ann-type dopant.

Preparation and properties of graphite grown in vapor phase

Abstract Preparation conditions and the electrical conductivity of carbon films prepared by plasma induced chemical vapor deposition (plasma CVD) of benzene were studied. It was found that the maximum electrical conductivity of carbon films was obtained when the benzene flow rate was 7 ml/hr, the substrate was stainless-steel, the substrate temperature was 1000°C and the plasma power was 40 W. The carbon films were heat-treated at various temperatures between 1500°C and 3300°C and the structure of the film obtained was analyzed by X-ray diffraction analysis and Raman spectroscopy. It was found that the carbon film prepared by plasma CVD could be graphitized at lower temperature than ordinary pyrolytic carbons. The graphite film which was obtained by the high temperature treatment (HTT) of the carbon films at 3300°C has the electrical conductivity of 2.1 × 10 4 S/cm. The highest electrical conductivity of AsF 5 intercalated graphite films was 9 × 10 5 S/cm. The stability of AsF 5 intercalated graphite films was also examined.

Electronic structure of ladder polysilane and related compounds

Abstract Electronic structures in the optimized geometries of polycyclotetrasilane, polycyclotetragermane and their alternating copolymer are studied theoretically using the one-dimensional tight-binding self-consistent-field crystal orbital (SCF-CO) method. These polymers have anti and syn ladder structures. The results show that anti -configurations are energetically favorable for these polymers and that anti -conformers have smaller bandgap values and greater σ-conjugation than syn -conformers.

Preparation and properties of highly conductive graphite intercalation compounds obtained by vapor deposition

Abstract Graphite films and fibers obtained by plasma CVD and subsequent heat treatment at 3000°C provide an excellent host for intercalation. The conductivities of intercalated graphites were higher than 10 5 S/cm. The ICI-intercalated graphites are thermally stable in air until 300°C. The air-stability for these is higher than that for CuCl 2 -intercalated graphites. Graphite films have been synthesized at 1340°C by plasma CVD using an Fe catalyst without subsequent heat treatment. These graphite films have a conductivity of 10 4 S/cm and high crystallinity, comparable to HOPG. The conductivity is enhanced by intercalation. The highest value was as high as 1.4×10 5 S/cm.

Preparation and properties of vapor grown graphite

Abstract Carbon films with various electrical conductivities have been prepared by plasma CVD in various preparation conditions. Especially, carbon films prepared on stainless steel showed good electrical conductivity. Conductive carbon films and fibers prepared by plasma CVD became high quality graphite materials comparable to HOPG after heat-treatment at over 3000°C. These graphite materials show electrical conductivity over 1×105 S/cm by intercalation of various acceptors; HNO3, AsF5, Br2, ICl and CuCl2. The electrical conductivity and structure of these intercalated films and fibers were hardly changed for almost 1.5 years. These films and fibers except intercalated with HNO3 are stable in the air atmosphere at room temperature. Stable structure of AsF5, ICl- and CuCl2-intercalated films and fibers are supposed to be 4th, 6th and 2nd stage, respectively, from X-ray diffraction patterns. Both CuCl2- and ICl-GIC were stable up to 350°C in the air and the conductivities of both rose in proportion to the temperature until 350°C. The limiting current density of plasma CVD graphite fibers and ICI-intercalated graphite fibers are measured to 5×104 and 7×104A/cm2, respectively.