Masukazu Hirata

Carbon nanofilm with a new structure and property

We have prepared a carbon film of nanometer thickness, which is called here a carbon nanofilm (CNF), starting from the oxidation of graphite. The structure and thickness of the CNF are determined by high-resolution transmission electron microscopy and electron diffraction. The structure is of a new type (S.G.: P3), in which carbon six-membered-ring planes are stacked with the sequence of ...AA.... According to electron energy loss spectroscopy, a substantial amount of oxygen is detected but the molar ratio of oxygen to carbon is possibly decreased to less than 0.1. The CNF changes from an insulator to a semiconductor when reduced on heating at 250°C.

Fabrication of SiO2-GeO2 glass optical waveguides by the gas-phase doping method

A new method of fabricating silica glass optical waveguides has been developed. Porous silica glasses made by the sol-gel method were used as substrates, into which a dopant was introduced by utilizing the adsorption equilibrium between porous glass and vapor of the relevant dopant material. Index distributions within the glass were produced by placing the doped glass under reduced pressure to outgas the dopant from the surface of the glass, followed by transforming the dopant into oxide by hydrolysis, and then the porous glass was densified to give nonporous glass. Combining this method with the selective photopolymerization method, where the undesired portion of pores was clogged by polymer, 3D waveguides have been fabricated. The SiO2–GeO2 waveguides thus fabricated have index differences of more than 0.02 with the propagation loss of less than 1 dB/cm.