Near-Edge X-ray Absorption Fine-Structure Study on Hydrogenated Boron-Doped Ultrananocrystalline Diamond/Amorphous Carbon Composite Films Prepared by Coaxial Arc Plasma Deposition

Abstract

Boron-doped ultrananocrystalline diamond/amorphous carbon composite films were deposited in the hydrogen pressure range up to 26.7 Pa by coaxial arc plasma deposition with a boron-blended graphite target, and the effects of hydrogenation on the electrical properties and chemical bonding structures of the films were discussed by near-edge X-ray absorption fine structure (NEXAFS) studies. The electrical conductivity decreased with increasing hydrogen pressure. Whereas the nonhydrogenated films showed a semimetallic behavior in the temperature dependence of the electrical conductivity, the hydrogenated films exhibited semiconducting behavior. The boron content estimated from X-ray photoelectron spectroscopic measurements hardly changed with the hydrogen pressure. NEXAFS spectra showed that π* resonance related to sp²-bonded carbon is evidently enhanced with decreasing hydrogen pressure, which is accompanied by a selective etching of sp² carbon. The results indicate that the carrier transports in UNCD/a-C films are strongly influenced by chemical bonding structure at a-C or grain boundaries.