Boron-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited by coaxial arc plasma deposition with a boron-blended graphite target at a base pressure of <10−3 Pa and at hydrogen pressures of ≤53.3 Pa. The hydrogenation effects on the electrical properties of the films were investigated in terms of chemical bonding. Hydrogen-scattering spectrometry showed that the maximum hydrogen content was 35 at. % for the film produced at 53.3-Pa hydrogen pressure. The Fourier-transform infrared spectra showed strong absorptions by sp3 C–H bonds, which were specific to the UNCD/a-C:H, and can be attributed to hydrogen atoms terminating the dangling bonds at ultrananocrystalline diamond grain boundaries. Temperature-dependence of the electrical conductivity showed that the films changed from semimetallic to semiconducting with increasing hydrogen pressure, i.e., with enhanced hydrogenation, probably due to hydrogenation suppressing the formation of graphitic bonds, which are a source of carriers. Carrier transport in semiconducting hydrogenated films can be explained by a variable-range hopping model. The rectifying action of heterojunctions comprising the hydrogenated films and n-type Si substrates implies carrier transport in tunneling.
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 * resonance related to sp 2 -bonded carbon is evidently enhanced with decreasing hydrogen pressure, which is accompanied by a selective etching of sp 2 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.
Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) and UNCD/non-hydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were prepared via coaxial arc plasma deposition, and their thermal conductivity and interfacial conductance in grain boundaries were measured using a time-domain thermoreflectance method. The interfacial conductance was estimated to be 1,010 and 4,892 MW/(m 2 &K) for UNCD/a-C:H and UNCD/a-C films, respectively. The reasons for the hydrogenated film having lower interfacial conductance than the non-hydrogenated film are 1) the reduced number of carriers that contribute to heat transport and 2) the hydrogen atoms, which are preferentially located at the grain boundaries and enhance phonon scattering.
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