Annealing-Induced Modification of Superhard Conductive Carbon Film

概要

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Carbon deposited by electron cyclotron resonance plasma sputtering (ECR-C) is known to have physical properties different from those of amorphous carbon (a-C), i.e., an unexpected high degree of hardness, despite the large proportion of sp2 bonding. We studied the effects of annealing (up to 700 °C) ECR-C films on the microstructure and electrical conductive property by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and conducting atomic force microscopy (AFM). Annealing causes the evaporation of argon atoms (7.4 at. %) in the film and decreases the sp3/sp2 ratio from 0.31 to 0.24, the full width half maximums (FWHMs) of $G$ and $D$ peaks and the $I(D)/I(G)$ ratio. The electrical conductivity and linearity of $I$–$V$ curves measured by conducting AFM increase with annealing temperature. This is explained by the ordering of the sp2 phase, i.e., the decrease in the numbers of argon atoms and defects in aromatic rings, which act as ionizable sites for Poole–Frenkel conduction. The variations in FWHM, $I(D)/I(G)$ ratio and electrical conductivity are much smaller than those caused by annealing a-C with an sp3 fraction lower than approximately 70%. This indicates that ECR-C is thermally stable compared with a-C, i.e., the basic structure of ECR-C is maintained during annealing up to 700 °C with a small increase in the size of sp2 nanocrystallites and a lowering of disorder.
2006-09-15