Surface analysis of CVD carbon using NEXAFS, XPS and TEM

Abstract

Chemical and morphological characterization of carbon thin films produced by chemical vapor deposition (CVD) of hydrocarbon gases onto a hard carbon substrate has been performed using various surface analytical techniques. Semiquantitative analyses of the surface concentration of C C double bonds have been conducted using near edge X-ray absorption fine structure (NEXAFS) at the C K edge and core level X-ray photoelectron spectroscopy (XPS). NEXAFS spectra of CVD carbon films are similar to those of well-ordered graphite. Rather surprisingly, however, it has been revealed that the CVD carbon films contain less C C double bonds than that of the hard carbon. Intensities of π-π * shake-up satellite of the C 1s XPS peak have been measured, and the results were consistent with those of NEXAFS. Smaller concentrations of C C double bonds can be attributed to the incomplete dehydrogenation due to the relatively low temperature of the CVD treatment. High resolution transmission electron microscope (TEM) images of CVD carbon showed preferential orientation of graphite-like plane units in the direction parallel to the surface, suggesting the formation of large molecules in gas phase reaction prior to deposition.