CHARACTERIZATION OF LOW-PRESSURE DEPOSITED DIAMOND FILMS BY X-RAY PHOTOELECTRON-SPECTROSCOPY

X-ray photoelectron spectroscopy (XPS) has been utilized to study the electronic structure of carbon films grown by a low pressure hot filament assisted chemical vapor deposition technique with a view to optimizing the growth parameters for the diamond films. A constant flow of a mixture of high purity methane and hydrogen was maintained at a pressure of 25 Torr in the reaction chamber. The films were prepared at three different concentrations of methane: 0.25%,0.5% and 1.0% by density. The XPS C 1s core level and valence band spectra of these films are compared with those of graphite. Diamond has covalent sp3 bonding while graphite has sp2 bonding. XPS spectra exhibit features related to the difference in bonding. The plasmon loss shoulder (characteristic of graphite) associated with the main C 1s peak is found to be absent in the spectrum of films grown when the gas composition contains 0.25% methane, while is is found to build up with increasing concentration of methane. The binding energy position of the C 1s peak shows that appreciable charging occurs for the 0.25% methane concentration film. These results show that the films grown with 0.25% methane concentration closely resembled diamond. The valence band region for films grown using a gas composition consisting of 0.25% methane concentration shows considerable s-p mixing as compared with graphite. The core level and valence band results show that the film grown with a gas composition consisting of 0.5% methane concentration represents a composite of diamond and graphite. Scanning electron micrographs and Raman spectra support the conclusions drawn on the basis of XPS investigation.