Determining hybridization differences for amorphous carbon from the XPS C 1s envelope

Abstract

Two kinds of amorphous carbon (a-C) thin film samples were synthesized, one by magnetron sputtering, the other by filtered cathodic arc deposition. X-ray photoelectron spectroscopy (XPS) showed that the C 1s envelope for each sample was primarily a convolution of three peaks which are assignable to sp 2 hybridized carbon, sp 3 hybridized carbon (shifted from the sp 2 peak by ∼ 1 eV) and an sp 2 satellite peak, possibly due to π-π ∗ transition. The satellite typically comprised just under 14% of the total sp 2 signal and was shifted from the main sp 2 peak by ∼ 2 eV. The relative amounts of each bonding type were determined by comparing the integrated areas of the sp 2 and sp 3 peaks. Auger electron spectroscopy (AES) was also performed on these samples, along with highly ordered pyrolytic graphite (100% sp 2) and natural diamond (100% sp 3) for comparison purposes. The binding energy width D between the highest maximum and lowest minimum values of the first derivative C (KLL) spectra were obtained and a linear relationship between D and the amount of sp 3 bonding assumed. When comparing sp 3 values obtained by AES and deconvoluted XPS spectra an error range within ±1.5% was found, making XPS a satisfactory method for obtaining hybridization information. It was noted that Ar + ion bombardment has a substantial effect on the surface sp 2/sp 3 ratio, as observed by XPS. These results are related to other studies of ion bombardment of graphite and diamond.