Direct evaluation of the sp3 content in diamond-like-carbon films by XPS

The analysis of the X-ray photoelectron spectra (XPS) of the C Is core level of pulsed laser deposited diamond-like carbon thin films, obtained at different laser intensities is presented. These spectra are deconvoluted into two different contributions, at 284.4 eV and 285.2 eV, which are respectively attributed to sp(2) and sp(3) hybridized carbon atoms. From the deconvoluted spectra, the sp(3) content in the films is evaluated. It is found to increase from 33% to about 60% as laser intensity is varied from 0.9 x 10(8) to 7.1 x 10(8) W/cm(2). These measurements have been compared to those obtained by the analysis of the C KLL X-ray excited Auger electron spectra. The two methods provide the same qualitative variation of the sp(3) content with laser intensity. However, the XPS of the C 1s core level yields systematically higher sp(3) content values. These differences are attributed to the presence of an sp(2) rich outer layer on the surface of the DLC films, as confirmed by angle-resolved XPS. The analysis of the C 1s peak is shown to be a very simple and direct method to evaluate the sp(3) content in unhydrogenated DLC thin films. (C) 1998 Elsevier Science B.V. All rights reserved.