Determination of sp² and sp³ phase fractions on the surface of diamond films from C1s, valence band X-ray photoelectron spectra and CKVV X-ray-excited Auger spectra

The practice of applying the methods for determining the relative contents of carbon atoms in sp² and sp³ hybridization states from the profiles of C1s X-ray photoelectron and carbon KVV (CKVV) Auger spectra is analyzed. Difficulties in using C1s and CKVV spectra for determining the sp²/sp³ ratios are discussed. A method is proposed for evaluating the fractions of sp² and sp³ phases based on the fitting of the valence band X-ray photoelectron spectra by superposition of valence band spectra of samples with carbon atoms in pure sp² and sp³ states. Relative fractions of sp² and sp³ phases on the virgin surfaces of two ultrananocrystalline diamond films, and on their surfaces subjected to friction, were determined using C1s spectra, CKVV Auger spectra, and valence band spectra. All three methods gave the results that are consistent for virgin film surfaces with accuracy of 2%, and for the surfaces of films subjected to friction, 15%. In contrast to the ultrananocrystalline films, three XPS-based methods applied to a microcrystalline diamond film yielded significantly different sp²/sp³ ratios. The reasons for this discrepancy are shown to lie in different analysis depths of these methods, and in different morphology of the film surfaces.