Towards reliable X-ray photoelectron spectroscopy: Sputter-damage effects in transition metal borides, carbides, nitrides, and oxides

Highlights: • We test the effect of Ar sputter etch on XPS core level spectra of thin films. • The extent of sputter damage varies greatly between material systems. • Spectra after Ar⁺ etch are affected even for very gentle sputtering conditions. • Effects of Ar⁺ ion irradiation on XPS spectra cannot be a priori neglected. • Referring to Ar⁺ etch as "surface cleaning" is very misleading and should be avoided. Ar⁺ sputter etching is often used prior to X-ray photoelectron spectroscopy (XPS) analyses with the intention to remove surface oxides and contaminants. Since the XPS probing depth is comparable to the thickness of the ion-beam modified layer the signal from the latter dominates the spectra. We check here the conditions for reliable XPS analysis by studying ion irradiation effects for single-phase Group IVB transition metal (IVB-TM) boride, carbide, nitride, and oxide thin film specimens. The extent of sputter damage, manifested by changes in the surface composition, binding energy shift, peak broadening, and the appearance of new spectral features, varies greatly between material systems: from subtle effects in the case of IVB-TM carbides to a complete change of spectral components for IVB-TM oxides. The determining factors are: (i) the nature of compounds that may form as a result of ion-induced mixing in the affected layer together with (ii) the final elemental composition after sputtering, and (iii) the thickness of the Ar⁺-affected layer with respect to the XPS probing depth. Our results reveal that the effects of Ar⁺ ion irradiation on XPS spectra cannot be a priori neglected and a great deal of scrutiny, if not restraint, is necessary during spectra interpretation.