Abstract
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.
Highlights
X-ray photoelectron spectroscopy (XPS) has experienced an un precedented growth over the last 30 years and is today by far the most commonly used surface analysis technique with 11 000 publications in 2019 only [1], leaving other techniques like Auger Electron Spectros copy and Secondary-Ion mass Spectrometry far behind [2]
IVB transition metal (IVB-TM) borides and nitrides constitute intermediate cases with changes in core level spectra increasing with TM mass
For the ideal case of perfectly flat surfaces, the thickness of the surface layer modified by the incident Ar+ ion beam ξ can be estimated from Transport of Ions in Matter (TRIM) simulations and equals the average primary recoil projected range accounting for straggle [83]
Summary
X-ray photoelectron spectroscopy (XPS) has experienced an un precedented growth over the last 30 years and is today by far the most commonly used surface analysis technique with 11 000 publications in 2019 only [1], leaving other techniques like Auger Electron Spectros copy and Secondary-Ion mass Spectrometry far behind [2]. This large popularity of XPS is to large extent caused by its ability to assess chemical state of the atoms [3,4], which is often done through advanced spectrum analysis [5,6], in addition to qualitative and quantitative elemental analysis [7]. Problems often encountered with XPS reports include incorrect charge referencing [11,12,13,14], mistaken peak fitting [15,16], and/or incomplete experimental protocol often without infor mation that is essential for spectra interpretation
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