Are measured values of the Auger parameter always independent of charging effects?

Abstract

In x-ray photoelectron spectroscopy (XPS) the Auger parameter is often used to study the electronic properties of elements, particularly in insulator materials, because this parameter is assumed to be independent of charging effects. In this paper we report on subtle differences in sample structure and experimental conditions for which the sample potential may not remain constant during the measurements for some spectrometers or experimental arrangements; for such conditions the Auger parameter is not independent of charging. We compare a series of measurements with insulating plate substrates of Al 2 O 3 on which different amounts of SnO 2 and Au were deposited. X-ray photoelectron spectra were collected for different conditions of the sample that was placed either grounded or left floating on a metallic sample holder during measurement. It is found that the Auger parameter is independent of the experimental conditions for Au but substantial differences were found for deposited SnO 2 . Surprisingly, measurement artifacts due to charging appeared in the Auger parameter for Sn when the sample holder was grounded but not when it was left floating. In the grounded samples differences up to 0.6 eV in the Auger parameter for Sn were found with respect to the actual value of this parameter measured with substrates where charging effects were not significant. Because no differences in peak broadening have been observed under different measurement conditions, it has been assumed that the shift was not caused by a conventional differential charging phenomenon. Considering the different response of the substrate and the deposited layer on stabilizing the charge when the sample is grounded, we have worked out a possible explanation to account for the observed artifacts. Instrumental specifications should be optimized very carefully, especially if (as here) relatively high charging shifts point to a non-optimum self-biasing of the surface potential at the insulating samples.

Monitoring Interface Interactions by XPS at Nanometric Tin Oxides Supported on Al2O3 and Sb2Ox

“…11,12,18 However, special care must be given to measurement conditions when investigations of nonconducting material on insulating bulk substrates are carried out. 29 For SnO 2 deposited on Al 2 O 3 we used the thin film substrate (cf. Experimental), whereas on Sb 2 O 3 single crystals charging artifacts in R′ were avoided by leaving the sample floating without a connection to earth during the measurement.…”

“…16,28 BE referencing of the spectra taken with the Al 2 O 3 substrate was done with respect to the Al 2p peak at 75 eV. With these reference values, the Sn photoemission parameters (i.e., Sn 3d 5/2 and R′) of a thick film of SnO or SnO 2 compare well with the BE and R′ values taken for thick SnO 2 and SnO layers on sputter-cleaned copper 29 or silver. 9 In a previous paper, 29 we found that for insulator plates as substrates, charging effects may influence the value of the Auger parameter.…”

“…This material was used as a substrate to avoid the influence of severe charging effects appearing for SnO 2 deposited on the insulating sapphire plates. 29 Tin oxide was deposited simultaneously on the two oxide substrates by resistive evaporation from a homemade Knudsen cell filled with SnO powder (Goodfellow). Evaporation was carried out in the preparation chamber of the spectrometer with a base pressure better than 5 × 10 -8 mbar.…”

Chemical composition and phase identification of sodium titanate nanostructures grown from titania by hydrothermal processing

“…When these lines split in two peaks, there are two Auger parameters for the same sample. Since each spectrum suffers shifts in the same amount, the Auger parameter should not depend on the charging effects or the procedure used to fix the energy scale, although some subtle dependence on charging effects has been reported [48]. The Auger parameter is shown in Table 1.…”

Surface chemistry of a Cu(I) beta-diketonate precursor and the atomic layer deposition of Cu2O on SiO2 studied by x-ray photoelectron spectroscopy

“…[37][38][39][40] However, a is also prone to higher measurement errors compared to the photoelectron BE position. As suggested in the literatures, 29,41 errors in a were minimized by stabilizing the surface potential using a constant low energy flood gun potential difference and current for different experiments and recording the measurement after sufficiently long periods of x-ray exposure (10 min) to reach equilibrium.…”