VALIDATION AND ACCURACY OF SOFTWARE FOR PEAK SYNTHESIS IN XPS

The development of a range of VAMAS format data files containing synth etic I:est spectra and their use in evaluating the peak fitting routin es of three commercial XPS data analysis systems A, B and C, is report ed. The synthetic spectra allow tests for: (1) acceptance of VAMAS for mats with kinetic energy or binding energy scales that may have positi ve or negative abscissa increments; (2) Gaussian-Lorentzian sum or pro duct function peaks; (3) effectiveness of Shirley background subtracti on; (4) effectiveness of Tougaard background subtraction; (5) peak syn thesis with partly resolved peaks with no background; and (6) peak syn thesis with a Shirley background. The results show that ail the data s ystems studied accept VAMAS format files but not all would accept both of the options of direction of scan. In addition, each data system ha d programming faults, some of which were later rectified. Synthetic sp ectra approximating the carbon Is peaks for poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl chloride) and poly(isobutylene) allow an analysis of accuracy of the fits in these tests. One full set of s pectra is constructed with Gauss-Lorentz product function peaks and a second full set with Gauss-Lorentz sum function peaks since each softw are was designed for fitting only one of these options. The fitting of the individual peaks is only good for software using the same peak sh apes as those of the data. The fit quality can deteriorate markedly fo r fitting to a peak shape different to that used in the peak fitting a lgorithm (ie fitting sum function peaks with product function software or vice versa). For unresolved peaks additional information is requir ed to provide meaningful intensities. The three software systems studi ed all have different facilities but it is clear that the quality of c onvergence to the correct result gives a general order of preference i n the fitting algorithm of B, A and C. Other aspects can favour softwa re A which has more facilities. (C) 1998 Elsevier Science B.V. All rig hts reserved.