New method to correct for the influence of organic contamination on intensity ratios in quantitative XPS

A new method is proposed to correct for attenuation effects by adventitious organic contamination in quantitative XPS, The corrected intensity ratio I -X(o)/I-Y(o) involving two different substrate peaks is determined as the s lope of the plot of I-X/I-C1s as a function of I-Y/I-C1s for samples covere d with organic overlayers of varying thickness. The thickness of deposited organic overlayers does not need to be perfectly uniform provided that it d oes not vary by more than +/-40%. The sample surface can either be flat or present a random roughness (e.g. powders), Shadowing effects accompanying o verlayer non-uniformity are taken into account by a simple model involving effective thickness and fractional coverage, which is shown to enhance grea tly the accuracy of computed intensity ratios. Constraints of the method an d possible implementations were examined with an NaCl powder covered with a dventitious contamination, polystyrene (PS) and polydimethylsiloxane (PDMS) . The most straightforward implementation of the method would be to record repeatedly the peaks of interest while decreasing the adventitious contamin ation overlayer thickness by thermal desorption, The error on I-Na2s(o)/I-N a1s(o) is +10%, with the apparent overlayer thicknesses varying from 1.1 to 0.3 nm, The method is applied to check the reliability of the spectrometer transmission functions reported previously by Weng et al, Copyright (C) 19 99 John Wiley & Sons, Ltd.