Resolution enhancement of X-ray photoelectron spectra by maximum entropy deconvolution

The maximum entropy method (MEM) has been applied to the deconvolution of X -ray photoelectron spectra. Spectral broadening, resulting from extrinsic c ontributions by the X-ray excitation source and the energy analyser, is rem oved using a Fourier transform procedure which employs a new approach to th e estimate of the spectral noise function. The MEM deconvolution algorithm avoids the subjective nature of many previous deconvolution methods by assu ming that the informational uncertainty is always maximised within the cons traint of the data provided. This large scale, non-linear optimisation prob lem can be solved on a fast PC using a sequential quadratic programming (SQ P) algorithm. For spectra with adequately high signal/noise, the linewidths produced approach the limiting core hole lifetime values. Two applications of this method are described. In the first, MEM treatment of Cr(2p) spectr a of a number of thin film Cr(III) oxides are studied for any changes in mu ltiplet structure. The improved resolution allows such changes to be distin guished from changes due to the presence of other minor compounds. In the s econd project, the identities of gold-aluminum alloy surface films could be clearly distinguished, making use of the relatively small Au(4f) chemical shifts for such alloys. (C) 1999 Elsevier Science B.V. All rights reserved.