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

Abstract

The maximum entropy method (MEM) has been applied to the deconvolution of X-ray photoelectron spectra. Spectral broadening, resulting from extrinsic contributions by the X-ray excitation source and the energy analyser, is removed using a Fourier transform procedure which employs a new approach to the estimate of the spectral noise function. The MEM deconvolution algorithm avoids the subjective nature of many previous deconvolution methods by assuming that the informational uncertainty is always maximised within the constraint of the data provided. This large scale, non-linear optimisation problem can be solved on a fast PC using a sequential quadratic programming (SQP) 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) spectra of a number of thin film Cr(III) oxides are studied for any changes in multiplet structure. The improved resolution allows such changes to be distinguished from changes due to the presence of other minor compounds. In the second 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.