Angle-resolved XPS depth-profiling strategies

Angle-resolved X-ray photoelectron spectroscopy ARXPS.can be used non-destructively to find the depth-distribution of chemical species. Although the experimental technique has been available for 25 years or more, approximately 20 different methods for calculating concentration depth-profile information from measured data have been published in this time. Some of the algorithms were originally developed in other areas of applied science, and implicitly impose vestigial constraints on the depth-profile inherited from their original application. In this paper we examine 1. why constraints are important, 2. which constraints are possible, and 3. which constraints are valid for different classes of XPS analysis problems. It is shown that three distinct regions of prior knowledge exist, and by fixing appropriate constraints for each in turn we reach definite conclusions on how to improve regularization methods for calculating depth-profiles from ARXPS data. q1999 National Physical Laboratory. Published by Elsevier Science B.V. All rights reserved.