Practical correction procedures for elastic electron scattering effects inARXPS

Angle-resolved XPS and AES (ARXPS and ARAES) are widely used for determinat ion of the in-depth distribution of elements in the surface region of solid s. It is well known that elastic electron scattering has a significant effe ct on the intensity as a function of emission angle and that this has a gre at influence on the determined overlayer thicknesses by this method. Howeve r the applied procedures for ARXPS and ARAES generally neglect this because no simple and practical procedure for correction has been available, Howev er recently, new algorithms have been suggested. In this paper, we have stu died the efficiency of these algorithms to correct for elastic scattering e ffects in the interpretation of ARXPS and ARAES. This is done by first calc ulating electron distributions by Monte Carlo simulations for well-defined overlayer/substrate systems and then to apply the different algorithms. We have found that an analytical formula based on a solution of the Boltzmann transport equation provides a good account for elastic scattering effects. However this procedure is computationally very slow and the underlying algo rithm is complicated. Another much simpler algorithm, proposed by Nefedov a nd coworkers, was also tested. Three different ways of handling the scatter ing parameters within this model were tested and it was found that this alg orithm also gives a good description for elastic scattering effects provide d that it is slightly modified so that it takes into account the difference s in the transport properties of the substrate and the overlayer. This proc edure is fairly simple and is described in detail. The model gives a much m ore accurate description compared to the traditional straight-line approxim ation (SLA). However it is also found that when attenuation lengths instead of inelastic mean free paths are used in the simple SLA formalism, the eff ects of elastic scattering are also reasonably well accounted for. Specific ally, from a systematic study of several overlayer/substrate systems it was found that by ARXPS analysis of the overlayer signal, the mean percentage deviation from the nominal heights is similar to5% when using the procedure proposed by Nefedov, and similar to 10% with the SLA using attenuation len gths while the deviation is 13-68% with the SLA using IMFPs. For ARXPS anal ysis of the substrate signal, the mean percentage deviation from the nomina l heights is similar to 10% both when using the modified Nefedov algorithm and when using the SLA with attenuation lengths as compared to 16-31% with the SLA using IMFPs. (C) 2001 Elsevier Science B.V. All rights reserved.