Intercomparison of methods for separation of REELS elastic peak intensities for determination of IMFP

The consistency and accuracy of inelastic electron mean free paths (IMFPs) determined from comparison of the intensity of elastically reflected electi ons with theoretical calculations were studied. The variation with experime ntal geometry, spectrometer energy resolution and the procedure for backgro und subtraction was studied. Four different types of spectrometers- double pass cylindrical mirror analyser (CMA) preretarded CMA, hemispherical analy ser (HSA) and retarding field analyser (RFA) - with widely different geomet ries and energy resolutions, placed in four different laboratories in three countries, were used. Four background subtraction methods (Shirley, linear , Tougaard and ELPSEP) were applied to isolate the elastic peak intensity f rom the reflected electron spectra. It was found that the IMFPs determined with data from the double pass CMA deviated considerably more (by a factor of 2) from the average values as well as from theoretical IMFP values than IMFPs determined with data from the other spectrometers. The data from the double pass CMA were therefore excluded from the statistical analysis. The root mean square (RMS) deviation of the IMFP from a function fitted to the data was 1.6-2.8 Angstrom depending on the background subtraction method, a nd it is smallest for the Tougaard method. The RMS deviation from IMFP valu es calculated by Tanuma et al. is 2.1-3.2 Angstrom again with the smallest value for the Tougaard method. The percentage deviation of the results usin g a Tougaard background from Tanuma et al. values is 12.6%. The results poi nt to the conclusion that the major contribution to the inaccuracies in IMF Ps determined with this method is not the background subtraction procedure but rather the lack of accuracy of the presently available models for elast ic electron scattering, i.e. atomic elastic scattering cross-sections and e ffects of crystallinity that are not included in the presently applied mode ls. Copyright (C) 2001 John Wiley & Sons, Ltd.