Quantitative Auger electron spectroscopy: Via the energy spectrum or the differential?

As part of an extended study of the quantitative analysis of surfaces by electron spectroscopy at the National Physical Laboratory, the quantification potential of Auger electron spectroscopy is examined in relation to the two modes of recording the spectra: the direct energy spectrum and the more customary differential energy spectrum. It is shown that it is not possible to describe a physically based routine procedure to obtain peak areas from the energy spectrum for Auger electron spectroscopy to be used, in the usual way, with a depth of analysis characterized by present values of the inelastic mean free path. These inelastic mean free paths are appropriate to measurements in the differential mode. The depth of analysis involved in peak areas form the energy spectrum may often be many times greater than these inelastic mean free paths, and may be rather indeterminate and matrix sensitive. In comparison, quantification in the differential mode is properly characterized in its depth of analysis. Quantification in this mode is most accurate in the usual framework of relative sensitivity factors, matrix factors, etc., by measurements at not too high a resolution (5 eV peak‐to‐peak modulation). The effects of peak shape changes, associated with changes in the energy loss structure with matrix, are removed by using the excursion of the negative peak as a measure of intensity instead of the usual peak‐to‐peak value. Other weak peak shape change are absorbed by the 5 eV modulation, whereas strong changes must be allowed for by relative sensitivity factors, etc., appropriate to the new peak shape.