Comparison of Auger electron spectroscopy, Auger electron appearance-potential spectroscopy, and disappearance-potential spectroscopy in a cylindrical-mirror-analyzer system

We describe a few modifications of a commercial CMA which allow us to complement Auger spectroscopy (AES) by two independent threshold spectroscopies: Auger electron appearance-potential spectroscopy (AEAPS) and disappearance-potential spectroscopy (DAPS). After establishing comparable conditions for AES and AEAPS, the signal-to-noise ratios are compared. AEAPS is found to be slightly more sensitive for Ti (factor of 2), much more for La (factor of 30), and much less for oxygen (factor of 0.02) than AES. Due to the small number of lines in the threshold spectroscopies and little line overlap, it is possible to detect minor constituents in multicomponent samples which cannot be found by AES. This is demonstrated for a stainless-steel alloy. DAPS has pronounced surface sensitivity, but a lower signal-to-noise ratio compared to AEAPS (a factor of 6 was determined for Ti). The differences in the depth of information of DAPS and AEAPS allow us to detect surface enrichment in alloys or preferential sputtering by ion bombardment without any further treatment of the sample. This is demonstrated for a Cr-16 Fe-84 alloy.