Chemical microanalysis by reflected electron energy loss microscopy

We test the potential of reflected electron energy loss microscopy (REELM) as a tool for imaging chemical change in systems that possess both lateral and in-depth inhomogeneities, as well as in insulator samples. Results obtained across the interface between an atomically clean InSb surface and the adjacent, heavily contaminated InSb surface show, in agreement with the findings of other workers, that the technique provides a much better chemical contrast than the one offered by scanning Auger microscopy (SAM). The depths probed by REELM span a range that is several times wider than by SAM, and REELM provides nondestructive depth profiling into the thickness of the contamination layer, as well as of the layer built up on the clean region after air exposure. Na metal, accumulated on the surface of long electron-irradiated NaF is easily imaged by REELM despite the severe surface charging that prevented Auger spectra and SAM imaging. Following the anticipated findings that appeared in the literature some time ago [A. J. Bevolo, Scanning Electron Microsc. Part IV 1449 (1985)], this is the first experimental evidence that REELM is virtually immune to surface charging in insulator surfaces. (C) 1996 American Vacuum Society.