Surface charging and other considerations

In any analysis involving focused electron beams variations in signal intensity from point to point on a surface will arise not only from variations in elemental concentrations but also from topographical effects, if the surface is at all rough. This is a particular problem in SAM, in which the elemental maps can be severely misinterpreted if topographical effects are not taken into account. As described in Chapter 5, the problem can be circumvented by applying a correc- 

The principal problem with ELS is that of spectral interference. Since the loss features that are recorded in the technique are usually broad, resolution of energy shifts of the same order of magnitude as the widths is difficult, and thus separation of different chemical states is not always possible. 

In addition to the above considerations, which are inherent to the techniques themselves, the artefacts induced by Ar+ etching [47] should be also borne in mind. Although the latter procedure is generally unavoidable when surface chemical analysis has to be extended into the sample, its effects on the alteration of the true chemical composition must be realized and taken into account. The reader is referred to the. several reviews dealing with this topic 47 (as well as to Chapters 6-9), while some Ar -induced artefacts will be discussed in the description of the surface analysis of Si/SiOi interfaces. 

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