Particle-beam-induced chemical alterations

In this section the attention of the reader is called to some particular problems the surface analyst may encounter in analyzing thin surface films treated by various particle beams, essentially in the sputtering regime (from I to 5 keV). In the following subsections some representative studies will be presented in which it is demonstrated how the effects of particle bombardment on surface chemistry can be evaluated, mainly by XPS, for various inorganic compounds (e.g., TiN layers, metal oxides, Cr-O-Si cermet films) and polymeric materials (e.g., polysulfone, polyimide and poly(organosiloxanes)). 

A minor problem specific to the analysis of particle-beam-treated thin surface films may arise if the conditions of the film preparation or modification do not coincide with those of the analysis. In particular, the sample position that is optimal for analysis may not always be optimal for the in situ ion beam treatment. If ignored, this circumstance may lead to the preparation of laterally inhomogeneous samples and, as a consequence, to erroneous surface analytical results. 

Another specific problem may arise when the thickness of the modified layer is less than the sampling depth of the analysis. This results in a vertical inhomogeneity, which, if neglected, can lead to distorted results. 

Spurious effects can also occur due to space charge, as when insulating materials are treated by charged-particle beams, and may include electric-field-enhanced diffusion, sample degradation by surface flashover, and peak shifting and broadening during XPS analysis [34, 35]. 

The presence of adventitious carbon contamination can have a drastic influence on the quantitative evaluation of XP spectra. The amount of the contamination will vary with the different treatments, and both removal and buildup can occur, the latter usually being faster on the freshly treated (active) surface than on the untreated one. 

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