Probing the buried interface

Adhesion is a consequence of the chemical or physical interaction between two surfaces, one of which is a solid and the other a liquid, temporarily more mobile. As a consequence of the way in which adhesion is achieved practically. the interface or interphase region, where the bonds responsible for adhesion occur, is buried below many im, or even mm, of solid sub.stratc and solidified (generally crosslinked) polymer. The dimensions of the interphasc region are likely to be of the order of nm at the most (unless an extended mechanical interphase is present of the type found in the adhesive bonding of anodized aluminum alloys) so that direct examination of interphase chemistry is best considered as an exercise in the analysis of a deeply buried interface. This situation is encountered frequently by those working in microelectronics and in corro,sion and oxidation research. Removal of material is invariably ac- 

A more elegant way to the same end of buried interface analysis, but one that moves away from the real situation, is the use of thin-film model sub- 

Another modeling approach involves the deposition of an ultrathin film onto a solid substrate. If the film is thin enough, XPS can then be used to look through the film to observe interfacial chemistry directly. Such an approach was first tried in a study of the process of polymer metallization for Cr, Fe, Ni [83,84], Ti [85] and A1 [86] and has recently been extended to the use of thin polymer films on metallic substrates [87], The best results have been achieved using very dilute polymer solutions (0.01-0.025 w/w/ 7f). polished substrates and very high resolution (monochromatic A1 Kq) XPS [88]. The information that can be gleaned from such studies is impressive but relies on careful peal-fitting of the Cls. spectra, as will be discussed in the. section on acid-ba.se interactions. 

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