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We have developed a technique for preparation of cross-sectional transmission electron microscopy samples of reacted and unreacted Nb/Al multilayer thin films on sapphire substrates. The choice of substrate was found to be extremely important. Sapphire sputters more slowly than Nb and Nb-compounds and therefore makes it possible to obtain the electron transparent regions in the thin films rather than in the substrate. However, the brittle nature of the sapphire restricts the types of thinning techniques that can be used, requiring extensive ion thinning as a final stage.
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Barmak et al. (1990) studied this question.
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