Film thickness change due to grain boundary migration in stressed thin films at elevated temperatures

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Two-beam CBED patterns in the vicinity of two grain boundaries exhibiting migration behavior were used to accurately determine the effect of grain boundary migration on film thickness. Comparison of the film thickness behind and ahead of the migrated grain boundaries indicated significant film thickening had occurred in the region swept out by the moving grain boundaries. The change in film thickness across the migrated grain boundaries was shown to be very abrupt and, therefore, not due to the wedge-shaped cross-section of the film produced during electropolishing. Also the extent of film thickening resulting from migration was observed to differ for the two boundaries studied. Finally, the results presented here were shown to be consistent with the proposed grain boundary step mechanism of migration in a compressive stress-state. Although the experimental observations made in this paper by no means fully substantiate the grain boundary step mechanism of migration cited, they were, however, in agreement with important aspects of that model. In the future, the effect of grain boundary crystallography as well as the influence of initial film thickness on the observed thickness changes should receive special attention since both have been shown to be important.

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Scripta Materialia