A novel method was developed for the preparation of thin film micro-tensile specimens, which enables the target preparation and mechanical testing of individual microstructural defects. It is based on a combination of focused ion beam (FIB) milling and electron-beam-assisted etching with xenon difluoride precursor gas. In contrast to existing FIB-based preparation approaches, the area of interest is never exposed to ion beam irradiation and a pristine microstructure is preserved. This is achieved by the use of a special shadow milling geometry with a thin silicon membrane simultaneously serving as a substrate and protective layer for the thin film of interest.
The method was applied to prepare sub-micron sized tensile specimens from nanotwinned Cu-Al thin films, which were tested in situ in the TEM. Loading of the specimens was performed by a TEM Nanoindenter combined with a Push-to-Pull conversion device.
Depending on the relative orientation of the twin lamellae to the tensile direction, different deformation modes were observed, which will be discussed in the presentation.