Direct observations of incipient plasticity during nanoindentation of Al

The mechanical testing technique for in situ nanoindentation in a transmission electron microscope is described and is shown to provide real-time observations of the mechanisms of plastic deformation that occur during nanoindentation. Here, the importance of this technique was demonstrated on an aluminum thin film deposited on a single-crystalline silicon substrate. Significant results include direct observation of dislocation nucleation, characterization of the dislocation distribution created by indentation, and the observation of indentation-induced grain boundary motion. The observations achieved by this technique provide unique insight into mechanical behavior studied with conventional instrumented nanoindentation techniques and also provide microstructural-level understanding of the mechanics of ultrasmall volumes.