The deformation mechanisms of crystalline (100) Ge were studied by using nano-indentation, cross-sectional transmission electron microscopy and Raman micro-spectroscopy. For a wide range of indentation conditions, using both spherical and pointed indenters, multiple discontinuities were found in the force versus displacement curves upon loading. No discontinuities were found upon unloading. Raman micro-spectroscopy, measured in samples which had plastically deformed upon loading, exhibited a spectrum shift from that in pristine Ge; thus suggesting the presence of only residual strains. No signs, such as extra Raman bands, were found which suggested that any pressure-induced phase transformations had occurred; in spite of the fact that the material had undergone severe plastic deformation. Selected-area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Cross-sectional transmission electron microscopy showed that, at low loads, plastic deformation occurred via twinning and dislocation motion. This indicated that the hardness of Ge, as measured by indentation, was not dominated by phase transformation but rather by the nucleation and propagation of twin bands and/or dislocations.

Nanoindentation-Induced Deformation of Ge. J.E.Bradby, J.S.Williams, J.Wong-Leung, M.V.Swain, P.Munroe: Applied Physics Letters, 2002, 80[15], 2651-3