OS06W0390 Deformation modes of semi-conductors: Determined from nano-indentation and transmission electron microscopy

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Recently Bradby et al. in a series of papers have investigated the mechanical properties of a range of elemental (Si and Ge) and a range of compound semiconductors (GaAs, InP, GaN, ZnO) using nano-indentation and associated cross-sectional TEM. In all instances cross-sections were made of impressions at various indentation loads using focused ion beam milling (FIB). Indentations were primarily made with a small spherical tipped indenter, which enabled the transition from elastic to elastic-plastic behaviour to be quantified. Complimentary observations of the residual impressions with AFM and Raman micro-probe spectroscopy were made as well as some electrical conductivity measurements during the indentation cycle. It was observed that only in the case of silicon was definitive evidence found for a pressure induced phase transformation beneath the indenter. In all other materials deformation occurred by classic plastic deformation, namely; dislocation motion and twinning. In the case of silicon it was found that the resultant phase transformation observed in TEM sections from beneath the indenter depended strongly on the unloading rate. More recent studies by the same authors have also simultaneously investigated the electrical resistivity during nano-indentation to quantify the onset of phase changes.