TEM, XRD and Raman scattering of germanium processed by severe deformation

Nanocrystalline (NC) Ge samples processed by severe plastic deformation under high pressure (6 GPa) were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman scattering. TEM studies of NC Ge revealed a mean grain size of about 24 nm and high angle misorientations of neighbouring grains. The XRD patterns showed decreasing peak intensities, peak broadening and a mean grain size of about 10.4 nm. The Raman spectrum revealed decreasing peak intensities, a peak shift to lower frequencies of 2 cm−1, peak broadening up to 14.0 cm−1, asymmetry of the peaks, additional peak at frequencies from 280 cm−1 to 300 cm−1 and a mean grain size of about 9 nm. A structural model for NC materials processed by severe plastic deformation is used to explain the results. This model deals with two grain areas: the interior with a perfect crystal lattice and the grain boundary (GB) defect structure associated with a high level of elastic strains and distortions of the crystal lattice.