Keywords: germanium crystals, amorphous germanium, nanoindentation, high-resolution transmission electron microscopy, HRTEM, Raman spectroscopy, phase transition, phase transformations, nanotechnology, plastic strain
Nanoindentation-induced structural phase transformations in crystalline and amorphous germanium
During hardness indentation with a diamond indenter, materials are subjected to highly localised pressures. These pressures may cause a complete change of atomic arrangement of the material within the indented zone. This paper reports that when a Berkovich or Vickers nanoindenter is loaded onto a submicrometer thick film of amorphous germanium (a-Ge) and germanium single crystals (Ge-I), they undergo structural phase transitions. These observations are based on Raman scattering investigations, and high resolution transmission electron microscopy. The results show that a-Ge transforms to a face centred cubic (FCC) Ge-I, and simple tetragonal ST12-phase (Ge-III). On the other hand, single crystals of germanium Ge-I transforms to Ge-III and a-Ge phases. It also shows that Ge-III phase is sensitive to the power of the exciting laser beam. It has been shown that structural phase transitions occur at a nanozone close to the indenter tip, where the plastic strain is the highest.