Nanoindentation: hardness and phase transition in silicon

The hardness of a thin film of silicon is studied in the framework of the 3D Hertzian contact theory. The anisotropy and the anharmonicity of silicon are taken into account for the first time. It is shown that the contribution of plasticity to the hardness of silicon is significant while we know that it possesses strong covalent bonds and dislocations must be thermally activated in this material. The semiconductor–metal phase transition, driven by the tetragonal shear strain superimposed on the non-hydrostatic pressure generated by a diamond indenter, is also studied. For this aim, the Landau theory of phase transitions and the contact theory are combined. The comparison with available nanoindentation experiments is made.