Mechanical properties of thermally evaporated germanium (Ge) and barium fluoride (BaF₂) thin-films

Elastic modulus and hardness of thin-films are critically important in determining the behaviour of free-standing actuatable microstructures. In this study, nanoindentation has been used to investigate the mechanical properties of thermally evaporated Ge and BaF2 thin-films. Nanoindentation experiments indicate that Ge and BaF2 thin-films are characterised by a reduced modulus of 95 ± 3 GPa and 33 ± 9 GPa, respectively, and hardness of 4.6 ± 0.4 GPa and 0.75 ± 0.4 GPa, respectively. The elastoplastic response of both thin-films was predominantly elastic for low indentation loads, but exhibited plasticity ≥ 60% for indentation loads approaching 8 mN. Indentation-induced creep deformation was found to be limited to ≤ 5%.