Brillouin scattering investigation of elastic properties of Cu–Mo solid solution thin films

Abstract

Brillouin scattering has been used to investigate the elastic properties of CuxMo1−x thin films with thicknesses varying from 200 up to 430 nm, elaborated by ion beam sputtering. Two compositions around Cu30Mo70 and Cu70Mo30 and pure Cu and Mo films have been studied. The samples are essentially randomly oriented polycrystals, leading to an isotropic effective symmetry. By fitting all the Brillouin spectral lines, two independent effective elastic constants of these films have been determined, allowing the calculation of their elastic moduli. Results indicate that pure copper thin films’ elastic properties are similar to the bulk copper ones whereas pure molybdenum thin films' Young's modulus is weaker (about 10%) than the bulk Mo one. Concerning Cu–Mo solid solutions, elastic constants values lie between pure copper and molybdenum ones. Finally, the effect of annealing at 760 K on the mechanical properties of the solid solutions in relation with the microstructural evolution is discussed. The annealed solid solutions show a hardening of the elastic moduli with respect to the as-deposited samples, which is supposed to reflect their full demixing.