Synthesis, structure and mechanical properties of nanostructured MoSi2Nx

A systematic study of the synthesis-structure-mechanical properties relationship is reported for MoSi2Nx films. MoSi2Nx films with nitrogen content x ranging between 0 and 4.2 were prepared by sputtering technique. Cross-sectional transmission electron microscopy was used to examine the as-sputtered and annealed microstructures when exposed to different annealing conditions. Nanoindentation was employed to characterize the mechanical response of the materials as a function of the structural changes. As-sputtered MoSi2Nx films exhibit an amorphous structure. Annealing at 900 °C causes different microstructural changes depending on the nitrogen content. The resulting microstructure consists of nanocrystalline C11b-MoSi2 for x = 0, nanocrystalline C40 phase for x = 1.5 and amorphous for x = 2.95 and 4.2. The hardness of the as-sputtered MoSi2Nx films increases with nitrogen content to a maximum of 17.8 GPa (x ~ 3) and then decreases for higher nitrogen contents. Annealing at 500 °C and 900 °C, respectively, results in an increase in hardness. The rate of increase decreases with increasing nitrogen concentration. Increase in modulus is strongly related to the crystallization process, which is also affected by the nitrogen content in the MoSi2Nx films. These results suggest the possibility of engineering MoSi2Nx by varying the composition and heat treatment to produce suitable materials properties for different materials applications.