Relation between composition and fracture strength in off-stoichiometric metal silicide free-standing membranes

In this work, we investigated the influence of composition on the polycrystalline structure, elastic properties and fracture strength, of ZrxSi1-x, NbxSi1-x, and MoxSi1-x free-standing thin films that were deposited by magnetron sputtering and subsequently annealed at 500 °C. Despite deviations from the stoichiometric composition, the crystalline structure of all films, except for the most Zr-rich ZrxSi1-x, corresponded to their respective stoichiometric disilicide structures, without the formation of a second-phase. Off-stoichiometry was found to be accompanied by the presence of lattice defects and a decrease of the grain size, which bring about a lower tensile stress in the films. The dependence of the fracture strength on the composition was remarkably similar for the three silicides, with the lowest and highest strength values occurring for samples with 30% and 37–40% of metal content, respectively. The observed dependence of strength on composition was attributed to the combination of the Hall-Petch effect, changes in the morphology and strength of grain boundaries, and the enhancement of crystal plasticity due to lattice defects induced by off-stoichiometry.