Low temperature synthesis of dense MoAlB thin films

Abstract

While bulk synthesis of MoAlB requires temperatures larger than 1000 °C with up to 40 % of excess Al in the feedstock, here we report the temperature range for the formation of single phase, orthorhombic MoAlB synthesized by magnetron sputtering from a stoichiometric target is 450–650 °C. Lower synthesis temperatures yield the formation of amorphous films, while at 700 °C, impurity phases form in addition to orthorhombic MoAlB. Amorphous MoAlB films were observed by in-situ X-ray diffraction to crystallize between 545 and 575 °C. Hence, we infer that the formation of orthorhombic MoAlB thin films is surface diffusion mediated below 545 °C. As bulk diffusion is activated between 545 and 575 °C the synthesis of fully dense MoAlB films with a maximum hardness of 15 ± 2 GPa and a Young’s modulus of 379 ± 30 GPa at 600 °C is surface and bulk diffusion mediated.