Low temperature synthesis of dense MoAlB thin films

While bulk synthesis of MoAlB requires temperatures larger than 1000 degrees 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 degrees C. Lower synthesis temperatures yield the formation of amorphous films, while at 700 degrees 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 degrees C. Hence, we infer that the formation of orthorhombic MoAlB thin films is surface diffusion mediated below 545 degrees C. As bulk diffusion is activated between 545 and 575 degrees 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 degrees C is surface and bulk diffusion mediated.

Automated summary

The temperature range for the formation of single phase, orthorhombic MoAlB synthesized by magnetron sputtering is 450-650 degrees C, with amorphous films forming at lower temperatures and impurity phases forming at 700 degrees C. Diffusion mechanisms play a crucial role in the synthesis of fully dense MoAlB films at 600 degrees C, with surface diffusion mediating below 545 degrees C and bulk diffusion being activated between 545 and 575 degrees C.