Strain-induced structural phase transformation in two-dimensional molydenum tungsten diselenide alloy*

Two-dimensional transition metal dichalcogenides (TMDCs) show intriguing mechanical properties compared to their bulk counterparts. This behavior can be modified in alloyed TMDCs due to doping and defects. In this work we develop CVD synthesis of large-area monolayer MoWSe2 alloy film on sapphire substrate. With Raman spectroscopy and mapping, we investigate the microscopic behavior of this alloy film transferred onto a flexible substrate as function of increasing bending strain. We observe the nature of crack propagation through the Mo and W-dominated regions in this 2D alloy film with differing stress concentration near the W-rich precipitates. Our molecular dynamics simulations illustrate how stress buildup at propagating crack tip in the film result in a 2H-1T phase transformation which is verified at micro- and nano-scale using Raman mapping and HAADF-STEM imaging. The MD simulations also predict increased crack resistance and healing in alloys compared to unalloyed pristine samples.