Optical Phase Transitions in 1T’-MoTe₂ from Thin Film Strain Engineering

MoTe₂ has been shown to have the ability to undergo a semimetallic to semiconducting phase transition induced by strain. In this work, we explore this phase change in 1T’-MoTe₂ through static strain induced by thin film stress capping layers, analogous to the ones used in industrial strained silicon processes. The optically transparent stressor film is chosen to be e-beam evaporated Al₂O₃/MgF₂/Al₂O₃. This film carries a controlled amount of tensile thin film stress depending on MgF₂ film thickness. Al₂O₃ is used as both an adhesion layer to MoTe₂, and as a protective capping layer for the MgF₂ from the environment. Significant optical contrast change in the few layered MoTe₂ flakes is observed after stressor film deposition, which is confirmed to be a phase change with Raman spectroscopy. Al₂O₃ capped control samples eliminate the possibility that this effect originates from defect formation during device fabrication process. Increasing thin film stress, changes the phase of a larger number of layers from the top of each MoTe₂ flake, resulting in thinner flakes to show larger proportional contrast change. Stress is a well-known technique to induce a phase change in MoTe₂ and potentially other 2D materials, which may lead to interesting applications in 2D electronics and optics.