Strain-Induced 2H to 1T′ Phase Transition in Suspended MoTe₂ Using Electric Double Layer Gating

MoTe₂ can be converted from the semiconducting (2H) phase to the semimetallic (1T′) phase by several stimuli including heat, electrochemical doping, and strain. This type of phase transition, if reversible and gate-controlled, could be useful for low-power memory and logic. In this work, a gate-controlled and fully reversible 2H to 1T′ phase transition is demonstrated via strain in few-layer suspended MoTe₂ field effect transistors. Strain is applied by the electric double layer gating of a suspended channel using a single ion conducting solid polymer electrolyte. The phase transition is confirmed by simultaneous electrical transport and Raman spectroscopy. The out-of-plane vibration peak (A_1g)─a signature of the 1T′ phase─is observed when V_SG ≥ 2.5 V. Further, a redshift in the in-plane vibration mode (E_2g) is detected, which is a characteristic of a strain-induced phonon shift. Based on the magnitude of the shift, strain is estimated to be 0.2-0.3% by density functional theory. Electrically, the temperature coefficient of resistance transitions from negative to positive at V_SG ≥ 2 V, confirming the transition from semiconducting to metallic. The approach to gate-controlled, reversible straining presented here can be extended to strain other two-dimensional materials, explore fundamental material properties, and introduce electronic device functionalities.