Phase-controllable laser thinning in MoTe₂

Laser thinning of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) has been considered a promising method to tune the bandgaps of TMDs via precise control of their thickness. However, the laser irradiation generates numerous chalcogen vacancies, which are known to cause a phase transition in polymorphic TMDs such as MoTe₂. Therefore, the delicate control of the thickness and the phase during laser thinning is highly demanded to study the intrinsic properties of few-layered TMDs. Here, we report power-dependent laser thinning and phase control of semiconducting hexagonal MoTe₂ (2H-MoTe₂). High-resolution X-ray nano diffraction with synchrotron radiation showed that laser-thinned 2H-MoTe₂ with low laser power (<2 mW) retained its hexagonal diffraction patterns with a single crystal orientation. In contrast, a phase transition to monoclinic (1T′) MoTe₂ occurred during laser thinning at a high laser power level. Confocal Raman spectroscopy and atomic force microscopy (AFM) revealed that the low-power laser thinning of 2H-MoTe₂ retained the crystal structure whereas high-power laser thinning created considerable amount of chalcogen vacancies and a phase transition. Power-dependent laser thinning thus provides a promising way to control the thickness and the phase of polymorphic 2D TMDs for next-generation optoelectronic devices.