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.