Local phase transition at crack edges of Mo_1−xW_xTe₂ polymorphs

The phase engineering of two-dimensional (2D) materials has attracted considerable attention in recent years, but nanometer-scale samples and experimental techniques have limited the rigorous study of the local phase engineering of 2D atomic crystals. Here, we report on a nanometer-scale probe of phase evolution in the Mo_1−xW_xTe₂ alloys, which exhibit a structural transition between the semiconducting 2H phase and the metallic 1T′ phase. We found that many crack edges are created by the accumulated tungsten atoms, resulting in poor crystallinity in the 2H-Mo_1−xW_xTe₂ flakes at the vicinity of phase transition with a tungsten content, x = 0.08. With mild laser irradiation of the 2H-Mo_1−xW_xTe₂ flakes, the 2H phase region near a crack edge was easily converted to the 1T′ phase, while other areas apart from the crack edge region retained their 2H phase under the same laser treatment. Our study clarifies the role of locally accumulated atoms and crystallinity for the phase engineering of 2D materials, which opens the way to various applications based on heterophase structures, ranging from energy conversion and storage to optoelectronic devices.