Size-dependent strain-engineered nanostructures in MoS2 monolayer investigated by atomic force microscopy

The strain has been employed for controlled modification of electronical and mechanical properties of two-dimensional (2D) materials. However, the thermal strain-engineered behaviors of the CVD-grown MoS₂ have not been systematically explored. Here, we investigated the strain-induced structure and properties of CVD-grown triangular MoS₂ flakes by several advanced atomic force microscopy. Two different kinds of flakes with sharp-corner or vein-like nanostructures are experimentally discovered due to the size-dependent strain behaviors. The critical size of these two kinds of flakes can be roughly estimated at ~17 μm. Within the small flakes, the sharp-corner regions show specific strain-modified properties due to the suffering of large tensile strain. While in the large MoS₂ flakes, the complicated vein-like nanoripple structures were formed due to the interface slipping process under the larger tensile strain. Our work not only demonstrates the size-specific strain behaviors of MoS₂ flakes but also sheds light on the artificial design and preparation of strain-engineered nanostructures for the devices based on the 2D materials.