Layer-engineered atomic-scale spalling of 2D van der Waals crystals

Abstract

Transition-metal dichalcogenides (TMDCs), whose physical proper-ties can be modified by the number of layers within the atomic thick-ness range, are emerging as an essential active interlayer for nano -electronic devices based on van der Waals (vdW) heterostructures. Here, we show the atomic spalling of vdW crystals that achieves large-area TMDCs with a controlled number of layers. Unlike 3D co-valent network solids, the TMDCs are layered crystals featuring strong in-plane covalent bonding and weak out-of-plane vdW inter-action, which allow the crack propagation depth to be reduced to the atomic scale. By adjusting the residual stress of the stressor film, we controlled the crack propagation depth at a scale corre-sponding to the monolayer thickness of the TMDCs. Consequently, mono-, bi-, and trilayer TMDCs were selectively separated from the vdW crystals. The presented results show huge potential for the manufacture of layer-engineered, high-quality vdW materials, which can be developed into functional optoelectronic devices.