Residue-Free Fabrication of van der Waals Heterostructures of Two-Dimensional Materials.

In this work, a unique methodology is presented that utilizes van der Waals (vdW) interactions to fabricate residue-free single flakes of two-dimensional (2D) materials, which are subsequently assembled into intricate heterostructures. The approach focuses on ensuring that the flakes are free from any residue that could affect their properties and performance. Evidence from atomic force microscopy and Raman spectroscopy confirms that the transferred hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2) flakes exhibit excellent flatness and strain-free characteristics, which are crucial for various applications in electronics and optoelectronics. Furthermore, the pick-up and release processes of a target flake are demonstrated using a residue-free stamp, controlled by the type of applied force at the interface, whether normal or shear. By carefully directing the movement of the residue-free stamp, successful assembly of h-BN/MoS2/h-BN heterostructures is achieved through both bottom-up and top-down stacking processes. Moreover, pre-assembled heterostructures were modularly stacked to create a more complex heterostructure, showcasing the versatility of the proposed methodology. This work not only enables to achieve residue-free single flakes of 2D materials, but also paves the way for improved fabrication techniques in vdW heterostructures.