  The key to achieving high-quality van der Waals heterostructure devices made
by stacking two-dimensional (2D) layered materials lies in having a clean
interface without interfacial bubbles and wrinkles. In this study, the pinpoint
pick-up and transfer system of 2D crystals is constructed using polymers with
lens shapes. We report the bubble-free and clean-interface assembly of 2D
crystals in which unidirectional sweep of the transfer interface precisely
controlled with the help of the inclined substrate pushes the bubbles away from
the interface.
