Dry Transfer of van der Waals Junctions of Two-Dimensional Materials onto Patterned Substrates Using Plasticized Poly(vinyl chloride)/Kamaboko-Shaped Polydimethylsiloxane

Two-dimensional (2D) materials can be transferred onto substrates with various surface structures, opening up multiple functions and applications for 2D materials in the form of suspended membranes. In this paper, we present a method for transferring exfoliated 2D crystal flakes from SiO2 substrates onto patterned substrates using a poly(vinyl chloride) (PVC) layer mounted on a polydimethylsiloxane (PDMS) stamp structure. 2D crystal flakes can be transferred onto various patterned structures such as grooves, round holes, and periodic hole or groove patterns. Our method can also be used to fabricate suspended van der Waals (vdW) heterostructures by assembling 2D crystal flakes on the PVC/PDMS stamp and then transferring them onto patterned substrates. The adhesiveness and curvature of the PVC/PDMS stamp were tuned, and a high successful transfer rate was realized due to the use of kamaboko-shaped (semicylindrical) PDMS and the addition of an appropriate amount of a high-viscosity plasticizer to the PVC layer. Taking advantage of this method, we demonstrate the facile fabrication, simply by transferring a vdW heterostructure onto an Au-coated groove substrate, of a suspended vdW field-effect transistor device with the carrier density tuned using ionic gating. This method enables the transfer of 2D crystal flakes and vdW heterostructures onto various patterned substrates, and hence it should help to advance suspended 2D materials research.