Abstract
Two-dimensional materials provide extraordinary opportunities for exploring phenomena arising in atomically thin crystals. Beginning with the first isolation of graphene, mechanical exfoliation has been a key to provide high-quality two-dimensional materials, but despite improvements it is still limited in yield, lateral size and contamination. Here we introduce a contamination-free, one-step and universal Au-assisted mechanical exfoliation method and demonstrate its effectiveness by isolating 40 types of single-crystalline monolayers, including elemental two-dimensional crystals, metal-dichalcogenides, magnets and superconductors. Most of them are of millimeter-size and high-quality, as shown by transfer-free measurements of electron microscopy, photo spectroscopies and electrical transport. Large suspended two-dimensional crystals and heterojunctions were also prepared with high-yield. Enhanced adhesion between the crystals and the substrates enables such efficient exfoliation, for which we identify a gold-assisted exfoliation method that underpins a universal route for producing large-area monolayers and thus supports studies of fundamental properties and potential application of two-dimensional materials.
Highlights
Two-dimensional materials provide extraordinary opportunities for exploring phenomena arising in atomically thin crystals
Density functional theory (DFT) calculations were employed to substantiate these arguments by comparing the interlayer binding energies of a large set of layered crystals with their adhesion energies to the Au (111) surface
These atoms, together with group 15 (VA) elements, are expected to have substantial interactions with Au substrates, which is verified by our differential charge density (DCD) plots
Summary
Two-dimensional materials provide extraordinary opportunities for exploring phenomena arising in atomically thin crystals. While exfoliation often suffers from low yield and small sizes of the exfoliated 2D flakes[5], many layered materials are, yet to be exfoliated into monolayers by established exfoliation methods Such challenge of exfoliation limits their utility for scalable production of 2D crystals and complicates further processing, e.g., to fabricate heterostructures. Promising candidate substrates for CLQB with 2D crystals are materials whose Fermi level falls in a partially filled band with mostly s- or p-electrons to prevent disrupting the electronic structure of 2D layers, and which have highly polarizable electron densities to ensure a large dispersion attraction Noble metals meet these criteria and are obtained as clean solid surfaces. Au is mechanically softer than Pt, which may improve the interfacial contact under the gentle pressure applied during the exfoliation process
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