Fig. 1

Selective etching of a vdW heterostructure with XeF₂ gas. a Schematic of the XeF₂ etching process for a vdW heterostructure of stacked hBN and graphene layers. b, c Optical micrographs of a corresponding heterostructure fabricated from stacked exfoliated flakes before and after exposure to XeF₂. The scale bar is 10 μm. Before etching, the heterostructure is composed (from bottom to top) of silicon oxide substrate, 5 nm hBN, 1 L graphene, 8 nm hBN, 1 L graphene, and 10 nm hBN. The inset in b shows a Raman map of the 2D graphene peak, indicating the positions of the two graphene layers (G1 and G2). c Optical micrograph of the sample after XeF₂ etching, with an inset illustration indicating the cross-sectional structure in the region indicated. The changes in color between b and c represent changes in film thickness as determined by thin-film interferometry. The substrate is brown, while the thinnest hBN is blue and increasing thickness, and the changes in color represent changes in the hBN thickness from dark blue (thinnest) to light blue to green to yellow (thickest). d False-color cross-sectional bright-field STEM image of the etched heterostructure. The scale bar is 10 nm. The hBN layers (hBN1 and hBN2) covered with graphene masks (FG1 and FG2) were protected from XeF₂ etching. e Annular dark-field STEM image taken from the white-dashed area of (c) shows atomically sharp and clear heterointerfaces. The scale bar is 5 nm