Thin ultraflat single crystals of arbitrary geometry via van der Waals injection molding

Confining quantum materials alters electronic structure and reduces bulk contributions while emphasizing boundary states. However, achieving nanostructures with precise geometries can require processing like etching which can introduce disorder. Here, we present a method to grow single crystals of arbitrary geometry in between layers of atomically flat van der Waals (vdW) materials [1]. Molten material is injection molded in a vdW encapsulated mold combining precise geometry control with an atomically smooth molding surface and environmental protection. Using this technique, we grow shapes such as hall bars of bismuth, tin, and indium with varying thicknesses between 10-90 nm with an ultraflat profile across the entire surface. Structural characterization reveals single crystals with large micron-scale atomically flat terraces. Cryogenic magnetotransport measurements of bismuth reveal exceptional electronic properties such as an enhanced residual-resistivity ratio, large magnetoresistance, quantum oscillations, and gated Landau fans. The geometric control afforded by this method provides a route towards on demand complex geometries such as nanowires and arrays of nanostructures without etching-induced disorder.

[1] Chen, L., Wu, A.X., Tulu, N. et al. Exceptional electronic transport and quantum oscillations in thin bismuth crystals grown inside van der Waals materials. Nat. Mater. 23, 741–746 (2024).