Defect-seeded lateral epitaxy and exfoliation on graphene-terminated surfaces

We exploit defects in a 2D barrier layer to drive the seeded lateral epitaxy of atomically smooth, exfoliatable, single-crystalline membranes. This growth mode offers many of the advantages of the recently discovered remote epitaxy, including novel strain relaxation pathways and the ability to exfoliate free-standing membranes, plus additional advantages of (1) tolerance for imperfect graphene/substrate interfaces and (2) the ability to engineer the growth by patterning the 2D graphene layer. We show that GaSb films grow on graphene-terminated GaSb (001) via a seeded lateral epitaxy mechanism, in which pinhole defects in the graphene serve as selective nucleation sites, followed by lateral epitaxy and coalescence into a continuous film. Importantly, the small size of the pinholes permits exfoliation of a continuous, free-standing GaSb membrane. By combining molecular beam epitaxy with \textit{in-situ} electron diffraction and photoemission, plus \textit{ex-situ} atomic force microscopy and Raman spectroscopy, we track the graphene defect generation and GaSb growth evolution a few monolayers at a time. Our discovery provides a highly tunable method to engineer single-crystalline 3D materials on precisely tuned 2D barriers.