GeS mixed-dimensional 1D nanowire–2D plate heterostructures on van der Waals substrates

Abstract

Vapor–liquid–solid (VLS) growth is widely used to synthesize 1D semiconductor nanostructures with high yield and crystal quality. Recently, the VLS concept has been extended from 3D-crystalline semiconductors to 2D/layered van der Waals crystals, e.g., providing nanowires and mixed-dimensional heterostructures of the layered semiconductor GeS. However, Au-catalyzed growth of GeS nanostructures on silicon is invariably limited to small, sparse areas. Here, we report how this issue can be overcome via epitaxial VLS growth on van der Waals substrates, in the present case quasi-continuous SnSe films on mica. We show that Au-catalyzed VLS growth on SnSe yields complete coverage with mixed-dimensional GeS heterostructures combining 1D nanowires and 2D plates. Transmission electron microscopy and electron diffraction demonstrate that the nanowire backbone and the attached plates have the same crystal structure and layer orientation, with the [001] (van der Waals) direction aligned along the axis of the nanowire, templated by the basal plane of the underlying SnSe film. In contrast to GeS nanowires grown on Si, which invariably include screw dislocations and are thus chiral (with Eshelby twist), GeS nanowires formed on SnSe are layered single crystals that do not contain any dislocations. The optoelectronic properties of individual 1D–2D GeS heterostructures, probed by cathodoluminescence, draw on their unique architecture incorporating a sequence of GeS plates with intense luminescence and size-tunable emission wavelengths. Our results pave the way for the high-yield synthesis of a wide range of layered nanostructures using epitaxial VLS growth on van der Waals substrates.