1D Wires of 2D Layered Materials: Germanium Sulfide Nanowires as Efficient Light Emitters

We considered the formation of one-dimensional (1D) nanowires from the two-dimensional (2D) layered material GeS. Growth by a low-temperature vapor–liquid–solid process over a Au catalyst gives rise to single-crystalline nanowires with typical diameters of ∼100 nm and length exceeding 10 μm that consist of a crystalline GeS core with layering along the nanowire axis, surrounded by an ultrathin, sulfur-rich GeSx shell with larger bandgap that provides chemical and electronic passivation of the nanowires. Combined variable-temperature in situ electron microscopy, chemical mapping, and single-nanowire cathodoluminescence spectroscopy are used to uncover key elements of the growth process and to identify the optoelectronic properties of the GeS/GeSx core–shell nanowires. Our results suggest that vapor–liquid–solid processes can readily be extended from conventional three-dimensional crystals to the growth of 1D wires from 2D layered crystals and may provide novel low-dimensional materials for electronic, optoelectronic, or energy conversion applications that benefit from the wide-ranging properties of van der Waals materials.