Germanium Diselenide Ribbons with Orthorhombic Crystal Structure.

Many materials are known to exist in several stable polymorphs, but synthesis only provides access to a subset. This situation is exemplified by the dichalcogenide semiconductor GeSe. Besides the amorphous form, which attracted intense interest, crystalline GeSe in the bulk and in nanostructures such as flakes and nanobelts invariably adopts the 2D/layered monoclinic β-phase.

Free-standing large, ultrathin germanium selenide van der Waals ribbons by combined vapor-liquid-solid growth and edge attachment.

Among group IV monochalcogenides, layered GeSe is of interest for its anisotropic properties, 1.3 eV direct band gap, ferroelectricity, high mobility, and excellent environmental stability. Electronic, optoelectronic and photovoltaic applications depend on the development of synthesis approaches that yield large quantities of crystalline flakes with controllable size and thickness.

1D Germanium Sulfide van der Waals Bicrystals by Vapor-Liquid-Solid Growth.

Defects in two-dimensional and layered materials have attracted interest for realizing properties different from those of perfect crystals. Even stronger links between defect formation, fast growth, and emerging functionality can be found in nanostructures of van der Waals crystals, but only a few prevalent morphologies and defect-controlled synthesis processes have been identified. Here, we show that in vapor-liquid-solid growth of 1D van der Waals nanostructures, the catalyst controls the selection of the predominant (fast-growing) morphologies.

Optoelectronics and Nanophotonics of Vapor-Liquid-Solid Grown GaSe van der Waals Nanoribbons.

2D/layered semiconductors are of interest for fundamental studies and for applications in optoelectronics and photonics. Work to date focused on extended crystals, produced by exfoliation or growth and investigated by diffraction-limited spectroscopy. Processes such as vapor-liquid-solid (VLS) growth carry potential for mass-producing nanostructured van der Waals semiconductors with exceptionally high crystal quality and optoelectronic/photonic properties at least on par with those of extended flakes.

Vapor-Liquid-Solid Growth and Optoelectronics of Gallium Sulfide van der Waals Nanowires.

Nanowires of layered van der Waals (vdW) crystals are of interest due to structural characteristics and emerging properties that have no equivalent in conventional 3D crystalline nanostructures. Here, vapor-liquid-solid growth, optoelectronics, and photonics of GaS vdW nanowires are studied. Electron microscopy and diffraction demonstrate the formation of high-quality layered nanostructures with different vdW layer orientation.

Single-Crystalline γ-GaS Nanotubes via Epitaxial Conversion of GaAs Nanowires.

The chemical transformation of nanowire templates into nanotubes is a promising avenue toward hollow one-dimensional (1D) nanostructures. To date, high-quality single crystalline tubes of nonlayered inorganic crystals have been obtained by solid-state reactions in diffusion couples of nanowires with deposited thin film shells, but this approach presents issues in achieving single-phase tubes with a desired stoichiometry. Chemical transformations with reactants supplied from the gas- or vapor-phase can avoid these complications, allowing single-phase nanotubes to be obtained through self-termination of the reaction once the sacrificial template has been consumed.