Growth and analysis of the tetragonal (ST12) germanium nanowires

<p>New semiconducting materials, such as state-of-the-art alloys, engineered composites and allotropes of well-established materials can demonstrate unique physical properties and generate wide possibilities for a vast range of applications. Here we demonstrate, for the first time, the fabrication of a metastable allotrope of Ge, tetragonal germanium (ST12-Ge), in nanowire form. Nanowires were grown in a solvothermal-like single-pot method using supercritical toluene as a solvent, at moderate temperatures (290&ndash;330 &deg;C) and a pressure of &sim;48 bar. One-dimensional (1D) nanostructures of ST12-Ge were achieved&nbsp;<em>via</em>&nbsp;a self-seeded vapour&ndash;liquid&ndash;solid (VLS)-like paradigm, with the aid of an&nbsp;<em>in situ</em>&nbsp;formed amorphous carbonaceous layer. The ST12 phase of Ge nanowires is governed by the formation of this carbonaceous structure on the surface of the nanowires and the creation of Ge&ndash;C bonds. The crystalline phase and structure of the ST12-Ge nanowires were confirmed by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The nanowires produced displayed a high aspect ratio, with a very narrow mean diameter of 9.0 &plusmn; 1.4 nm, and lengths beyond 4 &mu;m. The ST12-Ge nanowire allotrope was found to have a profound effect on the intensity of the light emission and the directness of the bandgap, as confirmed by a temperature-dependent photoluminescence study.</p>