Growth and analysis of the tetragonal (ST12) germanium nanowires

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 (290–330 °C) and a pressure of ∼48 bar. One-dimensional (1D) nanostructures of ST12-Ge were achieved <em>via</em> a self-seeded vapour–liquid–solid (VLS)-like paradigm, with the aid of an <em>in situ</em> 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–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 ± 1.4 nm, and lengths beyond 4 μm. 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.新型半导体材料，如最先进的合金、工程化复合材料以及成熟材料的同素异形体，可展现独特的物理特性，为诸多应用领域提供广阔的可能性。本研究首次实现了锗（Ge）的亚稳相同素异形体——四方相锗（ST12-Ge）的纳米线制备。本次制备采用类溶剂热单釜法，以超临界甲苯为溶剂，在290~330℃的温和温度和约48巴的压力下完成。ST12-Ge的一维（1D）纳米结构通过类自晶种气-液-固（VLS）生长范式实现，制备过程依托原位形成的无定形碳层完成。锗纳米线的ST12晶相由纳米线表面碳质结构的形成以及Ge-C键的生成所调控。通过X射线衍射（XRD）、高分辨透射电子显微镜（HRTEM）与拉曼光谱，证实了ST12-Ge纳米线的晶相与结构。所制备的纳米线具备较高长径比，平均直径仅为9.0±1.4 nm，长度则超过4 μm。经温度依赖性光致发光研究验证，ST12-Ge纳米线同素异形体对光发射强度以及带隙的直接性具有显著调控作用。