Université Grenoble Alpes, CNRS, LMGP, F-38000 Grenoble, France.
Nanoscale. 2015 Oct 28;7(40):16994-7003. doi: 10.1039/c5nr04394h.
ZnO nanowires are usually formed by physical and chemical deposition techniques following the bottom-up approach consisting in supplying the reactants on a nucleation surface heated at a given temperature. We demonstrate an original alternative approach for the formation of ZnO nanowire arrays with high structural and optical quality, which is based on the spontaneous transformation of a ZnO thin film deposited by sol-gel process following a simple annealing. The development of these ZnO nanowires occurs through successive shape transitions, including the intermediate formation of pyramid-shaped islands. Their nucleation under near-equilibrium conditions is expected to be governed by thermodynamic considerations via the total free energy minimization related to the nanowire shape. It is further strongly assisted by the drastic reordering of the matter and by recrystallization phenomena through the massive transport of zinc and oxygen atoms towards the localized growth areas. The spontaneous shape transition process thus combines the easiness and low-cost of sol-gel process and simple annealing with the assets of the vapor phase deposition techniques. These findings cast a light on the fundamental mechanisms driving the spontaneous formation of ZnO nanowires and, importantly, reveal the great technological potential of the spontaneous shape transition process as a promising alternative approach to the more usual bottom-up approach.
氧化锌纳米线通常通过物理和化学沉积技术形成，遵循自下而上的方法，即在给定温度下加热的成核表面上供应反应物。我们展示了一种用于形成具有高结构和光学质量的氧化锌纳米线阵列的原始替代方法，该方法基于溶胶-凝胶工艺沉积的 ZnO 薄膜在简单退火后的自发转变。这些 ZnO 纳米线的发展经历了连续的形状转变，包括金字塔形岛的中间形成。预计在近平衡条件下，它们的成核将受到热力学考虑的控制，这与纳米线形状相关的总自由能最小化有关。物质的剧烈重排和通过锌和氧原子向局部生长区域的大规模传输的再结晶现象进一步强烈地促进了这一点。因此，自发形状转变过程结合了溶胶-凝胶工艺和简单退火的简单性和低成本，以及气相沉积技术的优势。这些发现揭示了驱动氧化锌纳米线自发形成的基本机制，并重要的是，揭示了自发形状转变过程作为一种很有前途的替代更常用的自上而下方法的技术潜力。
