Three-dimensional semiconductor nanowire networks as model systems to study physical processes in nanostructured electrodes for light-driven water splitting

该项目旨在开发和表征三维Cu2O/TiO2和Si/TiO2核/壳纳米线网络，作为太阳能光电转化为氢气的模型系统。利用应用离子轨道技术的广泛选择，使我们能够以独立的方式定制线的长度，直径和结晶度，研究重点是纳米线系统的几何形状和结晶度如何影响相关的物理过程，如光吸收，电子-空穴对产生，载流子输运，表面化学反应以及化学和光腐蚀。我们的方法考虑了以下方面：-与薄膜技术相比，几十微米长的纳米线有望提供高效率的光吸收。这一优势与光产生的载流子在只有几十纳米宽的径向线轴上的有效收集相结合。-高度互连的圆柱形纳米线的独立三维阵列提供机械稳定的测试系统，并提供大型半导体/电解质界面。-纳米线网络将通过原子层沉积（ALD）的方式涂覆不同厚度的TiO2层，以研究外壳对网络的光电化学效率和化学和机械稳定性的影响。-选择Cu2O和Si作为系统是因为它们各自的带隙有望在可见光下最大化水分解效率。这两种材料的电学和光学性质彼此不同，但都被称为体和薄膜系统，为研究尺寸效应和材料对纳米结构光电化学性质的影响提供了良好的基础。

The aim of the proposed project is the development and characterization of three dimensional Cu2O/TiO2 and Si/TiO2 core/shell nanowire networks as model systems for photo-electrochemical conversion of solar energy into hydrogen production. Exploiting the wide options of the applied ion-track technology allowing us to tailor length, diameter, and crystallinity of the wires in an independent manner, the study focuses on the question how the geometry and crystallinity of the nanowire system affects the relevant physical processes such as light absorption, electron-hole pair generation, carrier transport, chemical reactions at the surface, and chemical- and photo-corrosion.Our approach takes into account the following promising aspects:- Compared to thin film technology, nanowires of several tens of µm length are expected to provide high efficiency in light absorption. This advantage is combined with efficient collection of photo-generated carriers across the only tens of nanometers wide radial wire axis.- Freestanding three dimensional arrays of highly interconnected cylindrical nanowires provide mechanically stable test systems and provide large semiconductor/electrolyte interfaces.- The nanowire networks will be coated conformally by means of atomic layer deposition (ALD) with TiO2 layers of various thicknesses to investigate the influence of the shell on the photoelectrochemical efficiency and chemical and mechanical stability of the networks.- Cu2O and Si are selected as systems because their respective band gaps promise maximize water splitting efficiency in the visible light regime. Electrical and optical properties of both materials are different from each other and yet well known as bulk and thin film systems, providing a good basis to investigate the influence of size-effects and material on the nanostructure photoelectrochemical properties.