Abstract
Direct growth of black Ge on low-temperature substrates, including plastics and rubber is reported. The material is based on highly dense, crystalline/amorphous core/shell Ge nanoneedle arrays with ultrasharp tips (̃4 nm) enabled by the Ni catalyzed vapor-solid-solid growth process. Ge nanoneedle arrays exhibit remarkable optical properties. Specifically, minimal optical reflectance (< 1 %) is observed, even for high angles of incidence (̃75°) and for relatively short nanoneedle lengths (̃1 μm). Furthermore, the material exhibits high optical absorption efficiency with an effective band gap of ̃1 eV. The reported black Ge could potentially have important practical implications for efficient photovoltaic and photodetector applications on nonconventional substrates. © 2010 American Chemical Society.