ZnO/Si hetero-structured nanotrees fabricated by all-solution process

ZnO/Si hetero-structured nanotrees have been fabricated by an all-solution-based hydrothermal process. First, urchin-shaped ZnO nanostructures were grown on ZnO-island seed layers by selective growth of ZnO nanorod bundles. In the hydrothermal solution, NH₄OH supplied OH^- source for ZnO growth to maintain the urchin-shaped ZnO nanostructures and etched the exposed Si surfaces simultaneously. The urchin-shaped ZnO nanostructures acted as a mask for undercut etching of the exposed Si surfaces. The Si {1 1 1} surfaces with the lowest surface energy were exposed and formed pyramid-shaped stems for the nanotrees during the etching. The final ZnO/Si hetero-structured nanotrees consisted of ZnO nanorod branches and pyramidal Si stems.