Modulating ZnO nanostructure arrays on any substrates by nanolevel structure control

A uniform high-aspect-ratio nanotextured surface with a very dense forest of vertically aligned nanowires that was produced by surface chemical postfabrication of ZnO was induced by a structural transformation at the nanolevel. X-ray photoelectron spectroscopy verified the formation of the heterogeneous surface structures (GaO_x on GaN and AuO_x on Au) at the nanolevel as well as the modification of surface stoichiometry by UV/ozone treatment. The structural transformation contributes to generating a surface charge, acting as nucleation sites for nanotip growth. This led to a significant increase in density and improvement in diameter of the nanotips for various substrates, such as ZnO, Au, GaN, and graphene. However, the surface oxygen by O₂ plasma treatment reduced the activity as activation sites of the exposed surface, resulting in the decrease of the density of the nanotips. This rational engineering of substrates by a structural transformation at the nanolevel may provide a promising method for producing highly dense one-dimensional nanomaterials.