Gold at the root or at the Tip of ZnO Nanowires: A Model

A study was conducted to investigate Au-assisted growth of ZnO nanowires and nanowire branches, with a special emphasis on the interaction between Au and adsorbed ZnO molecules. A simple growth model suggests that competition between the saturation rate and nucleation rate of ZnO on the Au particle results in two different growth models, leading either to the presence of the catalytic Au particles at the root or at the tip of the ZnO nanowires. The results of the study show that the diameter of the nanowires for the Au-catalyzed wire growth did not match that of the Au particles. It also found that the Au particle catalyzing the ZnO nanowire growth remains neither at the root nor the tip after extended nanowire growth periods. Finally, it was demonstrated that the surface migration of Au atoms on GaN/Si substrates limits position-controlled growth of ZnO nanowires.