Improvement in aligned GaN nanowire growth using submonolayer Ni catalyst films

We report a route to ultrahigh-density and highly aligned single-crystalline GaN nanowires on sapphire by employing ultrathin Ni catalyst films with submonolayer thickness. The nanowire density and the degree of alignment were found to be highly sensitive to changes in the Ni catalyst film thickness below 1 nm, a regime rarely explored in catalyzed nanowire growth before. For submonolayer Ni films on sapphire, high activation energy for Ni diffusion on sapphire surface is attributed to the formation of high-density and ultrasmall Ni islands with a narrow size distribution, which in turn leads to high-density and highly aligned GaN nanowires. (C) 2008 American Institute of Physics.