Gallium nitride (GaN) nanostructures are used in optoelectronic applications due to their unique optical and electronic properties. For some optoelectronic applications and potential photocatalytic systems, the growth of GaN nanowires on metallic substrates instead of expensive single crystalline semiconductors can be beneficial due to specific properties of metals. In this study, GaN nanowire systems were grown on 300 nm Ti-film/Si(1 0 0) and Ti-foil by plasma assisted molecular beam epitaxy (PA-MBE) and characterized in situ by Auger electron spectroscopy (AES) and ex situ by scanning electron microscopy (SEM). Effects of (i) the nature of substrate surface, (ii) Ga flux, and (iii) substrate temperature on the growth of GaN nanowires were investigated. Nearly vertical nanowires can be grown on Ti-films covered with amorphous TiOx or TiOxNy, which is formed during the nitridation process. To grow nearly vertical nanowires on Ti-foils, pre-nitridation of the substrate surface was found to be important. The orientation of GaN nanowires grown on nitridated Ti-foil is determined by the grain alignment of the original Ti-foil, however, GaN nanowires grown on nitridated Ti-foils are uniformly oriented to one direction within an individual grain, which is most likely due to the epitaxial relation between the nanowires and the underneath grains of the polycrystalline Ti-foils. Both the orientation and nanowire density vary on different grains
