Controlled growth behavior of chemical vapor deposited Ni nanostructures

Isolation of four distinct nanostructured Ni products is demonstrated in a well-controlled chemical vapor deposition process. These nanostructures include core-shell Ni-NiO nanowires, horizontally oriented nanowires, vertically oriented nanowires, and fully isometric cubic crystals all obtained upon an amorphous SiO ₂|Si growth substrate from an identical metal halide precursor. Transmission electron microscopy indicates the horizontally-and vertically-oriented nanowire products to be high-quality single crystals with a preferred growth axis along the 001 direction while the Ni-NiO core-shell nanowires are polycrystalline metal at the center and surrounded by an outer oxide. The differing crystal structures are reflected in the magnetic response of each nanowire type, as evidenced by magnetoresistance measurements. Detailed discussion of the formation mechanisms leading to each of the four nanostructured Ni products is presented along with a discussion of the general applicability of this non-epitaxial growth process to other material systems.