Microplasma-based synthesis of vertically aligned metal oxide nanostructures

Vertically aligned metal oxide nanostructures (e. g., wires, needles, pillars and trees) of CuO, PdO and NiO were synthesized on several substrates (e. g., Si and ITO (indium tin oxide)) using a high-pressure (similar to Torr) microplasma-based growth technique. Organometallic precursors were dissociated in the hollow cathode region of a supersonic plasma jet creating a directed flux of metal species (e. g., atoms, metastables, etc) which react with an oxygen background to form crystalline metal oxide films having a variety of nanomorphologies. Spiral-like growth fronts were seen in some cases for CuO, suggesting that nanowire growth may involve screw dislocations. Large area, nanowire films >1 cm(2) with good adhesion and electrical connection to ITO substrates were deposited by raster-scanning a single jet. Details of the microplasma operation, the dynamics of the growth process and the resulting materials are discussed.