Abstract
Ultralong cadmium oxide nanowires were synthesized in high yield on gold-coated silicon substrates by using a vapor transport process. Cadmium vapor generated by the carbothermal reduction of CdO powder in a tube furnace heated to 500 °C was carried to the substrate zone by an argon flow with a trace amount of oxygen. The CdO nanowires grew via a vapor - liquid - solid growth mechanism. The diameters of the nanowires are ∼40-80 nm, and can reach lengths of 30-50 μm. Because the nanowire formation was gold particle catalyzed, patterned nanowire growth on substrates can be achieved. These nanowires grew along the [111] direction and have slightly rough surfaces due to the presence of crystalline CdO shells formed via a physical vapor deposition process. Interesting CdO nanowires with a necklace-like morphology were also observed in a small region of the substrate, where the oxygen supply may be ample to facilitate the lateral growth of rhombohedron-shaped crystals over the straight wires. Electron diffraction and high-resolution TEM results suggest that these side crystals should grow epitaxially on the wire surfaces. The band gap of the CdO nanowires with smoother surfaces was determined to be ∼2.53 eV. These nanowires exhibit a relatively weak emission band centered at ∼550 nm. © 2006 American Chemical Society.