1. Impurity and Residual Effects on the Growth of Oxide NanowiresHaitao Zhang, University of North Carolina at Charlotte, DMR 1006547 Outcome: Sodium impurity has been found to affect the compositions and structures of tungsten-based oxide nanowires even at a low concentration level of 20 ppm. This effect and nanowire yield can be further enhanced by the presence of residue deposition. Impact: Tungsten oxide (WO3) is of great importance in applications of smart devices, batteries, and solar water splitting, etc. By adding another metal element (e.g. Na), the crystal structures and physical properties of ternary tungsten oxides can be tuned by the control of compositions. Explanation:The effects of Na impurity on the compositions and structures of nanowires can be explained by the differences of vapor pressures between Na- and W- species. The enhanced impurity effect and nanowire yield with growth time are due to the enhancement of the local oxide vapor pressures produced by the residue deposition. These effects can be used to realize scale up growth of binary and ternary tungsten oxide nanowires with controlled compositions and structures in order to tailor the properties of nanowires for different applications. The changes of nanowire with growth time: (Top left) Photo of nanowire coverage on substrates, (top-right) Na/W atomic ratios at different zones, and (bottom) XRD spectra of phase evolution. (courtesy of H. Zhang)