Phase Transformation Studies of Metal Oxide Nanowires

Here, we report that the postsynthesis nitridation of tungsten oxide nanowires can result in single crystal nitride nanowires when the initial diameters of the nanowires are less than 10 nm. For nanowires with diameters greater than 10 nm, the nitridation of nanowires resulted in polycrystalline but highly oriented tungsten nitride domains in nanowires. Partially nitrided nanowires show an epitaxial relationship between the nitride nuclei and the oxide nanowire, being oriented with respect to the axial direction of the nanowires. The stress resulting from the strain due to lattice mismatch between oxide and nitride phases seems to control the critical size of the nitride nuclei within oxide nanowires. The photoluminescence data show that the resulting bandgap of the tungsten nitride nanowires was downshifted to 2.95 eV from 3.54 eV for tungsten oxide nanowires.