Abstract: Large-scale, single-crystalline, cubic-structured tungsten oxide (WO3–δ) nanowire networks have been synthesized by the thermal evaporation of tungsten metal powder in the presence of oxygen. The formation of ordered planar oxygen vacancies is suggested to be the driving mechanism for the formation of these interpenetrative nanowire networks. With different growth temperatures, two kinds of tungsten suboxide nanowires (W18O49 and W20O58) were obtained. The structures, morphologies, and compositions of these two nanowires were characterized by scanning electron microscopy (SEM), electron probe microanalyzer (EPMA), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and Raman techniques. The results show that XRD and TEM are not good characterization techniques for identifying W18O49 and W20O58  nanowires; however, Raman spectroscopy (RS) is a powerful tool to distinguish the difference between them. This is due to the notable molecular bond contributing to the vibrational frequency.  The sequence of bulk WO3 crystal phases, in order of increasing temperature, is the following: monoclinic (ε phase) →triclinic (δphase)→monoclinic (γ phase)→orthorhombic (β phase)→ tetragonal (α phase). However, there are still no reports on the study of the phase transition determined for the one-dimensional WO3 nanostructure. In this letter, we report on a study of thermochromic phase transition that we have undertaken on WO3nanowires and the effects of hydrostatic pressures up to 42.5 GPa on the Raman-scattering spectrum of WO3 nanowires. Besides, a series of nano-devices fabricated from WO3 nanowires are also studied.

Location: 606 Conference Room
Date and time: Nov 25, 2011   14:30