The most powerful tool for the structural analysis of tungsten suboxide nanowires: Raman spectroscopy
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Jian Chena) State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Province Key Laboratory of Display Materials and Technologies, Sun Yat-Sen (Zhongshan) University, Guangzhou 510275, People’s Republic of China; and Instrumentation Analysis and Research Center, Sun Yat-Sen (Zhongshan) University, Guangzhou 510275, People’s Republic of China
Shao Zhi Deng and Ning Sheng Xub) State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Province Key Laboratory of Display Materials and Technologies, Sun Yat-Sen (Zhongshan) University, Guangzhou 510275, People’s Republic of China
Wei Hong Zhang Instrumentation Analysis and Research Center, Sun Yat-Sen (Zhongshan) University, Guangzhou 510275, People’s Republic of China (Received 4 May 2007; accepted 15 October 2007)
Crystalline tungsten suboxide nanowires were grown on silicon substrates by thermal evaporation of tungsten powder in a flow of argon gas without any catalyst. 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.
I. INTRODUCTION
Tungsten oxides, which belong to the family of transition metal oxides, are of great interest and have been investigated extensively for their promising physical and chemical properties. Their excellent photochromic, electrochromic, and gaschromic properties are commonly used in, for example, devices for flat-panel displays, smart windows, writing–reading–erasing optical devices, optical-modulation devices, gas sensors, and humidity and temperature sensors.1–5 In addition, some nonstoichiometric tungsten oxides have attracted considerable attention for their interesting electronic properties, especially superconductivity and charge-carrying ability.6 Recently, some studies on the one-dimensional nanoAddress all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2008.0056 402
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 2, Feb 2008 Downloaded: 07 Mar 2015
structure of WO3–x have been reported. Li et al.7 synthesized W18O49 nanowires through the controlled removal of surfactant from the presynthesized mesolamellar precursor, and Liu et al.8 fabricated W20O58 nanorods by the thermal-oxidation method in the same year. Both studies investigated the nanomaterials using similar characterization techniques. Later, Zhang et al.9 grew W18O49 and W20O58 nanorods w
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