Department of Physics and Astronomy, Howard University , 2355 Sixth Street NW, Washington, DC 20059, United States.
J Phys Chem A. 2013 Dec 19;117(50):13825-31. doi: 10.1021/jp408303p. Epub 2013 Oct 10.
Metal oxides are suitable for detecting, through conductive measurements, a variety of reducing and oxidizing gases in environmental and sensing applications. Metal-oxide gas sensors can be developed with the goal of sensing gases under specific conditions and, as a whole, are heavily dependent on the manufacturing process. Tungsten oxide (WO3) is a promising metal-oxide material for gas-sensing applications. The purpose of this paper is to determine the existence of a correlation between thermal effects and the changes in the Raman spectra for multiple WO3 structures. We have obtained results utilizing Raman spectroscopy for three different structures of WO3 (monoclinic WO3 on Si substrate, nanopowder, and nanowires) that have been subjected to temperatures in the range of 30-160 °C. The major vibrational modes of the WO3:Si and the nanopowder samples, located at ~807, ~716, and ~271 cm(-1), correspond to the stretching of O-W-O bonds, the stretching of W-O, and the bending of O-W-O, respectively; these are consistent with a monoclinic WO3 structure. However in the nanowires sample only asymmetric stretching of the W-O bonds occurs, resulting in a 750 cm(-1) band, and the bending of the O-W-O mode (271 cm(-1)) is a stretching mode (239 cm(-1)) instead, suggesting the nanowires are not strictly monoclinic. The most notable effect of increasing the temperature of the samples is the appearance of the bending mode of W-OH bonds in the approximate range of 1550-1150 cm(-1), which is related to O-H bonding caused by humidity effects. In addition, features such as those at 750 cm(-1) for nanowires and at 492 and 670 cm(-1) for WO3:Si disappear as the temperature increases. A deeper understanding of the effect that temperature has on the Raman spectral characteristics of a metal oxide such as WO3 has helped to extend our knowledge regarding the behavior of metal oxide-gas interactions for sensing applications. This, in turn, will help to develop theoretical models for the identification of specific metal oxide-gas relationships.
金属氧化物适合通过导电测量来检测环境和传感应用中的各种还原和氧化气体。金属氧化物气体传感器可以针对特定条件下的气体传感进行开发，并且总体上严重依赖于制造工艺。氧化钨 (WO3) 是一种用于气体传感应用的很有前途的金属氧化物材料。本文的目的是确定热效应与多种 WO3 结构的拉曼光谱变化之间是否存在相关性。我们已经使用拉曼光谱获得了在 30-160°C 范围内的三种不同 WO3 结构（硅衬底上的单斜 WO3、纳米粉末和纳米线）的结果。WO3:Si 和纳米粉末样品的主要振动模式位于807、716 和~271cm-1，分别对应于 O-W-O 键的拉伸、W-O 的拉伸和 O-W-O 的弯曲，这与单斜 WO3 结构一致。然而，在纳米线样品中，只有 W-O 键的不对称拉伸发生，导致 750cm-1 带，并且 O-W-O 模式（271cm-1）的弯曲是拉伸模式（239cm-1），表明纳米线不是严格的单斜晶系。样品温度升高的最显著影响是在大约 1550-1150cm-1 范围内出现 W-OH 键的弯曲模式，这与湿度效应引起的 O-H 键合有关。此外，随着温度的升高，纳米线的 750cm-1 处的特征以及 WO3:Si 的 492 和 670cm-1 处的特征消失。更深入地了解温度对金属氧化物（如 WO3）拉曼光谱特征的影响，有助于扩展我们对金属氧化物-气体相互作用在传感应用中的行为的认识。这反过来又有助于开发用于识别特定金属氧化物-气体关系的理论模型。
