Structures and optical properties of thin tungsten oxide nanowires treated with poly(ethylene glycol)

Tungsten oxide (W18O49) nanowires exhibit a unique near-infrared optical response due to their oxygen defects, which is important for both basic research and device applications. The diameter of W18O49 nanowires strongly affects the performance of their thin films, and samples with smaller diameters are required for improvement of such device performances by taking an advantage of larger surface area. However, in the conventional synthesis process, aggregation of nanowires and bundle formation inhibit the preparation of nanowires with small diameters. In this study, we prepared W18O49 nanowire samples with relatively small diameters through the control of the aggregation using a dispersant such as poly(ethylene glycol) (PEG), and evaluated their structures and optical properties. We found that PEG treatment can effectively reduce the diameter of the bundles, and W18O49 nanowire samples mainly containing relatively small bundles with an average diameter of less than 10 nm were obtained.