Characterization and Modeling of WO3 Nanowires Synthesized via the Solvothermal Method: A Proposed 8-Pointed Star Prism Structure

The solvothermal method is a popular approach for preparing multifunctional WO3 films. In this study, a WO3 film composed of nanowires with diameters of 40–50 nm and lengths of 400 nm to 1 μm was prepared on indium–tin oxide (ITO) glass via the solvothermal process. Transmission electron microscopy (TEM) analysis confirmed that each WO3 nanowire is a monoclinic single crystal with a [002]-selective growth direction. By analyzing the scanning electron micrography (SEM) images at ultrahigh magnifications and observing that the fast Fourier transform (FFT) images of all nanowires were identical, an 8-pointed star prism model was proposed for the morphology of WO3 nanowires. Based on this model, the exposed crystal planes on the outer surface of each WO3 single crystal are supposed to be {120} and {210}, thereby forming an 8-pointed star prism. Finally, the model was validated through focused ion beam (FIB) and TEM assessments. This study deepens our understanding of the morphology of solvothermally synthesized WO3 nanowires and may open up a window for future research on the subject.