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 preparingmultifunctionalWO(3) films. In this study, a WO3 film composedof nanowires with diameters of 40-50 nm and lengths of 400nm to 1 mu m was prepared on indium-tin oxide (ITO) glassvia the solvothermal process. Transmission electron microscopy (TEM)analysis confirmed that each WO3 nanowire is a monoclinicsingle crystal with a [002]-selective growth direction. By analyzingthe scanning electron micrography (SEM) images at ultrahigh magnificationsand observing that the fast Fourier transform (FFT) images of allnanowires were identical, an 8-pointed star prism model was proposedfor 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 formingan 8-pointed star prism. Finally, the model was validated throughfocused ion beam (FIB) and TEM assessments. This study deepens ourunderstanding of the morphology of solvothermally synthesized WO3 nanowires and may open up a window for future research onthe subject. An 8-pointed star prism modelwas proposed for the morphologyof solvothermally synthesized WO3 nanowires. Based on thismodel, each nanowire is a single crystal of which the growth directionis [002] and the exposed crystal planes on the outer surface are {120}and {210}.