Synthesis and structural characterization of tungsten trioxide nanoplatelet-containing thin films prepared by Aqueous Chemical Growth

We report the synthesis of WO ₃ thin films predominantly made up of nanoplatelets, on transparent plain glass microscope slides, by the low-temperature, soft chemistry method of Aqueous Chemical Growth (ACG). During the heterogeneous growth, by ACG, of WO ₃ thin films onto these plain glass substrates, nanoplatelet and nanorod-like structures of WO ₃ were also precipitated out of the Peroxotungstic acid precursor solutions and collected as slurries which were annealed at 500 °C to give ultra-fine powders of WO ₃. Scanning Electron Microscopy of the thin films and powders showed that nanoplatelets formed had thicknesses generally less than 300 nm and lengths and diameters in the 1-2 μm range. The thin films formed were less than 5 μm thick. Transmission Electron Microscopy (TEM) on one of the thin films confirmed the formation of nanoplatelets as well as nanorod-like structures, while High Resolution TEM alongside X-ray Diffraction and Raman spectroscopy suggested that the WO ₃ thin film grown on a plain glass microscope slide was monoclinic in crystal structure. While Energy Dispersive X-ray Spectroscopy, Fourier Transform-Infrared Spectroscopy, and Attenuated Total Reflection were used to establish the purity and bond structure of WO ₃ within the thin film, Selected Area Electron Diffraction gave further evidence of crystallinity within the nanostructures prepared. The potential use of the WO ₃ nanoplatelet-containing thin films for hydrogen sensing at 300 °C was demonstrated.