Hydrothermal preparation and characterization of nanocrystalline porous tin dioxide thin films

Nanocrystalline porous tin dioxide thin films have been successfully prepared on the ITO glass substrates via a simple hydrothermal synthetic process. Field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible transmittance spectrum were used to investigate the porous thin films. SEM results show that the thin films are porous with single-layer, monodisperse, nearly uniform depth, nano-sized pores homogeneously distributed over the surfaces of the films. The internal diameters of the pores range from about 20 to 240 nm, and main pore (above 85%) diameters range from 20 to 110 nm. XRD result indicates that the crystalline structure of the porous tin dioxide thin films is tetragonal rutile. These porous thin films show high optical transmittance (above 80%) in the visible-light range. The band gap of the porous thin film has been calculated to be 3.85 eV. Formation mechanism of the nanocrystalline porous tin dioxide thin films has been proposed. Hydrolysis and thermal decomposition of urea molecules play important roles in the formation of the nanocrystalline porous tin dioxide thin films.