Characterization of evaporated amorphous WO3 films by Raman and FTIR spectroscopies

The crystallinity of the frame work structure of evaporated amorphous tungsten oxide films was investigated using Raman spectroscopy. It was found from the deconvolution analysis of two W-O stretching modes that the full width at half maximum (FWHM) of the peak at 807 cm-1 was sensitive to the degree of crystallinity of a-WO3. The FWHM of the 807 cm-1 peak decreased by 35% as the substrate temperature was raised from 40 to 145°C. This change seems to be caused by the growth of clusters constituting the FWS. A characteristics splitting of the absorption peak of the O-H stretching mode was observed using FTIR spectroscopy for films deposited at substrate temperatures higher than 145°C and annealed subsequently at 150°C for 1 h. This was interpreted to be caused by the formation of structurally involved water molecules such as seen in crystalline MoO3·2H2O.