Structural and optical properties of tungsten-doped vanadium dioxide films

Thin films of tungsten (W)-doped thermochromic vanadium dioxide (VO2) were deposited onto soda-lime glass and fused silica by radio frequency magnetron sputtering. The doped VO2 films were characterized by X-ray diffraction, optical transmittance measurement, and near field optical microscopy with Raman spectroscopy. X-ray diffraction patterns show that the (011) peak of W-doped thermochromic VO2 film shifts to a lower diffraction angle with the increase of W concentration. The optical measurements indicated that the transmittance change (?T) at wavelength of 2500 nm drops from 65% (?T at 35 ?C and 80 ?C for undoped VO2 film) to 38% (?T at 30 ?C and 42 ?C for the doped VO2 film). At the same time, phase transition temperature drops from 65 ?C to room temperature or lower with the increase of W concentration. Near field optical microscopy image shows that the surface of W-doped VO2 film is smooth. Raman results show that the main Raman modes of W-doped VO2 are centered at 614 cm?1, the same as that of undoped VO2, suggesting no Raman mode changes for lightly W-doped VO2 at room temperature, due to no phase transition appearing under this condition.