The Investigation Of Fabrication And Properties To W-doped VO₂ Nanoscale Thin Films Via Sputtering Oxidation Coupling Method

It is known that vanadium dioxide (VO2) thin film, as a special functional material, which possesses high thermal resistance and temperature coefficient, has attracted great attention. The film displays a reversible crystallographic transition from the monoclinic insulating phase to the rutile metal phase at about 68℃, concurrently with a drastic change in electrical, magnetic and optical properties as well.As a result of the exceptional performance, VO2 has been widely applied in various fields. However, The phase transition temperature (Tc) of VO2 is about 68℃, which is higher for some special applications. Besides, nanoscale VO2 thin films have attracted much interest due to some noticeable distinguished properties from bulk VO2 in recent years. Therefore, the main researches recently concentrate in reducing phase transition temperature of VO2 to nearly ambient temperature and fabricate high-quality nanoscale films by some simple methods.Researches indicated that phase transition temperature of VO2 thin film can be reduced to room temperature even below room temperature by doping. In this paper, we adopt a simple and novel method-Sputtering Oxidation Coupling (SOC) to fabricate nanoscale W-doped VO2 thin films on sapphire substrate. According to different results of nano thin films in different oxidation temperatures, it is found that the best oxidation temperature of W doped VO2 nanoscale thin films is 430℃. The four-probe instrument was applied to test sheet resistance of all samples. The phase transition temperature of W-doped VO2 nanoscale thin films were decreased to about 40℃. Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS) were employed to analyze morphologies and components of thin films respectively. Finally, the optical transmittance of thin films was analyzed via UV/VIS Spectrometer. The curves of optical coefficient such as the refractive index (n) and extinction coefficient (κ) versus photon-energy (E) were achieved by applying Film Wizard software to fit optical transmittance. According to temperature-resistance curve and XPS, there should be certain linear relationship between content of doped W and semiconductor-metal phase transition temperature; Tc was gradually reduced with the increasing of tungsten components in the thin films, but the change range of the orders of magnitude and infrared transmission are gradually inconspicuous before and after thin film change. The refractive index (n) and extinction coefficient (κ) of W-doped VO2 nanoscale thin films have changed regularly in comparison with VO2 nanoscale thin films. According to the formula, energy band of W doped VO2 nanoscale thin films were calculated; the results show that energy band gradually decrease along with the increasing of tungsten components in the films.This paper also makes a comprehensive introduction and comparison between sputtering oxidative coupling (SOC) method and some commonly used preparation technology. It is obvious that Sputtering Oxidation coupling (SOC) possess more advantages in comparison with other preparation technologies, such as low cost, high yield, easy operation, simple doping process, beneficial to the instrument protection and good performance of their samples and so on.