Sol-gel method is treating metal organic / inorganic in solution, sol - gel and then heat-treated and cured to form an oxide or a solid compound. Preparation of sol-gel thin film material has simple process, low cost, low synthetic, highly chemical uniformity (including doping substances better uniformly distributed in the film), diversity of shape of material characteristics.
The step of using sol-gel method to produce tungsten oxide thin film is: preparation of precursor salt, forming of sol and film, drying, heat treatment. Sol-gel method producing tungsten oxide thin film can be divided as peroxopolytungstic acid method, tungstate ion exchange method, tungsten alcohol saline solution and alcoholization of tungsten chloride.
Peroxopolytungstic acid method
Peroxide sol - gel method is one of the methods for producing tungsten oxide thin film. Metal tungsten powder reacted with hydrogen peroxide, the obtained product is peroxy tungstic acid until tungsten powder is completely reacted. After filtration, and then react with ethanol of low boiling point, generating a peroxy ester derivative of W, after which is spinning coated or dipping into thin film.
Tungsten alcohol saline solution
Tungsten alkoxides (e.g., W (OC2H5) 6) reacted with an alcohol of small molecules (e.g. T alcohol), generally use nitrogen as protective gas, and shaken for about one hour in an ultrasound, there is obtained WO3 sol, and then by dipping deposition or spin coating method, placing the sample in the air before annealling to complete the hydrolysis and condensation reactions, and then after annealing treatment we can obtain tungsten oxide thin film. Features of the method are a high purity of film, but relatively complex preparation techniques, and require a more complicate condition.
Tungstate ion exchange method
Adding exchange resin into ion exchange column after acid treatment, then adding sodium tungstate into ion exchange column to undergo the kation exchange process, after several minutes the transparent yellow solution is obtained. The solution is unstable which would aggregate into gel in a couple hours. After precipitated hydrated tungstic acid, tungsten oxide thin film is formed by spin coating method and the dipping method. Adding an appropriate amount of organic solvent, such as alcohol, acetone, etc. can stabilize the sol. Also add an appropriate amount of hydrogen peroxide delay the formation of gel. The advantage of this method is that all of the manufacturing processes are obtained at room temperature, there is no decomposition produced. This method can be used to produce a thick film without stress. The sol is unstable, it can form into a gel coating rapidly, it is difficult to control the filming time which results in low film adhesion capacity.
Alcoholization of tungsten chloride
Under protection of N2, WCl6 fully reacted with an alcohol, hydrogen chloride generated during the reaction is taken away by nitrogen, gradually the tungsten alkoxide solution is obtained, then adding a certain amount of alcohol and crosslinking agent, mixed them under a nitrogen atmosphere. Then form a suitable solution for producing tungsten oxide thin film by dipping or spin deposition method, finally after heat treatment tungsten oxide thin film is obtained.