Preparation Of Optical WO₃-based Hydrogen-sensing Thin Film And Its Properties

Tungsten oxide film material is a important functional material. It is studied and applied extensively because of its electrochromic property, gasochromic property, photochromic property, electrochemistry, etc. Especially gasochromic property is applied to gas sensors extensively. A lot of studies manifest that tungsten oxide with doped catalyst(Pt,Pd) have excellent hydrogen sensitive properties even at room temperature. In this paper, a new method has been adopted to make WO₃-doped thin films,that is the tungsten oxide film with Pt(Pd) catalyst were prepared with sol-gel and DC reactive magnetron sputtering methods. The conditions of this new method have been studied. Some technical parameters have been optimized by experiment. The hydrogen-sensing property of the thin film has been tested. The optical properties and surface structures of the film have been characterized. The relationship between hydrogen-sensing mechanism of the film and its structure has been discussed.Firstly, the mechanism of hydrogen response and developmental actuality were summarized in brief. Secondly, the preparative methods, main materials, instrumentation and technological process of the new method were introduced in detail. Simultaneously, some importance factors which affect the properties of the films were analyzed particularly, and Some technical parameters have been optimized also. Thirdly, the film's hydrogen-sensing property has been tested. At last, the film's structures have been characterized, and its hydrogen-sensing mechanism has been analyzed.In the preparation of tungstenic acid sol, H₂O₂ and ethanol can make the sol become more stability. When the mol ration of H₂O₂ and tungstenic acid is 1:2, and the vol ration of ethanol and tungstenic acid is 1:2, the tungstenic acid sol can been preserved long, and the tungsten oxide film of it is preferably.In the preparation of WO₃-based films with catalyst, the experimental result indicated that, the anneal temperature has great impact on the film's hydrogen-sensing property. The film becomes blue from clearly as long as the anneal temperature is beyond 400℃, and then it has little hydrogen-sensing property. When the time of doped catalyst is 1s, the film has good hydrogen-sensing property. The viscidity of the tungstenic acid sol has impact on the film's hydrogen-sensing property also. When viscidity is 180～300mpa·s, the film has good hydrogen-sensing property and has a permeation variety of light about 30% to 0.2% H₂/N₂.WO₃-based film doped by Pt(orPd) prepared with both sol-gel method and reactive magnetron sputtering method have good hydrogen sensitive property. When respond to 80ppm～40000 ppm hydrogen, the film's permeation rate of light changes evidently, and it has a permeation variety of about 14% to 80ppm H₂/N₂. The film's resumptive time is less than 60s and it has good repeated property.WO₃-based film doped by Pt(orPd) prepared by optimized parameters were characterized by X-diffractometer, tunnel scan-atomic force microscope, double-beam UV-VIS spectrophotometer and X-ray Photoelectron Spectroscopy(XPS). As results of x-diffractometer, WO₃-based film doped by Pt(orPd) prepared by both sol-gel and DC reactive magnetron sputtering methods has higher crystal temperature than tungsten oxide films undoped. When annealed at 460℃the film is began crystal with bigger FWHM and diffractive acuti-apices.As results of UV-VIS spectrophotometer, pure tungsten oxide film has high transmission rate(>90%), but when doped by Pt(orPd), it has laigher transmission rate. And WO₃-based film doped by Pd has higher transmission rate than doped by Pt when prepared at the same condition. Transmission rate of the film falls as anneal temperature increasing.As results of tunnel scan-AFM, WO₃-based film doped by Pt(orPd) is planar in the surface when annealed at 100℃, WO₃ molecule is tend to tetrahedron structure; and when annealed at 400℃, the surface of the film is more planarer, and then WO₃ molecule become cube structure.As results of XPS, tungsten oxide films doped by Pt have evident colouring- bleaching domino offect; The transition between W4+,W5+ and W6+ is the main cause of arosing WO₃-x films changing colour.The Pt(Pd) sputtered WO₃-based hydrogen-sensing thin film by both DC reactive magnetron sputtering method and sol-gel method has better property as loosen holes which have fast hydrogen response ionized by Pt(Pd). The film has excellent hydrogen absorbing property and the method is preferred for the sensor to distinguish hydrogen.