Electrochemical Deposition VO₂ Film And Characterization

The researchers have paid a lot of attention to Vanadium oxide for the past two decades because of the unique and abundant physicochemical characteristics.Vanadium dioxide?VO₂?is a very interesting semiconductor material.VO₂ undergoes a sharp metal-insulator transition?MIT?around68?,which is caused by the structural phase transition from low temperature monoclinic?M₁?phase to a high temperature rutile-type?R?phase.Some research shows that there is another monoclinic?M₂?phase between the M₁ and R which can be obtained by uniaxial stress or doping.The MIT changes the electrical and optical properties of the VO₂.Because of the significant change in properties with the MIT,Vanadium oxide thin films is widely applied in the new thermal devices,optoelectronic devices,infrared detector and storage components aspect.A lot of methods have been used to fabricate vanadium oxide films such as CVD,MS,sol-gel method,reverse micelle technique.The same problem of all these methods is that it's difficult to make Vanadium films with a single phase.In this thesis the electrochemical deposition method is used to prepare vanadium oxides film.Electrodeposition can be a widely recognized simple method for producing vanadium oxides if we can control the microstructure,surface morphology and uniformity of oxide deposits by adjust the deposition variables.In this thesis,a variety of deposition variables were explored through a series of experiments.As a result,the relationship between the method and the properties has been found.First,the VO_x films were deposited onto Pt substrate.Depositions have been made with an anode potential of 1.3V?vs.SCE?in 30 min from solutions of 0.15mol/L VOSO₄,with pH kept constant at 2.0.A 200 nm thicked film V₂O₅ can be obtained according to the above conditions.Second,the film annealed at 550?in Ar atmosphere for an hour formed a single phase of VO₂.The resistance of the film change as a function of temperature was characterized.The resistance changes by 10⁴ at 65-70?.The optical and electrical conductivity of vanadium thin film can be modified by doping high-valence cations.In this thesis doping methods were explored.We doped Mn⁴⁺into VO_x film by Adding 0.05mol/L of Mn²⁺ions in the basic solution.After annealing the main phase of the film is still VO₂,but the phase transition temperature reduced to 55-60?.At the same time during MIT the resistivity variation decreased to 10³,and the doping increased the resistance of metallic state.In addition,dopint Mn⁴⁺can form three-dimensional porous structure V₂O₅ films.Experiments show that in 0.02mol/L the film capacitor reaches a maximum.Compared to 100F/g film capacitor made by other methods,film capacitor can reach 115F/g in our experiment and this method is more easier.