Study On The Preparation Of ZnO Film By Electrophoretic Deposition

ZnO films were prepared by electrophoretic deposition (EPD) using two suspension systems: ZnO colloid fabricated by colloid synthesis was deposited on ITO (Indium Tin Oxide) conductive glass, and ZnO powders fabricated by direct precipitation and homogeneous precipitation were dispersed in ethanol or isopropanol (IPA) to form stable suspensions and then deposited on iron sheets. Through XRD, TEM, SEM and Spectrophotometer, the colloid, powders and deposited films were characterized and investigated. By these tests, the effects of colloid, suspensions and EPD process on macro morphology, microstructure and visible optical transmittancy and absorbance property of deposited film were studied.The results show that the concentration of precursor liquid (zinc acetate dissolved in IPA) as well as NaOH IPA solution, the synthesis temperature and aging time at room temperature influence the film transparency, thickness, surface roughness, particle packing density and bond strength to the substrate obviously. The best hexagonal wurtzite ZnO colloid with particle size of 4⁸nm was obtained after 2³ days aging at room temperature when the concentration of precursor liquid and NaOH IPA solution were 5.5×10^-3mol/L and 1.25×10^-2mol/L respectively, and the synthesis temperature was minus 15℃. Using this optimized colloid, the porous ZnO film with high quality and excellent bond strength was obtained at constant voltage. It is found that the distribution of electric fields between electrodes and on the substrate surface affects the film macro morphology, and followed the formation of circinate recesses on film surface. With the increasing of deposition voltage and time, the film thickness and particle packing density increased, the visible optical transmittancy of film decreased and the absorbance curve of ultraviolet light appeared red shift.The film deposited via suspension with powder prepared by homogeneous precipitation has better quality with fine particles and uniform granularity. The addition of Zn(NO3)2 into the suspension with mol ration of 1:25 to ZnO powder, and diethanolamine (DEA) with volume ration of 1:50 to suspension, will stabilize the suspension, promote the EPD, improve the film surface morphology and enhance the bond strength. The organic medium and substrate have great impacts on the film deposition and EPD system. High quality films could be deposited on iron sheets by using of the suspension adopting both alcohol and isopropanol as dispersant; but the film could be deposited on ITO conductive glass only adopting isopropanol as dispersant.