Study On Infrared Emissivity Of Al-Doped ZnO Thin Films Prepared By Sol-Gel Process

In this paper, the properties, preparation methods, applications and developments of ZAO(Al-doped ZnO) thin films were reviewed. The ZAO thin films were deposited on quartz glass substrates by sol-gel method from isopropanol or 2-methoxyethanol solutions prepared by Zinc acetate as precursor, monoethanolamine as stabilizer and aluminum chloride as dopant. The dip coating method was used.The phase structure, surface morphology and infrared emissivity in 8～14μm waveband of the ZAO thin films prepared at different conditions(such as heat-treatment temperature, Al-doped concentration, sol concentration and film thickness) were investigated through X-ray diffraction (XRD), field-emission scanning electron microscopy(SEM) and SR5000 spectrum radiometer, respectively. The effects of heat-treatment temperature, Al-doped concentration, sol concentration and film thickness on properties of ZAO thin films were investigated systematically. The XRD results show that no peaks of Al₂O₃ occur in the XRD patterns and peaks shift to low 2θ, variation of d-spacing of ZnO in the films were found at the same time. They imply that Al was doped into ZnO lattice successfully. The phase structure of ZAO thin films are the same as ZnO with highly C-axis oriented.The microstructure of the films was related to content of sol, smoothness of the glass surface and heat treatment. ZAO grains in thinner films show random growth during heat treatment while certain orientation growth .of ZAO grains was found in the thick(?) films. The SEM results indicate that the thickness of ZAO thin films is related with sol concentration.The thickness of ZAO thin film is about 2.5μm with one time dip-coating when the sol concentration is 0.5mol/l. The experimental results of infrared emissivity in 8～14 μm waveband of the ZAO thin films show that the infrared emissivity of films decreases with increasing of heat-treatment temperature from 400 to 700℃. However, further increasing of heat-treatment temperature above 700℃, the infrared emissivity shows significantly increaseing. When the isopropanol was used as organic solvent, the infrared emissivity of ZAO thin films whose sol concentration was 0.3 mol/1 is lowest. The Al-doped concentrations have affected the infrared emissivity of ZAO thin films heavily. The infrared emissivity is lowest when the Al-doped concentration was 6at.%. In this paper, the thickness of films has...