Synthesis, Characterization Of Porous Anodic Alumina And ZnO Nanorod Arrays

ZnO is an important new semiconductor materials with a wide direct band gap of 3.32 eV and a hexagonal wurtzite structure. It has large excition bingding energy of 60 meV at room temperature. Higher Integration rate of nanometer structure are need in some complex systems. Controllable preparation of ZnO nanometer structure's is receiving people's high attention. Synthesis, characteriz- ation of porous anodic alumina and ZnO nanorod arrays were reported in this paper. Some meaningful results were obtained .In this paper, two-step anodization was used to fabricate porous anodic aluminiuma(PAA) films with the pore diameter ranges 20 to 50nm, in the electrolyte of oxalic acid. Through the measurements of PPA films by scanning electron microscopy(SEM) and X-ray diffraction, it was found that the PPA we prepared is an amorphous film, with the parallel-sided hexagonal pores ordering in a scale of a few micrometers. TEM micrographs show the pore diameter of porous anodic aluminiuma increases with the increase of anodizing voltage. The pore diameter of porous anodic aluminiuma was controlled by the anodizing voltage: from 20nm for 20V to 30nm for 30V to 40nm for 40V to 50nm for 50V with 0.3M oxalic acid. The pore diameter of porous anodic aluminiuma increases with the increase concentration of oxalic acid. But the pore spacing will be remain basically unchanged with the increase concentration of oxalic acid when other anodic oxidation conditions remain unchanged. The pore diameter of porous anodic aluminiuma was controlled by the concentration of oxalic acid: from 30nm for 0.2M to 40nm for 0.3M to 50nm for 0.4M. 0.3 M at 40 V voltage. 40 V voltage and 0.3M oxalic acid is the best condition . The pore diameter and the pore spacing of porous anodic aluminiuma were 40nm and 100nm at the best condition .Next ,we report the synthesis of HTlc-ZnAlCO₃ nanosheets on PPA by hydrothermal method in a zinc acetate and ammonia solution. HTlc- ZnAlCO₃ Nanosheets growth is impacted by concentration. Zinc acetate concentrati of 0.015M is the best solution at PH value in the solution for 10 conditions. The diameters and lengths of the obtained HTlc-ZnAlCO₃ nanosheets are in the range of 100nm and 4-6μm with 0.015M Zinc acetate solution.Then, large-scale symmetrical ZnO nanorod arrays on nanosheets were successfully synthesized by a hydrothermal method at lower tempera-ture.The as-prepared ZnO nanorods are wurtzite structure. The best condition for the synthesis of ZnO nanorod arrays is attempted to achieve by changing the solution concentration, reaction time, PH value. It was found that a very narrow range of pH value can grow symmetrical ZnO nanorod arrays . PH is about 10. Length of ZnO nanorods can be significantly increased by changing the growth ZnO time: from 350nm for 5h to 2μm. The ZnO orientation is bad with the reacting time of 2h. ZnO nanorods will be uniformand and closely arranged with 0.02M concentration of zinc acetate. ZnO nanorods will increase the length but uniform lower when further enhance the concentration to 0.03M. The best conditions are zinc concentration of 0.02 M, pH = 10 and the 5 hours reaction time..The diameters and lengths of the obtained ZnO nanorods array are in the range of 100nm and 350nm pespectively.The PL spectra of ZnO nanorod arrays contain a weak UV band peak at 383nm , a very strong broad blue band centered 433nm and a big band of luminescence. The UV emission is originated from excitonic recombination corresponding to the near-band-edge emission of ZnO. The luminescence emission peak located 433nm corresponds to the transition from the shallow level of oxygen vacancy to the valence band or transmit strap to the shallow level of zinc vacancy.The luminescence emission band corresponds to the transition from the shallow level of oxygen vacancy to the shallow level of zinc vacancy.The ZnO nanorods arrays gas sensor has higher sensitivity and lower operating temperature to ethanol。he best temperature is 230℃.Sensitivity measurement of ethanol showed that at the temperature of 230℃, the ZnO nanorods arrays gas sensor exhibited a sensitivity of 60 to 500ppm ethanol,the sensitivity achieved 20 even being exposed to the gas concentration as low as 100ppm ethanol.The sensitivity test of ethanol showed that the aligned zinc oxide nanorods devices had an improved sensing performance compared with the reported ZnO nanoparticle sensors.