Solution-grown And Characteristics Of Zinc Oxide Nano-materials

Integrating the unique nanomaterials properties with ZnO bulk materials, low-dimensional ZnO has wide range of potential applications in optoelectronic devicesoperated in the blue and UV spectral regions. However, the growth progress is difficultto control and the properties are easily influenced by the relevant preparation condition.In this paper, solution method was employed to prepare ZnO nanomaterials, which havesteerable morphologies, and the influence of preparation condition on optoelectricproperties was also studied.Different morphologies of ZnO were prepared on the ITO glass coated with ZnOnanocrystal seed layer by solution method. The films that grown in the solution, inwhich aqueous ammonia （NH₃·H₂O） served as the hydroxyl source, are all consist ofdense and uniform ZnO nano-particles, the size of which is between several tens ofnanometers and hundreds of nanometers. Using HMTA as the hydroxyl source, ZnOnanorod arrays with good preferred orientation can be obtained. The XRD analysisindicates that all the ZnO nanomaterials are all hexagonal wurtzite structure.The morphologies of ZnO nanorod arrays grown in the solution containing HMTAand Zn（CH3COO）2·2H2O can be modified by adjusting growth time, growthtemperature, the amount that sodium citrate added and the annealing progress. Thediameter increases quasi-linearly from50nm to120nm, and the length from0.64μm to2.1μm when the growth temperature increases from75℃to90℃. The length firstlyincreased from0.5μm to1.6μm quickly, then slowly to2.3μm with adjusting the growthtime from30min to90min. The preferred orientation is destroyed after sodium citrateadded to the nutrient solution, because sodium citrate changes the nucleation procedureon the ZnO seed layer. Because of the atom migrating among the ZnO nanorods, theaverage diameter increased after annealing treatment.ZnO nanorod arrays exhibit the characteristic band-edge emission with a peak at375nm, the intensity of the “green-band” emission related to oxygen vacancies is muchstronger. The crystal quality descend with the fast nucleation and growth speed whenusing NH3·H2O as the hydroxyl source, so that there are no obvious band-edge emission,but the “green-band” emission is stronger. Compared with the lower growth temperature,the intensity of the band-edge emission rises rapidly when the ZnO nanorod arraysprepared in HMTA at90℃, the reason is that the crystal quality is the best. The “green-band” emission enchance and blue-shift from550nm to485nm, and theband-edge emission weaken relatively with annealing treatment, which induce moreoxygen defects.365nm ultraviolet responses of ZnO nanorod arrays show well repeatability. Theoxygen adsorption and desorption can influence the thickness of the depletion layerclose to the surface, and then change the electric property. It need time to achieve thedynamic equilibrium between adsorption and desorption, so that the response andrecovery time are both long. The density of the defects which capture charge carrierreduce, the recombination speed between different carriers and the reaction rate betweenelectron and oxygen are both accelerate, so the recovery time of the resistance reducesafter the annealing treatment.