| ZnO nanostructures with well-defined shape and special size have attracted more and more interests because it has numerous potential applications in short wavelength optoelectronic devices and sensors due to its direct optical band gap and high exciton binding energy (-60mev) The properties of materials depend not only on the composition, structure, size, but also on the morphology and dimension. The control of structure, size and morphology during the growth of ZnO nanostructure has important application. It is important for application to control the structure, size and morphology of the ZnO nanostructures by adjusting the conditions during the synthesis process. In this paper, we had synthesized large scale ZnO nanorod arrays,flower-like ZnO nanosheets,flower-like ZnO nanorods and ZnO nanotub arrays by hydrothermal and electrochemical method. And we had studied their photoelectric properties.Specific research content as follows:1. High-density vertically aligned ZnO nanorods arrays,flower-like ZnO nanosheets,flower-like ZnO nanorods were synthesized on substrate by changing the substrate, solution pH value, and the growth mechanism of these ZnO nanostructures had discussed. When the solution concentration is 0.1 M/L and the pH value is 10.6, the uniform and tidy ZnO nanorod arrays can be prepared. The ZnO nanorods are hexagonal wurtzite structure. Different substrate determines different nanometer ZnO morphology. It is flower-like nanorods and flower-like ZnO nanosheets on Al substrate. But it is ZnO nanorod arrays on the other substrates.Such ZnO nanorods arrays exhibited strong ultraviolet emissions at 378 nm at room temperature and a broad green defect-related visible emission, indicating their high crystallinity and excellent optical quality. The current-voltage (Ⅰ-Ⅴ) characteristics show the typical rectifying behavior of heterojunctions, from which the turn-on voltage is about 2.28 V. The dark current density is about 0.05mA at 7.5V reverse bias.2. High-density vertically aligned ZnO nanotube arrays were prepared on p-Si substrates by a facile and simple chemical etching process from electrodeposited ZnO nanorods. The as-prepared nanotubes are hexagonal. Such ZnO nanotube arrays exhibited strong ultraviolet emissions at 378 nm at room temperature and a broad weak green defect-related emission, indicating their high crystallinity and excellent optical quality. Current-voltage measurements of the device showed good rectifying behavior, from which a turn-on voltage of about 1.8 V was obtained. And very good response to ultraviolet light illumination was observed from photocurrent measurements in the reverse biased condition. The result show the device is a promise candidate for UV detection.3. The ZnO flower-like structures of nanosheets and nanorods were synthesized by a simple hydrothermal method on the glass substrate with an Al layer, without the assistance of an additional surfactant, of which morphology was controlled by adjusting the pH of the solution. For the 3D nanostructures of nanosheets after annealing, the blue emission at about 410nm disappeared which may be due to zinc vacancy defect state. The yellow band emission at about 550nm was enhanced which could originated from the interstitial oxygen. These results indicated that the concentrations or types of the dominant defects could be changed because of the diffusion of Al substrates during annealing. The as-prepared flower-like nanostructures of nanorods exhibited a high UV emission (at about 380nm). After the samples were annealed, the green emission (at about 500nm) was also enhanced abnormally, except for the UV emission (at 380nm), indicating the only top crystalline quality could be improved by annealing for the complex nanostructures and the bottom could not be improved. Our results present a simple, reproducible and cost-competitive method to controllably synthesize ZnO three-dimensional flower-like structures and would provide useful information for the fabrication of optoelectronic devices at room temperature. |
PDF Full Text Request