Synthesis And Luminescence Of Quasi One Dimensional ZnO Nanomaterials

Quasi-one-dimensional nanomaterial is one of the most active fields in the research of nanomateirals. ZnO nanomaterials attract extensive interests due to its ultraviolet photoluminescence. In the present thesis, several ZnO quasi-one-dimensional nanomaterials with novel morphologies were fabricated by chemical vapor deposition method. ZnO powder and selective metal elements were used as starting materials. Among them, modified nanohelices, nanoleaves and indium-doped nanospirals were synthesized for the first time. The sample was characterized by X-ray diffraction, scanning electron microscopy, and transmission microscopy equipped with energy-dispersive X-ray spectroscopy. The growth mechanisms were discussed and the proper experimental parameters for synthesizing these materials were summarized. The photoluminescence were analysized, and some interesting results were obtained.Using ZnO and Sb powder as source, super-uniform single crystal ZnO nanohelices were synthesized. X-ray diffraction spectra showed that the sample is hexagonal wurtzite ZnO structure. Scanning electron microscopy images displayed the helical structure of the sample. The nanohelices are very uniform, up to several micrometers long. One period of nanohelix is built up by six nanorods of equal length. Calculation according to a simple model showed that the helical structure is energetically favorable. The nanostructures could be used as building blocks in micro-optoelectronic and micro-electromechanical systems. Experimental parameters suitable for the growth of the ZnO nanohelices were obtained according to a series of experiments.On the basis of the ZnO nanohelices, disk modified nanohelices of ZnO were synthesized. The ZnO nanohelices are constructed by nanorods which are regularly attached with disks. Within one period there are twelve disks symmetrically attached on the surfaces of the nanorods. The disks are composed of nanometer-sized cluster ZnO and SiOx shells. The Si comes from the evaporation of Si substrates in high temperature region. The photoluminescence of the sample showed that the ultra-violet emitting at room temperature comes from free-to-neutral acceptor transition. The exciton bound to neutral acceptor should be attributed to the Sb doping.ZnO nanocombs and nanoleaves were fabricated homoepitaxially. The ZnO nanocombs were synthesized by placing ZnO and Sb separately. The length of the nanocombs is up to several micrometers. The uniform teeth formed interesting nano-cantilevers. With the mixture of ZnO and Te, ZnO nanoleaves were formed. A polygonal nanodisk was grown epitaxially on one side of each ZnO nanowire near its top. High-resolution transmission microscopy showed that no dislocations or planar defects exist near the joints of the nanawire and the nanodisk. The nanodisks grew homoepitaxially on the nanowires. The room temperature photoluminescence of this sample shows a strong ultra-violet emitting and relatively week visible emitting. The visible emitting should come from the defects states on the surfaces. The temperature dependent photoluminescence reveals that the ultra-violet emitting at room temperature should be the recombination of free exciton. On the basis of our experiments, we summarized the proper experimental parameters for the growth of the leaflike ZnO nanostructures. The polar nanodisks should be useful in sensors and microdisk lasers.Indium-doped ZnO nanobelts, nanospirals, and superlattice nanostructures were synthesized by one-step chemical vapor deposition method with ZnO and In as sources. The indium-doped single crystal ZnO nanobelts have broad width of about 900 nm. High-resolution transmission electron microscope results show that the nanobelts are structurally uniform, free of defects. Indium is effectively doped into ZnO and replaces parts of Zn in it. The indium-doped ZnO nanospirals are constructed by rolling polar nanobelts. The typical radius-of-curvature of the nanospirals is several micrometers. The structure is energetically favorable in terms of the electrostatic polar charge model. Because of indium-doping, the photoluminescence of indium-doped ZnO nanomaterials shows a relatively weak ultra-violet emitting and a strong visible emitting with redshift.