Study On Preparation And Properties Of Si-based ZnO Nanostructures

Due to fascinating properties and novel applications of ZnO in optical, electrical, piezoelectric and other fields, ZnO nanomaterials attract great interests. In the display field, ZnO nanomaterials with a low turn-on and threshold field, high current density, stable emission current and low prepared-cost have been considered as one of the best promising field-emission cathode materials.In this dissertation, the field emission properties of ZnO have been improved by increasing the nanowire aspect ratios or adding the doped elements. On the self-made ultrathin alumina membrane (UTAM) substrates, we synthesized vertically aligned ZnO nanowire arrays and studied piezoelectric characteristics under atomic force microscope (AFM) contact mode. The morphologies of ZnO were found to be changed via adding surfactants in solution, and the growth mechanism and photoluminescence (PL) properties were studied. The main contents are as follows:1) We prepared vertically aligned ultralong ZnO nanowire arrays on the silicon (Si) substrate via CVD route without any catalysts. The length of nanowire arrays is up to 310μm and aspect ratios are as high as 660. In the process, nanowire arrays vertically grew on the silicon substrate via ZnO seed layers inducing. The results of field emission show that the turn-on, threshold field and field-enhancement factor of 60-min sample are 2.09 V/μm, 7.89 V/μm and 3582, respectively. The results exhibit that ultralong ZnO nanowire arrays have favorable field emission properties.2) We firstly synthesized leaf-like In-doped ZnO structure on the bare Si substrate by CVD method without assisted catalysts. The results of the high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), energy dispersive spectrometer (EDS) indicate that In-doped ZnO structures are being the superlattice. Compared to nanowire arrays, Leaf-like structures have a red shift phenomenon in the visible wavelength of PL and ultraviolet visible (UV) spectra. In addition, the turn-on field, threshold field and field-enhancement factor of leaf-like structures are 0.86 V/μm, 4.35 V/μm, and 4843, respectively. These measurements demonstrate that leaf-like ZnO structures have excellent field emission properties.3) We evaporated a layer of Au film on the UTAM and obtained ordered Au nanodot arrays after removing UTAM. We also synthesized vertically aligned ZnO nanowire arrays on coated-Au UTAM by CVD and measured their piezoelectric properties under the conductive atomic force microscopy (CAFM) with contact scan mode. However, on bare UTAM without Au-coated we prepared ordered ZnO nanopores arrays.4) We prepared rose-like ZnO nanostructures by a low-temperature solution route with assistance of ethylenediaminetetraacetic acid disodium (EDTA-2Na). Without adding EDTA-2Na in solution, we obtained nanowire arrays. The morphology of ZnO nanostructures is found to be changed from rose-like to tower-like architectures with increasing the molar ratios of EDTA-2Na/Zn²⁺ (from 1:5 to 1:2). Also, when EDTA-2Na/Zn²⁺ molar ratio is 1:2, the shape evolution of ZnO nanostructures is observed from flat nanosheets to wrinkled nanosheets, and finally to be rose-like nanostructures. EDTA-2Na as a strong complexing agent plays a key role in the shape evolution.