Synthesis And Field Emission Properties Of ZnO Nanotubes

Various morphologies of Zinc oxide(ZnO)nanostrueture are prepared by hydrothermal reaction in ammonia and zinc chloride solutions.Meanwhile,the photoluminescence and field emission properties of some products are analyzed and discussed.This thesis contains the following works and innovations:1.The ZnO nanotapers,nanorods,nanodisks and two kinds of ZnO nanotubes, including taper-like and flat-roofed tubes are synthesized by changing the solution concentration,PH value,reaction time,substrate,and growth temperature.And the growth mechanism of these ZnO nanostructures is discussed.2.The growth mechanism of two kinds of ZnO nanotubes in solution is investigated in detail.(1)We synthesize samples grew at 95℃for 3 hours,but the times of the subsequently dissolution at room temperature in the solution are different.The SEM images of these samples prepared at different stages clearly elucidate the evolution of tubular ZnO fabricated.(2)We show that ZnO tubular structure is originated from an aging process of ZnO rod.The preferential chemical dissolution of the metastable Zn-riched(0001)polar surfaces leads to the tubular structure.(3)A two-stage growth model is proposed based on the coexistence of the hydrothermal deposition and dissolution of ZnO in the fabricating process.The first growth stage corresponds to the precipitation of ZnO from Zn(NH₃)₄²⁺at higher temperature.The second stage is an etching process,Which happens when the precursor Zn(NH₃)₄²⁺is depleted at high temperature or the hydrothermal decomposition ceases at low temperature.(4)We find the morphologies of nanotubes are affected by the time of the first stage and the time of the dissolution process determines whether the tubular structure is completely hollow.3.Field emission measurements show that the tapering nanotubes have the good field emission performance with a low turn-on field of～2.1 Vμm-1 and a low threshold field of～3.8 Vμm-1,which suggests the possible applications of the ZnO tubular structures in field emission microelectronic devices.Furthermore,Room Photoluminescence of two kinds of ZnO nanotubes is studied.4.On the basis of the growth mechanism of ZnO nanotubes,a two-step solution process is developed to prepare ZnO nanotube arrays.It would probably provide a new way to produce hollow structure from well-defined morphologies such as rods, combs and tetragons for industrial applications.