Study On Morphologic Control And Optical Property Of Nano/Micro-meter Semiconductor Materials

In recent years, a considerable interest has been focused on the nano/micro-meter semiconductor materials because of their fascinating optical, electronic and magnetic properties. The structure, dimension, size, morphology of the as-prepared crystals are expected to be under control for valuable reasearch. In this thesis, we selected two kinds of important semiconductive materials, ZnO and Cu2O. Via a facil hydrothermal/alcohothermal method, novel single ice-cream cones, twinned ice-cream cones, dumbbell-like, hamburger-like, twinned microtubes with open ends and three-fin nano-structured ZnO were obtained respectively; hollow micro-spheres and 18-facet Cu2O were also prepared. The influences of reactant, surfactant, solvent and temperature on the size and morphology were investigated in detail. X-ray diffraction (XRD) has been employed to characterize the phase and structure of samples, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for the morphology and size observation. What's more, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) were taken for further confirmation of the structure. The mechanism was discussed primarily, meanwhile optical property was studied.The main works are as follows:In Chapter One, we briefly introduced the history of nanomaterials and semiconductors, depicted the properties, measurement, synthesis and potential use of the nano/micro-meter semiconductor materials. Recent work were summarized in the field of semiconductive materials, focusing on the application of hydrothermal method in fabricating nano/micro-meter semiconductor materials. In addition, morphologic control and mechanism study for nano/micro-meter semiconductor materials are proposed.In Chaptor Two, we mainly focused on the synthesis, characterise and mechanism of several nano/micro-ZnO with novel morphologies. Via simple alcohothermal method, we control over synthesis of single ice-cream cones, twinned ice-cream cones, dumbbell-like, hamburger-like microstructure ZnO by changing the quality of the reactant. In the mixture of ethanol and water with the help of CTAB, we got twinned ZnO microtubes with open ends. One can see a relatively sharp and strong UV emission band centered at 390nm and a broad visible emission band between 450nm and 550nm. It can be observed from the Visible absorption spectra that the UV absorbance peak for samples is located at about 376nm, comparable to the bulk exciton absorption (373nm). Visible absorption spectrum of ZnO microtubes is some differernt from that of other three samples, in consistent with PL results. A highly regular three-fin nanostructure of ZnO is created in high yield and assembled into a uniform film on Zn substrates via a simple hydrothermal route in dilute ammonia aqueous solution. And each fin consists of tactic nanoribbon blades of 0.6-1.0μm in lengh and 50-80nm in thickness. One can see a relatively sharp and strong UV emission band centered at 385nm and a broad visible emission band between 450nm and 700nm. The visible emission appears to consist of two main components at about 540nm and 610nm. The PL properties at room temperature are similar to that of 1D ZnO nanostructure and ZnO tetrapod nanorods. All ZnO samples are of a hexagonal phase structure with good crystalline quality. We primarily investigated the formation mechanism and optical properties of the as-prepared ZnO with different morphologies.In Chaptor Three, we mainly focused on the synthesis, characterization and mechanism of hollow microspheres and 18-facet Cu2O. Using the simple alcohothermal method as well, we investigated the influence of additive, reactant, solvent and time on the morphology. In anhydrous ethanol by additive-assisted alcohothermal method, we prepared Cu2O hollow microspheres with the diameter of 12-15μm and 1μm in the thickness of the shell. TEM picture showed that Cu2O hollow microspheres are formed by small particles with the diameter of 200-300nm. Lots of experiments showed that the additive hexadecoic acid plays crucial roles in the formation of hollow microspheres and the conversion from Cu²⁺ to Cu⁺. In additon, the temperature of 180℃, ethanol as the solvent and Cu(NO₃)₂·3H₂O as the reactant are necessary for such structure. The reaction time of 6-8h is the optimal condition for the formation of Cu2O hollow microspheres. In the mixture of ethanol and water with the help of hexadecoic acid, we got 18-facet Cu2O with the diameter of 2.2-3μm. In this polyhedron, it contains 18 facets which has two types of faces: six square and twelve hexagon planes; 32 vertices which also have two types: one is the joint of three hexagons and the other one is the joint of two hexagons and one square; and 48 edges, among which 24 edges with larger length form 6 square faces, and the rest of the 24 are shorter in length and form eight vertices, which are the joints of each of the three neighboring hexagons. This structure bears all the symmetric elements that a cube has and belongs to Oh point group. We primarily investigated the formation mechanism and optical properties of the as-prepared Cu2O with different morphologies.In chapter Four, a concise conclusion is present.In brief, our research mainly involved the morphologic control and optical properties characterization of ZnO and Cu2O. We believe it is meaningful for both basic research and application research by seeking novel methods for the synthesis of semiconductive nano/micro- materials and investigating their optical properties.