| Abstract:Due to its unique semiconductor, photonic and piezoelectric properties, ZnO with wurtzite structure has been widely used in electronics, optoelectronics and energy sectors. Mg (OH)2as a precursor of MgO, which has high resistivity and transmittance of a wide band gap, chemical stability, and high secondary electron emission coefficient, has been attempted to be applied in the optical device in recent years.Electrodeposition has become a powerful tool in the preparation of high-quality semiconductor thin films and nanostructures. In this thesis, ZnO and Mg(OH)2films were prepared by the cathodic electrodeposition method on SnO2electrode. The main research results are as follows:(1) The electrochemical behavior of the SnO2electrode in aqueous zinc nitrate solution were investigated. It is found that solution temperature, Zn2+ion concentration and initial solution pH showed significant influence on the electrochemical behavior of the electrode. Reaction kinetics were analyzed and related kinetic parameters were obtained. ZnO thin films were electrodeposited on SnO2electrode from aqueous zinc nitrate solution. The results shows that Solution temperature, applied potential and Zn2+concentration affec the ZnO thin films. The growth of granular and porous ZnO were also analyzed;(2) Passivation phenomena during ZnO electrodeposition at low temperature is studied. It was found that insufficient interfacial hydroxyl rather than low temperature is the direct reason for the passivation. Growth model was built based on the interfacial pH and surface charge and a passivation mechanism is proposed. Based on this mechanism, passivation takes place only when the interfacial pH is between PZC of SnO2and PZC of ZnO,6.6and9.3, i.e. insufficient hydroxyl causes the generation of a large number of-Zn-O-H terminated structure from a microscopic point of view or ZnOx(OH)y or Zn(OH)2from a macroscopic point of view;(3) Characterization of morphology, phase, optical properties of the porous Mg(OH)2thin films was carried out by FESEM, GAXRD and UV-Vis. The nanosheets of porous Mg(OH)2thin films obtained by electrodeposition were confirmed to be{011} surface by SAED and in-situ dehydration process during SAED course. A family of planes{011} with dihedral angle of120°in a12×12x2super cell are corresponding to the nanosheets in the films, i.e. family of planes{011} are growth surfaces of the electrodeposited Mg(OH)2nanosheets. The growth mechanisms of porous nanostructures compose of four stages:hydration, nucleation, growth, and thin film formation.(4) growth Mechanism of different morphologies of Mg (OH)2prepared under different conditions was analyzed based on the crystal structure, surface energy and ion hydration. It is found that concentration ratio of [OH-]/[Mg2+] at the electrode interface decided the final preferred orientation and morphology of the electrodeposited Mg(OH)2films by changing solvent molecules and coordination way during polymerization. Hydrated states of Mg(II) ions in higher concentration ratio of [OH-]/[Mg2+] are [Mg(OH)2(H2O)4], then form [Mg(OH)6]4-structure. While [Mg(H2O)6]2+is the most stable states in lower concentration ratio of [OH-]/[Mg2+], which can form structure of [Mg(OH)4(H2O)2]2". Different structures caused coordination number of Mg2+to be6or4, respectively, which decided (001) or (011) preferred planes and corresponding dense or porous morphology. |
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