Zno Crystal Morphology Control, Ion Doping And Growth Kinetics

In recent years, the study is focused on the luminescent properties and magneticcharacteristics of the wide bandgap oxide semiconductor ZnO because of its excellent opticalperformance. In this work, the effect on the growth of ZnO crystal by mineralizing agent andmetal ions is systematically studied under hydrothermal conditions. Higher concentration ofmagnetic metal ions doped in the semiconductor ZnO was obtained, and its optical properties,electrical properties, and magnetic properties were characterized. The mechanism of theformation of wurtzite ZnO crystal is studied using first-principles density functional theorymethods.1、Zinc oxide crystals show anosotropic growth characteristics with strong alkalinecompounds （KOH、NaOH）as mineralizer. The result is that the growth is faster at the c-axisdirection and it is conducive to the growth of crystal. However, the rapid growth of thepolarity is prone to more defects. The speed of growth was slow because of the dissolution islow with salts as mineralizer （KBr、NaCO3）. The speed of growth of ZnO crystal along thec–axis was weakened obviously by adding appropriate amount of LiOH、CaO or Mg(OH)2inthe strong alkaline mineralizers in the reaction system.2、The ZnO crystal morphology could be controlled by adding appropriate amount ofmetal ions（Sb、Sn、In）in the strong alkaline mineralizer in the reaction system. The speedof growth of ZnO crystal along c–axis was weakened obviously compared with a–axis andb–axis by adding Sn or In ions. Large exposures of the positive polar face{0001} of ZnOcrystals is obtained.. Meanwhile, it exhibits good conduction properties. However, the the{0001} and {000} surfaces of ZnO crystal are not exposed in.3、At the fill factor of35%of adding MnCl2、CoCl2.6H2O in the reaction system, theuniformly doped ZnO crystals were obtained with7mole%Mn and0.64-2.87mole%Cocontent after magnetic separation. SQUID test showed that the samples were mainlyparamagnetic in the uniformly doped ZnO crystals, and some Co single phase appearedsimultaneously. 4、In order to enhance the content of Co, more pressure-resistive reactor was used, andthe fill factor was enhanced to70%.Some CoO were added in the reaction system at the sametime. After magnetic separation, high content of Co, uniformly doped in ZnO crystals, wereobtained with the ratio of Co:Zn reaching10at%. The results showed that the samples weremainly paramagnetic.5、The physical mechanisms of wurtzite ZnO crystal morphology were studied usingdensity functional theory. The atomistic structure, the energy band structure, and density ofstates of ZnO crystal were analyzed, and the aspect-graph of the equilibrium state of ZnOcrystal was obtained by using Ulf Theorem. The adsorption structure of metal atoms on thesurface of polar and semi-polar was set up. The adsorption energies of K、Na、Li、Ca、Mgatom, singly adsorbed or in mixture, at the truncated surfaces of O atoms located at thenegative face and negative cone face were obtained., The ZnO crystal morphology diagramafter adsorption was predicted. The physical mechanism of the hydrothermal synthesis of ZnOcrystal morphology was discussed from the atomic level. We believe that the surface energiesare directly correlated with the saturation of dangling bonds from the metal atoms in theadditive and the crystal morphology was affected in turn.Innovations of this work:1、the relationship between the growth of ZnO crystal and the mineralizing agent andmetal ions were clarified and technical routes of controlling ZnO crystal morphology underthe hydrothermal conditions were obtained.2、 High concentrations of Mn/Co uniformly doped in the ZnO crystal underhydrothermal conditions were achieved and high qualities of ZnO crystals uniformly doped athigh concentrations were obtained. The results show that ZnO crystals doped high than7at%(10at%) of Mn（Co）do not show ferromagnetism.3、The physical mechanisms of wurtzite ZnO crystal morphology synthesized byhydrothermal method were studied from the atomistic level using density functional theoryand the results are consistent with experiments.