| Summary: | 博士 === 國立交通大學 === 材料科學與工程系所 === 96 === This thesis prepares the nanocomposite thin films containing ZnO quantum dots (QDs) in SiO2 and SiOxNy dielectric matrices by using the target-attached sputtering method. The optical and electrical properties of nanocomposite thin films as well as the effects of dielectric types on the characteristics of ZnO QDs are also investigated. Experiemental results indicate that such a simple physical deposition (PVD) method can effectively grow the ZnO QDs inside the dielectric material within good control on dot sizes and distribution. Via the analyses including microstructure, optical, and electrical properties in conjunction with theoretical modeling and calculation, the interactions of dielectric matrices on ZnO QD surface and the effects of dielectric types on optical ane electrical properties of ZnO QDs are explored.
Transmission electron microscopy (TEM) analysis revealed similar microstructure in both nanocomposite films and the ZnO QDs produced by target-attached sputtering method are crystalline rather then amorphous. In ZnO QDs-SiOxNy system, the incorporation of N atoms generates a distinct bonding configuration on ZnO dot surface and induces a stronger surface polarization in comparison with ZnO QDs-SiO2 system. This suppresses the defect chemical reactions relating to oxygen ions on ZnO dot and further affects the transmittance, refractive index and photoluminance properties of nanocomposite films. We also calculated the width of depletion region and dielectric confinement energy for the nanocomposite films and, in corelated with experimental data, the results evidenced the dielectric matrix type indeed affects the optical properties of ZnO QDs. We also built up a multi-shell two-electron system model to calculate the electron ground-state energy of a semiconductor QDs-dielectric matrix system. The calculated results enabled us to clarify the occurrence of quantum confinement and dielectric confinement effects in the ZnO QDs-SiO2 films.
In the dc and ac conductivity measurements of ZnO QDs-SiO2 and ZnO QDs-SiOxNy systems, the complex-plane analysis revealed that the ZnO QD content on affects the conduction properties of nanocomposite films. Furthermore, the two nanocomposite systems exhibited different response powers and sensitivities to the frequency dispersion relationship. Though both systems exhibited poor capacitance properties and a new design of sample structure and further investigations are required, the results above cleary demonstrated the feasibility to manipulate the electrical properties of ZnO QDs via the modification of dielectric matrix type.
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