One-dimensional Structures And Regulation Of Electronic States Of Metal Oxides

In recent years, semiconducting metal-oxide nanowires have been attracting great attention due to not only their physical properties but also their technical applications. The synthesis process of the metal-oxide directly affects the physical properties of the nanowires and plays a key role in their applications. A metal oxide may exist in phases depending on the thermodynamic environment, and also a metal oxide may stay in a metastable state/phase for a relatively long time. The electronic structures of the different phases of metal-oxides may be greatly different, and the electronic structures determine the performance of the devices in their applications. It is very important for their technical applications to investigate the phase structures, phase formation and transition, electronic structures and one-dimensional quantum transport properties of metal-oxide nanowires under thermodynamic envirenment.PbO is a semiconductor broadly used in industry, with applications to energy storage, imaging devices, electrophotography logic, electroradiography, and laser technology. PbO exits in two polymorphic forms:the low temperature red tetragonal phase (a-PbO) with a band gap of 1.9 eV, and the high temperature yellow orthorhombic phase ((3-PbO) with a band gap of 2.5 eV. At atmospheric pressure, a-PbO undergoes a phase transition toβ-PbO at 489℃, while below this temperature, including room temperature, the (3-PbO phase always exists in a metastable state. It is difficult to obtain a pure phase a-PbO by normal chemical synthesis methods.A method of thermal oxidation has been developed to synthesize pure phase metal-oxide nanowires by oxidizing metal nanowires. This method is simple and easy to be used. The phase structures and horizontal scales of lead-oxide one-dimensional nanowires are controlled and adjusted by thermodynamic environment, such as oxygen partial pressure, temperature, and as well as reaction time. X-ray diffraction, SEM, AFM and UV-visible absorption and other experimental methods, combined with theoretical calculation and analysis, were used to investigate the phase structures, phase formation and transition, electronic structures and one-dimensional quantum transport properties of the lead oxide nanowires. This thesis consists of the following parts:1. Set up a system, which is able to adjust temperature, gases and gas pressure, for the oxidation of metal lead nanowires.2. The controllable growth of lead oxide nanostructures was achieved by controlling the reaction time and reaction temperature in the reaction chamber, and the different horizontal scale nanowires of lead oxide and other one-dimensional structures were successfully obtained3. A simple and easy method has been developed to prepare pure phase metal-oxide nanowires by oxidation of metal nanowires. 4. The pure phases of lead oxide nanowires have been synthesized based on the analysis and investigation of the thermodynamic environment for the phase formation of pure phase lead oxide nanowires.5. This study reveals that the synthesis of the pure phase relies on both the process temperature and the oxygen flow/oxygen partial pressure. The pure phase oxide nanowires can be obtained only in a narrow, low temperature range under a low oxygen flow.6. This work shows that the wire morphology of lead nanowires has been perfectly maintained after being oxidized.7. A structure phase inversion phenomenon has been found. This is a first find in this field. The possible physical mechanism of this phenomenon has been studied, which may be associated with the scale.8.We investigated the quantum transport and its manipulation for a single particle held in a one-dimensional nanoscale bipartite lattice. In the high-frequency regime of external field, we derived the analytical solutions for the probability amplitude of the particle in localized states, which quantitatively describe the features of quantum tunnelling. The physical mechanism of the directed motion is revealed as the loss of stability of the system.9. The quantum entanglement, transport and their control of two particles in a nanoscale bipartite lattice are studied. Under the condition of selective coherent destruction of quantum tunnelling, we suggest an experimental scheme for manipulating the separated and co-site transports of the two particles in the same or opposite directions.