Zero-dimensional Ge And One-dimensional ZnO Nanostructures And Devices

Nanostructures - structures that are defined as having at least one dimension between 1 and l00nm - have received great interests due to their peculiar and fascinating properties, and applications superior to their bulk counterparts. In this dissertation, zero-dimensional germanium (Ge) and one-dimensional (1D) zinc oxide (ZnO) nanostructures were synthesized by vacuum electron-beam evaporation and thermal evaporation methods, respectively. And several novel and important applications of these nanostructures were investigated experimentally. Main innovative results are listed as below:1) Amorphous Ge nanoclusters embedded in high-K dielectric (Al2O3) were synthesized by vacuum electron-beam co-evaporation method at room temperature. Clear blue shift of the absorption edge as large as 1.5eV was observed due to the quantum confinement effects. Large third-order nonlinear optical susceptibility (Re x(3) =4.91 X 10-7 esu and Im x(3)2.78X 10-8 esu) was also experimentally demonstrated by Z-scanning method.2) Metal-insulator-semiconductor (MIS) structures with high-K gate dielectric (Al2O3/ZrO2) containing Ge nanocrystals were fabricated. Electron storage effects of the Ge nanoclusters were observed, which demonstrated the feasibility of kigh-K dielectric nanocrystal floating gate memory. Negative photoconductivity of the MIS structures due to the screen effects of the negatively charged Ge nanocrystals was also experimentally observed.3) Tetrapod-like and wire-like ZnO ID nanostructures were successfully synthesized by a novel thermal evaporation method. In all our methods, metal catalyst, graphite additive and vacuum were not necessary, and more importantly, it was very convenient andAbstracteffective for large-scale industrialization.4) Room temperature photoluminescence (PL) results indicated that the green emission at 510nm was attributed to the oxygen vacancy in the ZnO nanowires. Electrical studies also experimentally demonstrated that ambient and light had great influence to the electrical transporting properties of ZnO nanowires. Individual ZnO nanowire device were fabricated and the electrical and photo-sensing characteristics were also studied.5) The field emission characteristics of the tetrapod-like ZnO ID nanostructures were studied for the first time. The turn-on field was found to be as low as 1 .6V/[im at current density of luA/cm2. Our results demonstrated that tetrapod-like ZnO ID nanostructures had potential application in the field of vacuum electron devices.6) ZnO nanowires gas sensors with low power consumption were fabricated with micro-electromechanical system (MEMS) technology for the first time. Ethanol, H2 and CO sensing characteristics of the fabricated sensors was studied. Based on the mode of conductance switch, the sensing mechanism of the ZnO nanowires was discussed.7) Room temperature characteristics of the synthesized ZnO nanowires were studied for the first time. Hydrogen storage capacity of 0.83 wt% was achieved under the pressure of 3.03 Mpa at room temperature and about 71% of the stored hydrogen could be released under ambient pressure.8) The photocatalytic characteristics of Rhodamine B and 2,4-dichlorophenol by ZnO nanotetrapods were investigated. Our results indicated that the photodegradation reaction was a pseudo first-order reaction and the apparent rate constant of the degradation, K was found to be 0.046/min. Our results indicated that the photocatalytic ability of ZnO tetrapods was stronger than that of TiO2 (P-25) powders.