Preparation, Properties And Nano- Radiation Detectors Investigation Of One Dimensional Semiconductor Nanomaterials

Recently, one-dimensional nanostructured materials, such as nanotubes, nanowires, nanorods and nanobelts, have been received considerable attentions due to their novel physical and chemical properties. Comparing to the bulk counterparts, one-dimensional nanomaterials have shown the application potentiality in the nanodevices. Especially, owing to the important application in the military or the civilian fields, the radiation detectors based one-dimensional nanomaterials have attracted more and more interests. In this dissertation, syntheses, and physical properties of some one-dimensional semiconductor nanomaterials as well as nano-optic-electric devices were systematically investigated. Firstly, high quality one dimensional materials such as ZnO nanorod arrays, ZnS,ZnS/Ag nanowires, large-area arrays of highly oriented Co-doped ZnO nanorods, CeO₂ nanowires were prepared successfully by a simple hydrothermal method. Secondly, the optical, electrical, photocatalytic and magnetic properties of the nanomaterials were also studied. Finally, ZnO nanorods and ZnO nanorod arrays based UV photodetectors, CeO₂ nanowires based highly sensitiveγ-radiation dosimeter were fabricated, and in particular, applied in radiation detection. The main works are summarized as follows have been achieved:(1) Synthesis and Properties of Oriented ZnO Nanorod Arrays Directly Grown on Zinc SubstrateWell aligned ZnO nanorod arrays with a shape of pencil-like have been synthesized on the zinc foil in tetramethylammonium hydroxide solution via a simple hydrothermal method. The Zn foil serves as the substrate for ZnO nanorod arrays and the Zn source for ZnO nanorods. The morphology and structures of the obtained ZnO arrays were characterized by FE-SEM and XRD. Moreover, the key factors, e.g. the solution concentration and the reaction temperature, affecting the morphology, were explored carefully. It was found that the uniform-sized and oriented ZnO nanorod arrays with sharp end facets could be formed in 0.3 M TMAOH solution at 170℃. In addition, the growth mechanism of ZnO nanorod with complex structure was proposed.The optical properties, field emission properties and photoelectrochemical properties of the ZnO nanorod arrays were investigated. The Raman scattering and PL results confirmed that as-obtained ZnO nanostructures had a good crystal quality with a wurtzite hexagonal phase and exhibited good optical property. The ZnO nanorod arrays presented outstanding field emission properties (the stable and long time emission), which was due to the uniform distribution and good contact between the nanorods and the substrate. Therefore, the pencil-like nanorod arrays are ideal candidates for the material of flat panel field emission. Besides, the photoelectrochemical properties of the synthesized pencil-like ZnO nanorod arrays were further investigated in three-electrode system. Under the UV light irradiation, the photocurrents of the nanorods rose to a steady state immediately, and then kept at a constant value. The photocurrents decayed very sharply in the dark. The results suggested that the aligned nanorod grown along the c-axis with longer length supplied high surface area and superior carrier transport pathway, significantly enhancing the photoelectrochemical activites of ZnO nanorod.The annealing effects on the morphology and the optical properties of ZnO nanorod arrays were investigated. SEM analyses of the samples revealed that there was no distinct change in the morphology after thermal annealing in air. The results showed that after the annealing treatment at around 400℃in air atmosphere, the crystal structure and optical properties became much better due to the decrease of surface defects. The annealing treatment provides a new approach to study the optical properties of luminescent semiconductor materials.Micrometer scale hollow ZnO dandelions organized by ZnO nanorods were formed via hydrothermal method, following a modified Kirkendall process. In principle, a lot of metal oxides and metal-semiconductor composites can be obtained in this synthetic architecture. Hopefully, they can be applied in many fields, such as light-generated electrons, three-dimensional lasing, and new photocatalysts.(2) Photoelectric and Magnetic Properties of One-Dimensional Nanocomposite MaterialsIn order to improve the properties and expand the applications of one-dimensional semiconductor nanomaterials, we fabricated CdS-ZnO composite nanorod arrays, Co-doped ZnO nanorod arrays and the silver supported ZnS nanowires.We fabricated CdS nanocubes-ZnO nanorod heterostructure through a simple hydrothermal route. The photocatalytic properties of the CdS-ZnO nanorod arrays were investigated by measuring the photodegradation of methyl orange under ultraviolet radiation. It was found that the CdS nanoparticles-ZnO nanorod heterostructure arrays possessed enhanced photocatalytic activities compared with the bare ZnO nanorod arrays. The photo-generated electrons of CdS transferred to the conduction band of ZnO nanorod, which could efficiently separate electron-hole pairs and reduce their recombination. It can be expected that this kind of heterostructure arrays have a bright future in photocatalysts, photoelectrodes and solar-energy conversion materials.Large-area arrays of highly oriented Co-doped ZnO nanorods with hexagonal structure were grown on Zn substrates by single-step hydrothermal process. The intensity of UV emission peak decreased with the Co doping concentrations increasing. When Co was doped into ZnO lattice, oxygen vacancies and Zn interstitials were created. The concentration of these defects increased with rise of the Co concentration. Magnetic measurement revealed that the Co doped ZnO nanorod arrays exhibited clearly room-temperature ferromagnetic behavior, which was useful in building components for spintronics.ZnS/Ag nanocomposite wires were prepared by hydrothermal method. The morphology, structures and the optical properties of the obtained products were characterized. The photocatalytic properties of the nanowires were investigated by measuring the photodegradation of methyl orange under ultraviolet radiation. The ZnS/Ag nanowires exhibited higher photocatalytic activity in contrast with that of ZnS nanowires. The decolorizing rate of methyl orange could reach 97.07% after irradiating 60 min. The excellent photocatalytic activity was attributed to that Ag clusters promoted the separation of the pairs of photogenerated electrons and holes. The noble metal-semiconductor composite nanowires can be promising materials for photoelectrical energy conversion devices.(3) A Series of Functional Radiation Detector Nanodevices Were Fabricated by Using One-Dimensional Semiconductor NanomaterialsUsing a low temperature hydrothermal synthesis method, ZnO nanorod networks have been directly grown across trenched Au microelectrodes arrays. The characteristics of current-voltage (I-V) and photoresponse were obtained both in dark and under ultraviolet illumination. The bridged nanorods network demonstrated highly sensitive to UV illumination in atmosphere at room temperature. It can be useful for nanoscale optoelectronic applications serving as chemical, biological sensors, and switching devices.Large scale densely packed and vertically oriented ZnO nanorod arrays were grown on F-doped SnO2 (FTO) substrates through a simple hydrothermal synthesis route. Based on the arrays of hexagonal ZnO nanorod, a prototypical photoelectrical device was fabricated for ultraviolet detection, showing good reproducibility and a large photocurrent of around 6.71 mA at the applied voltage of 0.4 V. The large photocurrent and the ohmic I-V characteristics of the ZnO nanorods under the illumination could be ascribed to the decrease of the barrier height among the ZnO nanorods and the Schottky barrier between the nanorods and the Au electrodes .The photoresponse curve is well fitted to an exponential curve with the relaxation time constant representing the accumulation of conduction electrons. These well-aligned ZnO nanostructures of high quality could be easily fabricated by a cost-effective chemical route and used for constructing nanoscale devices with excellent performances.Solution of CeO₂ nanowires synthesized by a hydrothermal method was investigated for the purpose of developing a new aqueousγ-radiation dosimeter. The aqueous CeO₂ nanowire dosimeter exhibited high sensitivity toγ-radiation of dose less than 1000μGy and a good linearity of response in dose range from 20μGy to 500μGy. The relative absorption rate varied greatly at lower initial aqueous concentrations. By addition of radical scavenger, almost no change of the absorption occurred, indicating the radicals produced from water radiolysis were closely relevant to the reaction of the CeO₂ nanowires withγ-ray. The nanowires dosimeter may be used as a highly sensitive as well as cost-effective dosimeter in ultra-low-dose environment.