【作者】 李莹滢；

【导师】 张海黔；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2009， 博士

【摘要】 近年来,一维纳米材料由于其新颖的物理、化学性质在纳米器件等诸多领域所展示的潜在的应用前景,已成为当今纳米材料的前沿和研究热点。其中辐射探测器如紫外探测器和核辐射探测器无论在军用还是在民用上都有重要的应用价值,因此引起人们的极大关注。本文利用简单的水热合成方法制备了高质量的ZnO纳米棒阵列,ZnS、ZnS/Ag纳米线,过渡性元素Co掺杂的稀磁半导体ZnO纳米棒阵列,CeO₂纳米线,在研究了一维半导体纳米材料的光学、电学、磁学以及光电化学等性能的基础上,利用ZnO纳米棒及其棒阵列构筑了紫外光电导探测器,利用CeO₂纳米线研制出一种新型的γ射线液体辐射剂量计,对纳米探测器件进行了表征和性能测试,取得了如下主要研究成果:（1）基于锌基底的ZnO纳（微）米棒阵列的制备及性能研究利用锌片作为基底与有机强碱四甲基氢氧化铵水溶液进行水热反应,制备出有序排列的ZnO铅笔状纳米结构阵列。Zn片既可以直接充当反应物又可以作为一维纳米棒垂直生长的基底。对一维纳米材料进行了结构和形貌的表征,研究了四甲基氢氧化铵浓度及反应温度对产物形貌的影响。实验结果表明当TMAOH浓度为0.3 M,反应温度为170℃的时候,ZnO纳米棒阵列的形貌较为均匀,取向性较好。通过改变反应时间讨论了ZnO纳（微）米棒阵列的生长机制。通过光致发光光谱和拉曼光谱研究了铅笔状ZnO纳米棒阵列的光学性能,结果表明制备得到的ZnO纳米棒阵列具有高质量的六方纤锌矿晶体结构以及优异的光学性能,ZnO的表面缺陷较少,结晶度较高且没有其他元素掺杂。由于其在基底上均匀分布、一致的取向性以及与基底良好的接触,所制备的ZnO纳米棒阵列具有较好的场发射性能场,发射电流密度稳定,且随时间并没有明显的衰减趋势。因此,所制备的铅笔状ZnO纳米棒阵列结构是一种理想的场发射阴极材料。利用标准三电极体系,对ZnO纳米棒阵列的光电化学性能进行研究。在光照条件下（on）,光电流瞬间产生且保持稳定不衰减;在挡光的瞬间（off）,光电流迅速降到初始值。垂直于基底排列整齐、沿c轴统一取向生长,长度较长的纳米棒阵列具有更大的光电流。研究了退火温度对ZnO纳米棒阵列的形貌及光学特性的影响。检测结果表明,在退火过程中,纳米棒的形貌基本保持不变,但其发光性能有所变化。当退火温度在400℃时,ZnO纳米棒结晶质量较高且结构缺陷较少,发光特性得到了提高。这一研究为以后半导体发光材料光学性质的研究提供了新的途径。利用柯肯达尔效应原理,通过简单的水热法一步制备了由ZnO纳米棒自组装形成的结晶良好的“蒲公英”形状空心微球,并讨论了其形成机理。利用该原理可以制备其他金属氧化物的空心微球或具有特殊构造的金属-半导体纳米复合物,它们将在光生电子储存,三维激光器,传感器以及光催化等领域具有广阔的应用前景。（2）一维半导体复合纳米材料的水热法制备及其光电化学性能,磁学特性研究为了提高一维半导体纳米材料的性能和拓展其应用领域,对ZnO纳米棒阵列进行了CdS复合,Co掺杂,对ZnS纳米线进行了Ag负载,并研究了光电化学性能,磁学等特性。在ZnO纳米棒阵列表面沉积了立方体形的CdS纳米颗粒,对其形貌及其形成机理进行了讨论。研究了复合结构纳米棒阵列的光电化学性能,这种复合结构纳米棒阵列比单纯的ZnO纳米棒阵列薄膜具有更强的光催化活性。这是由于光生电子通过CdS传输到ZnO纳米棒的导带,从而使光生空穴和电子就得到了有效的分离。这种复合结构将有望在光催化,光电池及太阳能转换材料的研究等方面得到应用。通过简单的水热合成法在锌片基底上一步制备了Co掺杂的铅笔状ZnO纳米棒阵列。纳米棒在基底上均匀分布,取向一致,垂直于基底大面积生长。样品结构均为六方纤锌矿结构,具有高结晶质量,不含其它杂相。随着Co掺杂浓度的增加,紫外发射峰强度逐渐下降,近带隙发射峰的半峰宽也较纯ZnO变宽。拉曼光谱显示Co的掺杂使纳米棒出现了氧空位和锌填隙本征缺陷。掺杂纳米棒阵列的磁滞回线表明样品具有明显的铁磁特征。这种ZnO基稀磁半导体纳米棒阵列是一种在自旋电子器件中具有应用潜力的纳米材料。采用水热法制备了Ag负载的ZnS纳米线,对所合成的纳米线的结构、形貌以及光学性能进行了表征。研究了所制备的纳米线的光催化性能,讨论了ZnS/Ag纳米线光催化降解的机理。研究表明,ZnS/Ag复合纳米线比单纯的ZnS纳米线具有更强的光催化活性。经过60 min紫外光照,甲基橙脱色率可达到97.07%。这是由于Ag的加入,使电子不断向Ag迁移,减少了光生电子和空穴的复合,提高了光催化剂的活性。这种贵金属复合半导体纳米材料的方法将进一步拓展半导体在光电能量转化领域中的应用。（3）基于一维金属氧化物半导体纳米材料的辐射探测器件研究利用低温水热法,在金叉指微电极阵列中,制备了网络状的ZnO纳米棒紫外光电导型探测器。对该探测器在紫外光照下的I-V特性以及光电响应特性进行了测试研究。ZnO纳米棒之间相互接触搭桥在电极之间,有利于电子在其内部进行传输,使电子能够扩散,传递变得更加迅速,有利于光电流的快速收集。我们的结果表明这样的纳米结构具有制备简便、廉价、高响应度等优点,在大面积电子元件以及集成纳米光子和纳米电子器件方面具有重要的应用前景。在FTO（F掺杂SnO2）基底上制备出大面积紧密排列,垂直生长的ZnO纳米棒阵列。基于这种纳米棒阵列,研制出具有良好的可重现性、大光电流（在0.4 V电压下约为6.71 mA）的高灵敏度紫外光电探测原型器件。这种大的光电流以及欧姆I-V特性归因于在紫外光照下,纳米棒与金电极之间肖特基势垒宽度变窄以及ZnO纳米棒之间势垒的降低。光响应曲线可拟合为指数函数曲线,弛豫时间常数代表了在光生空穴与氧负离子结合的过程中电子的累积过程。这种低成本化学合成的高度有序排列的ZnO纳米结构可以用于构建性能优异的纳米电子器件。利用简单的水热合成方法,制备了CeO₂纳米线。对产物进行了形貌和结构表征并研制出基于这种CeO₂纳米线水溶液的一种新型γ射线液体辐射剂量计。结果表明,这种CeO₂纳米线水溶液辐射剂量计对γ射线具有很高的灵敏度,检测剂量小于传统化学剂量计的检测限1000μGy,且在20μGy到500μGy之间有较好的线性响应。研究了浓度对辐照变化率的影响,研究表明,随着浓度的降低,辐照变化率逐渐增大。加入自由基清除剂后,溶液的辐射变化率较小,表明水经辐照后产生的自由基及活性粒子对CeO₂的反应过程起着至关重要的作用。更多还原

【Abstract】 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.更多还原