【作者】 王洪哲；

【导师】 杨文胜； 杜祖亮；

【作者基本信息】 吉林大学 ， 物理化学， 2010， 博士

【摘要】 纳米粒子是纳米技术研究中的一个基本单元,它给人们提供了研究与尺寸相关特性的合适对象,因此,纳米粒子在纳米材料中也占有特别重要的地位,同时在能源、医药卫生、电子和计算机、环境保护、新材料设计等领域也都有着非常广泛的应用前景。近年来针对半导体纳米粒子（纳米晶）的制备方法、合成机理的研究一直是科研工作者所关注的领域,尤其以利用高温溶剂法制备半导体纳米晶所开展的研究工作为代表。目前合成纳米晶材料在前驱体的使用上有相对固定的选择,如在涉及CdSe纳米晶的制备中,除了早期毒性较大的有机金属盐（比如二甲基镉）外,大都选择氧化镉作为镉的前驱物,其它的离子型化合物则很少涉及;在含汞近红外发射半导体纳米晶的制备上,由于其高温下不稳定的特点,室温合成路线就具有很大的优势,但相应的研究报道却很少;在其它诸如金属氧化物半导体纳米晶的制备过程中的一些重要参数如介质的选择、反应温度的调节、反应时间的控制以及表面活性剂的运用对反应的结果都具有直接而重要的影响,如何通过相关实验的设计,深入理解其中相关参数的作用,从而更加有效地开展纳米晶的可控及规模合成也是目前合成、制备研究中亟待解决的问题。本论文即以上述问题为出发点,在高温溶剂法的基础上主要开展相关的合成研究及部分性质表征工作,主要包括以下内容:（1）选用离子型镉源作前驱体成功的在较低的反应温度下制备了ZnSe/CdSe复合结构纳米晶,并对其发光机理进行了深入的探讨。在此基础上,结合当前“绿色”环保的要求,开展了低毒、高效、低能耗的合成方法研究,针对目前广泛采用的含膦化合物的合成方法,创新性的采用无膦化合物的合成路线制备了较高质量的ZnSe纳米晶并开展了基于宽带隙ZnSe半导体纳米晶的过渡族元素中心掺杂体系ZnSe:Cu/ZnSe/ZnS复合结构纳米晶的绿色合成制备。通过Cu²⁺的引入,实现了对ZnSe纳米晶的荧光发射的有效调节。适当厚度的ZnS壳层则可以很好的钝化粒子表面,从而提高荧光发射强度;通过采用不同粒径的ZnSe纳米晶为核,该复合结构纳米晶的发射波长可在480⁵20 nm的范围内实现连续调节。（2）探索了室温环境下高质量近红外纳米晶的制备。在CdTe纳米晶结构控制合成的基础上,采用室温离子交换的间接制备方法实现了HgCdTe近红外纳米晶的制备,并进一步实现了具有近红外发射的HgTe纳米晶的室温合成。（3）利用高温热解等方法制备了一系列的金属氧化物等化合物,在探索新合成方法的同时,着重探讨了反应温度、复合表面活性剂的使用以及前驱物的选择对产物结构、成分和性质的影响,并对其机理也进行了相应的探讨。以上工作的开展为下一步开展基于纳米晶的器件研究奠定了基础。更多还原

【Abstract】 Nanoscience and nanotechnology have emerged to become one of the most exciting areas of research today and have attracted the imagination of a large number of researchers. The study on the preparation and properties of nanomaterials is the most active and most important part of applicable nanotechnology and it also constitutes the basic base of nanoscience. Nanoparticles are basic research elements for nanotechnology and nanocrystals occupy a special place amongst nanomaterials because the have enabled a proper study of size-dependent properties. Nanoparticles constitute the building blocks for nanotechnology and thus for numerous potential applications in fields such as energy and power, health and biomedicine, electronics and environmental applications, new engineering materials.The synthesis and preparation of nanomaterials are the primary foundation for researches of their applications, and the choose of reaction parameters such as solvents, reaction temperature, reaction time and the use of surfactants has important and direct effects on the results of reactions. The understanding of the reaction mechanism and some key factors in the progress of nuclea an growth will greatly help us to develop the new synthetic concept towards efficiently controllable scale-up preparation of nanocrystals through the elaborately design of synthesis procedures,. The dissertation focuses on the study of high temperature synthetic route and the effects of experimental parameters such as temperature, surfactants and precursors on the morphology, composition and properties of as-synthesized nanocrystals, correspondingly. The mechanism for the formation nanocrystals were discussed as well. Some representative nanocrystals systems including visible and infra-red emission semiconductor nanocrystals, metal chalcogenides nanocrystals and related nanocomposites, and metal oxides nanocrystals were used as the research subjects by meanse of the high boiling-point organic solvent procedure. In comparison with organic dyes and fluorescent proteins, quantum dots have unique optical and electronic properties including narrow size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. In chapter 2, based on previous work of phosphine-route synthesis of ZnSe nanocrystals, ZnSe/CdSe core-shell nanocrystals were successfully synthesized by utilizing Se （Se-TBP） in pre-prepared ZnSe precursors by the introduction of Cd²⁺. The crystal structures, shapes and optical properties of as-synthesized nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, UV-vis absorption and photoluminescence spectroscopies. The results indicate that the epitaxial growth of CdSe shell onto ZnSe nanocrystals led to the formation of ZnSe/CdSe core-shell structures with well-crystallized and the tunable PL emission peak from 500 nm to 620 nm by tuning the size of cores or the thickness of shells. A band-gap offset structure which was feathered by either reverse Type-I or Type-II was proposed to be responsible for the red-shift of PL emission. For the synthesis of high quality ZnSe nanocrystals, we developed a so-called“phosphine-free”approach where Se-ODE and zinc stearate were adopted as precursors for the preparation of ZnSe nanocrystals with various sizes. Susequently, the new PL windows covering from 480 to 520 nm was obtained by diffusing the Cu into as-synthesized ZnSe nanocrystals with different sizes. The PL efficiency was improved by coating the ZnS shell onto the ZnSe:Cu/ZnSe nanocrystals ,In chapter 3, we start from the morphology controllable synthesis of CdTe nanocrystals with multi-pods were obtained during the early stage of reaction. With increasing reaction time, the system entered into the Ostwald ripening regime and the tetrapod CdTe nanocrystals were then transformed into dot shaped particles. Besides high initial concentration of cadmium precursor and high ratio （up to 10） of Cd²⁺ to Te-TOP, ODA was found to be an activator and play a key role for forming zinc-blende CdTe tetrapods right after the injection due to activating cadmium-oleic acid precursors The PL efficiency of the nanocrystals was very low in the early stage of the reaction. The fast growth of the nanocrystals could cause many defects on the surface sites. The ripening process could modify the surface of the nanocrystals and generate a perfect surface so that the nanocrystals emitted strong PL. On the basis of tetrapod and particle CdTe nanocrystals synthesis, we adopted a simple cation exchange process to obtain infra-red emission HgCdTe nanocrystals by facile treatment on as-synthesized CdTe nanocrystals under room temperature. Through the comparation of cation exchange results, we found that the morphologies of CdTe precursors were well preserved as well as the good crystallinity. The introduction of Hg²⁺ ions into CdTe system resulted in a red-shift of PL to longer wavelength of about 827 nm for the maximum. In addation, we also tried the direct synthesis of fluorescent nanocrystals which were feathered with infrared characteristics. Monodisperse zinc blende HgTe nanocrystals were successfully synthesized at room temperature in noncoordinate organic solvent of ODE. Thiol was applied to control the reaction at a suitable nucleation and growth speed. In the early stage of the reaction, HgTe nanocrystals formed aggregates, and then became individual dot-shaped nanocrystals with stronger photoluminescence emission.In chapter 4, we prepared Cu, Cu₂S and CdS/Cu₂S core/shell nanocrystals in organic solvents and characterized as-prepared nanocrystals by TEM, XRD etc. For the preparation of copper nanoparticles, copper oleate was used as precursor and copper nanoparticles were obtained through the thermolysis of precursor at elevated temperature. The influences of applied reaction temperature on the final product were also tested. Monodisperse Cu₂S nanocrystals were also prepared with copper stearate and dodecanthiol act as copper and sulfur sources, respectively. The as-synthesized Cu₂S nanocrystals exhibit some kind of self-assemble characteristic under specific conditions. The composite of CdS/Cu₂S in form of hybrid film is a traditional solar cell material. At last, based on the synthesis of Cu₂S nanocrystals, we also tried the preparation of CdS/Cu₂S core/shell composite nanocrystals, and the red shift of its PL compared with CdS was explained by the bandgap offset between CdS and Cu₂S.The major work of the last chapter deals with the preparation of metal oxide nanocrystals in noncoordinating solvent of paraffin oil with metal acetylacetonate as precursors and OA, OAm and dodecanol as composite ligands, respectively. The general growth model of nanocrystals involves two steps, which ideally should occur separately: the nucleation of the nanocrystals and the actual process of growth were realized by injection of additional paraffin oil during the initial stage of reaction. The size of as-synthesized CoO and MnO nanocrystals can be easily adjusted by regulating the reaction temperature and reaction time. Novel structure of CoO such as flower-like morphology can be achieved by slowering the injection speed of paraffin oil, which was used to lower the temperature and steer the reaction into the second stage for nanocrystals growth. In the case of manganese oxide synthesis, a serial of experiments with different reaction temperatures were conducted to investigate the role of different surfactants during the thermal decomposition of metal acetylacetonates. The results indicate that the reaction temperature and the methods used to adjust the temperature and had an important effect on the formation of products. Especially the use of ligands is the guarantee for the preparation of monodisperse nanocrystals.更多还原