金属-半导体异质结构纳米晶的可控制备和光谱调控

本文简要综述了金属-半导体异质结构纳米晶的设计、可控制备和物性研究的相关工作.设计了异相成核与生长、选择硫化和种子介导液相外延生长3种不同的方法并以此制备了多种金属-半导体异质结构纳米晶,对其中所涉及的反应机制进行了论述,并简要探讨了金属-半导体异质结构纳米晶的热稳定性、表面等离子共振活性、荧光特性以及异质界面的电荷转移和保持能力.     

水相CdTe纳米晶的合成、生长机理和应用研究

纳米晶在生物检测、光电器件、光波导、可调激光器等领域有着广泛的应用前景．本文以CdTe为例,对近年来水相纳米品合成和生长机理方面的研究进展作了简要的归纳和论述．水相合成纳米晶具有操作简单、价格低廉、在水溶液中稳定性高等优点,并可以通过静电力、范德华力等弱相互作用实现一维、二维甚至三维结构的组装．对纳米晶的生长机理的研究涵盖了热力学主导的Ostwald熟化（Ostwaldripening）机理和动力学控制的聚集机理两个主要方面．文章最后对水相合成CdTe纳米晶的应用进行了总结和展望,     

基于单分散氟化物纳米晶的成核生长模型

在纳米介观尺度范围内实现对材料尺寸与形貌的调控,是纳米材料合成、制备、功能化及其应用的关键,对认识并解纳米晶的成核与生长规律具有重要意义.基于单分散氟化物纳米晶合成提出的扩散控制动力学模型(DCK,diffusion-controlled kinetic)和表面化学热力学模型(SCT,surface chemical thermodynamics)旨在探讨纳米晶的成核与生长规律.本文围绕纳米晶的成核、生长机理,在综述前人工作的基础上,归纳和总结了上述模型,有望对纳米晶的可控合成提供理论指导与借鉴.     

立方晶型Sb2O3纳米晶的合成及光催化性能

采用沉淀法合成了立方晶型Sb2O3纳米晶,通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、紫外-可见漫反射光谱(UV-Vis DRS)和电子自旋共振谱(ESR)等对样品进行了详细的表征。以紫外光光催化降解甲基橙为反应模型评价了样品的光催化性能。结果表明:沉淀法合成的立方晶型Sb2O3纳米晶颗粒小,表现出良好的光催化性能。对立方晶型Sb2O3纳米晶光催化降解甲基橙的原因进行了探讨,并提出了降解甲基橙的反应机理。     

金属纳米结构的氧化刻蚀调控与催化性能优化

金属纳米结构的可控合成,对其性能优化和高效应用至为关键．氧化刻蚀作为金属纳米晶可控合成中的新兴有效调控手段之一,受到越来越多的关注．本文以本课题组近期的研究工作为例,说明了氧化刻蚀对金属纳米晶的形貌、尺寸、结构及组成等合成参数的有效调控作用．由此总结认为,在金属纳米晶可控合成的一般过程,尤其是成核和生长过程中,氧化刻蚀的本质是有效调控“两个速率”和“两个力学”,即减缓原子的生成速率与晶种的形成速率、选择性接受反应热力学和反应动力学的控制作用．我们将通过氧化刻蚀法调控合成得到的具有独特结构的Pd,Pt纳米晶,用于氧活化和电催化这两个重要的催化体系,获得了理想的催化结果,表明氧化刻蚀在金属纳米晶的功能改性和应用拓展方面,具有令人称奇的广阔应用前景．     

球状、立方状及空心立方状PbS纳米晶的控制合成及其形成机理

以醋酸铅为铅源,硫代乙酰胺为硫源,在表面活性剂十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)共同作用下,通过简单地调节水热反应的反应温度控制合成出球状、立方状和空心立方状PbS纳米晶。利用XRD、TEM对合成产物的结构和形貌进行了表征,发现合成的球状、立方状和空心立方状PbS纳米晶尺寸均一,直径为100 nm左右。对球状、立方状和空心立方状PbS纳米晶的形成机理进行了初探,结果表明反应温度较低时,水热反应初始阶段形成的PbS小颗粒呈球形,在表面活性剂SDS的烷基链模板和CTAB微胶束软模板共同作用下生成球状PbS纳米晶;反应温度较高时,水热反应初始阶段形成的PbS小颗粒由于自身的立方相岩盐晶体结构的影响有呈立方状趋势,在SDS和CTAB共同作用下产物堆积成空心立方体状或立方状。     

燃烧法制备纳米晶氧化镍

纳米氧化镍可用作热敏元件、功能陶瓷、催化剂、玻璃、电极材料、涂料、气敏原件、电子元件等。目前文献制备的纳米氧化镍的方法有微波热分解法、化学沉淀法、溶胶-凝胶法、高分子网络法、离子交换树脂法、电化学法、共沸蒸馏法等。本文在500℃的马福炉中合成了面心立方晶系的纳米晶氧化镍,颗粒平均直径约为10nm,该法具有操作简便和省时等优点。     

BaTiO3纳米晶的合成与表征

以硬脂酸、硬脂酸钡和钛酸丁酯为原料合成了ＢａＴｉＯ３纳米晶，粒度为１０～２０ｎｍ，烧成温度为６５０℃，低于传统的合成温度。用红外光谱、差热分析、热重分析和Ｘ射线衍射对合成过程进行了研究，用透射电镜考察纳米晶的粒度和形貌。用发射光谱和Ｘ射线荧光光谱对样品纯度进行了分析。结果表明，此法合成的纳米晶ＢａＴｉＯ３纯度高、粒度小且较均匀，在常温下属立方钙钛矿型。     

铂纳米晶的形状控制合成及应用

形状控制的铂纳米晶由于具有高选择性和催化活性,近年来受到越来越多的关注。各种低指数晶面所围成的铂纳米晶,包括立方体、四面体、八面体、枝状晶体等可以通过胶体法或热解法来制备。表面具有高指数晶面结构的二十四面体等多面体也已经由电化学方法得到。本文评述了形状控制的铂纳米晶的合成方法、表征和应用等方面的进展,分析了铂纳米晶稳定性的影响因素,并对目前铂纳米晶合成及应用研究中存在的主要问题和发展前景进行了探讨和展望。     

无机纳米晶的形貌调控及生长机理研究

形貌及尺寸规整可控的纳米晶体的合成是目前十分引人注目的纳米材料研究领域．制备合成中的形貌调控及其功能化是这些纳米材料能够得到应用的关键问题．研究者们希望在纳米晶的任一阶段均能实现控制并在期望的阶段停止,从而得到尺寸、形态、结构及组成确定的纳米晶体．本文综述了近年来无机纳米晶体的典型合成路径,深入探讨了纳米晶在成核、生长及熟化阶段的控制原理,研究了液相合成纳米材料过程中晶体结构与生长行为的相关性问题,并总结了几类具有代表性的低维、多维纳米晶体的形成规律和生长机理．探索纳米粒子的调控合成对于纳米材料的规模化生产及应用具有重要的理论价值和指导意义．     

Quantitative analysis of the role played by poly(vinylpyrrolidone) in seed-mediated growth of Ag nanocrystals

This article presents a quantitative analysis of the role played by poly(vinylpyrrolidone) (PVP) in seed-mediated growth of Ag nanocrystals. Starting from Ag nanocubes encased by {100} facets as the seeds, the resultant nanocrystals could take different shapes depending on the concentration of PVP in the solution. If the concentration was above a critical value, the seeds simply grew into larger cubes still enclosed by {100} facets. When the concentration fell below a critical value, the seeds would evolve into cuboctahedrons enclosed by a mix of {100} and {111} facets and eventually octahedrons completely covered by {111} facets. We derived the coverage density of PVP on Ag(100) surface by combining the results from two measurements: (i) cubic seeds were followed to grow at a fixed initial concentration of PVP to find out when {111} facets started to appear on the surface, and (ii) cubic seeds were allowed to grow at reduced initial concentrations of PVP to see at which concentration {111} facets started to appear from the very beginning. We could calculate the coverage density of PVP from the differences in PVP concentration and the total surface area of Ag nanocubes between these two samples. The coverage density was found to be 140 and 30 repeating units per nm(2) for PVP of 55,000 and 10,000 g/mol in molecular weight, respectively, for cubic seeds of 40 nm in edge length. These values dropped slightly to 100 and 20 repeating units per nm(2), respectively, when 100 nm Ag cubes were used as the seeds.     

Nanocrystals composed of alternating shells of Pd and Pt can be obtained by sequentially adding different precursors

This paper describes a layer-by-layer epitaxial approach to the synthesis of multishelled nanocrystals composed of alternating shells of Pd and Pt by starting with seeds made of Pd or Pt nanocrystals. The synthesis was conducted by sequentially adding PtCl(4)(2-) and PdCl(4)(2-) salt precursors into a system containing either Pd or Pt seeds (in the shape of cuboctahedrons, octahedrons, plates, or cubes) together with a weak reducing agent such as citric acid (CA). The slow reduction kinetics associated with CA played an important role in the epitaxial growth of one metal on the other, resulting in the formation of Pd-Pt multishelled nanocrystals. Owing to the capping effect of CA for {111} facets of Pd and Pt, the multishelled nanocrystals tended to be enclosed by {111} facets in the form of octahedrons or thin plates, depending on the shapes of the Pd or Pt seeds: octahedrons for cuboctahedral, cubic, or octahedral seeds, and plates for platelike seeds.     

Controlling the size and morphology of Au@Pd core-shell nanocrystals by manipulating the kinetics of seeded growth

This article reports a systematic study of the seed-mediated growth of Au@Pd core-shell nanocrystals with a variety of controlled sizes and morphologies. The key to the success of this synthesis is to manipulate the reaction kinetics by tuning a set of reaction parameters, including the type and concentration of capping agent, the amount of ascorbic acid used as the reducing agent, and the injection rate used for the precursor solution. Starting from Au nanospheres of 11?nm in diameter as the seeds, Au@Pd core-shell nanocrystals with a number of morphologies, including octahedra, concave octahedra, rectangular bars, cubes, concave cubes, and dendrites, could all be obtained by simply altering the reaction rate. For the first time, it was possible to generate Au@Pd nanocrystals with concave structures on the surfaces while their sizes were kept below 20?nm. In addition, the as-prepared Au@Pd nanocubes can be used as seeds to generate Au@Pd@Au and Au@Pd@Au@Pd nanocrystals with multishelled structures.     

Formation of orientation-ordered superlattices of magnetite magnetic nanocrystals from shape-segregated self-assemblies

Magnetic magnetite (Fe3O4) nanocrystals have been synthesized by combining nonhydrolytic reaction with seed-mediated growth. The shape of these magnetite nanocrystals can be controlled either as pure spheres or a mixture of mainly faceted nanocrystals. Faceted magnetite nanocrystals consist of truncated tetrahedral platelets (TTPs), truncated octahedrons (TOs), and octahedrons (OTs). Transmission electron microscopy analysis indicates that the faceted nanocrystal mixture tends to self-segregate based upon the shape in a self-assembly process, and each shape forms its own distinct crystallographic orientation-ordered superlattice assemblies. Self-assemblies of the Fe3O4 nanocrystals in the shapes of TTP, TO, and OT show hexagonal, primitive cubic, and distorted body-centered cubic (bcc) superlattice structures, respectively. The possible mechanism for the formation of different superstructures is attributed to van der Waals interactions. Nanocrystals with different shapes provide diverse building blocks for bottom-up approaches in building nano- and mesosystems. Furthermore, the self-segregation phenomenon of different shaped nanocrystals in self-assembly processes could be very important in envisioning efficient assembly strategies for nanoscience- and nanotechnology-based devices.     

Synthesis of Pd-Pt bimetallic nanocrystals with a concave structure through a bromide-induced galvanic replacement reaction

This article describes a systematic study of the galvanic replacement reaction between PtCl(6)(2-) ions and Pd nanocrystals with different shapes, including cubes, cuboctahedrons, and octahedrons. It was found that Br(-) ions played an important role in initiating, facilitating, and directing the replacement reaction. The presence of Br(-) ions led to the selective initiation of galvanic replacement from the {100} facets of Pd nanocrystals, likely due to the preferential adsorption of Br(-) ions on this crystallographic plane. The site-selective galvanic replacement resulted in the formation of Pd-Pt bimetallic nanocrystals with a concave structure owing to simultaneous dissolution of Pd atoms from the {100} facets and deposition of the resultant Pt atoms on the {111} facets. The Pd-Pt concave nanocubes with different weight percentages of Pt at 3.4, 10.4, 19.9, and 34.4 were also evaluated as electrocatalysts for the oxygen reduction reaction (ORR). Significantly, the sample with a 3.4 wt.% of Pt exhibited the largest specific electrochemical surface area and was found to be four times as active as the commercial Pt/C catalyst for the ORR in terms of equivalent Pt mass.     

Bottom-up synthesis of gold octahedra with tailorable hollow features

Gold octahedra with hollow features have been synthesized in high yield via the controlled overgrowth of preformed concave cube seeds. This Ag(+)-assisted, seed-mediated synthesis allows for the average edge length of the octahedra and the size of the hollow features to be independently controlled. We propose that a high concentration of Ag(+) stabilizes the {111} facets of the octahedra through underpotential deposition while the rate of Au(+) reduction controls the dimensions of the hollow features. This synthesis represents a highly controllable bottom-up approach for the preparation of hollow gold nanostructures.     

Silver nanocrystals with concave surfaces and their optical and surface-enhanced Raman scattering properties

Shaped and dimpled: Silver nanocrystals enclosed by concave surfaces and thus high-index facets have been prepared by simply controlling the growth habit of Ag cubic seeds. Four types of concave nanocrystals, including octahedron, cube, octapod, and trisoctahedron, were obtained (see picture).     

Synthesis of Ag nanobars in the presence of single-crystal seeds and a bromide compound, and their surface-enhanced Raman scattering (SERS) properties

This Article describes the synthesis of Ag nanobars with different aspect ratios using a seed-mediated method and evaluation of their use for surface-enhanced Raman scattering (SERS). The formation of Ag nanobars was found to critically depend on the introduction of a bromide compound into the reaction system, with ionic salts being more effective than covalent molecules. We examined single-crystal seeds with both spherical and cubic shapes and found that Ag nanobars grown from spherical seeds had much higher aspect ratios than those grown from cubic seeds. The typical product of a synthesis contained nanocrystals with three different morphologies: nanocubes, nanobars with a square cross section, and nanobars with a rectangular cross section. Their formation can be attributed to the difference in growth rates along the three orthogonal <100> directions. The SERS enhancement factor of the Ag nanobar was found to depend on its aspect ratio, its orientation relative to the laser polarization, and the wavelength of excitation.     

A universal route with fine kinetic control to a family of penta-twinned gold nanocrystals

Some of the major difficulties hindering the synthesis of different types of colloidal nanocrystals are their complex synthetic methods and the lack of a universal growth mechanism in one system. Herein, we propose a general strategy of kinetically controlled seed-mediated growth to synthesize a family of penta-twinned gold nanocrystals. Specifically, different kinds of penta-twinned nanocrystals (truncated penta-twinned decahedra, truncated bipyramids, bipyramids, truncated bipyramids with tips, star-like penta-twinned nanocrystals, decahedra with concave edges, and decahedra) with tunable sizes and high purity were readily achieved in one system solely by tailoring the deposition kinetics of adatoms on different sites of decahedral seeds. The controllable deposition kinetics can be realized by changing the ratio of reductant/gold precursors (R), which dictates whether horizontal or vertical features along the 5-fold axis direction of Au decahedral seeds are produced. Additionally, the selective growth of a second metal (silver) on penta-twinned gold seeds can be reached through minor modification of R, which opens a new avenue for mechanistic investigation by visualizing the seed localization within the final particles. The present work demonstrates a general paradigm for the kinetic growth of penta-twinned crystals and would be extended to the synthesis of other families of nanocrystals.

We report the synthesis of linear ADPr oligomers of defined length up to a pentamer using an improved solid phase method. Binding study with human oncogenic helicase ALC1 shows that ADPr oligomers bind to ALC1 in a length-dependent manner.     

Controlling the Size and Morphology of Au@Pd Core–Shell Nanocrystals by Manipulating the Kinetics of Seeded Growth

This article reports a systematic study of the seed‐mediated growth of Au@Pd core–shell nanocrystals with a variety of controlled sizes and morphologies. The key to the success of this synthesis is to manipulate the reaction kinetics by tuning a set of reaction parameters, including the type and concentration of capping agent, the amount of ascorbic acid used as the reducing agent, and the injection rate used for the precursor solution. Starting from Au nanospheres of 11 nm in diameter as the seeds, Au@Pd core–shell nanocrystals with a number of morphologies, including octahedra, concave octahedra, rectangular bars, cubes, concave cubes, and dendrites, could all be obtained by simply altering the reaction rate. For the first time, it was possible to generate Au@Pd nanocrystals with concave structures on the surfaces while their sizes were kept below 20 nm. In addition, the as‐prepared Au@Pd nanocubes can be used as seeds to generate Au@Pd@Au and Au@Pd@Au@Pd nanocrystals with multishelled structures.