纳米球刻蚀法制备的二维有序的CdS纳米阵列及其光学性质的研究

采用纳米球刻蚀(nanosphere lithography)技术,以自组装的聚苯乙烯纳米小球(polystyrene,PS小球)的单层膜为掩模,制备出二维有序的CdS纳米阵列.利用扫描电子显微镜(SEM)对样品结构进行了表征,用紫外—可见分光光度计对样品光学性质进行了分析.结果表明：制备的二维CdS纳米阵列是高度有序的,且与作为掩模的纳米小球的原始尺寸及排布结构一致;禁带宽度为2.60eV,相对于体材料的2.42eV,向短波长蓝移了0.18eV,表现出CdS材料在纳米结构点阵中的量子尺寸效应;CdS纳米 关键词： 纳米球刻蚀 二维CdS纳米有序阵列     

Growth of self-assembled copper nanostructure on conducting polymer by electrodeposition

In the present work, self-assembled nanostructures of copper are grown by electrodeposition on a thin conducting polymer (polypyrrole) film electropolymerized on a gold electrode. The shapes, sizes and the densities of the nanostructures are found to depend on the thickness of the polypyrrole thin film, which provides an easy means to control the morphology of these nanostructures. In particular, for the same applied potential on the gold electrode, smaller nanocrystals with a higher density are observed on thinner polymer films while bigger nanocrystals at a lower density are found on thicker films.     

Microemulsion-mediated synthesis of cadmium zinc sulfide nanocrystals with composition-modulated optical properties

Cadmium zinc sulfide nanocrystals were synthesized by a microemulsion-mediated process, which involving two steps: the preparation of CdS (or ZnS) seeds and the succedent hydrothermal growth of ZnS (or CdS) component. The XRD results show that the cadmium zinc sulfide nanocrystals with CdS seeds present a hexagonally homogeneous alloyed structure, while the ones with ZnS seeds mainly take on the characteristic of hexagonal CdS nanocrystals. The intrinsic factors influencing the crystal structures were discussed. The UV-vis and photoluminescence (PL) spectra indicate that the optical properties of the obtained nanocrystals with CdS seeds can be continuously modulated by tuning their compositions, although their sizes and size distributions are not under a strict control. The composition-modulated strategy, along with the hydrothermal microemulsion process, will be an effective route to achieve semiconductor nanocrystals with tunable optical properties under more manageable conditions.     

溶剂热再结晶合成由纳米颗粒自组装成的一维CdS纳米棒

采用两种不同的溶剂热路径合成出了不同形貌和尺寸的CdS纳米晶, 一种是以无水乙二胺(en) 为溶剂, CdCl₂·2.5H₂O和硫脲(H₂NCSH₂N) 为镉源和硫源, 在不同反应温度(160 ℃-220 ℃ 下制备出了CdS纳米晶, 讨论温度对CdS纳米晶生长的影响; 另一种是以en为溶剂, 将在160 ℃下合成的产物在200 ℃下原位再结晶生长2-8 h, 分析原位生长时间对CdS纳米晶生长的影响. 通过X射线衍射(XRD)、 扫描电子电镜(SEM) 和透射电子电镜(TEM) 等表征产物的物相、 形貌和微结构, 分析可知: 两种路线合成的产物均为六方相CdS; 当温度为160 ℃时, 产物形貌为纳米颗粒状, 当温度高于160 ℃时, 产物为CdS纳米棒状; 同时, 在200 ℃下原位再结晶生长不同时间后发现产物形貌由纳米颗粒转变为纳米棒, 通过场发射扫描电镜(HRTEM) 分析可知: 纳米棒是由零维纳米颗粒自组装而成. 最后, 讨论了影响产物CdS纳米晶形貌转变的因素和纳米棒的生长机理.     

温度对CdS纳米颗粒形状和光致发光特性的影响

采用反胶束法,在常温和低温下(接近零度)合成了硅土包裹的CdS纳米颗粒.高分辨电镜表明常温下合成的颗粒呈现直径小于5 nm的球形,而在低温下出现了短棒形和长达微米量级的线形.通过对实验过程的分析表明:不仅合成CdS纳米颗粒溶液的浓度,而且温度对CdS纳米颗粒的形状产生了重要的影响.进一步研究了CdS纳米颗粒的光致发光特性.     

掺杂Mn2+的浓度对CdS纳米颗粒光致发光的影响

采用反胶束法,合成了硅土包裹的掺有不同浓度的Mn2 的CdS纳米颗粒.高分辨电镜表明这些颗粒的直径小于5 nm.仅仅改变Mn2 的掺杂浓度,研究了这些颗粒的光致发光谱和光致发光激发谱,结果表明:Mn2 浓度的大小对掺杂CdS纳米颗粒的发光产生了重要的影响.通过电子顺磁共振谱的测量和分析揭露了Mn2 浓度影响这些掺杂颗粒发光效率的原因.     

Role of ions in the colloidal synthesis of gold nanowires

Gold nanocrystals of different shapes have been made by a wet chemical approach based on a two-step, seed-mediated synthesis. In this paper, we demonstrate a one-step synthetic method for achieving simple and systematic control over the shape of gold nanoparticles. Gold nanowires, which have been prepared by multi-step approaches, are produced in very high yield in this single-step technique. The width of the rods can be varied over a broader range compared to previously reported methods. Rectangle-, cube- or tetrapod-like gold nanocrystals can also be prepared in aqueous solution at room temperature. The formation of various shapes, in the presence of silver nitrate, requires bromide ion and alkylammonium surfactant ion of appropriate hydrocarbon tail length. The shape, dimension and yield of the nanocrystals depend on the nature and concentrations of the stabilizing cationic surfactants and other additives, such as salts, in addition to the reactants.     

The nature of emission centers in CdS nanocrystals

Photoluminescence (PL) of CdS nanocrystals (NCs) grown in different polymeric matrices is investigated. It is shown that chemical nature of the matrix does not affect the nature of PL centers in NCs. PL centers of NCs are identical to the emission centers in CdS single crystals and are related to their intrinsic defects.     

Optical properties of cadmium sulfide nanocrystals obtained by the sol-gel method in gelatin

Based on analysis of optical absorption data for CdS nanocrystals obtained by sol-gel technology in gelatin, we have studied the effect of technological factors (reagent concentrations, gelatin concentration) on the growth process and size distribution of the synthesized nanocrystals. Depending on the reagent concentration, we synthesized CdS nanocrystals with mean radii in the range . We have shown that for a low gelatin content (1%), nanocrystals of different sizes are formed (1.7 nm and 2.6 nm). With an increase in the gelatin concentration, the size dispersion decreases and nanocrystals of a single mean radius (2.3 nm) are formed. We have established a correlation between the size dispersion and the shape of the photoluminescence spectrum of the CdS nanocrystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 556–562, July–August, 2008.     

CdSe/CdS核/壳型纳米晶的光谱特性

以巯基乙酸为稳定剂制备了CdSe/CdS核／壳型纳米晶。用光吸收谱（Abs)、光致发光谱（PL）及光致发光激发谱（PLE）研究了CdS壳层对CdSe纳米晶电子结构，从而对其吸收和发光性能的影响。根据PL和PLE的结果以及带边激子精细结构的计算结果，我们用尺寸很小的纳米晶中所形成的基激缔合物解释了PL光谱与吸收边之间较大的Stokes位移。     

Wurtzite and zinc-blende CdSe based core/shell semiconductor nanocrystals: Structure, morphology and photoluminescence

We report comparative study of core/shell nanocrystals based on wurtzite and novel zinc-blende CdSe core. Both wurtzite and zinc-blende CdSe are coated with CdS shell or CdS/ZnS multishell under identical synthetic parameters. Crystal structure analysis finds that CdS shell is wurtzite on either wurtzite or zinc-blende CdSe cores. Morphology and photoluminescence studies exhibit that for zinc-blende CdSe based samples, the shell growth is in fine epitaxy and the obtained core/shell nanocrystals show high quantum yield both before and after surface modification process; while wurtzite CdSe based samples have irregular shape indicating inhomogeneous shell growth, and are with lower quantum yield. Furthermore, in the photoluminescence spectra exited with UV radiation, wurtzite CdSe based samples show side peaks of independently nucleated nanocrystals from the shell material; while samples with zinc-blende CdSe cores are potent in restricting these byproducts, which may attribute to the highly effective arrestment of precursor ions onto the zinc-blende CdSe surface. These features manifest that zinc-blende CdSe is more talented than conventional wurtzite CdSe in achieving core/shell nanocrystals with higher qualities.     

纳米CdS-磺化聚苯胺（SPAn）多层复合膜的光学特性研究

研究了利用层-层自组织生长法制备的磺化聚苯胺-CdS纳米晶体复合膜的光学特性.研究发现，随样品中CdS 纳米晶体尺寸的减小，量子尺寸效应明显增强；在紫外吸收谱中表现为吸收边出现了明显蓝移；在光致发光谱中，不仅激子直接复合产生的带边发射产生了蓝移，而且陷阱态复合产生的宽带发射也发生了蓝移.还发现样品经低温退火处理后，激子复合产生的带边发射显著增强，发射带宽随纳米尺寸的减小而变窄.这说明退火后CdS 纳米晶粒的有序性和均匀度显著增加. 关键词： CdS 纳米晶体 SPAn 吸收 发光     

Multiple grains in nanocrystals: effect of initial shape and size on transformed structures under pressure

Pressure-induced structural transformations in spherical and faceted gallium arsenide nanocrystals of various shapes and sizes are investigated with a parallel molecular-dynamics approach. The results show that the pressure for zinc blende to rocksalt structural transformation depends on the nanocrystal size, and all nanocrystals undergo nonuniform deformation during the transformation. Spherical nanocrystals above a critical diameter >/=44 A transform with grain boundaries. Faceted nanocrystals of comparable size have grain boundaries in 60% of the cases, whereas the other 40% are free of grain boundaries. The structure of transformed nanocrystals shows that domain orientation and strain relative to the initial zinc blende lattice are not equivalent. These observations may have implications in interpreting the experimental x-ray line shapes from transformed nanocrystals.     

玻璃中CdSSe纳米晶体的光谱性能

对掺有镉、硒、硫的玻璃在650—800℃退火4?h，生长了不同尺寸的CdS0.13Se0.87纳米晶体，测量了纳米晶体的吸收光谱、光致发光（PL）谱和电调制光谱，确定了纳米晶体部分电子态的能量，讨论了CdSSe纳米晶体的光学性质与其尺寸之间的依赖关系.随着纳米晶体尺寸的增大，对应激子的吸收峰、PL峰及电吸收信号发生红移，表现出明显的量子尺寸效应.小尺寸纳米晶体的电吸收表现为量子受限的Stark效应，而大尺寸纳米晶体的电吸收线形与体材料的相似；随着纳米晶体尺寸的增大，电吸收信号增强.所有尺寸的纳米晶体都表现 关键词： CdSSe纳米晶体 吸收光谱 光致发光谱 电光响应     

Formation of nanostructures by the activated Stranski-Krastanow transition method

We propose that self-assembly of complicated nanocrystals can be realized by making patterns on the surface of the Stranski-Krastanow systems with the film thickness in a special range that gradual surface undulation is prohibited but island nucleation can be effected. The method has the potential to control the locations, the size, and the shapes of the self-assembled nanocrystals.     

CdS纳米粒子的自组装单分子膜制备研究

利用疏基乙酸与草酸的混合自组装单分子膜成功制备了粒径分布均匀的CdS纳米粒子，并用SEM，XRD，XPS，PL对样品进行了表征。SEM表明形成在自组装单分子膜表面上的CdS纳米粒子的平均粒径约为45nm。XPS表明在自组装单分子膜表面形成了CdS纳米粒子。PL谱表明CdS纳米粒子在675nm有一峰值波长，我们认为这一发光是由表面缺陷造成的。     

长方体形CdS微粒的合成及光谱性质

采用溶胶法,以硫脲为表面修饰剂,合成了长方体形CdS微粒,并用X射线粉末衍射、透射电子显微镜、红外光谱以及荧光光谱等手段进行了表征。实验结果表明,硫脲分子中的硫原子与CdS纳米晶表面的Cd2+离子存在配位作用;硫脲分子表面修饰的CdS纳米晶为立方闪锌矿结构,具有较好的荧光性质;长方体形CdS微粒可能是由硫脲分子表面修饰的CdS初级纳米晶粒自组装组成。该研究结果为硫脲分子表面修饰的CdS初级纳米晶粒在分子组装及作为新型发光材料方面的进一步研究奠定了基础。     

Investigation on shape variation of Au nanocrystals

A variety of shapes, such as rod, tripod, -shape and cube, of Au nanocrystals were synthesized by employing different reaction conditions. The nanocrystals and their shape variation were characterized by transmission electron microscopy and UV–vis spectrophotometry. The evolution of shape was accomplished by controlling the parameters used in their synthesis, the concentration of reducing agent and surface capping agent. The effect of synthetic parameters on shape was explored, to determine suitable conditions for producing each shape of nanocrystals. Nanocrystals with different shapes have different plasmon bands in the visible region of the spectrum, which is a valuable property for sensor applications.     

单核/双壳结构CdSe/CdS/ZnS纳米晶的合成与发光性质

以巯基乙酸为稳定剂,在水溶液中合成了单核/双壳结构的CdSe/CdS/ZnS纳米晶。在内核CdSe和外壳ZnS之间的内壳CdS作为晶格匹配调节层,能够很好的改善核/壳界面处的性能,而且,最外层ZnS能够最大程度地使激子受限。用TEM和XPS对纳米晶进行了表征,并且用光致发光光谱和吸收光谱对不同核壳结构的纳米晶的发光性能进行了比较,结果表明单核/双壳结构的纳米晶具有更加优异的发光特性。     

SELF-ASSEMBLY AND POLARIZABILITY OF CAPPED CdS NANOCRYSTALS ON SILICON SURFACES

The zinc-blende CdS nanocrystals with particle size less than 10nm were prepared in solution with a molecular surfactant. The particle surface was modified with capping molecules, bis(2-ethylhexyl) sulfosuccinate disodium salt (AOT) or hexametaphosphate (HMP). The colloid solution was deposited on silicon wafer and the assembly of these nanocrystals was studied by atomic force microscopy. It was found that the CdS/AOT formed a monolayer by simply dropping the colloid solution on silicon surface, while CdS/HMP exhibited 3D structure with prefered orientation in the similar deposition process. A dynamic electric force microscopy was performed and the polarizability was measured from the resonance of cantilever under applied alternating voltage between tip and substrate. The dielectric constant of CdS nanocrystal was estimated by comparing the different electric capacitance of Au and CdS nanocrystals.