Excitons emissions and Raman scattering of ZnO nanoparticles embedded in BaF2 matrices by reactive magnetron sputtering

ZnO nanoparticles embedded in BaF2 matrix were fabricated by rf magnetic sputtering technology. The optical properties of high quality ZnO nanoparticles, thermally post treated in a N2 atmosphere, were investigated by temperature-dependence photoluminescence measurement. Free exciton and localized exciton were observed at the low temperature. Free exciton peak was at 3.374 eV and localized exciton peak was at 3.420 eV, dominating the PL spectrum at 77 K. Free exciton transition was observed at 3.310 eV at room temperature, whereas the localized exciton transition was at 3.378 eV. The multiple-phonon Raman scattering spectrum showed that ZnO nanoparticles embedded in BaF2 matrix had a large deformation energy originated from lattice mismatch between ZnO and BaF2 matrix. Analysis of the fitting results from the temperature dependence of FWHM of ZnO exciton illustrated that the large value of gamma(ph) was good qualitative agreement with the large deformation potential.     

Formation of nanoparticle arrays on S-layer protein lattices

Crystalline bacterial cell surface layers (S-layers) composed of identical protein units have been used as binding templates for well-organized arrangements of nanoparticles. Isolated S-layer proteins were recrystallized into monomolecular arrays on solid substrates (such as silicon wafers and SiO2-coated grids) and in suspension forming so-called self-assembly products. These S-layer assemblies were studied by atomic force microscopy and transmission electron microscopy (TEM). The orientation of the S-layer lattice, exhibiting anisotropic surface properties, on the solid surface and on the self-assembly products, was compared with the orientation on the bacterial cell. On both bacterial cells and SiO2 surfaces the outer face of the S-layer protein was exposed. On the self-assembly products occasionally the inner face was also visible. Metal- and semiconductor nanoparticles 2 to 10 nm in mean diameter were covalently or electrostatically bound to the solid-supported S-layers and self-assembly products. TEM studies reveal that upon activation of carboxyl groups in the S-layer lattice with 1-ethyl-3,3'(dimethylaminopropyl)carbodiimide (EDC), a close-packed monolayer of 4-nm amino-functionalized CdSe nanoparticles could be covalently established on the S-layer lattice. Because of electrostatic interactions, anionic citrate-stabilized Au nanoparticles (5 nm in diameter) formed a superlattice at those sites where the inner face of the S-layer lattice was exposed. In contrast, cationic semiconductor nanoparticles (such as amino-functionalized CdSe particles) formed arrays on the outer face of the solid-supported S-layer lattices.     

Photoluminescence of ZnO nanocrystals embedded in BaF2 matrices by magnetron sputtering

This paper describes ZnO nanocrystals embedded in BaF2 matrices by the magnetron sputtering method in an attempt to use fluoride as a shell layer to embed ZnO nanocrystals core. BaF2 is a wide-band gap material, and can confine carriers in the ZnO films. As a result, the exciton emission intensity should be enhanced. The sample was annealed at 773 K, and X-ray diffraction (XRD) results showed that ZnO nanocrystals with wurtzite structure were embedded in BaF2 matrices. Raman-scattering spectra also confirmed the formation of ZnO nanoparticles. Abnormal longitudinal-optical (LO) phonon-dominant multiphonon Raman scattering was observed in the sample. Room-temperature photoluminescence (PL) spectra showed an ultraviolet emission peak at 374 nm. The origin of the ultraviolet emission is discussed here with the help of temperature-dependent PL spectra. The ultraviolet emission band was a mixture of free exciton and bound exciton recombination observed in the low temperature PL spectra (at 77 K). Abnormal temperature dependence of ultraviolet near-band-edge emission-integrated intensity of the sample was observed. The band tail state was observed in the absorption spectra, illustrating that the impurity-related defects were caused by the shell of the BaF2 grain layer. For comparison, ZnO films on BaF2 substrates were also fabricated by the magnetron sputtering method, and the same measurement methods were used.     

纳米/微米结构粒子合成技术进展

介绍了近年来纳米/微米结构粒子的合成技术进展,将纳米单元(纳米棒、纳米带、纳米片、纳米颗粒)自组装为各种尺度的有序结构会产生更优异的整体协同性质,这对纳米/微米结构粒子的性能研究有重要意义。主要介绍了表面活性剂法、水热法和模板诱导法等。表面活性剂由于具有多种特殊、优异的性能,包覆在纳米粒子表面可使其组装成具有新颖结构的聚集体,是目前研究热点。水热法所得粒子具有纯度高、分散性好、晶形可控,生产成本低等特点已被广泛采用。     

Preparation of polystyrene-encapsulated silver hollow spheres via self-assembly of latex particles at the emulsion droplet interface

In the present work, we have developed a novel route to wrap inorganic nanoparticles in polymer hollow spheres, which includes self-assembly polystyrene (PS) latex particles at the aqueous/oil interface, sintering and γ-ray radiation reduction. The Ag/PS composite microspheres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM). The advantage of this method is that the PS shell thickness, permeability, the size of composite spheres, and the quantity of the encapsulated Ag nanoparticles can be easily adjusted, which gives the product a brilliant prospect in the field of catalysis.     

Remanence properties of substituted Ba-ferrite particles for highdensity magnetic recording

In this paper, the remanence properties of Co-Sn, Co-Ti and Co-Ti-Sn substituted Ba-ferrite (BaF) oriented particulate samples are compared with those of some oriented acicular particulate samples. A new parameter, the minor remanence distribution (MRD), is proposed to review the remanence properties of magnetic particles and the capabilities for resisting the recording demagnetization of magnetic recording media. It is shown that the MRD values of the oriented BaF particulate samples were smaller compared to oriented Co-γ-Fe₂O₃ samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-γ-Fe₂O₃ samples. It Is the small MRD, SFD_r, IRS and large DH _r of a medium that can result in a large resistance to the effects of recording demagnetization and therefore in superior characteristics for high density magnetic recording. Since Co-Sn substituted BaF platelet-shaped particles exhibit these characteristics and have a very low temperature coefficient of coercivity, these particles can be expected to be a promising candidate for high density magnetic recording     

The Many Ways to Assemble Nanoparticles Using Light

The ability to reversibly assemble nanoparticles using light is both fundamentally interesting and important for applications ranging from reversible data storage to controlled drug delivery. Here, the diverse approaches that have so far been developed to control the self-assembly of nanoparticles using light are reviewed and compared. These approaches include functionalizing nanoparticles with monolayers of photoresponsive molecules, placing them in photoresponsive media capable of reversibly protonating the particles under light, and decorating plasmonic nanoparticles with thermoresponsive polymers, to name just a few. The applicability of these methods to larger, micrometer-sized particles is also discussed. Finally, several perspectives on further developments in the field are offered.     

One-step approach for the synthesis and self-assembly of silver nanoparticles

This study demonstrates a facile approach for one-step synthesis and self-assembly of silver nanoparticles at ambient conditions. It was found that pyrogallol acid (PYA) can play multiple roles in the proposed synthesis, including a reducing agent, a stabilizer, and a linking agent for assembly. Silver ions can be readily reduced by PYA at room temperature due to its powerful reducing capability. The capability in shape and size control can be evidenced by TEM images. A third function of PYA in this case is to link the generated silver particles into chains through the action of hydrogen bonding, which leads to a new plasmon resonance emerges in the longer wavelength region centered at approximately 650 nm. These results may be useful for shape-controlled synthesis and self-assembly of other metallic nanoparticles. The self-assembly structures would be imposed more functional applications in the areas of optics, plasmonics, biomedicine labeling and ionic sensing.     

Synthesis of magnetosome chain-like structures

Magnetite chains with a number of magnetite particles arranged in a line parallel to the outer amorphous carbon coating have been prepared. The sizes of the nanoparticles range from 40 to 120?nm, with nearly identical gaps between every two adjacent particles. The synthesized chains display ferromagnetic properties with several single-magnetic-domain (SD) nanoparticles assembled in an orderly fashion. Based on the formation process of chains in our reaction system, it is suggested that the localized environments favor the growth of SD nanoparticles, and the strong magnetic dipolar-dipolar interactions lead to the self-assembly of SD nanoparticles. This research could offer some useful information in studying the formation mechanism of magnetosome chains and the origin of the special chain-like nanostructures in magnetotactic bacteria.     

Controllable synthesis of uncapped metal nanoparticle assembly at the air–water interface

A two-dimensional self-assembly of uncapped Ag nanoparticles was prepared at the air–water interface. In the experiment, ethanol was added into the Ag-based colloid to reduce the surface charge density on the nanoparticles and the air–water interfacial energy, leading to the nanoparticles adsorption and assembling at the air–water interface. It was found that the array structure was controllable. The ordered nanoparticle array could be changed to a fractal structure by varying gradually the amount of the added ethanol. Moreover, it was demonstrated that the assembly was sensitive to the surface charge density on the particles, the Debye length in the colloid and the interfacial tension between nanoparticle/water (air).     

Synthesis and self-assembly of colloidal nanoparticles

We describe recent developments in the synthesis of semiconductor nanoparticles, which lead to a substantial improvement of the luminescence quantum efficiency. Concerning a theoretical model for the growth of an ensemble of nanoparticles, the highest quantum efficiencies are achieved in particles that grow under conditions of a rapid exchange of monomers at the particle surface, leading to a smooth surface structure. Selective etching, core-shell formation and doping of nanoparticles are also discussed as fluorescence-enhancing preparative techniques. Examples of self-assembly of almost-uniformly-sized nanoparticles are given, which result in two-dimensional and three-dimensional superlattices, colloidal crystals and crystalline structures built-up from particles of different sizes. Finally, the self-assembled oriented attachment of quasi-spherical ZnO nanoparticles onto single-crystalline nanorods is presented.     

Synthesis of SiO2-coated ZnMnFe2O4 nanospheres with improved magnetic properties

A core-shell structured composite, SiO2 coated ZnMnFe2O4 spinel ferrite nanoparticles (average diameter of approximately 80 nm), was prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of ZnMnFe2O4 nanoparticles (average diameter of approximately 10 nm) synthesized by a hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The magnetic measurements were carried out on a vibrating sample magnetometer (VSM), and the measurement results indicate that the core-shell samples possess better magnetic properties at room temperature, compared with paramagnetic colloids with a magnetic core by a coprecipitation method. These core-shell nanospherical particles with self-assembly under additional magnetic fields could have potential application in biomedical systems.     

Directing substrate morphology via self-assembly: ligand-mediated scission of gallium-indium microspheres to the nanoscale

We have developed a facile method for the construction of liquid-phase eutectic gallium-indium (EGaIn) alloy nanoparticles. Particle formation is directed by molecular self-assembly and assisted by sonication. As the bulk liquid alloy is ultrasonically dispersed, fast thiolate self-assembly at the EGaIn interface protects the material against oxidation. The choice of self-assembled monolayer ligand directs the ultimate size reduction in the material; strongly interacting molecules induce surface strain and assist particle cleavage to the nanoscale. Transmission electron microscopy images and diffraction analyses reveal that the nanoscale particles are in an amorphous or liquid phase, with no observed faceting. The particles exhibit strong absorption in the ultraviolet (～200 nm), consistent with the gallium surface plasmon resonance, but dependent on the nature of the particle ligand shell.     

Structure characterization of Ag-Ga/poly(methyl methacrylate) nanoparticles

The Ag-Ga/poly(methyl methacrylate) nanoparticles were prepared in-situ by emulsion polymerization method under ultrasonic irradiation without any initiators or metal reductant. HRTEM, EDS and XRD experiments were performed to characterize the nanoparticles. The results indicated that the nanocomposite particles possessed core-shell structure with diameters of 80-200 nm, as well as excellent monodispersity. The phenomenon that the polymer forms the shell via layer-by-layer self-assembly was found. XRD proved the existence of Ag0.72Ga0.28 and the probability of new Ag-Ga alloy because of two unknown diffraction peaks.     

OH~－和氧离子杂质对BaF_2晶体辐照损伤的影响

从理论和实验两方面研究ＯＨ－和氧离子杂质对ＢａＦ２晶体辐照损伤的影响，并对其机理进行讨论．理论上用（ＨＦＳ－ＤＶＭ－Ｘα）局域密度离散变分法计算ＯＨ－和氧离子杂质心在ＢａＦ２中的电子结构，得到ＯＨ－，Ｈｓ－（Ｕ心），Ｏｓ－，Ｏｓ２－和（Ｏｓ２－－Ｆ＋）都可能是引起辐照损伤的源泉．实验发现，ＢａＦ２晶体水解处理后，ＯＨ－和氧离子杂质很容易进入ＢａＦ２，在晶体中的存在形式主要是：ＯＨ－占据阴离子位置，氧离子以Ｏｓ２－的形式占据Ｆ－的晶格位置，并由氟空位（Ｆ＋）作电荷补偿，较大可能以（Ｏｓ２－Ｆ＋）形式存在．γ辐照前后水解处理样品的光吸收谱（ＶＵＶ，ＵＶ，ＩＲ）和电子顺磁共振谱（ＥＰＲ）验证了理论计算的正确性．综合理论和实验，我们认为ＯＨ－氧离子杂质引起ＢａＦ２晶体辐照损伤的主要原因是：ＯＨ－和（Ｏｓ２－Ｆ＋）辐照分解成Ｈｓ－（Ｕ心）和Ｏｓ－．上海硅酸盐研究所在晶体生长工艺中，有意识地对ＯＨ－和氧离子给予特别的注意，在改进辐照损伤上获得较好的效果．     

Hierarchically mesostructured doped CeO2 with potential for solar-cell use

Many properties provided by supramolecular chemistry, nanotechnology and catalysis only appear in solids exhibiting large surface areas and regular porosity at the nanometre scale. In nanometre-sized particles, the ratio of the number of atoms in the surface to the number in the bulk is much larger than for micrometre-sized materials, and this can lead to novel properties. Here we report the preparation of a hierarchically structured mesoporous material from nanoparticles of CeO(2) of strictly uniform size. The synthesis involves self-assembly of these 5-nm CeO(2) pre-treated nanoparticles in the presence of a structure directing agent (poly(alkylene oxide) block polymer). The walls of this hexagonal structured CeO(2) material are formed from the primary nanoparticles. The material possesses large pore volumes, high surface areas, and marked thermal stability, allowing it to be easily doped after synthesis whilst maintaining textural and mechanical integrity. It also exhibits a photovoltaic response, which is directly derived from the nanometric particle size-normal CeO(2) does not show this response. We have constructed operational organic-dye-free solar cells using nanometric ceria particles (in both mesostructured or amorphous forms) as the active component, and find efficiencies that depend on the illuminating power.     

Formation of Janus TiO2 nanoparticles by a pickering emulsion approach applying phosphonate coupling agents

Anisotropic surface modification of TiO2 nanoparticles was achieved applying a Pickering emulsion approach. TiO2 nanoparticles were prepared by sol-gel routes which allowed an excellent control over their size and morphology. The obtained colloids were further used as stabilizers in the formation of oil-in-water Pickering emulsion. For reasons of comparison, also commercially available titanium dioxide nanoparticles (Evonik AEROXIDE TiO2 P25) were used in the functionalization experiments. An organophosphorus coupling agent present in the oil phase coordinated to the surface of the anatase nanoparticles. In such a way an anisotropic surface modification of the particles was achieved which increased the stability of the Pickering emulsion. Spectroscopic studies revealed the presence of organophosphorus coupling agents which exhibited a covalent bonding to the surface of the particles. Thermogravimetric analyses confirmed a lower surface coverage of the particles modified in emulsion compared to those modified in suspension. Reactions of organophosphorus coupling agents containing an additional methacrylate group applying an organic monomer (methyl methacrylate) as the oil phase of the Pickering emulsion resulted in hybrid TiO2@polymer spheres. Spectroscopic characterization of the resulting particles revealed that the phosphonates were coordinated to the TiO2 surface and at the same time copolymerized with the MMA within the oil droplet. Morphological investigations of the isolated final product showed that the material was composed of polymer spheres with the stabilizing TiO2 nanoparticles on their surface.     

静电组装法在纳米SiO_2表面构筑高分子刷的合成与表征(英文)

本文采用静电自组装技术在表面阳离子化的SiO2粒子（SiO2-CBAFS）上构筑了高分子刷,并采用核磁、红外、热失重、接触角和原子力显微镜分别表征了组装粉体的结构、组装量以及自组装单层膜的组装行为和表面拓扑形貌。研究结果表明,采用静电自组装技术可以成功地在SiO2-CBAFS上构筑组装量高达27％的高分子刷,远远高于国际上已见报道的采用共价键合法构筑的高分子刷的组装量（20％）。研究发现,组装量随聚合物（PS-NH—SO3Na）分子量呈非线性增长,其组装行为受到PS-NH—SO3Na的分子量和溶液浓度的影响。     

Nickel nanoparticles decoration of ordered mesoporous silica thin films for carbon nanotubes growth

We report in situ successive depositions of nickel nanoparticles and carbon nanotubes (CNTs) on ordered mesoporous silica films used as template for the catalyst particles. The mesoporous films are synthesized by the evaporation-induced self-assembly process from tetraethyl orthosilicate derived oligomers and a di-block copolymer from dip-coating deposition method. The substrates are decorated with Ni nanoparticles through Ion Beam Deposition and posterior annealing to induce metal coalescence in the mesoporous cavities. CNTs were then grown by Chemical Vapor Deposition in the presence of an electric field. These techniques provide a simple control method producing ordered arrangements of catalyst nanoparticles and ordered nanostructures for large area applications.