Induced synthesis and characterisation of Ag and Ag2S assembly nanoparticle chains

A facile and efficient template method was developed for the fabrication of Ag and Ag₂S nanoparticle chains. The morphologies and structures of products were characterised by X-ray powder diffraction and transmission electron microscopy. The result shows that the length of Ag and Ag₂S nanoparticle chains are up to several micrometres. Systematic studies exhibit that the concentration of template (polyacrylamide) reagent, reaction solution and ageing time are important factors on the control synthesis of nanoparticle chains. The possible mechanism for the formation of Ag and Ag₂S nanoparticle chains was also discussed. The physical and chemical properties of the Ag and Ag₂S nanoparticle chains were investigated and their phytotoxicities were also researched for the first time. The phytotoxic result shows that the Ag and Ag₂S nanoparticle chains have obvious inhibition of seed germination.     

One-step wet chemistry for preparation of magnetite nanorods

A magnetite with high aspect ratio has been synthesized by a wet chemical process. A surfactant, polyethylene glycol, was used as the template, and a ferrous ammonia sulphate was used as iron source. In the one-step synthesis, a suitable ratio between the rates of deposition and oxidation of ferrous ions was achieved by adjusting the diffusion of ammonia and resulted in the iron oxide deposited with nanorod morphology. According to X-ray powder diffraction analysis, these nanorods crystallize in structure of magnetite phase. Transition electron microscopy and selected area electron diffraction investigations have revealed that nanorods are single crystal and up to 2000 nm long and their diameters generally range from 20 to 100 nm. The measurement by vibration sample magnetization shows the magnetization of the as-synthesized nanorods is higher than 50 emu/g. The presented one-step synthesis approach provides an advantageous access to large quantity of this important anisotropic nanomaterial.     

General assembly method for linear metal nanoparticle chains embedded in nanotubes

We demonstrate a flexible assembly method for producing linear metal nanoparticle chains embedded in nanotubes. The chain formation is based on the Rayleigh instability after annealing metal nanowires confined in nanotubes. Beginning with metal nanowires from arbitrary synthesis methods, atomic layer deposition (ALD) was applied to coat the wires first with a sacrificial layer then with a shell layer. Subsequently, the sacrificial layer was removed leading to confined wires in nanotubes with a free volume. Finally, embedded nanoparticle chains were produced inducing the Rayleigh instability by annealing the confined nanowires. This method is quite general not only for different metals but also for different shell materials. We are able to tune the particle spacing and diameter, the shape of the nanochains, the tube diameter and the shell thickness by ALD significantly.     

Non-lithographic SERS substrates: tailoring surface chemistry for Au nanoparticle cluster assembly

Near‐field plasmonic coupling and local field enhancement in metal nanoarchitectures, such as arrangements of nanoparticle clusters, have application in many technologies from medical diagnostics, solar cells, to sensors. Although nanoparticle‐based cluster assemblies have exhibited signal enhancements in surface‐enhanced Raman scattering (SERS) sensors, it is challenging to achieve high reproducibility in SERS response using low‐cost fabrication methods. Here an innovative method is developed for fabricating self‐organized clusters of metal nanoparticles on diblock copolymer thin films as SERS‐active structures. Monodisperse, colloidal gold nanoparticles are attached via a crosslinking reaction on self‐organized chemically functionalized poly(methyl methacrylate) domains on polystyrene‐block‐poly(methyl methacrylate) templates. Thereby nanoparticle clusters with sub‐10‐nanometer interparticle spacing are achieved. Varying the molar concentration of functional chemical groups and crosslinking agent during the assembly process is found to affect the agglomeration of Au nanoparticles into clusters. Samples with a high surface coverage of nanoparticle cluster assemblies yield relative enhancement factors on the order of 10⁹ while simultaneously producing uniform signal enhancements in point‐to‐point measurements across each sample. High enhancement factors are associated with the narrow gap between nanoparticles assembled in clusters in full‐wave electromagnetic simulations. Reusability for small‐molecule detection is also demonstrated. Thus it is shown that the combination of high signal enhancement and reproducibility is achievable using a completely non‐lithographic fabrication process, thereby producing SERS substrates having high performance at low cost.     

Electromagnetic energy transport in nanoparticle chains via dark plasmon modes

Using light to exchange information offers large bandwidths and high speeds, but the miniaturization of optical components is limited by diffraction. Converting light into electron waves in metals allows one to overcome this problem. However, metals are lossy at optical frequencies and large-area fabrication of nanometer-sized structures by conventional top-down methods can be cost-prohibitive. We show electromagnetic energy transport with gold nanoparticles that were assembled into close-packed linear chains. The small interparticle distances enabled strong electromagnetic coupling causing the formation of low-loss subradiant plasmons, which facilitated energy propagation over many micrometers. Electrodynamic calculations confirmed the dark nature of the propagating mode and showed that disorder in the nanoparticle arrangement enhances energy transport, demonstrating the viability of using bottom-up nanoparticle assemblies for ultracompact opto-electronic devices.     

Facile preparation of Ag/ZnO nanoparticles via photoreduction

Ag/ZnO nanoparticles can be obtained via photocatalytic reduction of silver nitrate at ZnO nanorods when a solution of AgNO₃ and nanorods ZnO suspended in ethyleneglycol is exposed to daylight. The mean size of the deposited sphere like Ag particles is about 5 nm. However, some of the particles can be as large as 20 nm. The ZnO nanorods were pre-prepared by basic precipitation from zinc acetate di-hydrate in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. They are about 50–300 nm in length and 10–50 nm in width. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) were used to characterize the resulting Ag/ZnO nanocomposites.     

利用湿化学法对不同粒径硅粉进行表面改性研究

通过湿化学方法,利用硅氢化反应,通过对刻蚀体系、脱氧方式、刻蚀后硅粒子的分离方法等工艺的优化,成功地实现了微米硅、纳米硅及硅量子点的表面烃基改性。傅里叶变换红外光谱及扫描电子显微镜测试结果表明,硅粒子的表面是通过Si—C键的连接方式实现了烃基改性。与改性前相比,改性后的硅粒子具有显著提升的抗氧化性和抗团簇能力,能够在有机溶剂中形成稳定的分散体系。值得一提的是,与未经改性的硅量子点相比,经烃基改性后的硅量子点的荧光发射性能有了大幅提高,有望应用于光电领域。     

Multiplexed dot immunoassay using Ag nanocubes,Au/Ag alloy nanoparticles,and Au/Ag nanocages

We report the first application of Ag nanocubes, Au/Ag alloy nanoparticles, and Au/Ag nanocages in a multiplexed dot immunoassay. The assay principle is based on the staining of analyte drops on a nitrocellulose membrane strip by using multicolor nanoparticles conjugated with biospecific probing molecules. Nanoparticles were prepared by a galvanic replacement reaction between the Ag atoms of silver nanocubes and Au ions of tetrachloroauric acid. Depending on the Ag/Au conversion ratio, the particle plasmon resonance was tuned from 450 to 700 nm and the suspension color changed from yellow to blue. The particles of yellow, red, and blue suspensions were functionalized with chicken, rat, and mouse immuno gamma globulin (IgG) molecular probes, respectively. The multiplex capability of the assay was illustrated by a proof-of-concept experiment involving simultaneous one-step determination of target molecules (rabbit anti-chicken, anti-rat, and anti-mouse antibodies) with a mixture of fabricated conjugates. Under naked eye examination, no cross-colored spots or nonspecific bioconjugate adsorption were observed, and the low detection limit was about 20 fmol.      

BPSCCO–Ag powders by a wet method and a low-carbon content for tape preparation

The preparation of BPSCCO-Ag composites by an innovative wet method is described, which allowed admixing of silver in the form of a solution to the solution containing all other cations, and the decomposition of the organic matter in a mild and reproducible way. The citrate route was used without the use of nitrates, ethylene glycol or other reticulating or complexing agents. After drying, silver was found to be dispersed in the powder in metallic form. The powders were treated in an atmosphere containing nitrogen oxides in order to reduce the carbon content. The powders so prepared were suitable for “powder in tube” processing in that they were very reactive toward the 2223 formation and may contain only the desired phases: 2212, metallic silver and Ca₂PbO₄ which, when present in excess, produce a flux that helps texturing and full phase conversion. Preliminary results on the high-purity samples prepared by the powder in tube process show a steady increase of J_c, with the absence of a maximum of J_c with number of treatments, and high texturing of the powder inside the tube. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation and characterization of lithium nickel cobalt oxide powders via a wet chemistry processing

Nickel-rich phases of the solid solutions, LiNi_1−yCo_yO₂ (y=0.1, 0.2, 0.3), were synthesized by a sol–gel method with citric acid as a chelating agent. Various initial conditions were studied in order to find the optimal conditions for the synthesis of LiNi_0.8Co_0.2O₂. The discharge capacity for the compound synthesized under an optimal synthesis condition of 800 °C for 12 h was found to be 187 mAh g⁻¹ in the 1st cycle and it was 176 mAh g⁻¹ after 10 cycles. The other nickel-rich phases, namely, LiNi_0.9Co_0.1O₂ and LiNi_0.7Co_0.3O₂ showed 1st-cycle discharge capacities of 144 and 163 mAh g⁻¹, respectively. The corresponding capacity values were 140 and 159 mAh g⁻¹ in the 10th cycle. Excess lithium stoichiometric phases, Li_xNi_0.8Co_0.2O₂, where x=1.10, 1.15 and 1.20, resulted in decreased capacity. Structural and electrochemical properties of the synthesized compounds were compared with those of a commercial LiNi_0.8Co_0.2O₂ sample. The effect of calcination temperature and duration, excess lithium stoichiometry and divalent strontium doping in LiNi_0.8Co_0.2O₂ are described. Doping with strontium improved both the capacity and cycling performance of LiNi_0.8Co_0.2O₂.     

Facile synthesis and characterization of hydroxylapatite nanoparticle chains

The hydroxylapatite nanoparticle chains were firstly synthesized by self-assembly with sodium polymethacrylic acid as the template. These high-quality HAP nanoparticle chains showed well-defined nanoscaled structures and regular morphology. The nanoparticle chains were 1.4-2 μm in length and the nanoparticles were about 45 nm in diameter. The structure of products has been studied with XRD and FT-IR spectrum. The forming conditions and mechanism of the products have been investigated. This synthesis method is facile and effective. The products will have potential applications in many fields such as biosensor, and biomimetic bone materials etc. The experimental outcomes present here will have potential values in crystal engineering research and practical applications.     

Comparison of surface plasmon resonance responses to dry/wet air for Ag, Cu, and Au/SiO2

We investigated the optical absorption spectra of Ag-, Cu-, and Au-mesoporous SiO(2) systems, respectively, after the samples were heated in dry air and in wet air. As expected, dry air at high temperature leads to the surface plasmon resonance (SPR) disappearance of Ag-SiO(2) and Cu-SiO(2) and a slight SPR increase of Au-SiO(2). However, a small amount of water vapor in air induces a strong SPR appearance for both Ag- and Au-containing samples, indicating that water vapor plays an abnormal reduction effect on both Ag and Au species in mesoporous SiO(2), despite the fact that it usually plays an oxidation role on Pt-group metals, but it cannot induce the SPR appearance for the Cu-containing sample under the same condition.     

Temperature-programmed assembly of DNA:Au nanoparticle bioconjugates

Temperature has been used to control the order of assembly events in a solution containing three types of particles to be linked by two different sets of complementary DNA. At higher temperatures, only the duplexes having higher thermal stability were able to form. By starting at a high temperature and then cooling the sample, these more stable sequences hybridized first, followed by the less stable sequences at lower temperatures. Because of the use of thiolated DNA on Au particles, some loss and exchange of the DNA strands occurred at elevated temperatures. However, since cooperativity favors the "correct" assemblies, Au-S bond lability did not appreciably impact the order of the assembly process. Temperature programming combines the selectivity of DNA-directed assembly with the ability to control the order in which several complementary strands hybridize in a common solution and could contribute to the synthesis of more complex nanostructured materials.     

Ultrasonic-template method synthesis of CdS hollow nanoparticle chains

A facile and efficient ultrasonic-template method has been developed for the fabrication of CdS hollow nanoparticle chains. The structures and morphologies of products were characterized by XRD and TEM. UV-Vis and photoluminescence (PL) spectra recorded the optical properties of CdS hollow nanoparticle chains, which showed obvious blue shift relative to the CdS bulk materials. Systematic studies found that the ultrasonic irradiation, concentration of template (polyacrylicamide) and injection method of reaction solution in the system were important factors on the controlled synthesis of hollow nanoparticle chains. The possible mechanism for the formation of CdS hollow nanoparticle chains was also discussed.     

Density and Thermal Expansion of Liquid Ag–Cu and Ag–Au Alloys

The densities of liquid Cu–Ag and Ag–Au alloys were measured using the technique of electromagnetic levitation. This technique involves producing shadow images of the sample from which the volume is calculated by an image processing algorithm. The density and thermal expansion of several alloys and the pure elements copper, gold, and silver are measured at temperatures above their melting points. In addition, they were investigated as a function of either the copper or gold concentration. It was found from data analysis that the densities can be derived from a linear combination of the molar volumes of the elements and that thermodynamic excess quantities are negligibly small.     

Role of nanoparticle in PNN-PZT/Ag nanocomposite

In the present work, we studied the role of nanoparticles in ferroelectric/silver composites, in which silver is the secondary particle. The ferroelectric system that we adapted was PNN-PZT. To make the PNN-PZT/silver nanocomposite, we hot-pressed the composite at 850 °C/2 h. A nanocomposite could be obtained with <0.5 vol.% of silver. We found that silver nanoparticles more effectively relieved the internal stresses than microparticles, which affected lattice parameter and transition temperature of the nanocomposites.     

Modulated optical properties in Ag and Au films

Modulation spectroscopy is a recent technique for investigating the optical properties of solids. Some results concerning piezo-reflectance, thermo-reflectance, electro-reflectance and electro-transmittance of Ag and Au films are given.     

High-temperature reliability of sintered microporous Ag on electroplated Ag,Au, and sputtered Ag metallization substrates

Ag sinter joining technology has been used in the advanced power applications to replace conventional soldering technology due to its high temperature stability, along with its excellent electrical and thermal conductivity. In this paper, we report the high-temperature reliability (250 °C for 1000 h) for die-attachment structures using Ag sintering technology on Cu substrates with different top metallization layers (Au and Ag), formed via different deposition processes (electroplating and sputtering). The bonding strength over 40 MPa and high-temperature reliability of sintered Ag on the sputtered Ag surface was the best among the systems studied here. Bonding quality and the bonding fracture behavior of sintered Ag on the different metallization substrates were characterized. Ag–Au solid solution was formed due to metallizaion Au atoms diffused into sintered Ag layer, leading to decreased shear strength under high temperature process. The influence of grain structure on the bonding quality at the interface between sintered Ag and the metallization Ag layers were discussed. It revealed that the grain size and orientation of the top metallization Ag layer influenced the bonding quality. The sintered Ag layer formed by Ag hybrid particles may have a selective orientation of metallization layer on the surface (111) of the Ag crystal. These results will be helpful to understand both technological perspectives for design and the applications of sintered Ag from the viewpoint of high-temperature reliability, as well as the fundamental understanding of its bonding quality mechanism with top metallization layers.