Cobalt-doped cadmium selenide colloidal nanowires

Co(2+)-doped CdSe colloidal nanowires with tunable size and dopant concentration have been prepared by a solution-liquid-solid (SLS) approach for the first time. These doped nanowires exhibit anomalous photoluminescence temperature dependence in comparison with undoped nanowires.     

Quantum confinement in silver selenide semiconductor nanocrystals

We prepare Ag(2)Se nanocrystals with average diameters between 2.7 and 10.4 nm that exhibit narrow optical absorption features in the near to mid infrared. We demonstrate that these features are broadly tunable due to quantum confinement. They provide the longest wavelength absorption peaks (6.5 μm) yet reported for colloidal nanocrystals.     

Study of the silver selenide—silver telluride system

The system Ag₂TeAg₂Se was investigated by DTA, X-ray diffraction and microstructural analysis within the composition interval from 0 to 100% Ag₂Te. Samples obtained after heating at 500°C for 720 h were studied.The high-temperature polymorphs form a continuous solid solution with a minimum at 35% Ag₂ Te and 835°C. At low temperatures solid-phase transformations take place. The break-down of the solid solution proceeds eutectoidally at about 110°C on the Ag₂Te side peritectoidally at about 150°C on the Ag₂Se side. The system Ag₂TeAg₂Se is rather complex.     

Negative and linear positive magnetoresistance effect in silver-rich silver selenide

In the non-magnetic semiconductor silver selenide (Ag_2+δSe) with a minor heterogeneous silver excess (0.79 × 10⁻⁴ < δ ≤ 1 × 10⁻²) we measured either a saturating negative magnetoresistance (MR) effect, a linear positive MR effect or a superposition of both. This complex MR behavior depends on the amount of the silver metal excess, but is also strongly influenced by the thermal treatment of the samples. Excess silver that cannot be accommodated homogeneously in the silver selenide lattice creates structural heterogeneities and forms a microstructure which is controlled by the thermal annealing procedure. We suggest that small silver segregations at the grain boundaries of the silver selenide matrix (“nanofilms”) are responsible for the negative MR effect, whereas nanoscale silver particles within the silver selenide matrix (nanoparticles) cause a linear positive effect.     

Machinable long PVP-stabilized silver nanowires

PVP-capped silver nanowires with a diameter range from 150 to 200 nm and a length range from 50 to 100 microm have been synthesized in large quantity by using a soft-template liquid-phase method. The so-obtained longer and thicker metallic nanowires exhibit fivefold-twinned structures bound by five [1 0 0] wall-planes and two spearlike ends around five [1 1 1] facets. X-ray photoelectron spectroscopy (XPS) investigations show that a strong interaction exists between the carboxyl oxygen atom (C=O) of PVP and the Ag core interface. The PVP-capped Ag nanowires can either self-assemble into ordered raft structures or form a complicated network, depending on the dispersive solvent employed. In addition, the Ag nanowires can also be specifically bent into various angles, demonstrating their excellent mechanical stability.     

Hyaluronan-assisted synthesis of silver nanoparticles and nanowires

Research on Chemical Intermediates - Silver nanowires (NWs) were successfully synthesized in high yield in cationic surfactant solutions of cetyltrimethylammonium bromide (CTAB) with hyaluronan...     

Large-scale synthesis of silver nanowires and platinum nanotubes

Silver nanowires have been synthesized by ethylene glycol reduction of silver nitrate with the assistance of polyvinyl pyrrolidone and sodium sulfide in a large scale. By adjusting the reaction temperature and Na₂S content, silver nanowires with lengths up to 3?4 μm can be achieved in high yield. Scanning electron microscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected areas electron diffraction (SAED), and X-ray diffraction (XRD) have been employed to characterize silver nanowires. Platinum nanotubes with length about 3 μm can be prepared using as-prepared silver nanowires as sacrificial templates. Platinum nanotubes were characterized by TEM, SAED, and HRTEM.     

Mercury selenide stoichiometry and phase relations in the mercury-selenium system

The phase relations in the 0–65 at% Hg portion of the condensed mercury-selenium system were determined from liquidus temperatures to 250°C by evacuated silica tube experiments in which vapor is always a phase. Stoichiometric HgSe melts at 795 ± 2°C whereas Hg_0.51Se_0.49 melts at 797 ± 2°C and Hg_0.49Se_0.51 melts at 793 ± 2°C. In the HgSeSe portion of the system a monotectic exists at 683 ± 3°C and 71.5 at% Se and a liquid immiscibility field at this temperature extends from 71.5 to 85.5 at% Se. The presence of HgSe depresses the melting temperature of Se by about 8°C. An eutectic exists between HgSe and Se at 208°C and a composition of more than 99.95 at% Se. In the HgHgSe portion of the system a monotectic exists at 708 ± 3°C and about 25 at% Se. The solubility of Hg in HgSe was found to exceed stoichiometry by 1.11 ± 0.25 at% at 650°C whereas the solubility of Se in HgSe exceeds stoichiometry by 0.75 ± 0.25 at% Se at the same temperature. All synthetic mercury selenides show the sphalerite type structure. The unit cell dimension of stoichiometric HgSe is a₀ = 6.080 ± 0.001 Å. Mercury selenide synthesized in equilibrium with liquid Se gives a₀ = 6.082 ± 0.001 Å and mercury selenide synthesized in equilibrium with Hg gives a₀ = 6.078 ± 0.001 Å.     

Controlling synthesis of silver nanowires and dendrites in mixed surfactant solutions

Using a simple wet chemical route, high-yield silver nanowires with an average diameter of 25+/-5 nm and length up to several microm and dendrites with a long central backbone and symmetrically ramified secondary branches have been successfully obtained by reducing AgNO(3) with L-ascorbic acid (AsA) in the mixed surfactant solutions of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). It was found that the architecture of silver nanocrystals was drastically influenced by the concentrations of ascorbic acid. At a given high concentration, a nonequilibrium system was easily built, which favored the formation of fractals. When the concentration was lowered, one-dimensional silver nanowires were successfully obtained. In addition, the presence of electrolyte (NaCl) plays an important role in the preparation of silver nanowires, influencing the silver crystallization process in surprising ways.     

Formation of assembled silver nanowires by reduction of silver thiolate in polyol/toluene medium

Reduction of silver nitrate in polyol/toluene biphasic medium containing dodecanethiol led to organised silver nanowires, results of an interaction between silver nanoparticles and the layered phase AgSC12H25.     

Preparation and optical properties of silver nanowires and silver-nanowire thin films

Silver nanowires and silver-nanowire thin films have attracted much attention due to their extensive applications in Surface-Enhanced Raman Scattering (SERS) and Surface-Enhanced Fluorescence (SEF). Thin films of silver nanowires within polyelectrolyte layers of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) were fabricated by the Spin-Assisted Layer-by-Layer (SA-LbL) method. The surface coverage, thickness, and absorbance properties of the silver-nanowire films were controlled by the number of layers deposited. Both transverse and longitudinal surface plasmon (SP) modes of the silver-nanowires were observed in the absorbance spectra, as was evidence for nanowire interaction. Two-dimensional finite difference time-domain (2D FDTD) simulations predict that the maximum field enhancement occurs at the ends and cross-sectional edges of the wires for the longitudinal and transverse modes, respectively. Silver nanowires were synthesized by a facile, high-yield solvothermal approach, which can be easily manipulated to control the aspect ratio of the nanowires. The effects of polyvinylpyrrolidone (PVP) concentration and molecular weight on the growth of the silver nanowires, which are not documented in the original procedure, are discussed. It is shown that the growth mechanism for silver nanowires in the solvothermal synthesis is similar to that reported for the polyol synthesis.     

Vapor phase synthesis of tungsten nanowires

A concept is presented for synthesizing metal nanowires directly from the vapor phase using chemical vapor transport to temperatures higher than the corresponding metal oxide decomposition temperature. Specifically, this concept is demonstrated with the synthesis of tungsten metal nanowires with sizes ranging from 70 to 40 nm by increasing the condensation temperature. The simultaneous condensation and decomposition of the tungsten oxide species during nucleation and growth is suggested for 1-D growth of metallic tungsten nanowires. This synthesis concept could potentially be extended to the vapor phase synthesis of metal nanowires of several other nonvolatile and refractory metals. The tungsten nanowires could find potential applications in gas sensors and as electron sources in electron microscopes.     

Room temperature synthesis of silver nanowires from tabular silver bromide crystals in the presence of gelatin

Long silver nanowires were synthesized at room temperature by a simple and fast process derived from the development of photographic films. A film consisting of an emulsion of tabular silver bromide grains in gelatin was treated with a photographic developer (4-(methylamino)phenol sulfate (metol), citric acid) in the presence of additional aqueous silver nitrate. The silver nanowires have lengths of more than 50 μm, some even more than 100 μm, and average diameters of about 80 nm. Approximately, 70% of the metallic silver formed in the reduction consists of silver nanowires. Selected area electron diffraction (SAED) results indicate that the silver nanowires grow along the [111] direction. It was found that the presence of gelatin, tabular silver bromide crystals and silver ions in solution are essential for the formation of the silver nanowires. The nanowires appear to originate from the edges of the silver bromide crystals. They were characterized by transmission electron microscopy (TEM), SAED, scanning electron microscopy (SEM), and powder X-ray diffraction (XRD).     

Synthesis of silver nanowires and their applications in the electrochemical detection of halide

A silver nanowires modified platinum (Ag NWs/Pt) electrode was developed for simultaneous and selective determination of chloride, bromide and iodide ions by cyclic voltammetry in aqueous solutions. Silver nanowires were synthesized by an l-cysteine-assisted poly (vinyl pyrrolidone) (PVP)-mediated polyol route. X-ray diffraction (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the prepared nanowires. The intrinsic high surface area and the fast electron transfer rate ascribed from the nanowire structure could further improve halide detection performance. The determination was based on measurement of the well-separated oxidation peak currents of respective silver halides formed on the surface of silver during an anodic potential sweep. The concentration range was linear from 50 μM to 20.2 mM for bromide and iodide and 200 μM to 20.2 mM for chloride, and the sensitivity was 0.059 μA/mM, 0.042 μA/mM and 0.032 μA/mM for chloride, bromide and iodide, respectively. The correlation coefficient was 0.999 in each case. The Ag NWs/Pt electrode offered a useful platform for the development of a highly sensitive halide sensor.     

Potassium silver tin selenide,K2Ag2Sn2Se6

The title compound was synthesized by a reactive salt reaction at 773 K over a period of 5 d. It has a one-dimensional chain structure consisting of K⁺ cations and one-dimensional [Ag₂Sn₂Se₆]²⁻ anions. The chain is constructed by edge-sharing bitetrahedral [Sn₂Se₆] units connected in a 1:2 ratio via linear Ag⁺ ions.     

Fluorescence amplification by electrochemically deposited silver nanowires with fractal architecture

Electrochemically deposited silver structures with nanowires 50-100 nm in diameter show high fluorescence amplification and strongly reduced fluorescence lifetimes. Both quantities depend on the structure thickness. With increasing thickness the fluorescence amplification proportionally increases and the fluorescence lifetime decreases. This thickness dependence is caused by fluorophore interaction with a system of plasmon excitations in coupled nanowires extending over micrometer size regions. Thus the amplification is attributed to a combination of extended structure area and strong plasmonic coupling between nanowires which also help to radiatively scatter the fluorescence emission.     

Growth of silver nanowires by an unconventional electrodeposition without template

We describe an unconventional electrochemistry approach to the preparation of silver nanowires. By the electrodeposition in the dilute solution without supporting electrolyte, silver nanowires with diameter 10–50 nm and length up to several μm have been synthesized. It was found that the absence of the supporting electrolyte played a key role in the formation of silver nanowires, and the products from the solution without supporting electrolytes were very different from those with supporting electrolytes. A possible mechanism concerning the transportation of silver ions by electro-migration and the diffusion was proposed.     

Coordinated organogel templated fabrication of silver/polypyrrole composite nanowires

A new method to fabricate metal/conducting polymer composite nanowires is presented by taking silver/polypyrrole composite nanowires as an example.A silver(Ⅰ)-coordinated organogel as template was prepared firstly,and redox-polymerization of pyrrole took place on the gel fiber,giving product of silver/polypyrrole nanowires.The silver/polypyrrole nanowires were characterized by multiple techniques.This strategy could be carried out in one-step procedure at room temperature,and it proves the utility of coordinated organogels in template synthesis of polymer nanostructures.     

Characterization of silver selenide thin films grown on Cr‐covered Si substrates

Thermal stability of silver selenide thin films formed from the solid‐state reaction of Ag‐Se diffusion couples on Si substrates covered with a thin Cr film, is investigated. Glancing angle X‐ray diffraction (GXRD), XPS, atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) are used to characterize the as‐deposited films and those annealed at 100, 200, 300, and 400 °C. The results reveal the formation of polycrystalline orthorhombic silver selenide films that remain stable without compositional change upon thermal annealing, in marked contrast to the agglomeration exhibited by silver selenide films deposited on Si without Cr film. The improvement in the thermal stability is attributed to compressive stress relief by a grainy morphology with large surface area, the formation of which is promoted by partially oxidized Cr adhesion film. Copyright © 2008 John Wiley & Sons, Ltd.