Hexagonal Ag Research Articles

Simulating Synthesis of Metal Nanorods, Nanoplates, and Nanoframes by Self-Assembly of Nanoparticle Building Blocks

A general synthesis strategy to prepare metal nanostructures by self-assembly was proposed by molecular dynamics (MD) simulation. In this simulating synthesis strategy, the metal nanostructures were generated by the self-assembly of the amorphous nanoparticles with the attractive forces of the nanoparticle−nanoparticle interactions by the annealing MD method at high temperatures, and finally, the resulting amorphous metal nanostructures were cooled to 10 K, which could resemble the nanoparticle self-assembly in experiment. By using the simulating synthesis, we obtained the full atomistic models of the shape-controlled metal nanostructures, including Au, Ag−Au, and beaded Ag−Cu nanorods, triangular and hexagonal Ag nanoplates, triangular Ag−Au and hexagonal Au, cubic hollow Fe, and Ag−Au nanoframes. It is found that these models are in good agreement with the experimental results. Moreover, we predicted a new metal nanostructure, Au nanoporous framework architecture, which has not been reported in experime...

Photocatalytic growth and plasmon resonance-assisted photoelectrochemical toppling of upright Ag nanoplates on a nanoparticulate TiO2 film

Triangular and hexagonal Ag nanoplates deposited on a TiO(2) film in a mostly vertical orientation topple under visible light, resulting in a decrease of extinction at the excitation wavelength and increase at longer wavelengths.

High Activity of Hexagonal Ag/Pt Nanoshell Catalyst for Oxygen Electroreduction

Hexagonal Ag/Pt nanoshells were prepared by using a hexagonal Ag nanoplate as the displacement template and by introducing Pt ions. The prepared Ag/Pt nanoshells played the role of an electrocatalyst in an oxygen reduction process. Compared to spherical Pt and Ag/Pt nanoparticles, the hexagonal Ag/Pt nanoshells showed higher activity for oxygen electroreduction.

Transformation of Ag Hexagonal Shape into Ag@Au Core-Shell Nanostructure in a Polymer-Mediated Polyol Process

In this article, we report the galvanic replacement reaction between an Ag template and HAuCl4 · 4H2O in aqueous solution transforms 33.3 nm hexagonal shape Ag to Ag@Au core-shell nanostructure in the presence of the surface-regulating polymer poly (vinyl pyrrolidone) (PVP). By controlling the molar ratio of Ag to HAuCl4 · 4H2O, the extinction peak of resultant can be continuously tuned from the blue to the near infrared sections for both absorption and scatting. The results of UV-vis, XRD, TEM, and SEM show the different characters on the Ag and Ag@Au core-shell nanostructure which suggest that the transformation of Ag into Ag@Au by controlling their dimensions as well as the thickness and porosity of their walls.

Single crystal Ag 7Te 4 nanowire arrays prepared by DC electrodeposition from aqueous solution

Ag 7Te 4 nanowires have successfully been synthesized into porous anodic alumina membranes by DC electrodeposition from aqueous solution. X-ray diffraction (XRD), selected-area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM) results show that the as-synthesized sample is single crystal hexagonal Ag 7Te 4. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) results demonstrate that the Ag 7Te 4 nanowire arrays with a high filling rate are dense, smooth, and uniform in large area. X-ray photoelectron spectroscopy (XPS) analysis indicates that the atomic ratio of Ag to Te is close to 7:4 stoichiometry. The effects of several electrodeposition parameters on the Ag 7Te 4 nanowire arrays are discussed.

Comparative Study of Irradiation-induced and Thermally Induced Structural Phase Transitions in Equilibrium Immiscible Fe–Ag Systems

In the equilibrium immiscible Fe–Ag systems, unique fcc-structured solid solutions were obtained in their nanosized multilayered films upon ion beam manipulation, indicating that the solid solubility of Fe in Ag can be extended from nearly zero up to 60 at. %. In contrast, an unusual hexagonal (4H) Ag phase was observed in the Fe–Ag multilayered films upon steady-state thermal annealing. We report, in this paper, the detailed structural phase transitions observed in the Fe–Ag multilayered films upon ion irradiation and thermal annealing, together with a brief discussion concerning the significantly different mechanisms involved in the two processes.

Quantum Size Effects in Adatom Island Decay

The decay of hexagonal Ag adatom islands on top of larger Ag adatom islands on a Ag(111) surface is followed by a fast-scanning tunneling microscope. Islands do not always show the expected increase in decay rate with decreasing island size. Rather, distinct quantum size effects are observed where the decay rate decreases significantly for islands with diameters of 6, 9.3, 12.6, and 15.6 nm. We show that electron confinement of the surface state electrons is responsible for this enhancement of the detachment barrier for adatoms from the island edge.

Electrodeposition of silver telluride thin films from non-aqueous baths

We describe a method for preparation of crystalline silver telluride films by cathodic deposition from dimethyl sulfoxide (DMSO) solutions containing 0.1 M NaNO 3, 5.0 mM AgNO 3 and 3.5–7.0 mM TeCl 4. X-ray diffraction data indicated that the deposited silver telluride films could be adjusted from Ag excess and stoichiometric monoclinic Ag 2Te to hexagonal Ag 7Te 4 by increasing the concentration of TeCl 4 in the electrolyte or lowering the deposition potential. The Ag 2Te film is gray and the Ag 7Te 4 film is dark blue-gray and mirror like adhered strongly to the substrates. Scanning electron microscopy images show that Ag 2Te films were formed with globular grains with average diameters of more than 1 μm. In contrast, Ag 7Te 4 film consists of triangles characteristic of a (1 1 1) single-crystal with a hexagonal structure in average sizes of about 0.4 μm. The X-ray photoelectron spectra (XPS) indicated that the binding energies deviation of Te3d in Ag 7Te 4 is less than that in Ag 2Te, which is consistent with the apparent valences of Te in Ag 2Te and Ag 7Te 4. Finally, the cathodic deposition reactions were studied by cyclic voltammetry.

Preparation of silver dispersed PbTiO 3 film by sol-gel method

Silver-dispersed PbTiO 3 thin films were prepared by a sol-gel process. The mole fraction of Ag was varied from 0 to 5%. Sintering temperature ranged from 300 to 600 °C. XRD, TEM and UV-VIS absorption spectra were carried out on the films. XRD results indicated that tetragonal PbTiO 3 began to crystallize between 400 and 500 °C and grew up when sintering temperature increased to 600 °C. According to TEM results, nanosized cubic Ag particles formed in films when sintered at 400 °C and after annealing at 600 °C for 30 min, both hexagonal Ag and cubic Ag were observed . Ag particle size was dominated by the nucleation of Ag grains during the sintering process. It decreased with the increase in sintering temperature and increased with the increase in Ag concentration and coated layers.

Thermal dependence of surface polymorphism: the Ag/Cu (111) case

The occurrence of an Ag layer on top of a Cu (111) substrate can result from either deposition of Ag atoms on a Cu (111) substrate or from strong segregation at the (111) surface of a dilute Cu (Ag) alloy. Quenched molecular dynamics simulations within many-body tight-binding potentials show that two structures compete at T=0 K. The first one corresponds to a Moiré structure built by the superposition of an hexagonal Ag (111) layer on top of a Cu (111) substrate, the lattice parameter of the Ag layer being very near of the bulk Ag one. The second structure involves constitutive vacancies forming a triangular loop of dislocation in the first Cu underlayer. We show here that increasing temperature slightly favours the Moiré structure along a free energy criterion, as a result of a complex interplay between internal energy and vibrational entropy. This indicates that the experimentally observed transition between the Moiré structure at low temperature and the triangular one at higher temperature has probably a kinetic origin and is not a true equilibrium phase transition.

Preparation of ultrafine composite particles of Ag+AlN/Al by nitrogen plasma metal reaction

Abstract Pure Ag and Al were melted simultaneously by nitrogen arc plasma in a common chamber using two electrodes. Ultrafine composite particles consisting of fcc-Ag, fcc-Al and hexagonal AlN are obtained together with 17% mixture of hexagonal Ag 2 Al ultrafine particles. Ag, Al and AlN ultrafine particles are formed through the condensation of element vapor, but Ag 2 Al ultrafine particles are formed through a solid reaction between Al and Ag ultrafine particles.

Three-Dimensional Hexagonal Close-Packed Superlattices of Passivated Ag Nanocrystals

Abstract Silver nanocrystals passivated by dodecanethiol self-assembled monolayers were produced using an aerosol technique described in detail elsewhere [1]. Self-assembling passivated nanocrystal-superlattices (NCS's) involve self-organization into monolayers, thin films, and superlattices of size-selected nanoclusters encapsulated in a protective compact coating [2,3,4,5,6,7]. We report the preparation and structure characterization of three-dimensional (3-D) hexagonal close-packed Ag nanocrystal supercrystals from Ag nanocrystals of ˜4.5 nm in diameters. The crystallography of the superlattice and atomic core lattices were determined using transmission electron microscopy (TEM) and high-resolution TEM. SEM was used to image the nanocrystal superlattices formed on an amorphous carbon film of an TEM specimen grid (fig. la). The superlattice films show well shaped, sharply faceted, triangular shaped sheets. Figure lb depicts numerous Ag nanocrystal aggregates uniformly distributed over the imaging region. Inset in this figure is an enlargement of the boxed region at the edge of a supercrystal typifying the ordered nanocrystal packing.

Structure of dental gallium alloys

The interest in gallium alloys as a replacement for amalgam has increased in recent years due to the risk of environmental pollution from amalgam. Alloy powders with compositions close to those for alloys of amalgam are mixed with a liquid gallium alloy. The mix is condensed into a prepared cavity in much the same way as for amalgam. The aim of the present work was to study the structure of: (1) two commercial alloy powders containing mainly silver, tin and copper, and (2) the phases formed by mixing these powders with a liquid alloy of gallium, indium and tin. One of the alloy powders contained 9 wt% palladium. Cross-sections of cylindrical specimens made by these gallium mixes were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Discrete grains of the following phases were found to be present in both gallium alloys: hexagonal Ag 2Ga, tetragonal Cu(Pd)Ga 2, cubic Ag 9In 4 and tetragonal β-Sn. Indications of hexagonal or orthorhombic Ag 2Sn were found in the remaining, unreacted alloy particles. In the palladium-containing alloy the X-ray reflections indicate a minor fraction of cubic Cu 9Ga 4 in addition to the Cu(Pd)Ga 2 phase. Particles of β-Sn are probably precipitated because Sn-Ga phases cannot be formed according to the binary phase diagram.

Properties of the AlAg surface alloy across the phase diagram

The atomic structure and the electronic properties of the (111) surface of Al can be modified by alloying with Ag which can be introduced to the surface either externally by vapor deposition or internally by segregation from the bulk in a dilute AlAg alloy. Evaporated Ag forms islands on Al(111) during the initial stage of growth, while perfect epitaxy is observed for layers that are as thick as 8 monolayers. Upon subsequent heat treatment of the sample at increasing temperatures Ag diffuses into the Al substrate, and the composition at the surface is changed from pure Ag to pure Al. During this process, the temperature-dependent changes in the local atomic structure of the surface is observed in real time using secondary-electron imaging. It is found that hexagonal Ag 2Al phase is formed at 410 K. This surface, when used for further Ag evaporation, imposes an hexagonal structure on the growing film. This observation points to a small stacking-fault energy for the (111) layers of Ag. The results on Al-3 at.% Ag show that, above 450 K, Ag segregates to the surface in form of small hexagonal Ag 2Al-like clusters. Between 610 and 690 K, the clusters reversibly dissolve without changing the average Ag concentration at the surface, suggesting a first-order phase transition.

Transport phenomena and growth modes of silver electrodeposits

Abstract A systematic investigation of the influences of migration, diffusion and convection on the growth modes of three-dimensional Ag electrodeposits on a Pt substrate was made using conventional electrochemical techniques combined with optical and scanning electron microscopic observations. The dependence of the growth mode on the dominant mass transport mechanism was established. Diffusion and migration influence the microscopic structure of the deposit. Migration dominates at the dendrite tip growth. Convection alters mainly the macroscopic growth of the deposit. Several transitions in the growth mode of Ag electrodeposits could be distinguished. One of these transitions was related to the initiation of dendrite formation, which appeared when a critical amount of electrodeposited Ag had been exceeded. The initiation of dendrite precursors was observed at borders and angles of the hexagonal Ag crystals formed first. These precursors continued to grow either as dendrites or lobular branched structures. Another transition which corresponded to a macroscopic shape transition of the deposit was dominated by free convection, whereas forced convection led to the development of a lobular rather than a dendritic deposit.

Microstructural Characterisation of Hexagonal (Ag, Cu)Zn4 Alloys in the Deformed and As-Cast State

Zn-based ternary alloys containing Ag and Cu as solutes having characteristic hexagonal close-packed (hcp) structure (Ag, Cu)Zn4 have been studied for microstructural evolution in the deformed and as-cast state in order to correlate the microstructure with mechanical property of the materials. X-ray diffraction (XRD) line profile analysis, optical microscopy and scanning electron microscopy (SEM) have been used to study the microstructure and the mechanical property studied through the measurement of microhardness. X-ray studies of the deformed alloys reveal increased influence of solute Cu in the generation of deformation stacking fault of density α with increasing solute concentration. A reasonably good estimate of stacking fault energy parameter (γ/µ) for the alloys has also been made. Increased influence of solute Cu has also been observed to control the grain sizes and microhardness. A close correlation could be establised between the microstructural parameters and microhardness signifying the interdependence of mechanical property with microstructure of the alloys.

Microstructural characterisation of hexagonal (Ag,Cu)Zn4alloys in the deformed and as-cast state

Zn-based ternary alloys containing Ag and Cu as solutes having characteristic hexagonal close-packed (hcp) structure (Ag, Cu)Zn4 have been studied for microstructural evolution in the deformed and as-cast state in order to correlate the microstructure with mechanical property of the materials. X-ray diffraction (XRD) line profile analysis, optical microscopy and scanning electron microscopy (SEM) have been used to study the microstructure and the mechanical property studied through the measurement of microhardness. X-ray studies of the deformed alloys reveal increased influence of solute Cu in the generation of deformation stacking fault of density α with increasing solute concentration. A reasonably good estimate of stacking fault energy parameter (γ/µ) for the alloys has also been made. Increased influence of solute Cu has also been observed to control the grain sizes and microhardness. A close correlation could be establised between the microstructural parameters and microhardness signifying the interdependence of mechanical property with microstructure of the alloys.

High-resolution transmission electron microscopy of growth and structures of Ag-Te and Cu-Se crystals produced by solid-solid reactions

The atomic scale transformation mechanisms in Ag-Te and Cu-Se films, which grew by solid-solid reactions of metal with chalcogen films, have been investigated by high-resolution transmission electron microscopy, with the aid of image simulation and optical diffraction. By increasing supply of metal atoms into the chalcogen films, a hexagonal Te crystal transforms to hexagonal Ag 2− x Te 1+ x and then monoclinic Ag 2− x Te; and amorphous Se transforms to trigonal Cu 1− x Se and then hexagonal CuSe . The structures of the nonstoichiometric crystals of Ag 2 − x Te 1 + x , Ag 2 − x Te and Cu 1 − x Se have been determined.

Band dispersions of Ag(111) monolayers on various substrates.

This paper describes angle-resolved photoemission and high-energy electron diffraction studies of the growth and electronic properties of Ag monolayers prepared on Ni(111), Ni(001), Cu(111), Cu(001), Au(111), and Si(111)-(7\ifmmode\times\else\texttimes\fi{}7). In all six systems, the Ag overlayer structure is very close to the hexagonal close-packed Ag(111) structure. Thus the effect of the substrate can be studied without the complication of major structural changes in the overlayer. The two-dimensional band dispersions for the Ag valence states have been determined along high-symmetry directions for these systems except Ag-Si(111). The Ag overlayers on Cu(111), Ni(001), and Ni(111) are incommensurate with the substrate structure, and the overlayer band dispersions are very similar despite the large differences in the electronic and atomic structures of the substrates. Ag on Cu(001) forms a c(10\ifmmode\times\else\texttimes\fi{}2) overlayer, and the photoemission results are somewhat different. Ag on Au(111) forms a lattice-matched epitaxial overlayer, and its band dispersions have a very different appearance. These similarities and differences are explained in terms of the degree of commensuration of the substrate-overlayer interaction as a perturbation on the overlayer properties. The growth of Ag on Si(111)-(7\ifmmode\times\else\texttimes\fi{}7) is not as well ordered as in the other systems. A severe broadening of the overlayer photoemission features is observed, preventing the determination of the band dispersions. Momentum broadening as well as random crystal potential variation within the overlayer are likely to be the cause of the broadening.

An analysis of the electrical conductivity of the Li 2SO 4Ag 2SO 4 system on the basis of the phase diagram

High-temperature high conducting phases of the Li 2SO 4Ag 2SO 4 system have been partially trapped by fast quenching in our laboratory. The electrical conductivities of these quenched samples have been measured as a function of frequency and temperature over the entire range of compositions. The maximum conductivity has been found for a sample containing 70 mole% Ag xSO 4 and it is caused by the partial trapping of the two high temperature phases bcc LiAgSO 4 and hexagonal Ag 2SO 4. The results have been discussed on the basis of the phase diagram of the system. The electrical conductivities of Li 2SO 4:Ag 2SO 4 solid electrolytes are much higher than those for the other sulphate-based electrolytes developed for ambient temperature applications.