Strain distributions of confined Au/Ag and Ag/Au nanoparticles

The strain distributions of Au/Ag and Ag/Au nanoparticles confined in the Al2O3 matrix with different core sizes are investigated by using the finite element method, respectively. The simulation results clearly indicate that the compressive strains exerted on the Au/Ag and Ag/Au nanoparticles can be induced by the Al2O3 matrix. Moreover, it can be found that the strain gradient existing in a Au/Ag nanoparticle is much larger than that in a Ag/Au nanoparticle, which could be due to the larger Young's modulus of Au than that of Ag. With the core size increasing, the strain gradient existing in the Au/Ag nanoparticle becomes larger, while the strain gradient existing in the Ag/Au nanoparticle keeps constant. These different strain distributions may have significant influences on the structures and morphologies of the Au/Ag and Ag/Au nanoparticles, leading to the different physical properties for potential applications.     

Surface composition of PdAu and PdAg catalysts by auger electron spectroscopy

Auger electron spectroscopy (AES) has been employed to examine the metal surface composition of PdAu and PdAg alloys as microspheres and as alumina-supported crystallites. For the PdAu system the observed PdAu ratios at the surface correspond closely to those of the bulk both for the microspheres and crystallites. However in the case of supported PdAg, the surface exhibits silver-enrichment relative to the bulk. By means of the regular solution monolayer model the results are interpreted theoretically and the binding energies between the dissimilar metal atoms are computed.     

Surface Plasmon Resonance and Field Enhancement of Au/Ag Alloyed Hollow Nanoshells

We investigate the nanostructure, surface plasmon resonance （SPR） absorption and nonlinear enhancement of Au/Ag alloyed hollow nanoshells prepared by the replacement reaction of Ag nanoparticles in a HAuCI4 aqueous solution. As the volume of HAuCl4 increases from OmL to 0.S mL, the SPR band of the Au/Ag alloyed nanoshells is tuned from 430nm to 780nm, and the third-order nonlinear optical susceptibility is enhanced nearly by an order of magnitude, which indicates a large enhancement of local field in the Au/Ag alloyed hollow nanoshells with hole defects.     

Superconductivity in α-phase alloys of Cu,Ag and Au

We have found f.c.c. alloys rich in noble metals to be superconducting. From these data, extrapo lated values for the transition temperatures of Au, Ag and Cu can be obtained.     

Alloying behaviors of AgMg,AuMg and AgAl alloys

An expression of the structure-dependent energy of simple metal-noble metal binary alloy is given on the basis of the pseudopotential method. The energy is expressed as a sum of three parts; a band-structure energy, an electrostatic energy and a repulsive overlap energy, each of which is characterized by the usual long-range and short-range order parameters.The energy in a disordered state and the ordering energy are calculated for the AgMg, AuMg and AgAl systems, using the pseudopotential form factors and the overlap potentials of noble metals given by Moriarty. The numerical results reproduce qualitatively the observed phase diagrams; the existences of β- and ?-phases in the AgMg system, of β-phase in AuMg and of β- and ζ-phases in AgAl. The L2₀-type ordered phase (β′-phase) of AgMg alloy which remains ordered up to the melting point is well explained. Further, an estimation of the local ordering energy suggests that a clustering appears in the Al-rich region of AgAl alloy. However, the calculations fail to interpret the ordering behavior of β′-phase in the AuMg system and the short-range order of Ag-rich AgAl alloy. The role of individual terms of the structure-dependent energy on alloying is discussed.     

Surface Plasmon Resonance and Raman Scattering Activity of the Au/AgxO/Ag Multilayer Film

The nanostructured Au/AgxO/Ag sandwich multilayer films on quartz substrates are prepared by the magnetron sputtering method. The morphology, plasmon resonance and surface enhanced Raman scattering （SERS） activi- ties of the multilayer films are studied. The resonant absorption wavelength of localized surface plasmon is tuned in a wide range from 618nm to 993nm by controlling the density of nanoparticles of Au and Ag. The SERS activity of the Au/AgxO/Ag multilayer films are enhanced over -10 times compared with those of bare Ag and bare Au films. These properties may find a potential application in biosensor and bioimaging.     

Laser synthesis of Au/Ag colloidal nano-alloys: Optical properties, structure and composition

We have successfully synthesized Au/Ag colloidal nano-alloys with a wide range of compositions by laser ablation of single metal targets in water and a re-irradiation of mixed colloidal suspensions. The optical extinction spectra have been obtained in the plasmon resonance region and their analysis by using the Mie-Gans approach has lead to a quantitative estimation of a number of different structural features for the sols. Some of the obtained results are supported by X-ray photoelectron data and transmission electron microscopy, while others are used to investigate the kinetics of formation of the nano-alloys under laser irradiation.     

Electric field gradients in dilute alloys of Cu,Ag and Au

In this paper we present perturbed angular correlation (PAC) measurements on¹⁰⁰Rh and¹¹¹Cd in a number of dilute alloys of Cu, Ag and Au. We discuss the electric field gradient (EFG) values derived from these and other experiments in the framework of a theory of the EFG at nearest neighbours of point defects in metals, essentially based on the screening of a point charge in a free electron gas. We include in our discussion the EFG due to a neighbour monovacancy for a number of fcc metals.     

Surface analysis of AgSn alloys by ESCA

The surface composition of AgSn alloys with low Cu and Zn contents was investigated by ESCA following various pretreatments. Exposure to air, especially at elevated temperatures, resulted in the surface being enriched, not only by Sn, but particularly by the Zn and Cu contents in the form of oxides. Zn and Cu enrichment is less pronounced when heating in a vacuum (10^?6 Torr). Any tin oxide present is partially reduced. The results obtained are compared with model concepts established by various authors from studies of binary alloys.     

AES studies of surface composition of AgCu alloys

The influence of pretreatments like sputtering, annealing and cleaving on the surface composition is important in quantitative Auger electron spectroscopy. The present paper deals with this influence for the binary alloy system AgCu with 100, 95, 80, 60, 50, 40, 20, 5, and 0 at% Ag. Sputtering causes an enrichment of Cu on the surface due to the higher sputter coefficient of Ag. In contrast cleaving yields an enrichment of Ag due to the lower tensile strength of Ag. The surface composition obtained by scribing is used as standard for the bulk composition because this technique is independent of parameters like sputter coefficient or tensile strength. The results are compared with previous measurements of homogeneous alloy systems.     

Surface composition and oxygen chemisorption on Ag-Pd alloys

Ag-Pd alloys prepared by room temperature coprecipitation from solutions of the corresponding nitrates have been subjected to surface analysis by Auger electron spectroscopy. Previous work on the adsorption of O₂ on the same alloys showed that except for very high Pd concentration the adsorption heat was independent of alloy composition. On untreated and Ar ion sputtered alloys Pd enrichment in the surface layers was found, while on thermally annealled alloys (<0.1 Ton or 1 atm of H₂ or O₂), surface segregation of Ag took place. This is the expected result from surface tension and/or atomic size considerations. The relation of these findings with the earlier data on the chemisorption heat of oxygen is discussed. The implications of these conclusions upon present models of metallic alloys is pointed out.     

Preparation of large-area surface-enhanced Raman scattering active Ag and Ag/Au nanocomposite films

Ag films on tinning glass substrates were fabricated by modified silver-mirror (Tollen’s) reaction with the advantage of low-cost, simple and quick fabrication process. The obtained Ag films were served as sacrificial materials for preparation of Ag/Au nanocomposite films by immersing in a chlorauric acid (HAuCl₄) solution at room temperature. After a short time of galvanic replacement reaction, Ag/Au bimetallic nanostructures were synthesized with “concave” structures. The morphology, properties and composition of the Ag and Ag/Au nanocomposite films were analyzed by using scanning electron microscopy (SEM), UV-visible spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDS) and surface enhanced Raman scattering (SERS). SEM images displayed that the large area of Ag film and Ag/Au bimetallic nanostructures experienced structural evolution process during galvanic reaction. The UV-Vis spectra showed the absorbencies characterization of Ag film and Ag/Au nanocomposite films. SERS measurements using methylene blue as an analyte showed that SERS intensities of bimetallic films were enhanced significantly compared with that of pure Ag films. The SERS enhancement ability of Ag/Au bimetallic films was dependent on the immersion time for galvanic replacement reaction.     

A comparison study of electroluminescence from Au/native oxide/p-Si and Au/porous Si diodes

Visible electroluminescence (EL) has been observed from a Au/native oxide/p-Si diode and has been studied in comparison with the EL from a Au/porous Si diode. Both diodes share similarities in current-voltage characteristics, EL spectra, and electrical input power dependence of integrated EL intensity. However, Au/porous Si exhibits quite strong photoluminescence (PL) while Au/native oxide/p-Si does not show any measurable PL. For the Au/native oxide/p-Si diode, when the native oxide layer was removed in 1% HF solution, no detectable EL has been observed. These experimental results indicate that the native oxide layer plays a key role in light emission from the Au/native oxide/p-Si diode, and show that the luminescence mechanism for Au/native oxide/p-Si diodes is similar to that for the Au/porous Si diode. This comparative study may aid in elucidation of the EL mechanism of porous silicon.     

芳香异腈的SERS光谱所揭示的金/银纳米颗粒阵列的表面组分特性(英文)

Amajortaskinmolecularelectronicsisthe precisedeterminationofthemolecule-metalinter facecharacteristics.Thisisparticularlybecause metalsandsinglemoleculeshaveintrinsicallyun avoidableelectricalmismatchesbutthereisnotyet anestablishedwaytoevaluatethemsyst…     

Thermodynamic instability of Ag/Au and Cu/Pd metal superlattices

We show how the formation energies of A_pB_q superlattices with arbitrary periods p and q and layer orientation Ĝ can be predicted via a 'cluster expansion' technique, given the formation energies of short period structures from first-principles calculations. We predict both bulk and epitaxial energies as well as the energies of the fully intermixed (alloyed) superlattices. Applications to Ag/Au and Cu/Pd superlattices illustrate our method, as well as a global classification scheme for superlattice stability.     

An AES study of surface segregation of AgAu alloys with ion bombardment and annealing

Equilibrium segregation and selective sputtering in the surface of AgAu alloys have been investigated systematically with argon ion bombardment and with annealing by means of AES measurements. Slight enrichment of Ag was observed on the alloy surfaces after the annealing of the alloys at 550°C, while relatively large enrichment of Au was observed on the ion-bombarded surfaces with the use of Au (240 eV) and Ag (300 eV) Auger electrons. With the aid of other Auger electrons with different escape lengths, it was found that the concentration varies with distance from the surface within the sampling depth of the Auger electrons. On the basis of the above facts, the depth profiles were proposed for the annealed and the ion-bombarded surfaces. The uppermost surface layer is enriched more with Ag than the apparent AES observations on both the ion-bombarded and the annealed surfaces. The proposed depth profiles on both the surface layers were compared with previous results by different authors.     

An insight into the effect of composition for enhance catalytic performance of biogenic Au/Ag bimetallic nanoparticles

A comprehensive knowledge of composition‐activity property relationship of nanoparticulate materials is highly desirable for applications in various catalysis reactions. We have addressed a facile green aqueous approach for preparation of Au, Ag monometallic, Au/Ag alloy as well as core‐shell bimetallic nanoparticles. The phytochemicals present in lemon grass leaves extract were employed both as natural reducing and capping agents at room temperature. X‐ray diffraction pattern, UV‐Vis spectroscopy, and energy dispersive X‐ray studies confirmed the formation of bimetallic system. The ensuing Au core/Ag shell and Au/Ag alloy bimetallic nanoparticles were crystalline and spherical in nature with identical average diameter of ~ 18 nm as measured via transmission electron microscopy. The bimetallic systems incredibly display higher catalytic potential than their monometallic counterparts which were vividly reckoned on structural effect, lattice compression, and synergistic electronic effect.