AgnSm^±和AunSm^±的激光产生与质谱研究

以高能量密度的脉冲激光束在高真空中直接溅射银(金)粉与硫的混合物, 产生了丰富的银-硫和金-硫二元原子族正负离子, 记录了它们的飞行时间质谱。通过对这些簇离子的组成与分布的分析, 发现了它们的一些结构规律。银硫簇离子以离子键为主, Ag2S是它们的主要结构单元, 其中Ag11S5^+和Ag9S5^-特别稳定; 金硫簇离子基本上是共价结构, 金原子间相互成键, 构成簇离子的核, 硫原子则仅与核表面的金原子配位, 其中Ag6S14^+, Au5S6^-的稳定性比较突出。     

Experimental determination of deposition induced cluster deformation

We describe an experimental method to measure the cluster deformation of metal clusters deposited on a substrate. It is based upon the sensitivity of the cluster plasmon resonance on the geometric shape of the clusters; it uses optical spectroscopy with polarized light in oblique incidence. The proposed method was applied to silver clusters (mean diameter 2R = 2nm) produced in a supersonic beam and deposited on a quartz glass substrate. Cluster deposition and optical measurements were performed in situ in vacuum. At an estimated particle velocity of 1.5 · 10³ ms ^-1, we evaluated an axial ratio of c/a = 0.86 for the deposition induced deformation. This result is compared to data from molecular dynamical simulations. By varying the substrate coverage, the critical cluster coverage for the onset of electromagnetic cluster-cluster coupling and coalescence was determined to amount to 0.1 cluster-monolayers.     

夹心三明治结构的二十五核银硫簇合物[Ag25(SC6H4Pri)18 (dppp)6](CF3SO3)7·CH3CN：结构表征及光学性能

在本研究中,使用(ⁱPrC₆H₄SAg)_n作为合成银硫纳米簇合物的前驱体。当存在辅助的双膦配体1, 3-双(二苯基膦)丙烷(dppp)及可溶性银盐(CF₃SO₃Ag),在超声合成条件下,获得了一例二十五核银硫簇合物Ag₂₅,并借助X射线单晶衍射技术确定相应的分子结构。该银硫簇合物具有夹心三明治的骨架结构：分别由两个结构相似的圆柱体共享一个七核纯银簇所构成的金属簇平面。固态紫外可见漫反射光谱测试表明该簇合物的能级带隙为2.5 eV,属于半导体材料的范畴。固态发光测试显示,该簇合物在室温下发射绿光。     

Effect of a surface charge on the halfwidth and peak position of cluster plasmons in colloidal metal particles

The optical response of colloidal particles depends on a variety of properties of the cluster, e.g., shape, size, size distribution and particle material. Since particles often are charged, also the surface charge may be a parameter which influences their optical properties. In this paper the effect of a surface charge on optical properties of spherical colloidal particles is studied and its magnitude is estimated by extended computations for silver clusters with surface plasmon in aqueous suspension. Two models are presented and discussed. The first model is based on the electrodynamic solution by Bohren and Hunt (Can. J. Phys. 55, 1930 (1977)), where a surface conductivity _S for a free surface charge yield an additional contribution _S to the dielectric constant of the particle material. In the second model, the surface charge contributes to the number density of free electrons in the cluster. Both models lead to a shift of the cluster plasmon peak, while an increase of the plasmon halfwidth could not be derived. The effect is quite small and limited on very small clusters.PACS 61.46+w 73.20.Mf 78.20.Dj     

Photoelectron spectroscopy of silicon doped gold and silver cluster anions

Photoelectron spectra of low temperature silicon doped gold cluster anions Au(n)Si(-) with n = 2-56 and silver cluster anions Ag(n)Si(-) with n = 5-82 have been measured. Comparing the spectra as well as the general size dependence of the electron detachment energies to the results on undoped clusters shows that the silicon atom changes the apparent free electron count in the clusters. In the case of larger gold clusters (with more than about 30 gold atoms) the silicon atom seems to consistently delocalize all of its four valence electrons, while in the case of the silver clusters a less uniform behavior is observed. Here the silicon atoms act partly as electron donors, partly as electron acceptors, without following an obvious simple principle. Additionally some structural information can be obtained from the measured spectra: while Ag(54)Si(-) seems to adopt an icosahedral structural motif, Au(54)Si(-) seems to take on a low symmetry structure, much like the corresponding pure 55 atom clusters. This indicates that for such larger clusters the incorporation of a single silicon atom does not change the ground state geometry significantly.     

Structure, bonding, and linear optical properties of a series of silver and gold nanorod clusters: DFT/TDDFT studies

DFT/TDDFT calculations have been carried out for a series of silver and gold nanorod clusters (Ag(n), Au(n), n = 12-120) whose structures are of cigar-type. Pentagonal Ag(n) clusters with n = 49-121 and hexagonal Au(n) clusters with n = 14-74 were also calculated for comparison. Metal-metal distances, binding energies per atom, ionization potentials, and electron affinities were determined, and their trends with cluster size were examined. The TDDFT calculated excitation energies and oscillator strengths were fit by a Lorentz line shape modification, which gives rise to the simulated absorption spectra. The significant features of the experimental spectra for actual silver and gold nanorod particles are well reproduced by the calculations on the clusters. The calculated spectral patterns are also in agreement with previous theoretical results on different-type Ag(n) clusters. Many differences in the calculated properties are found between the Ag(n) and Au(n) clusters, which can be explained by relativistic effects.     

银离子在二氧化硅粒子表面上的成核反应

在含有乙醇的SiO₂溶胶中,Ag⁺不管在碱性、中性或在弱碱、弱酸情况下都能在SiO₂粒子表面上还原成核,形成金属Ag颗粒.研究表明,银的等离子体共振吸收峰的移动是尺寸效应和表面效应共同作用的结果.     

The influence of CO on the surface plasmon absorption band of small silver clusters (D≤20 Å)

The surface plasmon absorption band of small Ag particles (diameter≤100 Å) in the gasphase as well as for clusters embedded in noble gas matrices is known to shift to higher energies and to broaden with decreasing diameter. This size effect depends sensitively on the microscopic surface properties of the clusters, which can be influenced by the interaction with the embedding matrix. Previous experiments with silver clusters in the size range 20 Å≤D≤100 Å proved that for SiO₂ and CO the matrix influence is strong enough to supersede the intrinsic size effect as observed in the noble gas matrices. The investigation of the influence of a CO matrix on smaller clusters with D≤20 Å reveals a novel feature: the position as well as the width of the surface plasmon absorption band become independent of the cluster size.     

Carbon monoxide adsorption on silver doped gold clusters

Well controlled gas phase experiments of the size and dopant dependent reactivity of gold clusters can shed light on the surprising discovery that nanometer sized gold particles are catalytically active. Most studies that investigate the reactivity of gold clusters in the gas phase focused on charged, small sized clusters. Here, reactivity measurements in a low-pressure reaction cell were performed to investigate carbon monoxide adsorption on neutral bare and silver doped gold clusters (Au(n)Ag(m); n = 10-45; m = 0, 1, 2) at 140 K. The size dependence of the reaction probabilities reflects the role of the electronic shells for the carbon monoxide adsorption, with closed electronic shell systems being the most reactive. In addition, the cluster's reaction probability is reduced upon substitution of gold atoms for silver. Inclusion of a single silver atom causes significant changes in the reactivity only for a few cluster sizes, whereas there is a more general reduction in the reactivity with two silver atoms in the cluster. The experimental observations are qualitatively explained on the basis of a Blyholder model, which includes dopant induced features such as electron transfer from silver to gold, reduced s-d hybrization, and changes in the cluster geometry.     

钯团簇碰撞沉积钯/银基板的分子动力学模拟

运用分子动力学模拟方法研究了常温下较大的钯团簇以不同初始速度撞击不同硬度基板的微观过程,着重分析了沉积形貌的变化、团簇的嵌入深度和原子的扩散程度、基板碰撞接触区域的温度演变以及碰撞过程中团簇与基板间的能量转化,获得了沉积过程中变形形貌、结构特征及能量转化随团簇尺寸、初始速度及基板材质的变化规律.并进一步探究了第二颗团簇以不同时刻沉积时前一团簇的变形形貌及基板接触区域温度变化的特点,发现短时间间隔下第二颗团簇的沉积更有利于团簇与基板的结合.     

纳米银碗阵列结构的高效制备及荧光增强性能

报道了一种以自组装单层聚苯乙烯纳米微球阵列为模板, 通过真空热蒸镀银纳米粒子高效制备大面积银碗阵列结构的方法. 测试结果表明, 制得的银碗阵列结构为微纳米复合分级结构, 银碗由平均粒径为10 nm的银纳米粒子组成. 紫外-可见吸收光谱测试结果表明, 银碗阵列结构表面具有银纳米粒子的局域表面等离子体共振吸收峰. 将荧光分子N,N'-二正丁基喹吖啶酮(DBQA)分别蒸镀到普通银膜和银碗阵列结构表面并测试了荧光光谱. 结果表明, 在银碗阵列结构表面的荧光分子强度得到了显著增强, 说明制备的银碗阵列结构是优良的荧光增强基底.     

Regularities of silver atom formation in gamma-irradiated aluminium silicate modified by yttrium

The ESR method was used to study the regularities of formation of silver atoms in gamma-irradiated aluminium silicate modified by yttrium and containing¹⁰⁹Ag istope ions introduced by various techniques. The existence of two types of silver atoms and an Ag ₂ ¹ complex stabilized an the surface of a gamma-irradiated carrier has been established. g-Factors and superfine structure constants of spectral lines of paramagnetic silver particles belonging to various types observed on the surface have been calculated. Quantitative correlations of paramagnetic silver particles and the nature of their kinetic dependences in a broad temperature range (from 77 to 353 K) are determined by the number of silver ions introduced into the carrier and by the mode of introduction, thermal and vacuum pretreatment of the samples, irradiation dose and the temperature of investigating the gamma-irradiated surface.     

Formation of bimetallic Ag-Pd nanoclusters via the reaction between Ag nanoclusters and Pd2+ ions

We have investigated systematically the mechanistic aspects of the Ag-Pd bimetallic cluster formation within sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles by using in-situ X-ray absorption spectroscopy (XAS). A two-step sequential reduction method is employed for the synthesis of Ag-Pd bimetallic clusters. The first step involves preparation of Ag nanoclusters, by mixing the Ag+ ions containing the AOT microemulsion system with a reducing agent hydrazine (N2H4) containing the AOT microemulsion system. In the second step, the addition of Pd2+ ions to Ag nanoclusters led to the formation of Ag-Pd bimetallic clusters via the reaction between Ag nanoclusters and Pd2+ ions in AOT reverse micelles. The reduction of silver ions and the formation of corresponding Ag nanoclusters are monitored as a function of the dosage of the reducing agent, hydrazine. In-situ XAS allowed probing of the reaction between Ag nanoclusters and Pd2+ ions during the formation of Ag-Pd bimetallic clusters. Analysis of Ag and Pd K-edge XAS spectra reveals that in the final stage Ag-Pd clusters, in which "Ag" atoms prefer to be surrounded by "Pd" and "Pd" atoms prefer to be surrounded by "Pd", were formed. On the basis of XAS results presented here, we are able to propose a structural model for each step so that this work provides a detailed insight into the mechanism of nucleation and growth of Ag-Pd bimetallic clusters. We also discussed the atomic distribution of Ag and Pd atoms in Ag-Pd bimetallic clusters based on the calculated XAS structural parameters.     

Synthesis, characterization and optical properties of silver and gold nanowires embedded in mesoporous MCM-41

Uniform nanowires of silver and gold inside the channels of MCM-41 were prepared by controlled reduction of their respective metal salts with sodium borohydride (NaBH₄). Presence of nanowires of silver and gold in MCM-41 were confirmed by high angle X-ray diffraction (XRD) data (peaks between 2ϑ = 30 − 60°) and transmission electron microscopy (TEM) confirmed the diameter of the nanowires. Diameter of nanowires is found to be ∼ 2.8 nm which is coincident with channel diameter of MCM-41. Optical properties of these heterostructured materials Ag-MCM-41 and Au-MCM-41 reveals the presence of surface plasmon absorption peaks of silver and gold respectively, and the shift in the absorption bands are associated to agglomeration of clusters inside the channels. Room temperature photoluminescence spectra exhibits interesting optical properties as observed for direct band gap semiconductors. Non-linear optical properties (NLO) corresponding to second harmonic generation (SHG) values were also recorded for self supported films of these heterostructured materials. Enhanced optical non-linearity was found to be arising from a corresponding increase of local field near the surface plasmon resonance. Further enhancement in SHG was found with poling due to an induction of orientation order.     

Structural variation of silver clusters from Ag13 to Ag160

The structures of silver clusters from Ag(121) to Ag(160) were optimized with a modified dynamic lattice searching (DLS) method, named as DLS with constructed core (DLSc). The interaction among silver atoms is modeled by the Gupta potential. Structural characteristic of silver clusters with the growth of cluster size is investigated with the newly optimized structures and our previous results from Ag(13) to Ag(120). A set of amorphous structures was obtained in the size range of 13-48, together with several ordered structures. The putative stable motif is an icosahedron from Ag(49) to Ag(61) and then changes to a decahedron in the size range of 62-160. Some of the results are consistent with experiments. Furthermore, it was also found that, for clusters with decahedral motif, the stable structure is a result of the competition among the different Marks decahedral motifs. On the other hand, different from the Lennard-Jones cluster, there are some silver clusters with the face-centered cubic (fcc) motif in the size range of 13-160. But the fcc motif can only be obtained for some specific sizes.     

Photoabsorption in sodium clusters on the basis of time-dependent density-functional theory

The photoabsorption spectra of a continuous series of Na(n) clusters (n相似文献   

Synthesis and structure of a water-soluble hexanuclear silver(I) nicotinate cluster comprised of a "cyclohexane-chair"-type of framework, showing effective antibacterial and antifungal activities: use of "sparse matrix" techniques for growing crystals of water-soluble inorganic complexes

The synthesis of a water-soluble anionic silver 2-mercaptonicotinate complex having effective antibacterial and antifungal properties is described. Its structure has been confirmed to be a hexameric cluster by an X-ray diffraction analysis of a mixed Na(+)/Tris(+) salt (Tris(+) = tris(hydroxymethyl)methylammonium cation). The [Ag(mna)](6)(6-) cluster has a Ag(6)S(6) core and an overall shape of twisted hexagonal cylinder with six sulfur atoms and six silver atoms alternating on a puckered drum-like surface. Each Ag atom is trigonally coordinated by one N and two S ligands. The overall [Ag(mna)](6)(6-).4Na(+).2[(HOCH(2))(3)CNH(3)](+).10H(2)O complex has a layered appearance in the crystal packing diagram, with a [Ag(mna)](6)(-) cluster layer alternating with a solvent layer consisting of sodium atoms, Tris buffer cations, and water molecules. The structure is almost identical to that of a neutral [Ag(Hmna)](6) complex reported earlier. The neutral and charged complexes are both known to possess antimicrobial activities, and some biological properties of these and related compounds are briefly discussed in this paper.     

Silica–silver nanostructured spheres prepared by spray pyrolysis of sol containing silver precursor

Silver–silica nanostructured composites were prepared by spray pyrolysis of aqueous sols of silica nanoparticles containing silver nitrate. The physical and chemical characteristics of the composites prepared at different Ag/Si atomic ratio in the sols and temperatures of pyrolysis were examined by TEM, SEM, XRD, FT-IR and UV-visible spectra. For the low silver ratios up to 0.2, well-dispersed silver particles were produced in the pore of the silica agglomerates with their size and surface plasmon resonance depending on the pore size and silver mobility, in addition to the loading and temperature. The formation of silver silicate and new-phase silica as well as crystallinity of the silver prepared was discussed. There was also explained how the temperature of preparation affected the morphologies of the composites produced with higher Ag/Si ratios greater than 1. Mechanism on the formation of silver–silica composites was proposed for the wide range of the ratios from 0.01 to 3.     

Surface Oxidation of Supported,Size-Selected Silver Clusters

We use surface second harmonic generation spectroscopy (s-SHG) to study the oxidation of supported, size-selected silver clusters under ultra-high vacuum conditions. The oxidation reaction of small silver clusters between \(\hbox {Ag}_{9}\) and \(\hbox {Ag}_{55}\) is monitored by means of their localized surface plasmon resonance. We observe a rapid decline of the SH-intensity, as soon as cluster samples are exposed to an oxygen partial pressure of \(5 \times 10^{-6}\) mbar, which is attributed to the formation of silver–oxygen-bonds. The evolution of the SH-intensity under exposure to oxygen shows a double-exponential character for all investigated cluster sizes. Since the oxidation of single crystalline silver surfaces follow single-exponential Langmuir-kinetics, the two independent pathways of SH-intensity loss are attributed to a surface- and an interface-oxidation of supported clusters, respectiveley. For small cluster sizes, a complete loss of the SH intensity is obtained, which suggests the complete oxidation of the clusters. For larger clusters a plasmonic resonance is still observed after oxidation, indicating a residual free-electron density.