Formation,growth mechanism and packing sequences of binary alloy cluster anions from laser ablation of mixtures of lead and transition metals

By using laser ablation of the mixtures of a transition metal (M: Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag) plus lead, M/Pb binary cluster anions were observed except for Zn, and the number of transition metal atoms contained in the binary clusters is at most 4. This behavior is different from that reported previously for M/Ge binary clusters. The experiments indicate that it is also very difficult to form Al/Pb clusters. The distribution patterns of M/Pb binary alloy cluster anions are remarkably similar to those of pure Pb clusters, consistent with a formation mechanism in which transition metal atoms are sequentially attached to [M(x-1)Pb(y)](-) clusters and thus form [M(x)Pb(y)](-) clusters by a simple condensation process. As the number of transition metal atoms increases, the intensities of binary clusters gradually decrease. It is proposed that [MPb(4)](-) and [MPb(5)](-) cluster anions might be the unit building blocks of M/Pb binary cluster anions, and the layer packing sequences for magic clusters are predicted on this basis. The [M(x)Pb(y)](-) binary clusters containing 13 atoms (x + y = 13; x not equal 0) are proposed to have an icosahedral structure.     

无锡钢电镀溶液中氟离子电化学行为的研究

采用交流伏安法、电化学阻抗谱(EIS)和Mott-Schottky 分析技术研究了无锡钢电镀液中氟离子电化学行为. 结果表明, 在氧化还原过程中氟离子抑制铬离子化学状态转变, 降低铅合金和铅氧化物阳极的氧化电流密度, 改变铅合金和铅氧化物阳极的氧化还原历程. EIS 结果表明电场作用下溶液中铬氧离子团发生聚合, 在铅合金阳极表面形成感抗现象. 含氟溶液中铬氧离子团在阳极表面的感抗现象消失, 溶液导电性提高. Mott-Schottky 曲线显示氟离子提高阳极材料的载流子密度, 铅合金阳极和铅氧化物阳极均为n 型半导体.     

Systematic investigation of trigonal-bipyramidal cyanide-bridged clusters of the first-row transition metals

Reactions between [M'(III)(CN)(6)](3-) anions (M' = Co, Cr, or Fe) and mononuclear complexes of M(II) ions (M = Cr, Mn, Co, Ni, or Zn) produce a family of pentanuclear clusters {[M(tmphen)(2)](3)[M'(CN)(6)](2)]}. The core of the clusters is formed by five metal ions that are bridged through six CN- linkers into a trigonal bipyramid, with M and M' ions occupying equatorial and axial positions of the bipyramid, respectively. Three of the CN- ligands from each M' center remain terminal and point toward the outside of the cluster, along the trigonal axes. Studies of magnetic coupling in the {[M(tmphen)(2)](3)[M'(CN)(6)](2)]} family of clusters revealed a similarity between the observed magnetic exchange constants and the values estimated for the molecule-based magnets of the Prussian blue family. The type of the magnetic exchange varies across the series, changing from antiferromagnetic for M = Cr and Mn to ferromagnetic for M = Co and Ni. Complexes {[M(tmphen)(2)](3)[M'(CN)(6)](2)]}, which contain diamagnetic Co(III) ions in the axial positions, serve as convenient model compounds for an accurate assessment of the magnetic parameters for the equatorial M ions in the absence of magnetic interactions. The {[Co(tmphen)(2)](3)[Cr(CN)(6)](2)]} cluster exhibits cyanide linkage isomerism, the relative amount of which depends on the synthetic conditions.     

Size-dependent reactions of ammonium bisulfate clusters with dimethylamine

The reaction kinetics of ammonium bisulfate clusters with dimethylamine (DMA) gas were investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Clusters ranged in size from 1 to 10 bisulfate ions. Although displacement of the first several ammonium ions by DMA occurred with near unit efficiency, displacement of the final ammonium ion was cluster size dependent. For small clusters, all ammonium ions are exposed to incoming DMA molecules, allowing for facile exchange ("surface" exchange). However, with increasing cluster size, an ammonium ion can be trapped in an inaccessible region of the cluster ("core" exchange), thereby rendering exchange difficult. DMA was also observed to add onto existing dimethylaminium bisulfate clusters above a critical size, whereas ammonia did not add onto ammonium bisulfate clusters. The results suggest that as the cluster size increases, di-dimethylaminium sulfate formation becomes more favorable. The results of this study give further evidence to suggest that ambient sub-3 nm diameter particles are likely to contain aminium salts rather than ammonium salts.     

Spontaneous formation of cluster array of gold particles by convective self-assembly

Cluster arrays composed of metal nanoparticles are promising for application in sensing devices because of their interesting surface plasmon characteristics. Herein, we report the spontaneous formation of cluster arrays of gold colloids on flat substrates by vertical-deposition convective self-assembly. In this technique, under controlled temperature, a hydrophilic substrate is vertically immersed in a colloid suspension. Cluster arrays form when the particle concentration is extremely low (in the order of 10(-6)-10(-8) v/v). These arrays are arranged in a hierarchically ordered structure, where the particles form clusters that are deposited at a certain separation distance from each other, to form "dotted" lines that are in turn aligned with a constant spacing. The size of the cluster can be controlled by varying the particle concentration and temperature while an equal separation distance is maintained between the lines formed by the clusters. Our technique thus demonstrates a one-step, template-free fabrication method for cluster arrays. In addition, through the direct observation of the assembly process, the spacing between the dotted lines is found to result from the "stick-and-slip" behavior of the meniscus tip, which is entirely different from the formation processes observed for the striped patterns, which we reported previously at higher particle concentrations. The difference in the meniscus behavior possibly comes from the difference in colloidal morphology at the meniscus tip. These results demonstrate the self-regulating characteristics of the convective self-assembly process to produce colloidal patterns, whose structure depends on particle concentration and temperature.     

过渡金属离子与乙腈团簇的反应

用激光溅射-分子束技术,研究了几种过渡金属离子与乙腈团簇分子的气相化 学反应,根据反射式飞行时间质谱检测的结果,不同的过渡金属离子可与乙腈分子 形成不同尺寸的团簇离子产物,其中Ti~+,V~+,Cr~+与乙腈反应的活泼性强于 Cu~+,Fe~+与乙腈反应的活泼性。分析过渡金属离子Ti~+,V~+,Cr~+与乙腈反应 所生成团簇离子的强度分布,发现它们都在n = 2和n = 3之间形成明显的强度间隙 。     

Reducing the Cost and Preserving the Reactivity in Noble‐Metal‐Based Catalysts: Oxidation of CO by Pt and Al–Pt Alloy Clusters Supported on Graphene

The oxidation mechanisms of CO to CO₂ on graphene‐supported Pt and Pt‐Al alloy clusters are elucidated by reactive dynamical simulations. The general mechanism evidenced is a Langmuir–Hinshelwood (LH) pathway in which O₂ is adsorbed on the cluster prior to the CO oxidation. The adsorbed O₂ dissociates into two atomic oxygen atoms thus promoting the CO oxidation. Auxiliary simulations on alloy clusters in which other metals (Al, Co, Cr, Cu, Fe, Ni) replace a Pt atom have pointed to the aluminum doped cluster as a special case. In the nanoalloy, the reaction mechanism for CO oxidation is still a LH pathway with an activation barrier sufficiently low to be overcome at room temperature, thus preserving the catalyst efficiency. This provides a generalizable strategy for the design of efficient, yet sustainable, Pt‐based catalysts at reduced cost.     

Magnetic circular dichroism spectroscopy on the Cr₈ antiferromagnetic ring

A Magnetic Circular Dichroism (MCD) spectroscopic study of the antiferromagnetic ring [Cr?F?Piv??] (Piv = pivalate) is reported. From the splitting of the MCD bands, the single ion anisotropy parameters in the cluster spin ground state at different fields were determined to be d(Cr) = -0.33 ± 0.02 cm?1, e(Cr) = 0.11 ± 0.01 cm?1. Analysis of the MCD intensity as a function of field and temperature revealed the influence of spin mixing effects and yielded independent estimates of the single ion anisotropies (d(Cr) = -0.19 cm?1, e(Cr) = 4.3 × 10-4 cm?1), as well as yielding the isotropic exchange interaction strength (J = -6.00 cm?1). Thus it is shown that MCD is a powerful method to unravel the relation between single-ion and cluster anisotropy, furthering the design of molecular magnets with desired properties.     

Gas phase reactivity of thermal metal clusters

Reaction kinetics of metal cluster ions under well defined thermal conditions were studied using a flow tube reactor in combination with laser vaporization. Aluminum anions and cations were reacted with oxygen, and several species which are predicted jellium shell closings, were found to have special stability. Metal alloy cluster anions comprised of Al, V and Nb were also seen to react with oxygen. Alloy clusters with an even number of electrons reacted more slowly than odd electron species, and certain clusters appeared to be exceptionally unreactive. Copper cation clusters were observed to associate with carbon monoxide with reactivities that approach bulk behavior at surprisingly small cluster size. These reactions demonstrate how the rate of reaction changes with cluster size.     

液态Ca7Mg3合金快速凝固过程中团簇结构的形成特性

采用分子动力学方法对液态Ca7Mg3合金凝固过程中团簇结构的形成特性进行了模拟研究. 采用双体分布函数、Honeycutt-Andersen(HA)键型指数法、原子团类型指数法(CTIM)以及遗传跟踪等方法对凝固过程中团簇结构的形成演变特性进行了分析. 结果表明: 在以冷速为1×1012 K·s-1 的快速凝固条件下, 系统形成以1551、1541、1431键型为主的非晶态结构; 二十面体基本原子团(12 0 12 0)在快速凝固过程中对非晶态结构的形成起决定性作用; 在合金凝固过程中, 团簇的稳定性不仅与构成团簇的基本原子团类型有关, 还与中心原子类型以及中心原子之间的连接方式有关. 由于(12 0 12 0)基本原子团能量较低并且在低温具有较好的遗传特性, 基本原子团之间很容易连接在一起组成更大的团簇. 所形成的团簇结构显著不同于那些由气相沉积、离子溅射等方法所获得的团簇结构.     

Experimental evidence of structural transition from fcc to bulk bcc in nanophase metal clusters of (Fe)n, (Cr)n, (Mo)n and (W)n produced by CO2 laser multiphoton decomposition of metal carbonyls

We have produced nanophase metal clusters, (Fe)_n, (Cr)_n, (Mo)_n and (W)_n, by multiphoton decomposition of the corresponding metal carbonyls with a 10.6 μm CO₂ laser in the presence of Ar and SF₆. The size distribution was narrow and the average diameter was 6, 3.5, 2 and 1 nm for Fe, Cr, Mo and W clusters, respectively. The structure was found to be bcc for both Fe and Cr clusters, fcc for Mo clusters, and amorphous for W clusters (note that all the bulk metals have bcc structure). Considering the cluster sizes (9630, 1870, 230 and 30 for Fe, Cr, Mo and W clusters, respectively) estimated from their average diameters, it is likely that there exists a structural transition from fcc to bulk bcc with increasing cluster size in these metal clusters.     

Atomic Velocity Distributions and Diffusing Behaviors in a Nano-Alloy Cluster

This paper studies the velocity distributions and diffusing behaviors of the atoms in a nano-alloy cluster. A series of ternary alloy clusters, Au₅₀Cu₂₅Ni₂₅, and binary alloy clusters, Cu_100−aNi_a are introduced in the molecular dynamics simulations. The velocity distributions of different types of atoms in both static and moving clusters are found to obey the Maxwell’s velocity distribution with the individual mass of atoms and the inner temperature of clusters. Furthermore, the velocity distribution of whole atoms of the cluster is obtained by synthesizing the velocity distributions of compositions in the cluster according to the proportions. The consistency of the atomic motions in a moving cluster is discussed by inspecting the backward velocities of atoms, which are correlated to the translational velocity and the inner temperature of the cluster. The diffusing behaviors of the atoms in a cluster are also investigated from a viewpoint of the interatomic interactions, i.e. Cu atoms enhance the activities of Ni atoms, or Ni atoms reduce that of Cu atoms in the alloy clusters.     

A Study About Nanocluster Deposition of Thin-film Formation by Molecular Dynamics Simulation

The thin-film growth has been confirmed to be assembled by an enormous number of clusters in ICBD method. In sequence of clusters’ depositions proceeds to form the thin-film to understand quantitatively the interaction mechanisms between the cluster atoms and the substrate atoms, we use molecular dynamics simulation with EAM potential. The quantitative of flatness of deposition and percent of disordered atoms were proposed to evaluate the property of thin-film. In this simulation, three different Co cluster sizes of 55, 70, and 100 atoms with different velocities (100 up to 800 m/s) were deposited on a Al(0 0 1) substrate whose temperatures were set between 300 and 500 K. The simulations begin at specific equilibrium temperature of clusters and the substrate. The simulations are performed at different temperatures of the clusters and substrate and for different sizes of clusters. We showed that the percent of disordered atoms of substrate are affected by the cluster size and velocity of the clusters. Temperature dependence of the number of disordered atoms for different cluster’s velocity was observed. We investigated the effect of cluster size and initial velocity of cluster on the value of flatness.     

相分离La0．33Pr0．34Ca0．33MnO3薄膜体系中的交换偏置效应

在相分离La0．33Pr0.34Ca0．33MnO3薄膜体系中发现了大的交换偏置效应．在4K时,交换偏置场的大小达到了约1kOe．交换偏置效应可能源自薄膜内禀的电子相分离特性或薄膜的表面效应．交换偏置效应表现出强的温度、冷却磁场以及厚度依赖的关系．     

m × n] metal ion arrays templated by coordination cages

Three-dimensional m × n arrays of metal ion clusters can be assembled as aromatic stacks of planar polynuclear metal complexes within columnar coordination cages. The polynuclear complexes and cage height program the final array structures of the metal ion clusters. Cyclic trinuclear Au(I) complexes (m = 3) assembled into trigonal prismatic arrays (n = 1-3) within the cages and the array structures were clearly shown by X-ray crystallographic analysis. A silver-sandwiched hetero-Au(3)-Ag-Au(3) cluster was also prepared by treating a hexanuclear Au(3)-Au(3) cluster with Ag(I) ion.     

A study of surface diffusion of ternary (Cu-Ag-Zr) adatoms clusters for applications in thin film formation

This study presents the diffusion of heterogeneous ternary (Cu-Ag-Zr) adatoms clusters on Ag(111) using molecular dynamics techniques which could be important for the surface phenomena's and helpful for the ternary cluster's growth and formation of ternary alloy-based thin films. The mechanism of nanoscale surface diffusion is investigated for 1Cu-1Ag-1Zr, 2Cu-2Ag-2Zr, 3Cu-3Ag-3Zr, and 4Cu-4Ag-4Zr clusters at temperatures 300, 500, and 700 K. The diffusion mechanism displays that the diffusion of trimer cluster exhibits hopping, sliding, and shearing at 300 K, whereas for hexamer, nonamer, and decamer, the diffusion rate is low; however, breathing, anchoring, and concentrated motion dominates. At 500 K, trimer and hexamer show the process of atomic exchange; however, the atomic exchange is not observed in the case of nonamer and decamer diffusion. The atomic exchange mechanism of Cu and Zr adatoms dominates at 700 K for all size clusters, except Ag adatoms, where Zr adatoms show a relatively more tendency. Separation and rejoining of the one and two adatoms (likely Zr adatom) are also witnessed at high temperature. The pop-up of Ag adatoms also occurs in very short intervals over the remaining adatoms of clusters. Interestingly, during trimer diffusion, the adsorption of the Zr- or Cu-adatom among the trimer cluster into the substitutional site is found. At 700 K, vacancy generation, filling of vacancies, and migration of vacancy, in the neighborhood of the adatoms cluster, also observed. Moreover, the rate of diffusion decreases with the size increase of the clusters and increases with the increase in temperature.     

Matrix isolation infrared spectroscopic and theoretical study of dinuclear chromium oxide clusters: Cr2On (n = 2, 4, 6) in solid argon

Dichromium oxide clusters, Cr2O2, Cr2O4, and Cr2O6, have been prepared and characterized by matrix isolation infrared spectroscopy and quantum chemical calculations. Laser-evaporated chromium atoms reacted with O2 in solid argon to form the previously characterized CrO2 molecules, which further reacted with chromium atoms to form Cr2O2 spontaneously on annealing. The Cr2O2 cluster is determined to have a chainlike CrOCrO structure. The rhombic ring isomer, which was predicted to be more stable than the CrOCrO structure, was not formed at the present experimental conditions. The Cr2O4 cluster was formed from the barrierless dimerization of the chromium dioxide molecules, which is characterized to have a planar D2h symmetry. TheCr2O6 cluster was produced under UV light irradiation. It is determined to have a singlet ground state with a nonplanar D2h symmetry.     

SYNTHESIS AND CATALYTIC PROPERTY OF POLYMER-SUPPORTED Fe-Co HETEROTETRAMETALLIC CLUSTERS

Four polymer-supported Fe-Co tetrametallic clusters have been prepared by ion exchange and ligand exchange. Their structures were characterized by IR, UV/visible diffuse reflectance spectra and elemental analysis, and by analogy with the reference cluster PhCH_2NMe_3FeCo_3 (CO)_2 . The four heterogenous clusters were efficient catalysts in the hydroformylation of 1-hexene, turnover numbers amounted to 823 —924 with the yield of 83.2—92.4% heptyl aldehydes and ratios of normal aldehyde to iso-aldehyde of 1.2—1.6, they are facilitated forming the normal aldehyde in comparison with the homogeneous analogue. For the polymer-supported clusters prepared by ion exchange, the polymer-cation parts had no obvious effect on the activity of the cluster anion. The polymer-phosphine substituted cluster prepared by ligand exchange was more stable than the clusters preparedby ion exchange.     

Is the trend of the polarizability per atom for all small 3d transition metal clusters the same? The case of Nin (n< or =5) clusters

The first theoretical study on static polarizability and polarizability anisotropy of small nickel clusters up to the pentamer is presented. All-electron-type calculations were performed using a finite field approach as implemented in the density functional program deMon2K. A newly developed first-order field-induced basis set for density functional calculations was employed. For the static polarizability per atom of these clusters, a different trend to the one reported in the literature for other transition metal cluster systems of similar size, is observed.     

Photodissociation of chromium oxide cluster cations

Chromium oxide cluster cations, Cr(n)O(m)+, are produced by laser vaporization in a pulsed nozzle cluster source and detected with time-of-flight mass spectrometry. The mass spectrum exhibits a limited number of stoichiometries for each value of n, where m > n. The cluster cations are mass selected and photodissociated using the second (532 nm) or third (355 nm) harmonic output of a Nd:YAG laser. At either wavelength, multiphoton absorption is required to dissociate these clusters, which is consistent with their expected strong bonding. Cluster dissociation occurs via elimination of molecular oxygen, or by fission processes producing stable cation species and/or eliminating stable neutrals such as CrO3, Cr(2)O(5), or Cr(4)O(10). Specific cation clusters identified to be stable because they are produced repeatedly in the decomposition of larger clusters include Cr(2)O(4)+, Cr(3)O(6)+, Cr(3)O(7)+, Cr(4)O(9)+, and Cr(4)O(10)+.