团簇淀积纳米结构薄膜的计算机模拟

对团簇的淀积方式作了简介。着重对团簇的淀积过程进行了计算机模拟,从中得出了淀积的尺寸分布与团簇在衬底上的徙动长度有关,而团簇的聚合长大存在一临界尺寸。并给出低能Ｐｂ团簇在碳膜表面的徙动长度和聚合的临界尺寸。     

(CoMn)n(n=1~5)合金团簇的结构和磁性

采用密度泛函理论中的局域自旋密度近似和广义梯度近似对(CoMn)n(n=1～5)团簇的几何构型进行优化、能量、频率和磁性计算,确定了团簇的基态,对其基态的磁性和电子结构进行了系统研究,并与相对应的一元团簇进行了结构和磁性比较.研究表明,两种方法确定的基态构型基本一致,当n=1～4时,等比CoMn二元合金团簇的几何形状仍与一元团簇相同;(CoMn)3和(CoMn)4团簇出现了磁性双稳态,显示铁磁性和反铁磁性耦合;二元CoMn合金团簇中Co、Mn原子磁性仍能保持一元Co、Mn团簇基态的磁性.     

FeBN (N≤3)团簇的结构与磁性

基于第一性原理,利用密度泛函理论中的广义梯度近似(GGA)对FeBN(N≤3)团簇进行了结构优化、能量和频率的计算,得到了FeBN(N≤3)团簇在不同自旋多重度下的平衡结构并确定了团簇的基态构型.结果表明,FeBN(N≤3)基态团簇的自旋多重度分别为4、3、2.我们对FeBN基态团簇的磁性做了系统的研究,得出了Fe原子磁矩和团簇总磁矩随团簇尺寸增大而减小的结论.     

团簇演积纳米结构薄膜的计算机模拟

对团簇的沉积方式作了简介。着重对团簇的淀积过程进行了计算机模拟,从中得出了淀积的尺寸分布与团簇在衬底上的徒动长度有关,而团簇的聚合长大存在一临界尺寸。并给出低能Ｐｂ团簇在碳膜表面的徒动长度和聚事的临界尺寸。     

二十面体Sc13,Sc+113,Sc-113团簇的稳定性与电子结构研究

采用密度泛函理论框架下的广义梯度近似(DFT/GGA),对Sc13团簇进行了几何结构优化,得到13原子钪团簇的基态结构为正二十面体(Ih),在此基础上对二十面体Sc13, Sc+113和Sc-113团簇的稳定性、电子结构和磁矩进行研究.结果发现Sc13,Sc+113和Sc-113团簇都在Ih结构时最稳定,该尺寸团簇的稳定性主要由二十面体密堆积构型决定;带电能使团簇的结构稍稍收缩从而使团簇的稳定性有所增强;团簇的键长和对称性对团簇的磁矩有很明显的影响.     

模拟进化法优化Si和Be的团簇结构

模拟生物进化的机理，建立了优化团簇结构的理论程序，并对Ｓｉ和Ｂｅ团簇结构进行了优化计算。并成功地得到了用其它方法已发现的团簇基态结构，还发现了用其它方法尚未得到的团簇基态结构；所得到的团簇基态能量等于或小于已发表的用其它方法所得到的相应团簇的基态能量，说明此方法对于优化团簇基态结构是可行和有效的。     

WnSi02,±(n=1～5)团簇结构与光谱的理论研究

利用密度泛函理论(DFT)在B3LYP/Lanl2dz水平上对WnSi0,2±(n=1～5)团簇的各种可能构型进行了几何结构优化,预测了各团簇的基态结构.并对基态构型的平均结合能、能隙、红外光谱及拉曼光谱进行了系统的理论分析.结果表明:WnSi0,2±(n=2～5)团簇的基态结构及亚稳态结构中的Si-Si原子不成键,W5Si0,2±团簇的基态构型与W7团簇的基态构型相似,W3Si2+团簇的基态构型与W0,5±团簇的基态构型相似;W5Si2-团簇是比较理想的复合材料;WnSi0,2±(n=1～5)团簇的所有IR吸收峰都属于红外光谱中的指纹区的特征吸收区域;除W4Si2-团簇外,其它团簇都具有非刚性特性.     

密度泛函理论计算Ga_nZn(n=1～7)团簇的几何结构和稳定性

采用密度泛函理论(Density Functional Theory,简称:DFT)中的广义梯度近似(Generalized Gradient Approximation,简称:GGA)中的B3LYP方法,选择LANL2DZ基组,对GanZn(n=1~7)小团簇的各种可能结构进行了优化,得到了每一种团簇的基态平衡结构.对每一种团簇中最稳定的团簇计算了平均键能、二阶差分能和分裂能,计算结果表明,Zn掺杂到Ga团簇中,稳定性出现奇偶交替的现象,当Ga原子为偶数时,团簇表现出较稳定的状态,当Ga原子为奇数时,团簇表现出不稳定的状态.与Gan纯团簇的比较发现Zn掺杂到Ga团簇时提高了其化学活性.     

Nin(n=1-9)小团簇的密度泛函理论研究

采用密度泛函理论(DFT)方法对Nin(n=1-9)团簇的结构, 稳定性和磁性进行了详细的研究. 得到了一些以前文献中没有提到的稳定结构, 并与其它方法得到的结构进行了比较, 得到的最稳定结构与实验结果相一致. 团簇能量的二阶差分、分裂能、HOMO-LUMO能隙随团簇尺寸的演化都没有表现出明显的奇偶振荡行为, 但在n=5、7时均有较大的值, 说明相对应的团簇具有较高的稳定性、较低的化学活性. 团簇磁性的研究表明团簇的平均每原子磁矩随团簇尺寸的增加有一定振荡, 但有逐渐减小的趋势, n≥5时团簇的构型对团簇磁性的影响较小.     

GaC_n/GaC_n~+/GaC_n~-(n=1-10)团簇磁性和极化率的理论研究

本文中我们采用密度泛函理论(DFT)的B3LYP方法,在6-311+G*和LANL2DZ水平上对碳基混合团簇GaC_n/GaC_n~+/GaC_n~-(n=1-10)的磁性和极化率进行了研究,计算结果发现,除了GaC_2/GaC_2~+/GaC_2~-以外,这一系列团簇的基态构型是Ga原子位于碳链的末端的直线型.对系列团簇基态的磁性进行了分析,得到的结果是:对于中性团簇,其磁矩是随着团簇尺寸的增加而单调减小,阳离子和阴离子团簇的磁矩都随团簇尺寸的增加呈现出明显的奇偶振荡,但阳离子是奇弱偶强,而阴离子团簇则是奇强偶弱.本文还研究了系列团簇的极化率,三种类型团簇的极化率张量的平均值和各向异性不变量都表现出基本相同的规律,都是随着团簇尺寸的增大而增大.     

Impact of silicon dopant on the absorption and Raman spectroscopy of metal clusters with seven atoms

The structural, optical, and magnetic properties of silicon-doped copper, silver, and gold clusters with D_5h symmetry and seven atoms have been investigated using density functional theory calculations. The global optimized structures of silicon-doped metal clusters are predicted to have a higher HOMO–LUMO gap and higher binding energy than nondoped metal clusters, and nondoped metal clusters have a higher magnetic moment than silicon-doped metal clusters. The silicon doping in metal clusters changes absorption strength and range of absorption wavelength. The silicon dopant also provides a significant impact on the absorption and Raman spectroscopy of nondoped metal clusters. The Raman activities of silicon-doped and nondoped metal clusters are helpful in determining the size and structure of the experimental clusters.     

Radiative transition mechanisms in metal clusters

Experimental data on the absorption of radiation by cold lithium, potassium, and silver clusters and on the emission of radiation by hot niobium and tungsten clusters are analyzed within the scope of two interpretive schemes of radiative transitions in clusters. The first scheme comprises plasmon model of light absorption by valence electrons of metal clusters. The second scheme treats radiative transitions in metal clusters as transitions of valence electrons interacting with surrounding electrons and atomic cores. The experimental data exhibit better agreement with the second interpretation. Zh. éksp. Teor. Fiz. 116, 1903–1911 (December 1999)     

Experimental studies of phase transitions in isolated metal clusters

The reactions of isolated, neutral transition metal clusters with small molecules are used to probe cluster structure and to identify changes in structure with cluster size. Examples are presented of reactivity, adsorbate uptake, and product composition studies. The general conclusion is that transition metal clusters seem to have structure (are “solid”) under typical experimental conditions, and that their structure, i.e., the way the atoms pack, can change many times in the growth sequence from small clusters to bulk metal. These phase changes are often accompanied by dramatic changes in both chemical and physical properties. Evidence is presented for the existence of isomers of certain cluster sizes for some metals. In a few cases, the chemical evidence can be used to propose possible cluster structure; this is illustrated for iron and nickel clusters.     

Metal Sulfide Cluster Complexes and their Biogeochemical Importance in the Environment

Aqueous clusters of FeS, ZnS and CuS constitute a major fraction of the dissolved metal load in anoxic oceanic, sedimentary, freshwater and deep ocean vent environments. Their ubiquity explains how metals are transported in anoxic environmental systems. Thermodynamic and kinetic considerations show that they have high stability in oxic aqueous environments, and are also a significant fraction of the total metal load in oxic river waters. Molecular modeling indicates that the clusters are very similar to the basic structural elements of the first condensed phase forming from aqueous solutions in the Fe–S, Zn–S and Cu–S systems. The structure of the first condensed phase is determined by the structure of the cluster in solution. This provides an alternative explanation of Ostwald’s Rule, where the most soluble, metastable phases form before the stable phases. For example, in the case of FeS, we showed that the first condensed phase is nanoparticulate, metastable mackinawite with a particle size of 2 nm consisting of about 150 FeS subunits, representing the end of a continuum between aqueous FeS clusters and condensed material. These metal sulfide clusters and nanoparticles are significant in biogeochemistry. Metal sulfide clusters reduce sulfide and metal toxicity and help drive ecology. FeS cluster formation drives vent ecology and AgS cluster formation detoxifies Ag in Daphnia magna neonates. We also note a new reaction between FeS and DNA and discuss the potential role of FeS clusters in denaturing DNA. An erratum to this article is available at .     

Defect studies in small CdTe clusters

We study Cd vacancy formation in prototype stoichiometric and non-stoichiometric CdTe clusters with and without passivation. For certain clusters like Cd₁₃Te₁₆, vacancy leads to severe distortion of the geometry due to propagation of defect. Annealing of the vacancy out of the cluster is observed in all unpassivated clusters. Passivated clusters retain their initial geometry and vacancy induced structural distortions are not seen in these clusters since the defect gets localized. Vacancy also induces intragap states. However, it was observed that the passivation of the dangling bonds created by the vacancy removes the intragap states. In an attempt to have CdTe clusters with extrinsic carriers, we substituted a Cd atom by its adjacent atoms Pd/Ag/In/Sn in these CdTe clusters. Substitutional doping of Cd by metal atoms increases the stability of unpassivated clusters. For certain clusters, metal atom doping leads to a half-metallic character. Pd/Ag-doped clusters are p-type semiconductors whereas In-doped clusters are n-type semiconductors. Sn doping in these clusters does not result in n-type semiconductors.     

Exciton-plasmon interaction in hybrid quantum dot/metal cluster structures fabricated by molecular-beam epitaxy

Hybrid structures consisting of InAs/AlGaAs quantum dots and In clusters on the surface separated by an AlGaAs spacer with a specified thickness are investigated. The enhancement of the photoluminescence signal in the long-wavelength region manifesting itself in the appearance of a new narrow emission line is observed. This line is absent in the control structure with a quantum-dot array and no metal clusters. It also disappears with increasing thickness of the dielectric spacer between the layers. These results are explained in terms of a model taking into account the resonance interaction of excitons in quantum dots with localized surface plasmons in metal clusters.     

The effect of cesium metal clusters on the optical properties of cesium iodide thin films

Cesium metal clusters strongly affect the optical properties of cesium iodide thin films. The metal clusters are formed during film formation by thermal evaporation. The cesium cluster of 30–40 nm in the matrix of cesium iodide insulating thin films results in Surface Plasmon Resonance (SPR). The peak position of these SPR peaks showed a red shift. This was shown to be due to changes in the dielectric constant of CsI resulting from the strains in the films caused by the metal clusters themselves.     

Sound generation by spheroidal metallic nanoclusters embedded in transparent matrix under the action of laser pulses

The theory of the photo-acoustical effect caused by a laser action on metal nanoclusters embedded in a dielectric matrix is build. The energy absorbed by clusters propagates through the dielectric matrix and generates the sound waves in it via the thermodeformation mechanism. The formulae for an acoustical signal are derived, and the high sensitivity of the sound wave amplitude to the shape of metal clusters, as well to such parameters of a laser irradiation as the frequency, polarization, and intensity, is revealed. The behavior of the sound vibrations amplitude in a region of the surface plasmons absorption is studied in detail. It is found that this amplitude at light absorption by a discrete metal film (a system of clusters in the matrix) can exceed the corresponding amplitude for the absorption by a continuous metal film in the region of plasmon resonances by several orders of magnitude.     

XPS study of bonding in ligated Au clusters

Ligated metal cluster compounds containing a core of metal atoms with well defined structure surrounded by a variety of organic and inorganic ligands are closely related to the bare metal clusters that are only now becoming available in uniform cluster size. The evolution of band structure and the development of metallic properties as a function of cluster size are of considerable interest. We report here a comparison of these two types of systems based on a study by X-ray photoelectron spectroscopy. The valence band spectra of ligated Au clusters compounds are similar in many respects to those of bare clusters, indicating significant participation of the d electrons in bonding. The core electron binding energy shifts of the central Au atom in Au₁₁(PPh₃)₇Cl₃ corresponds to the loss of approximation one 6 s electron. The total charge transferred to the halogens is accounted for by the shifts of the central and three halogenbonded Au atoms. No indication of metallic behaviour is found in the core of the ligated clusters.     

金属团簇在单晶表面的稳定性和扩散行为的Monte Carlo研究

采用MonteCarlo方法,研究了正二十面体结构的Cu、Ni、Pd和Pt等金属团簇在Pd(001)表面的稳定性和扩散行为.研究表明,载体对负载型金属团簇的稳定性和扩散性质有明显的影响.由于载体表面和金属团簇的振动偶合,金属团簇结构变化的温度要低于自由团簇的结构转化温度.负载型金属团簇的稳定性不仅取决于团簇内部原子之间的相互作用而且取决于团簇与载体之间的相互作用.对金属团簇扩散的研究表明,金属团簇的扩散常数与单金属原子的扩散常数相差不大,通过比较金属团簇的结构变化温度和扩散常数发现,团簇的稳定性和扩散行为有密切的联系.