初始温度和冷却速率对金属团簇凝固行为的影响

用分子动力学结合嵌入原子势研究了含有531个原子的Co₅₃₁, Cu₅₃₁和Ni₅₃₁团簇从不同初始温度以不同冷却速率凝固到200 K时的凝固行为. 结果表明初始温度和冷却速率对团簇的凝固点有很大影响. 初始温度越高, 冷却速率越小, 团簇的凝固点越高. 凝固条件的改变会对三种团簇的凝固结构产生不同的影响. Cu₅₃₁和Ni₅₃₁团簇尽管在不同条件下的凝固点不同, 但凝固结构都是二十面体. 而Co 关键词： 金属团簇 凝固 分子动力学模拟     

新型金属团簇化合物的光限幅特性研究

应用倍频 Nd:YAG脉冲激光 ,在波长为 5 32 nm、脉冲宽度为 8ns的条件下 ,研究了金属团簇化合物WOS3Cu3I(2 - Me Py) 3的光限幅特性。其光限福特性优于富勒烯。Z- Scan研究结果表明 :该团簇具有自聚焦特性 ,其光限幅起源于激发态吸收     

水溶液中金属团簇的脉冲辐解研究进展

介绍了以脉冲辐解技术为手段研究水溶液中单金属团簇的形成机理,并对团簇的性质及其反应进行了简要的概括,对今后团簇的发展趋势进行了展望。     

砷化镓离子团簇的稳定性研究

采用全势能线性糕模轨道分子动力学方法，详细研究了砷化镓离子团簇Ga_nAs_n(n=4，5，6)的几何结构和稳定性.分别找到了这些离子团簇的最低能量结构，通过计算发现这些结构明显不同于中性团簇的基态结构.还发现离子团簇的其他稳定结构与对应的中性结构相比也有较大的结构畸变.在这些砷化镓离子团簇中，相对于砷原子而言，镓原子更容易处在帽原子的位置上. 关键词： 离子团簇 基态结构 稳定性     

新型金属团簇(Et_4N)_3WOS_3Cu_3I_4的皮秒光限幅特性研究

应用波长为532nm,脉冲宽度为40ps的激光脉冲研究了新型金属团簇(Et4N)3WOS3Cu3I4的光限幅性能。实验结果表明,该金属团簇在皮秒激光脉冲的作用下,具有很强的光限幅特性。利用非线性吸收的唯象理论对实验结果进行了分析。     

非均质基底表面上团簇生长的Monte Carlo模拟

Monte Carlo方法模拟了在非均质基底表面上团簇的生长过程.非均质基底由规则分布的A，B两类不同性质的物质(不同材料、不同温度等)组成.沉积粒子的初动能为E₀，在不同相基底上单位长度扩散的能耗为E_A,E_B，粒子从A经过相界扩散到B的能耗为E_AB.模拟中粒子的初动能E₀.远大于E_A,E_B，粒子从B过相界到A能耗E_BA取为0.结果表明，沉积在此类基底表面的粒子凝聚成具有分形结构的团簇.当E_AB远大于E_A,E_B时，团簇的数目、团簇的回旋半径、团簇的分形维数均随E₀/E_AB呈周期性变化. 关键词： 分形团簇 非均质基底 Monte Carlo模拟 周期性     

西藏羊八井广延空气簇射阵列性能的Monte Carlo研究

本文用Monte Carlo方法研究西藏羊八井空气簇射阵列性能.确定好事例判选标准.簇射中心定位精度达3.4m.原初粒子到达方向角分辨率好于1.1°.原初粒子能量按lgE₀=lg(0.45ΣN_i)±0.226确定,其中E₀(TeV)为初级入射粒子能量,ΣN_i为FT探测器上探测到的粒子总数.     

水合金属团簇M~+(H_2O)_n(M=Cu,Ag,Au;n=1-4)的结构和稳定性研究

利用密度泛函理论B3LYP方法优化了M~+(H_2O)_n(M=Cu,Ag,Au;n=1-4)团簇的几何结构,并对它们的稳定性和电子性质进行了系统研究.计算结果表明,Cu~+(H_2O)_n和Ag~+(H_2O)_n团簇的水合骨架结构由三个氧原子与金属离子相连接而成,而Au~+(H_2O)_n团簇则由两个氧原子与金属离子形成的线性结构而得到.通过计算的结合能和HOMO-LUMO能隙也发现:三种水合金属离子体系的稳定性大小为:Eb(Cu)=Eb(Au)Eb(Ag),但是Ag~+(H_2O)_n团簇具有较高的动力学稳定性.这些研究对于今后过渡金属离子水溶液性质的研究和应用提供了重要的理论参考.     

铁磁纳米阵列膜温度稳定性的损伤扩散研究

利用损伤扩散方法研究了三角点阵量子磁盘的温度稳定性问题.为建立实际体系的伊辛模型,我们作了三方面考虑：1)计入自旋间的长程相互作用;2)考虑纳米线阵列中纳米线长度的不一致性,3)推导出矫顽力与自旋交换常数间的关系并利用矫顽力定量估算出自旋交换常数的数值.模拟结果表明,自旋间的作用范围越长,损伤扩散越难,即稳定性越好;而纳米线的长度混乱度越大,温度稳定性越差. 关键词： 量子磁盘 温度稳定性 损伤扩散方法     

二维全同Nb4团簇在Cu(100)表面的结构稳定性和电子性质

使用基于密度泛函理论的第一性原理赝势法和超原胞模型,研究了吸附在Cu(100)表面上的二维有序排列的幻数团簇Nb4的结构稳定性及其电子结构性质.计算表明,四面体结构和平面的菱形结构的Nb4团簇都可以稳定地吸附在Cu(100)表面上,这个体系很可能有重要的应用前景.在Cu(100)表面上,菱形结构的Nb4比四面体结构的Nb4更稳定,从Nb4团簇的四面体结构到菱形结构,需经过的势垒高度约为0.94 eV/团蔟.电子结构的计算表明,在Nb4吸附后,Cu(100)表面与Nb4团簇间有明显的电荷重新分布,表面Cu原子的电子态密度也明显改变.     

Diffusion and Growth of Metal Clusters in Nanocomposites: A Kinetic Monte Carlo Study

Noble metals that are deposited on a polymer surface exhibit surface diffusion and diffusion into the bulk. At the same time the metal atoms tend to form clusters because their cohesive energy is about two orders of magnitude higher than the cohesive energy of polymers. To selfconsistently simulate these coupled processes, we present in this paper a Kinetic Monte Carlo approach. Using a simple model with diffusion coefficients taken as input parameters allows us to perform a systematic study of the behavior of a large ensemble of metal atoms on a polymer surface eventually leading to polymer nanocomposites. Special emphasis is placed on the cluster growth, cluster size distribution and the penetration of clusters into the substrate. We also study the influence of surface defects and analyze how the properties of the resulting material can be controlled by variation of the deposition rate (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cu（001）表面CO吸附的电子结构效应

本文应用Ｒｅｃｕｒｓｉｏｎ方法，计算了ＣＯ在Ｃｕ（００１）表面不同位置（顶位、桥位和空位）吸附的电子结构，分析了ＣＯ与Ｃｕ表面原子之间的键作用。分析表明ＣＯ在顶位吸附时，Ｃｐｘ（ｐｙ）－Ｃｕｄｓ（１号）和Ｃｐｘ（ｐｙ）－Ｃｕｄ２（ｄｓ）（２号）之间存在较强的键作用，这有利于ＣＯ在顶位吸附。桥位和空位吸附时，ＣＯ与表面原子形成的键较弱，是不稳定的。计算结果得到了实验的支持。     

Diffusion of an Extra Ga Atom in GaAs(001)(2*4) Rich-As Surface

采用键序势计算了单个镓原子在GaAs(001) fi2(2￡4)富砷表面的迁移的势能面,发现了一些低能量的吸附位,这些吸附位与实验观测的结果一致. 同时也发现了多个可能的迁移路径,并根据迁移路径上的相对能量指出单个镓原子更优先在表面上平行于砷二聚体的两条路径上迁移. 这一结果可由吸附的镓原子所导致的应变予以理解. 此外,有限温度下单个镓原子迁移的动力学模拟结果支持了所计算的势能面.     

Surface electromigration of metals on Si(001): In/Si(001)

The possibility of surface electromigration (SE) of metals of In, Ga, Sb and Ag on a very flat Si(001)2×1 substrate (single domain 2×1) was examined by SEM, μ-RHEED and μ-AES under UHV conditions. It was found that Ga, Sb and Ag show no SE on Si(001) surface even at DC annealing temperatures for the desorption of these metals. For In on Si(001), a very fast SE (8000 μm/min) towards the cathode side was found that suddenly sets in at 450°C DC annealing, which was related to a surface phase transition. μ-RHEED and μ-AES observation showed that the SE is related to an ordered 4×3-In phase together with two-dimensional In gas phase over the 4×3-In phase and an In-disordered phase at the front end of SE. Single domain 4×3-In phases were found to occur under sequences of In deposition and DC annealing which involve the In SE on Si(001).     

Dynamics of Pd monomers and dimers adsorbed on the (001) surfaces of strongly correlated nickel oxides

The adsorption and diffusion of Pd monomers and dimers on the (001) surfaces of strongly correlated nickel oxides were investigated using density functional theory combined with the on-site Coulomb repulsion U. The results were compared with those of Pd on nonmagnetic MgO(001). For the Pd monomer, the most stable adsorption site was found to be near the surface O atom. The surface diffusion of the Pd monomer occurred by a hopping process over surface hollow sites. The diffusion energy barrier was 0.21 eV, which was lower than that for Pd on MgO(001). In the case of the Pd dimer, the smallest and stable cluster, the most stable adsorption structure had a flat geometry, with both Pd atoms sitting above the neighboring surface O atoms. The surface diffusion of the Pd dimer occurred by rotational and sliding processes, in contrast to that of the Pd dimer on MgO(001). The diffusion energy barriers ranged from 0.33 to 0.36 eV. The values for the surface diffusion of Pd dimers on NiO(001) were lower than those of Pd on MgO(001). This suggests that Pd dimers move more rapidly on NiO(001) than on MgO(001), and that the sintering of Pd clusters closely related to catalytic activities can occur more easily compared to that of Pd on MgO(001).     

(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.     

Els and leed study of CO adsorption on Pd(001) and Pd(001) 6° [110]

LEED studies indicate that both CO and carbon adsorb differently on Pd(001) surfaces with and without steps. However, electron energy loss spectra for Pd(001) samples with and without ordered steps show no detectible surface structural sensitivity to CO adsorption. For both samples an additional loss feature at 13.5 eV appears upon CO adsorption. This feature is identified as a (1π?5σ) to 2π^★ type intramolecular electronic excitation, and it appears to be a universal feature of molecular CO adsorption on metals. A second loss expected in the 6–7 eV range associated with a d to 2π^★ type charge-transfer excitation was not detected. Either the transition probability is low for this excitation or hybridization with surface plasmons may obscure its identification.     

密度泛函理论研究碱金属原子在完美氧化镁(001)表面的吸附

基于平面波赝势法的密度泛函理论系统地研究了孤立碱金属原子(锂、钠、钾、铷、铯)在完美氧化镁(001)表面的吸附. 锂在氧位表面上的吸附能是0.72 eV,大约是其它碱金属的3倍. 锂和表面氧之间较强的相互作用主要是来源于共价键的作用,这可由态密度和差分电荷密度的分析所证实. 讨论碱金属在MgO(001)表面吸附的成键机理.     

中等尺寸硫化锌团簇结构和稳定性

通过第一性原理方法研究中等尺寸硫化锌团簇(ZnS)_n(n=24,28,36,和48)的结构和稳定性.团簇初始结构主要通过手工搭建和从体材料中切割得来.研究表明:对于中等尺寸的团簇,空心的笼状和管状结构能量最低;随着团簇尺寸的增大,洋葱结构能量越来越低.此外,对中等尺寸硫化锌团簇,纤锌矿结构比闪锌矿结构更稳定.说明在小尺寸下,纤锌矿硫化锌结构更稳定.