低温下Au959团簇负载于MgO(100)表面后结构变化的分子动力学研究

采用基于Chen-Mbius反演方法,从金属/金属氧化物界面第一性原理计算的粘结能结果中推导出的Au/MgO原子间相互作用势的正则系综（NVT）分子动力学,模拟了在10 K条件下,Au₉₅₉团簇负载于MgO（100）表面后团簇结构的变化.根据原子对分析技术和对分布函数的分析表明,由于团簇界面处原子间距与载体原子间距相匹配,置于载体上的Au团簇经过一个变形过程后,较其孤立自由表面时的团簇体积变大. 关键词： 团簇 分子动力学 计算机模拟 表面     

Size-selected Au clusters deposited on SiO2/Si: Stability of clusters under ambient pressure and elevated temperatures

This study examined the oxidation and reduction behavior of mass-selected Au clusters consisting of 2-13 atoms deposited on silica. An atomic oxygen environment was used for the oxidation of Au. X-ray photoelectron spectroscopy (XPS) was used to identify Au(III) and Au(O). Au₅, Au₇ and Au₁₃ clusters deposited on the as-prepared SiO₂/Si substrates were highly inert towards oxidation, whereas the other clusters could be oxidized, i.e. the chemical property drastically changed with the number of atoms in a cluster. The size-selectivity in chemical reactivity remained unchanged upon air-exposure. The chemical properties of the deposited Au clusters were unchanged after annealing at 250 °C. Annealing at higher temperatures caused structural changes to the surface, as determined by the oxidation behavior. XPS of the deposited Au clusters upon annealing indicated charge transfer from Au to silica.     

A molecular dynamics study of the structural change differences between Au225 and Au369 clusters on MgO surfaces at low temperature

The differences in structural change between Au 225 and Au 369 clusters with their(111) facets supported on MgO(100) surfaces at 5 K are studied by using molecular-dynamics simulations with the atomic interchange potentials of the Au/MgO interface.The parameters are obtained from the ab initio energies using the Chen-Mo¨bius inversion method.Analyses of the pair distribution functions show that the two Au clusters use different deformation processes to adjust the distances between the interface atoms,owing to the misfit between the atom distances among the clusters and the substrates.The local structural changes are identified by atomic density profiles.     

Derivatives of the thiolate-protected gold cluster Au25(SR)18-1

Loss of small fragments (like AuL, Au₂L₃, Au₄L₄) have been found systematically in several MALDI and FAB experiments on thiolate-protected gold clusters of different sizes. When using the cluster Au₂₅L₁₈ ^-1 as parent cluster, the fragmented cluster Au₂₁L₁₄ ^-1 has been reported to be obtained in high proportion (L = SCH₂CH₂Ph). Here we analyse a few possible fragmentation patterns of the well-known parent cluster Au₂₅L₁₈ ^-1 (L = SCH₃). Using DFT calculations we study the different atomic configurations obtained after a AuL fragment is lost from Au₂₅L₁₈ ^-1. We found energetically favourable configurations that can be written as Au₁₃ [Au₂L₃]_6-z [AuL₂] _z ^-1, where the modification can be described as a replacement of the long protecting unit by a short one (Au₂L₃  →  AuL₂). A full replacement (z = 6) gives rise to a protected Au₁₉L₁₂ ^-1 cluster. This mechanism does not modify the super-atomic electronic structure of the gold core, i.e., all these fragments remain an 8 electron super-atom clusters exactly like the parent Au₂₅L₁₈ ^-1. We suggest that the Au₁₉L₁₂ ^-1 cluster could be realized by using a bulky thiolate, such as the tert-butyl thiolate SC(CH₃)₃ .     

CO adsorption on small Aun（n=1-7） clusters supported on a reduced rutile TiO2（110） surface:a first-principles study

CO adsorption on small Au n(n = 1-7) clusters which are supported by a partially reduced rutile TiO 2(110) surface has been investigated by the first-principles method.The low coordinated sites of Au clusters are favorable for CO adsorption.CO-Au n-TiO 2 system displays surface magnetism.There is a strong interaction between the adsorbed CO molecule and the supported Au clusters.     

Au10(TBBT)10:Aun(TBBT)m纳米团簇的起点与终点

Gold(I) thiolate compounds (i.e. Au^I-SR) are important precursors for the synthesis of atomically precise Au_n(SR)_m nanoclusters. However, the nature of the Au^I-SR precursor remains elusive. Here, we report that the Au₁₀(TBBT)₁₀ complex is a universal precursor for the synthesis of Au_n(TBBT)_m nanoclusters (where TBBT=4-tertbutylbenzenethiol/thiolate). Interestingly, the Au₁₀(TBBT)₁₀ complex is also found to be re-generated through extended etching of the Au_n(SR)_m nanoclusters with excess of TBBT thiol and O₂. The formation of well-defined Au₁₀(TBBT)₁₀ complex, instead of polymeric Au^I-SR, is attributed to the bulkiness of the TBBT thiol. Through 1D and 2D NMR characterization, the structure of Au₁₀(TBBT)₁₀ is correlated with the previously reported X-ray structure, which contains two inter-penetrated Au₅(TBBT)₅ rings. The photophysical property of Au₁₀(TBBT)₁₀ complex is further probed by femtosecond transient absorption spectroscopy. The accessibility of the precise Au₁₀(TBBT)₁₀ precursor improves the efficiency of the synthesis of the Au_n(TBBT)_m nanoclusters and is expected to further facilitate excellent control and understanding of the reaction mechanisms of nanocluster synthesis.     

All-electron relativistic calculation on Au5X (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) clusters

All-electron scalar relativistic calculations on Au₅X (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) clusters have been performed by using density functional theory with the generalized gradient approximation. Our calculation results indicate that all the lowest energy geometries of Au₅X clusters have planar structures; the doped X atoms prefer to occupy the fourfold coordination site. Except Au₅Fe, Au₅Co and Au₅Zn, for other clusters including pure Au₆ cluster, the HOMO are delocalized obviously with a contribution from all atoms in the cluster. On the contrary, the electron localization in Au₅Zn is very strong resulting in the least stability of this cluster. Au₅Cu cluster with six delocalized electrons being defined as magic number for two-dimensional system has the largest VIP and deepest HOMO energy level. With the substitution Au for X atoms, the metallicity of all Au₅X clusters is reinforced.     

Sputtering of amorphous ice induced by C60 and Au3 clusters

Molecular dynamics simulations were performed to study the behavior of cluster SIMS. Two predominant cluster ion beam sources, C₆₀ and Au₃, were chosen for comparison. An amorphous water ice substrate was bombarded with incident energy of 5 keV. The C₆₀ cluster was observed to shatter upon impact creating a crater of damage approximately 8 nm deep. Although Au₃ was also found to both break apart and form a damage crater, it continued along its initial trajectory causing damage roughly 10 nm deep into the sample and becoming completely imbedded. It is suggested that this difference in behavior is due to the large mass of Au relative to the substrate water molecule.     

Extended X-ray absorption fine-structure (EXAFS) of a complex oxide structure: a full multiple scattering analysis of the Au L3-edge EXAFS of Au2O3

Crystalline Au₂O₃ was obtained by hydrothermal synthesis at 3000 atm and its extended X-ray absorption fine-structure (EXAFS) at the Au L₃-edge was measured at room temperature. A detailed full multiple scattering (MS) analysis using FEFF8 theory shows that only a small number of scattering paths contribute significantly to the EXAFS of Au₂O₃. Because of the complex unit cell (low local symmetry) of the Au₂O₃ structure, contributions of MS paths are almost negligible. The results indicate that FEFF8 theory provides a good reference for the analysis of Au-O phases.     

Formation of Ag2, Au2 and AgAu particles on MgO(1 0 0): DFT study on the role of support-induced charge transfer in metal-metal interactions

The formation of Ag₂, Au₂ and AgAu particles oriented perpendicularly to the MgO(1 0 0) surface was studied using the density functional theory. While the support induces a slight enhancement of the Ag-Ag bond (by 0.3-0.4 eV), the Au-Au bond is strongly enhanced (by 0.8-1.1 eV). Concerning the bimetallic particle, the Ag-Au bond stabilization depends on the relative position of each atom. Thus, in general terms, the strength of the metal-metal bond is determined by the nature of the terminal atom; the bond is stronger in Au-terminal particles. The partial electronic charge transfer to the terminal Au atom and its ability to polarize this charge are responsible for this energetic stabilization.     

闭壳层金掺杂钛氧团簇阴离子解离氢分子研究

Dissociation of molecular hydrogen (H₂) is extensively studied to understand the mechanism of hydrogenation reactions. In this study, H₂ dissociation by Au₁-doped closed-shell titanium oxide cluster anions AuTi₃O₇^- and AuTi₃O₈^- has been identified by mass spectrometry and quantum chemistry calculations. The clusters were generated by laser ablation and massselected to react with H₂ in an ion trap reactor. In the reaction of AuTi₃O₈^- with H₂, the ion pair Au⁺-O₂^2- rather than Au⁺-O^2- is the active site to promote H₂ dissociation. This finding is in contrast with the previous result that the lattice oxygen is usually the reactive oxygen species in H₂ dissociation. The higher reactivity of the peroxide species is further supported by frontier molecular orbital analysis. This study provides new insights into gold catalysis involving H₂ activation and dissociation.     

Synthesis and Growth of New Compounds Au3In5Se9 and Au3Ga5Se9

The phase analysis was performed and a character of interaction in AuInSe₂ - In₂Se₃ and AuGaSe₂ -Ga₂Se₃ quasi-binary systems were considered. The technology of synthesis and growth of single crystals of new semiconducting compounds Au₃In₅Se₉ and Au₃Ga₅Se₉ were developed. The materials for ohmic contacts were chosen and the electrical, optical and thermal properties of obtained compounds have been investigated. The forbidden band gap, its temperature coefficient, the type of the optical transitions and heat capacity of Au₃In₅Se₉ and Au₃Ga₅Se₉ compounds were determined. The charge of entropy and enthalpy has been estimated by numerical integration.     

Au1-xNix合金(x=0.30-0.42)低温电阻率极小值的机理探讨

为了解释Au_1-xNi_x合金(x=0.30—0.42)低温出现电阻率极小值的实验结果,本文提出一个低浓度自旋集团顺磁态合金的模型,得到自旋集团孤立近似下和自旋集团耦合作用下的电阻率公式,并和晶格散射的贡献(由Au₈₀Ni₂₀合金或Au-Cu合金的ρ_i(T)实验数据代替)联合起来,得到ρ(T)的计算曲线,和实验结果符合得很好。当Tmin,电阻率随温度增高而下降,主要是自旋集团孤立近似下的Kondo效应引起的。自旋集团之间的RKKY耦合作用对电阻率的贡献在低温时大,随着温度增高按1/T规律迅速减小,所以ρ(T)-ρ_i(T)实验值在相当宽温度范围出现logT关系。随着温度增高,晶格散射对电阻率的贡献将变得重要,当T=T_min,电阻率出现极小值。 关键词：     

[Au25(SR)18]-团簇的相干振动动力学研究

利用飞秒时间分辨光谱,可观测叠加在电子态动力学上的相干振动动力学. 从金团簇的相干振动中,不仅能提取电子与振动的耦合信息,也能得到力学性质和电子结构,进而有望实现微小质量探测等应用. 本文利用飞秒时间分辨的瞬态吸收探测了[Au₂₅(SR)₁₈]^-团簇的相干振动动力学,通过对相干振动的频率、相位、波长分布的详细分析进一步揭示了其来源. 在[Au₂₅(SR)₁₈]^-团簇的飞秒瞬态吸收动力学中可以观测到频率为40 cm^-1和80 cm^-1的两种振动,均来源于团簇中心Au₁₃核的振动. 通过对相干振动的相位分析发现频率为80 cm^-1的振动来自于对电子态之间吸收频率的调制,而频率为40 cm^-1的振动来源于对电子态之间吸收强度的调制. 同时,研究发现[Au₂₅(SR)₁₈]^-团簇相干振动的频率对其表面配体不敏感,该振动是来源于Au₁₃核的本征性质.     

Charging effects on the vibrational properties of Au and Au2 on MgO(100)

Vibrational spectra of charge-neutral and charged Au and Au₂ on MgO(100) were investigated using ab-initio density functional perturbation theory. The calculated vibrational spectra showed vibrational features associated with the charge states of Au and Au₂ on MgO(100). Further analyses of surface in-plane and normal phonon modes of Au and Au₂ on MgO(100) were performed to extract vibrational features involving the Au modes. These features provide important information for experimentally explaining the charge states of Au and Au₂ on MgO(100).     

Geometric,stable and electronic properties of Aun-2Y2（n=3-8） clusters

Employing first-principles methods,based on the density function theory,and using the LANL2DZ basis sets,the ground-state geometric,the stable and the electronic properties of Aun-2Y2 clusters are investigated in this paper.Meanwhile,the differences in property among pure gold clusters,pure yttrium clusters,gold clusters doped with one yttrium atom,and gold clusters doped with two yttrium atoms are studied.We find that when gold clusters are doped by two yttrium atoms,the odd-even oscillatory behaviours of Aun-1Y and Aun disappear.The properties of Aun-2Y2 clusters are close to those of pure yttrium clusters.     

Cu3Au与Au3Cu中点缺陷的分子动力学研究——兼论L12型合金点缺陷的性质

讨论了Ｌ１２型合金中点缺陷的各种可能构型，然后运用分子动力学的方法，采用由Ａｃｋ-ｌａｎｄ等提出的Ｃｕ-Ａｕ体系的多体势函数，计算了具有Ｌ１₂结构的Ｃｕ₃Ａｕ与Ａｕ₃Ｃｕ中点缺陷的构型、形成能及缺陷体积，并进一步讨论了目前研究较为深入的Ｌ１₂型金属间化合物中点缺陷的性质 关键词：     

Substrate effects on the analysis of biomolecular layers using Au, Au3 and C60 bombardments

Effects of platinum silicon, graphite and PET substrates on the secondary ion yield of sub-monolayer and multilayer samples of Cyclosporin A following 20 keV Au⁺, Au₃⁺and C₆₀⁺ impacts have been investigated. The obtained results of sub-monolayer samples show that platinum enhances the yield of the pseudo-molecular ion following Au⁺ and Au₃⁺ impacts due to the high density of the substrate that enables the energy of the primary ions to be deposited near the surface. C₆₀⁺ impacts on sub-monolayer samples are less effective, but there is an enhancement on PET substrates. Impacts of 20 keV Au⁺ and Au₃⁺ are not very efficient on multilayer samples. 20 keV C₆₀⁺ impacts enhance the yields significantly, especially for the relatively high molecular weight [M+H]⁺ ion.     

Geometrical,electronic, and magnetic properties of Au n V (n = 1–8) clusters: A density functional study

The geometrical, electronic, and magnetic properties of small Au _n V (n?=?1–8) clusters have been investigated using density functional theory at the PW91 level. An extensive structural search indicates that the V atom in low-energy Au _n V isomers tends to occupy the most highly coordinated position and the ground-state configuration of Au _n V clusters favors a planar structure. The substitution of a V atom for an Au atom in the Au _{n +1} cluster transforms the structure of the host cluster. Maximum peaks are observed for the ground-state Au _n V clusters at n?=?2 and 4 for the size dependence of the second-order energy differences, implying that the Au₂V and Au₄V clusters possess relatively higher stability. The energy gap of the Au₃V cluster is the largest of all the clusters. This may be ascribed to its highly symmetrical geometry and closed eight-electron shell. For ground-state clusters with the same spin multiplicity, as the clusters size increases, the vertical ionization potential decreases and the electron affinity increases. Magnetism calculations for the most stable Au _n V clusters demonstrate that the V atom enhances the magnetic moment of the host clusters and carries most of the total magnetic moment.     

Polyethylene terephthalate (PET) bulk film analysis using C60, Au3, and Au primary ion beams

The damage characteristics of polyethylene terephthalate (PET) have been studied under bombardment by C₆₀⁺, Au₃⁺ and Au⁺ primary ions. The observed damage cross-sections for the three ion beams are not dramatically different. The secondary ion yields however were significantly enhanced by the polyatomic primary ions where the secondary ion yield of the [M + H]⁺ is on average 5× higher for C₆₀⁺ than Au₃⁺ and 8× higher for Au₃⁺ than Au⁺. Damage accumulates under Au⁺ and Au₃⁺ bombardment while C₆₀⁺ bombardment shows a lack of damage accumulation throughout the depth profile of the PET thick film up to an ion dose of ∼1 × 10¹⁵ ions cm⁻². These properties of C₆₀⁺ bombardment suggest that the primary ion will be a useful molecular depth profiling tool.