大小选择的金属支撑团簇研究进展*

从团簇的产生, 团簇的沉积过程, 团簇在固体表面的迁移和团簇的反应活性等方面对大小选择的金属支撑团簇的研究现状进行了综述, 并展望了这一领域的研究趋势。     

Fragmentation of Magic-Size Cluster Precursor Compounds into Ultrasmall CdS Quantum Dots with Enhanced Particle Yield at Low Temperatures

Colloidal small-size CdS quantum dots (QDs) are produced usually with low particle yield, together with side products such as the particular precursor compounds (PCs) of magic-size clusters (MSC). Here, we report our synthesis of small-size CdS QDs without the coexistence of the PC and thus with enhanced particle yield. For a conventional reaction of cadmium oleate (Cd(OA)₂) and sulfur (S) in 1-octadecene (ODE), we show that after the formation of the PC in the pre-nucleation stage, the addition of tri-n-octylphosphine oxide (TOPO) facilitates the production of small-size QDs. We demonstrate that TOPO fragmentizes the PC that have formed, which enables the nucleation and growth of small-size QDs even at room temperature. Our findings introduce a new approach to making small-size QDs without the coexistence of the PC and with improved particle yield. Providing experimental evidence for the two-pathway model proposed for the pre-nucleation stage of colloidal binary QDs, the present study aids in the advance of non-classical nucleation theory.     

The Intermetalloid Cluster [(Cp*AlCu)6H4], Embedding a Cu6 Core Inside an Octahedral Al6 Shell: Molecular Models of Hume–Rothery Nanophases

Defined molecular models for the surface chemistry of Hume–Rothery nanophases related to catalysis are very rare. The Al‐Cu intermetalloid cluster [(Cp*AlCu)₆H₄] was selectively obtained from the clean reaction of [(Cp*Al)₄] and [(Ph₃PCuH)₆]. The stronger affinity of Cp*Al towards Cu sweeps the phosphine ligands from the copper hydride precursor and furnishes an octahedral Al₆ cage to encapsulate the Cu₆ core. The resulting hydrido cluster M₁₂H₄ reacts with benzonitrile to give the stoichiometric hydrometalation product [(Cp*AlCu)₆H₃(N=CHPh)].     

AunAgm- (n+m=2～4)负离子团簇光脱附电子谱计算

利用密度泛函理论，通过几何优化和态密度计算了AunAgm- (n+m=2～4)团簇的光电子光谱，结果显示只有Au2Ag2-团簇的第一个峰发生了0.5eV的红移，而其它团簇的峰位置符合的很好，因此理论计算给出的团簇结构是合理的。     

Metal–Helix Frameworks Formed by μ3-NO3− with Different Orientations and Connected to a Heterometallic CuII10DyIII2 Folded Cluster

Metal nanoclusters have a certain rigidity due to their specific coordination patterns and shapes; thus, they face extreme difficulty in folding into a specific direction to form a double-helix structure and in further interconnecting to form metal–helix frameworks (MHFs). To date, no MHFs have been produced by the formation of heterometallic clusters. Selecting the appropriate “bonding molecules” to bond metal nanoclusters in a specific multiple direction is one of the most effective strategies for designing synthetic MHFs. In this study, we realized for the first time the control of different orientations of μ₃-NO₃⁻ to join heterometallic clusters (Cu₁₀Dy₂) and subsequently form a left-handed double helix chain, which further joins to form MHFs. In the structure of the MHFs, four different directions of bridging μ₃-NO₃⁻ exist, three of which are involved in the linkage of the double-helix chain. Each μ₃-NO₃⁻ is connected to three adjacent Cu₁₀Dy₂. Herein, we extend a new method for designing synthetic double-helix structures and MHFs, thereby further laying the foundation for the development of similar DNA double-helix structures and nucleic acid secondary structures in vitro.     

In situ observation of cascade damage under heavy ion irradiation

Abstract

Collision cascades initiated from high energy PKAs produce defect clusters in crystalline solids irradiated with fast neutrons or energetic ions. They will affect not only an early stage of microstructural evolution but that at high fluence by changing free defect survival rate. To elucidate fundamental processes of cascade damage evolution, in situ observation of microstructure in FCC metals under heavy ion irradiation has been carried out using a combined facility of a 400 kV accelerator and a 200 kV transmission electron microscope installed in the University of Tokyo, Tokai. Defect clusters produced by individual energetic ions are observed during irradiation to examine subcascade formation, interaction of point-defects from cascade damage and related point-defect processes.     

Fano fingerprints of Majoranas in Kitaev dimers of superconducting adatoms

We investigate theoretically a Fano interferometer composed by STM and AFM tips close to a Kitaev dimer of superconducting adatoms, in which the adatom placed under the AFM tip, encloses a pair of Majorana fermions (MFs). For the binding energy Δ of the Cooper pair delocalized into the adatoms under the tips coincident with the tunneling amplitude t between them, namely Δ=t, we find that only one MF beneath the AFM tip hybridizes with the adatom coupled to the STM tips. As a result, a gate invariance feature emerges: the Fano profile of the transmittance rises as an invariant quantity depending upon the STM tips Fermi energy, due to the symmetric swap in the gate potential of the AFM tip.     

Vibrational temperature of the adlayer in the ‘hot-atom’ reaction mechanism

The hot-atom reaction mechanism brings about reaction rates several orders of magnitude higher than those expected in the case of adatoms which have thermalized with the surface. This paper addresses the issue of a possible thermodynamic characterization of the adlayer under reactive conditions and at the steady state. In turn, this implies having to determine the temperature of the adatoms. This is done by means of a nonequilibrium statistical thermodynamic approach, by exploiting a suitable definition of the entropy. The interplay between reaction rate, vibrational temperature of the adatoms and adsorbed quantities is highlighted. This paper shows that the vibrational temperature depends on reaction rate, logarithmically and exhibits a non-linear scaling on physical quantities linked to the energetics of the reaction, namely the adsorption energy and the binding energy of the molecule. The present modeling is also discussed in connection with response equations of nonequilibrium thermodynamics.     

Surface diffusion of tungsten adatoms induced by low-energy bombardment with He atoms

Using low-temperature field ion microscope techniques, we studied at the atomic level the elementary events of radiation-induced surface diffusion of tungsten adatoms on the ideally pristine surface. The experiments on surface-damage formation and adatom displacements have been performed in situ with a source of neutral helium atoms with an energy of 5?keV. It was demonstrated that the low-energy He atomic bombardment at grazing incidence was able to induce a substantial surface mobility of adatoms. Most of the radiation-induced adatom displacements were oriented along the direction of irradiation. The long impact-induced jumps of adatoms, spanning more than a nearest-neighbor distance, were revealed. Performed molecular dynamics simulations reproduce the general experimental trends and conclusions.     

SYNTHESIS AND CHARACTERIZATION OF TWO NOVEL,NEST-SHAPED Mo-Cu-S CLUSTER COMPOUNDS, [MoOS3Cu3(Py)5X] (X = Br,I), AND THE SUBSTITUTION OF Mo-Cu-S CLUSTERS

Abstract

The title compounds [MoOS₃Cu₃(Py)₅Br] (3) and [MoOS₃Cu₃(Py)₅I] (4) were obtained through the nest-shaped cluster [(n-Bu)₄N]₂[MoOS₃Cu₃BrCl₂] (1) and twin-nest-shaped cluster [Et₄N]₄[Mo₂Cu₆S₆O₂Br₂I₄](2) by reacting with pyridine. They show nest-shaped skeletons, and are characterized structurally by single-crystal X-ray analysis. These are the first neutral nest-shaped Mo(W)-Cu(Ag)-S clusters.