Nonlinear electronic dynamics in free and deposited sodium clusters: Quantal and semi-classical approaches

The optical response of sodium clusters is studied using fully three-dimensional electronic dynamics, in real time, with an explicit ionic background. The obtained spectra are shown to come close to experimental results for free clusters. We use the approach also to compute the response of sodium clusters deposited on a NaCl(1 0 0) surface. The flattening of the clusters induced by the surface results in a shift and a large fragmentation of the plasmon resonance.     

Epistemic Communities and Cluster Dynamics: On the Role of Knowledge in Industrial Districts

This paper questions the prevailing notions that firms within industrial clusters have privileged access to “tacit knowledge” that is unavailable—or available only at high cost—to firms located elsewhere, and that such access provides competitive advantages that cause the growth and development of both firms and regions. It outlines a model of cluster dynamics emphasizing two mutually interdependent processes: the concentration of specialized and complementary epistemic communities, on the one hand, and entrepreneurship and a high rate of new firm formation on the other.     

Silver Atomic Quantum Clusters of Three Atoms for Cancer Therapy: Targeting Chromatin Compaction to Increase the Therapeutic Index of Chemotherapy

Nanomaterials with very low atomicity deserve consideration as potential pharmacological agents owing to their very small size and to their properties that can be precisely tuned with minor modifications to their size. Here, it is shown that silver clusters of three atoms (Ag₃‐AQCs)—developed by an ad hoc method—augment chromatin accessibility. This effect only occurs during DNA replication. Coadministration of Ag₃‐AQCs increases the cytotoxic effect of DNA‐acting drugs on human lung carcinoma cells. In mice with orthotopic lung tumors, the coadministration of Ag₃‐AQCs increases the amount of cisplatin (CDDP) bound to the tumor DNA by fivefold without modifying CDDP levels in normal tissues. As a result, CDDP coadministered with Ag₃‐AQCs more strongly reduces the tumor burden. Evidence of the significance of targeting chromatin compaction to increase the therapeutic index of chemotherapy is now provided.     

Ni对RPV模拟钢中富Cu原子团簇析出的影响

用原子探针层析技术和时效模拟方法,研究了不同N i含量并且提高了Cu含量的反应堆压力容器(RPV)用模拟钢中富Cu、富N i和富Mn原子团簇的形成。结果表明,提高钢中的N i含量会促使富Cu原子团簇的析出,富Cu原子团簇中含有N i和Mn。实验检测到富N i的原子团簇,团簇中含有Cu和Mn,富N i原子团簇可以作为富Cu原子团簇析出时的形核区。实验还检测到富Mn原子团簇,当Mn原子团簇中含有较高的N i时,它也可以成为富Cu原子团簇析出时成核的地方。由于钢中的合金元素N i在形成富N i原子团簇后会成为富Cu原子团簇析出时成核区,因而提高N i的含量将促进富Cu原子团簇的析出,这是合金元素N i会增加压力容器钢中子辐照脆化敏感性的本质原因。     

Superatomic Gallium Clusters in Dendrimers: Unique Rigidity and Reactivity Depending on their Atomicity

Superatoms have been investigated due to their possible substitution for other elements. The solution-phase synthesis of superatoms has attracted attention to realize the availability of superatoms. However, the previous approach is basically limited to the formation of a single cluster. Here, superatoms are investigated and the number of valence electrons in these superatoms is changed by designing the number of gallium atoms present. Based on the dendrimer template method, clusters consisting of 3, 12, 13, and other numbers of atoms have been synthesized. The halogen-like superatomic nature of Ga₁₃ is structurally and electrochemically observed as completely different to the other clusters. The gallium clusters of 13 and 3 atoms, which can fill the 2P and 1P superatomic orbitals, respectively, exhibit different reactivities. The 3-atom gallium cluster is suggested as being reduced to Ga₃H₂⁻ due to the lower shift of energy levels in the unoccupied orbitals. The results for these gallium clusters provide candidates for superatoms.     

Size and shape of nanoclusters: single-shot imaging approach

A method of single-shot imaging via aberration-corrected scanning transmission electron microscopy equipped with high angle annular dark-field detector (STEM-HAADF) has been applied to size-selected gold model catalysts (Au(25) and Au(39) ) on hydroxyapatite. Through quantitative intensity analysis, the size, in terms of number of atoms as well as 3D shape of the clusters are obtained.     

Catalysis by very small Au clusters

We review recent theoretical and experimental work on the catalytic properties of Au clusters that contain a few atoms and are supported on an oxide surface. The clusters are mass-selected and landed slowly on the oxide surface in ultra-high vacuum. STM measurements show that the clusters do not fragment and do not damage the surface when they are deposited nor do they coarsen after deposition. Their catalytic activity changes non-monotonically with the number of atoms and is sensitive to the nature of the support and to additives (hydroxyls, water, Na, Cl) present on the surface. Binary clusters (e.g. Au_nSr) can be more active than unary ones. Very recent work has managed to study catalysis by such clusters under realistic pressure conditions; their performance is very different from (and sometimes better than) that of large clusters.     

Mimicking Electrodeposition in the Gas Phase: A Programmable Concept for Selected‐Area Fabrication of Multimaterial Nanostructures

An in situ gas‐phase process that produces charged streams of Au, Si, TiO₂, ZnO, and Ge nanoparticles/clusters is reported together with a programmable concept for selected‐area assembly/printing of more than one material type. The gas‐phase process mimics solution electrodeposition whereby ions in the liquid phase are replaced with charged clusters in the gas phase. The pressure range in which the analogy applies is discussed and it is demonstrated that particles can be plated into pores vertically (minimum resolution 60 nm) or laterally to form low‐resistivity (48 µΩ cm) interconnects. The process is applied to the formation of multimaterial nanoparticle films and sensors. The system works at atmospheric pressure and deposits material at room temperature onto electrically biased substrate regions. The combination of pumpless operation and parallel nozzle‐free deposition provides a scalable tool for printable flexible electronics and the capability to mix and match materials.     

Electronic properties of chemically produced silver clusters: grain morphology studies

Abstract

The electronic properties of silver clusters formed on the surface of reduction- sensitized octahedral and cubic AgBr emulsions were studied. Prior to sensitization with dimethylamineborane, SnCl₂ or high pH, these emulsions had the same efficiency. The results suggest that the octahedral emulsion has more potential to achieve a higher maximum speed increase. This difference may be due to fewer available sites for silver cluster formation on cubic surfaces. Gelatin concentration studies showed that the gelatin and/or impurities do play a role in silver cluster formation by high pH treatment. The precise role of OH^? is uncertain.     

Non-collinear structure of Cr trimer on the surface of non-magnetic metals

Magnetic structure of Cr trimer clusters on non-magnetic metal substrate has been calculated by recursion method within Anderson model. The values of the moments are enhanced relatively to bulk bcc Cr due to the reduction of coordination number. Angles between the moments depend on the relations between hopping parameters V_ij, determined by the interatomic distance in the cluster. We performed systematic calculations of the ground state for different values of parameters V₁₂=V₁₃ and V₂₃. For V₁₂V₂₃ ground state corresponds to moments on the atoms 2 and 3 with opposite direction, whereas the moment on atom 1 is perpendicular to them. For V₁₂=V₂₃ the angle between each pair of moments equals 2π/3 and the total moment of the trimer is zero. A decrease of V₂₃ versus V₁₂ leads to collinear state with moment on the atom 1 antiparallel to the moments on second and third. Calculation in external magnetic field reveals the co-existence of two self-consistent states with essentially different total magnetic moments. In weak field these solutions are very close in energy whereas with the increase of the field the state with larger moment is stabilized.     

Plasma Cluster and Its Interaction with an Obstacle. Interaction of Incident and Reflected Flows

A physical-and-mathematical formulation is given of the problem on the interaction between two opposing (incident and reflected) flows of plasma formed upon collision of a plasma cluster with a target. Expressions are given for determining the rates of momentum and energy transfer upon elastic collisions of particles, and the kinetic processes are investigated which define the charge composition and radiation of plasma clusters. The main features are described that are characteristic of the construction of a computational model for the calculation of the dynamic and ionization-and-optical characteristics of interacting plasma flows. Results of preliminary numerical investigations are given.     

Metal encapsulation in zeolite particles: A rational design of zeolite-supported catalyst with maximum site activity

Zeolite-supported metal catalysts have been proven effective in many important catalytic reactions, such as hydrogenation, Fisher-Tropsch synthesis, automobile exhaust catalysis, selective catalytic reduction and many others. Despite the successful preparation of the catalyst through widely adopted methods, including ion exchange and impregnation, the metal dispersion over the zeolite is lack of control with high randomness. This renders the so-called “catalytic performance” an overall contribution from the metal sites located inside the zeolite micropores and those located on the external surface. This is exceptionally true for small to medium pore zeolites with typical free apertures of 0.3–0.6 nm (such as LTA and MFI). A more rational design of zeolite-supported metal catalysts is by encapsulating the metal nanoparticles or clusters within zeolite pores prior to the zeolite formation. Encapsulation of metals in zeolite prevents them from sintering and sulphur poisoning by cage confinement and molecular exclusion (via well-defined pore size and shape), respectively. This paper gives a new perspective on using metal clusters and nanoparticles as catalysts and the design of an effective zeolite-supported catalytic system.     

Comparing a Pharmaceutical and an Agro-food Bioregion: On the Importance of Knowledge Bases for Socio-spatial Patterns of Innovation

The aim of this paper is to compare the socio-spatial patterns of innovation and knowledge linkages of a biopharmaceutical and an agro-food biotech cluster. Dissimilarities can be expected based on differences in terms of historical technological regimes and sectoral innovation system dynamics between the agro-food and pharmaceutical industries in general and particularly the distinctive analytical (science-based) knowledge base of biopharmaceuticals in contrast with the more synthetic (engineering-based) knowledge base of agro-food biotechnology. Drawing on bibliometric data and case material the study compares two representative bioregions: a biopharmaceutical cluster in Scania, Sweden and an agro-food biotech cluster in Saskatoon, Canada. The empirical study supports the theoretical expectations and shows that knowledge dynamics in the agro-food cluster are more localized than in the biopharmaceuticals cluster. It is important, however, to acknowledge that these differences are relative. Both sectors display local and non-local patterns of collaboration following the general pattern for biotechnology.