5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

The structural properties of free nanoclusters are reviewed. Special attention is paid to the interplay of energetic, thermodynamic, and kinetic factors in the explanation of cluster structures that are actually observed in experiments. The review starts with a brief summary of the experimental methods for the production of free nanoclusters and then considers theoretical and simulation issues, always discussed in close connection with the experimental results. The energetic properties are treated first, along with methods for modeling elementary constituent interactions and for global optimization on the cluster potential-energy surface. After that, a section on cluster thermodynamics follows. The discussion includes the analysis of solid-solid structural transitions and of melting, with its size dependence. The last section is devoted to the growth kinetics of free nanoclusters and treats the growth of isolated clusters and their coalescence. Several specific systems are analyzed.

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Structural properties of nanoclusters: Energetic, thermodynamic, and kinetic effects

Surface studies of supported model catalysts

Metal nanoparticles have been the subject of widespread research over the past two decades. In recent years, noble metals have been the focus of numerous studies involving synthesis, characterization, and applications. Synthesis of an impressive range of noble metal nanoparticles with varied morphologies has been reported. Researchers have made a great progress in learning how to engineer materials on a nanometer length scale that has led to the understanding of the fundamental size- and shape-dependent properties of matter and to devising of new applications. In this article, we review the recent progress in the colloid-chemical synthesis of nonspherical nanoparticles of a few important noble metals (mainly Ag, Au, Pd, and Pt), highlighting the factors that influence the particle morphology and discussing the mechanisms behind the nonspherical shape evolution. The article attempts to present a thorough discussion of the basic principles as well as state-of-the-art morphology control in noble metal nanoparticles.

Nonspherical Noble Metal Nanoparticles: Colloid-Chemical Synthesis and Morphology Control

Data on the experimental structure of small particles is reviewed, the emphasis being an attempt to correlate experimental information with theoretical models. First, a general discussion of some of the controlling factors is presented, primarily equilibrium shapes of small particles, the effect of surface stresses, kinetics, and the role of chemisorption and the substrate. Experimental techniques for obtaining information about small particles are then described, primarily electron microscopy approaches. Experimental data on the static structure of small particles is then reviewed, both single crystals and the many, complicated twinned structures in face-centred cubic materials. An overview is then given of some of the more recent results on dynamic phenomena in small particles. Finally, a general model merging thermodynamic and kinetic factors is presented to attempt to rationalize the available data, followed by a brief discussion.

Experimental studies of small particle structures

Configuration of a photovoltaic (PV) power generator has influence on the operation of the generator, especially if it is prone to partial shading. In this paper, the mismatch losses and the power losses due to failure in tracking of the global maximum power point of a long string of 18 series-connected PV modules and three short strings of six series-connected PV modules connected in parallel are investigated under different partial shading conditions by using a MATLAB Simulink simulation model. The generators with parallel-connected short strings are studied in case when they have the same operating voltage and when they operate as separate strings. The results show that long series connection of modules and parallel connections of strings via a single inverter to the electrical grid should be minimized to avoid losses in case of partial shading conditions. Under partial shading conditions, short strings operating separately have the lowest power losses.

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Power Losses in Long String and Parallel-Connected Short Strings of Series-Connected Silicon-Based Photovoltaic Modules Due to Partial Shading Conditions

A Monte-Carlo simulation technique based on the screened Rutherford differential cross section for the elastic scattering and Gryzinski's semiempirical expression for the inelastic core and valence electron excitation is used to describe electrons and positrons slowing down in solids. The theoretical results are compared with the experimental backscattering, absorption and transmission results for aluminum, silicon, copper, and gold thin film and semi-infinite targets and good agreement is observed. The simulated stopping profiles are fitted with a simple analytic expression. The profiles are Laplace-transformed to give a useful data base for analyzing phenomena associated with slow positron re-emission from solids.

Monte-Carlo calculations of keV electron and positron slowing down in solids

A photovoltaic (PV) generator is internally a power-limited nonlinear current source having both constant-current- and constant-voltage-like properties depending on the operating point. This paper investigates the dynamic properties of a PV generator and demonstrates that it has a profound effect on the operation of the interfacing converter. The most important properties an input source should have in order to emulate a real PV generator are defined. These properties are important, since a power electronic substitute is often used in the validation process instead of a real PV generator. This paper also qualifies two commercial solar array simulators as an example in terms of the defined properties. Investigations are based on extensive practical measurements of real PV generators and the two commercial solar array simulators interfaced with dc-dc as well as three- and single-phase dc-ac converters.

Seppo Valkealahti

Papers

Power Losses in Long String and Parallel-Connected Short Strings of Series-Connected Silicon-Based Photovoltaic Modules Due to Partial Shading Conditions

Monte-Carlo calculations of keV electron and positron slowing down in solids

Photovoltaic Generator as an Input Source for Power Electronic Converters

Size-dependent icosahedral-to-fcc structure change confirmed in unsupported nanometer-sized copper clusters

Dynamic thermal model of solar PV systems under varying climatic conditions