1,721,319 research outputs found
Determining the equilibrium structures of nanoalloys by computational methods
No full textNanoalloys are bi- or multi-metallic nanoparticles with sizes in the range between 1 and 100 nm. They are the subject of intense research activity in the last decades, both in experiments and in theory/modelling. From a theoretical point of view, determining the equilibrium structure of nanoalloys at different temperatures is a quite complex task, which has stimulated the developments of specifically tailored methods and algorithms. Here, we review some recent developments in this field, considering first methods for the global optimization of nanoalloys, and then methods for studying their finite-temperature equilibrium properties
Symmetry breaking and morphological instabilities in core-shell metallic nanoparticles
No full textNanoalloys are bi- or multi-component metallic particles in the size range between 1 and 100 nm. Nanoalloys present a wide variety of structures and properties, which make them suitable for many applications in catalysis, optics, magnetism and biomedicine. This topical review is devoted to the structural properties of nanoalloys of weakly miscible metals, which are expected to present phase-separated arrangements of their components, such as core-shell and Janus arrangements. The focus is on singling out size- and composition-dependent transitions between these arrangements, showing that several transitions can be rationalized by a unifying concept, that is symmetry breaking, caused by the accumulation of strain at the atomic level and its subsequent release. The driving forces that rule the interplay between core-shell and other structures and determine the actual shapes of core and shell, and the placement of the core inside the shell are analyzed. Several systems, such as Ag - Cu, Ag - Co, Ag - Ni, Au - Co, Au - Pt, and Ir - Pt are treated, comparing computational results to experimental observations and simple analytical models. After treating the lowest-energy structures, which are representative of the equilibrium configurations at sufficiently low temperatures, high-temperature and growth kinetics effects are considered
Structure and Properties of Nanoalloys
No full textStructure and Properties of Nanoalloys is devoted to the topic of alloy nanoparticles, the bi-or multicomponent metallic nanoparticles that are often called nanoalloys. The interest in nanoalloys stems from the wide spectrum of their possible applications in the fields of catalysis, magnetism, and optics. Nanoalloys are also interesting from a basic science point-of-view due to the complexity of their structures and properties. Nanoalloys are presently a very lively research area, with impressive developments in the last ten years. This book meets the need to systematize the wealth of experimental and computational results generated over the last decade
Solid-solid transitions in Pd-Pt nanoalloys
No full textSolid-solid transformations in Pd-Pt nanoalloys in the size range 32-38 atoms and for different compositions are computationally studied by the superposition approximation to the partition function, and by molecular dynamics simulations. A broad spectrum of transition types is shown to take place. These transition types are: (i) one-to-one type, in which the global minimum, which is dominant at low temperatures, transforms into another single isomer with increasing temperature; (ii) one-to-many type, in which the transition is from a single isomer to a family of other isomers; (iii) many-to-many type, in which the transition is between two different families of isomers; (iv) many-to-one type, in which the effect of vibrational entropy is to greatly reduce the number of relevant structures with increasing temperatures. We provide a rationale for these behaviors, which stem from the interplay between energetics and vibrational entropy effects. The vibrational entropy is explained by analyzing the vibrational density of states and the specific features of the normal modes. Quantum effects on the structural transitions are also discussed
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