Exotic Behavior of the Outer Shell of Bimetallic Nanoalloys

Delfour, L.; Creuze, Jérôme; Legrand, Bernard

doi:10.1103/physrevlett.103.205701

Cited by 49 publications

(34 citation statements)

References 23 publications

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“…Besides being poorly miscible in bulk phases 42 , these systems have the element of larger atomic radius (Ag or Au) presenting smaller cohesive and surface energies than the other element. These features are all in favour of Ag or Au surface segregation in these nanoparticles, a behaviour that has been confirmed, both experimentally and computationally, by several studies 2,[5][6][7][9][10][11][13][14][15][16][17][19][20][21][22][23][24][25][29][30][31][32]35 . However, the fact that the cluster surface is expected to contain mostly Ag or Au does not determine completely chemical ordering.…”

Section: Introductionmentioning

confidence: 75%

Morphological instability of core-shell metallic nanoparticles

Bochicchio¹,

Ferrando²

2013

Phys. Rev. B

217

209

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Bimetallic nanoparticles (often known as nanoalloys) with core-shell arrangement are of special interest in several applications, such as in optics, catalysis, magnetism and biomedicine. Despite wide interest in applications, the physical factors stabilizing the structures of these nanoparticles are still unclear to a great extent, especially for what concerns the relationship between geometric structure and chemical ordering pattern. Here global-optimization searches are performed in order to single out the most stable chemical ordering patterns corresponding to the most important geometric structures, for a series of weakly miscible systems, including AgCu, AgNi, AgCo and AuCo. The calculations show that (i) the overall geometric structure of the nanoalloy and the shape and placement of its inner core are strictly correlated; (ii) centered cores can be obtained in icosahedral nanoparticles but not in crystalline or decahedral ones, in which asymmetric quasi-Janus morphologies form; (iii) in icosahedral nanoparticles, when the core exceeds a critical size, a new type of morphological instability develops, making the core asymmetric and extending it towards the nanoparticle surface; (iv) multi-center patterns can be obtained in polyicosahedral nanoalloys.Analogies and differences between the instability of the core in icosahedral nanoalloys and the StranskiKrastanov instability occurring in thin-film growth are discussed. All these issues are crucial for designing strategies to achieve effective coatings of the cores.a Corresponding author,

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Section: Introductionmentioning

confidence: 75%

Morphological instability of core-shell metallic nanoparticles

Bochicchio¹,

Ferrando²

2013

Phys. Rev. B

217

209

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“…Finally, empirical potentials are most efficient by dispensing completely with the quantum nature of the problem. If properly parameterized, they can provide useful semiquantitative information for clusters with more than 1,000 atoms or for the more complex case of nanoalloys (89,90). Electronic shell: the valence electrons in metal clusters are arranged in electronic shells due to angular momentum restrictions (like the electrons in an atom); particularly stable clusters occur at electronic shell closings Premelting: a peak or a shoulder in the heat capacity at a lower temperature than the melting transition of the caloric curve is the canonical heat capacity.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Melting and Freezing of Metal Clusters

Aguado

Jarrold

2011

Annu. Rev. Phys. Chem.

111

108

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Recent developments allow heat capacities to be measured for size-selected clusters isolated in the gas phase. For clusters with tens to hundreds of atoms, the heat capacities determined as a function of temperature usually have a single peak attributed to a melting transition. The melting temperatures and latent heats show large size-dependent fluctuations. In some cases, the melting temperatures change by hundreds of degrees with the addition of a single atom. Theory has played a critical role in understanding the origin of the size-dependent fluctuations, and in understanding the properties of the liquid-like and solid-like states. In some cases, the heat capacities have extra features (an additional peak or a dip) that reveal a more complex behavior than simple melting. In this article we provide a description of the methods used to measure the heat capacities and provide an overview of the experimental and theoretical results obtained for sodium and aluminum clusters.

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“…and automatically include statistical fluctuations, which are required to analyze the stability of small systems, inasmuch the different thermodynamic ensembles of finite systems are not equivalent. These approaches have been used to analyze the stability of specific particles and to explain non-trivial transformations such as the transition between the high miscibility in Cs 3 Na nanoparticles at low temperature and a demixtion at room temperature, 9 the dynamical equilibrium of the outer shell of Cu-Ag nanoalloys, 10 the formation of core-shell in size mismatched nano-alloys, 11 and the ordering in Au-Pd nanoalloys. 12 Using atomic approaches, the definition of a relevant size dependent phase diagram is much more complicated than with continuum approaches.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of phase-separating nanoalloys: Single particles and particle assemblies

2018

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The aim of this paper is to investigate the consequences of finite size effects on the thermodynamics of nanoparticle assemblies and isolated particles. We consider a binary phase separating alloy with a negligible atomic size mismatch and equilibrium states are computed using off-lattice Monte Carlo simulations in several thermodynamic ensembles. First, semi-grand canonical ensemble is used to describe infinite assemblies of particle with the same size. When decreasing the particle size, we obtain a significant decrease of the solid/liquid transition temperatures as well as a growing asymmetry of the solid state miscibility gap related to surface segregation effects. Second, a canonical ensemble is used to analyze the thermodynamic equilibrium of finite monodisperse particle assemblies. Using a general thermodynamic formulation, we show that a particle assembly may split into two sub-assemblies of identical particles. Moreover, if the overall average canonical concentration belongs to a discrete spectrum, the sub-assemblies concentrations are equal to the semi-grand canonical equilibrium ones. We also show that the equilibrium of a particle assembly with a prescribed size distribution combines a size effect and the fact that a given particle size assembly can adopt two configurations. Finally, we have considered the thermodynamics of an isolated particle to analyze whether a phase separation can be defined within a particle. When studying rather large nanoparticles, we found that the region in which a two-phase domain can be identified inside a particle is well below the bulk phase diagram but the concentration of the homogeneous core remains very close to the bulk solubility limit.

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Exotic Behavior of the Outer Shell of Bimetallic Nanoalloys

Cited by 49 publications

References 23 publications

Morphological instability of core-shell metallic nanoparticles

Morphological instability of core-shell metallic nanoparticles

Melting and Freezing of Metal Clusters

Thermodynamics of phase-separating nanoalloys: Single particles and particle assemblies

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