Single-component surface in binary self-assembled NaK nanoalloy clusters

Tchaplyguine, Maxim; Legendre, Sébastien; Rosso, Aldana; Bradeanu, I. L.; Öhrwall, Gunnar; Canton, Sophie E.; Andersson, Tomas; Mårtensson, Nils; Svensson, S.; Björneholm, Olle

doi:10.1103/physrevb.80.033405

Cited by 18 publications

(29 citation statements)

References 18 publications

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“…The additional degrees of freedom result in a rich diversity of structural and electronic behaviors, which can be fine tuned in order to optimize the catalytic selectivity for a particular chemical reaction, for example. Many experimental [1][2][3][4][5][6][7] and theoretical efforts have thus been devoted in recent years in order to understand the properties of nanoalloys at a fundamental level.…”

Section: Introductionmentioning

confidence: 99%

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Aguado

López²

2011

The Journal of Chemical Physics

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We locate the putative global minimum structures of Na x Cs 55−x and Li x Cs 55−x nanoalloys through combined empirical potential and density functional theory calculations, and compare them to the structures of 55-atom Li-Na and Na-K nanoalloys obtained in a recent paper [A. Aguado and J. M. López, J. Chem. Phys. 133, 094302 (2010)]. Alkali nanoalloys are representative of isovalent metallic mixtures with a strong tendency towards core-shell segregation, and span a wide range of size mismatches. By comparing the four systems, we analyse how the size mismatch and composition affect the structures and relative stabilities of these mixtures, and identify useful generic trends. The Na-K system is found to possess a nearly optimal size mismatch for the formation of poly-icosahedral (pIh) structures with little strain. In systems with a larger size mismatch (Na-Cs and Li-Cs), frustration of the pIh packing induces for some compositions a reconstruction of the core, which adopts instead a decahedral packing. When the size mismatch is smaller than optimal (Li-Na), frustration leads to a partial amorphization of the structures. The excess energies are negative for all systems except for a few compositions, demonstrating that the four mixtures are reactive. Moreover, we find that Li-Cs and Li-Na mixtures are more reactive (i.e., they have more negative excess energies) than Na-K and Na-Cs mixtures, so the stability trends when comparing the different materials are exactly opposite to the trends observed in the bulk limit: the strongly non-reactive Li-alkali bulk mixtures become the most reactive ones at the nanoscale. For each material, we identify the magic composition x m which minimizes the excess energy. x m is found to increase with the size mismatch due to steric crowding effects, and for Li x Cs 55−x the most stable cluster has almost equiatomic composition. We advance a simple geometric packing rule that suffices to systematize all the observed trends in systems with large size mismatch (Na-K, Na-Cs, and Li-Cs). As the size mismatch is reduced, however, electron shell effects become more and more important and contribute significantly to the stability of the Li-Na system.

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Section: Introductionmentioning

confidence: 99%

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Aguado

López²

2011

The Journal of Chemical Physics

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“…Aluminum, which has higher cohesive energy (3.4 eV against 1.6 eV for Yb 33 ) and which atoms are much smaller in size, is energetically considerably more favorable to place in the core. The reduction of the total energy of an atomic ensemble in the process of condensation from the vapor to the solid should be higher for a segregated final configuration, as has been experimentally observed by us for several bi-component nanoparticles produced by the same method (Yb/YbO, 16 NaK, 17 CuAg, 18 and Pb/PbO 19 ). The exposure of segregated Yb-Al nanoalloy particles to molecular oxygen oxidizes at least the outer shell of Yb atoms.…”

Section: Discussionmentioning

confidence: 82%

“…2 As in our previous works on bi-metallic nanoparticles, out of sodium and potassium, 17 and out of copper and silver, 18 the radial segregation has been explained by the difference in cohesive energy and atomic size of the two elements involved. The mobility in the formation process was high enough for the element with the lower cohesive energy to migrate to the surface of the particles.…”

Section: Introductionmentioning

confidence: 99%

“…17 Potassium on the surface reduced the vacuum-referenced Na 2p corelevel energy of sodium present only in the core by the amount corresponding to the work-function difference between K and Na metals. As we argued in the NaK studies, in the self-assembling process it is energetically favorable to place the high cohesive-energy element -Na in the NaK alloy or Al in the Yb-Al alloy -into the nanoparticle core.…”

Section: A Element Distribution In Free Yb-al Nanoalloy Particles Asmentioning

confidence: 99%

“…The fabrication method is based on vapor aggregation in a cryostat, [17][18][19] resulting in a collimated beam of nanoparticles propagating in vacuum. Thanks to its combined elementand site-sensitivity synchrotron radiation-based photoelectron spectroscopy (PES) could be successfully employed in the present work to disclose the free nanoparticles' chemical composition and structure and that -"on the fly."…”

Section: Introductionmentioning

confidence: 99%

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Alloying and oxidation of in situ produced core-shell Al@Yb nanoalloy particles—An “on-the-fly” study

Zhang

Andersson

Mikkelä

et al. 2014

The Journal of Chemical Physics

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Core-shell-structured nanoalloy particles with an Al-dominated interior covered by few Yb monolayers have been fabricated using a vapor-aggregation method involving magnetron sputtering. The radially segregated structure of the Yb-Al nanoparticles has been disclosed by “on-the-fly” photoelectron spectroscopy monitoring of the nanoparticle beam in Yb 4f and Al 2p electron binding energy regions. Both, the binding energy values and the electron microscopy images taken on the deposited nanoparticles, allow estimating their dimensions to be in the 5–10 nm range. The photoelectron spectroscopy results suggest that in these nanoparticles no trivalent Yb – the typical case for the macroscopic Yb-Al alloy – is present. The oxidation of preformed Yb-Al nanoparticles was successfully attempted, leading to the appearance of divalent Yb surface oxide – in contrast to the bulk macroscopic Yb which is trivalent in the oxide. Our results suggest that at intermediate oxygen exposures “sandwich-like” nanoparticles of YbO/Yb/Al were synthesized. At higher O2 exposures, the oxygen seems to penetrate all the way to the Yb-Al interface. The results of the present study have to be considered when photonic applications of Yb-doped garnet nanoparticles are planned.

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A detailed investigation on the global minimum structures of mixed rare‐gas clusters: Geometry, energetics, and site occupancy

Marques

Pereira

2012

J Comput Chem

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We performed a global minimum search of mixed rare-gas clusters by applying an evolutionary algorithm (EA), which was recently proposed for binary atomic systems (Marques and Pereira, Chem. Phys. Lett. 2010, 485, 211). Before being applied to the potentials used in this work, the EA was further tested against results previously reported for the Ar(N)Xe(38-N) clusters and several new putative global minima were discovered. We employed either simple Lennard-Jones (LJ) potentials or more realistic functions to describe pair interactions in Ar(N)Kr(38-N), Ar(N)Xe(38-N), and Kr(N)Xe(38-N) clusters. The long-range tail of the pair-potentials shows some influence on the energetic features and shape of the structure of clusters. In turn, core-shell type structures are mostly observed for global minima of the binary rare-gas clusters, for both accurate and LJ potentials. However, the long-range tail of the potential may have influence on the type of atoms that segregate on the surface or form the core of the cluster. While relevant differences for the preferential site occupancy occur between the two potentials for Ar(N)Kr(38-N) (for N > 21), the type of atoms that segregate on the surface for Ar(N)Xe(38-N) and Kr(N)Xe(38-N) clusters is unaffected by the accuracy of the long-range part of the interaction in almost all cases. Moreover, the global minimum search for model-potentials in binary systems reveals that the surface-site occupancy is mainly determined by the combination of two parameters: the size ratio of the two types of particles forming the cluster and the minimum-energy ratio corresponding to the pair-interactions between unlike atoms.

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Single-component surface in binary self-assembled NaK nanoalloy clusters

Cited by 18 publications

References 18 publications

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Alloying and oxidation of in situ produced core-shell Al@Yb nanoalloy particles—An “on-the-fly” study

A detailed investigation on the global minimum structures of mixed rare‐gas clusters: Geometry, energetics, and site occupancy

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