Diffusion of Palladium Clusters on Magnesium Oxide

Barcaro, Giovanni; Fortunelli, Alessandro; Nita, Florin; Ferrando, Riccardo

doi:10.1103/physrevlett.95.246103

Cited by 63 publications

(60 citation statements)

References 15 publications

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“…Surprisingly, the prefactors of different processes vary by more than a factor of 2000. This is quite different than recent molecular dynamics simulations using an analytic potential, which found that the prefactors for these processes ''all fall in the range of 2 · 10 12 s À1 '' [39].…”

Section: Diffusion Of Pd Clusterscontrasting

confidence: 41%

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Pd diffusion on MgO(100): The role of defects and small cluster mobility

Henkelman

Campbell

et al. 2006

Surface Science

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Density functional theory is used to explore the energy landscape of Pd atoms adsorbed on the terrace of MgO(1 0 0) and at oxygen vacancy sites. Saddle point finding methods reveal that small Pd clusters diffuse on the terrace in interesting ways. The monomer and dimer diffuse via single atom hops between oxygen sites with barriers of 0.34 eV and 0.43 eV respectively. The trimer and tetramer, however, form 3D clusters by overcoming a 2D-3D transition barrier of less than 60 meV. The trimer diffuses along the surface either by a walking or flipping motion, with comparable barriers of ca. 0.5 eV. The tetramer rolls along the terrace with a lower barrier of 0.42 eV. Soft rotational modes at the saddle point lead to an anomalously high prefactor of 1.3 · 10 14 s À1 for tetramer diffusion. This prefactor is two order of magnitude higher than for monomer diffusion, making the tetramer the fastest diffusing species on the terrace at all temperatures for which diffusion is active (above 200 K). Neutral oxygen vacancy sites are found to bind Pd monomers with a 2.63 eV stronger binding energy than the terrace. A second Pd atom, however, binds to this trapped monomer with a smaller energy of 0.56 eV, so that dimers at defects dissociate on a time scale of milliseconds at room temperature. Larger clusters bind more strongly at defects. Trimers and tetramers dissociate from monomer-bound-defects at elevated temperatures of ca. 600 K. These species are also mobile on the terrace, suggesting they are important for the ripening observed at P600 K during Pd vapor deposition on MgO(1 0 0) by Haas et al.

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Section: Diffusion Of Pd Clusterscontrasting

confidence: 41%

“…A brief communication of some of these kinetic results has been published previously [38] (see also Ref. [39]). Here we describe a systematic atomic-scale study of the formation and diffusion mechanisms of small Pd clusters (Pd 1 to Pd 4 ) on MgO(1 0 0), with and without oxygen vacancy defects.…”

Section: Introductionmentioning

confidence: 99%

Pd diffusion on MgO(100): The role of defects and small cluster mobility

Henkelman

Campbell

et al. 2006

Surface Science

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“…In this study, we build upon the many experimental and theoretical studies that have been devoted to understanding Pd particle growth, ripening and energetics on MgO(1 0 0) [2,[14][15][16][17][18][19]. Our main goals are to connect the microscopic transition mechanisms with ripening dynamics on experimental time scales through the use of kinetic Monte Carlo simulations, and to explore the implications of recent DFT calculations of Pd cluster energies and migration rates on perfect and defective MgO(1 0 0) [20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Kinetic Monte Carlo simulations of Pd deposition and island growth on MgO(100)

Campbell

Jónsson

et al. 2007

Surface Science

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“…Indeed, studies of dynamic properties (e.g. diffusion) of supported particles are limited to the smallest entities (dimers, trimers, tetramers) [78][79][80], and even in these simplest cases static evaluation of the energy barriers is often privileged [79,80]. However, as the system complexity increases, an input from moleculardynamics calculations becomes necessary in order to identify possible diffusion mechanisms (see e.g.…”

Section: Towards Realistic Simulationsmentioning

confidence: 99%

“…Ref. [80], where the PES [26] has been used). Indeed, the simple PES approach can be easily extended as to provide an efficient description of oxide-supported metal clusters at finite temperatures.…”

Section: Towards Realistic Simulationsmentioning

confidence: 99%

Non‐reactive metal/oxide interfaces: from model calculations towards realistic simulations

Goniakowski¹,

Mottet

Noguera

2006

Physica Status Solidi (b)

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International audienceIn the last decade two principal factors have stimulated the progressive regain of interest for non-reactive metal/oxide interfaces. On one hand, the efforts invested by the community of model catalysis in analyzing the reactivity properties of supported metal nano-clusters have resulted in an abundance of high quality experimental data. They have also risen several precise questions on the direct and indirect role played by the substrate in the determination of catalytic properties of deposited metal particles, and have thus reiterated the interrogations concerning the nature of interactions at the metal/oxide interfaces. On the other hand, conceptual improvements of first-principles calculations, such as implementations of various GGA functionals, have added enormously to the reliability of these methods, and have enlarged considerably their field of application. However, most ab initio simulations are sooner or later confronted to the constrains on the computational cost, inherent of this kind of approaches. It concerns principally the limited size of systems which can be treated in practice, a factor which turns out to be particularly limiting in realistic studies of interfaces, where the mismatch of lattice parameters is at the origin of incommensurate interface structures, long-range reconstructions, or/and complex structural deformations and dislocations. In this context, the goal of this paper is two-fold. First, we give an overview of essential metal/oxide interface characteristics as obtained from ab initio calculations on model systems, with a special focus on late transition metals, such as Pd, and on a highly ionic oxide substrate, such as MgO. It includes results on the relation between the strength of interfacial interaction and the type of deposited metal (transition, noble), the nature of metal deposit (isolated atoms, constituted interface), and the character of the substrate (non-polar, polar). We also comment on effects due to defects at the oxide surface. Secondly, we describe an effective approach to simulate non-reactive deposition of nano-scale metal objects on a surface of highly ionic oxide. The core of this approach is a many-body potential energy surface (PES) constructed on the basis of results of ab initio calculations for model metal/oxide interface structures. We present its application to studies on the deposition of late transition metals (Pd, Ag) on the MgO(100) surface, including the determination of substrate-induced change of equilibrium atomic structure and morphology of metal nano-clusters, the analysis of stress release at the interface, and the investigation of the role of the oxide substrate on the melting properties of supported clusters. (c) 2006 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim

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Diffusion of Palladium Clusters on Magnesium Oxide

Cited by 63 publications

References 15 publications

Pd diffusion on MgO(100): The role of defects and small cluster mobility

Pd diffusion on MgO(100): The role of defects and small cluster mobility

Kinetic Monte Carlo simulations of Pd deposition and island growth on MgO(100)

Non‐reactive metal/oxide interfaces: from model calculations towards realistic simulations

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