Atom diffusion of small Cu clusters across facet–facet barriers over Cu{1 1 1} surfaces

Aguilar, Boris; Flores, José C; Coronado, Alberto M.; Huang, Hanchen

doi:10.1088/0965-0393/15/5/003

Cited by 9 publications

(5 citation statements)

References 16 publications

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“…Due to the dimer's and trimer's increased degrees of freedom entirely new diffusion mechanisms are observed in simulations. For weakly bound atomic chains, incorporation effects at step-edges result in degeneracy of the step-edge barriers, [23][24][25][26] and new preferred diffusion paths are identified that otherwise are energetically unfavorable for single atoms or for rigid atomic chains. 27 Nowadays, conjugated organic molecules (COMs) are extensively studied with respect to their optoelectronic properties as they are used as organic semiconductors in a variety of applications such as field-effect transistors, light-emitting diodes or photovoltaic cells.…”

Section: Introductionmentioning

confidence: 99%

Characterization of step-edge barrier crossing of para-sexiphenyl on the ZnO (101̄0) surface

Pałczynski

Herrmann

Heimel

et al. 2016

Phys. Chem. Chem. Phys.

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Mass transport processes of conjugated organic molecules (COMs) on inorganic surfaces are essential elements in thin film deposition for hybrid optoelectronic devices. Defects and in particular surface step-edges dictate the molecular nucleation and growth morphology, which itself determine many physical properties of the resulting hybrid interface. Here, we explore the detailed molecular kinetics and transport rates of a single physisorbed para-sexiphenyl (p-6P) molecule crossing a step-edge (a "hetero-Ehrlich-Schwoebel barrier") on the inorganic ZnO (101[combining macron]0) surface by a combination of all-atom molecular dynamics simulations and passage time theory. We determine temperature- and charge-dependent (free) energy landscapes, position-dependent diffusion coefficients, and ultimately the mean first passage time over the step-edges. We find two completely different step-edge crossing mechanisms, the occurrence and rates of which simultaneously depend on both electrostatic and thermal molecule-surface coupling. In weakly coupled systems, the molecule crosses the step relatively quickly (in nanoseconds) by log-roll mechanisms while for strongly coupled systems, it crosses relatively slowly (in microseconds) in a strictly perpendicular fashion. In the latter process, "internal friction" from intramolecular bending and torsional degrees of freedom contribute a significant corrugation to the overall crossing barrier. Furthermore, we show that crossing pathways can also change qualitatively with step-edge height. The great complexity in hetero-barrier crossing of COMs (in contrast to simple atoms) revealed in this study has implications on the interpretation and possible control of nucleation and growth mechanisms at surface defects in hybrid systems.

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Section: Introductionmentioning

confidence: 99%

Characterization of step-edge barrier crossing of para-sexiphenyl on the ZnO (101̄0) surface

Pałczynski

Herrmann

Heimel

et al. 2016

Phys. Chem. Chem. Phys.

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“…The importance of these dynamical processes extends, for example, to metal oxidation rates 1,2 and functionality ͑catalytic, magnetic, etc.͒ of supported heterogeneous materials when surface/volume ratio and/or a complex structural pattern formation become important. 3,4 A good deal of work has thus been dedicated to explaining the motion of adatom clusters on surfaces in homoepitaxial metallic systems [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and, more recently, in heteroepitaxial systems. 15,[22][23][24][25] Heteroepitaxy of course exhibits a broad variety of growth modes and diffusion processes but, at the same time, introduces factors beyond those that need be considered in homoepitaxial models in order to comprehend the diffusivity of adatom clusters.…”

Section: Introductionmentioning

confidence: 99%

Diffusion of the Cu monomer and dimer on Ag(111): Molecular dynamics simulations and density functional theory calculations

et al. 2010

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We present results of molecular dynamics ͑MD͒ simulations and density functional theory ͑DFT͒ calculations of the diffusion of Cu adatom and dimer on Ag͑111͒. We have used potentials generated by the embedded-atom method for the MD simulations and pseudopotentials derived from the projected-augmentedwave method for the DFT calculations. The MD simulations ͑at three different temperatures: 300, 500, and 700 K͒ show that the diffusivity has an Arrhenius behavior. The effective energy barriers obtained from the Arrhenius plots are in excellent agreement with those extracted from scanning tunneling microscopy experiments. While the diffusion barrier for Cu monomers on Ag͑111͒ is higher than that reported ͑both in experiment and theory͒ for Cu͑111͒, the reverse holds for dimers ͓which, for Cu͑111͒, has so far only been theoretically assessed͔. In comparing our MD result with those for Cu islets on Cu͑111͒, we conclude that the higher barriers for Cu monomers on Ag͑111͒ results from the comparatively large Ag-Ag bond length, whereas for Cu dimers on Ag͑111͒ the diffusivity is taken over and boosted by the competition in optimization of the Cu-Cu dimer bond and the five nearest-neighbor Cu-Ag bonds. Our DFT calculations confirm the relatively large barriers for the Cu monomer on Ag͑111͒-69 and 75 meV-compared to those on Cu͑111͒ and hint a rationale for them. In the case of the Cu dimer, the relatively long Ag-Ag bond length makes available a diffusion route whose highest relevant energy barrier is only 72 meV and which is not favorable on Cu͑111͒. This process, together with another involving an energy barrier of 83 meV, establishes the possibility of low-barrier intercell diffusion by purely zigzag mechanisms.

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“…Adatoms diffusing over multiple-layer steps experience even larger energy barriers [ 6 - 9 ]; this barrier is referred to as three-dimensional (3D) ES barrier; for comparison, the conventional ES barrier is called the two-dimensional (2D) ES barrier. Further, even small clusters experience 3D ES barriers [ 10 ], and variations of 3D ES barriers exist when steps intersect [ 11 , 12 ].…”

Section: Introductionmentioning

confidence: 99%

From covalent bonding to coalescence of metallic nanorods

Lee

Huang

2011

Nanoscale Res Lett

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Growth of metallic nanorods by physical vapor deposition is a common practice, and the origin of their dimensions is a characteristic length scale that depends on the three-dimensional Ehrlich-Schwoebel (3D ES) barrier. For most metals, the 3D ES barrier is large so the characteristic length scale is on the order of 200 nm. Using density functional theory-based ab initio calculations, this paper reports that the 3D ES barrier of Al is small, making it infeasible to grow Al nanorods. By analyzing electron density distributions, this paper shows that the small barrier is the result of covalent bonding in Al. Beyond the infeasibility of growing Al nanorods by physical vapor deposition, the results of this paper suggest a new mechanism of controlling the 3D ES barrier and thereby nanorod growth. The modification of local degree of covalent bonding, for example, via the introduction of surfactants, can increase the 3D ES barrier and promote nanorod growth, or decrease the 3D ES barrier and promote thin film growth.

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Atom diffusion of small Cu clusters across facet–facet barriers over Cu{1 1 1} surfaces

Cited by 9 publications

References 16 publications

Characterization of step-edge barrier crossing of para-sexiphenyl on the ZnO (101̄0) surface

Characterization of step-edge barrier crossing of para-sexiphenyl on the ZnO (101̄0) surface

Diffusion of the Cu monomer and dimer on Ag(111): Molecular dynamics simulations and density functional theory calculations

From covalent bonding to coalescence of metallic nanorods

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