Crucial electronic contributions to measures of surface diffusion by He atom scattering

Fratesi, Guido; Alexandrowicz, Gil; Trioni, M. I.; Brivio, Gian Paolo; Allison, W.

doi:10.1103/physrevb.77.235444

Cited by 24 publications

(20 citation statements)

References 25 publications

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“…11 More recently, the much improved resolution of the 3 He spin-echo technique 12 has allowed for a deeper analysis of the diffusion process at larger coverage. 13 This study interpreted in terms of collective phenomena a coverage dependence of Na surface diffusion previously reported and unexplained: 14,15 indeed, the diffusion process involves nontrivial electrondensity rearrangements, 16,17 a phenomenon further showing the complexity of such systems. Additionally to the information on the given studied system, high-precision HAS measurements may act as a reference to other experimental and theoretical methods.…”

Section: Introductionsupporting

confidence: 67%

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Potential energy surface of alkali atoms adsorbed on Cu(001)

Fratesi

2009

Phys. Rev. B

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We report a comprehensive density-functional theory ͑DFT͒ calculation of the lateral adiabatic potentialenergy surface ͑PES͒ of individual alkali atoms adsorbed on the Cu͑001͒ surface. The corrugation of the PES monotonically decreases by one order of magnitude from Li to Cs, the latter being mobile on the surface even at low temperatures. Substrate relaxations in metastable configurations are consistent with a harmonic response to the adsorbate and account for a significant fraction of the PES corrugation. A simple nonseparable cosine expression provides a good description of values computed between high-symmetry configurations. Results are in good agreement with published He atom scattering measures of surface diffusion, especially at the saddle point, and with structural characterization, pointing out the accuracy of DFT calculations for this class of systems.

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Section: Introductionsupporting

confidence: 67%

“…The value of E dd has been previously adopted as a measure of local concentration of adsorbates for generic distributions of alkali atoms. 13,16 As already done for Na, 21 we define a refined adsorption energy by subtracting such dipole-dipole contribution, using the value of obtained by the corresponding DFT calculation…”

Section: Methodsmentioning

confidence: 99%

Potential energy surface of alkali atoms adsorbed on Cu(001)

Fratesi

2009

Phys. Rev. B

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“…Thus, surprisingly, the effective potential that binds electrons to the surface is independent of the local adatom density, unlike the behavior seen at lower coverages in Na/Cu͑001͒. 33 We can also now provide an atomistic interpretation of the turning point and gradual increase in work function measured from Li/Cu͑001͒ above 0.5 ML. 13 We find a significant depolarization of Li adatoms, from 0.66 D ͑type-A Li͒ to 0.39 D ͑type-B Li͒.…”

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confidence: 71%

Charge redistribution in the formation of one-dimensional lithium wires on Cu(001)

et al. 2010

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We describe the formation of one-dimensional lithium wires on a Cu͑001͒ substrate, providing an atomicscale description of the onset of metallization in this prototypical adsorption system. A combination of helium atom scattering and density-functional theory reveals pronounced changes in the electronic charge distribution on the formation of the c͑5 ͱ 2 ϫ ͱ 2͒R45°Li/Cu͑001͒ structure, as in-plane bonds are created. Charge donation from Li-substrate bonds is found to facilitate the formation of stable, bonded, and depolarized chains of Li adatoms that coexist with an interleaved phase of independent adatoms. The resultant overlayer has a commensurate charge distribution and lattice modulations but differs fundamentally from structurally similar charge-density wave systems. Self-organized, nanometric wires are ideal prototypes for exploring the electronic changes that occur during the process of bond formation at a surface. Epitaxial deposition onto intrinsically anisotropic substrates-such as ͑110͒ oriented, 1 stepped, 2-6 or reconstructed 7 single crystals-has been particularly useful in this regard. The approach can yield long, robust wires that are easier to study than freestanding structures.8 It is also of interest for the study of lowdimensional phenomena, including charge-density waves ͑CDWs͒, 9,10 which have been identified in a variety of lowdimensional p-block 11 and d-block 3,9 epitaxial systems. In contrast, one-dimensional ͑1D͒ s-block systems have not previously been identified but could offer nonlocal, freeelectronlike properties that would contrast with the local nature of d-band systems. In the case of alkali metals on lowindex surfaces, a difficulty in forming 1D surface structures is the nature of interadsorbate interactions.12,13 Heavy alkali metal adatoms are highly polarized and tend toward isotropic, hex-type overlayers. As we demonstrate in the present work, light alkali metals behave differently, a fact that can be attributed to stronger and more localized adatom-substrate interactions. The resulting atomic chains of Li have a 1D structural character and they offer a unique opportunity for the observation of the charge redistribution as metallic bonds form in the surface plane. We use a combination of helium atom scattering ͑HAS͒ and density-functional theory ͑DFT͒ to probe directly the electronic structure of these anisotropic Li films, which we show to be characterized by inhomogeneous electronic-charge distributions and the coexistence of two distinct Li adatom states.Previous electron 14,15 and atom 16 diffraction studies have shown that a series of well-ordered submonolayer Li adatom structures forms on Cu͑001͒ at low temperature. Upon deposition, Li adatoms condense from a dilute lattice gas into an ordered c͑2 ϫ 2͒ structure at 0.5 monolayers ͑ML͒ with adatoms occupying fourfold hollow sites, 17,18 as sketched in Fig. 1͑a͒. Adatoms in the c͑2 ϫ 2͒ structure have a large separation and Ne scattering indicates that they act as independent Einstein oscillators: 16,19 both factors po...

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“…In the field of heterogeneous catalysis, adatom diffusion is particularly relevant in cases where spill-over effects intervene and the reaction proceeds through different steps mediated by spatially separated active sites [3][4][5]: an enhanced atomic diffusivity can therefore boost the rate of the chemical reactions. On the other hand, in oxide supported metal clusters, catalysis, sintering due to Ostwald ripening, induced by atoms detaching from smaller clusters and diffusing to larger ones, often leads to catalyst deactivation [6].Various factors have been recognized to influence the diffusivity of atomic species on solid surfaces, for instance, (i) isotropic two-dimensional strain in heteroepitaxial systems, with an in-plane lattice mismatch between the film and the substrate [7,8]; (ii) mesoscopic strain, where the relaxations induced by the already nucleated islands significantly affect atomic motion [9]; (iii) availability of small amounts of foreign atoms (surfactants) that, being adsorbed on the substrate prior to the film deposition, can affect the intra-and/or interlayer mass transport [10-13]; (iv) presence of molecular species (chemisorbed or in the gas phase), such as, for instance, water [3] or CO [14]; and (v) long-range adatom-adatom interactions [15][16][17]. More recently, the enhancement of surface diffusion with acoustic standing waves has been proposed as a method for surface nanostructuring by driving atomic motion [18].…”

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Enhanced Atom Mobility on the Surface of a Metastable Film

et al. 2014

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A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization. DOI: 10.1103/PhysRevLett.113.046102 PACS numbers: 68.43.Jk, 68.55.J-, 81.15.Aa Atomic diffusion on solid surfaces is a ubiquitous phenomenon that plays a fundamental role in determining a large variety of physical and chemical processes. An example is represented by the self-assembly of metallic nanosized clusters stabilized on either oxide or metallic substrates, which is exploited to produce nanopatterned materials in fast and parallel bottom-up approaches [1,2]. In this frame, adatom diffusion is of paramount importance, since the kinetic constraints typically determine the final morphology of the self-assembled nanostructures. In the field of heterogeneous catalysis, adatom diffusion is particularly relevant in cases where spill-over effects intervene and the reaction proceeds through different steps mediated by spatially separated active sites [3][4][5]: an enhanced atomic diffusivity can therefore boost the rate of the chemical reactions. On the other hand, in oxide supported metal clusters, catalysis, sintering due to Ostwald ripening, induced by atoms detaching from smaller clusters and diffusing to larger ones, often leads to catalyst deactivation [6].Various factors have been recognized to influence the diffusivity of atomic species on solid surfaces, for instance, (i) isotropic two-dimensional strain in heteroepitaxial systems, with an in-plane lattice mismatch between the film and the substrate [7,8]; (ii) mesoscopic strain, where the relaxations induced by the already nucleated islands significantly affect atomic motion [9]; (iii) availability of small amounts of foreign atoms (surfactants) that, being adsorbed on the substrate prior to the film deposition, can affect the intra-and/or interlayer mass transport [10-13]; (iv) presence of molecular species (chemisorbed or in the gas phase), such as, for instance, water [3] or CO [14]; and (v) long-range adatom-adatom interactions [15][16][17]. More recently, the enhancement of surface diffusion with acoustic standing waves has been proposed as a method for surface nanostructuring by driving atomic motion [18].In this Letter, we report on a remarkable increase of atomic diffusion with the thickness of an ultrathin metastable film, namely, tetragonally distorted body-centered (bct) Co grown on Fe(001). Previous qu...

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Crucial electronic contributions to measures of surface diffusion by He atom scattering

Cited by 24 publications

References 25 publications

Potential energy surface of alkali atoms adsorbed on Cu(001)

Potential energy surface of alkali atoms adsorbed on Cu(001)

Charge redistribution in the formation of one-dimensional lithium wires on Cu(001)

Enhanced Atom Mobility on the Surface of a Metastable Film

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