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G Benedek - One of the best experts on this subject based on the ideXlab platform.
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evidence for a spin acoustic Surface plasmon from inelastic atom scattering
Scientific Reports, 2021Co-Authors: G Benedek, Davide Campi, M Bernasconi, V M Silkin, Igor V Silkin, I P ChernovAbstract:Closed-shell atoms scattered from a metal Surface exchange energy and momentum with Surface Phonons mostly via the interposed Surface valence electrons, i.e., via the creation of virtual electron-hole pairs. The latter can then decay into Surface Phonons via electron-phonon interaction, as well as into acoustic Surface plasmons (ASPs). While the first channel is the basis of the current inelastic atom scattering (IAS) Surface-phonon spectroscopy, no attempt to observe ASPs with IAS has been made so far. In this study we provide evidence of ASP in Ni(111) with both Ne atom scattering and He atom scattering. While the former measurements confirm and extend so far unexplained data, the latter illustrate the coupling of ASP with Phonons inside the Surface-projected phonon continuum, leading to a substantial reduction of the ASP velocity and possibly to avoided crossing with the optical Surface phonon branches. The analysis is substantiated by a self-consistent calculation of the Surface response function to atom collisions and of the first-principle Surface-phonon dynamics of Ni(111). It is shown that in Ni(111) ASP originate from the majority-spin Shockley Surface state and are therefore collective oscillation of Surface electrons with the same spin, i.e. it represents a new kind of collective quasiparticle: a Spin Acoustic Surface Plasmon (SASP).
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Surface Phonons theoretical methods and results
2020Co-Authors: G Benedek, J P Toennies, Davide Campi, M Bernasconi, M J VerstraeteAbstract:The theoretical methods currently in use for the calculation of Surface phonon dispersion curves and how they have evolved from the phenomenological force-constant models to the present day first principles theories are discussed. A selection of paradigmatic examples for the different classes of crystal Surfaces is presented with comparisons to the experimental data obtained from helium atom scattering or electron energy-loss spectroscopy.
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ab initio calculation of Surface Phonons at the sb2te3 111 Surface
Surface Science, 2018Co-Authors: G Benedek, Davide Campi, M BernasconiAbstract:Abstract Density functional perturbation theory is used to study the phonon dispersion relations at the (111) Surface of the topological insulator Sb2Te3. Inelastic Helium atom scattering experiments at the (111) Surface of the similar Bi2Se3 topological insulator suggested the occurrence of a deep Kohn anomaly related to the presence of the topological Surface metallic state. A slab made of three Sb2Te3 quintuple layers is used here to model the (111) Surface. This geometry is shown to be sufficient to generate metallic Dirac Surface states in good agreement with experimental data from Angle Resolved Photoemission Spectroscopy. The inclusion of spin-orbit interaction in the calculations of Surface Phonons at wavevectors corresponding to Fermi Surface nesting inside the Dirac cone allow us to address the possible occurrence of a Kohn anomaly in Sb2Te3(111) as well. No evidence is found in our calculations for any Kohn anomaly in Sb2Te3 due to electronic transitions across the Dirac cone.
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history of Surface Phonons and helium atom scattering
2018Co-Authors: G Benedek, J P ToenniesAbstract:The chapter starts with an overview of the history of the theory of Surface Phonons. Next the history of helium atom and electron inelastic scattering experiments are briefly reviewed. Present day helium atom scattering experiments are described next and some important related concepts are introduced. The chapter closes with a short history of the classical and quantum theory of inelastic Surface scattering.
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experimental results Surface Phonons
2018Co-Authors: G Benedek, J P ToenniesAbstract:In this chapter some exemplary high resolution HAS experiments on Surface phonon dispersion curves of single crystal Surfaces based largely on the TOF technique are reviewed. A selection is made of significant results for insulator, semiconductor and conducting Surfaces, with special attention to the HAS results for metals, semimetals, and layered materials, where evidence is found for important effects of, for example, electron-phonon coupling and the related observation of Kohn anomalies, anomalous longitudinal branches and deep subSurface modes. Studies on complex Surfaces with large-period unit cells due to reconstruction or high index orientation are also reviewed. Here also the comparatively high resolution of HAS permits to observe low energy dynamical excitations and their dispersion. Each section is meant as an introduction to the specific phenomena and issues characteristic to each of these different Surface types, with special consideration to the questions solved and the new theoretical issues raised. This chapter is complemented by Appendix A, which contains a comprehensive list of the available HAS experimental data on phonon dispersion curves and of the theoretical studies for the different classes of materials, as of early 2018 which update previous reviews: [1, 2] (all systems), [3, 4] (layered compounds), [5, 6] (semiconductors), [7] (metals) and Landot-Bornstein Chapters [8, 9, 10, 484].
Geertjan Kroes - One of the best experts on this subject based on the ideXlab platform.
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Accurate Probabilities for Highly Activated Reaction of Polyatomic Molecules on Surfaces Using a High-Dimensional Neural Network Potential: CHD3 + Cu(111)
2019Co-Authors: N. Gerrits, Khosrow Shakouri, Jörg Behler, Geertjan KroesAbstract:An accurate description of reactive scattering of molecules on metal Surfaces often requires the modeling of energy transfer between the molecule and the Surface Phonons. Although ab initio molecular dynamics (AIMD) can describe this energy transfer, AIMD is at present untractable for reactions with reaction probabilities smaller than 1%. Here, we show that it is possible to use a neural network potential to describe a polyatomic molecule reacting on a mobile metal Surface with considerably reduced computational effort compared to AIMD. The highly activated reaction of CHD3 on Cu(111) is used as a test case for this method. It is observed that the reaction probability is influenced considerably by dynamical effects such as the bobsled effect and Surface recoil. A special dynamical effect for CHD3 + Cu(111) is that a higher vibrational efficacy is obtained for two quanta in the CH stretch mode than for a single quantum
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vibrational excitation of h2 scattering from cu 111 effects of Surface temperature and of allowing energy exchange with the Surface
Journal of Physical Chemistry C, 2017Co-Authors: Geertjan Kroes, J I Juaristi, Maite AlducinAbstract:In scattering of H2 from Cu(111), vibrational excitation has so far defied an accurate theoretical description. To expose the causes of the large discrepancies with experiment, we investigate how the feature due to vibrational excitation (the “gain peak”) in the simulated time-of-flight spectrum of (v = 1, j = 3) H2 scattering from Cu(111) depends on the Surface temperature (Ts) and the possibility of energy exchange with Surface Phonons and electron–hole pairs (ehp’s). Quasi-classical dynamics calculations are performed on the basis of accurate semiempirical density functionals for the interaction with H2 + Cu(111). The methods used include the quasi-classical trajectory method within the Born–Oppenheimer static Surface model, the generalized Langevin oscillator (GLO) method incorporating energy transfer to Surface Phonons, the GLO + friction (GLO+F) method also incorporating energy exchange with ehp’s, and ab initio molecular dynamics with electronic friction (AIMDEF). Of the quasi-classical methods tes...
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accurate neural network description of Surface Phonons in reactive gas Surface dynamics n2 ru 0001
Journal of Physical Chemistry Letters, 2017Co-Authors: Khosrow Shakouri, Jorg Behler, Jorg Meyer, Geertjan KroesAbstract:Ab initio molecular dynamics (AIMD) simulations enable the accurate description of reactive molecule–Surface scattering especially if energy transfer involving Surface Phonons is important. However, presently, the computational expense of AIMD rules out its application to systems where reaction probabilities are smaller than about 1%. Here we show that this problem can be overcome by a high-dimensional neural network fit of the molecule–Surface interaction potential, which also incorporates the dependence on Phonons by taking into account all degrees of freedom of the Surface explicitly. As shown for N2 + Ru(0001), which is a prototypical case for highly activated dissociative chemisorption, the method allows an accurate description of the coupling of molecular and Surface atom motion and accurately accounts for vibrational properties of the employed slab model of Ru(0001). The neural network potential allows reaction probabilities as low as 10–5 to be computed, showing good agreement with experimental re...
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modeling Surface motion effects in n2 dissociation on w 110 ab initio molecular dynamics calculations and generalized langevin oscillator model
Journal of Chemical Physics, 2016Co-Authors: Francesco Nattino, M Alducin, Oihana Galparsoro, Francesca Costanzo, Ricardo Diez Muino, Geertjan KroesAbstract:Accurately modeling Surface temperature and Surface motion effects is necessary to study molecule-Surface reactions in which the energy dissipation to Surface Phonons can largely affect the observables of interest. We present here a critical comparison of two methods that allow to model such effects, namely, the ab initio molecular dynamics (AIMD) method and the generalized Langevin oscillator (GLO) model, using the dissociation of N2 on W(110) as a benchmark. AIMD is highly accurate as the Surface atoms are explicitly part of the dynamics, but this advantage comes with a large computational cost. The GLO model is much more computationally convenient, but accounts for lattice motion effects in a very approximate way. Results show that, despite its simplicity, the GLO model is able to capture the physics of the system to a large extent, returning dissociation probabilities which are in better agreement with AIMD than static-Surface results. Furthermore, the GLO model and the AIMD method predict very simila...
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thermal lattice expansion effect on reactive scattering of h2 from cu 111 at t s 925 k
Journal of Physical Chemistry A, 2013Co-Authors: Arobendo Mondal, Mark Wijzenbroek, Matteo Bonfanti, Cristina Diaz, Geertjan KroesAbstract:Surface Phonons and Surface temperature may have important effects on reactions of molecules at Surfaces, and at present much remains unknown about these effects. A question addressed here, which has received little attention so far, is how reaction at elevated temperature is affected by thermal lattice expansion. To answer this question for the benchmark reaction of H2 and D2 with Cu(111), we have performed quantum and quasi-classical dynamics calculations. The specific reaction parameter (SRP) approach to density functional theory (DFT) has been used to compute the required six-dimensional potential energy Surfaces (PES). Computed reaction probabilities and rotational quadrupole alignment parameters have been compared for Surface temperatures Ts = 0 and 925 K. Surface thermal expansion of the lattice leads to a considerable decrease of reaction barrier heights and thereby to increased reaction probabilities as well as decreased rotational quadrupole alignment parameter values in associative desorption.
P M Echenique - One of the best experts on this subject based on the ideXlab platform.
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Surface Phonons on pb 111
Journal of Physics: Condensed Matter, 2012Co-Authors: Yu I Sklyadneva, R Heid, K P Bohnen, P M Echenique, Eugene V ChulkovAbstract:We present an ab initio study of the lattice dynamics of the Pb(111) Surface. The calculations were carried out within the density-functional theory using a linear response approach in the mixed-basis pseudopotential representation. We observe a rich spectrum of Surface localized modes, and make a detailed assignment to measured modes in a recent helium-atom scattering experiment. We find that the inclusion of spin–orbit coupling considerably softens the phonon spectrum of the Surface, thereby improving the agreement with experiment significantly.
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theory of Surface Phonons at metal Surfaces recent advances
Journal of Physics: Condensed Matter, 2010Co-Authors: G Benedek, M Bernasconi, P M Echenique, Eugene V Chulkov, V Chis, B HellsingAbstract:Recent studies of the Surface dynamics of Al(001) and Cu(111) based on density functional perturbation theory have substantiated the existence of subSurface optical phonon resonances of all three polarizations, thus confirming early predictions of the embedded-atom method. The hybridization of the shear-vertical optical resonance with the longitudinal acoustic phonon branch accounts for the ubiquitous anomalous acoustic resonance as an intrinsic feature of metal Surfaces. The DFPT calculation of the phonon-induced Surface charge density oscillations shows that helium atom scattering spectroscopy (HAS) can indeed probe subSurface resonances. This opens new perspectives to HAS for the measurement of subSurface phonon dispersion curves in thin films, as proved by recent HAS studies on Pb and Fe ultrathin films on copper. After discussing these recent advances, this paper briefly reviews other important trends of Surface dynamics expressed in recent years.
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role of bulk and Surface Phonons in the decay of metal Surface states
Physical Review Letters, 2002Co-Authors: Asier Eiguren, P M Echenique, Eugene V Chulkov, B Hellsing, F Reinert, G Nicolay, V M Silkin, S HufnerAbstract:We present a comprehensive theoretical investigation of the electron-phonon contribution to the lifetime broadening of the Surface states on Cu(111) and Ag(111), in comparison with high-resolution photoemission results. The calculations, including electron and phonon states of the bulk and the Surface, resolve the relative importance of the Rayleigh mode, being dominant for the lifetime at small hole binding energies. Including the electron-electron interaction, the theoretical results are in excellent agreement with the measured binding energy and temperature dependent lifetime broadening.
U. Schröder - One of the best experts on this subject based on the ideXlab platform.
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Surface Phonons of thin gase and inse films epitaxially grown on the si 111 1 1 h Surface
Physical Review B, 1999Co-Authors: V Panella, A Glebov, J P Toennies, C A Sebenne, C Eckl, C Adler, P Pavone, U. SchröderAbstract:Surface-phonon-dispersion curves of the (001) Surfaces of the GaSe and InSe films epitaxially grown on the hydrogen-terminated $\mathrm{Si}(111)(1\ifmmode\times\else\texttimes\fi{}1)$ Surface have been investigated by high-resolution inelastic helium-atom scattering. The phonon-dispersion curves of the GaSe(001) thin epitaxial films are very similar to those of the single crystals investigated previously. For comparison with the experiments, density-functional theory based on the plane-wave pseudopotential method has been used to determine the phonon-dispersion curves of bulk GaSe and InSe in a consistent formalism. No difference is found between the Surface and bulk Phonons of these two layered compounds, as expected due to weak interlayer interaction forces. The high quality of the time-of-flight spectra presented here together with the ab initio calculations provide insight into the phonon dynamics of GaSe(001), and a characterization of the phonon modes of InSe(001).
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Density functional calculation of semiconductor Surface Phonons
Physics Reports, 1999Co-Authors: Julia Fritsch, U. SchröderAbstract:Abstract Vibrations on a Surface directly reflect the atomic arrangement and the force constants between the atoms in the outermost layers of a solid. Semiconductor Surfaces are particularly interesting, because of the covalent bonding nature of the bulk material. A thorough analysis of the vibrational modes therefore contributes essentially to a better understanding of the driving forces and processes that determine the geometry and the electronic properties in the Surface region. In this report, we summarize recent developments in density-functional theory which have substantially intensified theoretical investigation of semiconductor Surface dynamics. We briefly describe the conceptional details of ab initio linear-response theory, molecular-dynamics simulations, and frozen-phonon-like approaches which are the most successful computational schemes applied in the past few years. A collection of the most important results obtained on the basis of such computations will demonstrate how density-functional calculations of this kind contribute to a clear and detailed insight into the structural and dynamical properties of semiconductor Surfaces.
J P Toennies - One of the best experts on this subject based on the ideXlab platform.
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Surface Phonons theoretical methods and results
2020Co-Authors: G Benedek, J P Toennies, Davide Campi, M Bernasconi, M J VerstraeteAbstract:The theoretical methods currently in use for the calculation of Surface phonon dispersion curves and how they have evolved from the phenomenological force-constant models to the present day first principles theories are discussed. A selection of paradigmatic examples for the different classes of crystal Surfaces is presented with comparisons to the experimental data obtained from helium atom scattering or electron energy-loss spectroscopy.
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history of Surface Phonons and helium atom scattering
2018Co-Authors: G Benedek, J P ToenniesAbstract:The chapter starts with an overview of the history of the theory of Surface Phonons. Next the history of helium atom and electron inelastic scattering experiments are briefly reviewed. Present day helium atom scattering experiments are described next and some important related concepts are introduced. The chapter closes with a short history of the classical and quantum theory of inelastic Surface scattering.
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experimental results Surface Phonons
2018Co-Authors: G Benedek, J P ToenniesAbstract:In this chapter some exemplary high resolution HAS experiments on Surface phonon dispersion curves of single crystal Surfaces based largely on the TOF technique are reviewed. A selection is made of significant results for insulator, semiconductor and conducting Surfaces, with special attention to the HAS results for metals, semimetals, and layered materials, where evidence is found for important effects of, for example, electron-phonon coupling and the related observation of Kohn anomalies, anomalous longitudinal branches and deep subSurface modes. Studies on complex Surfaces with large-period unit cells due to reconstruction or high index orientation are also reviewed. Here also the comparatively high resolution of HAS permits to observe low energy dynamical excitations and their dispersion. Each section is meant as an introduction to the specific phenomena and issues characteristic to each of these different Surface types, with special consideration to the questions solved and the new theoretical issues raised. This chapter is complemented by Appendix A, which contains a comprehensive list of the available HAS experimental data on phonon dispersion curves and of the theoretical studies for the different classes of materials, as of early 2018 which update previous reviews: [1, 2] (all systems), [3, 4] (layered compounds), [5, 6] (semiconductors), [7] (metals) and Landot-Bornstein Chapters [8, 9, 10, 484].
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the physics of Surface Phonons
2018Co-Authors: G Benedek, J P ToenniesAbstract:The effect of the Surface termination on the phonon dispersion curves is illustrated by comparison with the bulk dispersion curves. After a review of Rayleigh’s theory of Surface waves in elastic media the atomistic Born-von Karman theory for bulk Phonons is presented. How the Surface affects the Surface vibrations is illustrated by the Green’s function theory and slab calculations. The chapter closes with some illustrations of Surface phonon dispersion curves and their classification.
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theory of atom scattering from Surface Phonons basic concepts and temperature effects
2018Co-Authors: G Benedek, J P ToenniesAbstract:The reflection coefficient determining the inelastic scattered intensity is defined and analysed theoretically. Various approximations including the Born approximation, the Distorted-Wave Born approximation (DWBA), the GR method and the eikonal approximation are discussed and illustrated with examples. From an expression for the DWBA inelastic reflection coefficient for n-phonon processes, factors determining the relative role of temperature for multiphonon processes and one-phonon scattering are analysed. Several approximate expressions for the Debye-Waller factor are derived and used to define experimental criteria favouring one-phonon scattering. Most of the examples dealt with are for insulator Surfaces. Chapter 8 then describes the scattering theory for metal and semiconductor Surfaces.
