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Silver films with a thickness below 50 nanometer were deposited on glass using DC magnetron sputtering. The chemical stability of the films was investigated by exposure of the film to a droplet of a HCl solution in a humid atmosphere. The affected area was monitored with a digital microscope. The affected area increases approximately linearly with time which points to a diffusive mechanism. The slope of the area versus time plot, or the diffusivity, was measured as a function of the acid concentration, the presence of an aluminum seed layer, and film thickness. The diffusivity scales linearly with the acid concentration. It is shown that the diffusivity for Al-seeded Ag films is much lower. The behavior as function of the film thickness is more complex as it shows a maximum.

Steps at metal surfaces may influence energetics and kinetics of catalytic reactions in unexpected ways. Here, we report a significant reduction of the CO saturation coverage in Pd vicinal surfaces, which in turn is relevant for the light-off of the CO oxidation reaction. The study is based on a systematic investigation of CO adsorption on vicinal Pd(111) surfaces making use of a curved Pd crystal. A combined X-ray Photoelectron Spectroscopy and DFT analysis allows us to demonstrate that an entire row of atomic sites under Pd steps remains free of CO upon saturation at 300 K, leading to a step-density-dependent reduction of CO coverage that correlates with the observed decrease of the light-off temperature during CO oxidation in vicinal Pd surfaces., We acknowledge financial support from the Spanish Ministry of Science and Innovation (Grants MAT-2017-88374-P, PID2019-107338RB-C63, PID2020-116093RB-C44), the Basque Government (Grants IT-1255-19), the Knut and Alice Wallenberg foundation (DNR KAW 2015.0058 ”Atomistic Design of new Catalysts”), and the Swedish Research Council (DNR 349-2011-6491 “Catalysis on the Atomic Scale”). Financial support is acknowledged from the Swedish Research Council (2016-5234). The DFT calculations were performed at C3SE (Göteborg) via a SNIC grant. We acknowledge MAX IV Laboratory support, in particular Alexei Preobrajenski, for their help in synchrotron experiments, which were carried out at the FlexPES beamline under Proposal 20190717. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. Moreover, the research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.

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)., The work of I.V.S. is supported by the Ministry of Science and Higher Education of the Russian Federation for funding in framework of State Task (No. 0721-2020-0033). V.M.S. and P.M.E. acknowledge support from the Spanish Ministry of Science and Innovation (Grant No. PID2019-105488GB-I00) and D.F. from Grant No. PID2019-109525RB-I00. E.V.C. acknowledges support from Saint Petersburg State University (project ID No. 51126254). R.M. and D.F. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “María de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M). IMDEA Nanociencia acknowledges support from the ’Severo Ochoa’ Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). Part of the calculations was performed at the SKIF-Cyberia supercomputer at the National Research Tomsk State University (Russian Federation) and the Supercomputer Center of D.I.P.C. (Spain).

4,4'-Bis(2,6-difluoropyridin-4-yl)-1,1':4',1 ''-terphenyl (BDFPTP) molecules underwent dehydrocyclization and covalent coupling reactions on Au(111) according to scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations. Self-assembly of the reactants in well-defined molecular domains prior to reaction could greatly enhance the regioselectivity of the dehydrocyclization reaction and suppress defluorinated coupling, demonstrating that self-assembly can efficiently steer on-surface reactions. Such a strategy could be of great importance in surface chemistry and widely applied to control on-surface reactions.

International audience; The immobilization of a copper calix[6]azacryptand funnel complex on gold-modified electrodes is reported. Two different methodologies are described. One is based on alkyne-terminated thiol self assembled monolayers. The other relies on the electrografting of a calix[4]arene platform bearing diazonium functionalities at its large rim and carboxylic functions at its small rim, which is post-functionalized with alkyne moieties. In both cases, the CuAAC electroclick methodology proved to be the method of choice for grafting the calix[6]azacryptand onto the monolayers. The surface-immobilized complex was fully characterized by surface spectroscopies and electrochemistry in organic and aqueous solvents. The Cu complex display a well-defined quasi-reversible system in cyclic voltammetry associated with the Cu(II)/Cu(I) redox process. Remarkably, this-redox process triggers a powerful selective detection of primary alkylamines in water at a micromolar level, based on a cavitary recognition process.

A methodology is proposed to investigate electron transfer reactions between redox-active biomolecular systems (e.g. a protein) and inorganic surfaces. The whole system is modelled at the atomistic level using classical molecular dynamics - making an extensive sampling of the system's configurations possible - and the energies associated with the redox-active complex reduction are calculated using a hybrid quantum/classical approach along the molecular dynamics trajectory. The non-adiabaticity is introduced a posteriori using a Monte Carlo approach based on the Landau-Zener theory extended to treat a metal surface. This approach thus allows us to investigate the role of the energy fluctuations, determined by the dynamical evolution of the system, as well as the role of non-adiabaticity in affecting the kinetic rate of the electron transfer reaction. Most notably, it allows us to investigate the two contributions separately, hence achieving a detailed picture of the mechanisms that determine the rate. The analysis of the system configurations also allows us to relate the estimated electronic coupling to the structural and dynamic properties of the system. As a test case, the methodology is here applied to study the electron transfer reaction between cytochrome c and a gold surface. The results obtained explain the different electron transfer rates experimentally measured for two different concentrations of proteins on the electrode surface.

The molecular description of chirality transfer on chirally modified metal surfaces is unclear due to the complexity of the systems and the weak energetic biases favoring specific enantioselective pathways. In order to move to an enhanced level of molecular understanding it is critical to define the chemisorption geometries of the modifiers responsible for enantiodifferentiation. Model surface science studies of chiral molecules on single crystals provide an indirect method to probe catalytic chirality transfer molecular mechanisms. Apart from the great difference between ultrahigh vacuum (UHV) and reaction conditions, the extent to which such studies can inform the interpretation of data obtained under reaction conditions depends on the degree to which the model systems are correctly defined. The same holds true for any comparison of UHV surface spectroscopy data to spectroscopic measurements made at the catalyst-solution interface under either in-situ or operando conditions.We present detailed reflection absorption infrared spectroscopy (RAIRS) data on (R)-1-(1-naphthyl)ethylamine, (R)-NEA, and its simple derivative, (R)-1-(8-methyl-1-naphthyl)ethylamine, on Pt(111). Various conflicting proposals for the structure of NEA and analogous modifiers on Pt catalyst particles and extended Pt surfaces are found in the literature. Here, we find that below high sub-monolayer coverages on Pt(111), (R)-NEA adopts a chemisorption geometry where the entire naphthyl group is sr-bonded to the surface and the amine group forms a dative bond to the surface. The same general adsorption geometry is found for the methyl-substituted derivative. The study provides reference spectra for these chiral modifiers and confirms the molecular structures described in our previous studies of diastereomeric complexes formed by the (R)-NEA/Pt(111) system. (C) 2018 Elsevier B.V. All rights reserved.

International audience; The adsorption of cis and trans 2-butenes on Pt(111) has been studied as a function of hydrogen coverage OH by means of calculations based on density functional theory (DFT) with the inclusion of dispersion forces. All hydrogen coverages have been considered, from 0 to 1.00 monolayer (ML). For each case, the di-sigma and pi adsorption geometries of the olefins have been compared at a surface coverage of theta(C4H8) = 0.11 ML. Calculations of the Gibbs free energies of these systems have identified the most stable 2-butene isomer (cis or trans) as a function of coverage, temperature, and pressure. In particular, focus was placed on two sets of conditions, namely, one with a pressure of 10(-7) Torr, a temperature of 80 K, and a gas ratio (P-H2/P-butene) of 25, similar to the conditions used in surface science studies, and a second with a pressure of 1 bar, a temperature range of 300-400 K, and a gas ratio (P-H2/P-butene) of 10, similar to catalytic hydrogenation conditions. With all selected functionals (PW91, PBE-TS, and optPBE), di-sigma bonding was found to be the most stable for both isomers of 2-butene and for all hydrogen coverages except for OH = 1.00 ML. At low pressures, 2-butene is physisorbed at low temperatures (

Molecules self-assemble on surfaces forming a variety of patterns that depend on the relative strength between the intermolecular and molecule–surface interactions. In this study, the effect of the physisorption/chemisorption interplay on self-assembly is investigated using Monte Carlo simulations. The molecules are modeled as hexagonal tiles capable of assuming two distinct adsorption states, with different diffusion properties, on a hexagonal lattice. The self-assembled structures that emerge by tuning the molecule–surface and molecule–molecule interactions are systematically mapped out to develop understanding of their phase behavior. The resulting phase diagrams will guide the engineering of novel molecules to obtain desired collective structural properties for the development of innovative two-dimensional devices.

First-principles studies of the electron-phonon coupling in graphene predict a high coupling strength for the $\sigma$ band with $\lambda$ values of up to 0.9. Near the top of the $\sigma$ band, $\lambda$ is found to be $\approx 0.7$. This value is consistent with the recently observed kinks in the $\sigma$ band dispersion by angle-resolved photoemission. While the photoemission intensity from the $\sigma$ band is strongly influenced by matrix elements due to sub-lattice interference, these effects differ significantly for data taken in the first and neighboring Brillouin zones. This can be exploited to disentangle the influence of matrix elements and electron-phonon coupling. A rigorous analysis of the experimentally determined complex self-energy using Kramers-Kronig transformations further supports the assignment of the observed kinks to strong electron-phonon coupling and yields a coupling constant of $0.6(1)$, in excellent agreement with the calculations., Comment: 11 pages, 3 figures

We have studied the topological insulator Bi$_2$Te$_3$(111) by means of helium atom scattering. The average electron-phonon coupling $\lambda$ of Bi$_2$Te$_3$(111) is determined by adapting a recently developed quantum-theoretical derivation of the helium scattering probabilities to the case of degenerate semiconductors. Based on the Debye-Waller attenuation of the elastic diffraction peaks of Bi$_2$Te$_3$(111), measured at surface temperatures between $110~\mbox{K}$ and $355~\mbox{K}$, we find $\lambda$ to be in the range of $0.04-0.11$. This method allows to extract a correctly averaged $\lambda$ and to address the discrepancy between previous studies. The relatively modest value of $\lambda$ is not surprising even though some individual phonons may provide a larger electron-phonon interaction. Furthermore, the surface Debye temperature of Bi$_2$Te$_3$(111) is determined as ${\rm \Theta}_D = (81\pm6)~\mbox{K}$. The electronic surface corrugation was analysed based on close-coupling calculations. By using a corrugated Morse potential a peak-to-peak corrugation of 9% of the lattice constant is obtained., Comment: 9 pages, 4 figures

Why use thiols in Molecular Electronics? They stink, oxidize readily, poison catalysts, and often require nontrivial protection/deprotection chemistry. In this communication we demonstrate the fabrication of tunneling junctions formed by contact of self-assembled monolayers (SAMs) of terminal alkynes onto silver and gold substrates. The SAMs form spontaneously upon exposure of the substrates to ethanolic solutions of the alkynes. Characterization by vibrational spectroscopy, XPS, and contact angles shows that the packing of the SAMs is nearly identical to those formed from equivalent thiols. Electrical characterization of the junctions revealed virtually no differences between SAMs on gold and silver, yielding beta(Au) = 1.17 +/- 0.04n(C)(-1), J(0) = (2.836 +/- 0.001) x 10(3) A cm(-2) for Au, and beta(Ag) - 1.23 +/- 0.09n(C)(-1), J(0) = (4.722 +/- 0.002) x 10(3) A cm(-2) for Ag. These values are in excellent agreement with junctions formed from alkanethiols of the same lengths as the alkynes, suggesting that there is no functional difference between thiols and alkynes as anchoring groups for SAMs. Yet alkynes are synthetically versatile, do not poison catalysts, are not odorous, and do not spontaneously oxidize, which are all attractive features for use in Molecular Electronics.

Elementary steps in enantioselective heterogeneous catalysis take place on the catalyst surface and the targeted synthesis of a desired enantiomer requires the implantation of chiral information at the surface, which can be achieved-for example-by adsorbing chiral molecules. Studies of the structures of complexes formed between adsorbed prochiral reagents and chiral molecules yield information on the forces exerting stereocontrol, but further insight could be gained by studying the dynamics of their interactions. Here, using time-lapsed scanning tunnelling microscopy and density functional theory, we observe coupling between multiple stereochemical states within individual non-covalently bonded chirality-transfer complexes on a metal surface. We identify two modes of transformation between stereochemical states and find that the prochiral reagent can sample several complexation geometries during the lifetime of a complex, switching between states of opposing prochirality in the process. These results provide insight on the contribution of individual stereochemical states to the overall enantioselectivity of reactions occurring on catalyst surfaces.

The adsorption, diffusion, and dissociation of pyridine, C5H5N, on Pt(111) are investigated with van derWaals-corrected density functional theory. An elaborate search for local minima in the adsorption potential energy landscape reveals that the intact pyridine adsorbs with the aromatic ring parallel to the surface. Piecewise interconnections of the local minima in the energy landscape reveal that the most favourable diffusion path for pyridine has a barrier of 0.53 eV. In the preferred path, the pyridine remains parallel to the surface while performing small single rotational steps with a carbon-carbon double bond hinged above a single Pt atom. The origin of the diffusion pathway is discussed in terms of the C-2-Pt pi-bond being stronger than the corresponding CN-Pt p-bond. The energy barrier and reaction enthalpy for dehydrogenation of adsorbed pyridine into an adsorbed, upright bound a-pyridyl species are calculated to 0.71 eV and 0.18 eV, respectively (both zero-point energy corrected). The calculations are used to rationalize previous experimental observations from the literature for pyridine on Pt(111). Published by AIP Publishing.

We report on the structural and electronic properties of a single bismuth layer intercalated underneath a graphene layer grown on an Ir(111) single crystal. Scanning tunneling microscopy (STM) reveals a hexagonal surface structure and a dislocation network upon Bi intercalation, which we attribute to a $\sqrt{3}\times\sqrt{3}R30{\deg}$ Bi structure on the underlying Ir(111) surface. Ab-initio calculations show that this Bi structure is the most energetically favorable, and also illustrate that STM measurements are most sensitive to C atoms in close proximity to intercalated Bi atoms. Additionally, Bi intercalation induces a band gap ($E_g=0.42\,$eV) at the Dirac point of graphene and an overall n-doping ($\sim 0.39\,$eV), as seen in angular-resolved photoemission spectroscopy. We attribute the emergence of the band gap to the dislocation network which forms favorably along certain parts of the moir\'e structure induced by the graphene/Ir(111) interface., Comment: 5 figures

Semilocal density functional theory is the most used computational method for electronic structure calculations in theoretical solid-state physics and quantum chemistry of large systems, providing good accuracy with a very attractive computational cost. Nevertheless, because of the non-locality of the exchange-correlation hole outside a metal surface, it was always considered inappropriate to describe the correct surface asymptotics. Here, we derive, within the semilocal density functional theory formalism, an exact condition for the image-like surface asymptotics of both the exchange-correlation energy per particle and potential. We show that this condition can be easily incorporated into a practical computational tool, at the simple meta-generalized-gradient approximation level of theory. Using this tool, we also show that the Airy-gas model exhibits asymptotic properties that are closely related to the ones at metal surfaces. This result highlights the relevance of the linear effective potential model to the metal surface asymptotics., Comment: 6 pages, 4 figures

Journal article The self-assembly of molecules on surfaces into 2D structures is important for the bottom-up fabrication of functional nanomaterials, and the self-assembledstructure depends on the interplay between molecule-molecule interactions and molecule-surface interactions. Halogenated benzene derivatives on platinum have been shown to have two distinct adsorption states: a physisorbed state and a chemisorbed state, and the interplay between the two can be expected to have a profound effect on the self-assembly and phase behaviour of these systems. We developed a lattice model that explicitly includes both adsorption states, with representative interactions parameterised using density functional theory calculations. This model was used in Monte Carlo simulations to investigate pattern formation of hexahalogenated benzene molecules on the platinumsurface. Molecules that prefer the physisorbed state were found to self-assemble with ease, depending on the interactions between physisorbed molecules. In contrast, molecules that preferentially chemisorb tend to get arrested in disordered phases. However, changing the interactions between chemisorbed and physisorbed molecules affects the phase behaviour. We propose functionalising molecules in order to tune their adsorption states, as an innovative way to control monolayerstructure, leading to a promising avenue for directed assembly of novel 2D structures. Academia Nazionale dei Lincei; Royal Society of Edinburgh peer-reviewed

By tuning the laser photon energy in the non-linear two-photons photoemission at a single-layer graphene/Cu(111) interface, it is possible to observe a strong resonance at h upsilon = 3.5 eV along with a weaker one at h upsilon = 3.85 eV. The main resonance photon energy is consistent with a direct optical transition between the occupied Cu(111) Shockley surface state and the n = 1 image potential state, located in the real gap-space between the single-layer graphene and the Cu( Ill) surface. The large amplitude of this resonance unveils a high value of the electric dipole matrix element integral that governs this transition. Furthermore, the Lorentzian shape of this resonance implies that these two states are decoupled from the continuum of states and the lifetime of the image potential state can be estimated. (C) 2015 Elsevier B.V. All rights reserved.

Imaging live molecular events within micro-organisms at single-cell resolution would deliver valuable mechanistic information much needed in understanding key biological processes. We present a surface-enhanced Raman (SERS) chemical imaging strategy as a first step toward exploring the intracellular bioreduction pockets of toxic chromate in Shewanella. In order to achieve this, we take advantage of an innate reductive mechanism in bacteria of reducing gold ions into intracellular gold nanoislands, which provide the necessary enhancement for SERS imaging. We show that SERS has the sensitivity and selectivity not only to identify but also to differentiate between the two stable valence forms of chromate in cells. The imaging platform was used to understand intracellular metal reduction activities in a ubiquitous metal-reducing organism, Shewanella oneidensis MR-1, by mapping chromate reduction.

In order to address the interplay of hydrogen bonding, dipolar interactions, and metal coordination, we have investigated the two-dimensional mono- and bicomponent self-assembly of three closely related diaminotriazine-based molecular building blocks and a complementary perylenetetracarboxylic diimide by means of scanning tunneling microscopy. The simplest molecular species, bis-diaminotriazine-benzene, only interacts via hydrogen bonds and forms a unique supramolecular pattern on the Au(111) surface. For the two related molecular species, which exhibit in addition to hydrogen bonding also dipolar interactions and metal coordination, the number of distinct supramolecular structures increases dramatically with the number of possible interaction channels. Deposition together with the complementary perylene species, however, always results in a single well-defined supramolecular arrangement of molecules. A detailed analysis of the observed mono- and bicomponent assemblies allows shedding light on the hierarchy of the competing interactions, with important implications for the fabrication of surface-supported supramolecular networks by design.

The present review on light emission stimulated by electrons tunneling inelastically through a junction formed by a sample and a tip of a scanning tunneling microscope (STM) focusses on the most relevant results obtained for a variety of systems, including metal surfaces, single molecules on ultrathin dielectric films, and molecules assembled in thin films or in nanostructures on metal surfaces or on dielectric films. The decisive role of the localized surface plasmon for the enhanced luminescence from supported molecules is highlighted. The progress so far achieved for both experimental techniques and theoretical analysis is addressed. Current trends are discussed and possible future developments are indicated. STM-induced photon emission has come a long way. More than a decade ago, simple photon maps reflected only the emitted light intensity on a local scale. Today this technique has advanced to spectroscopically resolve optical emission from electronic and vibrational molecular modes in single molecules, demonstrating the capability of STM-induced light emission for chemical recognition on the single-molecule scale. © 2010 Elsevier B.V. All rights reserved.

13 páginas, 12 figuras, 2 tablas.-- et al., The structural chemistry and reactivity of 1,3,8,10-tetraazaperopyrene (TAPP) on Cu(111) under ultra-high-vacuum (UHV) conditions has been studied by a combination of experimental techniques (scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy, XPS) and DFT calculations. Depending on the deposition conditions, TAPP forms three main assemblies, which result from initial submonolayer coverages based on different intermolecular interactions: a close-packed assembly similar to a projection of the bulk structure of TAPP, in which the molecules interact mainly through van der Waals (vDW) forces and weak hydrogen bonds; a porous copper surface coordination network; and covalently linked molecular chains. The Cu substrate is of crucial importance in determining the structures of the aggregates and available reaction channels on the surface, both in the formation of the porous network for which it provides the Cu atoms for surface metal coordination and in the covalent coupling of the TAPP molecules at elevated temperature. Apart from their role in the kinetics of surface transformations, the available metal adatoms may also profoundly influence the thermodynamics of transformations by coordination to the reaction product, as shown in this work for the case of the Cu-decorated covalent poly(TAPP--Cu) chains., We thank the Swiss National Science Foundation, the European Union through the Marie Curie Research Training Network PRAIRIES (MRTN-CT-2006-035810) and the University of Heidelberg for funding, and acknowledge the award of a predoctoral fellowship to S.M. by the Landesgraduiertenfçrderung Baden-Württemberg (Promotionskolleg “Molekulare Sonden”).

The present paper describes what happens at the surface of a crystal as its temperature steadily increases from zero Kelvin close to the bulk melting temperature. We treat thermal motion, such as the diffusion of individual adatoms establishing mass transport, the formation of adatom or vacancy gases coexisting with islands or steps of the condensed phase, surface phonons and the anharmonicity of the surface potential being markedly different from the one in bulk, as well as thermally induced reconstructions, surface roughening, and finally surface melting, which usually well precedes bulk melting. The paper intends to give an overview with references to the original and review literature.

A simple direct mechanism for methane-to-methanol conversion has been investigated by first principles on a series of oxygen-precovered transition-metal surfaces. Energy barriers and reaction paths have been determined for three competing elementary processes by the nudged elastic band algorithm. Indicators of reactivity toward each elementary step have been identified, providing significant insight into a rational search for a suitable catalyst. The effect of chemical environment, local geometry, strain, and coadsorption have been addressed, and general guidelines have been identified. On the basis of this analysis, we suggest that upon suitable conditions O-dosed Ag surfaces could display considerable reactivity toward direct methane-to-methanol conversion.

The study of the molecular mechanism of chemical reactions occurring at solid surfaces is of primary importance to understand heterogeneous catalysis from a microscopic point of view. The present paper reviews the state of the art methods of electronic structure and the surface models currently used in this type of studies by making use of three different examples. Those are the decomposition of azomethane on Pt( 111), the study of the different selectivity of Cu( 111) and Ag( 111) towards ethene partial oxidation and the comparative study of NO dissociation on Rh( 111) and bimetallic RhCu( 111) surfaces. These examples illustrate the power of the electronic structure computational approaches to predict the structure and stability of different intermediates and to unravel the molecular mechanism of these surface reactions.

Quantum effects of plasmonic phenomena have been explored through ab-initio studies, but only for exceedingly small metallic nanostructures, leaving most experimentally relevant structures too large to handle. We propose instead an effective description with the computationally appealing features of classical electrodynamics, while quantum properties are described accurately through an infinitely thin layer of dipoles oriented normally to the metal surface. The nonlocal polarizability of the dipole layer is mapped from the free-electron distribution near the metal surface as obtained with 1D quantum calculations, such as time-dependent density-functional theory (TDDFT), and is determined once and for all. The model can be applied to any system size that is tractable within classical electrodynamics, while capturing quantum plasmonic aspects of nonlocal response and a finite work function with TDDFT-level accuracy. Applying the theory to dimers we find quantum-corrections to the hybridization even in mesoscopic dimers as long as the gap is sub-nanometric itself., Comment: Supplemental Material is available upon request to authors

Single-layer graphene supported on a metal surface has shown remarkable properties relevant for novel electronic and optoelectronic devices. However, the nature of the electronic states derived from unoccupied surface states and quantum well states, lying in the real-space gap between the graphene and the solid surface, has not been explored and exploited yet. Herein, we use ultraviolet nonlinear angle-resolved photoemission spectroscopy to unveil the coexistence at the graphene/Cu(111) interface of a highest occupied Shockley surface state (HOSS) and the two lowest unoccupied surface states (LUSS). The experimental results and electronic structure calculations, based on one-dimensional model potential, indicate that the two unoccupied states originate from the hybridization of an n = 1 image potential state with a quantum well state. The hybridized nature of these unoccupied states is benchmarked by a similar experiment done on single-layer graphene grown on copper polycrystalline foil where only the image state survives being the quantum well state at this interface inhibited.

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., We investigate the evolution of attosecond to femtosecond screening and emergent potentials that govern the dynamics and energetics of electrons and holes excited in the various stages of multiphoton photoemission processes and control the photoelectron yield in recently reported experiments [X. Cui, C. Wang, A. Argondizzo, S. Garrett-Roe, B. Gumhalter, and H. Petek, Nat. Phys. 10, 505 (2014)1745-247310.1038/nphys2981]. The study is focused on the dynamical screening of holes created in preexistent quasi-two-dimensional Shockley state bands on Ag(111) and Cu(111) surfaces and of electrons excited to the intermediate and emerging screened states. Using the formalism of self-consistent electronic response, we analyze first the effects of screening on the dynamics of photoexcited electrons and holes and then of the Coulomb correlated photoexcited pair. Special attention is paid to the correlated primary electron-hole states, which commence as transient surface excitons and develop in the course of screening into uncorrelated electrons and holes propagating in the image potential and surface state bands, respectively. The obtained results enable to establish a consistent picture of transient electron dynamics at Ag(111) and Cu(111) surfaces that are becoming accessible by the time-, energy-, and momentum-resolved pump-probe multiphoton photoelectron spectroscopies., V.M.S. acknowledges partial support from the Basque Departamento de Educacion, UPV/EHU (Grant No. IT-756-13) and the Spanish Ministry od Economy and Competitiveness MINECO (Grant No. FIS2013-48286-C2-1-P). N.D. acknowledges the support of the Unity Through Knowledge Fund (UKF B1). H.P. was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy through Grant DE-FG02-09ER 16056.

Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse., LCLS, Stanford University through the Stanford Institute for Materials Energy Sciences (SIMES); Lawrence Berkeley National Laboratory (LBNL); University of Hamburg through the BMBF priority program; Center for Free Electron Laser Science (CFEL); BMBF priority program; VolkswagenStiftung

We demonstrate that surface hydration is a key factor in dictating the free energy of non-covalent peptide-materials recognition., Peptide sequences that can discriminate between gold facets under aqueous conditions offer a promising route to control the growth and organisation of biomimetically-synthesised gold nanoparticles. Knowledge of the interplay between sequence, conformations and interfacial properties is essential for predictable manipulation of these biointerfaces, but the structural connections between a given peptide sequence and its binding affinity remain unclear, impeding practical advances in the field. These structural insights, at atomic-scale resolution, are not easily accessed with experimental approaches, but can be delivered via molecular simulation. A current unmet challenge lies in forging links between predicted adsorption free energies derived from enhanced sampling simulations with the conformational ensemble of the peptide and the water structure at the surface. To meet this challenge, here we use an in situ combination of Replica Exchange with Solute Tempering with Metadynamics simulations to predict the adsorption free energy of a gold-binding peptide sequence, AuBP1, at the aqueous Au(111), Au(100)(1 × 1) and Au(100)(5 × 1) interfaces. We find adsorption to the Au(111) surface is stronger than to Au(100), irrespective of the reconstruction status of the latter. Our predicted free energies agree with experiment, and correlate with trends in interfacial water structuring. For gold, surface hydration is predicted as a chief determining factor in peptide–surface recognition. Our findings can be used to suggest how shaped seed-nanocrystals of Au, in partnership with AuBP1, could be used to control AuNP nanoparticle morphology.

We propose a model for MgCl2-supported Ziegler–Natta catalysts, which is capable to reconcile the discrepancies emerging in the last 20 years, in which attempts have been made to rationalize experimental data by molecular models. We show that step defects on the thermodynamically more stable (104) facet of MgCl2 can lead to sites for strong TiCl4 adsorption. The corresponding Ti-active site is stereoeselective, and its stereoselectivity can be enhanced by coordination of Al-alkyls or Lewis bases in the close proximity. The surface energy of the step defected (104) MgCl2 facet is clearly lower than that of the well accepted (110) facet.

In the atom probe microanalysis of steels, inconsistencies in the measured compositions of solutes (C, N) have often been reported, as well as their appearance as molecular ions. Here we propose that these issues might arise from surface migration of solute atoms over the specimen surface. Surface migration of solutes is evidenced by field-ion microscopy observations, and its consequences on atom probe microanalysis are detailed for a wide range of solute (P, Si, Mn, B, C, N). It is proposed that directional walk driven by field gradients over the specimen surface and thermally activated is the prominent effect., Comment: 30 pages , 10 figures

Using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. we studied the evolution of the structure and chemical state of a Rh(110) surface, modified by K adlayers and exposed to high O-2 doses at elevated temperatures, We find that oxygen coadsorption on the K-covered Rh(110) leads to massive reconstruction of the Rh(110) surface. Stable reconstructed (10 x 2) and (8 x 2) segmented phases with a local coverage of more than two oxygen atoms per surface Rh atom were observed. Formation of surface oxide, which coexists with the (10 x 2) and (8 x 2) segmented adsorption phases, is evidenced at the highest O-2 doses. The development of strongly reconstructed adsorption phases with oxide-like stoichiometry and surface oxide under UHV conditions is explained in terms of the stabilization of the (1 x 2) reconstruction and promotion of O-2 dissociation by the K adatoms.

A simple approach based on (i) the glue model for gold, (ii) an empirical force field for C60 and (iii) the charge equilibration plus the Born-Mayer potential for their interaction shows that the two experimentally detected structures for C60 on Au(110) 6] are competitive from 100 K. The model further shows the different nature of the Au-Au and Au-C60 interactions inside the two unit cells, which makes one structure prevail over the other as a function of the experimental conditions. More specifically, the calyx-like structure of ref. [6] is favoured by metal-organic interactions, while the regular structure of ref. [5] is characterized by a remarkable stability of the Au surface. Poster ECSCD-8 18-21 July, 2004 (Segovia, Spain)

We study how quenched impurities affect the surface diffusion and ordering of strongly interacting adsorbate atoms on surfaces. To this end, we carry out Monte Carlo simulations for a lattice-gas model of O/W~110!, including small concentrations of immobile impurities which block their adsorption sites. We examine the behavior of the diffusion coefficients and order parameters as a function of coverage corresponding to various ordered phases at low temperatures. The effects of impurities are examined under both equilibrium and nonequilibrium conditions, and the results are compared to recent studies on a completely clean surface. We find that even minute impurity concentrations affect the diffusion behavior considerably in equilibrium. The effects are strongest in ordered phases and close to phase boundaries, where quenched impurities lead to a reduction of order, which in turn leads to significant changes in the collective diffusion and phase behavior. As the impurity concentration is increased to a level of a few percent of the total surface area, the reduction in order becomes particularly prominent at high coverages. Further studies under nonequilibrium conditions reveal that nonequilibrium effects are strong in the absence of impurities, while for surfaces covered by impurities the nonequilibrium effects are relatively weaker. © 2002 American Institute of Physics. @DOI: 10.1063/1.1505856#

The adhesion of water to solid surfaces is characterized by the tendency to balance competing molecule-molecule and molecule-surface interactions. Hydroxyl groups form strong hydrogen bonds to water molecules and are known to substantially influence the wetting behaviour of oxide surfaces, but it is not well-understood how these hydroxyl groups and their distribution on a surface affect the molecular-scale structure at the interface. Here we report a study of water clustering on a moire-structured iron oxide thin film with a controlled density of hydroxyl groups. While large amorphous monolayer islands form on the bare film, the hydroxylated iron oxide film acts as a hydrophilic nanotemplate, causing the formation of a regular array of ice-like hexameric nanoclusters. The formation of this ordered phase is localized at the nanometre scale; with increasing water coverage, ordered and amorphous water are found to coexist at adjacent hydroxylated and hydroxyl-free domains of the moire structure.

Despite the development of crystal engineering, it remains a great challenge to predict the crystal structure even for the simplest molecules, and a clear link between molecular and crystal symmetry is missing in general. Here we demonstrate that the two-dimensional (2D) crystallization of heterocirculenes on a Au(111) surface is greatly affected by the molecular symmetry. By means of ultrahigh vacuum scanning tunneling microscopy, we observe a variety of 2D crystalline structures in the coverage range from submonolayer to monolayer for D-8h-symmetric sulflower (C16S8), whereas D-4h-symmetric selenosulflower (C16S4Se4) forms square and rectangular lattices at submonolayer and monolayer coverages, respectively. No long-range ordered structure is observed for C-1h-symmetric selenosulflower (C16S5Se3) self-assembling at submonolayer coverage. Such different self-assembly behaviors for the heterocirculenes with reduced molecular symmetries derive from the tendency toward close packing and the molecular symmetry retention in 2D crystallization due to van der Waals interactions.