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Electrocatalytic denitrifification is a promising technology for removing NOx species (NO3−, NO2− and NO). For NOx electroreduction (NOxRR), there is a desire for understanding the catalytic parameters that control the product distribution. Here, we elucidate selectivity and activity of catalyst for NOxRR. At low potential we classify metals by the binding of ∗NO versus ∗H. Analogous to classifying CO2 reduction by ∗CO vs ∗H, Cu is able to bind ∗NO while not binding ∗H giving rise to a selective NH3 formation. Besides being selective, Cu is active for the reaction found by an activity-volcano. For metals that does not bind NO the reaction stops at NO, similar to CO2-to-CO. At potential above 0.3 V vs RHE, we speculate a low barrier for N coupling with NO causing N2O formation. The work provide a clear strategy for selectivity and aims to inspire future research on NOxRR.

High harmonic generation (HHG) from semiconductors and insulators has become a very active area of research due to its great potential for developing compact HHG devices. Here we show that by growing monolayers (ML) of insulators on single-crystal metal surfaces, one can tune the harmonic spectrum by just varying the thickness of the ultrathin layer, not the laser properties. This is shown from numerical solutions of the time-dependent Schr\"odinger equation for $n$ML NaCl/Cu(111) systems ($n=1-50$) based on realistic potentials available in the literature. Remarkably, the harmonic cutoff increases linearly with $n$ and as much as an order of magnitude when going from $n$ $=$ 1 to 30, while keeping the laser intensity low and the wavelength in the near-infrared range. Furthermore, the degree of control that can be achieved in this way is much higher than by varying the laser intensity. The origin of this behavior is the reduction of electronic "friction" when moving from the essentially discrete energy spectrum associated with a few-ML system to the continuous energy spectrum (bands) inherent to an extended periodic system., Comment: 6 pages, 4 figures

Selenolate is considered as an alternative to thiolate to serve as a headgroup mediating the formation of self-assembled monolayers (SAMs) on coinage metal substrates. There are, however, ongoing vivid discussions regarding the advantages and disadvantages of these anchor groups, regarding, in particular, the energetics of the headgroup-substrate interface and their efficiency in terms of charge transport/transfer. Here we introduce a well-defined model system of 6-cyanonaphthalene-2-thiolate and -selenolate SAMs on Au(111) to resolve these controversies. The exact structural arrangements in both types of SAMs are somewhat different, suggesting a better SAM-building ability in the case of selenolates. At the same time, both types of SAMs have similar packing densities and molecular orientations. This permitted reliable competitive exchange and ion-beam-induced desorption experiments which provided unequivocal evidence for a stronger bonding of selenolates to the substrate as compared to the thiolates. Regardless of this difference, the dynamic charge transfer properties of the thiolate- and selenolate-based adsorbates were found to be nearly identical, as determined by the core-hole-clock approach, which is explained by a redistribution of electron density along the molecular framework, compensating the difference in the substrate-headgroup bond strength.

International audience; Carbon monoxide is a ubiquitous molecule in surface science, materials chemistry, catalysis and nanotechnology. Its interaction with a number of metal surfaces is at the heart of major processes, such as Fischer-Tropsch synthesis or fuel-cell optimization. Recent works, coupling structural and nanoscale in situ analytic tools have highlighted the ability of metal surfaces and nanoparticles to undergo restructuring after exposure to CO under fairly mild conditions, generating nanostructures. This Minireview proposes a brief overview of recent examples of such nanostructuring, which leads to a discussion about the driving force in reversible and non-reversible situations.

Applying time-dependent photoemission we unravel the graphene growth process on a metallic surface by chemical vapor deposition (CVD). Graphene CVD growth is in stark contrast to the standard growth process of two--dimensional films because it is self-limiting and stops as soon as a monolayer graphene has been synthesized. Most importantly, a novel phase of metastable graphene was discovered that is characterized by permanent and simultaneous construction and deconstruction. The high quality and large area graphene flakes are characterized by angle-resolved photoemission proofing that they are indeed monolayer and cover the whole 1$\times$1 cm Nickel substrate. These findings are of high relevance to the intensive search for reliable synthesis methods for large graphene flakes of controlled layer number.

Combinatorial bio-techniques have demonstrated that proteins can be good and even selective binders for several inorganic surfaces, including metals. However, the understanding of the basic physical mechanisms that govern such interactions did not keep up with the success in these experiments. The comprehension of such mechanisms would greatly benefit from the computational investigation of the problem. Because of the complexity of the system, classical molecular dynamics simulations based on an atomistic description appear to be the best compromise between reliability and feasibility. For proteins interacting with metal surfaces, however, methodological improvements with respect to standard Molecular Dynamics (MD) of proteins are needed, since the polarization of the metal induced by the protein (and the surrounding water) is not generally negligible. In this article, we present a simple approach to introduce metal polarization effects (often termed image effects) in MD simulations by exploiting standard features of bio-oriented MD codes such as the widely used GROMACS and NAMD. Tests to show the reliability of the proposed methods are presented, and the results for a model application showing the importance of image effects are also discussed. (C) 2008 Wiley Periodicals, Inc.

We report the first observation of the Goos-Hanchen shift in metallic reflection. The shift is found to be insensitive to surface flatness but it depends on the microscopic roughness of the metal surface.

The morphological development of step edge patterns in the presence of meandering instability during step flow growth is studied by simulations and numerical integration of a continuum model. It is demonstrated that the kink Ehrlich-Schwoebel barrier responsible for the instability leads to an invariant shape of the step profiles. The step morphologies change with increasing coverage from a somewhat triangular shape to a more flat, invariant steady state form. The average pattern shape extracted from the simulations is shown to be in good agreement with that obtained from numerical integration of the continuum theory., Comment: 4 pages, 4 figures, RevTeX 3, submitted to Phys. Rev. B

The effect of inelastic scattering processes on the angular distribution of positrons spontaneously emitted from metal surfaces is investigated. Angular and energy spectra are calculated for positrons suffering energy loss due to electron-hole excitation in emission from materials with low (aluminum) and high (tungsten) positron work functions.