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BACKGROUND Orthopedic implant-related infection remains one of the most serious complications after orthopedic surgery. In recent years, there has been an increased scientific interest to improve prevention and treatment strategies. However, many of these strategies have focused on chemical measures. AIM To analyze the effect of alternating current electrical fields on bacterial adherence to titanium surfaces. METHODS Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were exposed to 6.5 V electrical currents at different frequencies: 0.5 Hz, 0.1 Hz, and 0.05 Hz. After exposure, a bacterial count was then performed and compared to the control model. Other variables registered included the presence of electrocoagulation of the medium, electrode oxidation and/or corrosion, and changes in pH of the medium. RESULTS The most effective electrical model for reducing S. aureus adhesion was 6.5 V alternating current at 0.05 Hz achieving a 90% adhesion reduction rate. For E. coli, the 0.05 Hz frequency model also showed the most effective results with a 53% adhesion reduction rate, although these were significantly lower than S. aureus. Notable adhesion reduction rates were observed for S. aureus and E.coli in the studied conditions. However, the presence of electrode oxidation makes us presume these conditions are not optimal for in vivo use. CONCLUSION Although our findings suggest electrical currents may be useful in preventing bacterial adhesion to metal surfaces, further research using other electrical conditions must be examined to consider their use for in vivo trials.

Introduction. One of the main types of deposits in an internal combustion engine is an emulsion or sludge formed by water, decomposition of fuel residues and solid residues. The sludge usually settles on the colder surfaces of the engine, such as the bottom of the crankcase pan, valve chambers and upper boards. The main problem is that this type of deposits can be collected by the engine oil and transferred to areas such as the oil pump, intake valve or oil channels, where the sludge can interfere with the flow of oil and cause a failure of the lubrication mode. In addition to the disruption in the operation of the above-mentioned systems, the engine oil quality indicators are also undergoing changes for the worse.Materials and methods. To monitor the condition of the engine oil, it is necessary to determine the characteristics of its performance, such as: kinematic viscosity at 40 oC and at 100 oC, acid number, base number and determine the number of elements – indicators of additives and wear products contained in the engine oil. The viscosity was determined using a Stabinger SVM 3000 viscometer. It measures the dynamic viscosity and density of oils and fuels in accordance with ASTM D7042 and automatically calculates the kinematic viscosity, viscosity index and outputs the measurement results. The acid and base numbers were determined using an automatic titrator TitroLine alpha plus, and the presence of indicator elements in engine oil using an inductively coupled plasma optical emission spectrometer of the iCAP 7000 series, designed for analysis and determination of the number of indicator elements in liquid and solid samples.Results. The dynamics of changes in the performance characteristics of the Gazpromneft Diesel Ultra 10W-40 engine oil with an extended replacement interval, which is applicable for equipment operating in severe conditions, depending on the water content in the samples of this lubricant, was analyzed.Conclusion. The consequences that may occur due to water entering the engine oil are indicated.

Transmission electron microscopy (TEM) has become a valuable tool in the study of the structure and composition of metal surfaces, though its surface-sensitivity is known to be lower than that for reflection high energy electron diffraction (RHEED), low energy electron diffraction (LEED) and Auger electron spectroscopy. In the present work evaporated films of gold and clean and oxidized surfaces of copper single crystals have been studied using TEM. The gold films were used to test a dynamical theory analysis of coherent (Bragg) and diffuse background scattering involving first order Laue zone diffracted beams, with moderately good agreement between theory and experimental results being obtained. Monolayer thickness changes have been imaged in dark field on (111) Au films and a comparison of calculated and experimental values for bright field intensity changes identifies hillocks or depressions in the surfaces. Severe limitations are imposed on the imaging of surface steps by diffraction conditions, specimen thickness and cleanliness, and objective aperture size. Although surface features producing preferential nucleation of cuprous oxide on low index copper faces could not be analysed by the dark field technique mentioned above, detailed information is provided by two-beam dark field and weak beam imaging using copper reflections. The three-dimensional shape of the cuprous oxide is determined by weak beam imaging employing both copper and cuprous oxide reflections, showing that islands on (100) Cu specimens, grown at 250 to 400° C in 1 x 10$^{-3}$ torr of oxygen, have about 28% of the oxide above the substrate surface. A transfer device for transporting specimens under ultrahigh vacuum conditions from a U.H.V. chamber to a high resolution electron microscope has proved of value in the study of oxidized copper surfaces. By combining RHEED, in the U.H.V. system, and TEM analysis not only is cuprous oxide studied but the higher form, cupric oxide, is also detected and its morphology and epitaxy ascertained.

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.

The development of approaches for the non-thermal sterilization of instruments is an urgent task to ensure the safety of meat industry products, where the use of hot water leads to the formation of condensates and a deterioration in the hygienic condition of the premises. In this study, an installation for sterilizing knives was created, which works by activating aqueous salt solutions with a glow discharge. The power consumption of the installation reactor is only 125–150 Wh. The temperature rise of the sterilizing agent used is about 1.1 ± 0.2 °C/min/L. The effectiveness of the installation for plasma-activation of aqueous solutions of chloride and sodium sulfate by glow discharge (PAW) in relation to the inactivation of microorganisms, including Staphylococcus aureus, Salmonella typhimurium, Pseudomonas gessardii and L. monocytogenes, on steel surfaces was evaluated. Samples of stainless steel (parts of knives) were used in two versions (new and artificially aged). Mono- and polyspecies bacterial biofilms were grown on the surface of the samples. The treatment was carried out by immersing samples of steel plates in plasma-activated aqueous solutions. It was found that the treatment of plates in a knife sterilizer for 1 min had an effective effect on the inhibition of all types of studied bacteria.

We present a wave packet propagation-based method to study the electron dynamics in molecular species in the gas phase and adsorbed on metal surfaces. It is a very general method that can be employed to any system where the electron dynamics is dominated by an active electron and the coupling between the discrete and continuum electronic states is of importance. As an example, one can consider resonant molecule-surface electron transfer or molecular photoionization. Our approach is based on a computational strategy allowing incorporating ab initio inputs from quantum chemistry methods, such as density functional theory, Hartree-Fock, and coupled cluster. Thus, the electronic structure of the molecule is fully taken into account. The electron wave function is represented on a three-dimensional grid in spatial coordinates, and its temporal evolution is obtained from the solution of the time-dependent Schrödinger equation. We illustrate our method with an example of the electron dynamics of anionic states localized on organic molecules adsorbed on metal surfaces. In particular, we study resonant charge transfer from the I orbitals of three vinyl derivatives (acrylamide, acrylonitrile, and acrolein) adsorbed on a Cu(100) surface. Electron transfer between these lowest unoccupied molecular orbitals and the metal surface is extremely fast, leading to a decay of the population of the molecular anion on the femtosecond timescale. We detail how to analyze the time-dependent electronic wave function in order to obtain the relevant information on the system: The energies and lifetimes of the molecule-localized quasistationary states, their resonant wavefunctions, and the population decay channels. In particular, we demonstrate the effect of the electronic structure of the substrate on the energy and momentum distribution of the hot electrons injected into the metal by the decaying molecular resonance, This work was partially supported by the MICINN-Spanish Ministry of Science and Innovation-projects CTQ2016-76061-P and PID2019-110091GBI00 and the “María de Maeztu” (CEX2018-000805-M) Program for Centers of Excellence in R&D

In this study, we demonstrate the structural evolution of a two-dimensional (2D) supramolecular assembly system, which is steered by the thermally activated deprotonation of the primary organic building blocks on a Ag(111) surface. Scanning tunneling microscopy revealed that a variety of structures, featuring distinct structural, chiral, and intermolecular bonding characters, emerged with the gradual thermal treatments. According to our structural analysis, in combination with density function theory calculations, the structural evolution can be attributed to the successive deprotonation of the organic building blocks due to the inductive effect. Our finding offers a facile strategy towards controlling the supramolecular assembly pathways and provides a comprehensive understanding of the 2D crystal engineering on surfaces.

Hydrogen transfer reactions play a significant role in many technological applications and fundamental processes in nature. Despite appearing to be simple reactions, they constitute complex processes where nuclear quantum effects (NQE) such as zero-point energy and nuclear tunneling play a decisive role even at ambient temperature. Moreover, the anharmonic coupling between different degrees of freedom that take place in realistic systems leads to hydrogen dynamics that, in many cases, are hard to interpret and understand. Systematic and quantitative ab initio studies of hydrogen dynamics were performed in systems ranging from gas phase molecules to adsorbates on metallic surfaces using state-of-the-art methodologies based on the path integral formulation of quantum mechanics in combination with the density functional approximation. In order to achieve this task, the construction of a general infrastructure that made the required ring polymer instanton simulations feasible was created, and a new approximation which considerably reduces the computational cost of including NQE on weakly bound systems was proposed and tested in the study of water dissociation at Pt(221) surface. Practical guidelines and limitations were also discussed to help the adoption of such methodologies by the community. The system of choice for most of the studies presented in this thesis was the porphycene molecule, a paradigmatic example of a molecular switch. The are a large number of experimental results in well-controlled environments available in the literature which have demonstrated the importance of NQE and multidimensional coupling for this molecule. Therefore, the porphycene molecule provides the unique possibility to theoretically address these effects and compare the theoretical predictions with experimental results in different environments. A portion of this thesis focuses on the study of porphycene molecule in the gas phase. For this purpose, the intramolecular double hydrogen transfer (DHT) rates and vibrational spectrum were calculated. The theoretical results showed a remarkable agreement with the experiments, and enabled the explanation of the unusual infrared spectra, the elucidation of the dominant DHT mechanism, and the understanding of their temperature dependence. In all the cases, the coupling between low- and high-frequency modes proved to be essential to get qualitatively correct trends. Another portion of this thesis examines molecules adsorbed on surfaces. Studies of porphycene molecules adsorbed on (111) and (110) metal surfaces showed that the stronger the surface-molecule interaction is, the more the molecule buckles upon adsorption, leading to an overall decrease of the DHT rates. The simulations identified different temperature regimes of the DHT mechanism, which was not possible by experimental measurements, and evidenced the importance of surface fluctuations on the DHT rates. In conclusion, this thesis provides a stepping stone towards the understanding of the impact of NQE, anharmonic effects, and multidimensional mode coupling on hydrogen dynamics, and also describes novel computational tools to approach their study by using first-principle calculations., Wasserstofftransferreaktionen spielen in vielen technologischen Anwendungen und grundlegenden Prozessen in der Natur eine bedeutende Rolle. Obwohl es sich um einfache Reaktionen zu handeln scheint, umfassen sie komplexe Prozesse, bei denen nukleare Quanteneffekte (NQE) wie Nullpunktsenergie und nukleares Tunneln auch bei Raumtemperatur von entscheidender Bedeutung sind. Darüber hinaus führt die anharmonische Kopplung zwischen verschiedenen Freiheitsgraden, die in realistischen Systemen stattfindet, zu einer Dynamik des Wasserstoffs, die in vielen Fällen schwer zu interpretieren und zu verstehen ist. In der vorliegenden Arbeit werden systematische und quantitative ab initio Studien zur Wasserstoffdynamik in Systemen durchgeführt, die von Molekülen in der Gasphase bis zu Adsorbaten auf metallischen Oberflächen reichen. Hierbei werden Methoden eingesetzt, die auf der Pfadintegralformulierung der Quantenmechanik in Kombination mit Dichte-Funktional-Approximationen basieren. Um diese Aufgabe zu erfüllen, wird eine Infrastruktur entwickelt, die die erforderlichen Ringpolymer-Instanton-Simulationen ermöglicht. Weiterhin wird eine neue Näherung für schwach-bindende Systeme vorgeschlagen und für die Wasserdissoziation auf Pt(221) Oberfläche getestet, welche die Rechenkosten für die Berücksichtigung von NQE deutlich reduziert. Ebenso werden praktische Richtlinien und Einschränkungen dieser Methode erörtert, die deren Verwendung in der Community erleichtern soll. Das Porphycenmolekül - ein paradigmatisches Beispiel für einen molekularen Schalter - bildet die Grundlage für die meisten in dieser Arbeit vorgestellten Untersuchungen. In der Literatur gibt es eine große Anzahl von experimentellen Ergebnissen in gut kontrollierten Umgebungen, die die Bedeutung von NQE und mehrdimensionaler Kopplung für dieses Molekül gezeigt haben. Daher bietet das Porphycenmolekül die einzigartige Möglichkeit, diese Effekte theoretisch anzugehen und die theoretischen Vorhersagen mit experimentellen Ergebnissen in verschiedenen Umgebungen zu vergleichen. Ein Teil dieser Arbeit befasst sich mit der Untersuchung von Porphycenmolekülen in der Gasphase. Zu diesem Zweck wurden die intramolekularen Doppelwasserstofftransferraten (DHT) und das Vibrationsspektrum berechnet. Die theoretischen Ergebnisse zeigen eine bemerkenswerte Übereinstimmung mit Experimenten und ermöglichen die Erklärung der ungewöhnlichen Infrarotspektren und die Aufklärung des dominanten DHT-Mechanismus, sowie das Verständnis ihrer Temperaturabhängigkeit. In allen Fällen erwies sich die Kopplung zwischen Nieder- und Hochfrequenzmoden als entscheidend um qualitativ korrekte Trends zu erhalten. Ein weiterer Teil dieser Arbeit untersucht Moleküle, die an Oberflächen adsorbiert sind. Untersuchungen von an (111)- und (110)-Metalloberflächen adsorbierten Porphycenmolekülen zeigen, dass die Wechselwirkung zwischen Oberfläche und Molekül umso stärker ist, je mehr sich das Molekül bei der Adsorption verbiegt, was insgesamt zu einer Abnahme der DHT-Raten führt. Die Simulationen identifizieren unterschiedliche Temperaturregime des DHT-Mechanismus, was bisher durch experimentelle Messungen nicht möglich war und hebt die Bedeutung von Oberflächenfluktuationen für die DHT-Raten hervor. Zusammenfassend bildet diese Arbeit die Grundlage zum Verständnis des Einfluss von NQE, anharmonischen Effekten und mehrdimensionaler Modenkopplung auf die Wasserstoffdynamik und beschreibt zudem neuartige Simulationswerkzeuge für die ab initio Untersuchungen dieser Effekte.

Polymeric molecular coatings of thiol-terminated polymers were investigated for prevention of formation of oxide layer on the surface. Effect of the molecular weight of polymeric coatings on oxidation resistance properties was also examined.

Objectives To evaluate the effects of the surface modification of 316L stainless steel (SS) by lowtemperature plasma nitriding on endothelial cells for stent applications. Results X-ray diffraction (XRD) confirmed the incorporation of nitrogen into the treated steel. The surface treatment significantly increased SS roughness and hydrophilic characteristics. After 4 h the cells adhered to the nitride surfaces and formed clusters. During the 24 h incubation period, cell viability on the nitrided surface was higher compared to the polished surface. Nitriding reduced late apoptosis of rabbit aorta endothelial cell (RAEC) on the SS surface. Conclusion Low temperature plasma nitriding improved the biocompatible of stainless steel for use in stents.

Ullmann coupling or, more generally, dehalogenative aryl-aryl coupling, is one of the most widely exploited chemical reactions to obtain one- and two-dimensional polymers on metal surfaces. It is generally described as a two-step reaction: (i) dehalogenation, resulting in the formation of a stable intermediate organometallic phase and subsequent (ii) C-C coupling. The topology of the resulting polymer depends on the number and positions of the halogen atoms in the haloaromatic precursor, although its orientation and order are determined by the structure of the intermediate phase. Hitherto, only one intermediate structure, identified as an organometallic (OM) phase, has been reported for such a reaction. Here we demonstrate the formation of two distinct OM phases during the temperature-induced growth of poly(para-phenylene) from 1,4-dibromobenzene precursors on Cu(110). Beyond the already known linear-OM chains, we show that a phase reorganization to a chessboard-like 2D-OM can be activated in a well-defined temperature range. This new intermediate phase, revealed only when the reaction is carried out at low molecular coverages, was characterized by X-ray photoelectron spectroscopy, scanning tunneling microscopy and near-edge X-ray absorption fine structure spectroscopy, and modeled by density functional theory calculations. Our data show that the 2D-OM remains stable after cooling down the sample and is stabilized by four-Cu clusters at each node. The observation of such unexpected intermediate phase shows the complexity of the mechanisms underlying on-surface synthesis and broadens the understanding of Ullmann coupling, which continues to be astonishing despite its extensive use.

Inert metal surfaces present more chances of hosting organic intact radicals than other substrates, but large amounts of delocalized electronic states favor charge transfer and thus spin quenching. Lowering the molecule-substrate interaction is a usual strategy to stabilize radicals on surfaces. In some works, thin insulating layers were introduced to provide a controllable degree of electronic decoupling. Recently, retinoid molecules adsorbed on gold have been manipulated with a scanning tunneling microscope (STM) to exhibit a localized spin, but calculations failed to find a radical derivative of the molecule on the surface. Now the formation of a neutral radical spatially localized in a tilted and lifted cyclic end of the molecule is presented. An allene moiety provokes a perpendicular tilt of the cyclic end relative to the rest of the conjugated chain, thus localizing the spin of the dehydrogenated allene in its lifted subpart. DFT calculations and STM manipulations give support to the proposed mechanism., M.‐L.B. thanks the national computational center CINES, and TGCC (Grant 2017‐ [GENCI project: A0010807364]) for a computer grant and acknowledges the Mercator fellowship of SFB 677 in CAU Kiel. N.L. acknowledges financial support from MINECO (MAT2015‐66888‐C3‐2‐R) and FEDER funds, and he is thankful to the Mercator fellowship of SFB 677 in CAU Kiel. M.G. acknowledges financial support of SFB 677. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 766726.

Optica 6(11), 1431 - 1436 (2019). doi:10.1364/OPTICA.6.001431, Intense THz fields can be used to excite specific low-frequency modes in condensed matter or drive confined currents in nano-structured arrays, paving the way for a new class of optoelectronic devices. The long wavelength enables spatially confined field enhancement due to interaction with metallic structures and interference effects at dielectric interfaces. We use THz photoelectron streaking for the polarization-sensitive reconstruction of all electric field components at dielectric and metallic interfaces. This is realized in a THz/x-ray pump–probe experiment where x-ray emitted photoelectrons probe the effective THz field in close surface proximity. We observe distinct differences in the THz response of a nano-structured Pt thin film and a Pt(111) bulk crystal, in particular for the parallel field component. Simulations of the nanoscale spatial field modulation at metallic islands on the thin film provide design parameters for different sensitivity regimes with respect to local fields., Published by OSA, Washington, DC

In this work we present a model for the surface oxidation growth of thin films considering the influence of space charge. The space charge field Esp is assumed proportional to the charge of moving metal ions and electrons in the oxide layer. The surface charge field Eox decreases as the Cabrera and Motts’ oxide thickness X grows to its limit X1 (Eox=VM/X). Eox remains constant for further growth of the oxide film (Eox=VM/X1). The obtained equation for the growing rate of the oxide film covers two stages. The first stage is characterized by a negligible space charge and is described by the typical inverse logarithmic law. During transition from thin to thick film the oxidation growth rate is described by a direct logarithmic law which is confirmed by many experiments. At the end of this stage the drift of metal ions is replaced by their diffusion that leads to parabolic law.

Interface between oxides and metals appears in a large number of technological fields and has thus been, so far, the focus of scientific investigations in physics, chemistry, and materials science. Among those research fields, oxide/metal interfaces play a relevant role also in magnetism and spintronics applications, where the metallic counterpart is typically a ferromagnet. This article briefly summarizes such a scientific context and provides some concepts and examples related to the particular case of layered magnetic structures. In such systems, ultrathin oxide films can be used, for instance, as tunneling barrier in so-called magnetic tunnel junctions and, in case of oxides that show a long-range antiferromagnetic order, as active layers in exchange bias systems. In such cases, in fact, thin and ultrathin oxides are in proximity to ferromagnetic metals, and the effects of this proximity, in particular those related to the chemistry at the interface, directly influence the magnetic properties of the system. A thorough understanding of these issues is of great importance in the long-term perspective of tailoring the magnetic effects, thus opening the possibility of designing novel technological applications.

Conversion of energy at the gas–solid interface lies at the heart of many industrial applications such as heterogeneous catalysis. Dissipation of parts of this energy into the substrate bulk drives the thermalization of surface species, but also constitutes a potentially unwanted loss channel. At present, little is known about the underlying microscopic dissipation mechanisms and their (relative) efficiency. At metal surfaces, prominent such mechanisms are the generation of substrate phonons and the electronically non-adiabatic excitation of electron–hole pairs. In recent years, dedicated surface science experiments at defined single-crystal surfaces and predictive-quality first-principles simulations have increasingly been used to analyze these dissipation mechanisms in prototypical surface dynamical processes such as gas-phase scattering and adsorption, diffusion, vibration, and surface reactions. In this topical review we provide an overview of modeling approaches to incorporate dissipation into corresponding dynamical simulations starting from coarse-grained effective theories to increasingly sophisticated methods. We illustrate these at the level of individual elementary processes through applications found in the literature, while specifically highlighting the persisting difficulty of gauging their performance based on experimentally accessible observables.

Summary In this study, two eco-friendly nanostructured systems were designed for a controlled release of protective agents, commonly used in traditional restoration treatments, for the preservation of metal and stone artifacts. ?-Cyclodextrin and its derivative were used as nanocarriers, since their capability to form "host-guest" complexes with hydrophobic molecules. The loaded agents were commercial products: 1H-Benzotriazole (BTA) and BIOTIN R®, commonly used, respectively, as corrosion inhibitor of copper-based artifacts and as biocide for stone protection against the proliferation of algae and lichens. Motivation Despite a general good preservative effect, commercial products can be often toxic and/or easily subjected to leaching, resulting in a not long lasting intervention. In order to obtain non-toxic systems and to increase the durability of the protective treatments, two different systems were developed by loading the chemical agents in suitable nanocarriers, which could be, then, applied as polymeric or crosslinked coating on the surface of the artifacts. Results An organic system based on ?-Cyclodextrin/BTA complex was produced for the corrosion inhibition of Cu-based surfaces. An organic/inorganic hybrid system, based on ?-Cyclodextrin/BIOTIN R® supported on mesoporous silica, was developed for the protection of stone biodeterioration. Both systems were characterized by surface chemical analysis (XPS) and structural analysis by X-ray diffraction (XRD). The kinetics of release of ?-Cyclodextrin/BTA system was investigated by UV-VIS spectroscopy in 3%NaCl solution in order to simulate the marine environment. The kinetics of release of the ?-Cyclodextrin/BIOTIN R® system was investigated in acidic solution in order to simulate an urban polluted environment (rain water). The gradual release of the protective agent encourages the use of ?-Cyclodextrin/BTA system as non-toxic, self-healing and long-lasting corrosion inhibitor of Cu-based alloys. Acknowledgements. This work was financially supported by the PON03PE_00214_1 TECLA Project: "Nanotecnologie e nanomateriali per i Beni Culturali", Distretto di Alta Tecnologia per l'Innovazione nel settore dei Beni Culturali della Regione Sicilia.

We demonstrate that reflectance difference spectroscopy (RDS) is sensitive to defects induced by ion bombardment, located either in the topmost layer or in the subsurface region. Most importantly, these two kinds of defects can be spectrally discriminated, since the corresponding signatures in the RD spectrum arise from perturbations of different types of electronic states: The defects in the topmost surface layer mainly lead to a quenching of the optical anisotropy related to surface states, whereas the subsurface defects strongly affect the optical anisotropy originating from transitions between surface-modified bulk electronic states. Consequently, RDS can be used to simultaneously monitor the defects in the topmost surface layer and in the subsurface region in-situ during ion bombardment and thermal annealing. Characteristic RD spectra and the corresponding STM images for a Cu(110) substrate before and after healing of the subsurface defects.

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

Coupling of Rayleigh waves propagating along two metal surfaces separated by a narrow fluid channel is predicted and experimentally observed. Although the coupling through a fluid (water) is weak, a strong synchronization in propagation of Rayleigh waves even for the metals with sufficiently high elastic contrast (brass and aluminum) is observed. Dispersion equation for two polarizations of the coupled Rayleigh waves is derived and experimentally confirmed. Excitation of coupled Rayleigh waves in a channel of finite length leads to anomalously low transmission of acoustic energy at discrete set of resonant frequencies. This effect may find useful applications in the design of acoustic metamaterial screens and reflectors. (C) 2012 Acoustical Society of America. [http://dx.doi.org/10.1121/1.4744939], Work supported by the DOE Grant No. DE-FG02-06ER46312, and by the ONR Grant No. N00014-12-1-0216. A. K. acknowledges the support from the Spanish MEC under Grant No. SAB2009-0006 and the UPV program "Ayda para Estancia de Investigadores de Prestigio." We thank Ciprian Sarl for technical support. T.L.-R. acknowledges useful discussions with P. Halevi and A. Wirgin.

Silicene–the silicon-based counterpart of graphene–has a two dimensional structure that is responsible for the variety of potentially useful chemical and physical properties. The existence of silicene has been achieved recently owing to experiments involving epitaxial growth of silicon as stripes on Ag(001), ribbons on Ag(110), and sheets on Ag(111). The nano-ribbons observed on Ag(110) were found–by both high definition experimental scanning tunneling microscopy images and density functional theory calculations–to consist of an arched honeycomb structure. Angle resolved photo-emission experiments on these silicene nano-ribbons on Ag(110), along the direction of the ribbons, showed a band structure which is analogous to the Dirac cones of graphene. Unlike silicon surfaces, which are highly reactive to oxygen, the silicene nano-ribbons were found to be resistant to oxygen reactivity. On the theoretical side, recent extensive efforts have been deployed to understand the properties of standalone silicene sheets and nano-ribbons using both tight-binding and density functional theory calculations. Unlike graphene it is demonstrated that silicene sheets are stable only if a small buckling (0.44 A) is present. The electronic properties of silicene nano-ribbons and silicene sheets were found to resemble those of graphene. Although this is a fairly new avenue, the already obtained outcome from these important first steps in understanding silicene showed promising features that could give a new future to silicon in the electronics industry, thus opening a promising route toward wide-range applications. In this review, we plan to introduce silicene by presenting the available experimental and theoretical studies performed to date, and suggest future directions to be explored to make the synthesis of silicene a viable one.

Surface enhanced Raman spectra from molecules (bipyridyl ethylene) adsorbed on gold dumbells are observed to become increasingly asymmetric (Fano-like) at higher incident light intensity. The electronic temperature (inferred from the anti-Stokes (AS) electronic Raman signal increases at the same time while no vibrational AS scattering is seen. These observations are analyzed by assuming that the molecule-metal coupling contains an intensity dependent contribution (resulting from light-induced charge transfer transitions as well as renormalization of the molecule metal tunneling barrier). We find that interference between vibrational and electronic inelastic scattering routes is possible in the presence of strong enough electron-vibrational coupling and can in principle lead to the observed Fano-like feature in the Raman scattering profile. However the best fit to the observed results, including the dependence on incident light intensity and the associated thermal response is obtained from a model that disregards this coupling and accounts for the structure of the continuous electronic component of the Raman scattering signal. The temperatures inferred from the Raman signal are argued to be only of qualitative value., 20 pages, 12 figures

We study the effect of electron and phonon degrees of freedom on the relaxation dynamics of adsorption processes in gas-surface systems by using ab initio molecular dynamics that incorporates an electronic friction force (AIMDEF). As representative cases we have chosen three systems with different adsorption energies and adsorbate-to-surface atom mass ratios: H on Pd(1 0 0), N on Ag(1 1 1), and on Fe(1 1 0). We show, through inspection of the total energies and trajectories of the hot adsorbates on the surface, that electron–hole (e–h) pair excitations dominate relaxation of the light gas species, while the phonon channel is dominant for the heavy species. In the latter case e–h pairs become more important at the final thermalization stages., This work has been supported by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economía y Competitividad (Grant No. FIS2013-48286-C2-2-P).

We present microwave-frequency NbTiN resonators on silicon, systematically achieving internal quality factors above 1?M in the quantum regime. We use two techniques to reduce losses associated with two-level systems: an additional substrate surface treatment prior to NbTiN deposition to optimize the metal-substrate interface and deep reactive-ion etching of the substrate to displace the substrate-vacuum interfaces away from high electric fields. The temperature and power dependence of resonator behavior indicate that two-level systems still contribute significantly to energy dissipation, suggesting that more interface optimization could further improve performance.

Metallocene (MCp2) wires have recently attracted considerable interest in relation to molecular spintronics due to predictions concerning their half-metallic nature. This exciting prospect is however hampered by the little and often-contradictory knowledge we have concerning the metallocene self-assembly and interaction with a metal. Here, we elucidate these aspects by focusing on the adsorption of ferrocene on Cu(111) and Cu(100). Combining low-temperature scanning tunneling microscopy and density functional theory calculations, we demonstrate that the two-dimensional molecular arrangement consists of vertical- and horizontal-lying molecules. The noncovalent T-shaped interactions between Cp rings of vertical and horizontal molecules are essential for the stability of the physisorbed molecular layer. These results provide a fresh insight into ferrocene adsorption on surfaces and may serve as an archetypal reference for future work with this important variety of organometallic molecules. (Figure Presented)., This work has been supported by the Agence Nationale de la Recherche (Grant No. ANR-13-BS10-0016). L.L. acknowledges also financial support from the Agence Nationale de la Recherche through projects LabEx NIE and LabEx CSC. R.R. and N.L. acknowledge financial support from Spanish MINECO (Grant No. MAT2012-38318- C03-02 with joint financing by FEDER Funds from the European Union). P.A. acknowledges financial support from CONICET. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

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.

We present microwave-frequency NbTiN resonators on silicon, systematically achieving internal quality factors above 1 M in the quantum regime. We use two techniques to reduce losses associated with two-level systems: an additional substrate surface treatment prior to NbTiN deposition to optimize the metal-substrate interface, and deep reactive-ion etching of the substrate to displace the substrate-vacuum interfaces away from high electric fields. The temperature and power dependence of resonator behavior indicate that two-level systems still contribute significantly to energy dissipation, suggesting that more interface optimization could further improve performance., Comment: 4 pages, 3 figures, plus Supplemental Material (8 figures)

Surface plasmon resonance (SPR) based sensors are usually designed using the Kretschmann prism coupling configuration in which an input beam couples with a surface plasmon through a thin metal film. This is generally preferred by sensor developers for building planar devices instead of the Otto prism coupling configuration, which, for efficient coupling, requires the metal surface to be maintained at a distance on the order of the wavelength from the input prismsurface. In this paper, we report on the microfabrication and characterization of an Otto chip device, which is suitable for applications of the SPR effect in gas sensing and biosensing. (C) 2015 Optical Society of America

Inorganically driven fouling of metal heat-transfer surfaces employed in crude oil refining operations is not well understood. The object of this study is twofold: First, we systematically elucidate the time-dependent mechanism of the interrelated carbonaceous and sulfidic build up that occurs at high temperatures on a metal surface (540 °C metal temperature, 250 °C oil bath temperature). Second, we demonstrate that additions of 0.5, 1.3 and 5.7 vol% thiophene (C 4 H 4 S) cause a 2×, 10×, and 20× reduction in the fouling factor after a 1400 min exposure. Analytical techniques including TEM, SEM–EDX, FIB, Auger electron spectroscopy and XRD were employed to detail the fouling phenomenology for a heated stainless steel wire immersed in atmospheric bottoms fraction crude oil, exposed for 1–1400 min. A key microstructural observation is the transformation of the wire’s as-received near-surface textured austenitic grain structure into a micron scale (e.g. ∼10 μm at 1400 min) highly porous inner-sulfide/chromium oxide bilayer composite. Additionally, we observe significant localized sulfidic attack into the bulk of the metal. During testing, an iron sulfide (pyrrhotite Fe (1 − x ) S) corrosion product forms almost instantaneously at the metal surface, followed by coke formation around its periphery at longer times. This temporal sequence, combined with the observation that the thicker regions of the foulant are clearly associated with detached plumes of the sulfide, leads us to argue that the sulfide is essential for promoting organic fouling. This is brought about by the sulfide’s action as a potent dehydrogenation catalyst that drives the transformation of pitch to coke. We hypothesize that the tremendous fouling inhibition effect of the thiophene originates from its adsorption onto the sulfide surfaces, thereby blocking the dehydrogenation reactions.

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.

Adhesion of the bacterial strain Staphylococcus epidermidis 3399 to titanium-oxy-nitride (TiNOX (R)) substrata with different specific resistivities was studied in a parallel plate flow chamber, while simultaneously measuring the electric potential of the substrata. During adhesion, bacteria either donated or accepted electrons to the substrata depending on the specific resistivity of the substratum and bacteria that had donated electrons to the substratum adhered more strongly than bacteria that had accepted electrons from the substratum. These results demonstrate that electron transfer plays a role in bacterial adhesion to conducting surfaces, which has hitherto been neglected. (C) 2000 Elsevier Science B.V. All rights reserved.

Adhesion of the bacterial strain Staphylococcus epidermidis 3399 to titanium-oxy-nitride (TiNOX (R)) substrata with different specific resistivities was studied in a parallel plate flow chamber, while simultaneously measuring the electric potential of the substrata. During adhesion, bacteria either donated or accepted electrons to the substrata depending on the specific resistivity of the substratum and bacteria that had donated electrons to the substratum adhered more strongly than bacteria that had accepted electrons from the substratum. These results demonstrate that electron transfer plays a role in bacterial adhesion to conducting surfaces, which has hitherto been neglected. (C) 2000 Elsevier Science B.V. All rights reserved.

Observation of microorganisms adhering to metal surfaces is more difficult than of those adhering to glass or translucent polymers and usually requires special techniques as e.g. epifluorescent microscopy, scanning electron microscopy or removal of adhering microorganisms followed by plating. In this paper, the use of metallurgical microscopy to observe microorganisms adhering to metal surfaces is described. The method is simple, attachment of the vertical illumination set up required to an ordinary light microscope is relatively cheap, and no additional manipulations are necessary. The image quality is high and individual adhering microorganisms can be easily observed, even without employing additional image analysis techniques. As an example of the application of this technique, the influence of Ca2+ ions on the adhesion of three strains of dairy Streptococcus thermophilus to 316-L stainless steel was studied. Using a parallel plate flow chamber with a stainless steel bottom plate and a glass top plate, adhesion was measured in situ on the bottom plate under moderate flow (15 s(-1)) in an adhesion buffer with various amounts of CaCl2 added. Neither the initial deposition rates nor the numbers of organisms adhering after 200 min showed systematic variation with the amounts of CaCl2 added. However, for S. thermophilus G1 initial the deposition rates with 1 mM CaCl2 were much higher (2170 cm(-2) s(-1)) than was the case without CaCl2, or with 5 mM CaCl2 added (approximately 1300 cm(-2) s(-1)). For S. thermophilus B and N-12 the initial deposition rates were only slightly higher with 5 mM CaCl2 than without CaCl2 or without 1 mM CaCl2 added. Thus in order to study adhesion of thermophilic, dairy streptococci under different conditions, such as in a pasteurizer, calcium must be added as its presence can have a major effect.

Observation of microorganisms adhering to metal surfaces is more difficult than of those adhering to glass or translucent polymers and usually requires special techniques as e.g. epifluorescent microscopy, scanning electron microscopy or removal of adhering microorganisms followed by plating. In this paper, the use of metallurgical microscopy to observe microorganisms adhering to metal surfaces is described. The method is simple, attachment of the vertical illumination set up required to an ordinary light microscope is relatively cheap, and no additional manipulations are necessary. The image quality is high and individual adhering microorganisms can be easily observed, even without employing additional image analysis techniques. As an example of the application of this technique, the influence of Ca2+ ions on the adhesion of three strains of dairy Streptococcus thermophilus to 316-L stainless steel was studied. Using a parallel plate flow chamber with a stainless steel bottom plate and a glass top plate, adhesion was measured in situ on the bottom plate under moderate flow (15 s(-1)) in an adhesion buffer with various amounts of CaCl2 added. Neither the initial deposition rates nor the numbers of organisms adhering after 200 min showed systematic variation with the amounts of CaCl2 added. However, for S. thermophilus G1 initial the deposition rates with 1 mM CaCl2 were much higher (2170 cm(-2) s(-1)) than was the case without CaCl2, or with 5 mM CaCl2 added (approximately 1300 cm(-2) s(-1)). For S. thermophilus B and N-12 the initial deposition rates were only slightly higher with 5 mM CaCl2 than without CaCl2 or without 1 mM CaCl2 added. Thus in order to study adhesion of thermophilic, dairy streptococci under different conditions, such as in a pasteurizer, calcium must be added as its presence can have a major effect.

Nonadiabatic energy transfer from the translational motion (T) of a molecule impinging on metal surface to the metal's electrons may determine whether the molecule can lose enough energy to adsorb or react. Although it is thus relevant to heterogeneous catalysis, little is known about the strength of the coupling of T to electron hole pair (ehp) excitation. We present adiabatic ab initio molecular dynamics (AIMD) predictions of the scattering of 5 eV H-atoms from Cu and Au surfaces. Calculations of angularly resolved scattering reveal experimentally realizable conditions where only about 2% of the incidence energy is lost to the metal's phonons. Under these conditions, measurements of the translational energy loss should be able to determine the magnitude of any additional energy loss due to ehp excitation, information that is very valuable to the development of accurate theoretical descriptions of T→ehp coupling. © 2013 American Chemical Society., The Göttingen group acknowledges support of a grant under the joint Programme ANR-DFG-CHEMISTRY 2011 entitled Dynamics of Hydrogen and Deuterium on Gold and Silver Surfaces (DRAGS). D.J.A. and A.M.W. are grateful for support of the Alexander von Humboldt Foundation. M.B.-R. acknowledges financial support from the Gipuzkoako Foru Aldundia and the European Commission through Project No. FP7-PEOPLE-2010-RG276921. M.A. acknowledges the Gobierno Vasco-UPV/EHU project IT-366-07 and the Spanish MICINN project FIS2010-19609-C02-02.

Orientador: João Batista Fogagnolo Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica Resumo: O resumo poderá ser visualizado no texto completo da tese digital Abstract: The abstract is available with the full electronic document Mestrado Materiais e Processos de Fabricação Mestre em Engenharia Mecânica

Texto completo. Acesso restrito. p. 100–105 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-06-27T18:02:15Z No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Material de Física on 2013-08-16T19:14:04Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-19T16:51:54Z No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Unidade fora da demanda on 2013-08-23T22:08:24Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-26T12:35:35Z No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-15T15:14:36Z (GMT) No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Made available in DSpace on 2013-10-15T15:14:36Z (GMT). No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Previous issue date: 2013 In this paper we present a combined low-energy electron diffraction (LEED) and a DFT study of the Au(110)c(2 × 2)–Sb surface in order to determine its atomic structure. The DFT calculations, using both LDA and GGA approaches, have indicated that the adsorption of antimony atoms on the Au(110) surface hollow sites is energetically more favored as compared with other possible adsorption sites. The LEED analysis also showed a Sb-overlayer termination with the Sb atoms segregating to the hollow sites instead of forming an Au–Sb surface alloy. This overlayer results to be contracted of about 0.16 Å with the first gold layer presenting a small expansion (0.04 Å) with respect to the Au bulk interlayers distance. The agreement between the LEED and DFT results is very good Salvador

Texto completo. Acesso restrito. p. 100–105 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-06-27T18:02:15Z No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Material de Física on 2013-08-16T19:14:04Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-19T16:51:54Z No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Unidade fora da demanda on 2013-08-23T22:08:24Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-26T12:35:35Z No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-15T15:14:36Z (GMT) No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Made available in DSpace on 2013-10-15T15:14:36Z (GMT). No. of bitstreams: 1 11111.pdf: 733467 bytes, checksum: f8354f1796f0e4b4d3f70d73d2d7f125 (MD5) Previous issue date: 2013 In this paper we present a combined low-energy electron diffraction (LEED) and a DFT study of the Au(110)c(2 × 2)–Sb surface in order to determine its atomic structure. The DFT calculations, using both LDA and GGA approaches, have indicated that the adsorption of antimony atoms on the Au(110) surface hollow sites is energetically more favored as compared with other possible adsorption sites. The LEED analysis also showed a Sb-overlayer termination with the Sb atoms segregating to the hollow sites instead of forming an Au–Sb surface alloy. This overlayer results to be contracted of about 0.16 Å with the first gold layer presenting a small expansion (0.04 Å) with respect to the Au bulk interlayers distance. The agreement between the LEED and DFT results is very good Salvador

We report evidence that the body-centered cubic (bcc)-face-centered cubic (fcc) transition that occurs during Ni film growth on a Fe(001) substrate is preceded by a pre-martensitic phase, as demonstrated by low-energy electron diffraction. The corresponding film superstructure is characterized by a displacement of Ni atoms along the main h100i crystallographic axes of iron, without any rotation of the unit cell with respect to the (001) plane, in contrast with the martensitic transition that shows four fcc Ni domains with the Nih211i crystallographic directions aligned with the Feh110i axes. In addition, the martensitic transition is detected not at 6ML, as previously believed, but above 20ML if the Ni sample is rigorously kept at room temperature. The surface morphology of the bcc-fcc transition is characterized by the development of Ni mounds oriented along the h110i directions, as shown by scanning tunneling microscopy.

"We present the calculated electronic band structure of ideal Pt(100) and Pt(110) surface by using density functional theory and the empirical tight-binding method. A detailed discussion of the surface- and resonance-states is given. It is shown that the calculated surface- and resonance-states of ideal Pt(100) surfaces agree very well with the available experimental data. For Pt(110), some of the surface- and resonance-states are characteristic of the low symmetry of the surface and are identified as being independent of surface reconstruction effects. As in the previous paper, the density functional calculations were performed using the full potential linearized augmented plane wave method, and the empirical calculations were performed using the tight-binding method and Surface Green's Function Matching Method."

In this letter, we demonstrate a refractive index sensor based on a subwavelength plasmon interferometer. Illumination of an atilt subwavelength slit-grove pair on a metal surface with monochromatic light generates high-contrast interference fringes of the transmitted light. Detection of the refractive index of the dielectric medium on the metal surface is based on examining the relative position of the interference fringes. Integration of the plasmon interferometer with a microfluidic channel provides a sensitive, high-throughput sensor with small detection volume. (C) 2012 Optical Society of America

[EN] In this work, we demonstrate experimentally the use of an array of gold nanodisks on functionalized silicon for chemosensing purposes. The metallic nanostructures are designed to display a very strong plasmonic resonance in the infrared regime, which results in highly sensitive sensing. Unlike usual experiments which are based on the functionalization of the metal surface, we functionalized here the silicon substrate. This silicon surface was modified chemically by buildup of an organosilane self-assembled monolayer (SAM) containing isocyanate as functional group. These groups allow for an easy surface regeneration by simple heating, thanks to the thermally reversible interaction isocyanate-analyte, which allows the cyclic use of the sensor. The technique showed a high sensitivity to surface binding events in gas and allowed the surface regeneration by heating of the sensor at 150°C. A relative wavelength shift ¿¿max/¿0 = 0.027 was obtained when the saturation level was reached. © 2011 Optical Society of America., Financial support by the Spanish MICINN under contracts CONSOLIDER EMET (CSD2008-00066) and TEC2008-06871-C02-02 and European Commission FP7 under the FET-Open project TAILPHOX 233833 is gratefully acknowledged.

Highly ordered self-assembled organic monolayers (SAM) on metallic surfaces have attracted considerable attention recently due to their possible applications as opto-electronic devices (organic light-emitting diodes (OLED), organic field-effect transistors (OFET), solar cells, etc) as well as due to their use in a vast number of economically important surface processes (such as catalysis in chemical production, corrosion protection, control of surface properties like wettability or friction, molecular sensing, etc). For all these applications, a fundamental understanding of the surface-molecule bonding (in terms of bonding strength, charge injection barriers) and of the molecule-molecule interactions (in terms of steric interactions, hydrogen bonding, etc.) is essential, as these factors significantly affect the performance and the stability of the molecular-deposited systems. We have performed using the VASP code density functional theory calculations to examine the structural, electronic, vibrational and optical properties of oxalic acid molecules (HOOC – COOH) and of 2,5 pyrazine di-carboxylic acid molecules (PDA,HOOC – C4N2H2 – COOH) in vacuum and adsorbed onto the Cu(011) surface. A series of experimentally accessible quantities such as adsorption geometries, binding energies, Ultraviolet Photoelectron Spectroscopy (UPS) spectra, work-function values, Scanning Tunneling Microscopy (STM) images, Reflection Adsorption Infrared Spectroscopy (RAIRS) spectra has been calculated and compared with the available experimental data. The main results are: (a) For the experimental found vertical orientations of the adsorbed molecules (oxalic acid, PDA) the orientation of the vacuum exposed COOH H atom ("up" or "down") is a crucial structural property. This largely influences both the 2D organization of the molecular layer, as well as its reactivity. Thus, if the H atom is found to be stable in an up-orientation, it has a smaller chance to get involved in inter-molecular hydrogen bonds. If the H atom is however down-oriented, it will promote the formation of inter-molecular hydrogen bonds with consequences on the molecular layer stability and ordering. From the reactivity point of view, a H atom up-oriented means that this can be replaced/substituted easiest by a molecule which has a reactive positive side group. If the H atom is down- oriented, the most natural replacement will be that of the entire OH group by a molecule having a negative side group. (b) The H atom has a decisive influence on the value of the dipole moment of molecule layer and thus on the work function of the Cu-molecular-layer system. A change from "up" to "down" in the position of the H atom causes a change in work function of ~ 1.5 eV (for the oxalic acid layer) and of ~ 2.5 eV for the PDA layer. This is an interesting result as a lot of work is put nowadays in finding efficient ways for the in-situ variation of the systems work-function. (c) For both investigated systems ( Cu-oxalic, Cu-PDA ) we find that the hole injection barrier (HIB) is smaller than the electron injection barrier (EIB). For the Cu-oxalic system HIB ~ 0.75 eV and EIB ~ 2.86 eV. For Cu-PDA system HIB ~ 1.1 eV and an EIB ~ 1.5 eV. These systems are therefore p-type organic semiconductors and good candidates for the anode in opto-electronic components. (d) The simulated STM images show characteristic differences for the up-and down-conformations, allowing one to know what kind of organization is present on the surface. (e) The calculated infra-red spectrum is found to be in good agreement with the experimental one.

A novel composite photocatalyst of indium doped cadmium sulfide dispersed on zirconium oxide has been synthesized, which shows enhanced photocatalytic activity for hydrogen generation from water. In this system, cadmium sulfide exists as a separate dispersed phase on the zirconia support. Optical absorption spectra indicate a blue shift of absorption edge for CdS and In doped CdS dispersed on ZrO2 compared to pure CdS and indium doped CdS. Among the supported CdS, In doped CdS exhibits better optical absorption property. Photocatalytic studies for hydrogen generation from water show an enhanced activity for CdS dispersed on ZrO2 and indium doping in CdS enhances the activity further. Fluorescence lifetime studies indicate that, in the supported CdS, the charge carriers have higher lifetime than that in the unsupported CdS. Photocurrent response experiments show a relatively higher current output for the In doped CdS dispersed on ZrO2 support. The enhanced photocatalytic activity of this composite sample is attributed to a combination of factors like enhanced lifetime of the photogenerated charge carriers, increased photoresponse and improved surface area. The present study leads to a new observation that the photocurrent response and photocatalytic activity of CdS and indium doped CdS are enhanced when they are dispersed on a support like ZrO2. These composites with Pd as co-catalyst exhibit a large increase in the photocatalytic activity due to the increased availability of electrons on the metal surface by the interfacial transfer of electrons from CdS to Pd, when irradiated. � 2011 The Royal Society of Chemistry.

We present a model for oxygen reduction in water-filled, cylindrical nanopores with platinum walls. At one end, the pores are in contact with a polymer electrolyte membrane. The electrostatic interaction of the protons with the charged pore walls drives proton migration into the ionomer-free channels. We employ the Stern model to relate the surface charge density at the pore walls to the electrode potential. Proton and potential distributions within the pores are governed by the Poisson-Nernst-Planck theory and the oxygen distribution by Ficks law. Assuming a small local current density from oxygen reduction, we found an approximate analytical solution to the transport equations. The metal surface charge density and the corresponding proton conductivity of the pores are tuned by the deviation of the electrode potential from the potential of zero charge of the metal phase, which is the key determinant of the effectiveness of platinum utilization. Other determinants of pore performance are the Helmholtz capacitance, electrokinetic parameters, and pore size and length. Upon upscaling, the model is consistent with polarization data for ionomer-free, ultrathin catalyst layers in polymer electrolyte fuel cells (PEFCs). We discuss the implications of the model for the materials selection and nanostructural design of such catalyst layers. © 2010 The Electrochemical Society.

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.

Self-assembly represents a promising strategy for surface functionalisation as well as creating nanostructures with well-controlled, tailor-made properties and functionality. Molecular self-assembly at solid surfaces is governed by the subtle interplay between molecule-molecule and molecule-substrate interactions that can be tuned by varying molecular building blocks, surface chemistry and structure as well as Substrate temperature. In this review, basic principles behind molecular self-assembly of organic molecules on metal surfaces will be discussed. Controlling these formation principles allows for creating a wide variety of different molecular surface structures ranging from well-defined clusters, quasi one-dimensional rows to ordered, two-dimensional overlayers. An impressive number of studies exist, demonstrating the ability of molecular self-assembly to create these different structural motifs in a predictable manner by tuning the molecular building blocks as well as the metallic substrate. Here, the multitude of different surface structures of the natural amino acid cysteine on two different gold surfaces observed with scanning tunnelling microscopy will be reviewed. Cysteine on Au(110)-(1x2) represents a model system illustrating the formation of all the above mentioned structural motifs without changing the molecular building blocks or the substrate surface. The only parameters in this system are substrate temperature and molecular coverage, controlling both the molecular adsorption state (physisorption versus chemisorption) and molecular surface mobility. By tuning the adsorption state and the molecular mobility, distinctly different molecular structures are formed, exemplifying the Variety of structural motifs that can be achieved by molecular self-assembly. (C) 2008 Elsevier Ltd. All rights reserved.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics., This letter provides an experimental demonstration of extraordinary transmission in a closed waveguide system loaded with an electrically small diaphragm. This is a situation where the standard surface plasmon polariton SPP theory does not apply. The theoretical explanation is then based on the concept of impedance matching. This concept has previously been applied by some of the authors to account for enhanced transmission in situations where surface plasmon theory can be used: periodic arrays of small holes or slits in flat metal screens. The experiment in this letter supports the impedance matching model, valid for when SPPs are present or not. © 2009 American Institute of Physics, The authors would like to acknowledge the support of this research by the Spanish Ministry of Science and Innovation and European Union Feder Funds Grant Nos. TEC2007-65376 and Consolider Ingenio 2010 CSD2008- 00066 and by the Spanish Junta de Andalucía Project No. TIC-253