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Depth profiling using surface sensitive analysis methods in combination with sputter ion etching is a common procedure for thorough material investigations, where clean surfaces free of any contamination are essential. Hence, surface analytic studies are mostly performed under ultra-high vacuum (UHV) conditions, but the cleanness of such UHV environments is usually overrated. Consequently, the current study highlights the in principle known impact of the residual gas on metal surfaces (Fe, Mg, Al, Cr and Zn) for various surface analytics methods, like X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and low-energy ion scattering (LEIS). The investigations with modern, state-of-the-art equipment showed different behaviors for the metal surfaces in UHV during acquisition: (i) no impact for Zn, even after long time, (ii) solely adsorption of oxygen for Fe, slight and slow changes for Cr and (iii) adsorption accompanied by oxide formation for Al and Mg. The efficiency of different counter measures was tested and the acquired knowledge was finally used for ZnMgAl coated steel to obtain accurate depth profiles, which exhibited before serious artifacts when data acquisition was performed in an inconsiderate way. [ABSTRACT FROM AUTHOR]

Chirality is a property of matter which manifests at any length scale and can equally appear as quantum phenomena and in three-dimensional macroscopic structures. However, while chirality can be easily achieved by removing the inversion symmetry operation in hexagonal or tetragonal metal structures, chirality in metals is an unusual and barely developed phenomenon. Nevertheless, chirality can greatly alter mechanical and functional features of materials, making them suitable for catalysis, optics, electromagnetism, thermoelectricity and superconductivity; properties strictly dependent on the anisotropy of the crystal and on the direction of the applied force. This review aims to extend the definition of chirality to describe nanoclusters, metal surfaces and crystals and to provide an interdisciplinary overview on how symmetry can affect their properties. This review was submitted as part of the 2016 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged. [ABSTRACT FROM AUTHOR]

The energetics at organic-metal interfaces are, to large extend, determined by the structure of the molecular adsorbate on the substrate surface. As shown by low-energy electron diffraction (LEED) the zigzag shape of picene leads to a peculiar monolayer structure on Ag(111), Ag(110), and Cu(111) with one molecule in the unit cell lying essentially flat and the other one adopting an edge-on orientation. The adsorbate-substrate coupling is weak as shown by ultraviolet photoelectron spectroscopy (UPS). This is in striking contrast to monolayers of straight pentacene, where all molecules lie flat and are strongly coupled, involving charge transfer complex formation on most of these surfaces. The peculiar packing structure of picene leads to weak interfacial coupling on clean metal surfaces. In contrast, pentacene is chemisorbed on Ag and Cu surfaces involving electron transfer from the substrate. [ABSTRACT FROM AUTHOR]

• Dopant atoms enhanced the adsorption behavior of benzene. • The highest adsorption energy was found in Pt 2 Pd 2 -Ag configuration AB. • A remarkable change from physisorption to chemisorption binding for benzene molecule. Heterogeneous catalysis, molecular sensors, and photovoltaics all rely on the interfaces between organic molecules and metal surfaces. Here, we study the adsorption of benzene on Ag(100) surface doped by Au n , Pd n , Pt n (n = 1–4), Au 2 Pd 2 , Au 2 Pt 2 and Pd 2 Pt 2 using density-functional theory (DFT), with the inclusion of van der Waals interactions, and compare with available computational and experimental result. The calculated quantities reveal that the interaction strength of Benzene with the surface gradually increases when it is doped by Pd or Pt atoms, showing a change in the nature of the interaction, from physisorption to chemisorption. We found that with surface allowing, one can tune the interaction strength. The charge transfer was found to occur from the molecule to the clean and doped surfaces with Au atoms and from the doped surface with Pd to the molecule. The redistribution of charge density indicates modifications in the features of the interface between the doped Ag(100) surfaces and benzene. In addition, alloying the Ag(100) surface with reactive TM changes substantially its electronic properties, which impacts its interactions with benzene. Finally, mixing two dopants or more can tune the electronic structure in designing more effective interfaces for various applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Charge transfer interactions between C 60 and the metal surfaces of Ag(111), Cu(111), Au(111) and Pt(111) have been studied using synchrotron-based photoemission, resonant photoemission and X-ray absorption spectroscopies. By placing the X-ray absorption and valence band spectra on a common binding energy scale, the energetic overlap of the unoccupied molecular orbitals with the density of states of the underlying metal surface have been assessed in the context of possible charge transfer pathways. Resonant photoemission and resonant Auger data, measuring the valence region as a function of photon energy for C 60 adsorbed on Au(111) reveals three constant high kinetic energy features associated with Auger-like core-hole decay involving an electron transferred from the surface to the LUMO of the molecule and electrons from the three highest occupied molecular orbitals, respectively and in the presence of ultra-fast charge transfer of the originally photoexcited molecule to the surface. Data for the C 60 /Ag(111) surface reveals an additional Auger-like feature arising from a core-hole decay process involving more than one electron transferred from the surface into the LUMO. An analysis of the relative abundance of these core-hole decay channels estimates that on average 2.4 ± 0.3 electrons are transferred from the Ag(111) surface into the LUMO. A core-hole clock analysis has also been applied to assess the charge transfer coupling in the other direction, from the molecule to the Au(111) and Ag(111) surfaces. Resonant photoemission and resonant Auger data for C 60 molecules adsorbed on the Pt(111) and Cu(111) surfaces are shown to exhibit no super-Auger features, which is attributed to the strong modification of the unoccupied molecular orbitals arising from stronger chemical coupling of the molecule to the surface. [ABSTRACT FROM AUTHOR]

Water and its fragments are present on metal surfaces under all but the most extreme conditions, acting both as a reactive species and as a ligand in ways that have yet to be fully explored. This review focuses on experimental studies of the chemical species and hydrogen bonding structures that form in the first layer adsorbed on a metal surface. The development of non-invasive probes that avoid dissociating water, or disrupting fragile bonding structures, now allows experiments to distinguish between different structural models for water and its fragments at the surface, allowing us to test the accuracy of modern structural calculations and provide a better picture of how the metal surface influences the structures and chemical species present. We start by describing the behaviour of Pt(1 1 1), whose redox chemistry is important in electrochemical fuel cells and has been studied in detail, providing a good reference system against which to discuss the effect changing the surface symmetry and metal reactivity has on the interface structure. Evidence for the presence and the role of hydroxyl and hydrated ‘hydronium’ species is described and we discuss the outlook for future experiments and identify some questions that remain to be resolved. [ABSTRACT FROM PUBLISHER]

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 N 2 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. [ABSTRACT FROM AUTHOR]

Bacterial adhesion can be dictated by different surface characteristics. In this study we concentrate on the surface roughness of a stainless steel material. We prepared the stainless steel surfaces by 3D polishing, brushing, grinding and electropolishing. Untreated stainless steel surfaces were also considered. The corresponding surface roughness was assessed by profilometry and atomic force microscopy. In experiments we have used different types of bacteria. The rate of adhered bacteria on metal surfaces was determined spectrophotometrically. The results showed that the rate of adhered bacteria increases with increasing surface roughness. Scanning electron microscopy was used to image surfaces in order to determine locations of adhered bacteria. The increased adhesion of bacteria on more rough surfaces results from an increased interplay between the increasing effective surface area and increasing numbers of cracks, voids and gaps. [ABSTRACT FROM AUTHOR]

Visual appearance of an object significantly influences a consumer's choice and largely controls the market economy. The perceived quality of products is governed by surface's optical properties (reflection, refraction, etc.), geometrical properties (roughness, waviness, etc.), and chemical properties (oxide layer formation, thermal variation, etc.). Surface shininess attracts researchers from many different disciplines, in particular manufacturing, metrology, psychology, physiology, and computer science. Unfortunately, there are still huge knowledge gaps on characterizing and appraising shiny surfaces in a reproducible way. This paper introduces the main definitions and physics of shininess and gloss, methods of gloss sensing, and relates these definitions and methods to surface generation by grinding. Automated gloss measurement is difficult in particular for free-form surfaces, and optical quality is still often evaluated by human workers. Gloss models are often based on the bidirectional reflection distribution function (BRDF) of the surface, but the models are commonly not connected with the manufacturing process. This study proposes to consider the geometrical features (defects, waviness, lay, and roughness) of metal surfaces as well as the physical and chemical features (grain structure and microlayers) to understand surface appearance and manufacturing in a holistic way. Preliminary tests show that 2D roughness measurements are not connected well with measured gloss units (GUs) and subjective, perceived quality. More fundamental research on the generation and measurement of surface appearance is needed and would benefit many industries. [ABSTRACT FROM AUTHOR]

In this article, we propose a Frozen Gaussian Sampling (FGS) algorithm for simulating nonadiabatic quantum dynamics at metal surfaces with a continuous spectrum. This method consists of a Monte-Carlo algorithm for sampling the initial wave packets on the phase space and a surface-hopping type stochastic time propagation scheme for the wave packets. We prove that to reach a certain accuracy threshold, the sample size required is independent of both the semiclassical parameter ε and the number of metal orbitals N , which makes it one of the most promising methods to study the nonadiabatic dynamics. The algorithm and its convergence properties are also validated numerically. Furthermore, we carry out numerical experiments including exploring the nuclei dynamics, electron transfer and finite-temperature effects, and demonstrate that our method captures the physics which can not be captured by classical surface hopping trajectories. • An efficient Frozen Gaussian Sampling (FGS) algorithm for simulating nonadiabatic dynamics at metal surfaces is proposed. • The sample size required is independent of the number of orbitals N and the semiclassical parameter ε. • FGS algorithm can capture the physics that classical surface hopping trajectories fail to capture. [ABSTRACT FROM AUTHOR]

Understanding molecular interactions with metal surfaces in high reliability is critical for the development of catalysts, sensors, and therapeutics. Obtaining accurate experimental data for a wide range of surfaces remains a critical bottleneck and quantum-mechanical data remain speculative due to high uncertainties and limitations in scale. We report molecular dynamics simulations of adsorption energies and assembly of organic molecules on elemental metal surfaces using the INTERFACE force field (IFF). The force field-based simulations reach up to 8 times higher accuracy than density functional calculations at a million-fold faster speed, as well as more than 1 order of magnitude higher accuracy than other force fields relative to accurate measurements by single-crystal adsorption calorimetry. Uncertainties of prior computational methods are effectively reduced from on the order of 100% to less than 10% and validated by experimental data from multiple sources. Specifically, we describe the molecular interactions of benzene and naphthalene with even and defective platinum surfaces across a wide range of surface coverage in depth. We discuss molecular-scale influences on the heat of adsorption and clarify the definition of surface coverage. The methods can be applied to 18 metals to accurately predict binding and assembly of organic molecules, ligands, electrolytes, biological molecules, and gases without additional fit parameters.

Possible adsorbate induced reconstruction effects of methanethiolate (MeS) and methaneselenolate (MeSe) on Au(111) are studied employing density functional theory (DFT). For the purposes of this study these simple alkanechalcogenates prove to be representative models for chalcogenate molecules with larger rest groups. MeS and MeSe show very similar properties regarding the adsorption at the unreconstructed and reconstructed surfaces. The latter are constructed by systematically introducing defects at various adsorbate coverages. It turns out that only if the defect site is occupied by at least two molecules the costs of creating the defect can be counterbalanced by the energetic gain and thus adsorbate induced reconstruction gets energetically feasible. Furthermore, for various molecular coverages the adatom-dichalcogenate model, as found by Maksymovych et al. (Phys. Rev. Lett. 97 (2006) 146103), is indeed the most stable reconstruction motif among the simple models studied herein. In order to mimic the impact of the environment, e.g. solvent effects, temperature or electric potentials, the stability of the reconstruction motifs was studied as a function of both the chemical potential of the adsorbate and the energy needed to create the defect substrate structure following the ansatz of ab initio atomistic thermodynamics. This approach hints at the fact that different reconstruction motifs can be realized in different chemical environments. [ABSTRACT FROM AUTHOR]

We review several representative experimental results of action spectroscopy (AS) of single molecules on metal surfaces using a scanning tunneling microscope (STM) by M. Kawai’s group over last decade. The experimental procedures to observe STM-AS are described. A brief description of a low-temperature STM and experimental setup are followed by key experimental techniques of how to determine an onset bias voltage of a reaction and how to measure a current change associated with reactions and finally how to observe AS for single molecule reactions. The experimental results are presented for vibrationally mediated chemical transformation of trans -2-butene to 1.3-butadiene molecule and rotational motion of a single cis -2-butene molecule among four equivalent orientations on Pd(1 1 0). The AS obtained from the motion clearly detects more vibrational modes than inelastic electron tunneling spectroscopy with an STM. AS is demonstrated as a useful and novel single molecule vibrational spectroscopy. The AS for a lateral hopping of water dimer on Pt(1 1 1) is presented as an example of novelty. Several distinct vibrational modes are detected as the thresholds in the AS. The assignment of the vibrational modes determined from the analysis of the AS is made from a view of the adsorption geometry of hydrogen-bond donor or acceptor molecules in water dimer. A generic theory of STM-AS, i.e., a reaction rate or yield as a function of bias voltage, is presented using a single adsorbate resonance model for single molecule reactions induced by the inelastic tunneling current. Formulas for the reaction rate R ( V ) and Y ( V ) , i.e., reaction yield per electron Y ( V ) = eR ( V ) / I are derived. It provides a versatile framework to analyze any vibrationally mediated reactions of single adsorbates on metal surfaces. Numerical examples are presented to demonstrate generic features of the vibrational generation rate and Y ( V ) at different levels of approximations and to show how the effective broadening of the vibrational density of states (as described by Gaussian or Lorentzian functions) manifest themselves in Y ( V ) near the threshold bias voltage corresponding to a vibrational excitation responsible for reactions. A prefactor of Y ( V ) is explicitly derived for various types of elementary processes. Our generic formula of Y ( V ) also underlines the need to observe Y ( V ) at both bias voltage polarities, which can provide additional insight into the adsorbate projected density of states near the Fermi level within a span of the vibrational energy. The theory is applied to analysis of some highlights of the experimental results: Xe transfer, hopping of a single CO molecule on Pd(1 1 0), a dissociation of a single dimethyl disulfide (CH 3 S) 2 and a hopping of a dissociated product, i.e., single methyl thiolate CH 3 S on Cu(1 1 1). It underlines that an observation of Y ( V ) at both bias polarities permits us to certain insight into the molecular alignment with respect to the Fermi level. [ABSTRACT FROM AUTHOR]

Graphene, a two-dimensional (2D) material with unique electronic properties, appears to be an ideal object for the application of surface-science methods. Among them, a family of scanning probe microscopy methods (STM, AFM, KPFM) and the corresponding spectroscopy add-ons provide information about the structure and electronic properties of graphene on the local scale (from [ABSTRACT FROM AUTHOR]

Silicene is emerging as a two-dimensional material with very attractive electronic properties for a wide range of applications; it is a particularly promising material for nano-electronics in silicon-based technology. Over the last decade, the existence and stability of silicene has been the subject of much debate. Theoretical studies were the first to predict a puckered honeycomb structure with electronic properties resembling those of graphene. Though these studies were for free-standing silicene, experimental fabrication of silicene has been achieved so far only through epitaxial growth on crystalline surfaces. Indeed, it was only in 2010 that researchers presented the first experimental evidence of the formation of silicene on Ag(1 1 0) and Ag(1 1 1), which has launched silicene in a similar way to graphene. This very active field has naturally led to the recent growth of silicene on Ir(1 1 1), ZrB 2 (0 0 0 1) and Au(1 1 0) substrates. However, the electronic properties of epitaxially grown silicene on metal surfaces are influenced by the strong silicene–metal interactions. This has prompted experimental studies of the growth of multi-layer silicene, though the nature of its “silicene” structure remains questionable. Of course, like graphene, synthesizing free-standing silicene represents the ultimate challenge. A first step towards this has been reported recently through chemical exfoliation from calcium disilicide (CaSi 2 ). In this review, we discuss the experimental and theoretical studies of silicene performed to date. Special attention is given to different experimental studies of the electronic properties of silicene on metal substrates. New avenues for the growth of silicene on other substrates with different chemical characteristics are presented along with foreseeable applications such as nano-devices and novel batteries. [ABSTRACT FROM AUTHOR]

We review the recently developed three-dimensional (3D) atom-superposition approach for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) based on ab initio electronic structure data. In the method, contributions from individual electron tunneling transitions between the tip apex atom and each of the sample surface atoms are summed up assuming the one-dimensional (1D) Wentzel-Kramers-Brillouin (WKB) approximation in all these transitions. This 3D WKB tunneling model is extremely suitable to simulate spin-polarized STM and STS on surfaces exhibiting a complex noncollinear magnetic structure, i.e., without a global spin quantization axis, at very low computational cost. The tip electronic structure from first principles can also be incorporated into the model, that is often assumed to be constant in energy in the vast majority of the related literature, which could lead to a misinterpretation of experimental findings. Using this approach, we highlight some of the electron tunneling features on a prototype frustrated hexagonal antiferromagnetic Cr monolayer on Ag(111) surface. We obtain useful theoretical insights into the simulated quantities that is expected to help the correct evaluation of experimental results. By extending the method to incorporate a simple orbital dependent electron tunneling transmission, we reinvestigate the bias voltage- and tip-dependent contrast inversion effect on the W(110) surface. STM images calculated using this orbital dependent model agree reasonably well with Tersoff-Hamann and Bardeen results. The computational efficiency of the model is remarkable as the k-point samplings of the surface and tip Brillouin zones do not affect the computational time, in contrast to the Bardeen method. In a certain case we obtain a relative computational time gain of 8500 compared to the Bardeen calculation, without the loss of quality. We discuss the advantages and limitations of the 3D WKB method, and show further ways to improve and extend it. [ABSTRACT FROM AUTHOR]

Enhanced colors can be formed when white light is irradiated on the surface ripples induced by femtosecond laser. In this paper, we have demonstrated the ability to display the diverse colors by simultaneously adjusting the incident white light angle and the ripples orientation. Furthermore, our investigation revealed that multi-patterns constituted by ripples with different orientations could be designed on metal surfaces. The diverse display for the desired ones can be realized by exquisitely varying the incident light angle and rotating sample angle. More interestingly, it is found that, although the same patterns could be displayed under different conditions, the colors might be different. These findings can provide a novel method to carry and identify high quantity of information, which may find potential applications in the fields of information storage, identifying codes and anti-counterfeiting patterns. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An inspection of mechanically damaged areas on manufactured metal parts is necessary to produce high-quality products. A scanning probe on a sample is necessary for a conventional surface inspection system, which is time-consuming. We propose a novel high-speed detection method for defects on metal surfaces with rolling indentations. To obtain a large field of view in a measurement, we used a laser sheet that was expanded with a laser line generator and also used an expanded collimated beam, rather than a small laser spot as used in conventional techniques. Furthermore, we used an obliquely incident laser beam to suppress the effect of the rolling indentations surrounding defects, and also applied spatial frequency filtering to extract only defects. The spatial frequency filtering under oblique incidence is theoretically explained and defect extraction was investigated in experiments. [ABSTRACT FROM AUTHOR]

Highlights: [•] Bond breaking of general RO–H organic compounds on various metal surfaces. [•] Brønsted–Evans–Polanyi like relationships for the O–H bond break in organics. [•] Activation energy for the O–H bond break versus adsorption energy of the products. [•] Mean absolute error for the BEP is 0.13eV. [•] Good agreement between estimated and calculated data for a test set. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we have investigated the surface structure of Cu3Au(001) using low energy electron diffraction analysis and ab initio calculations by density functional theory. Our results indicate a different structure from that usually reported in the literature, where we have observed a stacking fault between the first and third layers of the surface. The rippling effect and the interlayer distances belonging to the first six layers of the surface were calculated and compared with other works too. Specifically, a rippling with gold atoms moving towards the vacuum in the first layer of 0.09Å was observed and of 0.02Å in the third layer. A small expansion of the first interlayer distance of 1.3% and a contraction of 0.8% at the second also were observed. Finally, ab initio calculations performed in this work are in good agreement with the experimental results. [Copyright &y& Elsevier]

We validate a computational setup based on density functional theory to investigate hexagonal boron nitride ( h-BN) monolayers grown on different transition metals exposing hexagonal surfaces. An extended assessment of our approach for the characterization of the geometrical and electronic structure of such systems is performed. Due to the lattice mismatch with the substrate, the monolayers can form Moiré-type superstructures with very long periodicities on the surface. Thus, proper models of these interfaces require very large simulation cells (more than 1,000 atoms) and an accurate description of interactions that are modulated with the specific registry of h-BN on the metal. We demonstrate that efficient and accurate calculations can be performed in such large systems using Gaussian basis sets and dispersion corrections to the (semi-)local density functionals. Four different metallic substrates, Rh(111), Ru(0001), Cu(111), and Ni(111), are explicitly considered, and the results are compared with previous experimental and computational studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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 0.16Å with the first gold layer presenting a small expansion (0.04Å) with respect to the Au bulk interlayers distance. The agreement between the LEED and DFT results is very good. [Copyright &y& Elsevier]

Abstract: 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 Å) 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. [Copyright &y& Elsevier]

Abstract: In this work we report on a very accurate low-energy electron diffraction (LEED) and a DFT study of Au(110)-(1×2) in order to determine its surface geometry. The LEED results indicate a surface missing row reconstruction with a large contraction of , a pairing in the second layer and in the fourth layer , and a buckling in the third layer of 0.30Å and in the fifth layer of 0.01Å. These LEED results are in very good agreement with those found by the DFT calculations. [Copyright &y& Elsevier]

Abstract: We present vibrational dynamics and thermodynamics for the (100) surfaces of Cu, Ag, Pd, Pt and Au using a real space approach. The force field for these systems is described by density functional theory. The changes in the vibrational dynamics and thermodynamics from those in bulk are confined mostly to the first-layer. A substantial enhancement of the low-frequency end of the acoustic branch was found and is related to a loosening of the bond at the surface. The thermodynamics of the first-layer also show significant differences (higher heat capacity, lower free energy and higher mean vibrational square amplitudes) from what obtains in bulk. Comparing these results with those calculated using embedded-atom method potentials, we discovered that for Ag(100) and Cu(100), the two methods yield very similar results while for Pd(100), Pt(100) and Au(100) there are substantial differences. [Copyright &y& Elsevier]

Abstract: Water adsorption at metal surfaces is governed by a subtle balance between water–water hydrogen bonding and water–metal interactions, which together determine the stability of the water structures formed. This review describes recent experimental and theoretical studies of water and OH/water coadsorption on well-defined single crystal metal surfaces, systems that have seen an upsurge in interest as new results modify our picture of how water adsorbs on metal surfaces. These results reveal that the simple, conventional ice ‘bilayer’ description of water adsorption, in which water is only marginally distorted from its bulk ice arrangement, is inadequate to describe wetting. Instead, optimisation of the water–metal interaction distorts the local hydrogen bonding geometry of water monolayers significantly from that of bulk ice, with consequent effects on the lateral size and geometry of ice clusters, on the structure of water monolayers and on the wetting of first layer water and growth of ice multilayers. Here we compare adsorption across different metal surfaces, review evidence for the formation of mixed OH/H2O co-adsorption structures and highlight issues that remain uncertain. [Copyright &y& Elsevier]

Abstract: Nanoscience and nanotechnology are tremendously increasing fields of research that aim at producing, characterizing and understanding nanoobjects and assemblies of nanoobjects. Their new physical or chemical properties, which arise from confinement effects, intimately depend on their morphological properties, i.e. their shapes, their sizes and their spatial organization. This calls for dedicated morphological characterization tools, among which is the Grazing Incidence Small Angle X-Ray Scattering (GISAXS). This reciprocal space technique has emerged in the last two decades as a powerful tool that allows investigating in a non-destructive way the morphological properties from one to billions of nanoparticles, either on a surface, or embedded in a matrix, with sizes ranging from 1 nm to several microns. The advantages of the technique are that it is non-destructive; it yields statistical information averaged on a large number of nanoparticles; it allows probing both the surface or deep below it, by changing the incident angle of the X-ray beam; it can be used in very different sample environments, in particular in situ in the course of a given process such as growth, annealing, gas exposure; and it may be given chemical sensitivity by use of anomalous scattering. This report presents a review of the GISAXS technique, from experimental issues to the theories underlying the data analysis, with a wealth of examples. The physical morphological information contained in GISAXS data and its analysis are presented in simple terms, introducing the notions of particle form factor and interference function, together with the different cases encountered according to the size/shape dispersion. The theoretical background of X-ray diffuse scattering under grazing incidence is presented in a general way, and then applied to the particular case of grazing incidence small angle X-ray scattering from assemblies of particles either on a substrate, or buried below it. Most of the GISAXS measurements published to date are reported, covering the fields of ex situ studies of embedded metallic nanoparticles, granular multilayered systems, implanted systems, embedded or stacked or deposited semi-conductor nanostructures, porous materials and copolymer thin films. A special emphasis is brought on in situ experiments, performed either in ultra-high vacuum during nanoparticle growth by molecular beam epitaxy, or in gas-reactors during catalytic reactions. This covers a very broad field, from (i) the 3D island (Volmer–Weber) growth of metals on oxides surfaces to (ii) the organized growth of metals on surfaces that are nanopatterned either by surface reconstruction or by underlying dislocation networks or by deposit-induced nanofacetting, to (iii) the in situ investigation of the self-organized Stranski–Krastanow hetero-epitaxial growth of semi-conductor quantum dots on semi-conductor surfaces, or (iv) the in situ surface nanopatterning by ion bombardment. Many examples are discussed in detail, to illustrate the large diversity of systems and morphologies that can be addressed as well as the different analysis issues and the conclusions of the technique in terms of growth mode. [Copyright &y& Elsevier]

A chemicurrent is a flux of fast (kinetic energy ≱ 0.5-1.3 eV) metal electrons caused by moderately exothermic (1-3 eV) chemical reactions over high work function (4-6 eV) metal surfaces. In this report, the relation between chemicurrent and surface chemistry is elucidated with a combination of top-down phenomenology and bottom-up atomic-scale modeling. Examination of catalytic CO oxidation, an example which exhibits a chemicurrent, reveals 3 constituents of this relation: The localization of some conduction electrons to the surface via a reduction reaction, 0.5O2 + δe- → Oδ- (Red); the delocalization of some surface electrons into a conduction band in an oxidation reaction, 0δ- + CO → CO → CO2δ- → CO2+ δe- (Ox); and relaxation without charge transfer (Rel). Juxtaposition of Red, Ox, and Rel produces a daunting variety of metal electronic excitations, but only those that originate from CO2 reactive desorption are long-range and fast enough to dominate the chemicurrent. The chemicurrent yield depends on the universality class of the desorption process and the distribution of the desorption thresholds. This analysis implies a power-law relation with exponent 2.66 between the chemicurrent and the heat of ad- sorption, which is consistent with experimental findings for a range of systems. This picture also applies to other oxidation-reduction reactions over high work function metal surfaces. [ABSTRACT FROM AUTHOR]

Abstract: The article reviews work on graphene monolayers adsorbed on metal surfaces. Graphene layers on metals have been prepared by surface segregation of carbon and by decomposition of hydrocarbons. The films are often not rotationally aligned to the metal surface. However, for a number of hexagonally close-packed surfaces perfectly ordered epitaxial overlayers have been obtained, with domains larger than the terraces of the metal substrate. In most cases the well-ordered overlayers display moiré structures with large periodicities, resulting from the lattice mismatch between graphene and the underlying metal. These structures are connected with a buckling of the graphene layer indicating local variations of the binding to the metal. For the metal–graphene spacings values between approximately 2.1 and 3.8Å have been found, depending on the metal. Reasons for these strong variations are not yet clear, but there are indications that the systems fall into two classes that differ qualitatively with respect to the metal/graphene interaction. These variations are also reflected by the electronic structure. There are metal–graphene systems in which the π band is significantly downshifted in energy compared to the free-standing graphene, and a band gap of order eV has opened at the point of the Brillouin zone. In other systems, the electronic structure of free-standing graphene is almost intact. The perfectness of the epitaxial moiré phases offers promising applications, e.g., as templates for nanostructures. [Copyright &y& Elsevier]

Abstract: A quantitative analysis of infrared absorption spectra to determine coadsorbate induced relative changes of the vibrational polarizability α v of an adsorbate mode and of the dielectric screening ϵ due to this extra species is presented. Four (ternary) coadsorption systems consisting of the Ru(0001)-(2×2)-(X+CO+O) layer with additional coadsorbates X=H, NO, CO, or O (all of them occupying the remaining empty fcc site) have been studied with FT-IRAS, TDS, LEED and work function change measurements. On-top CO is thereby used as a probe molecule to monitor coadsorbate effects on the dielectric properties of the layer. The vibrational polarizability α v associated with the internal C–O stretch mode (ν C–O) of on-top CO is lowered by all coadsorbates. The dielectric screening ϵ within the adsorbate layer is reduced in the presence of the atomic coadsorbates O and H whereas an increase of ϵ is found for the molecular coadsorbates, threefold coordinated CO and NO. The derived changes of α v and dielectric screening ϵ, as well as the involved line shifts of ν C–O and ν Ru–CO can be understood in terms of the standard Blyholder backbonding model, i.e. CO 5σ charge donation to the metal combined with a backdonation to electronic states with 2π∗ character. [Copyright &y& Elsevier]

Abstract: 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)-(1×2) 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. [Copyright &y& Elsevier]

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. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [ABSTRACT FROM AUTHOR]

The present paper analyses the time that wetness sensors on Zn and galvanised steel plates stayed wet in four locations within Australia: two in inland zones, one in a marine zone, and the other in a severe marine zone. All locations are classified as having a temperate climate. At each location, wetness was determined from interdigitated gold grids in thermal contact with plates openly exposed to the atmosphere. Individual periods of wetness were analysed, and it was found that the duration of wetness fell into three modes: short wetness periods of 1–4 h, but centred on <2 h; part day wetness periods of 8–20 h, depending on environmental severity; and multiple day wetness periods of three to five days, but with odd occurrences out to 20 days. The relative occurrence of each mode depended on the severity of the sites. To illustrate the dependence of corrosion events on the duration of wetness, time factors regulating secondary spreading were examined. It was observed that secondary spreading on Zn and galvanised steel only occurred if the duration of a drop on a plate exceeded certain critical limits. Furthermore, the spread of secondary spreading was highly dependent on the time period for which the drop remained stable. The implication of these findings to developing accelerated tests and to modelling atmospheric corrosion are discussed. [ABSTRACT FROM AUTHOR]

For optical-waveguiding structures composed of uniform segments that are invariant in the longitudinal direction, the Dirichlet-to-Neumann (DtN)-map method is highly competitive. Instead of computing the eigenmodes, it calculates the DtN operators of the uniform segments using an efficient Chebyshev collocation scheme. In this paper, a new formulation of the DtN-map method is developed for periodic piecewise uniform waveguiding structures. The method involves a recursive-doubling process so that the overall required computation time is proportional to log2 N, where N is the number of periods. We illustrate our method by analyzing the scattering of surface plasmon polaritons due to Bragg gratings on metal surfaces and thin metal films. [ABSTRACT FROM PUBLISHER]

Abstract: We present ab initio calculation results for electron–phonon (e–ph) contribution to hole lifetime broadening of the surface state on Al(001). We show that e–ph coupling in this state is significantly stronger than in bulk Al at the Fermi level. It makes the e–ph decay channel very important in the formation of the hole decay in the surface state at . We also present the results for e–e lifetime broadening in a quantum-well state in 1ML K/Cu(111). We show that this contribution is not negligible and is much larger than that in a surface state on Ag(111). [Copyright &y& Elsevier]

Abstract: We present calculation results for electron–phonon (e–ph) coupling in one monolayer (ML) of Na on the Cu(111) surface. We show that the e–p coupling parameter λ decreases compared to that for clean Cu(111) due to the significant decrease of the Na vertical vibrational mode contribution to the Eliashberg function in the 1ML Na/Cu(111) system. The corresponding phonon induced lifetime broadening Γ e–ph of a quantum-well state at low temperature decreases by 30% compared to that on clean Cu(111). [Copyright &y& Elsevier]

This is the seventh paper outlining a holistic model of atmospheric corrosion. Previous papers have outlined how airborne salinity can be estimated at any given location, how salt deposition onto a surface can be modelled and what forms moisture can take on a plate surface. The present paper develops a model for rain induced cleaning of deposited aerosols from metal surfaces. The individual phenomena of splash and wash off are modelled, and then the effect of these processes on salt retention is discussed. The results of the models are compared with data from field exposures and laboratory tests. Simplified rules to allow the process to be incorporated into the holistic model framework are proposed. [ABSTRACT FROM AUTHOR]

First principles periodic density functional theory (DFT) has been applied to simulate the electrochemical interface between water and various (111) metal surfaces. The chemistry of water at these electrified interfaces is simulated and the parameters relevant to the macroscopic behavior of the interface, such as the capacitance and the potential of zero charge (PZC) are examined. In addition, we examine the influence of co-adsorbed CO upon the equilibrium potential for the activation of water over Pt(111). We find that for copper and platinum there is a potential window over which water is inert, but on Ni(111) water is always found in some dissociated form (as adsorbed OH* or H*, depending on the applied potential). Furthermore, the relaxation of water molecules via the flip/flop rotation is an important contribution to the interfacial capacitance. Our calculations for the coadsorbed H2O/CO system indicate that the adsorption of CO affects the binding energy of OH, such that water activation occurs at a higher equilibrium potential. [ABSTRACT FROM AUTHOR]

Abstract: The formation energies of isolated vacancy and adatom–vacancy pair (where the two are separated by a large distance) at low-index surfaces of fcc metals calculated by using the modifies analytical embedded atom method (MAEAM). The results predict the prevailing formation of vacancies on the surfaces (111), (100) (but Pd), Cu and Ni on the (110) surfaces at low temperature, and the defect formation energies consistently create in the sequence (110)→(100)→(111). With good accuracy, the calculated energy values coincide with those obtained by the embedded atom methods (EAM) and from experiments. The correctness of the method by which calculated the formation energies of point defects on the surface was proved. [Copyright &y& Elsevier]

The paper describes a number of studies relating to the retention of marine salts on atmospheric corrosion test plates and the cleaning of such salts in field exposures. Data from three separate field studies are presented. In each study, instrumented zinc plates were openly exposed to the atmosphere. Plates were exposed in tropical, subtropical and temperate regions of Australia in severe marine, marine, urban and inland exposure conditions. Plates were washed at various times during exposure and, in some cases, they were ultrasonically cleaned after exposure. Ion chromatographic analysis was undertaken to determine the ion contents of the wash-off and ultrasonic cleaning solutions, and thus the salts present on the exposed plates. Sites and plates were also instrumented with rain gauges, salt candles, relative humidity sensors, surface temperature sensors and surface wetness sensors. Changes in the relative humidity at which the surfaces became wet were determined and used as a guide to infer the presence of salts on the surfaces. The effect of rainfall on the presence of salt was then determined. The factors controlling salt retention on surfaces are discussed, including the possibility that the ability of a surface to retain salt changes with time, and that sources of chloride other than crystalline salt may exist. The relevance of the study to atmospheric corrosion is discussed. [ABSTRACT FROM AUTHOR]