Search

The dissociation of methane is not only an important reaction step in catalytic processes, but also of fundamental interest. Dynamical effects during the dissociative chemisorption of methane on metal surfaces cause significant differences in computed reaction rates, compared to what is predicted by typical transition state theory (TST) models. It is clear that for a good understanding of the catalytic activation of methane dynamical simulations are required. In this paper, a general blueprint is provided for performing dynamical simulations of the dissociative chemisorption of methane on metal surfaces, by employing either the quasi-classical trajectory or ring polymer molecular dynamics approach. If the computational setup is constructed with great care-since results can be affected considerably by the setup - chemically accurate predictions are achievable. Although this paper concerns methane dissociation, the provided blueprint is, so far, applicable to the dissociative chemisorption of most molecules. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to review the current one-step electrodeposition of superhydrophobic coatings on metal surfaces. Design/methodology/approach: One-step electrodeposition is a versatile and simple technology to prepare superhydrophobic coatings on metal surfaces. Findings: Preparing superhydrophobic coatings by one-step electrodeposition is an efficient method to protect metal surfaces. Originality/value: Even though there are several technologies, one-step electrodeposition still plays a significant role in producing superhydrophobic coatings. [ABSTRACT FROM AUTHOR]

Vision-based defect recognition in the metal industry is an important and challenging task. Many mainstream methods based on supervised learning need a large amount of annotated defect data. However, the data acquisition in industrial scenarios is quite difficult and time-consuming. To alleviate the problem, in this paper, we propose a few-shot defect recognition (FSDR) method for metal surfaces by attention-embedding and self-supervised learning. The proposed method includes two stages,pre-training and meta learning. In the pre-training stage, an attention embedding network (AEN) is designed for better learning the defect local correlation of multi-receptive field and reducing the background interference, and to train a robust AEN without any annotations, a multi-resolution cropping self-supervised method (MCS) is developed for better generalizing the few-shot recognition task. Then, in the meta learning stage, to generate the embedding features, the defect images are encoded by the pre-trained AEN, and we also design a query-guided weight (QGW) to address the bias of embedding feature vector. The classification information is gained by computing the distance of the embedding feature vector of each category. We evaluate the proposed FSDR on the NEU dataset and the experiments show competitive results in 1-shot and 5-shot defect recognition tasks compared with the mainstream methods. [ABSTRACT FROM AUTHOR]

This study focuses on depositing Ni/W-Al2O3 nanocomposites onto a low-carbon substrate using the pulse electrodeposition technique. The effects of pulse current density on microstructural characteristics, microhardness, phase structure, and wear/corrosion properties of Ni/W-Al2O3 nanocomposites were investigated. Among the investigated nanocomposites, Ni/W-Al2O3 deposited at 0.6 A/dm2 current density showed the finest structure with average Ni-W grain and Al2O3 nanoparticle sizes of 66.7 nm and 39.1 nm, respectively. The Ni/W-Al2O3 nanocomposite deposited under the same conditions exhibited a maximum microhardness of ~ 825.7 HV, while also demonstrating the lowest corrosion current density of ~ 0.72 A/cm2. After 60 min of wear testing, wear loss of Ni/W-Al2O3 nanocomposite deposited at 0.6 A/dm2 was recorded as 42.8 mg, indicating its excellent wear resistance. In contrast, Ni/W-Al2O3 nanocomposite deposited at 0.8 A/dm2 displayed the highest wear loss value of 101.5 mg. [ABSTRACT FROM AUTHOR]

The paper deals with the task of automated segmentation of images of defects metal surfaces. The aim of the study is to improve segmentation algorithms using deep learning methods. The expediency of using the U-Net neural network, which is effective in the tasks of semantic image segmentation, is substantiated. With the help of a special architecture, the network can create segmentation masks with high efficiency. The training dataset for the neural network contained images of four classes of defects, including chips, cracks, and stains. As a result of analyzing the distribution of defect classes in the training dataset, it was concluded that the classes were unbalanced, which negatively affects the training results. To evaluate the quality of network training, a set of metrics such as Accuracy, F1 Score, and IOUScore is considered. The feasibility of using these metrics is analyzed, taking into account the features of the training data set. It is proved that under conditions of significant imbalance of classes, the Accuracy metric does not reflect the real quality of the model. The influence of different variants of the ResNet architecture backbone on the training results is analyzed. It is determined that the best results are shown by the ResNet18 model, which managed to obtain a Dice coefficient of 69 % and an IOUScore of 53 % on the test data set. It is proved that an increase in the number of model parameters does not always lead to an improvement in the reliability of the results. The article provides examples of test images and defect masks and countures predicted by the neural network. [ABSTRACT FROM AUTHOR]

Electrocatalytic denitrification 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 provides a clear strategy for selectivity and aims to inspire future research on NOxRR. [ABSTRACT FROM AUTHOR]

Purpose: We investigated the recovery and extraction efficiency of DNA from three metal surfaces (brass, copper, steel) relevant to forensic casework, and plastic (control) using two different swabbing systems; Rayon and Isohelix™ swabs, with sterile water and isopropyl alcohol respectively, as the wetting solutions. Methods: Twenty nanograms of human genomic DNA were applied directly to Isohelix™ and Rayon swabs; and to the metal and plastic substrates. All substrates were left to dry for 24 h, followed by single wet swabbing and extraction with the DNA IQ™ System. DNA extracts were quantified using real time quantitative PCR assays with SYBR green chemistry. Results: DNA was extracted from directly seeded Isohelix™ swabs with a high efficiency of 98%, indicating effective DNA-release from the swab into the extraction buffer. In contrast, only 58% of input DNA was recovered from seeded Rayon swabs, indicating higher DNA retention by these swabs. Isohelix™ swabs recovered 32 – 53% of DNA from metal surfaces, whilst the Rayon swabs recovered 11—29%. DNA recovery was lowest from copper and highest from brass. Interestingly, Rayon swabs appeared to collect more DNA from the plastic surface than Isohelix™ swabs, however, due to the lower release of DNA from Rayon swabs they returned less DNA overall following extraction than Isohelix™ swabs. Conclusion: These results demonstrate that DNA samples deposited on metal surfaces can be more efficiently recovered using Isohelix™ swabs wetted with isopropyl alcohol than Rayon swabs wetted with sterile water, although recovery is affected by the substrate type. [ABSTRACT FROM AUTHOR]

This study illustrates pervasive challenges in studying wetting dynamics, including dynamic contact angles, on irregularly roughened surfaces. We demonstrate that asymmetric water droplet shapes occur more than 50% of the time during static and dynamic contact angle measurements on sandblasted Zn-plated stainless steel with a polymeric overcoat. The pinning that causes the asymmetric drop shape distortion on horizontal surfaces also influences the sliding behavior on inclined surfaces. These effects lead to a poor correlation between the measured dynamic contact angles and the observed sliding angles (critical tilt angles). Our work emphasizes that large variations in the values of these dynamic wetting parameters are inherent to the heterogeneity of the surface roughness, and thus they limit the usefulness of standard dynamic wetting criteria. These findings have implications for academic and industrial research focused on making coated materials that have consistent wettability properties throughout their usage life cycle. [ABSTRACT FROM AUTHOR]

The modification of metal electrode surfaces with functional organic molecules is an important part of organic electronics. The interaction of the buckminsterfullerene fragment molecule pentaindenocorannulene with a Cu(100) surface is studied by scanning tunneling microscopy, dispersion‐enabled density functional theory, and force field calculations. Experimental and theoretical methods suggest that two adjacent indeno groups become oriented parallel to the surface upon adsorption under mild distortion of the molecular frame. The binding mechanism between molecule and surface is dominated by strong electrostatic interaction owing to Pauli repulsion. Two‐dimensional aggregation at room temperature leads to a single lattice structure in which all molecules are oriented unidirectionally. Their relative arrangement in the lattice suggests noncovalent intermolecular interaction through C−H⋅⋅⋅π bonding. [ABSTRACT FROM AUTHOR]

The salinization and contamination of metal surfaces by chloride‐containing aerosols is of great importance with regard to corrosion phenomena of damaged coated metal surfaces and stainless steels in the maritime sector and in offshore applications. Detailed questions have to be answered to clarify whether and to what extent salinization of the surface has an influence on the adhesion and durability of coatings in repairing applications and on pitting occurrence on stainless steels under atmospheric conditions. The questions arise which degree of salinization is reached after which period of time and how a defined and reproducible salinization can be simulated in the laboratory for further systematic investigations. The article is dedicated to these questions. Results of a field trial on the Island of Heligoland are presented and a simple procedure for a defined loading of metal surfaces with chlorides at a laboratory scale using a design of experiments (DoE) approach is introduced. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deposition rate affects roughness, activation barrier influences. • Unrestricted diffusion model leads to higher roughness. • Temperature smooth surfaces, alters growth mechanisms. • Higher temperatures increase layer occupancy, favor diffusion. • Steady state is not reached for any materials in unrestricted model. • Dynamic exponent Beta depends of the diffusion mechanism. The growth behavior of Cr and W surfaces using kinetic Monte Carlo (KMC) simulations based on Density-Functional Theory (DFT) is presented in this study. Three models, a growth model with random deposition and no diffusion, a growth model with restricted diffusion and a growth model with unrestricted diffusion model, were compared to understand their influence on the predicted surface roughness and layer density. The impact of deposition rate and temperature on surface growth for both metals were analyzed. For deposition rate studies, five different rates (0.01 ML/s, 0.1 ML/s, 1.0 ML/s, 10.0 ML/s, and 100 ML/s) were considered at 550 K for Cr and W respectively. The effect of temperature on roughness was also studied employing various temperatures from 300 K to 1100 K for both metals and under the two different evolution models. The results show that the unrestricted diffusion model exhibits higher roughness compared to the restricted model for both metals. The restricted model shows a stable region of roughness, whereas the unrestricted model shows a continuous increase in roughness throughout the simulation. Furthermore, layer density analysis revealed that temperature affects the filling of lower monolayers. Finally, dynamic exponents β and α for each studied model were calculated and discussed. The results highlight the influence of diffusion models, deposition rate and temperature on surface, roughness, and layer density. [ABSTRACT FROM AUTHOR]

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. Spinning on the surface: An allene formed by a sigmatropic reaction on retinoic acid shows a long‐lived magnetism on a gold surface after dehydrogenation. 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 product in its lifted subpart. [ABSTRACT FROM AUTHOR]

Abstract We review our recent studies of photochemistry and plasmon chemistry of dimethyl disulfide, (CH 3 S) 2 , molecules adsorbed on metal surfaces using a scanning tunneling microscope (STM). The STM has been used not only for the observation of surface structures at atomic spatial resolution but also for local spectroscopies. The STM combined with optical excitation by light can be employed to investigate chemical reactions of single molecules induced by photons and localized surface plasmons. This technique allows us to gain insights into reaction mechanisms at a single molecule level. The experimental procedures to examine the chemical reactions using the STM are briefly described. The mechanism for the photodissociation reaction of (CH 3 S) 2 molecules adsorbed on metal surfaces is discussed based on both the experimental results obtained with the STM and the electronic structures calculated by density functional theory. The dissociation reaction of the (CH 3 S) 2 molecule induced by the optically excited plasmon in the STM junction between a Ag tip and metal substrate is also described. The reaction mechanism and pathway of this plasmon-induced chemical reaction are discussed by comparison with those proposed in plasmon chemistry. [ABSTRACT FROM AUTHOR]

In this work we present a model for the surface oxide film growth 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. [ABSTRACT FROM AUTHOR]

Most traditional techniques to recover latent fingermarks from metallic surfaces do not consider the metal surface properties and instead focus on the fingermark chemistry. The scanning Kelvin probe (SKP) technique is a non-contact, non-destructive method, used under ambient conditions, which can be utilised to recover latent prints from metallic surfaces and does not require any enhancement techniques or prevent subsequent forensic analysis. Where a fingermark ridge contacted the metal, the contact potential difference (CPD) contrast between the background surface and the fingermark contact area was 10-50mV. Measurements were performed on the untreated brass, nickel-coated brass and copper metal surfaces and compared to traditional forensic enhancement techniques such as Vacuum Metal Deposition (VMD) using Au-Zn and Au-Ag. Using VMD, the CPD change ranged from 0 to 150mV between the dissimilar metal surfaces affected by the fingermark. In general, SKP worked best without additional enhancement techniques. Scanning Electron Microscope (SEM) scans were used to identify the fingermark contact areas through a sodium, chlorine and oxygen electron probe micro-analyzer (EPMA). The fingermark was observed in the backscattered electron image as the carbon deposits scattered the electrons less than the surrounding metal surface. The fingermark is shown clearly in a Cathodoluminescence scan on the copper sample as it blocks the photon emission at band gap (2.17eV) from the underlying copper oxide (Cu2O) surface. For the first time, SEM, EPMA and Cathodoluminescence techniques were compared to SKP data. Visible and latent fingermarks were tested with latent, eccrinous fingermarks more easily imaged by SKP. Results obtained were very encouraging and suggest that the scanning Kelvin probe technique, which does not need vacuum, could have a place as a first stage analysis tool in serious crime investigation. [ABSTRACT FROM AUTHOR]

The transmissivity of metal-metal sealing joints is investigated experimentally and compared to predictions obtained by modeling. The focus is laid upon a wavy surface contacting a flat rigid part, representative of a seat-to-plug contact in an internal sealing valve encountered in nuclear power plants for instance. Experimental transmissivities are obtained from water leak-rate and pressure drop measurements carried out on a model ring-shape sample seat holding a controlled wavy defect and pressed against a rigid flat plug with a controlled normal load. The sample seat surface is manufactured by face turning a tubular part under radial stress and waviness is obtained after elastic relaxation. Modeling is performed on a three-dimensional finite element model of the assembly, composed of the plug, the sample seat, and its holder. The upper sample seat surface, in which topography is recorded by confocal microscopy, is reconstructed using a modal decomposition on the basis of vibrational eigenmodes. Its lower surface, in contact with the holder, is considered as perfectly flat or with its own defects. The contact aperture field between the seat and the plug is computed for a given normal load and is used to solve the incompressible Reynolds equation with a boundary element method, yielding the transmissivity. Predicted transmissivities reveal to be in good agreement with experimental data at low clamping loads and are overestimated for larger ones. Defects on the lower surface of the seat are shown to have a significant impact on the seat-to plug contact transmissivity. [ABSTRACT FROM AUTHOR]

There is an increased interest in incorporating multi-wall carbon nanotubes (MWCNTs) into polymer matrices to control the adhesion of bacteria to surfaces and the subsequent formation of biofilm growth on the surface of water pipes, food packages, and medical devices. Microbial interactions with carbon nanotube-polymer composites in the environment are not well understood. The growth of Pseudomonas fluorescens (gram-negative) and Mycobacterium smegmatis (gram-positive) biofilms on copper, polyethylene (PE), polyvinyl chloride, and stainless steel was compared with growth on MWCNT-PE composites in order to gain insight into the effect of the surface properties of nanomaterials on the attachment and proliferation of microorganism which could result in the engineering of better, non-fouling materials. A statistical analysis of the biofilm growth showed a significant impact of materials for both P . fluorescens ( p  < 0.0001) and M . smegmatis ( p  = 0.00426). Biofilm growth after 56 days on PE compared to biofilm growth on copper surfaces decreased by 46.4% and 34.9% for P . fluorescens and M . smegmatis , respectively. Biofilm growth on PE-multiwall-carbon-nanotubes (MWCNTs)-composites surface compared to PE decreased by 89.3% and 29% for P . fluorescens and M . smegmatis , respectively. Bacterial species ( p  < 0.0006) and surface roughness ( p  < 0.0001) were important factors in determining the attachment and initial biofilm growth rate. The interactions between cells and material surface could be attributed to the complicated and collective effect of electrostatic forces, hydrophobic interactions, and hydrogen/covalent bonding. Further study is needed to determine whether or not there is a difference between the cell attachment in the exponential growth phase and the stationary, or decay, phase cells. [ABSTRACT FROM AUTHOR]

This paper presents a review of the experimental and theoretical investigations of halogen interaction with metal surfaces. The emphasis was placed on the recent measurements performed with a scanning tunneling microscope in combination with density functional theory calculations. The surface structures formed on metal surface after halogen interaction are classified into three groups: chemisorbed monolayer, surface halide, bulk-like halide. Formation of monolayer structures is described in terms of surface phase transitions. Surface halide phases are considered to be intermediates between chemisorbed halogen and bulk halide. The modern theoretical approaches in studying the dynamics of metal halogenation reactions are also presented. [ABSTRACT FROM AUTHOR]

The effect that the ionizing radiation caused by radioactive contamination of soil exerts on the surface of carbon steel 20 samples, on their corrosion resistance, and on operation reliability according to lowcycle fatigue tests (taking into account that fatigue is one of the main causes of failures resulting from corrosion and mechanical damage of thin-wall metal structures, in particular, of pipelines) was studied. It was shown that even low activity levels (below maximum permissible levels) caused corrosion loss of the metal and a decrease in the operation reliability. Synergistic protective compounds suppressing the destructive radiation effects and ensuring reliable operation of metal structures due to chelation of the surface metal atoms were developed using computer simulation. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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]

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]

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]

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: 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: 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]

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]

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 time taken for wetness sensors on zinc plates, openly exposed to the atmosphere, to dry was analysed at four sites in southern Australia. The sites cover a range of environmental conditions from inland to marine. A number of typical drying patterns were observed, and it was found that these patterns could be related to the environmental severity and the probable presence of various salt contaminants. Therefore, at the marine site drying was frequently slow (>4 h) and appeared to be controlled by the presence of salts with a low deliquescent relative humidity (DRH) such as MgCl2. In contrast, at the inland sites drying was generally more rapid, which was consistent with either the drying of a clean surface or that of a surface controlled with salts of high DRH such as NaCl. The present paper presents histograms of drying rate for each site and the relationship between the distributions in drying rate and the environmental conditions is discussed. The relevance of the present study to modelling of atmospheric corrosion and to the design of cyclic tests to duplicate atmospheric corrosion is also discussed. [ABSTRACT FROM AUTHOR]

The present study reports on an investigation into the dependence of the surface temperature of metal plates on environmental parameters. Monitored plates were exposed at three locations (one coastal and two inland) in southern Australia. The following parameters were monitored: surface temperature, surface wetness, wind speed, ambient relative humidity, air temperature and lifting condensation level. (The lifting condensation level is the height at which a parcel of air rising from the ground will reach saturation.) An analysis was undertaken of the temperature difference between the exposed plate surfaces and ambient air. It was found that the maximum temperature difference during the day depended on season, wind speed and, to a lesser extent, the lifting condensation level. The maximum undercooling during the night showed a relatively limited range and a weak dependence on wind speed. The rate of rise in temperature difference after sunrise was found to be only slightly dependent on season, but highly dependent on whether the surface was wet or dry. If the surface was dry, the rise in temperature difference depended on the wind speed and lifting condensation level. The relevance of these findings to moisture formation and evaporation from surfaces, and thus to corrosion processes, is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Experimental and theoretical studies on the quantum delocalization of hydrogen atoms, in particular in vibrationally excited states, on transition-metal surfaces are reviewed. The present status and remaining problems are discussed. The quantum delocalization of hydrogen atoms in the ground state is briefly reviewed. [Copyright &y& Elsevier]

This paper outlines an experimental programme aimed at determining the mechanisms of salt removal from metallic surfaces by wind and rain. The paper provides data and process understanding that will be integrated into a holistic model of atmospheric corrosion. Experiments are reported in which fine salt crystals were deposited either wet (as fine droplets of seawater) or dry onto a surface. The surfaces were then placed in a wind tunnel and salt loss was determined as a function of wind speed. In another experiment, the motion of simulated raindrops falling onto metal plates was determined. Finally, in a third series of experiments, video footage of simulated rain on metal surfaces was studied in order to determine both the subsequent motion of rain and its cleaning efficiency. The efficiency of surface cleaning by wind and rain, as determined by these experiments, was then related to Australian climatic conditions. A future paper will present mathematical models of the processes defined in this paper. [ABSTRACT FROM AUTHOR]

We have treated the surfaces of Al, SUS and Cu metals using an atmospheric-pressure plasma jet generated by nitrogen and oxygen gases under the atmospheric pressure at room temperature. The plasma ignition occurred by flowing mixed gases between two coaxial metal electrodes, and the voltage was applied with impulse type and 16–20 kHz frequencies. The treated surfaces were basically characterized by means of a contact angle analyzer for the activation property on their surfaces. From the results of XPS, FE-SEM, OES and AFM, we could confirm that the main phenomena such as the reactive etching and oxidation were observed on their surfaces as well as even the aggregation of particles by the activated atoms, radicals and metastable species in the plasma space. However, all treated surfaces contained only oxygen and carbon without nitrogen, even though the excited nitrogen species were generated in the plasma due to its higher reactivity than oxygen ones observed in the OES data. The aging effect on the duration time of the surface energy, moreover, was also studied because of the production cost on the industrial applications in addition. [Copyright &y& Elsevier]

The manifestation of chirality at surfaces has attracted much attention in recent years. In this review, some of main features of chiral endowments by complex organic molecules at defined metal surfaces are reviewed. Detailed surface spectroscopic data have enabled a hierarchy of chiral expressions to be delineated, from point group chirality expressed by local chiral motifs, to space group chirality in which these motifs act as building blocks which self-assemble into organised chiral structures, to deeper propagation of chirality into the metal leading to chiral reconstructions. Chiral endowments by both chiral and achiral molecules is discussed alongside the implications for progressing chirality from the local to the global level. [Copyright &y& Elsevier]

It is known that the exchange-correlation (XC) potential vXC obtained using the nonlocal weighted density approximation (WDA) does not yield the image behavior −1/4z outside a metal surface. This limitation might be due to the fact that the WDA is based on an isotropic scaling of the electron pair correlation function. In this work we present a WDA scheme based on an anisotropic scaling for the pair correlation function showing that, in this case, the potential vXC has the correct imagelike decay. This new scheme does not entail a significant additional effort if compared with the standard WDA method. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [ABSTRACT FROM AUTHOR]