Underlying Metal Substrate Research Articles

H-BN Defective Layers as Giant N-Donor Macrocycles for Cu Adatom Trapping from the Underlying Metal Substrate

In the confined zone between a bidimensional material and a metal surface, unexpected effects can take place. In this study, we show that when a nonregular two-dimensional h-BN layer is grown on a Cu(111) surface, metal adatoms spontaneously pop up from the bulk to fill the holes in the structure. We provide ample theoretical support to our findings based on a large set of dispersion-corrected density functional theory calculations and on a detailed analysis of the electronic properties and of the chemical processes at this peculiar interface. The observation can be rationalized in terms of a high affinity of Cu adatoms toward N-donor species. Defective h-BN, exposing N-terminated edges, behaves like a giant multi-N-donor macrocyclic ligand that can encapsulate metal atoms as a consequence of a huge stabilization deriving from the Cu–N bond formation. Our conclusions could apply to other metal surfaces and could even stimulate the idea of trapping different metal atoms from those of the underlying surface...

A Novel Non-Destructive Sensing Technology for On-Site Corrosion Failure Evaluation of Coatings

The quality of coating and the resulting rate of corrosion of the underlying metal substrate can be measured by a variety of corrosion measurements (Tafel, electrochemical impedance spectroscopy) by using standard laboratory electrochemical cells. However, there is always a need of low cost, portable, and non-destructive electrochemical cells, which can be used on-site field for condition monitoring of large structures for example bridges and large infrastructures, complex operating systems as aircrafts, precision machines, petrochemical processes, automotive, and locomotives. This research has developed state of the art cells fabricated by using a special magnetic aluminum compound (AlnXn), which is highly electrically conductive and corrosion resistive. The research has commissioned for deploying this novel sensing technology for micro-defects detection, corrosion rate measurement, and condition assessment of the defected coatings. Tafel measurement facilitated by these non-destructive cells is used to detect micro-defects and corrosion rate measurement while electrochemical impedance spectroscopy measurement is facilitated to measure the coating condition. This technology has been successfully tested and commissioned on automotive, hazardous compartments with polymeric coatings and bridges to assess their coating condition in terms of their structural integrity. Post design testing involved the installation of these cells, running diagnostics, data acquisition, and macrographs to predict structural defects and the resulting corrosion rate. This technology enables the design process to incorporate operational conditions and fully realize more durable and reliable solutions to be applied to high-value large structures and complex interacting systems. Current developments in corrosion condition monitoring especially cost effective and non-destructive techniques to assess structural integrity beneath nonconductive and polymeric coating were long awaited. This reported development will revolutionize durability and reliability assessment techniques to enhance safety and mitigate catastrophic failures for cost savings and avoiding fatal accidents.

Orbital Symmetry of the Kondo State in Adsorbed FePc Molecules on the Au(110) Metal Surface

The Kondo ground state can arise in surface-supported organometallic systems, such as the 3d transition metal phthalocyanines, as a result of the hybridization of the 3d localized orbitals with the underlying metal substrate electrons. Low-temperature scanning tunneling spectroscopy can identify the Kondo states as a zero-bias anomaly in the differential conductance curves, often localized in close proximity with the 3d metal center. However, the information on the symmetry of the Kondo state, on the exact shape of the spectral function, and on the magnetic state is generally missing from the experimental data. We apply complementary techniques, i.e., scanning tunneling spectroscopy, resonant photoemission spectroscopy, and X-ray magnetic circular dichroism, to identify the Kondo state, the orbital symmetry, and the magnetic moment of Fe-Phthalocyanine chains formed by two structural phases with increasing molecular density: first ×5 and at higher coverage ×7 FePc ordered chain structures assembled on the...

The microstructure and mechanical properties of tantalum nitride coatings deposited by a plasma assisted bias sputtering deposition process

Abstract In this study, two tantalum nitride-based coatings were synthesized onto Ti-6Al-4V substrates with two different Ar/N 2 flux ratios using a form of plasma assisted bias sputtering deposition termed the double cathode glow discharge deposition technique. Their microstructures and mechanical properties were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy and nanoindentation tests. At a low nitrogen partial pressure, the tantalum nitride coating consists of a hexagonal Ta 2 N phase, with a preferred (101) orientation, while at a high nitrogen partial pressure, the as-deposited coating is composed of a face-centered cubic (fcc) TaN phase with a strongly (200) oriented texture. The two as-deposited coatings exhibited striated nanostructured composed of equiaxed grains about ~ 10 nm in diameter, embedded with an array of homogenously distributed nanopores. The mechanical properties and damage resistance of the coatings were evaluated by nanoindentation techniques. The hardness and elastic modulus of the Ta 2 N coating was higher than those of the TaN coating, indicating that the Ta 2 N coating may offer better protection ability for the underlying metal substrate under load-bearing conditions. In addition, the presence of nanopores is beneficial to the contact damage resistance for both coatings.

Corrosion-resistant hybrid coatings based on graphene oxide–zirconia dioxide/epoxy system

The hybrid coatings based on graphene oxide–zirconia dioxide/epoxy (GO–ZrO2/EP) system were fabricated and applied for corrosion protection of metal substrate. First, GO–ZrO2 hybrid was synthesized through two different silane coupling agents and the morphology and structure were confirmed by Field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. Then, GO–ZrO2 was incorporated into EP to investigate the corrosion protection of metal substrate. Investigations revealed that the corrosion protective properties were significantly enhanced by the addition of GO–ZrO2 to EP. The enhancement attributed to the sheet-like structure, uniform dispersion and exfoliation of GO–ZrO2 hybrid within EP matrix, which effectively prevented the underlying metal substrate from corrosion attack.

Graphene: the ultimately thin sputtering shield

Scanning tunneling microscopy methods are applied to investigate the potential of monolayer graphene as a sputtering shield for the underlying metal substrate. To visualize the effect, a bare and a graphene protected Ir(111) surface are irradiated with 500 eV Xe+, as well as 200 eV Xe+ and Ar+ ions, all at 1000 K. By quantitatively evaluating the sputtered material from the surface vacancy island area, we find a drastic decrease in metal sputtering for the graphene protected surface. It is demonstrated that efficient sputter protection relies on self-repair of the ion damage in graphene, which takes place efficiently in the temperature range of chemical vapor deposition growth. Based on the generality of the underlying principles of ion damage, graphene self-repair, and graphene growth, we speculate that efficient sputter protection is possible for a broad range of metals and alloys.

Greatly Enhancing Catalytic Activity of Graphene by Doping the Underlying Metal Substrate.

Graphene-based solid-state catalysis represents a new direction in applications of graphene and has attracted a lot of interests recently. However, the difficulty in fine control and large-scale production of previously proposed graphene catalysts greatly limits their industrial applications. Here we present a novel way to enhance the catalytic activity of graphene, which is highly efficient yet easy to fabricate and control. By first-principles calculations, we show that when the underlying metal substrate is doped with impurities, the catalytic activity of the supported graphene can be drastically enhanced. Graphene supported on a Fe/Ni(111) surface is chosen as a model catalyst, and the chemical reaction of CO oxidation is used to probe the catalytic activity of graphene. When the underlying Fe/Ni(111) substrate is impurity free, the graphene is catalytically inactive. When a Zn atom is doped into the substrate, the catalytic activity of the supported graphene is greatly enhanced, and the reaction barrier of the catalyzed CO oxidation is reduced to less than 0.5 eV. Intriguing reaction mechanism of catalyzed CO oxidation is revealed. These studies suggest a new class of graphene-based catalysts and pave the way for future applications of graphene in solid-state catalysis.

Effects of laser ablation coating removal (LACR) on a steel substrate: Part 1: Surface profile, microstructure, hardness, and adhesion

The effects of laser ablation coating removal (LACR) from a high strength shipbuilding steel have been assessed. The LACR process was shown to be effective for the removal of a typical epoxybased coating. However, multiple passes were required to remove the coating, with an increased number of passes required at higher sweep speeds. Scanning electron microscope (SEM) imaging of the surface and cross-sections reveals that the underlying metal substrate is melted and re-solidified during LACR. The appearance of the surface is clearly changed at the microscopic level. However, conventional surface roughness (profile) measurements indicate no statistically significant change in the roughness, using conventional metrics such as average roughness, Ra. Finally, studies performed on samples repainted after LACR confirm equivalent, or superior, adhesion as compared to the abrasive blasted and painted samples.

Comparison of Ar+ Monoatomic and Cluster Ion Sputtering of Ta2O5 at Different Ion Energies, by XPS: Part 2 - Cluster Ions

A standard 30 nm thick Ta2O5 oxide layer grown on Ta was examined by XPS after Arn+ cluster ion bombardment at ion energies of 4 keV, 5 keV and 6 keV, with a cluster size of 1000 atoms. The reduction of Ta2O5, resulting from the preferential sputtering of oxygen after ion beam bombardment at different energies has been investigated. Survey spectra, C 1s, Ta 4f and O 1s spectra are presented for each profile at three stages: native surface, after reaching the steady-state oxide composition, and from the underlying metal substrate. It is necessary to reach a voltage of 6 keV to obtain a good sputter rate. The use of the cluster source seems to be promising to reduce the preferential sputtering phenomenon.

Comparison of Ar+ Monoatomic and Cluster Ion Sputtering of Ta2O5 at Different Ion Energies, by XPS: Part 1 - Monoatomic Ions

A standard 30 nm thick Ta2O5 oxide layer grown on Ta was examined by XPS after Ar+ ion bombardment at ion energies of 200 eV, 500 eV, and 3 keV. The reduction of Ta2O5, resulting from the preferential sputtering of oxygen after ion beam bombardment at different energies has been investigated. Survey spectra, C 1s, Ta 4f and O 1s spectra are presented for each profile at three stages: native surface, after reaching the steady-state oxide composition, and from the underlying metal substrate. Reducing the Ar+ energy from 3 keV to 200 eV makes no substantial difference in the degree of Ta2O5 reduction observed following ion bombardment.

Electronic and Vibrational Properties of meso-Tetraphenylporphyrin on Silver Substrates

The electronic and vibrational properties of meso-tetraphenylporphyrin (mtpp) on silver substrates are investigated using UV-vis and surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Whereas the vibrational signatures associated with the tetrapyrrole backbone exhibit minor variations throughout sequences of consecutively recorded SERRS spectra, the C═C stretching vibrational modes localized on the meso-phenyl moieties of mtpp exhibit noticeable intensity fluctuations, masked in the average SERRS response. We attribute the observed vibrational-state-specific blinking events to conformational changes in mtpp, namely, torsional flexibility which mediates the coupling between the π-framework of the meso-phenyls and the underlying metal substrate.

Tuning the hole injection barrier in the intermolecular charge-transfer compoundDTBDT-F4TCNQ at metal interfaces

Molecular monolayers of the charge-transfer salt dithienobenzodithiophene-tetrafluorotetracyanoquinodimethane (DTBDT-F${}_{4}$TCNQ) have been deposited on C(R$15\ifmmode\times\else\texttimes\fi{}3$)/W(110), Co/W(110), and hcp Co(0001) using molecular beam epitaxy in an ultrahigh vacuum. The integrity of the deposited molecules has been confirmed by scanning tunneling microscopy. Scanning tunneling spectroscopy has been used to determine the energetic positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital of acceptor and donor in the pure and in the mixed phase. The mixed charge transfer phase exhibits a new HOMO close to the Fermi edge depicting a charge transfer of less than one elementary charge. The total amount of the transferred charge depends on the underlying metal substrate. The binding energy of the HOMO decreases from $0.4$ eV for C(R$15\ifmmode\times\else\texttimes\fi{}3$)/W(110) to $0.16$ eV for Co(0001), thus revealing the tunability of the hole injection barrier. The energy gap between HOMO and LUMO decreases from $0.96$ eV ($0.81$ eV) for C(R$15\ifmmode\times\else\texttimes\fi{}3$)/W(110) [ps-ML Co/W(110)] to $0.66$ eV for Co(0001), demonstrating a strong reduction compared to the value of the pure moieties.

Identification of Active Sites in a Realistic Model of Strong Metal–Support Interaction Catalysts: The Case of Platinum (1 1 1)‐Supported Iron Oxide Film

AbstractWe report DFT+U results on oxygen adsorption and extraction characteristics obtained for a realistic model of a strong metal–support interaction catalyst, exemplified by a Pt(1 1 1)‐supported FeOx ultra‐thin film. Derived from recent experimental results, the model enables a coherent analysis of the activity towards oxygen at a large variety of sites, which range from FeO and FeO2 oxide terraces to different oxide–metal and oxide–oxide boundaries. We show that the trends in calculated adsorption and desorption energetics are to a large extent specific to the small thickness of the supported oxides and are mainly driven by electron exchange with the underlying metal substrate. The thorough mapping of the activity of different local surface environments enables the identification of the sites that are most likely responsible for the observed low‐temperature activity of FeOx/Pt films in CO oxidation. Beyond the oxide–metal boundaries known for their higher activity than the separate materials, we find that the sites at boundaries between the coexisting oxide phases of different compositions can easily adsorb and release oxygen.

Strength and adhesion properties of acrylic polyol‐epoxy polyol resin protective coating on mild steel substrate

PurposeThe purpose of this paper is to improve the strength and adhesion properties of modified acrylic polyol resin using epoxy polyol resin (DEGBA).Design/methodology/approachThe hybrid systems were prepared by blending acrylic resin with epoxy polyol resin (Diglycidyl Ether of Bisphenol‐A, DGEBA) and polyisocyanate resin as hardener in various weight ratios with xylene as a solvent. The samples were applied on the pre‐treated cold rolled mild steel panels. The mechanical property of the blend has been evaluated using rapid impact tester (Sheen 806/40) and adhesion tester (Sheen Cross‐Hatch 750). Intended panels were checked for cracks using Dino‐Lite and Pinhole detectors (Elcometer 270/4). Crossed panels were observed for damages using digital polarized microscope (Dino‐Lite, AM413ZT). The thermal properties were studied using thermal analysis system (TGA TA‐Q500, DSC TA‐Q200).FindingsThe modification of acrylic polyol resins using DGEBA showed significant improvement of toughness compared to pure acrylic polyol resins. The blending systems with 10 wt percent of DGEBA and 90 wt percent of acrylic resin showed good adhesion and impact resistance properties on mild steel substrate.Research limitations/implicationsThe hybrid coating system has contributed to the basic conceptual understanding of the corrosion protection property, focusing mainly on recent research available.Practical implicationsThe blending method provided a simple and practical solution to improve the toughness of acrylic polyol resins.Originality/valueThe method for enhanced toughness of cured acrylic was novel and functionality of coating critically depends on adhesion between the coatings and underlying metal substrate.

SAM-like arrangement of thiolated graphene nanoribbons: decoupling the edge state from the metal substrate

Density functional theory calculations have been used to analyze the electronic and magnetic properties of ultrathin zigzag graphene nanoribbons (ZGNRs) with different edge saturations. We have compared a symmetric hydrogen saturation of both edges with an asymmetric saturation in which one of the edges is saturated with sulphur atoms or thiol groups, while the other one is kept hydrogen saturated. The adsorption of such partially thiolated ZGNRs on Au(111) has also been explored. We have considered vertical and tilted adsorption configurations of the ribbons, reminiscent of those found for thiolated organic molecules in self-assembled monolayers (SAM) on gold substrates. We have found that saturation with sulphur atoms or thiol groups removes the corresponding edge state from the Fermi energy and kills the accompanying spin polarization. However, this effect is so local that the electronic and magnetic properties of the mono-hydrogenated edge (H-edge) remain unaffected. Thus, the system develops a spin moment mainly localized at the H-edge. This property is not modified when the partially thiolated ribbon is attached to the gold substrate, and is quite independent of the width of the ribbon. Therefore, the upright adsorption of partially thiolated ZGNRs can be an effective way to decouple the spin-polarized channel provided by the H-edge from an underlying metal substrate. These observations might open a novel route to build spin-filter devices using ZGNRs on gold substrates.

From vertical-cavities to hybrid metal/photonic-crystal nanocavities: towards high-efficiency nanolasers

We provide a numerical study showing that a bottom reflector is indispensable to achieve unidirectional emission from a photonic-crystal (PhC) nanolaser. First, we study a PhC slab nanocavity suspended over a flat mirror formed by a dielectric or metal substrate. We find that the laser's vertical emission can be enhanced by more than a factor of six compared with the device in the absence of the mirror. Then, we study the situation where the PhC nanocavity is in contact with a flat metal surface. The underlying metal substrate may serve as both an electrical current pathway and a heat sink, which would help achieve continuous-wave lasing operation at room-temperature. The design of the laser emitting at 1.3 um reveals that relatively high cavity Q of over 1,000 is achievable assuming room-temperature gold as a substrate. Furthermore, linearly-polarized unidirectional vertical emission with the radiation efficiency over 50 % can be achieved. Finally, we discuss how this hybrid design relates to various plasmonic cavities and propose a useful quantitative measure of the degree of the `plasmonic' character in a general metallic nanocavity.

Quadratic Dispersion and Damping Processes of π Plasmon in Monolayer Graphene on Pt(111)

High-resolution electron energy-loss spectroscopy has been used to study the π plasmon in monolayer graphene grown on Pt(111). A quadratic dispersion has been observed, in contrast to the linear dispersion reported for monolayer graphene grown on SiC(0001) and in agreement with recent experiments on graphene/Ni(111). Despite the weak interaction of the monolayer graphene with the Pt(111) surface, our results indicate that the screening by the underlying metal substrate strongly influences both the dispersion relation and the damping processes of the plasmon mode of π electrons.

THE EXCITATION OF PLASMON MODES AT A MISMATCHED SILVER/COPPER INTERFACE

The influence of structural, thermal and electronic properties on collective electronic excitations (plasmon modes) has been investigated for thin Ag films grown at room temperature on Cu(111) . For the (9 × 9)-Ag/Cu(111) structure the excitation of the two-dimensional plasmon, observed in Ag/Si(111) , is forbidden by both the high corrugation of the Ag layer and the presence of the underlying metal substrate. The increase of the sp density of states at the Fermi energy induces the appearance of a broad peak a 7–8eV, assigned to a free-electron collective excitation. For increasing Ag coverage (above 20 layers), surface plasmon is confined within Ag grains, as indicated by the analysis of its dispersion relation, which is dispersionless up to a critical wave-vector. Surface plasmon confinement is removed upon annealing at 400 K. The thermal treatment induces a flattening of the Ag adlayer with a merging of Ag islands, and moreover, a strong enhancement of surface conductivity.

Influence of Structural and Electronic Properties on the Collective Excitations of Ag/Cu(111)

Herein, we report on the interplay between structural and electronic properties in the dynamical screening processes and the excitation of collective modes in Ag/Cu(111). For the (9 × 9)-Ag/Cu(111) structure, the excitation of the two-dimensional plasmon, observed in Ag/Si(111), is forbidden by both the high corrugation of the Ag layer and the presence of the underlying metal substrate. The increase of the sp density of states at the Fermi energy induces the appearance of a broad peak at 7–8 eV assigned to a free-electron collective excitation.

Evidence for acoustic-like plasmons on epitaxial graphene on Pt(111)

The dispersion and the damping of the sheet plasmon in a graphene monolayer grown on Pt(111) have been studied by using angle-resolved electron energy loss spectroscopy. We found that the dispersion relation of the plasmon mode confined in the graphene sheet is linear, as a consequence of the screening by the metal substrate. Present results demonstrate that the presence of an underlying metal substrate could have striking consequences on the plasmon propagation even in the case of a system which exhibits a weak graphene-substrate interaction. Moreover, we found that Landau damping essentially occurs via interband excitations starting above the Fermi wave vector. On the contrary, intraband transitions do not have a significant influence on the collective mode.