Search

Three-dimensional (3D) time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging is a promising tool in the analysis of surface modifications of alloy matrix and intermetallic particles induced by localized corrosion due to its good spatial resolution and very high sensitivity to chemical identification especially involving light mass elements like Li. In this paper, ToF-SIMS 3D chemical mapping combined with scanning electron microscopy was performed to study the localized corrosion of Al-Cu-Li alloy (AA2050-T8) in a region around an Al-Cu-Fe-Mn intermetallic particles (IMPs) in 0. 1 M NaCl solution. Initiation of corrosion was locally observed on the IMPs and between IMPs and matrix substrate. Moreover, a modified oxide/hydroxide layer was observed over IMPs compared to the matrix. This new corrosion layer was enriched with chlorides and Cu hydroxides. ToF-SIMS 3D imaging revealed that Li was present over the alloy matrix, while no Li was present over the IMPs in regions where localized corrosion occurred. [ABSTRACT FROM AUTHOR]

Highlights • Current developments of nanoscale insight into passive oxide films. • Cr(III) enrichment and its homogeneity at the nanoscale in passive films. • Corrosion properties of grain boundaries in early intergranular corrosion. • Interaction of organic inhibitor molecules with passivated metallic surfaces. Abstract Oxide passive films are a key for the durability of metals and alloys components as well as a central issue in corrosion science and engineering. Herein, we discuss current developments of the nanometer and sub-nanometer scale knowledge of the barrier properties and adsorption properties of passive oxide films brought by recent model experimental and theoretical investigations. The discussed aspects include (i) the chromium enrichment and its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys such as stainless steel, (ii) the corrosion properties of grain boundaries in early intergranular corrosion before penetration and propagation in the grain boundary network, and (iii) the interaction of organic inhibitor molecules with incompletely passivated metallic surfaces. In all three cases, key issues are highlighted and future developments that we consider as most relevant are identified. [ABSTRACT FROM AUTHOR]

Contemporary aspects of corrosion science are reviewed to show how insightful a surface science approach is to understand the mechanisms of corrosion initiation at the atomic and nanometric scales. The review covers experimental approaches using advanced surface analytical techniques applied to single-crystal surfaces of metal and alloys exposed to corrosive aqueous environments in well-controlled conditions and analysed in situ under electrochemical control and/or ex situ by scanning tunneling microscopy/spectroscopy, atomic force microscopy and X-ray diffraction. Complementary theoretical approaches based on atomistic modeling are also covered. The discussed aspects include the metal-water interfacial structure and the surface reconstruction induced by hydroxide adsorption and formation of 2D (hyd)oxide precursors, the structure alterations accompanying anodic dissolution processes of metals without or with 2D protective layers and selective dissolution (i.e. dealloying) of alloys, the atomic structure, orientation and surface hydroxylation of ultrathin passive films, the role of step edges at the exposed surface of oxide grains on the dissolution of passive films and the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at passive films grain boundaries, and the structure of adlayers of organic inhibitor molecules. [ABSTRACT FROM AUTHOR]

To elucidate the role of noble metal impurities on corrosion of Mg, 3D time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging in combination with X-ray photoelectron spectroscopy and optical microscopy measurements were carried out on Mg samples (99.9%) before and after Mg polarization at EOCP+0.5 V in 0.1 M NaCl. A significant segregation of Fe (and of Mn and Al) metallic impurities at grain boundaries (GBs) was observed on the Mg surface by 3D ToF-SIMS. A 3-step mechanism of Mg corrosion was proposed, including a catalytic effect of Fe segregated at the GBs on the hydrogen evolution reaction (HER). In the 1st stage, the initiation of Mg corrosion is accompanied by the HER occurring over Fe impurities segregated at GBs leading to formation of small circular defects and propagation with occurrence of dark filiform-like pattern corrosion enriched in Cl-. In the 2nd stage, segregated Fe metallic particles are released by Mg matrix undermining, and are dissolved into Fe2+ ions and in the 3rd stage a redeposition of Fe in the clear areas of Mg surfaces, corresponding to areas with low concentration of Cl-, takes place. [ABSTRACT FROM AUTHOR]

The effects of post-treatment applied on Trivalent Chromium Protection (TCP) coatings deposited on aluminum alloy 2024-T3 was studied by electrochemical and surface analytical techniques: X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The aim of the post-treatment was to improve the corrosion resistance of the TCP coating. To understand the influence of the post-treatment, using a bath containing H2O2 and a lanthanum salt as an inhibitor, our approach was to study the effect of these two components separately. It was found that the improved corrosion protection provided by the post-treated TCP was related to a synergetic effect of the two components. XPS and ToF-SIMS analyses showed that (i) the thickness of the TCP coating is not modified by the post-treatment, (ii) lanthanum is present on the surface and in the bulk of the TCP and (iii) is found in very small amount only on the extreme surface. The total concentration of Cr(VI) (oxide/hydroxide) was estimated to be below 0.1 wt% in the post-treated TCP layer. It was concluded that lanthanum plays a significant role in improving the coating density and homogeneity and has a beneficial effect on the TCP coating cracking as observed by Scanning Electron Microscopy. [ABSTRACT FROM AUTHOR]

Corrosion protection by ultra-thin (< 50 nm) alumina films deposited by atomic layer deposition (ALD) on copper at 250°C was studied in 0.5 M NaCl aqueous solution by combining electrochemical and surface analytical methods. Time-of-Flight Secondary Ion Mass Spectrometry revealed a homogenous in-depth stoichiometry of the alumina coatings and their residual bulk contamination by organic and water precursor fragments. Trace contamination by a spurious Cu oxide was evidenced at the interface with the Cu substrate despite a reducing pre-treatment. Atomic force microscopy images revealed conformal substrate coverage and a granularlike coating morphology at the nanometer scale. Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS) showed no electrochemical activity of the coating and a corrosion decrease reaching 4 orders of magnitude for coated samples in comparison with bare copper. Uncoated surface fraction was quantified by application of three different methods using the LSV and EIS data which led to results in excellent agreement. The uncoated surface fraction for 50 nm Al2O3 layers was ~0.01%, confirming ALD alumina as an excellent coating for corrosion protection with spectacularly low residual corrosion activity restricted to the bottom of channel defects connecting the substrate to environment through the coating. [ABSTRACT FROM AUTHOR]

Atomic layer deposited (ALD) 50 nm Al xTa yO z mixture coatings are grown on steel for corrosion protection. In morphological and compositional analyses the coatings are found to be uniform, conformal, well-adhered, and low in defect density. Corrosion protection properties are evaluated with polarization measurements and neutral salt spray (NSS) testing. The sealing properties of the mixtures improve with increasing aluminum oxide content, whereas the protection durability improves with increasing tantalum oxide content. In comparison to single-layer and nano-laminate ALD Al2O3 and Ta2O5 coatings, all mixtures are found to have better protective properties. [ABSTRACT FROM AUTHOR]

The equilibrium E-pH lines limiting the stability domains of lead adsorbed under the monolayer level onto surfaces of copper and nickel from aqueous solution have been calculated using recent electrochemical data on lead underpotential deposition. Pourbaix diagrams are drawn for Pb adsorption on Cu(l 11) surfaces at 25°C and polycrystalline Ni surfaces at 25 and 300°C. Besides the interest of such diagrams for surface electrochemistry, the diagram predicting the conditions of Pb adsorption on Ni at 300°C is of interest in the corrosion field, as Pb adsorption in the domain of formation of the passive Ni layer could explain lead-induced stress corrosion cracking which is a cause of life time reduction of Ni-base alloys used in nuclear power plants. [ABSTRACT FROM AUTHOR]

Abstract: The nanometer scale chemical and structural aspects of ultrathin oxide passive films providing self-protection against corrosion to metals and alloys in aqueous environments are reviewed. Data on the nucleation and growth of 2D anodic oxide films, details on the atomic structure and nanostructure of 3D passive films, the preferential role of surface step edges in dissolution in the passive state and the preferential role of grain boundaries of the passive films in passivity breakdown are presented. Future perspectives are discussed, and exemplified by new data obtained on the relationship between the nanostructure of oxide passive films and their local electronic properties. Atomistic corrosion modeling by ab initio density functional theory (DFT) is illustrated by the example of interactions of chloride ions with hydroxylated oxide surfaces, including the role of surface step edges. Data obtained on well-defined substrate surfaces with surface analytical techniques are emphasized. [Copyright &y& Elsevier]

Atomic layer deposited (ALD) aluminum and tantalum oxide (Al2O3 and Ta2O5) and their nanolaminates were applied as corrosion protection coatings on AISI 52100 steel. The aim was to combine the good sealing properties of Al2O3 with the chemical stability of Ta2O5 and to optimize the coating architecture in order to obtain the best possible long-term durability. Coating composition and morphology were studied with time-of-flight elastic recoil detection analysis (ToF-ERDA), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and field emission scanning electron microscopy (FESEM) and energy dispersive x-ray spectrometry (EDS). Electrochemical properties were studied with voltammetry and electrochemical impedance spectroscopy (EIS), and corrosion durability with neutral salt spray (NSS) testing. The coatings were observed to be conformal and uniform over rough surfaces, and contained some carbon and hydrogen as impurities. The electrochemical results showed that the Al2O3 coating had superior sealing properties compared to the Ta2O5 coating, and nanolaminates had properties in between those of Al2O3 and Ta2O5. However, in the NSS test the laminate-coated samples survived the best demonstrating long-term durability. Analysis of the laminate structure showed that for 40 and 80 nm laminates the best protection was achieved with 10 and 20 nm layers, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A new Ce, Zr and Nb-based conversion coating was designed for AZ91 and AM50 magnesium alloys. The corrosion protection provided by this coating was evaluated by electrochemical measurements (polarization curves, electrochemical impedance spectroscopy) in Na2SO4 electrolyte, and accelerated atmospheric corrosion tests (humid, SO2 polluted air, and salt spray). Its chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). Electrochemical measurements showed that Mg alloys treated during 24h in the Ce–Zr–Nb conversion bath exhibit: (i) increased corrosion potential, (ii) decreased corrosion and anodic dissolution current densities, and (iii) increased polarization and charge transfer resistances. The accelerated corrosion tests revealed excellent atmospheric corrosion resistance for all Ce–Zr–Nb-treated samples, with or without an additional layer of epoxy–polyamide resin lacquer or paint. XPS analysis showed that the coating includes CeO2, Ce2O3, ZrO2, Nb2O5, MgO, and MgF2 as main components. No significant modification of the chemical composition was observed after cathodic and anodic polarization in Na2SO4. This new coating provides improved corrosion resistance, and excellent paint adhesion. It offers an alternative to the chromate conversion coating for magnesium alloys. [Copyright &y& Elsevier]

• 5-sulfosalicylate as an inhibitor in 0.6 M NaCl electrolyte is used for Mg-air battery. • Upon the inhibitor application the improved discharge voltage and battery lifetime are observed. • Almost a four-fold reduction of the hydrogen evolution and a reduced Mg corrosion are noticed. • A modified structure and composition of the surface layer is observed. This work aims at employing sodium 5-sulfosalicylate (5-S-Sal) corrosion inhibitor into aqueous NaCl electrolyte to improve the discharge performance of Mg-air battery and decrease the side reactions of Mg anode. The corrosion tests at open circuit potential show a four-fold decrease of hydrogen evolution when 5-S-Sal inhibitor is added. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses show that due to the presence of 5-S-Sal inhibitor, a corrosion resistant layer has a lower quantity of Mg(OH) 2 (by ∼15%) than that formed in NaCl electrolyte. The surface enrichment in S-like species originating from inhibitor molecule could have an important effect on a decreased corrosion and slow down the H 2 evolution. Within a range of concentrations of 5-S-Sal in NaCl electrolyte (0.05 to 0.15 M), the best discharge performances are achieved with 0.1 M inhibitor. The discharge voltage of full Mg-air battery improves from ∼1.58 to ∼1.82 V at 0.5 mA/cm2 and the discharge lifetime is extended from around 12.5 to around 80 h. Scanning electron microscopy and 3D topography laser microscopy indicate that during the discharge tests much smaller surface degradation occurs and a more uniform surface layer is formed in the presence of inhibitor in the NaCl-based electrolyte. [ABSTRACT FROM AUTHOR]

Electrochemical and surface analyses were applied to study the corrosion mechanisms of aluminium protected by ultra-thin (≤50 nm) alumina coatings grown by atomic layer deposition. Corrosion takes place via residual channel defects connecting the substrate to the electrolyte through the insulating coating. The data evidence the growth of a spurious aluminium oxide film at the substrate/coating interface in the reactor, that is beneficial to the sealing performance of the thinner films (10 nm). The resistance to the initiation of localized corrosion by pitting is increased with thicker films (20 and 50 nm) owing to improved sealing and barrier properties. [ABSTRACT FROM AUTHOR]

The effect of the interfacial air-formed native copper oxide layer on the corrosion protection of copper with 20 nm Atomic Layer Deposited (ALD) alumina was investigated in 0.5 M NaCl using electrochemical and surface analysis techniques. The results show that dissolution of the interfacial native oxide by a pre-treatment of the copper substrate with phosphoric acid is beneficial to the sealing property of the coating and to the corrosion resistance of the substrate exposed through channel defects. Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) elemental depth profiling evidenced the modifications of the interfacial copper oxide on a pre-treated substrate including cleaning from organic contaminants. The beneficial effects of the pre-treatment include improved ALD nucleation and growth due to interface cleaning and decreased cathodic electrochemical activity (assigned to oxygen reduction) at the end of the channel defects exposing the substrate to the environment. Electrochemical Impedance Spectroscopy (EIS) analysis revealed a remarkably lower porosity of the bulk of the ALD alumina layers as compared to the coating/substrate interface, suggesting interfacial trenching as a major failure mechanism for the corrosion protection. Interfacial trenching can be reduced with a freshly re-grown interfacial oxide on the pre-treated substrate surface. The necessity for better controlling the interface chemistry for improved corrosion protection by ALD alumina is demonstrated. [ABSTRACT FROM AUTHOR]

Sublayers grown with filtered cathodic arc deposition (FCAD) were added under atomic layer deposited (ALD) oxide coatings for interface control and improved corrosion protection of low alloy steel. The FCAD sublayer was either Ta:O or Cr:O-Ta:O nanolaminate, and the ALD layer was Al2O3-Ta2O5 nanolaminate, AlxTayOz mixture or graded mixture. The total thicknesses of the FCAD/ALD duplex coatings were between 65 and 120 nm. Thorough analysis of the coatings was conducted to gain insight into the influence of the FCAD sublayer on the overall coating performance. Similar characteristics as with single FCAD and ALD coatings on steel were found in the morphology and composition of the duplex coatings. However, the FCAD process allowed better control of the interface with the steel by reducing the native oxide and preventing its regrowth during the initial stages of the ALD process. Residual hydrocarbon impurities were buried in the interface between the FCAD layer and steel. This enabled growth of ALD layers with improved electrochemical sealing properties, inhibiting the development of localized corrosion by pitting during immersion in acidic NaCl and enhancing durability in neutral salt spray testing. [ABSTRACT FROM AUTHOR]

Abstract: Copper alloys often used in cooling circuits of industrial plants can be affected by biocorrosion induced by biofilm formation. The objective of this work was to study the influence of protein adsorption, which is the first step in biofilm formation, on the electrochemical behavior of 70Cu–30Ni (wt.%) alloy in static artificial seawater and on the chemical composition of oxide layers. For that purpose, electrochemical measurements performed after 1h of immersion were combined to surface analyses. A model is proposed to analyze impedance data. In the presence of bovine serum albumin (BSA, model protein), the anodic charge transfer resistance deduced from EIS data at Ecorr is slightly higher, corresponding to lower corrosion current. Without BSA, two oxidized layers are shown by XPS and ToF-SIMS: an outer layer mainly composed of copper oxide (Cu2O redeposited layer) and an inner layer mainly composed of oxidized nickel, with a global thickness of ~30nm. The presence of BSA leads to a mixed oxide layer (CuO, Cu2O, Ni(OH)2) with a lower thickness (~10nm). Thus, the protein induces a decrease of the dissolution rate at Ecorr and hence a decrease of the amount of redeposited Cu2O and of the oxide layer thickness. [Copyright &y& Elsevier]

Highlights: [•] 40–50nm mixed alumina–tantala coatings were grown by atomic layer deposition. [•] Effects of substrate surface finish and oxide mix were analysed. [•] Nanolaminate stacks are better resistant to breakdown. [•] Localised corrosion occurs at pre-existing coating defects exposing substrate sites. [•] Substrate brushing and H2–Ar plasma pre-treatment hinder pit initiation. [Copyright &y& Elsevier]

Besides their noteworthy tribological and corrosion protection properties, Plasma Electrolytic Oxidation (PEO) coatings feature a porous microstructure that is able to host corrosion inhibitors. This study reveals that although 2,5pyridindicarboxylate (2,5PDC) shows a remarkable corrosion inhibition effect for bare AZ21 Mg alloy, it can extensively deteriorate a PEO coating on the same Mg substrate, resulting in an overall accelerated failure of the PEO-coated AZ21 alloy. The deteriorative behavior of 2,5PDC towards PEO-coated AZ21 is explained based on the characterization of the bare and PEO-coated AZ21 exposed to the NaCl electrolyte with and without inhibitor using EIS, SEM, STEM and ToF-SIMS. • 2,5PDC could effectively inhibit the corrosion of AZ21 in 3.5 wt% NaCl. • 2,5PDC could accelerate the degradation of AZ21 coated with the phosphate-based PEO. • The inhibition/adverse effect of 2,5PDC on bare/coated AZ21 is intensified with its concentration. • Formation of a soluble complex between Mg2+ and 2,5PDC destabilizes the PEO layer. • Formation of a relatively thick corrosion layer on AZ21 accelerates the failure of PEO coating. [ABSTRACT FROM AUTHOR]

Abstract: The effect of H2–Ar plasma pre-treatment prior to thermal atomic layer deposition (ALD) and plasma-enhanced atomic layer deposition (PEALD) of Al2O3 films on steel for corrosion protection was investigated. Time-of-flight secondary ion mass spectrometry and transmission electron microscopy were used to observe the changes in the interface. The electrochemical properties of the samples were studied with polarization measurements, and the coating porosities were calculated from the polarization results for easier comparison of the coatings. Prior to thermal ALD the plasma pre-treatment was observed to reduce the amount of impurities at the interface and coating porosity by 1–3 orders of magnitude. The anti-corrosion properties of the PEALD coatings could also be improved by the pre-treatment. However, exposure of the pre-treatment plasma activated steel surface to oxygen plasma species in PEALD led to facile oxide layer formation in the interface. The oxide layer formed this way was thicker than the native oxide layer and appeared to be detrimental to the protective properties of the coating. The best performance for PEALD Al2O3 coatings was achieved when, after the plasma pre-treatment, the surface was given time to regrow a thin protective interfacial oxide prior to exposure to the oxygen plasma. The different effects that thermal and plasma-enhanced ALD have on the substrate-coating interface were compared. The reactivity of the oxygen precursor was shown to have a significant influence on substrate surface in the early stages of film growth and thereafter also on the overall quality of the protective film. [Copyright &y& Elsevier]

Abstract: Combined analysis by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS), polarization curves and Electrochemical Impedance Spectroscopy (EIS) of the relation between chemical architecture of thin (10 and 50nm) chromium and tantalum oxide coatings grown by filtered cathodic arc deposition (FCAD) on carbon steel and their corrosion protection properties is reported. Pre-etching in the deposition process allows reducing the substrate native oxide layer to traces of iron oxide. A carbidic interlayer is then formed by reaction between the first deposited metallic particles and the residual carbon surface contamination of the alloy. The bulk coatings mostly consist of Cr2O3 or Ta2O5 with no in-depth variation of the stoichiometry. Surface and bulk of the coatings are contaminated by hydroxyl and organic groups. The 50nm coating has a relatively large porosity assigned to a columnar growth preventing good sealing at grain boundaries. The duplex structure (Ta/Ta–C) of the carbidic interlayer promotes a less defective growth of tantalum oxide than the single Cr–C interlayer for chromium oxide, thereby improving the sealing properties. The dielectric constants suggest poor insulating properties in line with a defective and porous nanostructure of the coatings. No dissolution was observed for both oxide nanocoatings in neutral 0.2M NaCl. Penetration of the electrolyte and access to the interface with the carbon steel surface cause the dissolution of the Cr–C interlayer, but not that of the Ta/Ta–C interlayer, and a more rapid initiation of localized corrosion. [Copyright &y& Elsevier]

Abstract: Combined analysis by electrochemical impedance spectroscopy (EIS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and field emission scanning electron microscopy (FESEM) of the corrosion protection provided to carbon steel by thin (50nm) Al2O3 coatings grown by atomic layer deposition (ALD) and its failure mechanism is reported. In spite of excellent sealing properties, the results show an average dissolution rate of the alumina coating of ∼7nmh−1 in neutral 0.2M NaCl and increasing porosity of the remaining layers with increasing immersion time. Alumina dissolution is triggered by the penetration of the solution via cracks/pinholes through the coating to the substrate surface where oxygen reduction takes place, raising the pH. At defective substrate surface sites of high aspect ratio and concentrated residual mechanical stress (along scratches) presumably exposing a higher steel surface fraction, localized dissolution of the coating is promoted by a more facile access of the solution to the substrate surface enhancing oxygen reduction. De-adhesion of the coating is also promoted in these sites by the ingress of the anodic dissolution trenching the steel surface. Localized corrosion of the alloy (i.e. pitting) is triggered prior to complete dissolution of the alumina film on the elsewhere still coated surface matrix. [Copyright &y& Elsevier]

Abstract: Periodic DFT calculations have been performed on a (533)-oriented hydroxylated NiO surface to model the influence of step edges on the adsorption and sub-surface insertion of Cl at the surface of the passive film on nickel. With increasing Cl coverage, substructures of Ni(OH)2, Ni(OH)Cl or Ni(Cl)2 composition are formed and detached from the surface, suggesting a major role of the step edges in the Cl adsorption-induced thinning mechanism of the oxide film. The calculated energies show the promoting effect of the adsorption of Cl on the energy of detachment of the substructures. At surface saturation, sub-surface insertion becomes energetically more favourable than adsorption. The results suggest a possible bifurcation from the Cl adsorption-induced oxide thinning mechanism to the penetration-induced mechanism of passivity breakdown at saturation in adsorbed Cl of the step edges. [Copyright &y& Elsevier]

Abstract: Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) was used to examine the film formed on pure magnesium by immersion for 2min in ultra pure water. The ToF-SIMS data indicates that there is magnesium hydride within the surface film. The presence of MgH2 is a result of the Mg corrosion mechanism. [Copyright &y& Elsevier]

Abstract: The structural modifications of Ni(111) single-crystal surfaces induced by prolonged polarization at the onset of the active/passive transition have been studied at the (sub-)nanometer scale by in situ electrochemical STM (EC-STM) in 0.1M NaOH(aq). The results evidence the effect of the structural order in the passivating monolayer on the corrosion resistance properties and the initiation of localized corrosion. 2D pits are initiated by dissolution on the terraces covered by disordered islands of nickel hydroxide particles and at the boundaries of the crystalline Ni(OH)2(0001) islands. The pits propagate preferentially in the disordered areas. Dissolution is blocked in the well-ordered islands of the passivating monolayer and by the 3D nuclei of the passive film formed at the pre-existing step edges of the nickel substrate. This competitive mechanism of dissolution and passivation, repeated on the terraces newly formed by local dissolution, initiates the growth of 3D pits of nanometer dimensions, i.e. localized corrosion at the nanoscale. A tip effect, promoting the dissolution reaction by a mechanical and/or chemical interaction with the passivating particles, contributed to reveal these local properties. This fundamental understanding of the depassivation/repassivation at the nanoscale opens the way to the search for functional surfaces with self-repair properties. [Copyright &y& Elsevier]

• Adsorption of MBT corrosion inhibitor studied at atomic scale on oxidized copper. • DFT modelling performed on Cu(111) covered by ultrathin Cu 2 O(111) film. • Strong covalent bonding between exo cyclic sulfur atom and under coordinated Cu site. • Saturation monolayer coverage favored over single molecular low coverage adsorption. • Protective layer formed by substituting surface H 2 O and OH in aqueous environment. 2-mercaptobenzothiazole (MBT) is known as an efficient corrosion inhibitor for copper. In the present work, we performed quantum chemical DFT calculations of the interaction of MBT on Cu(111) surfaces covered by an ultrathin Cu 2 O(111) film, in order to bring atomic scale insight on the corrosion inhibition properties of MBT on oxidized copper surfaces. Thione and thiolate forms of MBT are found to interact strongly with the oxidized surfaces. The formation of a monolayer at full coverage is favored over single molecular adsorption at low coverage with the molecules adopting a perpendicular orientation. Thione binds strongly via covalent bonding between the exocyclic sulfur atom and the under coordinated Cu site, and additional H-bonding between the NH group and surface oxygen atoms (NH...O H-bond). Thiolate binds more strongly via a second covalent bond between the N atom and saturated Cu site. Bonding interaction is confirmed by the electronic structure analysis and charge transfer. The adsorption process leads to the reconstruction of the topmost oxide surface. The calculations suggest that both forms of MBT may substitute H 2 O and OH at the Cu 2 O film surface, and thus may form a protective layer on oxidized copper surfaces in aqueous environment. [ABSTRACT FROM AUTHOR]

• MBT and MBI adsorption on Cu in thiol, thiolate and thione forms is studied with DFT. • The Cu(111) surface is considered. • The adsorption is considered from the isolated molecule to the full layer. • MBT and MBI form dense films on Cu via the sulfur atom(s). • Relationship with corrosion inhibition is discussed. This work describes 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzimidazole (MBI) adsorption on Cu(111) by a systematic DFT study. Whatever the surface coverage of the adsorbed molecule, the adsorption is favored when the exocyclic sulfur atom is unprotonated (i.e. thione and thiolate forms). At low molecular density, the molecules adsorb forming a Cu-S(exo) and a Cu-N bond, and the adsorption energies of both molecules are similar, around 1.2 eV. To investigate a coverage corresponding to the density of self-assembled films, two strategies were applied: on the one hand, the best epitaxial relationship between the molecular layer and the Cu(111) surface was searched. A reasonable accommodation was found for a molecular density of 3.9 molecule/nm² in the honeycomb (3 × 3) Cu(111) superstructure, in which the molecules are adsorbed with the C2v axis tilted, forming two Cu-S bonds for MBT and one Cu-S and one Cu-N bond for MBI. On the other hand, the best structure for atomic S on Cu(111), the (√7 x √7) R19° superstructure, with a molecular coverage of 5 molecule/nm2, was considered. We find that the honeycomb MBT and MBI layer is the most stable arrangement, showing that in this case, the molecular organization prevails over the head-group/surface interaction. The MBI molecule adsorbs more strongly than the MBT molecule, due to better lateral interactions in the organic layer. [ABSTRACT FROM AUTHOR]

• 2-MBT bonds to metallic Cu via S atoms and decomposes partially at room temperature. • 2-MBT is lying flat in the monolayer on metallic Cu prior to forming multilayers. • Pre-oxidation prevents decomposition and accelerates the initial growth of 2-MBT. • 2-MBT decomposes and partially desorbs to give atomic S when annealed above 100 °C. • A pre-adsorbed monolayer of 2-MBT on metallic Cu inhibits surface corrosion. Adsorption of 2-mercaptobenzothiazole (2-MBT) at ultra-low pressure and room temperature on metallic and pre-oxidized Cu(111) surfaces and its thermal stability were investigated using X-ray photoelectron spectroscopy in order to better understand the interfacial corrosion inhibiting properties. 2-MBT is lying flat in the monolayer with two sulphur atoms bonded to Cu and decomposes partially yielding atomic sulphur when interacting with metallic copper prior to forming molecular multilayers. Decomposition is prevented by surface pre-oxidation with 2D oxide dissociation accelerating the 2-MBT initial adsorption kinetics. 2-MBT further decomposes and partially desorbs above 100 °C. A pre-adsorbed 2-MBT monolayer on metallic copper inhibits surface corrosion. [ABSTRACT FROM AUTHOR]

• 2-mercaptobenzothiazole adsorbs through S bonding on metallic and pre-oxidized Cu(1 1 1). • 2-mercaptobenzothiazole decomposes partially on metallic copper surface at room temperature. • Multilayers are formed with the outermost molecules lying flat. • Pre-oxidation favors the formation of a more compact and homogeneous molecular layer. • 2-mercaptobenzothiazole adsorbed layers decompose to form a S atomic layer at temperature higher than 100 °C. 2-mercaptobenzothiazole (2-MBT) is used for its corrosion inhibition properties. In this study, the adsorption of 2-MBT on metallic and pre-oxidized Cu(1 1 1) surfaces was investigated using Auger Electron Spectroscopy and Scanning Tunneling Microscopy. Growth and structure of molecular films adsorbed at ultra low pressure and room temperature on clean and pre-oxidized Cu(1 1 1) surfaces were characterized. On clean metallic Cu(1 1 1) surface, local triangular (7 × 7) R19.1° structures are formed at low exposures (3–4 L), which are assigned to the adsorption of atomic S resulting from partial decomposition of 2-MBT. At 10 L, a full non-ordered monolayer of 2-MBT is formed, and further exposure leads to the formation of a non-ordered multilayer. The thickness of the outermost 2-MBT layer is 1.3 Å, which suggests that the outermost molecules of the multilayer are lying flat. Oxidation of the copper surface prior to exposure to 2-MBT results in more compact and homogeneous molecular films. The initial 2D oxide is dissociated and replaced by 2-MBT. Thermal stability at different temperatures was studied on clean and pre-oxidized copper surfaces saturated with 2-MBT. A (7 × 7) R19.1° structure is observed in both cases for temperatures higher than 100 ° C, indicating the decomposition of 2-MBT and a copper surface covered with atomic S. [ABSTRACT FROM AUTHOR]