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We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42±0.03) eV, leading to a clock frequency shift rate of 2.7×10-9/K in fractional unit. A hyperfine population lifetime, T1, and a microwave coherence lifetime, T2, of 1.6 and 0.5ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed. [ABSTRACT FROM AUTHOR]

Abstract In situ Electro-Chemical Scanning Tunneling Microscopy (ECSTM) and Electron Back-Scatter Diffraction analysis of the same local microstructural region were combined to study the relationships between grain boundary (GB) type and structure and passivation on microcrystalline copper in 0.1 M NaOH aqueous solution. The results show that, for high angle random boundaries, passivation in the Cu(I) oxidation range is characterized by a decrease of the depth of GB edge region due to the formation of a passive film locally thicker than on the adjacent grains and thus to anodic oxidation being locally less efficient since it consumes more copper at the grain boundaries. For Σ3 CSL boundaries, the Cu(I) passivation efficiency was observed to be dependent on the local structure of the boundaries. A transition from more to less efficient passivation was observed for a deviation angle of 0.4–0.5° of the {111} GB plane with respect to the perfect geometry of an ideal coherent twin boundary. This transition would result from the effect on the local anodic oxidation properties of an increased density of misfit dislocations accommodating the increased deviation of the boundary plane from the exact CSL plane. Graphical abstract Image 1 Highlights • Local passivation at surface termination of grain boundaries studied in situ on copper. • Microstructure characterized by coupled ECSTM and EBSD local analysis. • Cu(I) passivation less efficient at random grain boundaries than on grains. • Cu(I) passivation efficiency dependent on local structure for Σ3 CSL boundaries. [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]

The role of the SiC substrate surface on the resistance to the local initiation of tarnishing of thin-layered silver stacks for demanding space mirror applications was studied by combined surface and interface analysis on model stack samples deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H 2 S. It is shown that suppressing the surface pores resulting from the bulk SiC material production process by surface pretreatment eliminates the high aspect ratio surface sites that are imperfectly protected by the SiO 2 overcoat after the deposition of silver. The formation of channels connecting the silver layer to its environment through the failing protection layer at the surface pores and locally enabling H 2 S entry and Ag 2 S growth as columns until emergence at the stack surface is suppressed, which markedly delays tarnishing initiation and thereby preserves the optical performance. The results revealed that residual tarnishing initiation proceeds by a mechanism essentially identical in nature but involving different pathways short circuiting the protection layer and enabling H 2 S ingress until the silver layer. These permeation pathways are suggested to be of microstructural origin and could correspond to the incompletely coalesced intergranular boundaries of the SiO 2 layer. [ABSTRACT FROM AUTHOR]

In this work, we addressed the local degradation mechanisms limiting the prelaunch environmental durability of thin-layered silver stacks for demanding space mirror applications. Local initiation and propagation of tarnishing were studied by combined surface and interface analysis on model stack samples consisting of thin silver layers supported on lightweight SiC substrates and protected by thin SiO2 overcoats, deposited by cathodic magnetron sputtering and submitted to accelerated aging in gaseous H2S. The results show that tarnishing is locally initiated by the formation of Ag2S columns erupting above the stack surface. Ag2S growth is promoted at high aspect ratio defects (surface pores) of the SiC substrate as a result of an imperfect protection by the SiO2 overcoat. Channels most likely connect the silver layer to its environment through the protection layer, which enables local H2S entry and Ag2S growth. The silver sulfide columns grow in number and size eventually leading to coalescence with increasing H2S exposure. In more advanced stages, tarnishing slows down owing to saturation of all pre-existing imperfectly protected sites of preferential sulfidation. However, it progresses radially at the basis of the Ag2S columns underneath the protection layer, consuming the metallic silver layer and deteriorating the protecting overcoat. [ABSTRACT FROM AUTHOR]

Atomic level characterization brings fundamental insight into the mechanisms of self-protection against corrosion of metals and alloys by oxide passive films and into how localized corrosion is initiated on passivated metal surfaces. This is illustrated in this overview with selected data obtained at the subnanometre, i.e. atomic or molecular, scale and also at the nanometre scale on singlecrystal copper, nickel, chromium and stainless steel surfaces passivated in well-controlled conditions and analysed in situ and/or ex situ by scanning tunnelling microscopy/spectroscopy and atomic force microscopy. A selected example of corrosion modelling by ab initio density functional theory is also presented. The discussed aspects include the surface reconstruction induced by hydroxide adsorption and formation of two-dimensional (hydr)oxide precursors, the atomic structure, orientation and surface hydroxylation of three-dimensional ultrathin oxide passive films, the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at grain boundaries of passive films and the role of step edges at the exposed surface of oxide grains on the dissolution of the passive film. This article is part of the themed issue 'The challenges of hydrogen and metals'. [ABSTRACT FROM AUTHOR]

Porous TiN xO y-based particles were synthesized by an aerosol spray process. At first, the starting sol solution containing the metal precursor and the nitrogen source is sprayed to form an aerosol that is subsequently pyrolysed at different temperatures. The obtained dried particles are an amorphous coordination 'polymer' rich in carbon and nitrogen. These 'glassy' particles are finally thermally treated at 800 °C, promoting the crystallization of the particles and the release of a major part of the carbon. As the particles keep their original shape, carbon loss and density increase during the crystallization step and lead to the development of an accessible pore structure. The process was analyzed and extended to the synthesis of other metal nitrides, such as VN and W2N, thereby showing its general validity for the production of functional nanocrystalline nitride ceramics with high porosity still occupying a relatively small volume, and otherwise not easily accessible. [ABSTRACT FROM AUTHOR]

Electrochemical scanning tunneling microscopy (ECSTM) was applied to analyze in situ the passivation of grain boundaries on microcrystalline copper in 0.1 M NaOH aqueous solution. Two types of boundaries, assigned to coherent twin and random grain boundaries, were studied in three different states of the copper surface: metallic after cathodic reduction of the air-formed native oxide film, passive after anodic polarization at 0.7 V vs. SHE to form the duplex Cu(I)/Cu(II) oxide film, and metallic after cathodic reduction of the passive film. The depth measured at several sites along the grain boundaries was extracted from statistical line profile analysis and discussed using an original model allowing differentiating metal consumption by dissolution or by passive film formation at grains and grain boundaries. The results highlight different local passivation properties between randomly oriented grains and grain boundaries and also between the two different types of grain boundaries. Both at coherent twin and random grain boundaries, it is found that more copper irreversibly dissolves during passivation and less copper is consumed to grow the passive film, suggesting a more hydroxylated/hydrated composition less dense in copper than on grains. At random grain boundaries, irreversible dissolution is found to be enhanced and the passive film to be thicker. [ABSTRACT FROM AUTHOR]

Highlights: [•] Passive films grown on stainless steel in high temperature water analysed by C-AFM. [•] Electrical resistance of grains and grain boundaries measured at nanometre scale. [•] Local electrical resistance influenced by changes in resistivity of the oxide film. [•] Local resistivity assigned to balance in Fe(II)/Cr(III) composition of inner layer. [•] Grain boundaries of outer layer would promote Cr(III) enrichment of inner layer. [Copyright &y& Elsevier]

Abstract: The electronic properties of the granular and intergranular sites of passive films grown on Ni(111) single-crystal surfaces in alkaline solution have been studied with scanning tunnelling spectroscopy. The results show no effect of the grain boundaries on the intrinsic semiconductive properties of the single layer hydroxide passive film. In contrast the local properties of the duplex oxide/hydroxide passive film are changed from nearly intrinsic on the grains to p-type at the grain boundaries. The implications of these local modifications of the electronic properties on oxidative and reductive electronic transfer and on the corrosion resistance are discussed. [Copyright &y& Elsevier]

Pegylated silicon nanoparticles (SiNPs) are of great interest for applications in bio-imaging as fluorescent tracers. Poly(ethylene glycol) (PEG) covalently attached to SiNPs may improve the (bio)compatibility, solubility in water and stability of SiNPs, without inhibiting their optical properties. SiNPs are first coated with silica followed by a silanization of the surface. Then, two versatile 'grafting to' methods are used to provide pegylated SiNPs. Both peptide type coupling and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) are conducted and compared to graft PEG of different chain lengths. Infra-red spectroscopy, thermogravimetric analysis and transmission electron microscopy prove that theses methodologies are simple and efficient for the preparation of functional inorganic nanoparticles with luminescent properties. [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]

This article presents a process for surface coating and functionalization of luminescent silicon nanoparticles. The particles were coated with silica using a microemulsion process that was adapted to the fragile silicon nanoparticles. The as-produced core-shell particles have a mean diameter of 35 nm and exhibit the intrinsic photoluminescence of the silicon core. The silica layer protects the core from aqueous oxidation for several days, thus allowing the use of the nanoparticles for biological applications. The nanoparticles were further coated with amines and functionalized with polyethylene glycol chains and the toxicity of the particles has been evaluated at the different stages of the process. The core-shell nanoparticles exhibit no acute toxicity towards lung cells, which is promising for further development. [ABSTRACT FROM AUTHOR]

This article deals with the first covalent grafting of an enzyme on twice functionalized γ-Fe2O3@SiO2 core–shell magnetic nanoparticles. First, amino-PEG functionalized nanoparticles were synthesized in order to comply with non-toxic platforms that would be stable in high concentration and would exhibit chemical groups to allow further coupling with biomolecules. This approach produces a colloidal suspension of covalently grafted enzymes that remains stable for months and mimics the enzyme–substrate interactions in solution. Secondly, nanoparticles synthesis and enzyme coupling process were reported and the catalytic properties of bound enzymes were measured and compared with that of the free one. These new materials appear to be useful tools for enzymatic catalysis research and may be extended to other biomolecules. Furthermore, magnetic properties of these materials open the way to separation, purification, and transport under magnetic field. [ABSTRACT FROM AUTHOR]

Abstract: Ultra-thin Cr2O3 films (12.0, 17.3 and 29.6nm thick) were produced on Cr metal by thermal oxidation, and their electrochemical properties in 1M LiClO4 in propylene carbonate (PC) were investigated by cyclic voltammetry and chronopotentiometry. The reductive electrolyte decomposition and the conversion/deconversion process were observed and analyzed by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The initial irreversible capacity due to the reduction of electrolyte and the incomplete deconversion process during the first cycle is 70% of the first discharge capacity. A stable charge/discharge capacity of 460mAhg−1 was obtained in the 3rd to 10th cycles. XPS and PM-IRRAS evidenced the growth of a solid electrolyte interphase (SEI) layer that is constituted of Li2CO3 formed by reductive decomposition of the electrolyte. The SEI layer thickness and/or density is modified by the conversion/deconversion reaction. ToF-SIMS evidenced the volume expansion/shrink resulting from the conversion/deconversion reaction. ToF-SIMS also revealed an incomplete conversion process limited by mass transport, which partitions the oxide into a converted outer part assigned to Li2O containing Cr traces and an unconverted inner part ascribed to Cr2O3 or lower Cr oxide containing Li. It was found that the deconversion re-homogenizes the oxide film in a single layer but with lithium trapped in it. The present study provides a detailed understanding of the interfacial reaction on the oxide anode undergoing a conversion/deconversion reaction. [Copyright &y& Elsevier]

Abstract: Amino and/or polyethyleneglycol (PEG) functionalized core–shell γFe2O3–SiO2 magnetic nanoparticles were synthesized and characterized. Amino–PEG-functionalized core–shell nanoparticles have calibrated sizes and a good colloidal stability. These bi-functionalized core–shell nanoparticles are potentially useful as biocompatible particles for magnetically targeted chemotherapy. [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]

Abstract: EC-AFM was used to study in situ the surface nanostructure of V2O5 thin films grown on vanadium metal and its changes during lithium electrochemical intercalation corresponding to the reversible α-to-δ phase transition. The results evidence the lateral extension and contraction of the oxide nanograins and the flattening of the oxide film surface. The increase and decrease of the lateral dimensions of the grains show that the surface reflects the volume expansion and contraction resulting from the dimensional changes of the oxide structure when lithium is inserted and de-inserted. An increase of ∼10% and ∼15% with respect to pristine oxide film was observed after the formation of the ε and δ phases, respectively. The lateral extension of the grains (∼7%) and surface flattening subsist after de-intercalation showing the non-fully reversible change of the oxide nanostructure at the interface with the electrolyte. Repeated cycling causes aging characterized by the amplification of the lateral extension of the grains (∼17%) and flattening of the oxide surface with respect to the pristine oxide film. It also modifies the surface of the oxide grains by creating new planes indicative of surface reconstruction and/or the emergence of slip planes. [Copyright &y& Elsevier]

Abstract: Cyclic voltammetry, XPS, RBS and AFM have been combined to study the ageing mechanism of Li intercalation in V2O5 thin films prepared by thermal oxidation of vanadium metal. Multi-cycling tests were performed in 1M LiClO4-PC in the potential range E ∈[3.8, 2.8V] versus Li/Li+, corresponding to the α-to-δ phase transition. XPS and AFM were performed using direct anaerobic and anhydrous transfer. Capacity fading remains inferior to 20% during ∼2500 cycles. XPS shows slight modifications of the oxide composition with a V4+ concentration increasing from ∼5% prior to cycling to ∼16–27% after cycling, due to Li trapped in the oxide film and to the loss of V2O5 active material. The presence of lithium carbonate and lithium-alkyl carbonate species evidences the formation of the so-called SEI layer. AFM evidences the loss of crystalline material by grain exfoliation from the outer V2O5 layer of the oxide film. By further exfoliation, the inner VO2 layer of the oxide film is reached and pits are formed, occupying ∼9–13% of the surface. This de-cohesion at grain boundaries is attributed to the strain generated by repeated lattice distortions. After 3300 cycles, the disappearance of lithium carbonates, whereas Li-alkyl carbonates and/or Li-alkoxides remain on the surface, indicates the dissolution and/or conversion of the SEI layer. After 4500 cycles, the oxide film became very labile and could be stripped away by rinsing to reveal the vanadium metal substrate. [Copyright &y& Elsevier]

Abstract: The intercalation and deintercalation mechanisms of lithium into V2O5 thin films prepared by thermal oxidation of vanadium metal have been studied by X-ray photoelectron spectroscopy (XPS) using a direct anaerobic and anhydrous transfer from the glove box (O2 and H2O<1ppm), where the samples were electrochemically treated, to the XPS analysis chamber. Vanadium in the as-prepared oxide films is mostly (from 93 to 96% depending on samples) in a pentavalent state (V5+) with a stoichiometric O/V concentration ratio fitting that of V2O5. Four to seven percent of VO2 is also observed. After the 1st and the 2nd intercalation steps at E =3.3 and 2.8V versus Li/Li+, respectively, the V2p core level spectra evidence a partial reduction to V4+ states with a remaining concentration of 73 and 56% of V5+, in agreement with the intercalation of about 1/2mol of Li per V2O5 mol at each intercalation step. Intercalated lithium was observed at a binding energy of 56.1eV for Li1s. Changes of the electronic structure of the V2O5 thin film after intercalation are evidenced by the observation, at a binding energy of 1.3eV, of occupied V3d states (V4+) originally empty in the pristine film (V5+). The V2p and Li1s core level spectra show that the process of Li intercalation is partially irreversible. In the first cycle, 34 and 14% of the vanadium ions remain in the V4+ state after deintercalation at E =3.4 and 3.8V versus Li/Li+, respectively, indicating a partially irreversible process already after the 1st deintercalation. The analyses of C1s and O1s XP spectra show the formation of a solid–electrolyte interface (SEI). The analyzed surface layer includes lithium carbonate and Li-alkoxides. [Copyright &y& Elsevier]

Abstract: In order to produce thin films of crystalline V2O5, vanadium metal was thermally oxidised at 500°C under oxygen pressures between 250 and 1000mbar for 1–5min. The oxide films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). The lithium intercalation performance of the oxide films was investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS). It was shown that the composition, the crystallinity and the related lithium intercalation properties of the thin oxide films were critically dependent on the oxidation conditions. The formation of crystalline V2O5 films was stimulated by higher oxygen pressure and longer oxidation time. Exposure for 5min at 750mbar O2 at 500°C resulted in a surface oxide film composed of V2O5, and consisting of crystallites up to 200nm in lateral size. The thickness of the layer was about 100nm. This V2O5 oxide film was found to have good cycling performance in a potential window between 3.8 and 2.8V, with a stable capacity of 117±10mAh/g at an applied current density of 3.4μA/cm2. The diffusion coefficients corresponding to the two plateaus at 3.4 and 3.2V were determined from the impedance measurements to (5.2 and 3.0)×10−13 cm2 s−1, respectively. Beneath the V2O5 layer, lower oxides (mainly VO2) were found close to the metal. At lower oxygen pressure and shorter exposure times, the oxide films were less crystalline and the amount of V4+ increased in the surface oxide film, as revealed by XPS. At intermediate oxygen pressures and exposure times a mixture of crystalline V2O5 and V6O13 was found in the oxide film. [Copyright &y& Elsevier]

Abstract: STM, STS, LEED and XPS data for crystalline θ-Al2O3 and non-crystalline Al2O3 ultra-thin films grown on NiAl(001) at 1025K and exposed to water vapour at low pressure (1×10−7–1×10−5 mbar) and room temperature are reported. Water dissociation is observed at low pressure. This reactivity is assigned to the presence of a high density of coordinatively unsaturated cationic sites at the surface of the oxide film. The hydroxyl/hydroxide groups cannot be directly identify by their XPS binding energy, which is interpreted as resulting from the high BE positions of the oxide anions (O1s signal at 532.5–532.8eV). However the XPS intensities give evidence of an uptake of oxygen accompanied by an increase of the surface coverage by Al3+ cations, and a decrease of the concentration in metallic Al at the alloy interface. A value of ∼2 for the oxygen to aluminium ions surface concentration ratio indicates the formation of an oxy-hydroxide (AlO x OH y with x + y ∼2) hydroxylation product. STM and LEED show the amorphisation and roughening of the oxide film. At P(H2O)=1×10−7 mbar, only the surface of the oxide film is modified, with formation of nodules of ∼2nm lateral size covering homogeneously the surface. STS shows that essentially the valence band is modified with an increase of the density of states at the band edge. With increasing pressure, hydroxylation is amplified, leading to an increased coverage of the alloy by oxy-hydroxide products and to the formation of larger nodules (∼7nm) of amorphous oxy-hydroxide. Roughening and loss of the nanostructure indicate a propagation of the reaction that modifies the bulk structure of the oxide film. Amorphisation can be reverted to crystallization by annealing under UHV at 1025K when the surface of the oxide film has been modified, but not when the bulk structure has been modified. [Copyright &y& Elsevier]

Oxide layers grown on the surface provide an effective way of protecting metallic materials against corrosion for sustainable use in a broad range of applications. However, the growth of cavities at the metal/oxide interface weakens the adherence of the protective layer and can promote its spallation under service conditions, as observed for alumina layers formed by selective oxidation of aluminide intermetallic alloys used in high-temperature applications. Here we show that direct atomic-scale observations of the interface between an ultrathin protective oxide layer (alumina) grown on an intermetallic titanium aluminide substrate (TiAl) can be performed with techniques sensitive to the topmost atomic layers at the surface. Nanocavities resulting from the self-assembling of atomic vacancies injected at the interface by the growth mechanism of the protective oxide are observed for the first time, bringing new insight into the understanding of the fate of injected cavities in oxidation processes. [ABSTRACT FROM AUTHOR]

In situ electrochemical scanning tunneling microscopy (ECSTM) investigations of the anodic Cu(I)/Cu(II) duplex passive layers grown on Cu(1 1 1) and Cu(0 0 1) in 0.1 M NaOH are reported. The outer Cu(II) part of the duplex film formed on both substrates is crystalline with a terrace and step topography. The observed lattices are consistent with a bulk-like terminated CuO(0 0 1) surface on both substrates. This common crystallographic orientation is explained by the hydroxylation of the otherwise polar and unstable oxide surface at the passive film/electrolyte interface. The epitaxy of the oxide layers is governed by the parallel alignment of the close packed directions of the CuO outer layers and Cu2O inner layers on both substrates. A granular and amorphous layer covering the crystalline CuO(0 0 1) oxide has been observed on Cu(0 0 1) but not on Cu(1 1 1). It is assigned to a film of copper hydroxide corrosion products formed by a dissolution–precipitation mechanism. Its absence on the passivated Cu(1 1 1) surface is explained by the higher stability of the Cu2O(1 1 1) precursor oxide formed on this substrate in the initial stages of growth of the duplex passive film, resulting in a lower amount of dissolved copper. [Copyright &y& Elsevier]

In situ electrochemical scanning tunneling microscopy measurements of the anodic oxidation of Cu(0 0 1) in 0.1 M NaOH are reported. Adsorption-induced surface reconstruction is observed in the underpotential range of oxidation with the formation of dimers of superimposed Cu atoms ejected from the substrate and stabilized by adsorbed OH groups, presumably in bridging positions. The reconstruction causes the reorientation of the substrate step edges and the formation of holes and ad-islands of monoatomic height. The dimers of superimposed Cu atoms are alternatively aligned along the 〈1 0 0〉 directions to form zig-zag arrangements. Long range ordering is observed in areas of limited lateral extension with c(2×6) and c(6×2) domains. In the potential range of Cu(I) oxide formation, a facetted Cu2O layer grows with a Cu2O(0 0 1)[1 1¯ 0] ∣∣ Cu(0 0 1)[1 0 0] epitaxial relationship. The 45° rotation between the close-packed directions of the oxide lattice and metal lattice results from the orientation of the dimers of superimposed Cu atoms in the precursor adsorbed OH layer. The surface of the oxide layer is facetted due to a tilt of ∼3% between oxide and metal lattices. Its (0 0 1) terraces have an identical chemical termination and are presumably hydroxylated. [Copyright &y& Elsevier]

In situ electrochemical scanning tunneling microscopy (STM) has been applied to study the mechanisms of growth of passive layers on Cu(111) in NaOH solutions in the presence of chlorides. For [Cl−]/[OH−]=0.01, the same ordered precursor phase of adsorbed OH is observed in the underpotential region of oxidation as in Cl−-free solutions. Atomically resolved images reveal the structure of the reconstructed topmost metal plane and the threefold hollow adsorption site of the hydroxide. The induced reconstruction causes the ejection of Cu atoms that contribute to the observed lateral growth of the terraces and to the formation of 2D Cu ad-islands in the final stages of the adsorption process. For [Cl−]/[OH−]=0.1, threadlike nanostructures resulting from the reaction of the ejected Cu atoms with chlorides are formed before agglomeration with the 2D Cu ad-islands formed in the final stage of the hydroxide adsorption process. For [Cl−]/[OH−]=10, the step edges, which are normally the preferential sites of the reaction with hydroxide, are blocked by the formation of non-ordered surface chloride complexes. Hydroxide adsorption still predominates the surface reaction on the terraces but the 2D ad-islands form immediately due to the blocking of the step edges. In the potential range of Cu(I) oxide formation, crystalline Cu(I) oxide layers are formed with a high density of steps and (111) terraces. Their step edges are rougher in the presence of chlorides which indicates a Cl−-enhanced localized dissolution reaction of the oxide layers at step edges. [Copyright &y& Elsevier]

The initial stages of growth of ordered layers of Al[sub 2]O[sub 3] on NiAl(001) single-crystal surfaces at 1025 K and 10[sup -7] mbar (10[sup -5]Pa) in O[sub 2] have been studied using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The STM results evidence the formation of elongated strips (26 Å wide and 11 Å high) of Al[sub 2]O[sub 3] oriented along the [100] and [010] directions of the substrate. With longer oxidation, the substrate is increasingly covered by rectangular and striped islands resulting from the vicinal and parallel growth of the strips. On the ultrathin oxide film formed after 500 L (1 L = 10[sup -6] torr-s (∼1.33 × 10[sup -4] Pa·s)) of exposure, STM atomic resolution images have been obtained for the first time. They evidence the [001] orientation of the oxygen sublattice in Bain epitaxy on the substrate. The observation of one-dimensional atomic trenches together with the strips observed on the nanometer scale is consistent with the growth of θ-Al[sub 2]O[sub 3]. The STS local measurements evidence the insulating behavior of the oxide layer formed with a gap value ranging from 7 and 8 eV for amorphous and ordered domains, respectively. [ABSTRACT FROM AUTHOR]

New insight on local inhibition effects of 2-mercaptobenzimidazole (MBI) on early stage intergranular corrosion of copper in hydrochloric acid solution is reported from in situ analysis at the nanometer scale and comparison with 2-mercaptobenzothiazole (MBT) effects in the same pre-adsorption and corrosion testing conditions. Macroscopic cyclic voltammetry analysis, including grains and grain boundary (GB) network, showed a passivation-like behavior in the Cu(I) oxidation range, specific to MBI since not observed with MBT and assigned to the anodic formation of a surface film of Cu(I)-MBI reaction products protecting against dissolution. Electrochemical scanning tunneling microscopy analysis revealed net intergranular dissolution, mitigated by the imperfect protection provided by the anodically formed MBI layer. It also showed local accumulation of reaction products in the GB surface regions, blocking preferential dissolution. For random GBs, blocking by local accumulation of reaction products was dominant, in agreement with the expected higher reactivity of these GBs generating more Cu(I) ions under anodic polarization and thus less efficiently protected by the anodically formed MBI layer. For Coincidence Site Lattice (CSL) boundaries, mitigated net dissolution was more frequently observed. Coherent twins showed equally efficient inhibition in the GB surface region than on adjacent grains. MBI inhibition was less efficient than MBT inhibition with more Cu(I) reaction products generated on the grains to form a surface film and their preferential local accumulation more frequently observed in the GB surface regions. [ABSTRACT FROM AUTHOR]

Magnetostrictive thin films, exhibit significant utility as functionalization materials for Surface acoustic wave sensors designed for magnetic field measurements. This research investigates the influence of annealing under vacuum and magnetic field at various temperatures on the magnetic properties of the FeCo/TbCo2 thin film and therefore on the sensitivity of shear and Rayleigh acoustic waveguides functionalized with these magnetic layers. The observed effects include a reduction in magnetic anisotropy field and an increase in magnetostriction. XPS and TEM coupled with EDS microanalysis provide insights into the variations in the properties of the nanostructured magnetic film. To safeguard the magnetic film, a thin layer of SiO2 is deposited on top, serving as a protective shield. The inclusion of this layer amplifies sensitivity to applied magnetic fields for modes with shear polarization while reducing sensitivity for Rayleigh mode. In ST‐cut Quartz, the shear waves become waveguided upon the incorporation of magnetic thin films, with further enhancement achieved by introducing a SiO2 layer. Rayleigh waves are evanescent modes, the penetration depth is in the order of wavelength, and the addition of SiO2 decrease the wave confinement and therefore the sensitivity. The findings are supported by a theoretical model and experimentally validated results. [ABSTRACT FROM AUTHOR]

Surface spectroscopy analysis and electrochemistry were applied to study the effects of surface preparation by vibratory polishing on the passivity of stainless steel 304L surfaces. Compared to grinding by traditional mechanical polishing, vibratory polishing promotes the enrichment of Cr(III) oxide and hydroxide species in the duplex chemical structure of the surface native oxide film by enhancing selective Fe oxidation and dissolution. As a result, spontaneous passivity, tested in aggressive sulphuric acid electrolyte, is enhanced. However, in the absence of enrichment in Mo(IV) and Mo(VI) species in the passive film, the Cr enrichment does not enhance passivity upon anodic polarisation nor increase the resistance to Cl-induced passivity breakdown and initiation of localised corrosion in accelerated testing conditions. The results provide comprehensive insight into the mechanisms underlying the passivity enhancement of stainless steel by surface engineering. [ABSTRACT FROM AUTHOR]

The durability of passivable metals and alloys is often limited by the stability of the surface oxide film, the passive film, providing self-protection against corrosion in aggressive environments. Improving this stability requires to develop a deeper understanding of the surface structure and initial surface reactivity at the nanometric or atomic scale. In this work we applied scanning tunneling microscopy to unravel the surface structure of a model stainless steel surface in the metallic state and its local modifications induced by initial reaction in dioxygen gas. The results show a rich and complex structure of the oxide-free surface with reconstructed atomic lattice and self-organized lines of surface vacancies at equilibrium. New insight is brought into the mechanisms of initial oxidation at steps and vacancy injection on terraces leading to Cr-rich oxide nuclei and locally Cr-depleted terraces, impacting the subsequent mechanism of chromium enrichment essential to the stability of the surface oxide. Unlabelled Image • Surface atomic structure unraveled on oxide-free model austenitic stainless steel • Terraces terminated by reconstructed atomic lattice and self-organized vacancies • Cr oxide nucleation at defect sites of reduced atomic coordination (step edges) • Cr vacancy injection on terraces leading to Cr depletion on terraces [ABSTRACT FROM AUTHOR]

This paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation. Then, the length of the cavity where light interacts with alkali atoms can be extended. We demonstrate that a longer cell allows to reduce the beam diameter, while preserving the clock performances. As the cavity depth and the beam diameter are reduced, collimation can be performed in a tighter space. This solution relaxes the constraints on the device packaging and is suitable for wafer-level assembly. Several cells have been fabricated and characterized in a clock setup using coherent population trapping spectroscopy. The measured signals exhibit null power linewidths down to 2.23 kHz and high transmission contrasts up to 17%. A high contrast-to-linewidth ratio is found at a linewidth of 4.17 kHz and a contrast of 5.2% in a 7-mm-long cell despite a beam diameter reduced to 600 μm. [ABSTRACT FROM AUTHOR]

In situ X-ray photoelectron spectroscopy real-time measurements and angular-dependent high resolution core level analysis were used for the first time to investigate the Cr enrichment and oxide growth mechanisms on a model 304 austenitic stainless steel surface in the very initial stages of oxidation leading to pre-passivation. The oxidation kinetics was followed for increasing oxygen exposure and temperature, revealing an early nucleation regime (for exposure <10 L) leading to the formation of a strongly Cr-enriched Cr 3+ /Fe 3+ mixed layer followed by an oxide growth regime where preferential iron oxidation takes over and mitigate the initial chromium enrichment. [ABSTRACT FROM AUTHOR]

Fe-based air alkaline batteries are promising candidates for large scale energy storage due to their low cost, eco-friendliness and high energy density. In this work, pure iron was studied as negative electrode of Fe-air batteries with and without Na 2 S added to the KOH alkaline electrolyte in order to bring new insight on the mechanisms of inhibition of the hydrogen evolution reaction (HER) and improvement of the electrochemical performances of the Fe electrode. Electrochemical (CV, galvanostatic discharge), spectroscopic (XPS, ToF-SIMS) and microscopic (SEM) analysis were applied to characterize the effect of the sulfide additive (Na 2 S) on the electrochemical behavior of Fe electrodes and their chemical and morphological modifications. Surface analysis performed by XPS and ToF-SIMS revealed the formation of a markedly thicker oxide/hydroxide layer. The mechanism of formation of this thick oxide/hydroxide layer is initiated by the adsorption of sulfur (S ads ) at the oxide/metal interface that inhibits the HER during the first stages of electrochemical process and promotes subsequent anodic oxidation. With the Na 2 S electrolyte additive, Fe(0)/Fe(II) conversion/deconversion is suppressed and charge/discharge proceeds mostly by Fe(II)/Fe(III) conversion/deconversion with improved capacity owing to the porous morphology of the oxide/hydroxide layer. [ABSTRACT FROM AUTHOR]

X‐ray photoelectron spectroscopy analysis was applied to investigate the thermal stability under ultra‐high vacuum environment of the surface oxide film formed by electrochemical passivation of a newly designed Cr15Fe10Co5Ni60Mo10 (at.%) multi‐principal element alloy and providing the alloy superior localized corrosion resistance compared to conventional stainless steels and alloys. A spectral decomposition methodology involving the subtraction of Auger peaks overlapping the Fe 2p and Co 2p core level regions was applied for quantification of the oxide film composition and thickness. The results show that, at 100°C, the passive oxide film is mainly dehydrated and dehydroxylated. Obvious loss of Ni hydroxide and conversion of Mo (VI) to Mo (IV) species are observed at 200°C, with further reduction of Mo species to Mo (III) observed at 300°C. In this temperature range, the total cation quantity in the oxide film remains stable despite the compositional alteration. At 400°C, Cr (III) oxide forms at the expense of Fe and Mo oxides, resulting in an oxide film essentially consisting of chromium oxide. At 500°C, Cr (III) oxide is eliminated, making the passive film unstable at this temperature. Possible Cr oxide removal mechanisms are discussed. [ABSTRACT FROM AUTHOR]

We report on the stability of large sulfur islands, formed by exposing the nanostructured O/Cu(110) surface to H 2 S. We have found that these islands, composed of several hundreds of atoms, show a dynamic behavior at room temperature and undergo both Smoluchowski and Ostwald ripening. An additional decay mechanism has been observed at sub-saturation sulfur coverages. The island decay can be described by a classical power law. However, oscillatory deviations from the model have been observed and possible reasons for their occurrence are discussed. At saturation sulfur coverage, the islands are still mobile and undergo ripening, but no decay is observed. In these conditions, a new nanostructured S/Cu(110) surface is formed. [ABSTRACT FROM AUTHOR]

DFT calculations bringing atomic scale insight into the corrosion inhibition properties of 2-mercaptobenzothiazole on copper are reported. Energetic and electronic analysis show that both the thione and thiolate conformers strongly chemisorb on oxide-free Cu(110) surfaces and can self-order to form dense and stable organic barriers saturating all Cu atoms of the topmost metal plane. Increasing monolayer density occurs at the cost of the metal and molecule deformations, but the energy loss is compensated by the layer cohesion energy. The copper vacancy creation energy is higher with thiolate than with thione monolayers, indicating more efficient mitigation of dissolution by adsorbed thiolate. • DFT atomic scale insight into 2-MBT corrosion inhibition properties on copper. • Strong chemisorption of thione and thiolate conformers on metallic Cu(110) surfaces. • Formation of dense and stable organic barriers saturating all Cu surface atoms. • Energy cost of metal and molecule deformations balanced by layer cohesion energy. • More efficient local mitigation of dissolution with thiolate than with thione. [ABSTRACT FROM AUTHOR]

Surface smoothening by substrate annealing was studied as a pre-treatment for improving the corrosion protection provided to copper by 10, 20 and 50 nm thick alumina coatings deposited by atomic layer deposition. The interplay between substrate surface state and deposited film thickness for controlling the corrosion protection provided by ultrathin barrier films is demonstrated. Pre-annealing at 750 °C heals out the dispersed surface heterogeneities left by electropolishing and reduces the surface roughness to less than 2 nm independently of the deposited film thickness. For 10 nm coatings, substrate surface smoothening promotes the corrosion resistance. However, for 20 and 50 nm coatings, it is detrimental to the corrosion protection due to local detachment of the deposited films. The weaker adherence of the thicker coatings is assigned to the stresses accumulated in the films with increasing deposited thickness. Healing out the local heterogeneities on the substrate surface diminishes the interfacial strength that is bearing the stresses of the deposited films, thereby increasing adhesion failure for the thicker films. Pitting corrosion occurs at the local sites of adhesion failure. Intergranular corrosion occurs at the initially well coated substrate grain boundaries because of the growth of a more defective and permeable coating at grain boundaries. [ABSTRACT FROM AUTHOR]

Passivation at grain boundaries was investigated on copper with Electrochemical Scanning Tunneling Microscopy. The depth in intergranular regions was measured and its variation was discussed in terms of dissolution or passive film formation. The Cu(I) passive film is found to be thicker at grain boundaries than on grains but with a similar stoichiometry. A thicker Cu(I) passive film is observed at random grain boundaries than at coherent twins. No metal is preferentially consumed at grain boundaries by transient dissolution during Cu(I) passivation. Comprehensive comparison with Cu(I)/Cu(II) passivation shows that transient dissolution is a revelator of the grain boundary-type dependent behavior. [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]

(Fe,Cr)-binary oxide thin film electrodes were prepared as negative electrode material for lithium-ion micro-batteries by thermal growth on a stainless steel (AISI 410, FeCr 12.5 ) current collector. The mechanisms of lithiation/delithiation were investigated by means of electrochemical (CV, galvanostatic cycling), spectroscopic (XPS, ToF-SIMS) and microscopic (SEM, AFM) analytical techniques. The as-prepared (Fe, Cr)-binary oxide electrodes exhibit a good cycling performance except the first discharge/charge cycle where a high irreversible capacity is observed due to formation of a solid electrolyte interphase (SEI) layer. The influence of substituting an oxidized iron by an oxidized chromium (Cr x Fe 2− x O 3 phase) was evaluated. The data show that the inferior electrochemical conversion activity of substituted oxidized chromium results in hindering lithium transport in the bulk thin film electrode. It was observed that the irreversible morphology modifications together with SEI evolution are critical to capacity degradation while retaining good coulombic efficiency. [ABSTRACT FROM AUTHOR]

Spectroscopic(XPS, ToF-SIMS) and microscopic (SEM, AFM) analyticalmethods have been applied to iron oxide (∼Fe2O3) using a thin film approach to bring new insight into theaging mechanisms of conversion-type anode materials for lithium-ionbatteries. The results show that repeated lithiation/delithiationcauses both chemical and morphological modifications affecting theelectrochemical performance. The SEI layer formed by reductive decompositionof the electrolyte remains stable in composition (mostly Li2CO3) but irreversibly thickens upon multicycling. Irreversibleswelling of the material accompanied by penetration of the SEI layerand accumulation of non-deconverted material in the bulk of the oxidethin film occurs upon repeated conversion/deconversion. After initialpulverization of the thin film microstructure, grain growth and aggregationare promoted by multicycling. This leads to capacity increase in thefirst few cycles, but upon further cycling volume expansion and accumulationof non-deconverted material lead to deterioration of the electrodeperformances. [ABSTRACT FROM AUTHOR]

Abstract: The morphological and chemical modifications induced by repeated cycling of conversion-type negative electrode material were studied for iron sulfide thin films in 1M-LiClO4/PC by combining AFM, XPS and ToF-SIMS analysis with electrochemical control. The topographical changes were consistent with irreversible swelling of the material caused by repeated volume expansion/contraction. A 3% capacity fading measured after 9 conversion/deconversion cycles resulted mainly from the loss of electroactive material forming pinhole defects in the thin film electrode. Repeated cycling caused increasing accumulation of non deconverted material in the bulk thin film electrode. Repeated cycling also resulted in continuous surface up-take and increasing accumulation of the SEI layer in the bulk thin film electrode, rich in Li2CO3. Formation of a duplex-like structure with organic and inorganic compounds primarily distributed in the outer and inner parts, respectively, was suggested by ToF-SIMS depth profiling of the SEI layer. [Copyright &y& Elsevier]

Hydrous Cr 2 O 3 and Fe 2 O 3 surfaces without and with substitutional molybdenum were simulated by DFT modelling to investigate at the atomic scale the role of Mo in improving the corrosion resistance of passive films on stainless steels. The surface structures most energetically favoured were determined in the conditions of interest. For surfaces with a high degree of hydroxylation, the preferential location of substitutional Mo is just under the hydroxyl groups, in agreement with the experimental observations. The substitution by Mo is exothermic and Mo preferentially substitutes in Fe- than in Cr-rich zone of the inner barrier layer of passive films. • DFT modelling of (0001) hydrous Cr 2 O 3 and Fe 2 O 3 surfaces to study passivity. • Determination of energetically favoured terminations in the conditions of interest. • Exothermic substitution by Mo more favoured on Fe 2 O 3 than on Cr 2 O 3 surfaces. • Preferential location of Mo on the surface after highly hydroxylation. [ABSTRACT FROM AUTHOR]

Highlights: [•] XPS, ToF-SIMS analyses are combined with electrochemical control. [•] Conversion/deconversion mechanism of iron monosulfide thin film electrode is reported. [•] Incomplete process of conversion/deconversion and expansion/shrinkage is evidenced. [•] SEI layer thickness variation upon conversion/deconversion is shown. [•] Penetration of SEI layer into the bulk electrode is demonstrated. [Copyright &y& Elsevier]

Abstract: A comparative study by Time-of-Flight Secondary Ions Mass Spectrometry and X-ray Photoelectron Spectroscopy, i–E polarization curves and Electrochemical Impedance Spectroscopy of the corrosion protection of low alloy steel by 50nm thick tantalum oxide coatings prepared by low temperature Atomic Layer Deposition (ALD) and Filtered Cathodic Arc Deposition (FCAD) is reported. The data evidence the presence of a spurious oxide layer mostly consisting of iron grown by transient thermal oxidation at the ALD film/substrate interface in the initial stages of deposition and its suppression by pre-treatment in the FCAD process. Carbonaceous contamination (organic and carbidic) resulting from incomplete removal of the organic precursor is the major cause of the poorer sealing properties of the ALD film. No coating dissolution is demonstrated in neutral or acid 0.2M NaCl solutions. In acid solution localized corrosion by pitting proceeds faster with the ALD than with the FCAD coating. The roles of the pre-existing channel defects exposing the substrate surface and of the spurious interfacial oxide promoting coating breakdown and/or delamination are emphasized. [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]