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The load cell is an indispensable component of many engineering machinery and industrial automation for measuring and sensing force and torque. In this article, we propose to investigate a force sensor design combining surface acoustic wave (SAW) strain sensor with binocular load cell structure. For this purpose, we use a binocular test body instrumented with both resistive strain gauge as a reference and SAW strain sensor. The system enables the generation of extremely localized and accurate positive and negative strains. Static and dynamic measurements are performed using calibrated weights and a shock hammer respectively. For SAW sensor, a one-port resonator with frequency operation in the range of 410 MHz was fabricated and mounted on the test body. For electronic conditioning, we use a low-cost RF electronic conditioning based on radar architecture using the integrated circuit AD8302. The system enables the measurement of ${S}_{{11}}$ reflection coefficient (module and phase) with sensitivity and noise spectral density of (29 mV/dB, 250 nV/ $\surd $ Hz) and (10 mV/°, 83 nV/ $\surd $ Hz) respectively. The SAW sensor mounted on body proof was successfully tested in static and dynamic mode using this electronic architecture. The results show good linearity, sensitivity values of 0.023 and 0.09 mV/ppm were obtained for amplitude and phase measurements respectively. The dynamic response was performed using a shock hammer and a comparison with conventional strain gauge shows a good agreement.

We describe a high-performance, compact optical frequency standard based on a microfabricated Rb vapor cell and a low-noise, external cavity diode laser operating on the Rb two-photon transition at 778 nm. The optical standard achieves an instability of 1.8×10^−13τ^−1/2 for times less than 100 s and a flicker noise floor of 1×10^−14 out to 6000 s. At long integration times, the instability is limited by variations in optical probe power and the ac Stark shift. The retrace was measured to 5.7×10^−13 after 30 h of dormancy. Such a simple, yet high-performance optical standard could be suitable as an accurate realization of the meter or, if coupled with an optical frequency comb, as a compact atomic clock comparable to a hydrogen maser.

Protection of silver mirror stacks from environmental degradation before launching is crucial for space applications. Hereby, we report a comparative study of the advanced protection of silver mirror stacks for space telescopes provided by SiO 2 and Al 2 O 3 coatings in conditions of accelerated aging by sulfidation. The model silver stack samples were deposited by cathodic magnetron sputtering on a reference silica substrate for optical applications and a surface-pretreated SiC substrate. Accelerated aging was performed in dry and more severe wet conditions. Optical micrographic observations, surface and interface analysis by Time-of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and reflectivity measurements were combined to comparatively study the effects of degradation. The results show a lower kinetics of degradation by accelerated aging of the stacks protected by the alumina coating in comparable test conditions. [ABSTRACT FROM AUTHOR]

In many applications, metallic copper can be covered by an ultrathin native or a passive oxide film depending on the redox conditions of the interface formed with the environment, which governs its surface properties. In the present work, we constructed and optimized through quantum chemical density functional theory (DFT) calculations a model of this Cu(111)||Cu2O(111) stoichiometric oxide supported in parallel epitaxy on a Cu(111) substrate. Energetic analysis of the metal–oxide interface shows the stable formation of the interface between the oxide film and metal substrate. The Cu2O(111) film binds to the Cu(111) surface via the unsaturated oxygen atoms bonded to copper metal atoms in top, bridge, and hollow sites. Structural analysis of the Cu2O(111) film surface shows reconstruction with modifications of the distances between the unsaturated and the saturated copper atoms. The surface interlayer relaxation is inward for Cu(111)||Cu2O(111), whereas it is outward for the nonsupported Cu2O(111) oxide and converges to that of bulk oxide with increasing the Cu2O(111) thickness. The electronic work function is not significantly modified with respect to the Cu(111) electronic work function, whatever the oxide thickness. The hydration of the surface is energetically favorable, and water molecular adsorption is favored over dissociative adsorption. Water molecules chemisorb on top over unsaturated copper atoms. The hydroxylation of the surface shows two adsorption modes of the OH groups on top over unsaturated Cu atoms and on a bridge site between unsaturated and saturated Cu atoms.

The adsorption of 2-mercaptobenzothiazole (2-MBT) vapor on a Cu(111) surface under ultra-low pressure was investigated. For an exposure of 45 L at 150 °C, a Moiré pattern was observed as a result of the superposition of an underlying (3×3)R30° structure and an outer layer compressed by 18% and rotated by 1.2°. The Moiré pattern was rich in S bonded to Cu as a result of molecular decomposition and partial desorption and was transformed to a (7×7)R19.1° structure when the sample temperature was increased above 250 °C during deposition. This pre-adsorbed Moiré structure led to the sharp decrease of the oxidation kinetics, which better protects copper against corrosion than the non-ordered 2-MBT monolayer formed at room temperature. Upon further exposure to 2-MBT at room temperature, an equivalent monolayer of the molecule was adsorbed on the Moiré structure at saturation whereas a multilayer was formed for the direct deposition on Cu(111) at room temperature.

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 SiO2overcoats, 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 SiO2overcoat. 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.

Organic coatings are often required for the protection of metals against environmental degradation. Despite their extensive use, only limited information is available on the initial stages of adsorption and formation of protective films, especially at the molecular and atomic levels. As a model system for coating formation, this study investigates the adsorption of glycerol molecules on the single-crystalline Cu(111) surface. A combined electrochemical and scanning tunneling microscopy study in NaOH aqueous solution enabled following the adsorption process in detail, providing molecular information on the glycerol film structure. A potential-driven adsorption of glycerol was observed, suppressing the adsorption of hydroxyl molecules and copper oxidation. The adsorbed species assembled in a nearest neighbor arrangement fitting a (√3 × √3) R30° hexagonal structure with respect to the Cu(111) lattice. This experimentally observed configuration was confirmed by density functional theory (DFT) calculations. DFT modeling indicates that a mixed adsorption mode involving the two primary alcohol groups adsorbed at different z-positions relative to the surface is the most favorable. This mixed configuration enabled the formation of an extended network of hydrogen bonds that aids in stabilization of the glycerol film. This implies that interactions between glycerol molecules have a non-negligible effect on the growth process of such an organic film, allowing the formation of organic layers in the absence of strong interfacial interactions.

Laboratory optical atomic clocks achieve remarkable accuracy (now counted to 18 digits or more), opening possibilities for exploring fundamental physics and enabling new measurements. However, their size and the use of bulk components prevent them from being more widely adopted in applications that require precision timing. By leveraging silicon-chip photonics for integration and to reduce component size and complexity, we demonstrate a compact optical-clock architecture. Here a semiconductor laser is stabilized to an optical transition in a microfabricated rubidium vapor cell, and a pair of interlocked Kerr-microresonator frequency combs provide fully coherent optical division of the clock laser to generate an electronic 22 GHz clock signal with a fractional frequency instability of one part in 10^13. These results demonstrate key concepts of how to use silicon-chip devices in future portable and ultraprecise optical clocks.

Time of Flight Secondary Ion Mass Spectroscopy, X-Ray Photoelectron Spectroscopy, in situ Photo-Current Spectroscopy and electrochemical analysis were combined to characterize the physicochemical alterations induced by electrochemical passivation of the surface oxide film providing corrosion resistance to 316L stainless steel. The as-prepared surface is covered by a [?]2 nm thick, mixed (Cr(III)-Fe(III)) and bi-layered hydroxylated oxide. The inner layer is highly enriched in Cr(III) and the outer layer less so. Molybdenum is concentrated, mostly as Mo(VI), in the outer layer. Nickel is only present at trace level. These inner and outer layers have bandgap values of 3.0 and 2.6[?]2.7 eV, respectively, and the oxide film would behave as an insulator. Electrochemical passivation in sulfuric acid solution causes the preferential dissolution of Fe(III) resulting in the thickness decrease of the outer layer and its increased enrichment in Cr(III) and Mo(IV-VI). The further Cr(III) enrichment of the inner layer causes loss of photoactivity and improved corrosion protection with the anodic shift of the corrosion potential and the increase of the polarization resistance by a factor of [?]4. Aging in the passive state promotes the Cr enrichment in the inner barrier layer of the passive film.

Pulsed coherent population trapping (CPT) spectroscopy is applied in buffer-gas filled Cs–Ne vapor microfabricated cells. The properties of the Ramsey-CPT clock transition central fringe (linewidth, signal amplitude, and contrast) are studied versus several experimental parameters, including the Ramsey sequence and the input laser intensity, and are compared to those obtained in the conventional continuous (CW) interrogation mode. In the pulsed case and for short Ramsey-free evolution times T_R, the central fringe linewidth is found to exhibit a small but visible power broadening and is measured to be narrower than the value of 1/(2T_R) that is reached for long T_R. The microwave hyperfine coherence lifetime T_2 in the Cs–Ne microcells is measured to be in the 50–500 μs range. Its dependence to the buffer gas pressure or cell temperature is briefly studied.

The initiation of intergranular corrosion at various types of grain boundaries (GBs) was studied at the nanometer scale on microcrystalline copper in 1 mM HCl aqueous solution. In situ Electrochemical Scanning Tunneling Microscopy (ECSTM) and Electron Back-Scatter Diffraction analysis of the same local microstructural region were combined using an innovative methodology including micro marking performed with the STM tip. The results demonstrate that electrochemically-induced intergranular dissolution, at the surface termination of GBs, is dependent on the grain boundary character. It is found that random high angle boundaries as well as S9 coincidence site lattice (CSL) boundaries are susceptible to nanoscale initiation of intergranular corrosion while for S3 CSL boundaries the behavior is dependent on the deviation angle of the GB plane from the exact orientation. For the S3 twins, a transition from resistance to susceptibility occurs between 1deg and 1.7deg of deviation as a result of the increase of the density of steps (i.e. misorientation dislocations) in the coincidence boundary plane. The work emphasizes the precision needed in the design of the grain boundary network in applications where intergranular corrosion or its initiation must be controlled at the nanoscale.

The corrosion resistance of stainless steels is determined by the thickness, structure, composition and electronic properties of the oxide layers grown on their surface and isolating the metallic substrate from the environment. In the present work, ex situ XPS (X-Ray Photoelectron Spectroscopy) and ToF-SIMS (Time of Flight Secondary Ions Mass Spectrometry) have been combined to in situ PCS (PhotoCurrent Spectroscopy) in order to perform an integrated physicochemical characterization of surface oxide films grown on bright annealed ferritic stainless steel (AISI 434) as-received and after thermal post-treatment in air. The surface oxide film on as-received samples has a bilayer structure with an inner layer close to pure Cr(III) oxide and an outer layer of mixed Fe(III) and Cr(III) oxide enriched in Cr. After thermal post-treatment in air at 350degC and 550degC, the surface oxide films thicken and the outer layers are enriched in Fe(III). Linear voltammetry and electrochemical impedance spectroscopy analysis evidence a decrease of the polarization resistance in the passive range, a cathodic shift of the corrosion potential and an increased cathodic current after thermal post-treatment. The bilayer structure, composition and electronic properties of these surface oxide films and their modifications are discussed to rationalize their corrosion behavior.

The composition and stratification of the passive oxide films formed on three Cr-Fe-Co-Ni(-Mo) multi-principal element alloys by electrochemical anodic passivation in sulfuric acid electrolyte containing 0.2 and 4.7 M NaCl were investigated, combining X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry surface analysis. The passive films show a bilayer structure similar to that formed in Cl−-free electrolyte with an inner layer mostly consisting of Cr oxide and an outer layer containing of Cr hydroxide, Ni hydroxide, Mo oxides, and Fe (hydr)oxide. The Mo-free alloy exhibits a thickening of the inner Cr oxide layer and the thinning of the outer layer in 0.2 M Cl−, whereas the two Mo-containing alloys do not show significant alteration even in 4.7 M Cl−evidencing their higher stability in Cl−-containing solutions. The chloride penetration is limited to the external part of the outer oxide layer, except in the most severe tested conditions where traces reach the inner barrier layer, and the chloride entry into the layer is strongly reduced after pre-passivation in Cl−-free solution. The results allow us to discuss the beneficial effects of pre-passivation in Cl−-free conditions and Mo addition providing these alloys enhanced resistance to passivity breakdown.

We report on the metrological characterization of novel commercially available 894.6 nm vertical-cavity surface-emitting lasers (VCSELs), dedicated to Cs D_1 line spectroscopy experiments. The thermal behavior of the VCSELs is reported, highlighting the existence of a minimum threshold current and maximum output power in the 55°C–60°C range. The laser relative intensity noise, measured to be −108  dB/Hz at 10 Hz Fourier frequency f for a laser power of 25 μW, is reduced with increased power. The VCSELs frequency noise is 10^8  Hz^2/Hz at f=100  Hz. The spectral linewidth of the VCSELs is about 30 MHz. VCSELs injection current can be directly modulated at 4.596 GHz with microwave power in the range of −10 to +0  dBm to generate optical sidebands. A VCSEL was used in a microcell-based Cs atomic clock based on coherent population trapping. A preliminary clock short-term fractional frequency stability of 8×10^−11τ^−1/2 up to about 100 s is reported, demonstrating the suitability of these VCSELs for miniature atomic clock applications.

In situ electrochemical (by electrochemical impedance spectroscopy, EIS) and ex situ surface (by time-of-flight secondary ions mass spectrometry, ToF-SIMS) analysis were applied to investigate solid-state diffusion coefficient (DLi) into conversion-type α-Fe2O3negative electrode for Li-ion batteries. DLivalues obtained from EIS were in the range of 10–16to 10–15cm2s–1for electrodes partially and fully lithiated, respectively, showing that pulverization of the converted material promotes Li-ion migration. ToF-SIMS ion depth profiling performed after partial lithiation enabled discriminating the surface solid electrolyte interphase (SEI) region, a converted electrode region (Li2O/Fe0matrix) of slow diffusion (DLi= 6 × 10–16cm2s–1) and an unconverted region (intercalated Fe2O3matrix) of faster diffusion (DLi= 2 × 10–13cm2s–1) ahead of the conversion front. Comparison of the ex situ and in situ results indicates that the electrode conversion kinetics is limited by Li-ion diffusion in the converted matrix and suggests a hindering effect of the passivating SEI layer. ToF-SIMS depth profile analysis appears as a most appropriate and direct methodology to measure Li-ion diffusion solely in electrode materials, excluding SEI layer effects.

Corrosion protection by ultra-thin ([?] 50 nm) alumina films deposited by atomic layer deposition (ALD) on copper at 250degC 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 granular-like 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.

In situ electrochemical scanning tunneling microscopy (ECSTM) was applied to analyze the local susceptibility to corrosion at different grains of cryogenically rolled microcrystalline copper in a HCl solution, and combined with electron backscatter diffraction (EBSD) and field emission scanning electron miscroscopy (FE-SEM) to discuss the relationship between nanometer scale corrosion resistance and crystallographic orientation. The results show that the thickness of the air-formed oxide layer is grain-dependent with the largest values exceeding locally by a factor of 2 the macroscopic value (2.8 nm) measured electrochemically. Anodic dissolution is also grain-dependent with dissolving grains observed to neighbor corrosion-resistant grains. A nearly random texture prevented an EBSD-based assignment of the crystallographic orientation of the grains observed by ECSTM. However, comparison of the etched surface morphology measured in situ by ECSTM and ex situ by FE-SEM suggested that the faster dissolving grains were oriented closer to ⟨111⟩//ND or in between ⟨111⟩//ND and ⟨110⟩//ND while the neighboring corrosion-resistant grains were oriented closer to ⟨001⟩//ND. The higher step density measured by ECSTM on the grains corroding faster despite possibly ⟨111⟩//ND oriented terraces confirms the role of surface defects related to misorientation on the corrosion susceptibility.

Atomic layer deposition (ALD) is a thin film deposition technique that is based on alternating and saturating surface reactions of two or more gaseous precursors. The excellent conformality of ALD thin films can be exploited for sealing defects in coatings made by other techniques. Here the corrosion protection properties of hard CrN and diamond-like carbon (DLC) coatings on low alloy steel were improved by ALD sealing with 50 nm thick layers consisting of Al2O3and Ta2O5nanolaminates or mixtures. In cross sectional images the ALD layers were found to follow the surface morphology of the CrN coatings uniformly. Furthermore, ALD growth into the pinholes of the CrN coating was verified. In electrochemical measurements the ALD sealing was found to decrease the current density of the CrN coated steel by over 2 orders of magnitude. The neutral salt spray (NSS) durability was also improved: on the best samples the appearance of corrosion spots was delayed from 2 to 168 h. On DLC coatings the adhesion of the ALD sealing layers was weaker, but still clear improvement in NSS durability was achieved indicating sealing of the pinholes.

Iron oxide (mostly α-Fe2O3) model thin-film electrodes were prepared by thermal oxidation of pure metal iron substrates at 300 ± 5 °C in air and used for comprehensive investigation of the lithiation/delithiation mechanisms of anode material undergoing an electrochemical conversion reaction with lithium ions. Surface (X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS)) and electrochemical (cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)) analytical techniques were combined. The results show that intercalation of Li in the Fe2O3matrix and solid electrolyte interphase (SEI) layer formation both precede conversion to metallic iron and Li2O upon lithiation. Depth profile analysis evidences stratification of the converted thin-film electrode into fully and partially lithiated outer and inner parts, respectively, due to mass transport limitation. The SEI layer has a stable composition (Li2CO3with minor ROCO2Li) but dynamically increases/decreases in thickness upon lithiation/delithiation. Conversion, proceeding mostly in the outer part of the electrode, causes material swelling accompanied by SEI layer thickening. Upon delithiation, lithium is trapped in the deconverted electrode subjected to shrinking, and the SEI layer mostly decomposes and reduces in thickness after deconversion. The nonreversibility of both conversion and surface passivation mechanisms is demonstrated.

Oxide layers play a crucial role in the corrosion resistance of metals and alloys and the growth kinetics of these films is of major interest. To express the oxide growth kinetics, three main models are available: the Cabrera-Mott model, the Fehlner-Mott model and the Point Defect Model (PDM). These models are reviewed in the first part of the paper. Among these models, the PDM is the only one that takes into account the interfacial potential drops during the oxide growth. However, in this model: (i) no parameters relative to the substrate alloy are taken into account, and (ii) the growth is limited by the flow of oxygen vacancies through the film (transport via both cation interstitial and vacancy positions are not taken into account). Here we present a "generalized model" for the kinetics of oxide growth in which the evolution of the interfacial potential drops during oxide growth is included, as well as the variation of the electric field in the oxide during film growth. This new model allows us to describe the growth of oxide films on alloys under non-steady-state conditions. The link between oxide growth and cation release into the solution is also included.

Electrochemical Scanning Tunneling Microscopy (ECSTM) has been employed to investigate in situ the nanometer scale morphology and the atomic structure of a (100)-oriented Fe-l8Cr-l3Ni single crystal stainless steel surface passivated in 0.5 M H2SO4(aq). The results show that polarization in the pre-passive or passive domain does not destroy the typical as-prepared substrate topography but modifies the nanogranular morphology of the air-formed native oxide film initially covering the surface. In the pre-passive range ([?]0.06 V/SHE), dissolution of iron-rich oxide species has the main effect on the local changes, digging the surface preferentially on the substrate terraces where the native oxide film is thinner. In the passive domain, the 3D growth of oxide grains counteracts dissolution more rapidly than in the pre-passive range limiting the dissolution-induced modifications. The growth of the Cr(III)-enriched passive film is preferential along the substrate steps. Increasing the passivation potential (from 0.35 to 0.7 V/SHE) does not markedly influence the amplitude of the passivation-induced modifications of the morphology of the covering oxide film. However, it causes crystallization of the oxide. The atomic lattice measured in situ is consistent with the oxygen sublattice of the major oxide component (Cr2O3) of the Cr(III)-enriched passive film.

Electrochemical scanning tunneling microscopy has been employed to investigate the growth mechanism of the 2D adlayer formed on Ag(111) surfaces in the potential range negative to 3D sulfide growth in HS–-containing alkaline aqueous solution. The results show that (2√3 × 2√3)R30°, (√3 × √3)R30°, and (√7 × √7)R19° superstructures are formed with potential-driven increasing uptake of sulfur up to saturation and that extraction of Ag adatoms from the terrace edges is induced by adsorption already at low surface coverage. Irreversible surface fragmentation is produced at the nanometer scale. It is concluded that S uptake occurs via a two-electron oxidative reaction forming S adatoms in the whole range of potential. No extracted Ag adatoms participate to the construction of the (2√3 × 2√3)R30° and (√3 × √3)R30° superstructures. However, the formation of the (√7 × √7)R19° saturated adlayer involves surface reconstruction and the immobilization of the Ag adatoms extracted from the terrace edges at lower potential and diffusing on the surface to form “AgS” bilayers and “Ag2S” trilayers on the substrate terraces. The saturated adlayer can be considered as a structural precursor of the 3D growth of Ag2S formed at higher anodic potential. Upon reductive desorption of sulfur, the disruption of the Ag–S bonds in the adlayer destabilizes the Ag adatoms that become again mobile on the surface and cluster to form dispersed adislands of smaller dimensions than the initial terraces, thus amplifying surface roughening at the nanometer scale.

Scanning tunneling spectroscopy has been applied to characterize the electronic properties of the granular and intergranular sites of the passive film grown on Ni(111) single-crystal surfaces in acid solution. The passive film, essentially consisting of NiO, shows p-type grains (valence band edge at 0.54 +- 0.03 eV below Fermi level) with unoccupied Ni 3d surface states at 0.5-1.5 eV above Fermi level in the bandgap. At grain boundaries, the p-type semiconductivity is attenuated as evidenced by a downward shift of 0.12 +- 0.06 eV of the valence band edge, and the density of surface states is markedly reduced, both effects indicating the presence of oxygen vacancies in these sites. The dominant point defect in the film is metallic vacancies but oxygen vacancies attenuate locally the resulting p-type property at the grain boundaries. The implications of these local electronic properties on oxidative and reductive electronic transfer and on the corrosion resistance are discussed. The oxygen vacancies at intergranular boundaries imply local changes of the properties of anionic mass transport through the passive film and enhancement of Cl[?] adsorption and/or penetration, which is consistent with the view of passive film grain boundaries playing a key role in passivity breakdown.

The characterization of electrode processes induced by lithiation/delithiation of Sn−Ni alloy films electroplated on a copper substrate is presented. Galvanostatic discharge/charge measurements were combined with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS shows the buildup of a solid electrolyte interphase (SEI) layer formed by reductive decomposition of the electrolyte at the surface of the Sn−Ni anode during the first discharge. The SEI layer is constituted of a mixture of Li2CO3, ROCO2Li, Li2C2O4, and/or ROLi whose balance is not markedly modified upon cycling. ToF-SIMS depth profiling evidences an incomplete initial alloying process of lithium ion with Sn and the resulting partition of the Sn−Ni layer alloy into a fully lithiated outer part and a partially lithiated inner layer during the first discharge. After the first cycle, the volume expansion/shrink associated with the alloying/dealloying reaction, also evidenced by ToF-SIMS, irreversibly cracks and divides the Sn−Ni alloy into island-like morphology with gaps filled by the SEI layer. Multicycling (tested up to 9 cycles) amplifies the division of the Sn−Ni alloy layer and the related penetration of the SEI layer as indicated by the increase of trapped lithium and chlorine but with no apparent loss of active material or drop of capacity.

The structure of the γ-TiAl(111) alloy surface was studied with combined experimental and theoretical approaches. The experimental scanning tunneling microscopy (STM) images indicate surface reconstruction with a (2 × 2) superstructure as a result of Al depletion of the alloy surface after preparation. The atomic protrusions form a zigzag pattern oriented along the direction of the shorter surface unit vector of the (2 × 2) supercell, that is, the [101̅] direction. The theoretical investigations performed with molecular dynamics in combination with simulated annealing based on the density functional theory (DFT) show that the surface starts to reconstruct at temperatures higher than 950 K, in agreement with the experimental annealing temperature. Geometric analysis and simulated STM images obtained from periodic DFT calculations show that the atomic protrusions forming the zigzag patterns correspond to Al atoms of the reconstructed topmost plane. The persistence of the reconstructed structure up to the simulated melting temperature of 1800 K shows the high stability of Al vacancies injected in the topmost plane of the alloy.

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.

X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been combined to study the modifications and growth of alumina thin films on NiAl(001) induced by exposure to water vapor at low pressure (10−6mbar) and by immersion in ultrapure liquid water at room temperature. The film thickness and stoichiometry, as well as the alloy composition changes, were analyzed by angle-resolved XPS measurements. Ultrathin (∼0.7 nm) hydroxylated native oxide films were compared to thicker (∼4 nm) anhydrous and oxygen-deficient thermal oxide films grown at 900 °C under low air pressure (10−4mbar). The results show that immersion in liquid water causes the formation of one to two equivalent additional monolayers of aluminum oxide at the interface between the native oxide film and the alloy, suggesting anion transport along the oxide/alloy interface after entry at intergranular oxide sites. The hydroxylated oxide surface remains unchanged. In contrast, immersion of the thicker thermal oxide films in liquid water causes the formation of ∼3 equivalent additional aluminum oxide monolayers at the oxide/water interface, indicating cation transport through the film. AFM suggests a preferential growth at the boundaries between the oxide grains due to faster ion transport. The ∼4 nm thick thermal oxide film is inert when exposed to water at low vapor pressure (10−6mbar) confirming the pressure gap for the water-induced modifications of transitional alumina films. Exposure to ambient air partially annihilates the oxygen deficiency observed after formation as shown by the variation of the O−Al stoichiometry and core level shift effects.

For the first time, voiding mechanisms resulting from the condensation of atomic vacancies injected at oxide/alloy interfaces by the growth of oxide layers have been studied by means of periodic density functional theory (DFT) calculations. Several interfaces were built by superimposing ultrathin films of alumina on the γ-TiAl(111) surface, and their relative stabilities were compared by calculating the interface energy variation. The formation energy of single Ti or Al vacancies and clustered and dispersed ensembles of 2Ti + 1Al or 2Al + 1Ti vacancies injected into the alloy were calculated. The results show that it is easier to inject the vacancies into the oxide/alloy interface than into the bare alloy surface and into the bulk alloy. The injected vacancies, trapped at the oxide/alloy interface, condense in the topmost plane of the alloy to form 2D clusters. The minimization of the coordination number of the vacancies with metal atoms of the alloy and O atoms of the overlaying oxide favors vacancy condensation and interfacial voiding. The data are relevant for a detailed understanding of the adherence and breakdown of protective oxide films and the lifetime of metallic materials.

The effects of surface finish by mechanical polishing, vibratory polishing, and high-temperature annealing were studied on 316L stainless steel by combining microscopic and spectroscopic analysis of the surface morphology and composition and electrochemical analysis of the corrosion resistance. Compared to mechanical polishing, vibratory finishing promotes passivity at the active-passive transition in acid solution and enhances resistance to chloride-induced passivity breakdown. Cr and Mo enrichments in the native oxide film increase owing to preferential iron etching. The bilayer structure develops a thicker Cr(III) oxide inner barrier layer and an outer exchange layer further enriched in Cr(III) hydroxide and Mo(IV/VI) oxides. The Fe-rich weak sites of passivity are reinforced. High-temperature annealing in reducing hydrogen environment enables us to fully reconstruct the cold-worked layers left by mechanical or vibratory finishing, thus allowing us to expose the bulk microstructure at the topmost surface. The benefits brought by vibratory finishing are lost upon reducing the initial native oxide. The re-formed native oxide develops a bilayer structure with similar Cr and Mo enrichments as that obtained from mechanical polishing and no beneficial effects on passivity. The results provide comprehensive insight into how the passivity of stainless steel can be enhanced by surface enrichment engineering.

A key factor for effective inhibition by organic molecules of the initiation of localized corrosion by pitting is their ability to form a protective organic film in locally de-passivated zones exposing the bare metal next to the oxide-covered surface. Herein, based on quantum chemical DFT calculations, we study the chemistry of the interface between 2-mercaptobenzimidazole (MBI) and a copper surface partially covered by a Cu2O passive oxide film. The results show the adaptability of the molecule to adsorb strongly on the different zones, oxide or metal, of a locally de-passivated surface. However, differences in the local adsorption configurations, involving covalent bonding with H-bonding depending on oxide or metal and on conformer, thione or thiolate, lead to the formation of an inhomogeneous organic film. Increasing order of local adsorption strength is oxide walls < metal surface < oxide surface < oxide edges for the thione species, whereas there is no significant difference of local adsorption strength for the thiolate species. Our results suggest that both species of MBI can heal the oxygen and copper low coordinated sites as well as can protect the exposed metal surface, thus enhancing the barrier properties of the passivated surface even when locally defective.

Thermal barrier systems, used for turbine blades, are made of a nickel-based superalloy, a nickel aluminide bond coat layer and a ceramic thermal barrier. The aim of the present work is to study the initial stages of oxidation of the AM1/NiAl(Zr) system. It is currently of prime importance to characterize the initial thin oxide layer that covers the bond coat prior to the topcoat deposition. Indeed, the adhesion of the thermal barrier layer and the lifetime of the system are partly influenced by the substrate pre-heating oxidizing treatment. In order to determine the contribution of zirconium during this intermediate temperature range oxidation, the AM1/NiAl(Zr) system was heat treated at 950°C, in two vacuum conditions, that were close to the industrial ones. The compositions of the extreme surface of the nickel aluminide and of the thermally grown oxide were investigated by Xray photoelectron spectroscopy. In particular, these experiments allowed us to detect zirconium at the surface of the system and to determine its oxidation state.

XPS, RBS, and NRA have been combined to study the mechanisms of Li-ion electrochemical intercalation in MoO 3thin films prepared by thermal oxidation of molybdenum metal. A direct anaerobic and anhydrous transfer was used from a glovebox (O 2and H 2O < 1 ppm), where the samples were electrochemically treated at selected potentials between 1.7 and 3.2 V versus Li +/Li, to the XPS analysis chamber. The thermal oxide film grown at T= 450 ± 10 °C and P(O 2) = 100 ± 10 mbar for t= 5 min consisted of a 20 nm thick MoO 3outer layer overlying a 13 nm thick inner layer of lower oxides (Mo 2O 5and MoO 2). Combined RBS/NRA analysis allowed the dosing of intercalated lithium and the determination of the composition of the lithiated phases. Li 0.50MoO 3, Li 1.20MoO 3, and Li 0.21MoO 3were obtained after intercalation at 2.58 and 1.73 V and deintercalation at 3.2 V, respectively, showing that ∼1.2 mol of Li can be initially intercalated in the potential range 1.7−3.2 V (capacity of 223 mA h/g), and ∼0.2 mol of Li per mol of MoO 3is trapped in the oxide matrix after the initial stages of intercalation. The XP Mo3d core level spectra evidenced the reduction of Mo 6+ions to Mo 5+ions after intercalation at 2.58 V and further to Mo 5+and Mo 4+ions after intercalation at 1.73 V with resulting Mo 6+/Mo 5+/Mo 4+ratios of 53:47:00 at % and 37:39:24 at %, respectively. Reoxidation of molybdenum is observed after deintercalation but 40 at % Mo 5+subsist at 3.2 V due to the trapping of lithium strongly bonded to the oxide matrix. The Li1s core level (at EB= 55.80 eV) is most intense at 1.73 V and does not vanish at 3.2 V. Broadening of the Mo3d core level peaks are assigned to the distortion of the oxide matrix. Changes of the electronic structure after intercalation result from the occupation of the Mo4d states (at EB= 1.0 eV) originally empty in the pristine oxide. The XP C1s and O1s core level spectra show the irreversible formation of a solid electrolyte interphase (SEI) layer including lithium carbonate and Li-alkoxides.

For the first time the surface of brass (Cu−Zn alloy) and its chemistry have been characterized by scanning tunneling microscopy/spectroscopy at the subnanometer (atomic) scale. The comparative results obtained on Cu 70Zn 30(111) and Cu(111) single-crystal surfaces evidence the random distribution of Zn atoms substituted to Cu atoms at the extreme surface of brass, the Zn-depleted concentration in the topmost layer of the alloy and the associated modifications of the surface density of states. The initial stages of interaction with oxygen and sulfur highlight the role of Zn in the surface chemistry. The reactivity becomes governed by the chemical defects (Zn atoms) introduced by alloying. The nucleation mechanism and the nature of the surface oxide compounds are modified. Surface reconstruction is promoted in the reaction with sulfur, and S vacancies are introduced in the surface sulfide compounds. The data are relevant for the detailed understanding of the effect of alloying a noble or seminoble metal matrix with a more reactive chemical element on the growth mechanisms of adhesion conversion layers and on corrosion mechanisms by dealloying.

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Quantitative XPS data complemented by low‐energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) results of the very first stages of oxidation of an NiAl(001) single‐crystal surface are reported. The thickness, stoichiometry and alloy composition at the oxide/alloy interface and, when possible, the structure have been analysed after oxidation at room temperature and 750°C and under 10−7, 10−5and 200 mbar of oxygen. The growth of alumina layers is essentially two‐dimensional in the initial stages. Thin oxide films grown up to 50 Å show an oxygen enrichment that decreases with increasing thickness. The competition between the segregation of aluminium and its consumption by oxygen in the growth kinetics of the oxide layers is evidenced by the variation of the stoichiometry of the oxide films and alloy composition at the oxide/alloy interface. Copyright © 2002 John Wiley & Sons, Ltd.

The effects of two organic corrosion inhibitors, 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzimidazole (MBI), on grain boundary passivation was investigated on copper at the nanometer scale in NaOH solution using electrochemical scanning tunneling microscopy (ECSTM). Global electrochemical analysis by cyclic voltammetry showed that the organic surface layers, pre-formed after reductive dissociation of the native oxide in the presence of the inhibitors, block the formation of a Cu(I) surface oxide and thus passivation, but do not entirely suppress residual reactivity. Local ECSTM analysis in initial metallic, subsequently oxidized, and final reduced states confirmed residual intergranular reactivity except for coherent twins. On coincidence site lattice (CSL) and random boundaries, residual dissolution with accumulation of corrosion products or residual passivation was observed, depending on the barrier effect of the pre-formed inhibitor layer on oxide formation. For low ? CSLs, no difference of barrier effect was observed between MBT and MBI. For more reactive high ? CSLs and random boundaries, pre-adsorbed MBT formed a stronger barrier against passivation by oxide growth than pre-adsorbed MBI. The results provide deeper understanding of how passivation is altered by a pre-formed surface layer of organic corrosion inhibitor, including locally at different grain boundary types.

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Corrosion inhibition by 2-mercaptobenzothiazole (MBT) at the surface termination of various types of grain boundaries (GBs) was studied at the nanometer scale on microcrystalline copper in HCl acid solution using in situ electrochemical scanning tunneling microscopy (ECSTM). Macroscopic electrochemical analysis by cyclic voltammetry showed highly effective inhibition of Cu(I) active dissolution blocked by MBT pre-adsorption in a potential range of 0.15-0.2 V. ECSTM analysis of the initial stages of intergranular corrosion confirmed the mitigation of net intergranular dissolution by the pre-adsorbed MBT surface layer but also revealed the local accumulation of reaction products in the GB regions. For Coincidence Site Lattice boundaries other than coherent twins, intergranular dissolution, mitigated by the pre-adsorbed MBT layer, and protection by intergranular formation of a film of reaction products were observed. For random GBs, protection by reaction products was dominant, in agreement with their more reactive intrinsic character, generating more Cu(I) ions under anodic polarization and thus promoting the formation of a protective film of reaction products. Coherent twins did not show preferential intergranular reactivity compared to adjacent grains, indicating equally strong efficiency than on grains. These results bring new insight on how inhibition operates locally at various types of GBs.

High corrosion inhibition efficiency of the 2-mercaptobenzimidazole (MBI) molecule for copper in different aqueous solutions is well established. We propose a first principle DFT study of the surface chemistry of the adsorption of MBI on preoxidized Cu(111). For both thione (MBIH) and thiolate (MBI?) species, the formation of a full monolayer (ML) is favored over low coverage adsorption. At the ML coverage, the molecules adopt a perpendicular orientation with respect to the surface. MBI?interaction with the surface is stronger than MBIH one. MBIH and MBI?bond to the surface forming a S-Cu bond; for MBIH, the NH moiety forms a H-bond with a surface oxygen atom; for MBI?, a N-Cu bond is formed. For MBI?at low coverage, a Cu-C bond is also formed. The charge analyses show a charge transfer between the surface and the molecule. Comparing the MBIH/MBI?adsorption energies with that of water/OH, we find that MBI?can replace H2O and OH at the preoxidized Cu surface. The results are compared with those obtained with 2-mercaptobenzothiazole, a similar azole derivative with corrosion inhibition properties.

Kinetics expressions for passivity breakdown have been determined based on a model taking into account the presence of intergranular defective sites in passive films. It is shown that depending on the interface at which the potential drop increase predominates, passivity breakdown can occur by enhanced dissolution (i.e., oxide thinning) at the oxide/electrolyte interface or by accelerated interfacial voiding at the metal/oxide interface. In all cases, the rate of the interfacial processes leading to passivity breakdown is increased at the intergranular defective sites of the passive film.