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Summary: Objectives: Pulsed-laser deposition (PLD) is a development process to obtain hydroxyapatite (HA) thin film. It is an alternative to hydroxyapatite deposition techniques usually employed to cover orthopaedic or dental titanium implant surfaces. The aim of this study is to find out the characteristic ratio for Ca/P (1.66) deposit on titanium implant with the PLD process. Methods: In a preliminary study, the coating parameters of pure and highly crystalline HA on Ti or Ti-6Al-4V substrates were verified by analysing the deposit by Rutherford backscattering spectroscopy (RBS). Ablation parameters to reach a stoichiometric hydroxyapatite composition (ideal Ca/P atomic ratio) and to control the growth of crystalline phases were: 575°C for the substrate temperature, 0.4mbar H2O vapour pressure in the ablation chamber, the target substrate distance was 40mm and the deposition time was 120min. In a second part, the film properties were analysed by means of XRD, SEM, AFM. The coating adhesion of the HA to the substrate was determined with a micro scratch tester. Results: The analysed HA thin films showed a perfect crystallized and textured deposit. Sample observation and surface quality analysis demonstrated a surface roughness and adhesion of the films to the substrates compatible with biological applications. Significance: These results suggest that pulsed-laser deposition is a suitable technique to obtain crystalline and adherent hydroxyapatite films on Ti or Ti-6Al-4V substrates. The quality of the HA deposit with the PLD process could be an interesting option for coating dental implant. [Copyright &y& Elsevier]

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]

The ideal solid oxide fuel cells (SOFCs) can be powered by readily available hydrocarbon fuels containing impurities. While this is commonly recognized as a key advantage of SOFC, it also, together with the elevated operating temperature, becomes the main barrier impeding the in-situ or operando investigations of the anode surface chemistry. Here, using a well-designed quenching experiment, we managed to characterize the near-surface structure of La 0.4 Sr 0.6 TiO 3+δ (LST) anode in SOFCs fuelled by H 2 S-containing methane. This new method enabled us to clearly observe the surface amorphization and sulfidation of LST under simulated SOFC operating conditions. The ∼1 nm-thick two dimensional sulfur-adsorbed layer was on top of the disordered LST, containing –S, –SH and elemental sulfur species. In SOFC test, such “poisoned” anode showed increased performances: a ten-fold enhanced power density enhancement (up to 30 mW cm −2 ) and an improved open circuit voltage (from 0.69 V to 1.17 V). Moreover, its anodic polarization resistance in methane decreased to 21.53 Ω cm 2 , a difference of 95% compared with the sulfur-free anode. Control experiments confirmed that once the adsorbed sulfur species were removed electrochemically, methane conversion slowed down simultaneously till full stop. [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]

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]

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]

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]

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]

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]

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]

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]

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]