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

A model experimental approach, providing molecular scale insight into the build up mechanisms of a corrosion inhibiting interface, is reported. 2-mercaptobenzimidazole (2-MBI), a widely used organic inhibitor, was deposited from the vapor phase at ultra-low pressure on copper surfaces in chemically-controlled state, and X-ray photoelectron spectroscopy was used in situ to characterize the adsorption mechanisms upon formation of the inhibiting film. On copper surfaces prepared clean in the metallic state, the intact molecules lie flat at low exposure, with sulfur and both nitrogen atoms bonded to copper. A fraction of the molecules decomposes upon adsorption, leaving atomic sulfur on copper. At higher exposure, the molecules adsorb in a tilted position with sulfur and only one nitrogen bonded to copper, leading to a densification of 2-MBI in the monolayer. A bilayer is formed at saturation with the outer layer not bonded directly to copper. In the presence of a pre-adsorbed 2D oxide, oxygen is substituted and the molecules adsorb intactly without decomposition. A 3D oxide prevents the bonding of sulfur to copper. The molecular film formed on metallic and 2D oxide pre-covered surfaces partially desorbs and decomposes at temperature above 400 °C, leading to the adsorption of atomic sulfur on copper. [ABSTRACT FROM AUTHOR]

Photoelectron spectroscopy and low energy electron diffraction have been used to investigate the thermal behavior of the Au/c-Si3N4/Si(111) interface in a temperature range extending from room temperature to 1000 °C. The interface consisted of 3.2×1015 atoms cm-2 of gold deposited at room temperature on a crystalline silicon nitride layer, which was previously grown on a Si(111) surface. At room temperature, no evidence of any reaction between gold and the substrate has been detected. Between 300 and 400 °C, Au–Si reaction takes place. A comparison of the spectra reveals that the Au–Si reaction occurs in the silicon matrix and on top of the nitride layer, due to silicon atom segregation. Nitrogen atoms do not participate in the reaction up to 600 °C, at which point a Au–Si–N ternary compound is formed. Subsequently, the silicon nitride desorption begins. Below 600 °C, the nitride layer appears to be cracked but not disrupted. In the range of 800–900 °C, a 3×3 pattern was recorded, and finally, gold and nitrogen disappear leading to the 5×1-reconstructed bare Si surface at 1000 °C. [ABSTRACT FROM AUTHOR]

Stainless steels are widely used as metal components owing to self-protection in aggressive environments, provided by an extremely thin surface oxide film enriched in chromium oxide. Yet, despite decades of research, the mechanisms distributing the chromium enrichment at small length scale are poorly understood, although it may cause loss of stability and local failure of the corrosion resistance. Here, we apply high resolution surface analysis to investigate at small time and length scales the nucleation and growth mechanisms of the surface oxide on a model stainless steel. Starting from an oxide-free surface, we report the direct observation of the oxide nucleation and local oxidation of chromium, which governs the nanoscale heterogeneity of the growing surface oxide by chromium pumping from the atomic terraces to the steps for preferential Cr(III) oxide nucleation and subsequently by segregation from the atomic planes below to grow the Cr(III) layer incompletely saturating the stainless steel surface. This work provides new insight on corrosion chemistry, by evidencing local chemical and structural defects self-generated at the nanoscale by the building process of the protective oxide barrier, and affecting the passive film stability. [ABSTRACT FROM AUTHOR]