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Trivalent Chromium Process (TCP) was developed as a promising conversion process aiming at enhancement of corrosion properties and adhesion of aluminium alloys. The alkaline etching and acid pickling are usually applied as surface pretreatments on aluminium alloys before TCP deposition in order to optimize their properties. In this work, the surface modifications of an Al-Cu- Li alloy (AA2050-T8) at different stages of pretreatment (alkaline degreasing and acid pickling) and subsequent TCP are investigated by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and scanning electron microscopy. The pretreatments leading to significant enrichments in Cu and less marked in Ag, show also a strong influence on the subsequent formation of TCP in comparison to the non-pretreated, polished AA2050-T8 alloy. A slight decrease in Li content is observed in the oxide layer after pretreatment and no Li is present in the outer TCP layer. A thicker TCP conversion coating (outer oxide) with less cracks is formed on the pretreated alloy surface than on the polished one. Moreover, a Cu enrichment is evidenced in the TCP layer of the pretreated sample, which results in enhanced cathodic activity of pretreated sample with reference to polished sample as demonstrated by linear sweep voltammetry. [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]

Abstract: The thermal stability of the Co/β-Si3N4/Si(111) interface has been studied by high-resolution photoemission spectroscopy in a temperature range extending from room temperature to 650°C. It is demonstrated the ability of a very thin crystalline buffer layer of silicon nitride to prevent the interfacial reaction between cobalt and silicon at room temperature. The behaviour of the interface at higher temperature shows the formation of cobalt silicides already at 300°C. Moreover, the presence of new components in the decomposition of the photoemission spectra is discussed in the light of the existing literature. [Copyright &y& Elsevier]