Fundamental investigations of the selective dissolution of Cu3_{3}Au(111)

Legierungen spielen eine wichtige Rolle in vielen technischen Anwendungen. Jedoch sind sie anfällig für Korrosion. Ein Sonderfall der Korrosion ist die Entlegierung. Dabei handelt es sich um die selektive Zersetzung der Legierung durch Herauslösen mindestens einer Legierungskomponente. In dieser Arbeit wird die Entlegierung von Cu$_{3}$Au(111) an Hand eines Cu$_{3}$Au(111) Einkristalles untersucht. Das Ziel ist es ein Bild auf atomarer Ebene von den zugrunde liegenden Prozessen im Anfangsstadium der Entlegierung im saueren Medium zu entwickeln. Dabei wird in-situ Röntgenbeugung, sowie ex-situ Rasterkraftmikroskopie und (Raster-Auger-) Elektronenmikroskopie zur Charakterisierung herangezogen. Der Übergang von einer reinen Einkristalloberfläche über die Ausbildung von Goldinseln und porösen Goldstrukturen wird als Funktion der Elektrolytzusammensetzung und des angelegten Potentials beschrieben

Colloidal Mechanisms of Gold Nanoparticle Loss in Asymmetric Flow Field-Flow Fractionation

Flow field-flow fractionation is a powerful method for the analysis of nanoparticle size distributions, but its widespread use has been hampered by large analyte losses, especially of metal nanoparticles. Here, we report on the colloidal mechanisms underlying the losses. We systematically studied gold nanoparticles (AuNPs) during asymmetrical flow field-flow fractionation (AF4) by systematic variation of the particle properties and the eluent composition. Recoveries of AuNPs (core diameter 12 nm) stabilized by citrate or polyethylene glycol (PEG) at different ionic strengths were determined. We used online UV–vis detection and off-line elementary analysis to follow particle losses during full analysis runs, runs without cross-flow, and runs with parts of the instrument bypassed. The combination allowed us to calculate relative and absolute analyte losses at different stages of the analytic protocol. We found different loss mechanisms depending on the ligand. Citrate-stabilized particles degraded during analysis and suffered large losses (up to 74%). PEG-stabilized particles had smaller relative losses at moderate ionic strengths (1–20%) that depended on PEG length. Long PEGs at higher ionic strengths (≥5 mM) caused particle loss due to bridging adsorption at the membrane. Bulk agglomeration was not a relevant loss mechanism at low ionic strengths ≤5 mM for any of the studied particles. An unexpectedly large fraction of particles was lost at tubing and other internal surfaces. We propose that the colloidal mechanisms observed here are relevant loss mechanisms in many particle analysis protocols and discuss strategies to avoid them

Self‐Assembled Monolayers: Star‐Shaped Crystallographic Cracking of Localized Nanoporous Defects

Star-like dealloying corrosion morphology that appears during the localized attack of smooth well-prepared Cu–Au surfaces. The surfaces are initially protected by thiol or selenol inhibitior films. Localized dealloying of Cu–Au produces nanoporous gold under stress and crystallographic cracks – thereby opening a new approach combining surface science with nanoscale mechanical testing.info:eu-repo/semantics/publishe

Initiation and Inhibition of Dealloying of Single Crystalline Cu₃Au (111) Surfaces

Dealloying is widely utilized but is a dangerous corrosion process as well. Here we report an atomistic picture of the initial stages of electrochemical dealloying of the model system Cu₃Au (111). We illuminate the structural and chemical changes during the early stages of dissolution up to the critical potential, using a unique combination of advanced surface-analytical tools. Scanning tunneling microscopy images indicate an interlayer exchange of topmost surface atoms during initial dealloying, while scanning Auger-electron microscopy data clearly reveal that the surface is fully covered by a continuous Au-rich layer at an early stage. Initiating below this first layer a transformation from stacking-reversed toward substrate-oriented Au surface structures is observed close to the critical potential. We further use the observed structural transitions as a reference process to evaluate the mechanistic changes induced by a thiol-based model-inhibition layer applied to suppress surface diffusion. The initial ultrathin Au layer is stabilized with the intermediate island morphology completely suppressed, along an anodic shift of the breakdown potential. Thiol-modification induces a peculiar surface microstructure in the form of microcracks exhibiting a nanoporous core. On the basis of the presented atomic-scale observations, an interlayer exchange mechanism next to pure surface diffusion becomes obvious which may be controlling the layer thickness and its later change in orientation