title: A multi-technique approach to the analysis of SAMs of aromatic thiols on copper.
abstract: The adsorption of aromatic thiols on Cu and the SAM film stability in acidic solutions have been studied by XPS, contact angle and electrochemical techniques. Three short molecules, benzenethiol (BT), 2-naphthalenethiol (2-NT) and 4-acetamidothiophenol (4-AA), were selected as representatives of aromatic thiols to highlight the effect of aromatic rings and hydrophilic terminal groups on the copper protection. All the three molecules form stable S-Cu bonds as a consequence of their adsorption process on polycrystalline copper. Although none of them provides a full copper passivation, the adsorbed films persist without major degradation on Cu electrodes even after 12 h immersion in 0.5 M sulfuric acid. Comparing the freshly prepared adsorbed films, the larger 2-NT molecule provides a better Cu passivation, but the shorter BT molecule favours a higher surface coverage. The terminal groups of 4-AA are responsible for a higher Cu surface wettability in water, compared to that with SAMs of the other molecules, and allow for an easier charge-transfer to the electrolyte and for a higher electrochemical capacitance. After long enough ageing, however, the 4-AA-based molecular films are able to self-organize and to provide a steadily improving copper passivation. Adlayers of the BT and 2-NT molecules, on the contrary, over a long time tend to protect less and less the Cu substrate, probably because of progressive electrolyte infiltration.
authors.affiliation: Dipartimento di Chimica, Sapienza Università, p.le Aldo Moro 5, I-00185 Roma, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Caprioli
authors.forename: Marco
authors.initials: M
authors.lastname: Beccari
authors.forename: Andrea
authors.initials: A
authors.lastname: Martinelli
authors.forename: Valeria
authors.initials: V
authors.lastname: Di Castro
authors.forename: Franco
authors.initials: F
authors.lastname: Decker