title: Complex surface chemistry of 4-mercaptopyridine self-assembled monolayers on Au(111).
abstract: The adsorption of 4-mercaptopyridine on Au(111) from aqueous or ethanolic solutions is studied by different surface characterization techniques and density functional theory calculations (DFT) including van der Waals interactions. X-ray photoelectron spectroscopy and electrochemical data indicate that self-assembly from 4-mercaptopyridine-containing aqueous 0.1 M NaOH solutions for short immersion times (few minutes) results in a 4-mercaptopyridine (PyS) self-assembled monolayer (SAM) with surface coverage 0.2. Scanning tunneling microscopy images show an island-covered Au surface. The increase in the immersion time from minutes to hours results in a complete SAM degradation yielding adsorbed sulfur and a heavily pitted Au surface. Adsorbed sulfur is also the main product when the self-assembly process is made in ethanolic solutions irrespective of the immersion time. We demonstrate for the first time that a surface reaction is involved in PyS SAM decomposition in ethanol, a surface process not favored in water. DFT calculations suggest that the surface reaction takes place via disulfide formation driven by the higher stability of the S-Au(111) system. Other reactions that contribute to sulfidization are also detected and discussed.
authors.affiliation: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad Nacional de La Plata-CONICET, La Plata, Argentina.
authors.forename: E A
authors.initials: EA
authors.lastname: Ramírez
authors.forename: E
authors.initials: E
authors.lastname: Cortés
authors.forename: A A
authors.initials: AA
authors.lastname: Rubert
authors.forename: P
authors.initials: P
authors.lastname: Carro
authors.forename: G
authors.initials: G
authors.lastname: Benítez
authors.forename: M E
authors.initials: ME
authors.lastname: Vela
authors.forename: R C
authors.initials: RC
authors.lastname: Salvarezza