Complex Surface Chemistry of 4-Mercaptopyridine Self-Assembled Monolayers on Au(111)

EDUARDO A. RAMÍREZ; EMILIANO CORTÉS; ALDO A. RUBERT; PILAR CARRO; GUILLERMO BENÍTEZ; MARÍA E. VELA; ROBERTO C. SALVAREZZA

LANGMUIR

AMER CHEMICAL SOC

Lugar: Washington; Año: 2012 vol. 28 p. 6839 - 6847

0743-7463

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 selfassembly 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.