Electrochemical, High-Resolution Photoemission Spectroscopy and vdW-DFT Study of the Thermal Stability of Benzenethiol and Benzeneselenol Monolayers on Au(111)

FERNANDO P. COMETTO; EDUARDO M. PATRITO; PATRICIA PAREDES OLIVERA; GUILLERMO ZAMPIERI; HUGO ASCOLANI

LANGMUIR

AMER CHEMICAL SOC

Lugar: Washington; Año: 2012 vol. 28 p. 13624 - 13635

0743-7463

The preparation and thermal stability of benzenethiol and benzeneselenol self-assembled monolayers (SAMs) grown on Au(111) have been investigated by electrochemical experiments and high-resolution photoemission spectroscopy. Both techniques confirm the formation of monolayers with high packing densities ( = 0.27-0.29 ML) and good degree of order in both cases. Despite many similarities between the two SAMs, the thermal desorption is distinctly different: while the benzenethiol SAM desorbs in a single steplike process, the desorption of the benzeneselenol SAM occurs with a much lower activation energy and involves the cleavage of some Se−C bonds and a change of molecular configuration from standing up to lying down. This behavior is explained by considering the different nature of the bonding of the head group with the metal surface and with the phenyl ring. Density functional theory calculations show that the higher thermal stability of benzenethiol is attributed to the presence of Au adatoms which produce an important increase in its binding energy. The selenium−suface bonding is more flexible than the sulfur−surface bonding and the activation energy barrier for the breakage of the Se−C bond is lower than that for the breakage of the S−C bond, which correlates with the appearance of Se atoms observed experimentally.