title: New insight into the electrochemical desorption of alkanethiol SAMs on gold.
abstract: A combination of Polarization Modulation Infrared Reflection Absorption Spectroscopy (PMIRRAS) under electrochemical control, Electrochemical Scanning Tunneling Microscopy (ECSTM) and Molecular Dynamics (MD) simulations has been used to shed light on the reductive desorption process of dodecanethiol (C12) and octadecanethiol (C18) SAMs on gold in aqueous electrolytes. Experimental PMIRRAS, ECSTM and MD simulations data for C12 desorption are consistent with formation of randomly distributed micellar aggregates stabilized by Na(+) ions, coexisting with a lying-down phase of molecules. The analysis of pit and Au island coverage before and after desorption is consistent with the thiolate-Au adatoms models. On the other hand, PMIRRAS and MD data for C18 indicate that the desorbed alkanethiolates adopt a Na(+) ion-stabilized bilayer of interdigitated alkanethiolates, with no evidence of lying down molecules. MD simulations also show that both the degree of order and tilt angle of the desorbed alkanethiolates change with the surface charge on the metal, going from bilayers to micelles. These results demonstrate the complexity of the alkanethiol desorption in the presence of water and the fact that chain length and counterions play a key role in a complex structure.
authors.affiliation: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA - CONICET), 1900 La Plata, Buenos Aires, Argentina.
authors.forename: Evangelina
authors.initials: E
authors.lastname: Pensa
authors.forename: Carolina
authors.initials: C
authors.lastname: Vericat
authors.forename: Doris
authors.initials: D
authors.lastname: Grumelli
authors.forename: Roberto C
authors.initials: RC
authors.lastname: Salvarezza
authors.forename: Sung Hyun
authors.initials: SH
authors.lastname: Park
authors.forename: Gabriel S
authors.initials: GS
authors.lastname: Longo
authors.forename: Igal
authors.initials: I
authors.lastname: Szleifer
authors.forename: Lucila P
authors.initials: LP
authors.lastname: Méndez De Leo
mesh_terms: D000327:Adsorption; D000473:Alkanes / Q000737:chemistry*; D055664:Electrochemical Techniques; D006046:Gold / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D000473:Alkanes; D013438:Sulfhydryl Compounds; D014867:Water; D006046:Gold