title: Orientational analysis of dodecanethiol and p-nitrothiophenol SAMs on metals with polarisation-dependent SFG spectroscopy.
abstract: Polarisation-dependent sum frequency generation (SFG) spectroscopy is used to investigate the orientation of molecules on metallic surfaces. In particular, self-assembled monolayers (SAMs) of dodecanethiol (DDT) and of p-nitrothiophenol (p-NTP), grown on Pt and on Au, have been chosen as models to highlight the ability of combining ppp and ssp polarisations sets (representing the polarisation of the involved beams in the conventional order of SFG, Vis and IR beam) to infer orientational information at metallic interfaces. Indeed, using only the ppp set of data, as it is usually done for metallic surfaces, is not sufficient to determine the full molecular orientation. We show here that simply combining ppp and ssp polarisations enables both the tilt and rotation angles of methyl groups in DDT SAMs to be determined. Moreover, for p-NTP, while the SFG active vibrations detected with the ppp polarisation alone provide no orientational information, however, the combination with ssp spectra enables to retrieve the tilt angle of the p-NTP 1,4 axis. Though orientational information obtained by polarisation-dependent measurements has been extensively used at insulating interfaces, we report here their first application to metallic surfaces.
authors.affiliation: Research Centre in Physics of Matter and Radiation (PMR), University of Namur (FUNDP), rue de Bruxelles 61, 5000 Namur, Belgium. francesca.cecchet@fundp.ac.be
authors.forename: Francesca
authors.initials: F
authors.lastname: Cecchet
authors.forename: Dan
authors.initials: D
authors.lastname: Lis
authors.forename: Julien
authors.initials: J
authors.lastname: Guthmuller
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.forename: Yves
authors.initials: Y
authors.lastname: Caudano
authors.forename: Christophe
authors.initials: C
authors.lastname: Silien
authors.forename: Alaa Addin
authors.initials: AA
authors.lastname: Mani
authors.forename: Paul A
authors.initials: PA
authors.lastname: Thiry
authors.forename: André
authors.initials: A
authors.lastname: Peremans