Orientational analysis of dodecanethiol and p-nitrothiophenol SAMs on metals with polarisation dependent SFG spectroscopy

Francesca Cecchet, Dan Lis, Julien Guthmuller, Benoît Champagne, Yves Caudano, Christophe Silien, Alaa Addin Mani, Paul A. Thiry, André Peremans

Research output: Contribution to journalArticle

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. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.

Original languageEnglish
Pages (from-to)607-615
Number of pages9
JournalChemPhysChem
Volume11
Issue number3
DOIs
Publication statusPublished - 22 Feb 2010

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Keywords

  • Density functional calculations
  • Self-assembled monolayers
  • Sum frequency generation
  • Surface analysis
  • Vibrational spectroscopy

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