title: PM-IRRAS investigation of self-assembled monolayers grafted onto SiO2/Au substrates.
abstract: Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was used to characterize self-assembled monolayers (SAMs). Novel ester-terminated organosilicon coupling agents possessing a trialkoxysilyl headgroup and a urea group in the linear alkyl chains (4) were synthesized and grafted onto SiO(2)/Au substrates (SiO(2) film of 200 Å thickness deposited on gold mirror). This composite substrate allowed the anchoring of SAMs and preserved the high reflectivity for infrared radiation. PM-IRRAS spectra with very high signal-to-noise ratios have been obtained in the mid-infrared spectral range allowing monitoring of the grafted SAMs. Quantitative analysis of the measured signal is described to compare PM-IRRAS and conventional IRRAS spectra. This quantitative analysis has been validated since the band intensities in the corrected PM-IRRAS and conventional IRRAS spectra are identical. Orientation information on the different functional groups has been obtained comparing the corrected PM-IRRAS spectrum with the one calculated using isotropic optical constants of ester-terminated organosilicon coupling agents 4. The carbonyls of the urea groups are preferentially parallel to the substrate surface favoring intermolecular hydrogen bonding and consequently a close packing of the molecules attached to the surface. By contrast, the alkyl chains present gauche defects and are poorly oriented.
authors.affiliation: Institut des Sciences Moléculaires (UMR 5255-CNRS), Université Bordeaux 1, 351 Cours de la Libération, 33405 Talence, France.
authors.forename: Michaël A
authors.initials: MA
authors.lastname: Ramin
authors.forename: Gwénaëlle
authors.initials: G
authors.lastname: Le Bourdon
authors.forename: Nicolas
authors.initials: N
authors.lastname: Daugey
authors.forename: Bernard
authors.initials: B
authors.lastname: Bennetau
authors.forename: Luc
authors.initials: L
authors.lastname: Vellutini
authors.forename: Thierry
authors.initials: T
authors.lastname: Buffeteau
mesh_terms: D000042:Absorption; D000473:Alkanes / Q000737:chemistry; D002138:Calibration; D004952:Esters; D006046:Gold / Q000737:chemistry*; D055620:Optical Phenomena; D012822:Silicon Dioxide / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods*; D014508:Urea / Q000737:chemistry
chemical_list: D000473:Alkanes; D004952:Esters; D006046:Gold; D012822:Silicon Dioxide; D014508:Urea