PM-IRRAS Investigation of Self-Assembled Monolayers Grafted onto SiO2/Au Substrates
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- 作者：Michae虉l A. Ramin ; Gwe虂nae虉lle Le Bourdon ; Nicolas Daugey ; Bernard Bennetau ; Luc Vellutini ; Thierry Buffeteau
- 刊名：Langmuir
- 出版年：2011
- 出版时间：May 17, 2011
- 年：2011
- 卷：27
- 期：10
- 页码：6076-6084
- 全文大小：955K
- 年卷期：v.27,no.10(May 17, 2011)
- ISSN：1520-5827
文摘
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 SiO2/Au substrates (SiO2 film of 200 脜 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.