Spectroscopic Characterization and Modeling of Methyl- and Hydrogen-Terminated Oligo(ethylene glycol) Self-Assembled Monolayers

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• 作者：Lyuba Malysheva ; Alexander Onipko ; Timmy Fyrner ; Hung-Hsun Lee ; Ramu虆nas Valiokas ; Peter Konradsson ; Bo Liedberg
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：June 7, 2012
• 年：2012
• 卷：116
• 期：22
• 页码：12008-12016
• 全文大小：436K
• 年卷期：v.116,no.22(June 7, 2012)
• ISSN：1932-7455

文摘

Two series of oligo(ethylene glycol) (OEG) thiol compounds HS-(CH₂CH₂O)_nR, with R = CH₃, H and n = 5, 6, 7, have been synthesized and used to form self-assembled monolayers (SAMs) on gold. The data from null ellipsometry, infrared reflection鈥揳bsorption spectroscopy, and ab initio calculations of this type of OH- and CH₃-terminated OEG SAMs are used to examine the rarely addressed in-SAM orientation of oligo(ethylene glycols) and to provide detailed assignments of infrared bands in the fingerprint and CH-stretching regions. On the basis of these results, a new spectral band has been observed at 2947 cm^鈥? and identified by the first-principle calculations as localized vibrations that are specific for hydrogen-terminated OEG thiolate SAMs. This band can be used as an indicator of a high crystalline-like ordering. It is furthermore stressed that theory agrees with the experimentally obtained CH-stretching spectra remarkably well if, and only if, the OEG helix axis within studied SAMs is tilted by about 20掳 with respect to the surface normal.