Spectroscopic Characterization and Modeling of Methyl- and Hydrogen-Terminated Oligo (ethylene glycol) Self-Assembled Monolayers
2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 22, 12008-12016 p.Article in journal (Refereed) Published
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-absorption 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. Based on these results, a new spectral band has been observed at 2947 cm-1 and identified by the firstprinciple 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 further more 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 20o with respect to the surface normal.
Place, publisher, year, edition, pages
2012. Vol. 116, no 22, 12008-12016 p.
Oligo(ethylene glycol) self-assembled monolayers, infrared reflection absorption spectroscopy, first-principle calculations
National CategoryNatural Sciences
IdentifiersURN: urn:nbn:se:liu:diva-77052DOI: 10.1021/jp212400zISI: 000304888700021OAI: oai:DiVA.org:liu-77052DiVA: diva2:524725