No abstract

In the present work, we have used reflection−absorption infrared spectroscopy (RAIRS) to investigate the temperature behavior of n-alkanethiols adsorbed on gold substrates. A careful examination of the spectra (frequencies, integrated intensities, and line widths) reveals at least two different types of thermally induced disorder as the temperature is increased. These observations are discussed in light of other recent studies using complementary techniques. The overall picture that emerges is that an initial stage is characterized by a gradual untilting of the alkyl chain and the appearance of gauche conformational defects near the surface, and both of these effects are largely reversible. The subsequent nonreversible disordering of the monolayer is characterized by a large number of defects located below the surface. Infrared spectroscopy is particularly well suited for detecting these changes.

The effect of immersion time on the ordering properties of self-assembled docosanethiolate (C22) monolayers has been studied by reflection/absorption infrared spectroscopy (RAIRS). Starting with a chemically cleaned polycrystalline gold surface, we have found that an immersion time of 45 s in micromolar thiol solutions is sufficient to produce ordered “monolayer” films. These films have RAIR spectral features (peak position, line width, and integrated intensity) similar to those obtained with much longer immersion times. Decreasing the immersion time below 45 s gradually increases the disorder. The temperature dependence of the CH2 antisymmetric stretching (d-) peak position of thiol films obtained with an immersion time of 120 s is identical to ones obtained with very long immersion time (0.5 h to several days). In contrast, films obtained with a 5 s immersion time disorder at a lower temperature. Apart from immersion time and temperature, a large solvent effect has been observed based on real-time RAIRS measurements of the continuing film ordering during aging in vacuum. Finally, a new assignment of the shoulder appearing around 2931 cm-1 is proposed. We present arguments suggesting that the generally accepted Fermi resonance assignment of this shoulder should be modified to include a contribution from another vibrational mode.

/npsi/ctrl?action=rtdoc&an=8894813&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=8894813&lang=frAccess and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. Langmuir, 14, pp. 6579-6587, 1998 Characterization of self-assembled bilayers: silver-alkanethiolates Bensebaa, Farid; Ellis, T.; Kruus, E.; Voicu, R.; Zhou, Y.