Molecular Orientation Analysis of a Single-Monolayer Langmuir−Blodgett Film on a Thin Glass Plate by Infrared Multiple-Angle Incidence Resolution Spectrometry

Abstract

Molecular orientation analysis in a single monolayer deposited on a glass substrate has been a difficult matter, since the glass substrate absorbs infrared rays so strongly that the measurements of infrared spectra are difficult to perform, and the single monolayer is not suitable for X-ray diffraction analysis because no periodical structure is available. When a thin glass is used as the substrate, in particular, the infrared analysis becomes more difficult, since optical fringes appear strongly on the absorption spectra due to the multiple reflections in the glass. In the present study, infrared multiple-angle incidence resolution spectrometry (MAIRS) has been employed to remove the fringes from the spectra of single- and five-monolayer Langmuir-Blodgett (LB) films of cadmium stearate deposited on a thin glass plate. The MAIRS in-plane spectra gave quantitatively reliable infrared transmission spectra for both films with little fringes, which made it possible for the first time to analyze the molecular orientation in the single-monolayer LB film on glass. As a result, it has been revealed that the molecule in the single-monolayer LB film on thin glass exhibits a significantly larger molecular tilt angle than those prepared on other substrates such as gold and germanium.

Analysis of the Surface Coverage of a Self-Assembled Monolayer of Octadecyl Silane on a Si(100) Surface by Infrared External-Reflection Spectroscopy

“…25 . 24 The good agreement within an analytical error between the analyzed orientation angle of the SAM by Method #2 and the LB film strongly indicates that the surface coverage of the SAM on Si(100) is almost the same as that of the LB film. Since the LB film is known to consist of highly packed molecules and the surface coverage is known to be 100%, the coverage of the present SAM has also been confirmed to be nearly 100%.…”

Optimal Experimental Condition of IR pMAIRS Calibrated by Using an Optically Isotropic Thin Film Exhibiting the Berreman Effect

“…Since the molecular tilt angle in a monolayer of a heptadecyl-or an octadecyl-containing compound has already been known (ca. 25° from the surface normal), 25,26,27 the IP and OP bands of the (CH 2 ) modes were used to calculate the orientation angle in the present SAM ( ; Table 2) to check the accuracy of the ordinate scale. Details of the calculation of the orientation angle are referred to literature.…”

Adsorption Isotherm and Orientation of Alcohols on Hydrophilic SiO2 under Ambient Conditions

“…Therefore, α s and α as are indistinguishable in the laboratory coordinate and, in fact, both are measured to have almost identical values. 5,6 In this case, the molecular tilt angle can be estimated using the only one α value (either α s or α as ) using the following equation: 6 α φ from the surface normal. The low molecular axis tilt angle of the alkyl chain and the red-shifted peak position of the CH 2 asymmetric stretching vibration to 2918 cm -1 suggest that the annealed calculated to be 2.5nm from the CH 2 peak intensities, which is in good agreement with the values reported for well-packed octadecanol SAMs.…”