A novel measurement technique of pure out-of-plane vibrational modes of thin films on a nonmetallic substrate has recently been proposed, which is named multiple-angle incidence resolution spectrometry (MAIRS). Since this technique could not be replaced by other conventional techniques, MAIRS was expected to be a promising tool for analysis of thin soft materials and surface adsorbates. Nevertheless, some experimental conditions have been found to be inappropriate for MAIRS, which yields incorrect results. In the present study, therefore, the problems in the technique have been investigated in terms of optics to improve the accomplishments of MAIRS. The problems have been found to have a strong relationship with optics in FT-IR, which is influenced by refractive index of the sample material and angle of incidence. In particular, optimization of the size matching of the detector surface and the infrared spot at the detector was a key to having MAIRS perform properly. It has been concluded that reliable MAIRS measurements require overfilling of the detector and a substrate with a high-refractive index.

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In the traditional concept, a stable Langmuir monolayer can be formed from amphiphilic molecules at the air−water interface with their hydrophobic alkyl chains oriented toward the air and the polar moieties embedded in the water. The intermolecular interactions between the polar moieties and the water subphase as well as the van der Waals interactions between the alkyl chains are requisite to hold together the molecules of the ordered Langmuir monolayers. Pure hydrocarbon chains without any polar moieties cannot form a Langmuir monolayer. In contrast to this traditional concept, we now report the discovery of an unusual Langmuir monolayer formed from a disubstituted urea lipid molecule (PDA-UR). The unique property of this monolayer exists in the fact that the polar moiety of the lipid molecule is actually suspended in the air phase while one of the hydrophobic tails is in contact with water. The existence of such a nontraditional monolayer is attributed to the strong hydrogen bonding network formation between the urea functional groups in the air phase. This unusual Langmuir monolayer model is soundly supported by various experimental investigations, which include the surface pressure−area isotherm and ellipsometry measurements, FT-IR and UV−vis absorption spectroscopic studies, as well as Brewster angle and scanning tunneling microscopic observations.