Advanced Multiple-Angle Incidence Resolution Spectrometry for Thin-Layer Analysis on a Low-Refractive-Index Substrate

Abstract

A long-time issue that thin films supported on a substrate with low refractive index cannot be subjected to multiple-angle incidence resolution spectrometry (MAIRS) has been resolved, and an advanced MAIRS technique has been developed. Infrared multiple-angle incidence resolution spectroscopy (IR MAIRS) is being recognized as a powerful spectroscopic tool for revealing molecular orientation in thin films or molecular adsorbates. MAIRS has been, however, employed with only IR spectroscopy thus far, since MAIRS requires high refractive index substrates such as germanium and silicon, and shorter wavelength regions have no appropriate substrates. Although one of the most commonly useful substrates for IR spectroscopy is CaF2, unfortunately it cannot be employed for IR MAIRS because of the low refractive index. To overcome this experimental limitation, the principle of MAIRS has been studied theoretically, and it has been found that polarization effects on transmission intensity is the main cause that disturbs a proper MAIRS analysis. As a result, now it is possible to employ IR MAIRS for analysis of thin films on CaF2 by removing the s-polarization and by use of the advanced MAIRS algorithm.

Experimental Optimization of p-Polarized MAIR Spectrometry Performed on a Fourier Transform Infrared Spectrometer

“…2b in Ref. 2. In a previous paper, 2 a monotonous decrease of the single-beam intensities was found to be necessary for MAIRS.…”

“…1,2 In this case, the external-reflection (ER) technique [9][10][11][12][13][14][15][16][17] is useful in place of the transmission one, since reflection occurs no matter what wavenumber range is opaque for the transmittance. On glass, however, the reflectivity is very low, 2 especially for p-polarization, due to the low refractive index (ca.…”

“…Although we have already demonstrated a variety of application studies by the use of infrared MAIRS, 21 they were all carried out by using a substrate with high refractive index, such as germanium and silicon. This experimental limitation is due to optical reasons in relation to the polarization 2 and optics 22 in the spectrometer. To make the best use of the MAIRS' potential, the issue of the refractive index of the substrate should be overcome; otherwise, a practically useful material, glass (n = 1.53), and one of the most useful infrared transparent substrates, CaF2 (n = 1.42), could not be used for infrared MAIRS analysis.…”

“…One of the reasons, the polarization issue, has recently been theorized, 2 and a way for overcoming the limitation has been proposed: s-polarization should be removed, so that the transmitted p-polarization ray would readily obey the advanced MAIRS formula based on a regression equation. In this manner, a fundamental basis of the new p-polarized MAIRS has been prepared.…”

Effect of Casting Solvent on Interfacial Molecular Structure and Proton Transport Characteristics of Sulfonated Polyimide Thin Films

“…43,44 The surface of the original Si wafer was natively oxidized before the measurement. The pMAIRS measurements were collected with a Fourier-transform infrared (FTIR) spectrometer (Nicolet 6700; Thermo-Fisher Scientific) equipped with a mercury cadmium telluride (MCT) detector.…”