Field Manipulation of Band Properties in Infrared Spectra of Thin Films

Journal article, 2024

This comprehensive optical study analyzes field manipulations of bands in infrared (IR) spectra of thin films and functional surfaces for varying measurement and sample conditions. Band variations related to the materials dielectric functions, the measurement geometry, the film thickness as well as the direction dependence of the probing electromagnetic fields are demonstrated. Examples are discussed for isotropic polymer films (approximate to 200 nm polymethylmethacrylate [PMMA]) on gold and silicon as well as an anisotropic hydrogen monolayer on a Si(111) surface, characterized by IR-attenuated total reflection, IR microscopy, and incidence-angle-dependent IR polarimetry. Even for fixed optical material properties, significant manipulations of band frequency and shape (shifts up to approximate to 14 cm-1 for PMMA, up to approximate to 3 cm-1 for H-Si) occur in not only polarization-dependent but also unpolarized spectra. The shown data underline that polarimetric measurements and optical analyses are essential for a detailed interpretation of band shapes. Field manipulations of bands in infrared spectra of thin films and functional surfaces are discussed. Examples are isotropic polymer films on gold and silicon as well as an anisotropic hydrogen monolayer on Si(111). Band variations relate to the materials dielectric functions, the measurement geometry, the film thickness as well as the polarization of the probing electromagnetic fields.image (c) 2023 WILEY-VCH GmbH