Field Manipulation of Band Properties in Infrared Spectra of Thin Films

Abstract

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 (≈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 ≈14 cm−1 for PMMA, up 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.