Anisotropy of 3D Columnar Coatings in Mid-Infrared Spectral Range

Polarisation analysis in the mid-infrared fingerprint region was carried out on thin (∼1 [Formula: see text] m) Si and SiO(2) films evaporated via glancing angle deposition (GLAD) method at [Formula: see text] to the normal. Synchrotron-based infrared microspectroscopic measurements were carried out on the Infrared Microspectroscopy (IRM) beamline at Australian Synchrotron. Specific absorption bands, particularly Si-O-Si stretching vibration, was found to follow the angular dependence of ∼ [Formula: see text] , consistent with the absorption anisotropy. This unexpected anisotropy stems from the enhanced absorption in nano-crevices, which have orientation following the [Formula: see text] angular dependence as revealed by Fourier transforming the image of the surface of 3D columnar films and numerical modeling of light field enhancement by sub-wavelength nano-crevices.