Infrared reflectance spectroscopy for surface topographic analysis of reststrahlen materials

Stefan K. Andersson; Carl-Gustaf Ribbing

doi:10.1117/12.192048

4 November 1994 Infrared reflectance spectroscopy for surface topographic analysis of reststrahlen materials

Stefan K. Andersson, Carl-Gustaf Ribbing

Proceedings Volume 2253, Optical Interference Coatings; (1994) https://doi.org/10.1117/12.192048
Event: 1994 International Symposium on Optical Interference Coatings, 1994, Grenoble, France

Abstract

Materials with ionic bonding exhibit high reflectance somewhere in the infrared spectral range: the reststrahlen band. This arises because of lattice vibrations that are excited by the incident light. For some materials, e.g. the alkali halides NaF, NaCl, KCl and polycrystalline samples of BeO, SiC, secondary minima in the reststrahlen band have been observed, which have previously not been fully understood. We show, theoretically and experimentally, that small inhomogeneities on the surface are sufficient to cause a measurable absorption and a substructure in the reststrahlen band. The electric field of the incident light beam excites surface mode resonances in the inhomogeneities which absorb light. Inhomogeneities with different shapes have surface modes with different resonance frequencies because of the strong dispersion in the reststrahlen band region. The position and width of the absorption band is determined by the details of the surface roughness: in particular the mixture of spherical, ellipsoidal and disk-shaped irregularities which can be used to describe the actual tomography. IR reflectance spectral can be used to monitor the departure from a perfect smooth surface and to determine the concentration density and shape of topographic defects on ceramic surfaces. Light scattering measurements over the wavelength range 5 - 20 micrometers for bulk samples of polycrystalline beryllium oxide and 5 - 20 micrometers for silicon carbide powder are reported in verify this interpretation.

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Stefan K. Andersson and Carl-Gustaf Ribbing "Infrared reflectance spectroscopy for surface topographic analysis of reststrahlen materials", Proc. SPIE 2253, Optical Interference Coatings, (4 November 1994); https://doi.org/10.1117/12.192048

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