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Infrared 45° Reflectometry of Anisotropic Ultrathin Films and Heterostructures

The theory of infrared 45° reflectometry is revised and generalized to the case of anisotropic very-thin films and heterostructures on substrate. We obtain approximate expressions for the difference Δ 45 = R p - R 2 s between the reflectivity for p-polarized light (Rp) and the squared reflectivity for s-polarized light (R 2 s ) at 45° angle of incidence. These results give a good interpretation of frequency spectra of Δ 45 and allow to associate correctly the resonances in Δ 45 with transverse and longitudinal optical phonons in anisotropic films. The application of the infrared 45° reflectometry to superlattices is discussed.