Reflection at Thin Films

Thin films can be investigated either by reflection absorption (cf. Section 5.2.2) or by a sort of internal reflection measurement using the occurrence of multiple reflections. In the case of plane, parallel-sided, homogeneous and isotropic thin films (Fig. 5.6), the amplitude of the reflected light can be expressed in the form 

Spectral features arises from two properties (i) the intrinsic absorption strength and (ii) the orientation of the transition dipole with respect to the wave vector of the incident fight. In samples with random distribution an averaged spectmm will be recorded. In highly ordered films the absorption depends upon the ordering within the film and the orientation of the sample. Therefore the angle of incidence and polarization of the light have to be chosen carefully. 

The analysis of thin films is often performed by infrared spectroscopy. Compared to reflection absorption measurements on metal surfaces using p-polarized fight at grazing incidence, investigation of self-supported thin films or of thin films on transparent substrates shows weaker infrared absorption bands. Weaker absorption bands are caused by the absence of the surface enhancement mechanism and the poorer reflectivity. On the other hand, due to the absence of the metal selection rule, spectra of p- and s-polarization can be recorded in the case of freestanding films or of transparent substrates. Complex spectral features may arise 

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