Surface Electromagnetic Wave Spectroscopy of Overlayers

If a crystal surface is covered with a film of thickness d much smaller than the wavelength of the incident radiation, the absorption coefficient, of the 

The absorption spectrum of thin films can most conveniently be obtained by a differential method. Here, one measures the ratio of the SEW intensity for a clean surface, Iq, to that for a surface covered with a film, I, at different distances between the prisms, r. Then the SEW absorption is determined as 

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