Spectroscopy at Metal Surfaces and Interfaces

Any overlayer or a film deposited onto a metal surface modifies fhe SPP dispersion relation determined for a clean surface. If its thickness, d, is much less than the SPP wavelength. A, the corresponding change in the SPP wave vector modulus can be written as (Abells and Lopez-Rios 1982) 

SPPs can be excited at an interface between two metals. In the Drude model their dielectric functions, ei and 62, are determined by their plasma frequencies, Wpi and u p2- If ojpi ( p2, then in the frequency range ojp2 co cupi one has 62 0 and ei 0, i.e., the condition of the existence of SPP is fulfilled. It is worthwhile to note that, at such frequencies, 2 1 and, hence, total internal reflection, necessary for SPP excitation, is realized at an interface between metal 2 and a vacuum without a prism. 

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