Surface Differential Reflectivity SDR

Whereas SE measures the ratio of reflection coefficients for different polarizations, various reflection difference techniques probe relative differences in reflectivity. Among these techniques one distinguishes surface differential reflectivity (SDR), surface photoabsorption (SPA) and reflection anisotropy spectroscopy (RAS). 

In SDR one obtains the relative difference in reflectivities measured at nearnormal incidence in p-polarization given by 

The basic components of the experimental setup used for SDR are the same as those for SE (Section 5.1). Relative changes in reflectivity by as much as 10  

2) Generally, the polarization of light reflected from an anisotropic sample differs from that of the incident light (see Section 3.1.3). 

A special case of SDR which uses p-polarized lighf af an angle of incidence af or near the Brewster angle is known as the surface phofoabsorption (SPA) technique. In a two-phase model the reflectivity in such a geometry is equal to zero. For a real interface, however, the reflected light intensity has a minimum at the Brewster angle but does not vanish (see Problem 3.3.). The value of this minimum reflected intensity is therefore very sensitive to the interface properties. 

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Rg. 5.2-M Surface differential reflectivity (SDR) spectra for Si(l 11)2 X1, obtained with two polarizations with the electric vector parallel [011],filledcircles) and perpendicular ([211], open circles) to the chains of the r-bonded chain model. For the transitions shown by arrows in Fig. 5.2-36 hv < leV) the change in reflectivity can be observed only with the electric vector parallel to the chains. The spectrum for hv > 1 eV is associated to transitions along FJ in the SBZ. The change of anisotropy at approximately 1.2 eV is conform to the sum rule / Cxtodto = / eytodo) [2.70]... 

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