Angle-resolved Auger Electron Emission ARAES

Taking the RT-shell as an important example, the probability of photon absorption is given in the dipole approximation by 

Using the single scattering approximation and assuming that the atoms are very small (so that the incident wavefront is effectively plane) it is found that the oscillatory component of the EXAFS is given by 123,125 

The photoelectron wave vector is k, the magnitude of the amplitude for backscattering from the th atom is f k) and A is the electron mean free path. The phase shift 5j is the sum of contributions from the p-wave shift in the absorbing-atom s potential and the shift in the backscattering amplitude from the th atom. The final exponential term is a Debye-Waller-type factor representing the probability distribution caused by lattice vibrations and disorder, Oj being the root mean square deviation from Rj (also known as the thermal correlation factor ). 

The phenomenon of EXAFS has been known for a considerable time (see ref. 126) but it has been applied to obtain structural information within the last decade only. From equation (2) it is seen that neighbour separation depends on the phase of the EXAFS oscillations, while the co-ordination number Nj and thermal correlation factor (Tj depend on the signal amplitude. In 1971 it was shown by Sayers, Stern, and Lytle that an appropriate Fourier analysis of the data gives a radial structure factor (j) R) from which one can locate the positions of the atoms surrounding the atom which absorbs the X-ray photon (for detailed discussion see refs. 123, 128—130). A second method of data analysis, involving curve fitting techniques, has been used also.  

Data analysis involves a number of problems related to determination of the inner potential, phase shifts, multiple-scattering effects, etc. in many ways the difficulties are similar to those encountered in FEED theory.Multiple scattering may be 

---