THICKNESS DEPENDENCE OF THE CHARACTERISTIC X-RAY YIELD AND THE AUGER BACKSCATTERING FACTOR

A Monte Carlo model employing a screened Rutherford scattering cross-section and the Bethe energy loss approximation has been used to investigate the thickness dependence of the backscattering coefficient, eta, the depth distribution of inner shell ionization, phi(rho-z), the surface ionization function, phi(0), the Auger backscatter factro, r, and the initial gradient of the phi(rho-z) curve, d-phi(0)/dz. Backscatter coefficients obtained for thick samples are in good agreement with experimental values. The surface ionization functions for C, Al, Cu, Ag and Au display an S-shape thickness dependence, which is explainable in terms of the different scattering behaviour for samples of high and low atomic number. A direct relationship between the normalized surface ionization function, phi(0), and the Auger electron backscattering enhancement factor, r, is found, and a preliminary investigation has been made into the target thickness dependence of d-phi(0)/dz.