BETHE IONIZATION CROSS-SECTIONS - A QUANTITATIVE SURVEY ON CALCULATING THE BACKSCATTERING FACTOR IN AES

The objective of this work is to investigate the usefulness of the Bethe cross-section with Powell parameters for possible future use in quantitative AES. The Powell energy-dependent parameters are obtained from a least-squares fit to various experimental and calculated work on ionization cross-sections and are proven to have an accuracy of better than about 1% for U(nl) > 4 (U(nl) = E0/E(nl), where E0 is the incident electron energy and E(nl) is the binding energy of the electrons in the nl-shell. This cross-secton was quantum mechanically derived from the first Born approximation by Bethe and its use can be extended to lower-energy ranges as evidenced from the Fano plots available. This means that the cross-section has the advantages of a closer fit to experimental data and is within the energy range of interest in AES. A simple Monte Carlo approach has been adopted to calculate the backscattering factor and related Auger intensity lines using this cross-section for C, Si, Cu and Ag elements. Results compared with both recent experimental data and Gryzinski cross-section results indicate strongly that the Bethe cross-section can be used for future quantitative analysis in AES.