2s photoionization and subsequent Auger cascade in atomic Si

The 2s photoionization and subsequent Auger transition cascade in atomic Si were studied by means of synchrotron-radiation-induced electron spectroscopy. After the 2s photoionization, the core hole states decay predominantly by a two-step Auger transition cascade into the triply ionized [Ne]nl states. The ionization channels of the 2s core-ionized Si+ atoms to Si3+ ions were observed by measuring the conventional Auger electron spectra of the L-1-L2,3M Coster-Kronig transitions and the L2,3M-MMM Auger transitions. The observed L-1-L2,3M and L2,3M-MMM Auger spectra were analyzed by means of extensive multiconfiguration Dirac-Fock computations. We found that the electron correlation plays a prominent role in the Auger cascade, especially for the final-step Auger L2,3M-MMM spectrum. Additionally, it was seen that the L2,3M-MMM Auger spectrum of Si includes more Auger groups than the isoelectronic L-2,L-3-MMAuger spectrum of Al. Thus, more information on the intermediate ionic states is obtained if they are produced by Auger cascade rather than by direct photoionization.