Comparison of the Auger photoelectron coincidence spectroscopy (APECS) spectra of Ag and InP with Cu and GaAs

Auger photoelectron coincidence spectroscopy (APECS) has been used to study the properties of the Auger and photoelectron emissions from a number of materials in the past. Much of this work has been with members of the first transition series, where the effects of filling the 3d band have been studied. In this current work, we report on a study of the M_4,5-N_4,5N_4,5 emission from two members of the second transition series, Ag and In (in InP), in coincidence with the 3d_5/2, 3d_3/2 and 3p_3/2 photoemission lines. In contrast to the Coster-Kronig (CK)-preceded L₂-L₃M_4,5-M_4,5M_4,5(M _4,5) Auger process seen in Cu, the analogue of Ag, we find that there is no contribution from the CK-preceded M₄-M₅N_4,5-N_4,5N_4,5(N _4,5) process in either Ag or In. In contrast to Ga (in GaAs), individual peaks in the In singles Auger line are not so well reproduced by a single APECS spectrum. There is intensity missing in the main In M₅-N_4,5N_4,5 line in coincidence with the 3d_5/2 line which is only accounted for by intensity coming from the CK-preceded M₃-M₅N_4,5-N_4,5N_4,5(N _4,5) process. It is seen that the CK-preceded M₃-M₄N_4,5-N_4,5N_4,5(N _4,5) and M₃-M₅N_4,5-N_4,5N_4,5(N _4,5) processes contribute to the shape of the M_4,5-N_4,5N_4,5 line of both Ag and In. Interestingly, in contrast to what is observed in the coincidence experiment in Cu, the low-energy tail in Ag is not significantly reduced in the coincidence experiment and the Ag singles line shape is reproduced in the coincidence spectrum. This is interpreted as indicating that the probability for shake-up/shake-off in the initial state is significantly higher for Cu than for Ag, and indicates that the intrinsic processes in Ag are easily identified and assigned to particular photoemission lines. We conclude from these data that the Auger lines of elements from the second row of transition metals show many of the same effects as seen in the first transition series, but now with the added complication of Auger cascades that have greater complexity, and the broader background features due to shake-up/shake-off are not as intense.