Anomalous Auger-electron spectra of metallic calcium

A1 Kα-excited L_{2, 3} MM and L_{2, 3} MV Auger-electron spectra of Ca have been measured in ultrahigh vacuum from a metallic sample evaporated onto an Ag substrate. An interpretation of the spectra is made by applying a line-fitting procedure. The lineshape and the solid-state-free-atom kinetic-energy shift are also studied. The extrinsic loss structure in the L_{2, 3} MM Auger-electron emission is found to be similar to that in 2p photoelectron emission. Spin-density-functional (SDF) calculations for the singularity index describing the intrinsic lineshape give a value of ∼ 0.35 for both processes. Thus the experimental 2p _{3 2} photoelectron line broadened from 1.2 to ∼ 5 eV FWHM has been used as a standard line in the line fitting of the L_{2, 3}MM transitions. The term splitting of the L_{2, 3} M_{2, 3} M_{2, 3} transition is larger than in the corresponding free-atom spectrum. This result is also supported by the SDF calculations. The L_{2, 3} M_{2, 3} V spectrum is anomalously sharp, probably both because of the structure of the local density of states at the site of the core-ionized atom and because of differences in the transition probabilities into the different parts of the band. The experimental solid-state shift is 20.3 eV for the L_{2, 3} M_2,3 M_{2, 3}:¹ D transition, and the binding-energy shifts are 8.3 and 6.1 eV for the 2p and 3p levels, respectively. The SDF shifts for the above transitions are 19.9 (configurational average), 9.4 and 8.0 eV, consecutively, in agreement with the experimental values. The calculations also show a localized d-type (atomic-like) structure for the screening of the initial- and final-state core hole (s). This is the origin of the large values of both the singularity index and the solid-state shift.