Autoionization in bulk, multilayer, and monolayer Cr

Angle-resolution techniques in combination with a tunable synchrotron radiation source are used in resonant photoemission from bulk, multilayer, and monolayer Cr. The striking double-peak structure of the resonant 3p→3d transition in bulk Cr is found to turn gradually into a single peak when going to a multilayer and eventually to a monolayer of Cr. The evolution of the double peak into a single peak is also confirmed in electron-energy-loss spectra. The constant-initial-state (CIS) spectra of bulk Cr are strongly angle dependent. This is an indication of a multichannel autoionization process in the neighborhood of the $M_2$,3 absorption threshold. We attempt to describe this angle dependence by the empirical Kabachnik-Sazhina two-channel autoionization formula. For describing the two-peak-structure angular dependence in Cr we find the following values for the Fano-profile parameters q and the level widths Γ: $q_1$=+0.8, $q_2$=-1.5, ${\Gamma }_1$=5 eV, and ${\Gamma }_2$=7 eV. The double-peak structure in the Cr $M_2$,3 resonant transition is found to disappear in high-energy transmission electron-energy-loss spectroscopy of a ${\mathrm{Cr}}_{20}$ ${\mathrm{Au}}_{80}$ alloy. For comparison reasons angle-integrated resonant photoemission studies were also carried out on vanadium for photon energies around the $M_2$,3 binding energy and only a single peak was detected, in agreement with previously published results.