Line-shape analyses of XVV Auger spectra of p(1 x 1)-V/sub 3/Si(00): Evidence for autoionization emission

In the light of recent advances in understanding the Auger process, the local electronic structural origins of selected core-valence-valence (XVV) Auger line shapes are analyzed for a transition-metal silicide prototype, V/sub 3/Si. We report for clean p(1 x 1)-V/sub 3/Si(100) Auger spectra that include the region of the vanadium M/sub 2,3/VV and M/sub 1/VV and the Si L/sub 2,3/VV transitions. We compare the measured line shapes to spectra we generated based on the muffin-tin local density of states (DOS) calculated self-consistently by Klein et al. Good agreement in both the Si pp(L/sub 2,3/M/sub 2,3/M/sub 2,3/) and the V dd(M/sub 2,3/M/sub 4,5/M/sub 4,5/) peak positions between experiment and calculation verified that the final-state hole-hole repulsion for Si (U/sub p/p) and V (U/sub d/d) are both approx.0 eV. Also, the Si L/sub 2,3/VV spectrum resembles that of elemental Si in that the line shape is predominantly a self-fold of the Si 3p DOS. However, an unexpected result is that the V spectral region above the M/sub 2,3/VV threshold possesses a broad (approx.30-eV-wide) intense feature that is not amenable to conventional interpretation in terms of the M/sub 1/VV transition or M/sub 2,3/VV double-ionization or plasmon-gain satellites. We attribute this observation to the presencemore » of Fano autoionization emission associated with deexcitation of the resonant 3p..-->..3d transition. Supporting evidence comes from a comparison of our p x-ray- and electron-stimulated Auger spectra, and to the line shape of the 3p loss spectrum. In addition, oxygen-dosing Auger and x-ray photoelectron spectroscopy experiments p (0--20 L) (1 langmuir = 1 L = 10/sup -6/ Torr sec) indicate dramatic Si L/sub 2,3/VV line-shape changes associated with oxidation, similar to that observed previously for Pd/sub 4/Si. The initial oxidation rate is approx.10/sup 2/ faster than that for elemental Si.« less