Line-shape analyses ofXVVAuger spectra ofp(1×1)-V3Si(100): 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 ($\mathrm{XVV}$) Auger line shapes are analyzed for a transition-metal silicide prototype, ${\mathrm{V}}_3$Si. We report for clean $p(1\mathrm{}\times 1)$-${\mathrm{V}}_3$Si(100) Auger spectra that include the region of the vanadium $M_{2,3}\mathrm{VV}$ and $M_1\mathrm{VV}$ and the $\mathrm{Si}{L}_{2,3}\mathrm{VV}$ 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 $\mathrm{Si}pp\left(L_{2,3}{M}_{2,3}{M}_{2,3}\right)$ and the $\mathrm{V}dd\left(M_{2,3}{M}_{4,5}{M}_{4,5}\right)$ peak positions between experiment and calculation verified that the final-state hole-hole repulsion for $\mathrm{Si} \left(U_{\mathrm{pp}}\right)$ and $\mathrm{V} \left(U_{\mathrm{dd}}\right)$ are both ∼0 eV. Also, the $\mathrm{Si}{L}_{2,3}\mathrm{VV}$ spectrum resembles that of elemental Si in that the line shape is predominantly a self-fold of the $\mathrm{Si}3p$ DOS. However, an unexpected result is that the V spectral region above the $M_{2,3}\mathrm{VV}$ threshold possesses a broad (∼30-eV-wide) intense feature that is not amenable to conventional interpretation in terms of the $M_1\mathrm{VV}$ transition or $M_{2,3}\mathrm{VV}$ double-ionization or plasmon-gain satellites. We attribute this observation to the presence of Fano autoionization emission associated with deexcitation of the resonant $3p\to 3d$ transition. Supporting evidence comes from a comparison of our 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 (0-20 L) (1 langmuir = 1 L = ${10}^{-6\mathrm{}}$ Torr sec) indicate dramatic $\mathrm{Si}{L}_{2,3}\mathrm{VV}$ line-shape changes associated with oxidation, similar to that observed previously for ${\mathrm{Pd}}_4$Si. The initial oxidation rate is ∼${10}^2$ faster than that for elemental Si. We hypothesize that the dissociation of ${\mathrm{O}}_2$ is a...