Photon-stimulated desorption of fluorine from silicon via substrate core excitations

Photon-stimulated desorption (PSD) of ${\mathrm{F}}^{+}$ was performed for silicon (111) surfaces terminated with fluorine atoms. The surfaces were prepared by exposure of clean silicon to ${\mathrm{XeF}}_2$. The onset for PSD at the Si 2p edge correlated with the transition from the 2p level of the bonding silicon atom to the conduction-band minimum, and was thus a function of the oxidation state of the bonding atom. The ions originating from a SiF surface species desorbed along the surface normal while the ions from a ${\mathrm{SiF}}_3$ group desorbed in off-normal directions. Localized 3s and 3p Rydberg-like resonances were observed in the quasimolecular ${\mathrm{SiF}}_3$ moieties. The ion kinetic-energy distributions were measured as an aid to elucidating the desorption mechanism. Measurements of the PSD of ${\mathrm{F}}^{+}$ at the Si 2s edge were used to confirm the 3s and 3p character of the measured resonances.