Band effects on stimulated desorption of F from CaF and fluorinated TiC(111) surfaces

The mechanism of stimulated F desorption has been investigated from fluorinated TiC(111) and CaF surfaces by He, Ne, Ar, H, and D irradiation. Upon He+ irradiation, the F+ ion is ejected from the surface of Cap2 via both kinetic and potential sputtering, whereas the potential sputtering of F is dominant from the fluorinated TiC(111) surface. The kinetically sputtered F+ ion from the metal surface undergoes efficient resonant neutralization due to the band effect. The probability for potential sputtering of F from the F/TiC(111) surface is dependent upon the primary ion species on the order of He > Ne » Ar. The F desorption is not simply related to the ionization potential of the projectile as evidenced by the fact that H, though having the ionization potential smaller than Ar induces F emission with the yield about 70 times as large as that by Ar and almost one-fourth that by He. The comparison between H and D irradiations clearly shows that the swifter ion leads to a higher F emission probability. From these facts, it is concluded that the F emission is initiated by formation of the F 2s core-hole state having the antibonding character as a consequence of the nonadiabatic transition of the primary ion's hole during collision. The ionization of the core-excited fluorine occurs due to the intra-atomic Auger decay (autoionization) after breakage of the chemisorptive bond, so that the resulting F ion can avoid efficient reneutralization even at metal surfaces. © 2000 American Chemical Society.