Ion-stimulated desorption of O+ from the oxygenated TiC(111) surface: The role of nonadiabatic electronic transitions and the band effect

The mechanism of secondary O+ ion emission from the oxygenated TiC(111) sur face has been investigated by noble-gas ion irradiation. The O+ ion is ejec ted from the surface by He+ irradiation due to an electronic transition wit hout violent collisions. The O+ ion occurs preferentially from the weakly b ound oxygen species, but very little O+ arises from the strongly chemisorbe d oxygen on the threefold hollow site. The O+ emission is not caused by two localized valence holes resulting from the Auger decay of the primary ions , but is rather initiated by the formation of a long-lived O 2s core-hole s tate with an antibonding character. The O 2s hole is created by He+ via the nonadiabatic electronic transition during moderate impact-parameter collis ions (1.0-3.0 a.u.), which is accompanied by very little kinetic energy tra nsfer (< 1 eV) to the target oxygen atom. The probability for O 2s hole cre ation increases with increasing velocity of the primary ions. The ionizatio n of oxygen occurs due to the Auger decay of the O 2s hole on the way out f rom the surface after breakage of the chemisorptive bond; this is essential for the emission of very low-energy (< 10 eV) O+ ions without resonant neu tralization. This mechanism is consistent with that developed in low-energy ion scattering and successfully explains the O+ emission even from metal s urfaces without the need for any assumption of the localization of valence holes. (C) 2000 American Institute of Physics. [S0021-9606(00)70602-7].