SPUTTERING OF CS-CARRYING DIATOMIC CATIONS FROM SURFACES BY KEV CS+ IRRADIATION

The sputter ejection of diatomic molecular ions carrying a Cs atom fro m cesium loaded surfaces is investigated. Experiments indicate that th ese MCs+ ions (where M stands for any sample element) are formed throu gh the association, in the emission event, of a neutral M atom and a C s+ ion. The (preceding) incorporation of Cs+ primary ions into the nea r-surface region of the specimen is a necessary prerequisite; it is st udied via computer simulations. The resulting build-up of a Cs surface concentration effects a lowering of the local work function. This is monitored experimentally from a shifting of the secondary ion energy d istributions with an accuracy of similar to 0.1 eV. The gradual reduct ion of the work function causes positive ion yields to decrease. A clo se correlation between Cs(+)f and MCs+ yields is found during both the transient build-up of Cs upon irradiation of pristine surfaces and th e sputter depth profiling of Cs-implanted samples, supporting the comb inative formation mechanism. The observed scaling of the MCs+ formatio n probability with the polarizability of M indicates that a dipole ind uced binding is relevant for these molecular species. (C) 1998 Elsevie r Science B.V.