Interaction of swift ion beams with surfaces: Sputtering of secondary ions from LiF studied by XY-TOF-SIMS

Sputtering occurs as a result of deposition of kinetic or potential energy in solids irradiated with swift particles. We studied ejection of secondary ions from LiF induced by swift heavy ion impact. A new UHV system allows measuring the mass distributions and the velocity vectors of each emitted secondary ion by means of time-of-flight and imaging techniques (XY-TOF-SIMS) with controlled target surfaces. We present results performed at GANIL (Caen) with Ca beams at 7.6 and 9 MeV/u (electronic stopping regime). Under UHV conditions, particles emitted from cleaved LiF monocrystals include the omnipresent hydrogen, and the two isotopes of natural LiF (6Li+ and 7Li+). Two groups of clusters, namely Lin+ and (LiF)nLi+ appear. The cluster size (n) dependence of the cluster ion yields Y(n) can be described by an exponential function. LiF emission as ionic clusters (LiF)nLi+ with n ≥ 2 is dominant over emission as monomers LiFLi+.