Cationization agent affects the stability of secondary ions in MeV-SIMS

The work presents studies of the cationization agent effect on the ionization efficiency, and on the stability of secondary molecules, which are desorbed from the surface as a result of bombardment by MeV primary ions. Different organic molecule standards were mixed with various trifluoroacetate (TFA) salts, namely AgTFA, LiTFA, NaTFA and KTFA, with Ag, Li, Na and K being common cationization agents of secondary ions besides hydrogen. Results show modest differences in ionization efficiency, and significant variation of secondary ions’ stability when different cationization agents are attached to the molecule. For all reference samples, lithium provided the most stable secondary ions with almost none detected fragmentations after the desorption, while secondary ions with attached potassium were measured as much less stable, and the ratio between neutrals (fragments) and normal positive ions is estimated to be more than 0.2. However, even potassium – ionized molecules were recognized as more stable than protonated molecules.