Soft landing of ions onto self-assembled hydrocarbon and fluorocarbon monolayer surfaces

Low energy (less than or equal to 10 eV) ion beams can be soft landed onto a C-12-hydrocarbon self-assembled monolayer (H-SAM) surface. The H-SAM surface causes much less collateral fragmentation of the deposited ions under the same conditions than the corresponding fluorinated self-assembled monolayer (F-SAM) surface. The energy dependence for release of ions deposited onto an F-SAM monolayer surface shows that smaller ions are ejected more readily than sterically bulky species. The threshold energy for release of the soft-landed species by Xe+. coincides with that of the typical chemical sputtering product CF3+ implying that the deposited species are strongly held inside the SAM matrix and that C-C bond cleavage assists in efficient release of the trapped ions. In cases where fragment ions of the deposited projectile are released from the surface, it is shown, by varying the energy and nature of the releasing projectile ion, that dissociation primarily occurs upon impact of the soft-landed ion and not upon its release. Examination of various odd- and even-electron ions confirms the earlier conclusion that the former are efficiently neutralized and only the latter can be soft landed as ions onto F-SAM surfaces. (C) 1999 Elsevier Science B.V.