LOW-ENERGY COLLISIONS OF GROUP IIIA, IVA, VA, VIA, AND VIIA IONS WITHFLUOROALKYL SAM SURFACES - REACTIONS, CHEMICAL SPUTTERING, AND MECHANISTIC IMPLICATIONS

Low-energy (10-90 eV) atomic ions of group IIIA, IVA, VA, VIA, and VII A elements (E) undergo reactions with a fluorinated self-assembled mon olayer surface to give fluoride cations, EF(n)(+). One, two, or three fluorine atoms can be abstracted. Ion/surface reactions are also obser ved with polyatomic ions of these elements, but in general, atomic ion s are much more reactive and react at lower collision energies than th e corresponding polyatomic species. The higher collision energies refl ect increased energy consumption needed for fragmentation. Most of the ion/surface reactions investigated in this study are endothermic and are driven by the translational energy of the projectile, although the re remains a high degree of thermochemical control over reactivity. Th ermochemical control over neutralization of the primary beam is also e vident; ions with high recombination energies, like N+ and O+, complet ely neutralize at the fluorocarbon surface. In addition, certain gener al trends in behavior have been observed for elements within the same periodic group. The reactions occur in single scattering events, and t hey are not associated with electron transfer from the surface to the ion, as are the well-known hydrogen and alkyl group abstractions by or ganic radical ions. In most cases, the ion/surface reaction seems to o ccur after, or in concert with, dissociation of the polyatomic project ile. When multiple abstractions occur, the fluorine atoms can be lost from the same alkyl chain; evidence for this is the enhanced intensity of specific sputtering products, e.g. C3F3+, upon collisions of ions such as Sb+, which readily abstract more than one fluorine atom. Ion/s urface reactions in which new bonds are formed in the surface alkyl gr oup are also observed; such reactions give rise to unusual product ion s which are sensitive to the chemical nature of the projectile. Exampl es include chlorine-for-fluorine atom substitution at the surface and PCF2+ formation in p(+) collisions. These processes suggest the possib ility of selective chemical modification of the outermost monolayers o f surfaces using low-energy reactive ion beams.