Sputtering of tetrafluoro- and tetraphenylborate anions adsorbed to an amine-terminated self-assembled monolayer surface
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Secondary ion mass spectrometry was used to monitor the exchange of tetrafluoro- and tetraphenylborate anions to the surface of an amine-terminated self-assembled monolayer. The exchanged surfaces were prepared by soaking aminoethanethiol (AET) monolayers on Au in solutions of the respective sodium salts. The mass spectra produced from the monolayer surface and those from Au blank and propanethiol monolayers soaked in the same salt solutions demonstrate that the protonated amine terminus of the AET monolayer is important to the uptake of the inorganic anion. The exchanged monolayer surfaces were used to measure secondary ion yields produced from ultrathin films by (CsI)nCs+ (n = 0-2) projectiles at the limit of single-ion impacts. The yield trends produced from the monolayer surface as a function of projectile complexity and energy differ dramatically from those generated from thicker targets of solid NaBF4 and NaB(Ph)4. Nonlinear enhancements (expressed as an increase in the secondary ion yield per projectile atom) in the yield of BF4- and B(Ph)4- are observed for the polyatomic ion impacts on the thick targets. For the yields of the same anions sputtered from the exchanged monolayer, however, a slight nonlinear enhancement was observed only for the (CsI)Cs+ projectile, and the enhancement is greatly reduced compared to the thick target. 1999 American Chemical Society.
