Sputtering of tetrafluoro- and tetraphenylborate anions adsorbed to an amine-terminated self-assembled monolayer surface

Secondary ion mass spectrometry was used to monitor the exchange of tetrafl uoro- and tetraphenylborate anions to the surface of an amine-terminated se lf-assembled monolayer. The exchanged surfaces were prepared by soaking ami noethanethiol (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 demo nstrate that the protonated amine terminus of the AET monolayer is importan t to the uptake of the inorganic anion. The exchanged monolayer surfaces we re used to measure secondary ion yields produced from ultrathin films by (C sI)(n)Cs+ (n = 0-2) projectiles at the limit of single-ion impacts. The yie ld trends produced from the monolayer surface as a function of projectile c omplexity 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 o f BF4- and B(Ph)(4)(-) are observed for the polyatomic ion impacts on the t hick targets. For the yields of the same anions sputtered from the exchange d 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.