Probing aqueous-organic interfaces with soft-landed ions

A very low energy ion source (1 eV) is used to dose hydronium ions on or in to epitaxially grown amorphous thin films of water and organic solvent, fro m tens to thousands of monolayers thick. This is done to probe the structur e of the organic film, ion diffusion and solvation, and the kinetics of tra nsfer of hydronium ions from an aqueous environment into a non-aqueous one. The organic solvent used is methyl cyclohexane. Water dosed from 0 to 0.5 monolayer on top of 60 monolayer films of methyl cyclohexane causes a solva tion of ions co-adsorbed with the water, slowing the subsequent diffusion o f ions through the solvent him. Water in excess of a monolayer causes extre me slowing of ion transfer into the organic phase. Structures in the film, clue to intentional doping or crystallization, are also probed via the ion motion. (C) 1999 Elsevier Science B.V. All rights reserved.