We are able to synthesize a wide variety of ionic interfaces by depositing ions in or on molecular-scale films, using a newly developed, very low energy, molecular ion source. This accomplishment is illustrated in two examples, one of hydronium ions interacting with amorphous water films, the other, of cesium ions with hexane multilayers. In these cases we report on stress-induced dielectric responses and ion diffusion, as probed by Kelvin probe measurements of the potentials created by the ions in the films.
Ions play an important role in most chemical systems in everyday life.
For example, the chemistry of soils or cells is often dominated by dissolved ions interacting with molecules and the surrounding interfaces at thermal energies. Ion beams, on the other hand, made in vacuum chambers, typically smash into their targets at tens to hundreds of eV's of energy, far in excess of the bond energies of molecules, leading to high energy, fragmentation-dominated chemistry. We describe an experimental apparatus which combines the ease of manipulations of ions afforded by ion beams with the low ion energies encountered in solutions. We show how a chemical system can be assembled stepwise and then ions can be monitored as the system is allowed to evolve. This technique should enable new ways to measure complex processes involving ion migration and charge transfer mechanisms, with applications in fields as diverse as photosynthesis, photography, and electrochemistry.