LOW-ENERGY (LESS-THAN-5 EV) F+ AND F- ION TRANSMISSION THROUGH CONDENSED LAYERS OF WATER - ENHANCEMENT AND ATTENUATION PROCESSES

We have studied the transmission of F+ and F- ions through ultrathin films of condensed water at 20 K. The F+ and F- ions are produced by electron stimulated desorption of a PF3 monolayer adsorbed on a Ru(0001) surface. We find two surprising results: (a) the F+ signal is attenuated to similar to 1% by only similar to 2.5 ML (monolayer) of H2O, while a much thicker layer, similar to 10 ML of H2O, is necessary for equivalent attenuation of the F- ion emission, and (b) 1 ML of H2O increases the emission of F- ions and causes a dramatic change in the ion angular distribution.