Dissociative electron attachment in nanoscale ice films: Thickness and charge trapping effects

The yield and kinetic energy (KE) distributions of D- ions produced via dissociative electron attachment (DEA) resonances in nanoscale D2O ice films are collected as a function of film thickness. The B-2(1), (2)A(1), and B-2(2) DEA resonances shift to higher energies and their D- ion yields first increase and then decrease as the D2O films thicken. The D- KE distributions also shift to higher energy with increasing film thickness. We interpret the changes in the DEA yield and the D- KE distributions in terms of modifications in the electronic and geometric structure of the surface of the film as it thickens. A small amount of charge build-up occurs following prolonged electron beam exposure at certain energies, which primarily affects the D- KE distributions. Charge trapping measurements indicate that an enhancement in the trapping cross section occurs at energies near zero and between 6 and 10 eV. (C) 1998 American Institute of Physics.