PNNL

Abstract

The electron-stimulated sputtering of thin amorphous solid water films deposited on Pt(111) is investigated. The sputtering appears to be dominated by two processes: 1) electron-stimulated desorption of intact water molecules and 2) electron-stimulated reactions leading to the production of molecular hydrogen and molecular oxygen. The electron-stimulated desorption of water increases monotonically with increasing film thickness. In contrast, the total sputtering – which includes all electron-stimulated reaction channels – is maximized for films of intermediate thickness. The sputtering yield versus thickness suggests that erosion of the film occurs due to reactions at both the water/vacuum interface and the Pt/water interface. Experiments with layered films of D2O and H2O demonstrate significant loss of hydrogen due to reactions at the Pt/water interface. The electron-stimulated sputtering is independent of temperature below ~80 K and increases rapidly at higher temperatures. A simple one-dimensional random walk model qualitatively accounts for the experimental observations.