Thickness-dependent effects in H2O desorption from glycine/amorphous solid water films

The desorption characteristics of H2O from glycine-on-amorphous solid water (ASW) ultrathin films have been systematically investigated as a function of underlying ASW thickness and the amount of top-deposited glycine using TPD. At the early stages of deposition, substantial amounts of glycine molecules penetrate into the water multilayers and, therefore, thermal destabilization of water layers is detected. Glycine diffusion is governed by the thickness-dependent structure of the ASW as revealed by work function measurements and XPS. For higher glycine coverages, a kinetic restriction of water desorption by the continuous amino acid overlayers is observed independent of the ASW substrate thickness.