First-Principles Study of Water Ice Adsorption on the Methyl-Terminated Si(111) Surface

Abstract

The properties of water adsorbed on the methyl-terminated Si(111) surface, CH3:Si(111), are investigated using a first principles approach to complement a recent experimental study. We confirm the existence of weak hydrogen bonds between water and the substrate; however we show that the bonding configuration is different from that assumed in the analysis of the experimental data. In fact, a water molecule prefers to interact with the substrate by adopting a “face” approach direction in which a H atom points toward the C atom of the methyl group; instead the suggested “vertex” configuration, characterized by a weak C–H···OH2 hydrogen bond, turns out to be clearly unfavored. This behavior resembles that observed in the study of hydrogen bonding in the methane–water complex. Our energetic analysis indicates that water–water interactions are much stronger than those between water and the substrate, thus confirming the hydrophobic behavior of the CH3:Si(111) surface, although the contact-angle estimate (73°), ...