Interfacial water on Cl- and H-terminated Si(111) surfaces from first-principles calculations

The properties of interfacial water on Cl- and H-terminated Si( 111) surfaces are investigated using a first-principles approach and characterized by means of energetic analysis combined with hydrogen-bond counting. The interaction of water with both substrates is found to be significantly weak, although bonding with the Cl- terminated Si( 111) surface is relatively stronger because of the electrostatic contribution. According to a molecular picture for attributing the hydrophilic/hydrophobic character, both surfaces should be considered hydrophobic, at variance with the interpretation of recent ultrafast electron crystallography experiments, which seems instead to support a hydrophilic nature of the Cl- terminated Si( 111) substrate.