The hydrophilic/hydrophobic nature of a Cl-terminated Si surface

Abstract

The hydrophilic/hydrophobic nature of a Cl-terminated Si surface, which is slightly controversial, was investigated on the molecular level by depositing CTAB-silica 2D-hexagonal mesostructured films on it as well as on OH- and H-terminated Si surfaces and determining their structures by combining X-ray reflectivity and grazing incidence small angle X-ray scattering measurements. The contact angle measurements, which provide macroscopic level information, confirm that the Cl-Si surface is hydrophilic in nature but less hydrophilic than the OH-Si surface. The initial attachment of a film (through a silica layer) and the (near circular) shape of the micelles, which provide microscopic level information, clearly indicate that the Cl-Si surface is hydrophilic in nature and its hydrophilicity is comparable to that of the OH-Si surface. The relatively strong electronegativity of Cl is probably the reason for the hydrophilic nature of the Cl-Si surface, while the lack of hydrogen bonding and/or the lack of complete chlorination are a hindrance. © 2013 The Royal Society of Chemistry.