Water Adsorption on SiO2 Surfaces Functionalized with −OH, −NH2, and −F Groups by Plasma Treatments

Abstract

Understanding water adsorption on SiO2 surfaces is crucial for controlling the electrostatic resistivity of glass surfaces and suppressing their electrostatic discharge. In the present study, we investigated the water adsorption behavior of SiO2 surfaces processed using H2O, NH3, and CF4 plasmas. SiO2 surfaces treated with NH3 plasma exhibited the highest water adsorption, followed by the H2O and CF4 plasma-treated surfaces. Since no correlation was observed between the functional group density and the amount of adsorbed water after various plasma treatments, the observed variation in water adsorption can be mainly attributed to the types of functional groups. X-ray photoelectron spectroscopy revealed that the NH3 and CF4 plasma treatments partially replaced surface Si–OH groups with Si–NH2 and Si–F groups, respectively. Density functional theory calculations demonstrated that the partial replacement of Si–OH groups by Si–NH2 groups enhanced the bond polarity of the coexisting Si–OH groups. Water adsorption energy analysis revealed that water molecules were most stable when interacting with both Si–NH2 and Si–OH groups, whereas they were least stable when interacting with both Si–F and Si–OH groups. Finally, we demonstrated that the resistivity of SiO2 glass can be controlled through functional group modification.