Wetting of thin layers of SiO2 by water

Abstract

We have measured the contact angle θ of water on silicon and on very thin layers of silicon dioxide grown on silicon. The silicon is hydrophobic and θ is near 90°. Oxides thicker than 30 Å are hydrophilic and θ is near 0°. For intermediate thicknesses, θ varies smoothly between these limits. Our results show that the interactionenergy between water and the solid surface depends strongly on the oxide thickness. Consideration of different possible interactions leads us to conclude that this is due to corresponding changes in the structure or composition of the oxide surface.