Control of Hydrophilicity in Aqueous Environment in Local Anodic Oxidation of Si

Abstract

Si surfaces covered with self-assembled monolayers were locally anodically oxidized using atomic force microscopy (AFM). The surface chemistry of the oxides was characterized by frictional force measurements using AFM in air and in solution. It was found that the chemical states can be controlled by the oxidizing voltages applied between the AFM tip and the substrate surfaces. Hydroxyl-group densities on the anodically oxidized surfaces affect the frictional forces in both air and solution. A thick water layer bound on an OH-terminated surface prevents AFM-tip motion during the frictional force measurement in air. On the other hand, water molecules tightly bound on the anodically oxidized surface weaken the frictional force during the scan in a solution. It is concluded that surface chemistry on the anodically oxidized Si is basically the same in the aqueous environment as in air.