The approaching force curves between the OTS-hydrophobized surfaces in water without the removal of surface bubbles are shown in Fig. 1. The contact angle of the surface against water was 106°, and the force curves were measured at three different points on the silicon wafer surface. In the same figure, the theoretical curve for the van der Waals force between a sphere and a plate is also shown for comparison. The van der Waals force was calculated by