Effect of water thin film on the adhesion force between two silica surfaces using AFM

The adhesion force between two silica surfaces was measured with different experimental parameters to investigate the effect of water thin film adsorbed on the surfaces using atomic force microscopes (AFM) at various relative humidities (RH). Results show that the adhesion force behavior largely depends on a water film. Under extremely dry condition, the adhesion force is independent of contact time without a water film. With a small (large) film thickness, the adhesion force is time-dependent (time-independent) and decreases (increases) with retraction velocity, and vice versa. For repeated contacts at one location, the time-dependent adhesion force shows larger fluctuations than the time-independent one. There may be a threshold thickness of water film to distinguish time-dependent and time-independent ones. The thickness can be changed to reach a certain value via RH adjustment, with which the adhesion force is almost independent of retraction velocity, and which may be very close to the threshold value. The adhesion force behavior by adjusting RH is closely related to water film thickness instead of RH itself, since the equilibrium of vapor-film interface may be difficult to reach. These results may help facilitate the anti-adhesion design of small-scale silicon-based systems under different conditions.