Temperature-dependence of water bridge formation in atomic force microscopy

When an Atomic Force Microscope (AFM) is operated in air, capillary condensation induces meniscus formation between the AFM tip and substrate. At present, no models account for the temperature-dependence of meniscus formation. This paper describes experiments measuring capillary forces between an AFM tip and mica at various temperatures and times. At low humidity, the capillary force decreases with increasing surface temperature in a manner unaccounted for by merely the dependence of water surface energy on temperature. We propose that this is due to water evaporation off the heated surface. The adhesion is also shown to decrease significantly with time until stabilizing after approximately an hour of experiments. Localized heating of the surface by the AFM laser is proposed as the cause of adhesion decrease. The decrease in force occurring at high surface temperatures implies a reduction in meniscus size that may potentially improve the resolution of AFM-based nanolithography techniques.