Fundamental understanding of surface forces at the nanoscale is a paramount requirement in the design, fabrication and manipulation of nanosystems. Force-displacement curve measurement in the atomic force microscope (AFM) is widely used as a measure of adhesion to quantify surface forces. However, the role of separate constituent forces in nanoscale contact formation and interfacial adhesion is not obvious. In this work, a sharp Si3N4 tip was used in adhesion measurements to study the effect of capillary condensation by comparing pull-off forces measured using AFM in different environments. To distinguish the contribution of the capillary meniscus on adhesion, and to understand its role in contact modification in ambient conditions, an equivalent stress field between two surfaces with a meniscus is proposed, based on the water-screened van der Waals interaction and capillary condensation. Maugis-Dugdale mechanics are employed to evaluate the contact modification in ambient conditions. Calculations supporting the experimental observation suggest that although the meniscus height is less than 1 nm it is enough to modify the nanocontact significantly.

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