Monte Carlo Study on the Water Meniscus Condensation and Capillary Force in Atomic Force Microscopy

The water meniscus condensed between a nanoscale tip and an atomically flat gold surface was examined under humid conditions using grand canonical Monte Carlo simulations. The molecular structure of the meniscus was investigated with particular focus on its width and stability. The capillary force due to the meniscus showed a dampened oscillation with increasing separation between the tip and surface because of the formation and destruction of water layers. The layering of water between the tip and the surface was different from that of the water confined between two plates. The humidity dependence of the capillary force exhibited a crossover behavior with increasing humidity, which is in agreement with the typical atomic force microscopy experiment on a hydrophilic surface.