Field-induced meniscus dynamics and its impact on the nanoscale tip-surface interface

We describe the spatiotemporal evolution of the nanoscale tip-surface junction during field-induced water meniscus formation in the junction. The motion of the meniscus and tip was analyzed on the basis of typical parameters concerning the nanoscale meniscus and tip-surface configuration. Being attracted by the electric field, the meniscus generates a repulsive hydrodynamic impact force counteracting the electrostatic force on the tip. The imbalance of the forces leads to an increase of the tip-surface separation distance, and the increase is related to the initial experimental parameters including tip bias voltage and tip spring constant. An explicit equation was derived for the estimation of the tip-surface junction enlargement effect. The theoretical results were confirmed by atomic force microscope (AFM) in situ observations of tip repulsion under electric fields. The induced tip-surface junction enlargement has significant implications in AFM nanolithography, e.g., it could facilitate the formation of nanostructures with high vertical dimensions/aspect ratios.