Enhanced formation of a con?ned nano-water meniscus using a 780 nm laser with a quartz tuning fork-atomic force microscope

Demonstrated herein is the optical-?eld-induced enhancement of the formation of a con?ned nanowater meniscus using a distance-regulated quartz tuning fork-atomic force microscope (QTF-AFM) with a 780 nm laser. While a pulled optical ?ber tip approaches the surface, the laser is suddenly turned on and focuses on the front spot of the tip by the shape of the pulled optical ?ber, which plays the role of an objective lens and induces the gathering effect of the water molecules directed to the electromagnetic-?eld gradient in air. This phenomenon facilitates a new boundary condition to form a long-range con?ned nano-scale liquid bridge between the tip and the surface. After the pulling of the optical ?ber, 20-nm-thick gold was sputtered on the apex (diameter: ∼100 nm) of the tip to guide and focus the beam on the spot. The critical power of the laser to overcome the barrier for the formation of a new boundary is 100 μW at the distance of 22 nm from the substrate.