Capillary forces during liquid nanodispensing.

We present a comprehensive study of the capillary force measured during the liquid nanodispensing of attoliter droplets with an atomic force microscope tip. Due to the presence of a nanochannel drilled at the tip apex and connected to a reservoir droplet deposited on the cantilever, we observe a large variety of force curves during the deposition process. We propose a numerical method which accounts for most of the experimental observations. In particular, we clearly demonstrate the influence of the nanochannel diameter. This study leads to a better understanding of the mechanisms of liquid transfer from the tip to the surface and also provides a real time monitoring of the dispensing. Besides these applications, the method we use, which can handle a large variety of conditions and also complex geometries, may find a wide range of applications.