Properties of droplet formation made by cone jet using a novel capillary with an external electrode

A capillary with an external electrode for cone-jet mode of electrospray has been developed to spot a droplet accurately on a substrate surface. The external electrode is made by gold deposition around tip of a glass capillary. The electrospray was made by applying a positive pulsed dc voltage to the solution in the capillary. Using a positive bias voltage to the external electrode, the meniscus of the solution at the tip deformed to be more sharp, and center of the meniscus was prolonged. This deformation stabilized the trajectory of the jet from the Taylor cone at the tip. From the experimental result, accuracy of positioning of the droplet having 0.3 pL volume was improved with the standard deviation of 1.1 μm, from that of 2.5 μm for conventional capillary without the external electrode.