Electrospray deposition from AFM probes with nanoscale apertures

Electrospray deposition utilizes a high electric field to extract liquid droplets from a capillary nozzle. In this contribution we demonstrate non-contact droplet deposition by electrospray from atomic force microscopy (AFM) probes with a fully integrated microfluidic system, so called FluidFM probes. Electrospray experiments were performed using probes with a pyramidal tip with a sub-micron size aperture in a dedicated setup. The onset voltage as function of the gap between the probe tip and the substrate was measured and compared with a numerical model. Onset voltages in the range 360-410 V were found at 8.5 μm gap height. We observed a reduction in onset voltage with an increase in external pressure. Wetting of the outside of the tip could be reduced by applying a fluorocarbon coating.