Hollow Atomic Force Microscopy Probes for Nanoscale Dispensing of Liquids

To enable the printing of nanometer sized droplets with volumes in the femto and attoliter range and sub-micron droplet spacing, a nanoscale dispenser (NADIS) based on an atomic force microscopy probe has been developed and microfabricated. The probe consists of a cantilever with a hollow core, which is connected to a reservoir located in the chip. The hollow cantilever acts as a microfluidic channel that connects the reservoir to the dispensing tip located at the free end of the cantilever. The tip possesses an opening at its apex with a typical size of 200 nm, realized by focus ion beam milling. The transfer of liquid from the tip opening to the surface occurs by contacting the probe tip with the sample surface and is driven by capillary pressure alone. To overcome the serial manner of writing by using a single probe, arrays of hollow AFM probes were fabricated. The feasibility to dispense droplets in parallel has been demonstrated.