Control of droplet size in liquid nanodispensing

In this Letter, the phenomena and parameters governing the nanoscale dispensing of liquid through an apertured atomic force microscope probe milled by focused ion beam lithography are characterized in detail. We show that the size of deposited droplets can be reproducibly defined by controlling the aperture size on the probe and the surface energies of both tip outer wall and substrate surface. On the basis of these findings, tips with aperture diameter as small as 35 nm enabled the deposition of regular arrays of nanodroplets with diameter down to 70 nm on an alkylamine-modified surface. The fine control of droplet volumes down to a few tens of zeptoliters (10(-21)L) provides a unique tool for creating devices and probing the fundamentals of wetting at the nanometer scale.