  Liquid dispensing and writing in the extremely small size regime are
important for applications in many current technologies, such as micro/nano
fabrication, biological/chemical patterning and analysis, and drug discovery.
Most of current dispensing/writing methods can be sorted into a category of
liquid flowing through tiny tubes or nozzles that requires inputting an impulse
energy, which leads to complex procedures, expensive equipment and narrow
material applicability, especially for biomaterials. Here, we report a method
that may lead to a new category: liquid flows over the tapered surface of a pin
with longitudinal nano grooves on the surface to uninterruptedly perform
droplet dispensing and direct writing. The dispensed droplet diameters were
controllable from several microns down to 150 nm, and the written line heights
were as low as 5 nm. The mechanism underlying automatic liquid storage on
conical surface and spontaneous liquid transport through nano grooves is
revealed and well modeled by a simple relationship. Furthermore, the
nano-grooved pins are much simpler and cheaper in fabrication than nanoscale
tubes and nozzles, and pins have much depressed clogging problems that are
typically troublesome for tubes and nozzles. Our new strategy may constitute a
basis for creating liquid dispensing/writing technologies that are
simultaneously smaller, simpler, faster and applicable for more types of
materials.
