To make a droplet out of just a few thousand atoms and then measure it is tricky. Thermodynamically, a drop that size is exceedingly delicate and can abruptly evaporate or freeze. The drive to reduce its free energy can also prompt a drop on a surface to shrink or grow at its neighbors’ expense, a process known as Ostwald ripening. And the huge surface-to-volume ratio makes it prone to contamination from stray impurities.

Two physicists from Brookhaven National Laboratory have now developed an exotic approach to the challenge. Last year, Peter Sutter and Eli Sutter figured out how to coat a germanium nanowire with a protective carbon shell using the beam of a transmission electron microscope (TEM) in high vacuum. During that study, the husband–wife team realized that the process, with just a few modifications, would enable them to transform the coated nanowire into a syringe or pipette of sorts...

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