Magazine article Science News

A New Low: Lilliputian Pipette Releases Tiniest Drops

Magazine article Science News

A New Low: Lilliputian Pipette Releases Tiniest Drops

Article excerpt

Physicists have constructed a pipette that dispenses a billionth of a trillionth of a liter, a droplet that's a thousand times as small as volumes previously achieved. The behavior of these zeptoliter-size drops challenges an accepted theory describing how drops crystallize as they cool, the researchers say.

To build the pipette, Eli A. Sutter and Peter W. Sutter of the Brookhaven National Laboratory in Upton, N.Y., started with a germanium nanowire. It supports an initially solid reservoir of a gold-germanium alloy. A carbon shell encapsulates the assembly, which is about 2 micrometers long.

The researchers place the pipette in a vacuum chamber within a transmission-electron microscope. To dispense liquid, they melt the reservoir of gold-germanium alloy and then focus a beam of electrons on the tip. The beam punctures the carbon shell, Peter Sutter says.

The liquid alloy oozes through the hole and slowly forms a drop up to 40 nanometers in diameter and 35 zeptoliters in volume. "It's the smallest amount of fluid that, to our knowledge, anybody has dispensed in a controlled fashion," Peter Sutter says.

A filament of liquid alloy connects the drop to the tip. Having the drop almost free of contact makes it useful for studies of crystallization, explains Peter Sutter. Typically, researchers have supported drops on another surface, which influences how they crystallize.

For their crystallization studies, the researchers slowly cooled the pipette and its drop until they were a few degrees above the liquid alloy's freezing temperature of 300[degrees]C. …

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