‘Machining’ with a microscope

Drilling with the beam of an electron microscope, scientists at the U.S. Department of Energy’s Oak Ridge National Laboratory precisely machined tiny, electrically conductive cubes that can interact with light and organized them in patterned structures that confine and relay the electromagnetic signal of light. This demonstration is a step toward potentially faster computer chips and more perceptive sensors. The seeming wizardry of these structures comes from the ability of their surfaces to support collective waves of electrons, which are called plasmons, with the same frequency as light waves but with much tighter confinement. The light-guiding structures are measured in nanometers, or billionths of a meter — 100,000 times thinner than a human hair.

Plasmonic phenomena first were observed in metals, which are conductive because of their free electrons. The ORNL team used cubes made of a transparent semiconductor that behaves like a metal: indium oxide doped — that is, a small impurity is added — with tin and fluorine.

The study builds on prior work to sculpt 3D structures as small as a nanometer with an electron beam.

ORNL scientists used an electron beam for precision machining of nanoscale materials. Cubes were milled to change their shape and also could be removed from an array. K. Roccapriore/ORNL, U.S. Department of Energy

“The current paper proves that the plasmonic effect, as well as the structure, can be sculpted,” said ORNL’s Kevin Roccapriore, first author of the study. “At the end of the day, we’re interested in the electron wave: Where is it, and what is its energy? We’re controlling those two things.”