When a beam of electrons hits a carbon nanotube, some carbon atoms are knocked away, causing the remaining atoms to contract and the tube to shrink. When the tube is filled with even incredibly hard substances like iron carbide, the contraction squeezes the substance out as ultra-thin wires.

Credit: Zina Deretsky, National Science Foundation

Electron micrographs reveal the patterned atomic structure of the carbon nanotube (light grey) and the iron-carbide interior material (dark grey). Image 1 depicts the nanotube before contraction; image 2 shows material compressing during contraction. Image 3 shows how the wire pinches off at the conclusion of the process.

Credit: F. Banhart, University of Mainz, Germany