Researchers in Japan and China describe a reliable means of producing free-standing, single strands of carbon atoms, which could be used as the building blocks for an all-carbon nanoscale electric circuit.

There are two approaches to the miniaturization of electronics: start with tiny elements and build up a circuit, or cut down large materials with sophisticated chemistry, optics or high-energy beams. The latter ‘top-down’ approach has dominated the semiconductor industry, but with the discovery of carbon nanotubes, scientists have become interested in a ‘bottom-up’ method for building nanoscale circuits.

Unfortunately, it is almost impossible to fabricate and position large numbers of identical carbon nanotubes precisely. Now, bringing the top-down philosophy to carbon, a team of scientists at AIST and Meijo University in Japan and Peking University in China1 has found a way to carve out atomically thin carbon wires from graphene flakes. Ling-Mao Peng, a member of the group, says, “These wires are the ultimate thin interconnect and possibly the smallest functional device unit.”

Fig. 1: Electron micrographs of a carbon nanoribbon before (left) and after (right) an electron beam has knocked out all but one atomically thin strand of carbon atoms.

The group started by suspending a nanoscale flake of graphite (stacks of carbon layers) on the grid of a transmission electron microscope. Using the microscope’s high-energy electron beam, they thinned down the flake to a single layer, in which they then formed two closely spaced holes that were separated by a ‘nanoribbon’ of carbon atoms (Fig. 1, left). To form a single strand of carbon atoms from the nanoribbon, they lowered the energy of the electron beam and gently stripped away carbon atoms, row by row. The process was stopped when only one or two rows of carbon were left (Fig. 1, right).

The carbon chains were about 2 nm (or 16 carbon atoms) in length, and although they were fragile, they survived for 1–2 minutes before breaking.

For Peng, the next challenge is to measure the electronic properties of the chains. He says, “It will be extremely interesting to see how charges move through carbon depending on if it is in the form of three-dimensional graphite, two dimensional graphene, a one-dimensional carbon chain, and perhaps, eventually, a zero-dimensional carbon dot.”