Atomically thin sheets of carbon, called nanotubes, are prized for their electronic properties. The sheets all look to have the same honeycomb structure. But the edges of those sheets can combine in dozens of different ways, which influences whether the nanotubes conduct electricity like a metal or like a semiconductor. Researchers can separate out one variety, but at a high cost, Physics World reports. Now, researchers in Switzerland report in Nature that by placing carbon “seeds” on a platinum surface, they can grow nanotubes of only one metallic variety.