Using atomically flat materials to cut ultrathin metal sheets from a video produced by Zhang on a forged copper strip with an anvil
Metals don’t have this peelable layered structure, and most have been unstable when scientists have tried to shape them into ultrathin sheets. Researchers created a small swath of atoms-thick metals. Last year, for instance, a team reported a method3 that produces flakes of gold, called ‘goldene’, that are hundreds of nanometres wide. Other methods involve depositing vaporized metal atoms onto a surface to form thin sheets4. But studying these materials has been challenging because metal atoms bind tightly to whatever they are placed on, making it difficult to isolate their properties from those of the surface material. Researchers have only been able to study the ultrathin sheets inside vacuum chambers because they oxidize when exposed to air.
Zhang was inspired to develop the latest technique by a video of copper forging. To make sheets of copper, the metal is heated in a furnace, then hammered and squeezed on a large anvil.
It took his team seven years to adapt the concept to work at the nanoscale. The biggest challenge was finding a sufficiently flat anvil to squeeze the metal layers. The researchers eventually selected sapphire, which is very hard, and they coated it in molybdenum disulfide (MoS2), which is atomically flat.
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