Capacitors store electrical energy on the surfaces of two conducting plates separated by an insulating layer. Because they release energy more quickly than chemical batteries, they are good for providing a sudden burst of power.

In large-scale devices, the layers are usually rolled up into a cylinder to make the device more compact. Now Carlos César Bof' Bufon and his team at the Leibniz Institute for Solid State and Materials Research in Dresden, Germany, have created nanoscale capacitors in a similar way. They begin by depositing thin layers of metal and insulating material on top of a host substrate. The lowest metal layer of titanium and chromium is placed under strain, so once the substrate is removed, the layers roll themselves up (Nano Letters, DOI: 10.1021/nl1010367).

Shrinking the nanoscale capacitors allows more electrical power to be stored in a small space. The rolled-up device provides a capacitance of 200 microfarads per square centimetre of chip surface. That's at least twice what is possible with other capacitors using the same material, says team member Oliver Schmidt.