Less than 100 zeptojoules

(100 × 10⁻²¹ joules, or 0.6 eV) to operate a molecular switch. That is some 10⁻⁴ of the energy needed by transistor switches in current high-speed computers. The porphyrin-based molecule Cu-TBPP (structure shown at left) was in the “on” position when one of its four legs was perpendicular to the copper surface on which it sat, and “off” when the leg was parallel. In a recent experiment, scientists from the University of Basel and IBM Zurich in Switzerland, and from the CEMES-CNRS lab in Toulouse, France, used an atomic force microscope tip not only to rotate the leg but also to measure the required force from which they determined the energy. The authors suggest that a machine made from 10¹² such interconnected nanodevices, operating at 1 GHz, would consume less than 100 W of power. (Ch. Loppacher et al Phys. Rev. Lett. 90, 066107,...