A Single-Molecule Engine

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Science  09 Nov 2012:
Vol. 338, Issue 6108, pp. 754-755
DOI: 10.1126/science.1230530

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In physical systems, mechanical energy usually flows from the large to the small in the form of dissipation into the random thermal motion of the molecules and atoms in the system. In biology, many natural systems have evolved to reverse this trend, enabling the flow of energy from the small to the large, with examples including photosynthesis (1) or motor protein motion (2). The desire to recreate this ability in artificial systems motivates a search for strategies and concepts that enable energy harvesting from very small subsystems. On page 779 of this issue, Lotze et al. (3) now show how the motion of a macroscopic cantilever beam can be excited using the driven motion of only a single molecule. In this case, a single hydrogen molecule is trapped between a copper surface and a scanning tunneling microscopy tip mounted on a flexible springlike cantilever. The authors find that when a particular bias voltage between the tip and copper is applied, the electric current causes the hydrogen to switch stochastically between two different positional states and the cantilever begins to oscillate spontaneously.