Machine Design

Single molecule drives nanomachines

Evanston, Ill. ... Northwestern University chemists have shown that an electric current applied to a single molecule can create enough internal energy to drive a molecular machine.

In a proposed molecular machine, a carbon molecule (C60) sits between two gold electrodes. As electric current passes through the electrodes, electronic energy converts to vibrational energy as the C60 molecule bounces against the gold surface. This produces a nanoscale, unidirectional oscillator. Sharp dependence of the conductivity on the location of the C60 within the junction gives rise to large amplitude oscillations of the current.

In contrast, other researchers have conventionally devised such nanoscale machines from many molecules and drive them by either external light or via a chemical reaction which makes them difficult to control.

In their proposed molecular machine, Tamar Seideman, professor of chemistry and postdoctoral fellow Chao-Cheng Kaun, place a carbon molecule (C60), known as a fullerene or "buckyball," between two gold electrodes. (This is called a molecular junction.) When an electric current runs through the electrodes, the electrons transfer energy to the molecule. The molecule vibrates and creates its own internal energy source.

Essentially, the buckyball oscillates between the electrodes, as if on an invisible spring. Because the conductivity of this tiny junction depends strongly on the location of the buckyball between the electrodes, the current oscillates with time at the frequency of the C60 oscillations. The oscillating current translates into an oscillating electromagnetic field, so the fullerene junction becomes a nanoscale generator of a radiation field — a phenomena not demonstrated before. Because the single molecule can be driven individually the resulting motion is reportedly more easily controlled.

Understanding the process that produces the movements is key to controlling the dynamics and hence making use of the tiny molecular motor. Applications are likely to include sensors, bioengineering devices, and solar cells. Research was supported by the National Science Foundation.

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