Scientists at Freie Universität Berlin have demonstrated how energy can be extracted from the stochastic motion of individual hydrogen molecules to drive a “mechanic machine.” They succeeded in transferring random fluctuations (which underlie many processes in nature, for example, the flow of fluids or electromagnetic radiation, and that are referred to as “noise”) to artificial nanostructures. In the experiments the scientists were able to drive periodic oscillations of a macroscopic tuning fork with the stochastic movement – noise – of a single hydrogen molecule. These results could pave the way for developing a molecular engine.
“This means that the smallest possible molecule, the hydrogen molecule, can oscillate a mass 1019 times greater than itself,” explains Nacho Pascual, one of the authors. The experiment is based on the principle of “stochastic resonance,” by which the interaction of the random motion of a hydrogen molecule with the periodic movement of the oscillator results in an increased energy transfer from molecule to oscillator. For this purpose, the hydrogen molecule was enclosed in a tiny gap between a flat metal surface and the atomically sharp wire tip of a scanning force microscope. In the microscope the tip was attached to a tuning fork whose tone, or frequency, was dependent on forces at the nanometer scale. The stochastic motion of the hydrogen molecule exerted a driving force on the tip. The oscillation of the tuning fork (and thus the tip) set the molecules in motion. The interaction led to a common “dance” of the molecule and the tip, where the vibration of the tuning fork swung far beyond the extent of the molecule.
The experiments were performed at the Department of Physics, Freie Universität Berlin, in the framework of the Collaborative Research Center 658, Elementary Processes in Molecular Switches at Surfaces. “With the atomic force microscope, the detection of molecular motion is not really difficult,” say Christian Lotze and Martina Corso. “The real achievement is the identification and interpretation of the effect.” According to Katharina Franke, the next goal is “to find other sources of molecular noise such as electronic or magnetic fluctuations, in order to optimize the efficiency of energy transfer to the oscillator.”