Title: Organized Brownian Motion in Freestanding Graphene: A New Thermal Force
Speaker: Paul Thibado, University of Arkansas
Abstract:
In his renowned 1964 lecture series, Richard Feynman argued that obtaining useful work from Brownian motion is impossible, citing detailed balance and the second law of thermodynamics. Effectively, his point was that connecting a resistor to a diode will not generate a direct current [1]. Considering the noise voltage of a resistor is at best 500 micro-volts, while forward bias requires a minimum of 0.7 volts, this is a reasonable inference. The question is, in the fifty years since Feynman’s talk, has a system been found that has a noise voltage larger than forward bias [2]? In our current studies of the continuous motion of freestanding graphene, we have discovered such a system, with a noise voltage in excess of 50 volts. As a freestanding monolayer, graphene isn’t flat; instead, it features alternately concave and convex ripples, forming its characteristic “egg carton” contours. Interestingly, these ripples undergo spontaneous curvature inversion in response to the ambient temperature [3]. As each ripple flips from concave to convex, more than 10,000 atoms move coherently in the same direction, creating an extremely large force [4]. We have converted this collective thermal motion into stored electrical charge using a variable-capacitance machine [5]. This brings to mind another well-known assertion by Feynman: he stated that there is “plenty of room at the bottom” as he challenged scientists to successfully develop tiny motors.
[1] L. Brillouin, CAN THE RECTIFIER BECOME A THERMODYNAMICAL DEMON, Physical Review, 78 (1950) 627-628. [2] M.O. Magnasco, FORCED THERMAL RATCHETS, Physical Review Letters, 71 (1993) 1477-1481. [3] P. Xu, M. Neek-Amal, S.D. Barber, J.K. Schoelz, M.L. Ackerman, P.M. Thibado, A. Sadeghi, F.M. Peeters, Unusual ultra-low-frequency fluctuations in freestanding graphene, Nat. Comm., 5 (2014) 3720. [4] M.L. Ackerman, P. Kumar, M. Neek-Amal, P.M. Thibado, F.M. Peeters, S. Singh, Anomalous Dynamical Behavior of Freestanding Graphene Membranes, Physical Review Letters, 117 (2016) 126801. [5] S.F. Philp, Vacuum-Insulated, Varying-Capacitance Machine, IEEE Transactions on Electrical Insulation, 12 (1977) 130-136.
Host: Einstein
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