(106e) Thermopower Wave Dynamics: Nanoscale Alternating Current Sources and Geometry Effects

Mahajan, S. G., Massachusetts Institute of Technology
Schonenbach, N. S., Massachusetts Institute of Technology
Park, J., Massachusetts Institute of Technology
Han, J., Massachusetts Institute of Technology
Strano, M. S., Massachusetts Institute of Technology

The nonlinear coupling between exothermic chemical reactions and a nanostructure with large heat conduction results in a self-propagating thermal wave guided along the nano-conduit in the direction of its greatest thermal diffusivity [1,2]. The resulting reaction wave pushes charge carriers along, creating a concomitant thermopower wave and electrical current in the same direction. For carbon nanotubes, examples of one-dimensional conduits, we have measured high power density (> 7 kW/kg) from such waves.  However, two-dimensional conduits such as graphene should also provide new avenues for control of wave velocity and temperature due to additional degrees of control from geometry and boundaries. We have developed the theory and mathematics of such waves for one- and two-dimensional conduits.

For one-dimensional conduits, our models predict that certain values of the chemical reaction kinetics and thermal parameters produce oscillating reaction wave velocities with well-defined frequency and amplitude [3]. We demonstrate such oscillations experimentally using a cyclotrimethylene-trinitramine/multiwalled carbon nanotube system, which produces frequencies in the range of 400 to 5000 Hz.  The propagation velocity oscillations and the frequency dispersion are well described by our theoretical calculations and are linked to oscillations in the voltage generated by the reaction.  These thermopower oscillations may enable new types of nanoscale power and signal processing sources. 

[1] W. Choi, S. Hong, J. T. Abrahamson, et al. Nature Materials, 9, (2010), 423.

[2] W. Choi, J. T. Abrahamson, J. M. Strano, M. S. Strano. Materials Today, 13, (2010), 22.

[3] J. T. Abrahamson, et al. ACS Nano 5, (2011), 367.