Heat-to-Mechanical Energy Conversion in Graphene: Manifestation of Umklapp Enhancement with Strain

Conversion of heat-flux, from a steady state temperature difference, to mechanical vibration is demonstrated in graphene nanoribbons using direct non-equilibrium molecular dynamics (NEMD). We observe that this effect is independent of the method of imposing the temperature gradient, heat flux as well as imposed boundary conditions. We propose that simply dividing the nanoribbon in long and short sections using a partially immobilized area will lead to excitation of long-wavelength vibrations in the long section of the nanoribbon. This results in simpler architectures for heat-to-vibration converter devices based on graphene or other 2D materials. Furthermore we observe that applying tensile axial strain to nanoribbons, facilitates vibrational instability by reducing the required threshold heat flux or temperature gradient. Finally, we discuss the role played by Umklapp scattering for physical mechanisms behind these observations.