Effects of temperature variation on a variable capacitor graphene circuit

The discovery of graphene has inspired extensive research due to the 2D material's multiple novel properties. One such property is the formation of ripples when suspended, that spontaneously invert due to thermal fluctuations. This spontaneous motion makes graphene ripples suitable for the creation of small variable capacitors in graphene energy harvesting (GEH) devices. The motion of a graphene ripple can be modeled using a Langevin equation for a single particle in a double well potential. Simulations of systems with a graphene variable capacitor coupled to a resistor with an applied bias voltage have demonstrated that the power generated by the capacitor is equal to the power dissipated by the resistor when the temperature of the resistor and capacitor are the same. However, research regarding such systems with components at different temperatures is lacking. In this talk, we present one such study, involving two series of Langevin simulations: one where the capacitor temperature is fixed while the higher resistor temperature is varied, and one where the resistor temperature is fixed while the higher capacitor temperature is varied. The temperature difference, as well as the direction of the temperature gradient, play an important role in the time dynamics of the motion and accumulation of charge on the ripple, as well as heat flow and work. While the work done by one component on the other increases linearly in temperature, the efficiency of the system peaks when the absolute temperature of the capacitor is a few times that of the resistor, suggesting that GEH systems could benefit greatly from having the graphene capacitor component in the proximity of a high-temperature heat dump.