A field emission device is configured as a heat engine, wherein the configuration of the heat engine is variable as a function of time. A method corresponding to a field emission device comprises applying an anode electric potential to an anode region that is greater than a cathode electric potential of a cathode region, applying a gate electric potential to a gate region to release a set of electrons from the cathode region, passing the set of electrons from the gate region to a suppressor region, applying a suppressor electric potential to decelerate the set of electrons between the suppressor region and the anode region, binding the set of electrons in the anode region, and varying at least one of the anode electric potential, gate electric potential, and suppressor electric potential as a function of time.