Molecular Electronic Junctions Achieved High Thermal Switch Ratios in Atomistic Simulations

Abstract

The development of devices that improve thermal energy management requires thermal regulation with efficiency comparable to the ratios R ∼ 10 5 in electric regulation. Unfortunately, current materials and devices in thermal regulators have only been reported to achieve R ∼ 10. We use atomistic simulations to demonstrate that Ferrocenyl (Fc) molecules under applied external electric fields can alter charge states and achieve high thermal switch ratios R = G q /G 0 , where G q and G 0 are the high and low limiting conductances. When an electric field is applied, Fc molecules are positively charged, and the SAM-Au interfacial interaction is strong, leading to high heat conductance G q . On the other hand, with no electric field, the Fc molecules are charge neutral and the SAM-Au interfacial interaction is weak, leading to low heat conductance G 0 . We optimized various design parameters for the device performance, including the Au-to-Au gap distance L, the system operation temperature T, the net charge on Fc molecules q, the Au surface charge number Z, and the SAM number N. We find that G q can be very large and increases with increasing q, Z, or N, while G 0 is near 0 at L > 3.0 nm. As a result, R > 100 was achieved for selected parameter ranges reported here.