Electrostatic control of thermoelectricity in molecular junctions, Youngsang Kim, Wonho Jeong, Kyeongtae Kim, Woochul Lee and Pramod Reddy, Nature Nanotechnology (5 October 2014)
Molecular junctions hold significant promise for efficient and high-power-output thermoelectric energy conversion. Recent experiments have probed the thermoelectric properties of molecular junctions. However, electrostatic control of thermoelectric properties via a gate electrode has not been possible due to technical challenges in creating temperature differentials in three-terminal devices. Here, we show that extremely large temperature gradients (exceeding 1 × 109 K m−1) can be established in nanoscale gaps bridged by molecules, while simultaneously controlling their electronic structure via a gate electrode. Using this platform, we study prototypical Au–biphenyl-4,4′-dithiol–Au and Au–fullerene–Au junctions to demonstrate that the Seebeck coefficient and the electrical conductance of molecular junctions can be simultaneously increased by electrostatic control. Moreover, from our studies of fullerene junctions, we show that thermoelectric properties can be significantly enhanced when the dominant transport orbital is located close to the chemical potential (Fermi level) of the electrodes. These results illustrate the intimate relationship between the thermoelectric properties and charge transmission characteristics of molecular junctions and should enable systematic exploration of the recent computational predictions that promise extremely efficient thermoelectric energy conversion in molecular junctions.
See also : http://arxiv.org/abs/1106.5208
Thermoelectric transport with electron-phonon coupling and electron-electron interaction in molecular junctions, Jie Ren, Jian-Xin Zhu, James E. Gubernatis, Chen Wang and Baowen Li, Phys. Rev. B, 85, 155443 (23 April 2012)
Within the framework of nonequilibrium Green’s functions, we investigate the thermoelectric transport in a single molecular junction with electron-phonon and electron-electron interactions. By transforming into a displaced phonon basis, we are able to deal with these interactions nonperturbatively. Then, by invoking the weak tunneling limit, we are able to calculate the thermoelectricity. Results show that at low temperatures, resonances of the thermoelectric figure of merit, ZT, occur around the sides of resonances of electronic conductance but drop dramatically to zero at exactly these resonant points. We find ZT can be enhanced by increasing electron-phonon coupling and Coulomb repulsion, and an optimal enhancement is obtained when these two interactions are competing. Our results indicate a great potential for single molecular junctions as good thermoelectric devices over a wide range of temperatures.