The Effect of Anchor Group on the Phonon Thermal Conductance of Single Molecule Junctions

There is a worldwide race to convert waste heat to useful energy using thermoelectric materials. Molecules are attractive candidates for thermoelectricity because they can be synthesised with the atomic precision, and intriguing properties due to quantum effects such as quantum interference can be induced at room temperature. Molecules are also expected to show a low thermal conductance that is needed to enhance the performance of thermoelectric materials. Recently, the technological challenge of measuring the thermal conductance of single molecules was overcome. Therefore, it is timely to develop strategies to reduce their thermal conductance for high performance thermoelectricity. In this paper and for the first time, we exploit systematically the effect of anchor groups on the phonon thermal conductance of oligo (phenylene ethynylene) (OPE3) molecules connected to gold electrodes via pyridyl, thiol, methyl sulphide and carbodithioate anchor groups. We show that thermal conductance is affected significantly by the choice of anchor group. The lowest and highest thermal conductances were obtained in the OPE3 with methyl sulphide and carbodithioate anchor groups, respectively. The thermal conductance of OPE3 with thiol anchor was higher than that with methyl sulphide but lower than the OPE3 with pyridyl anchor group.

Significantly enhanced thermoelectric performance of molecular junctions by the twist angle dependent phonon interference effect

The twist angle can induce phonon interference effect in the intermediately coupled molecular junctions and significantly suppress phonon thermal conductance.

Enhanced thermoelectric properties in nanowires of InAs modulated with multiple-stub structures

The thermoelectric properties of InAs nanowires modulated with the multiple-stub structures are studied using the scattering-matrix method. Owing to the very large surface-to-volume ratio, both the phonon and electron transport sensitively depend on the geometric structure. Carrier energy filtering which locally distorts electronic density of states strongly enhances the thermopower. Thus optimized thermopower, together with the significant reduction of the phonon thermal conductance, yields the high thermoelectric figure of merit ZT to 0.3∼1.9.