Thermo-Electrical Conduction of the 2,7-Di([1,1'-Biphenyl]-4-yl)-9H-Fluorene Molecular System: Coupling between Benzene Rings and Stereoelectronic Effects

Theoretical and analytical thermal and electrical properties are studied through the 2,7-Di([1,1′-biphenyl]-4-yl)-9H-fluorene aromatic system as a prototype of a molecular switch. Variations of the dihedral angles between the two Benzene rings at each end of the molecule have been considered, thus determining the dependence on the structural variation of the molecule when the aromatic system is connected between metal contacts. The molecule is modeled through a Tight-Binding Hamiltonian where—from the analytical process of decimation and using Green’s functions—the probability of transmission (T) is calculated by using the Fisher–Lee relationship. Consequently, the thermal and electrical transport properties such as I−V curves, quantum noise (S), Fano factor (F), electrical conductance (G), thermal conductance (κ), Seebeck coefficient (Q), and merit number (ZT) are calculated. The available results offer the possibility of designing molecular devices, where the change in conductance or current induced by a stereoelectronic effect on the molecular junctions (within the aromatic system) can produce changes on the insulating–conductive states.

Tuning the thermoelectric response of silicene nanoribbons with vacancies

In this work, we present a thorough study of the thermoelectric properties of silicene nanoribbons in the presence of a random distribution of atomic vacancies. By using a linear approach within the Landauer formalism, we calculate phonon and electron thermal conductances, the electric conductance, the Seebeck coefficient and the figure of merit of the nanoribbons. We found a sizable reduction of the phonon thermal conductance as a function of the vacancy concentration over a wide range of temperature. At the same time, the electric properties are not severely deteriorated, leading to an overall remarkable thermoelectric efficiency. We conclude that the incorporation of vacancies paves the way for designing better and more efficient nanoscale thermoelectric devices.

Thermal transport and spin-dependent Seebeck effect in parallel step-like zigzag graphene nanoribbon junctions

By using nonequilibrium molecular dynamics, thermal transport through a series of parallel step-like graphene nanoribbon (GNR) junctions is investigated. The theoretical results show that the thermal current flows preferentially from wide GNRs to narrow ones, displaying a pronounced thermal rectification effect. Moreover, several step-like GNR-based devices are designed, and the thermally driven spin-dependent currents are calculated by using density functional theory combined with the nonequilibrium Green's function approach. We find that thermal spin-dependent currents with opposite flow directions are generated when a temperature gradient is applied along the GNRs, indicating the occurrence of a spin-dependent Seebeck effect (SDSE). More interestingly, a negative differential SDSE occurs in the thermal spin currents, and the odd and even law appears in the spin-dependent currents, thermopowers and thermoelectric conversion efficiencies. Our theoretical results indicate that the parallel step-like GNRs are potential candidates to design spin caloritronics devices hosting thermal rectification and multiple thermal-spin transport functionalities.

Thermal Properties of Ordered and Disordered DNA Chains: Efficient Energy Conversion

Considering the numerous possibilities of having suitable thermoelectric energy conversion at nano-scale level, especially for molecular systems, in the present work we put forward a new proposal along this using a flat DNA segment as a functional element. It is modeled by coupling two chains to a form a two-stranded ladder like geometry, with interactions to first neighbors, within the tight-binding prescription. We critically investigate electrical and thermal properties of DNA molecule depending on the length of the system, temperature, molecule-to-lead coupling and the degree of (correlated) disorder. Our analysis might be helpful in analyzing thermoelectric signatures of correlated and uncorrelated disordered systems, and can be verified in laboratory.