Thermal conductance and thermoelectric figure of merit of 
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-based single-molecule junctions: Electrons, phonons, and photons

Klöckner, Jan-Christopher; Siebler, Robert; Cuevas, Juan Carlos; Pauly, Fabian

doi:10.1103/physrevb.95.245404

Cited by 44 publications

(52 citation statements)

References 61 publications

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“…This regime is still challenging for experimentalists, since signals are rather small and contamination of surfaces may play a crucial role [79]. Moreover, as the gap between the electrodes increases, at some point the thermal radiation via photon tunneling may give a contribution of similar order [54]. show that in the tunneling regime the electronic Lorentz ratio L el /L 0 stays close to 1.…”

Section: Dft-based Transport Results: Phonon Transportmentioning

confidence: 99%

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Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

et al. 2017

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], we present here an extensive theoretical analysis of the thermal conductance of atomic-size contacts made of three different metals, namely gold (Au), platinum (Pt), and aluminum (Al). The main goal of this work is to elucidate the role of phonons in the thermal transport through these atomic contacts as well as to study the validity of the Wiedemann-Franz law, which relates the electrical and the thermal conductance. For this purpose, we have employed two different custom-developed theoretical approaches. The first one is a transport method based on density functional theory (DFT) that allows one to accurately compute the contributions of both electrons and phonons to the thermal transport in few-atom-thick contacts. The second technique is based on a combination of classical molecular dynamics (MD) simulations and a tight-binding model that enables the efficient calculation of the electronic contribution to the thermal conductance of atomic contacts of larger size. Our DFT-based calculations show that the thermal conductance of few-atom contacts of Au and Pt is dominated by electrons, with phonons giving a contribution typically below 10% of the total thermal conductance, depending on the contact geometry. For these two metals we find that the small deviations from the Wiedemann-Franz law, reported experimentally, largely stem from phonons. In the case of Al contacts we predict that the phononic contribution can be considerably larger with up to 40% of the total thermal conductance. We show that these differences in the phononic contribution across metals originate mainly from their distinct Debye energies. On the other hand, our MD-based calculations demonstrate that the electronic contribution to the thermal conductance follows very closely the Wiedemann-Franz law, irrespective of the material and the contact size. Finally, the ensemble of our results consistently shows that the reported observation of quantized thermal transport at room temperature is restricted to few-atom contacts of Au, a monovalent metal in which the transport is dominated by the s valence orbitals. In the case of multivalent metals like Pt and Al this quantization is statistically absent due to the fact that additional orbitals contribute to the transport with conduction channels that have intermediate transmissions between 0 and 1, even in the case of single-atom contacts.

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Section: Dft-based Transport Results: Phonon Transportmentioning

confidence: 99%

“…(5), we use our previous work [23,40,53,54] and combine DFT and NEGF techniques in the same spirit as for the electron transport. Briefly our starting point is the description of the phonons or vibrational modes of the atomic contacts within the harmonic approximation.…”

Section: Phonon Transportmentioning

confidence: 99%

Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

et al. 2017

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“…The goal is to show that in these junctions the thermal transport is dominated by phonons and that the interference effects, predicted here, should therefore be observable experimentally. We neglect contributions to the thermal conductance from near field radiative heat transfer, whose significance can be controlled by the macroscopic shape of the electrodes 57 . As in the phononic case we assume that the electronic transport is dominated by elastic tunneling processes.…”

Section: Discussionmentioning

confidence: 99%

“…We compute the transmission function τ pn (E) by means of a combination of DFT and non-equilibrium Green's function techniques, as we have described in detail in Refs. [55][56][57].…”

Section: Theoretical Methodsmentioning

confidence: 99%

Tuning the thermal conductance of molecular junctions with interference effects

2017

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We present an ab initio study of the role of interference effects in the thermal conductance of single-molecule junctions. To be precise, using a first-principles transport method based on density functional theory, we analyze the coherent phonon transport in single-molecule junctions made of several benzene and oligo-phenylene-ethynylene derivatives. We show that the thermal conductance of these junctions can be tuned via the inclusion of substituents, which induces destructive interference effects and results in a decrease of the thermal conductance with respect to the unmodified molecules. In particular, we demonstrate that these interference effects manifest as antiresonances in the phonon transmission, whose energy positions can be tuned by varying the mass of the substituents. Our work provides clear strategies for the heat management in molecular junctions and more generally in nanostructured metal-organic hybrid systems, which are important to determine, how these systems can function as efficient energy-conversion devices such as thermoelectric generators and refrigerators.

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“…A major problem that currently remains for singlemolecule analysis methods that has yet to be solved is that thermal conductivity measurements of SMJs are difficult to conduct. 135,136 In addition to technical problems such as how to apply a thermal gradient to an SMJ that is only several nanometers in size or how to actually measure the temperature of an SMJ, there is also the fundamental issue that the temperature obtained from such measurements has not yet been defined. This problem also applies to the temperature obtained from the lifetime measurements in an SMJ.…”

Section: Perspectivementioning

confidence: 99%

Single-Molecule Analysis Methods Using Nanogap Electrodes and Their Application to DNA Sequencing Technologies

Taniguchi

2017

Bulletin of the Chemical Society of Japan

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Single-molecule analysis methods facilitate the investigation of the properties of single-molecule junctions (SMJs), in which single molecules are connected between a pair of nanoelectrodes that use nanogap electrodes having a spacing of less than several nanometers. Various methods have been developed to investigate numerous useful parameters for SMJs; for example, the number of molecules connected between a pair of nanoelectrodes can be determined, the types and structures of single molecules can be revealed, localized temperatures within SMJs can be evaluated, and the Seebeck coefficient and the bond strength between single molecules and electrodes can be ascertained. Single-molecule analysis methods have also been used to analyze biopolymers in solutions, and this has resulted in single-molecule sequencing technologies being developed that can determine sequences of base molecules in DNA and RNA along with sequences of amino acids in peptides. Singlemolecule analysis methods are expected to develop into digital analysis techniques that can be used to investigate the physical and chemical properties of molecules at single-molecule resolutions.

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Thermal conductance and thermoelectric figure of merit of C60 -based single-molecule junctions: Electrons, phonons, and photons

Cited by 44 publications

References 61 publications

Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

Thermal conductance of metallic atomic-size contacts: Phonon transport and Wiedemann-Franz law

Tuning the thermal conductance of molecular junctions with interference effects

Single-Molecule Analysis Methods Using Nanogap Electrodes and Their Application to DNA Sequencing Technologies

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