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Redox control of thermopower and figure of merit in phase-coherent molecular wires

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Redox control of thermopower and figure of merit in phase-coherent molecular wires. / Garcia-Suarez, Victor M.; Lambert, Colin J.; Manrique, David Zs et al.
In: Nanotechnology, Vol. 25, No. 20, 205402, 23.05.2014.

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Garcia-Suarez VM, Lambert CJ, Manrique DZ, Wandlowski T. Redox control of thermopower and figure of merit in phase-coherent molecular wires. Nanotechnology. 2014 May 23;25(20):205402. doi: 10.1088/0957-4484/25/20/205402

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Bibtex

@article{391193556a1e4a4db7deabee7e582560,
title = "Redox control of thermopower and figure of merit in phase-coherent molecular wires",
abstract = "We demonstrate how redox control of intra-molecular quantum interference in phase-coherent molecular wires can be used to enhance the thermopower (Seebeck coefficient) S and thermoelectric figure of merit ZT of single molecules attached to nanogap electrodes. Using first principles theory, we study the thermoelectric properties of a family of nine molecules, which consist of dithiol-terminated oligo (phenylene-ethynylenes) (OPEs) containing various central units. Uniquely, one molecule of this family possesses a conjugated acene-based central backbone attached via triple bonds to terminal sulfur atoms bound to gold electrodes and incorporates a fully conjugated hydroquinonecentral unit. We demonstrate that both S and the electronic contribution Z(el)T to the figure of merit ZT can be dramatically enhanced by oxidizing the hydroquinone to yield a second molecule, which possesses a cross-conjugated anthraquinone central unit. This enhancement originates from the conversion of the pi-conjugation in the former to cross-conjugation in the latter, which promotes the appearance of a sharp anti-resonance at the Fermi energy. Comparison with thermoelectric properties of the remaining seven conjugated molecules demonstrates that such large values of S and ZelT are unprecedented. We also evaluate the phonon contribution to the thermal conductance, which allows us to compute the full figure of merit ZT = Z(el)T/(1 + kappa(p)/kappa(el)), where kappa(p) is the phonon contribution to the thermal conductance and kappa(el) is the electronic contribution. For unstructured gold electrodes, kappa(p)/kappa(el) >> 1 and therefore strategies to reduce kappa(p) are needed to realize the highest possible figure of merit.",
keywords = "molecular wires, single molecule conductance, thermopower, OPE, quantum interference, SINGLE-MOLECULE, THERMOELECTRIC-MATERIALS, THERMAL CONDUCTANCE, JUNCTIONS, HETEROJUNCTIONS, TRANSPORT, ELECTRONICS, DEVICES",
author = "Garcia-Suarez, {Victor M.} and Lambert, {Colin J.} and Manrique, {David Zs} and Thomas Wandlowski",
year = "2014",
month = may,
day = "23",
doi = "10.1088/0957-4484/25/20/205402",
language = "English",
volume = "25",
journal = "Nanotechnology",
issn = "0957-4484",
publisher = "IOP Publishing Ltd.",
number = "20",

}

RIS

TY - JOUR

T1 - Redox control of thermopower and figure of merit in phase-coherent molecular wires

AU - Garcia-Suarez, Victor M.

AU - Lambert, Colin J.

AU - Manrique, David Zs

AU - Wandlowski, Thomas

PY - 2014/5/23

Y1 - 2014/5/23

N2 - We demonstrate how redox control of intra-molecular quantum interference in phase-coherent molecular wires can be used to enhance the thermopower (Seebeck coefficient) S and thermoelectric figure of merit ZT of single molecules attached to nanogap electrodes. Using first principles theory, we study the thermoelectric properties of a family of nine molecules, which consist of dithiol-terminated oligo (phenylene-ethynylenes) (OPEs) containing various central units. Uniquely, one molecule of this family possesses a conjugated acene-based central backbone attached via triple bonds to terminal sulfur atoms bound to gold electrodes and incorporates a fully conjugated hydroquinonecentral unit. We demonstrate that both S and the electronic contribution Z(el)T to the figure of merit ZT can be dramatically enhanced by oxidizing the hydroquinone to yield a second molecule, which possesses a cross-conjugated anthraquinone central unit. This enhancement originates from the conversion of the pi-conjugation in the former to cross-conjugation in the latter, which promotes the appearance of a sharp anti-resonance at the Fermi energy. Comparison with thermoelectric properties of the remaining seven conjugated molecules demonstrates that such large values of S and ZelT are unprecedented. We also evaluate the phonon contribution to the thermal conductance, which allows us to compute the full figure of merit ZT = Z(el)T/(1 + kappa(p)/kappa(el)), where kappa(p) is the phonon contribution to the thermal conductance and kappa(el) is the electronic contribution. For unstructured gold electrodes, kappa(p)/kappa(el) >> 1 and therefore strategies to reduce kappa(p) are needed to realize the highest possible figure of merit.

AB - We demonstrate how redox control of intra-molecular quantum interference in phase-coherent molecular wires can be used to enhance the thermopower (Seebeck coefficient) S and thermoelectric figure of merit ZT of single molecules attached to nanogap electrodes. Using first principles theory, we study the thermoelectric properties of a family of nine molecules, which consist of dithiol-terminated oligo (phenylene-ethynylenes) (OPEs) containing various central units. Uniquely, one molecule of this family possesses a conjugated acene-based central backbone attached via triple bonds to terminal sulfur atoms bound to gold electrodes and incorporates a fully conjugated hydroquinonecentral unit. We demonstrate that both S and the electronic contribution Z(el)T to the figure of merit ZT can be dramatically enhanced by oxidizing the hydroquinone to yield a second molecule, which possesses a cross-conjugated anthraquinone central unit. This enhancement originates from the conversion of the pi-conjugation in the former to cross-conjugation in the latter, which promotes the appearance of a sharp anti-resonance at the Fermi energy. Comparison with thermoelectric properties of the remaining seven conjugated molecules demonstrates that such large values of S and ZelT are unprecedented. We also evaluate the phonon contribution to the thermal conductance, which allows us to compute the full figure of merit ZT = Z(el)T/(1 + kappa(p)/kappa(el)), where kappa(p) is the phonon contribution to the thermal conductance and kappa(el) is the electronic contribution. For unstructured gold electrodes, kappa(p)/kappa(el) >> 1 and therefore strategies to reduce kappa(p) are needed to realize the highest possible figure of merit.

KW - molecular wires

KW - single molecule conductance

KW - thermopower

KW - OPE

KW - quantum interference

KW - SINGLE-MOLECULE

KW - THERMOELECTRIC-MATERIALS

KW - THERMAL CONDUCTANCE

KW - JUNCTIONS

KW - HETEROJUNCTIONS

KW - TRANSPORT

KW - ELECTRONICS

KW - DEVICES

U2 - 10.1088/0957-4484/25/20/205402

DO - 10.1088/0957-4484/25/20/205402

M3 - Journal article

VL - 25

JO - Nanotechnology

JF - Nanotechnology

SN - 0957-4484

IS - 20

M1 - 205402

ER -