Probing the Chemistry of Molecular Heterojunctions Using Thermoelectricity

Baheti, Kanhayalal; Malen, Jonathan A.; Doak, Peter; Reddy, Pramod; Jang, Sung‐Yeon; Tilley, T. Don; Majumdar, Arun; Segalman, Rachel A.

doi:10.1021/nl072738l

Cited by 257 publications

(383 citation statements)

References 21 publications

(47 reference statements)

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“…To this end, significant progress has been achieved in performing thermoelectric measurements in molecular junctions [14][15][16][17] .…”

Section: Abstract: a Quantum Dots; D Tunnelingmentioning

confidence: 99%

Transient thermoelectricity in a vibrating quantum dot in Kondo regime

Goker¹,

Uyanik²

2012

Physics Letters A

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We investigate the time evolution of the thermopower in a vibrating quantum dot suddenly shifted into the Kondo regime via a gate voltage by adopting the time-dependent non-crossing approximation and linear response Onsager relations. Behaviour of the instantaneous thermopower is studied for a range of temperatures both in zero and strong electron-phonon coupling. We argue that inverse of the saturation value of decay time of thermopower to its steady state value might be an alternative tool in determination of the Kondo temperature and the value of the electron-phonon coupling strength. Keywords: A. Quantum dots; D. TunnelingInvestigation of time-dependent electron transport in single electron transistors has gained considerable traction lately as a result of tremendous advances in the burgeoning field of nanotechnology and their perceived potential to replace MOSFET transistors 1 one day. Development of quantum computers 2 and single electron guns 3 are expected to benefit from advances in detection of electrons in real time too 4 .Transient current ensuing after sudden shifting of the gate or bias voltage 5,6,8 displays different time scales 9,10 . For an asymmetrically coupled system, interference between the Kondo resonance and the sharp features in the contacts' density of states gives rise to oscillations in the long time scale 11 . Modeling the contacts' density of states in a realistic fashion via ab initio calculations yielded accurate predictions about transient current 12,13 .Measurement of thermopower (Seebeck coefficient) S can provide additional insight into transport experiments because its sign is a valuable tool to determine the alignment of orbitals of the impurity with respect to the Fermi levels of the contacts. To this end, significant progress has been achieved in performing thermoelectric measurements in molecular junctions [14][15][16][17] .Theoretical studies focused on incorporating strong correlation effects into this prototype. Kondo effect, arising from a hybridization between the net spin localized within the impurity and the electrons in the contacts, is a prime example of strong electronic correlations. Schemes employing Ng's ansatz 18 and Wilson's numerical renormalization group 19 both found that the sign of the thermopower can be adjusted by tuning the energy level of the quantum dot in the presence of Kondo correlations. When the electrodes are ferromagnetic, it was found that the thermopower is suppressed at low temperatures in parallel configuration and asymmetrically coupled antiparallel configuration 20 .Nevertheless, all of the aforementioned studies only took into account the steady state behaviour of thermoelectric transport and there was very little understanding of the temporal evolution of thermopower until now. Indeed, a recent work made the first attempt to elucidate the time-dependent behaviour of the Seebeck coefficient for a noninteracting system 21 . In this paper, we will take a step forward and study the transient response of thermopower for an interacting q...

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“…To this end, significant progress has been achieved in performing thermoelectric measurements in molecular junctions [14][15][16][17] .…”

Section: Abstract: a Quantum Dots; D Tunnelingmentioning

confidence: 99%

Transient thermoelectricity in a vibrating quantum dot in Kondo regime

Goker¹,

Uyanik²

2012

Physics Letters A

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“…5,7,[20][21][22][23][24][25][26][27][28][29] In the former, a gold nano-contact is created by stretching a gold wire and, just before rupture, a solution containing the target molecules is added to the system. Subsequently, the metallic contact is further stretched until rupture and in some cases the molecules remain trapped between the Au-Au tips forming the molecular junctions.…”

Section: Introductionmentioning

confidence: 99%

Stretching of BDT-gold molecular junctions: thiol or thiolate termination?

et al. 2014

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It is often assumed that the hydrogen atoms in the thiol groups of a benzene-1,4-dithiol dissociate when Au-benzene-1,4-dithiol-Au junctions are formed. We demonstrate, by stability and transport property calculations, that this assumption cannot be made. We show that the dissociative adsorption of methanethiol and benzene-1,4-dithiol molecules on a flat Au(111) surface is energetically unfavorable and that the activation barrier for this reaction is as high as 1 eV. For the molecule in the junction, our results show, for all electrode geometries studied, that the thiol junctions are energetically more stable than their thiolate counterparts. Due to the fact that density functional theory (DFT) within the local density approximation (LDA) underestimates the energy difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital by several electron-volts, and that it does not capture the renormalization of the energy levels due to the image charge effect, the conductance of the Au-benzene-1,4-dithiol-Au junctions is overestimated. After taking into account corrections due to image charge effects by means of constrained-DFT calculations and electrostatic classical models, we apply a scissor operator to correct the DFT energy level positions, and calculate the transport properties of the thiol and thiolate molecular junctions as a function of the electrode separation. For the thiol junctions, we show that the conductance decreases as the electrode separation increases, whereas the opposite trend is found for the thiolate junctions. Both behaviors have been observed in experiments, therefore pointing to the possible coexistence of both thiol and thiolate junctions. Moreover, the corrected conductance values, for both thiol and thiolate, are up to two orders of magnitude smaller than those calculated with DFT-LDA.This brings the theoretical results in quantitatively good agreement with experimental data.

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“…It can be compared to a tunneling barrier, which charge carriers have to overcome to generate a current. Ultraviolet photoelectron spectroscopy (UPS) 1 , thermopower [2][3][4] , and transition voltage spectroscopy (TVS) [5][6][7][8][9][10] represent current methods to estimate the relative alignment of the dominant molecular orbital from experimental data.…”

Section: Introductionmentioning

confidence: 99%

A quantum chemical study from a molecular transport perspective: ionization and electron attachment energies for species often used to fabricate single-molecule junctions

Bâldea

2014

Faraday Discuss.

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Abstract:The accurate determination of the lowest electron attachment (EA) and ionization (IP) energies for molecules embedded in molecular junctions is important for correctly estimating, e.g., the magnitude of the currents (I) or the biases (V ) where an I −V -curve exhibits a significant non-Ohmic behavior. Benchmark calculations for the lowest electron attachment and ionization energies of several typical molecules utilized to fabricate single-molecule junctions characterized by n-type conduction (4,4'-bipyridine, 1,4-dicyanobenzene, and 4,4'-dicyano-1,1'-biphenyl) and p-type conduction (benzenedithiol, biphenyldithiol, hexanemonothiol, and hexanedithiol] based on the EOM-CCSD (equation-of-motion coupled-cluster singles and doubles) state-of-the-art method of quantum chemistry are presented. They indicate significant differences from the results obtained within current approaches to molecular transport. The present study emphasizes that, in addition to a reliable quantum chemical method, basis sets much better than the ubiquitous double-zeta set employed for transport calculations are needed. The latter is a particularly critical issue for correctly determining EA's, which is impossible without including sufficient diffuse basis functions. The spatial distribution of the dominant molecular orbitals (MO's) is another important issue, on which the present study draws attention, because it sensitively affects the MO-energy shifts Φ due to image charges formed in electrodes. The present results cannot substantiate the common assumption of a point-like MO midway between electrodes, which substantially affects the actual Φ-values.

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Probing the Chemistry of Molecular Heterojunctions Using Thermoelectricity

Cited by 257 publications

References 21 publications

Transient thermoelectricity in a vibrating quantum dot in Kondo regime

Transient thermoelectricity in a vibrating quantum dot in Kondo regime

Stretching of BDT-gold molecular junctions: thiol or thiolate termination?

A quantum chemical study from a molecular transport perspective: ionization and electron attachment energies for species often used to fabricate single-molecule junctions

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