Universal Temperature Crossover Behavior of Electrical Conductance in a Single Oligothiophene Molecular Wire

Lee, See Kei; Yamada, Ryo; Tanaka, Shoji; Chang, Gap Soo; Asai, Yoshihiro; Tada, Hayato

doi:10.1021/nn3006976

Cited by 42 publications

(42 citation statements)

References 33 publications

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“…Temperature-dependent transport with a small β-value has been associated with activated hopping between sites in both single molecules (35,36) and ensemble junctions (16,23), presumably governed by MarcusLevich kinetics. The low-V, high-T Arrhenius slopes of 150-300 meV listed in Table 1 are comparable to those reported for bulk polythiophene, e.g., 128-143 meV (37) and 280 meV (38), in which interchain charge transfer dominates transport (39,40).…”

Section: Resultsmentioning

confidence: 99%

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Yan

Bergren

McCreery

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

160

259

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In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d < 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling.all-carbon molecular junction | attenuation coefficient | field ionization | strong electronic coupling C harge transport mechanisms in organic and molecular electronics underlie the ultimate functionality of a new generation of electronic devices. Understanding, controlling, and designing molecular devices for use as practical components requires an intimate knowledge of the system energy levels and operative transport mechanisms, and how key variables such as molecule length, identity, temperature, etc., affect device performance parameters. Especially interesting in this context is the relationship between organic electronic devices, which typically have active layer thicknesses of tens to hundreds of nanometers, and molecular electronic devices reported to date, in which at least one dimension for charge propagation is below 10 nm. Indeed, many types of functional organic electronic devices have been demonstrated, including thinfilm transistors, organic light-emitting diodes, and memory cells (1, 2). Bridging the gap between organic and molecular devices may therefore reveal pathways for improving the performance of such devices, or even lead to new types of devices based on alternative transport mechanisms.The great majority of molecular electronic devices investigated to date have transport distances of <5 nm between the contacts, where the prevalent transport mechanism is quantum-mechanical tunneling. For this distance range, there is general agreement that the conductance scales exponentially with length, with an attenuation coefficient (β), defined as the slope of ln J vs. thickness (d), equal to 8 to 9 nm −1 for aliphatic molecules (3-6) and 2-3 nm −1 for aromatic molecules (7)(8)(9)(10)(11)(12)(13)(14). A few molecular electronic systems have been investigated beyond 5 nm (15, 16), some of which exhibit a decrease in β to less than 1 nm −1 . Such small values of β ar...

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Section: Resultsmentioning

confidence: 99%

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Yan

Bergren

McCreery

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

160

259

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“…However, if one's objective is to learn about electron-vibration interaction effects (inelastic scattering, heat generation, phonon transport, phonon damping, phonon cooling), that are intrinsic to the molecular entity, one should aim to reduce the "irrelevant" ballistic contribution, so as to observe signatures of electron-nuclei interaction effects, in particular, the tunneling-to-hopping crossover. This challenge is especially relevant to relatively short molecular junctions in which the three mechanisms discussed above can show up simultaneously, to confound the identification of the dominant transport mechanism [4][5][6][7][8][9]11,16,17,21,22,24,25 . In this paper, we propose a simple design for molecular junctions, with the objective to suppress phasecoherent resonant conduction.…”

Section: Introductionmentioning

confidence: 99%

Controlling charge transport mechanisms in molecular junctions: Distilling thermally induced hopping from coherent-resonant conduction

Kim

Segal

2017

The Journal of Chemical Physics

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The electrical conductance of molecular junctions may strongly depend on the temperature, and weakly on molecular length, under two distinct mechanisms: phase-coherent resonant conduction, with charges proceeding via delocalized molecular orbitals, and incoherent thermally-assisted multi-step hopping. While in the case of coherent conduction the temperature dependence arises from the broadening of the Fermi distribution in the metal electrodes, in the latter case it corresponds to electron-vibration interaction effects on the junction. With the objective to distill the thermally-activated hopping component, thus expose intrinsic electron-vibration interaction phenomena on the junction, we suggest the design of molecular junctions with "spacers", extended anchoring groups that act to filter out phase-coherent resonant electrons. Specifically, we study the electrical conductance of fixed-gap and variable-gap junctions that include a tunneling block, with spacers at the boundaries. Using numerical simulations and analytical considerations, we demonstrate that in our design, resonant conduction is suppressed. As a result, the electrical conductance is dominated by two (rather than three) mechanisms: superexchange (deep tunneling), and multi-step thermally-induced hopping. We further exemplify our analysis on DNA junctions with an A:T block serving as a tunneling barrier. Here, we show that the electrical conductance is insensitive to the number of G:C base-pairs at the boundaries. This indicates that the tunneling-to-hopping crossover revealed in such sequences truly corresponds to the properties of the A:T barrier.

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“…1); electron-donating substituents (Me−, MeO−) resulted in significantly higher junction conductances and the electron-deficient C 6 F 4 group resulted in a lower conductance [18]. Many studies of metal-molecule-metal junctions have probed the molecular structural requirements for obtaining high junction conductance [19][20][21][22][23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Resonant transport and electrostatic effects in single-molecule electrical junctions

et al. 2015

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In this contribution we demonstrate structural control over a transport resonance in HS(CH 2 ) n [1,4 − C 6 H 4 ](CH 2 ) n SH (n = 1, 3, 4, 6) metal-molecule-metal junctions, fabricated and tested using the scanning tunneling microscopy-based I (z) method. The Breit-Wigner resonance originates from one of the arene π -bonding orbitals, which sharpens and moves closer to the contact Fermi energy as n increases. Varying the number of methylene groups thus leads to a very shallow decay of the conductance with the length of the molecule. We demonstrate that the electrical behavior observed here can be straightforwardly rationalized by analyzing the effects caused by the electrostatic balance created at the metal-molecule interface. Such resonances offer future prospects in molecular electronics in terms of controlling charge transport over longer distances, and also in single-molecule conductance switching if the resonances can be externally gated.

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Universal Temperature Crossover Behavior of Electrical Conductance in a Single Oligothiophene Molecular Wire

Cited by 42 publications

References 33 publications

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

Controlling charge transport mechanisms in molecular junctions: Distilling thermally induced hopping from coherent-resonant conduction

Resonant transport and electrostatic effects in single-molecule electrical junctions

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