Length‐Dependent Conductance of Molecular Wires and Contact Resistance in Metal–Molecule–Metal Junctions

Li, Hongmei; Wang, Nan; Zhao, Jianwei; Guo, Yan; Yin, Xian‐Hong; Boey, Freddy Yin Chiang; Zhang, Hua

doi:10.1002/cphc.200800032

Cited by 112 publications

(131 citation statements)

References 88 publications

Supporting

Mentioning

108

Contrasting

Order By: Relevance

“…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 .…”

mentioning

confidence: 84%

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.

156

259

View full text Add to dashboard Cite

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...

show abstract

mentioning

confidence: 84%

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.

156

259

View full text Add to dashboard Cite

show abstract

“…Calculations using different formalisms resulted in ␤ = 0.17-0.51 Å −1 . [25][26][27][28][29][30][31][32][33] Kondo et al 27 and Liu et al 31 have studied the influence of the ring torsion angle between the phenyl rings and found ␤ as low as 0.17 and 0.24 Å −1 for planar para-phenylene systems, i.e., no torsion angle between adjacent phenyl rings. The experimentally determined coefficients in large-area molecular junctions match closely to these values.…”

Section: Electrical Characteristics Of Conjugated Self-assembled Monomentioning

confidence: 99%

Electrical characteristics of conjugated self-assembled monolayers in large-area molecular junctions

et al. 2010

View full text Add to dashboard Cite

“…In each model, the molecule was sandwiched between two equilateral triangles of Au atoms, with an Au-Au bond length of 2.88 Å. 10,31,32 The thiol lost a hydrogen atom when it attached to the gold triangle, making a strong covalent bond with Au atoms, providing the good electrical contact between the organic molecule and the metal electrode. In our calculation, we considered sulfur atom chemisorbed at the hollow site of the Au cluster, which is energetically favorable.…”

Section: A Geometric Optimizationmentioning

confidence: 99%

“…9 Both experimental and theoretical investigations inferred that many factors affect the transportation behavior of a molecular junction. Among them, the intrinsic property of the molecules, 10 including their length, 10,11 conformation, 12 the charged state, 13 the gap between the highest occupied molecular orbital ͑HOMO͒ and the lowest unoccupied molecular orbital ͑LUMO͒, 10 and the alignment of the energy gap to the metal Fermi level, 14 interaction from the neighboring molecules, 15 and anchoring group 16 received special attention. The particular electron transfer pathway has been considered recently.…”

Section: Introductionmentioning

confidence: 99%

Nonequilibrium Green’s function study on the electronic structure and transportation behavior of the conjugated molecular junction: Terminal connections and intramolecular connections

Zhao

et al. 2009

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

In the recent density functional-based calculations, it was found that the conductivity of naphthalene molecular wires can be modulated by altering the linking position of the molecule to the electrode ͓D. Walter, D. Neuhauser, and R. Baer, Chem. Phys. 299, 139 ͑2004͔͒. A quantum interference model was proposed to interpret the observation. In this paper, we further studied the conductance of a series of conjugated molecules containing aromatic rings using density functional theory combined with nonequilibrium Green's function method. For polyacene systems with different terminal connections, the conductivity is dependent on the substitution position of anchoring groups even with similar electron transport distance. The conductance of trans-substitution can be ten times or more as large as that of the cis-substitution. However, for the biphenyl system with different intramolecular connections, adding more connections between two benzene rings does not change the junction conductance. All these results indicate that the junction conductance is strongly dependent on the particular electron transport pathway. The alternating double-single linkage is the most probable one, since others are impeded by the single bonds.

show abstract

Length‐Dependent Conductance of Molecular Wires and Contact Resistance in Metal–Molecule–Metal Junctions

Cited by 112 publications

References 88 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

Electrical characteristics of conjugated self-assembled monolayers in large-area molecular junctions

Nonequilibrium Green’s function study on the electronic structure and transportation behavior of the conjugated molecular junction: Terminal connections and intramolecular connections

Contact Info

Product

Resources

About