Ambipolar transition voltage spectroscopy: Analytical results and experimental agreement

Bâldea, Ioan

doi:10.1103/physrevb.85.035442

Cited by 143 publications

(302 citation statements)

References 32 publications

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“…‡ E-mail: ioan.baldea@pci.uni-heidelberg.de. Also at National Institute for Lasers, Plasmas, and Radiation Physics, Institute of Space Sciences, Bucharest, Romania can be quantitatively reproduced by assuming that molecular transport is dominated by a single level (to be identified with HOMO or LUMO) 7,9,[11][12][13][14] . This is an enormous simplification.…”

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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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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“…Besides the zero-bias resistance R, ℎ = − (the HOMO position with respect to the Fermi level EF) is a basic quantity of this approach. 47 In a non-resonant situation (which turned out to be the case for all our junctions), ℎ can be found straightforwardly from the minimum V=Vt in a Fowler-Nordheim (F-N) plot of the same I-V characteristic. The transition voltage Vt is a characteristic voltage evident by inspection of the F-N plot, that can be related analytically to ℎ (see Eqs.…”

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confidence: 99%

Experimental and Theoretical Analysis of Nanotransport in Oligophenylene Dithiol Junctions as a Function of Molecular Length and Contact Work Function

et al. 2015

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We report the results of an extensive investigation of metal-molecule-metal tunnel junctions based on oligophenylene dithiols (OPDs) bound to several types of electrodes (M1-S-(C6H4)n-S-M2, with 1 ≤ n ≤ 4 and M1,2 = Ag, Au, Pt) to examine the impact of molecular length (n) and metal work function (Φ) on junction properties. Our investigation includes (1) measurements by scanning Kelvin probe microscopy of electrode work function changes (ΔΦ = ΦSAM - Φ) caused by chemisorption of OPD self-assembled monolayers (SAMs), (2) measurements of junction current-voltage (I-V) characteristics by conducting probe atomic force microscopy in the linear and nonlinear bias ranges, and (3) direct quantitative analysis of the full I-V curves. Further, we employ transition voltage spectroscopy (TVS) to estimate the energetic alignment εh = EF - EHOMO of the dominant molecular orbital (HOMO) relative to the Fermi energy EF of the junction. Where photoelectron spectroscopy data are available, the εh values agree very well with those determined by TVS. Using a single-level model, which we justify via ab initio quantum chemical calculations at post-density functional theory level and additional UV-visible absorption measurements, we are able to quantitatively reproduce the I-V measurements in the whole bias range investigated (∼1.0-1.5 V) and to understand the behavior of εh and Γ (contact coupling strength) extracted from experiment. We find that Fermi level pinning induced by the strong dipole of the metal-S bond causes a significant shift of the HOMO energy of an adsorbed molecule, resulting in εh exhibiting a weak dependence with the work function Φ. Both of these parameters play a key role in determining the tunneling attenuation factor (β) and junction resistance (R). Correlation among Φ, ΔΦ, R, transition voltage (Vt), and εh and accurate simulation provide a remarkably complete picture of tunneling transport in these prototypical molecular junctions.

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“…The Trp indole ring of W-7 is apparently sufficiently close to the top Au electrode to increase the interface coupling term, T C , ∼5× compared with the other Ala-terminated peptides (SI Appendix, section SI-5). the Landauer formula (20,59), simplified by ignoring all transmission function features, except for one peak. The energy position of this peak, « 0 (see the dashed line in Fig.…”

Section: Significancementioning

confidence: 99%

Tuning electronic transport via hepta-alanine peptides junction by tryptophan doping

Guo

Refaely-Abramson

et al. 2016

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

111

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Charge migration for electron transfer via the polypeptide matrix of proteins is a key process in biological energy conversion and signaling systems. It is sensitive to the sequence of amino acids composing the protein and, therefore, offers a tool for chemical control of charge transport across biomaterial-based devices. We designed a series of linear oligoalanine peptides with a single tryptophan substitution that acts as a "dopant," introducing an energy level closer to the electrodes' Fermi level than that of the alanine homopeptide. We investigated the solid-state electron transport (ETp) across a selfassembled monolayer of these peptides between gold contacts. The single tryptophan "doping" markedly increased the conductance of the peptide chain, especially when its location in the sequence is close to the electrodes. Combining inelastic tunneling spectroscopy, UV photoelectron spectroscopy, electronic structure calculations by advanced density-functional theory, and dc current-voltage analysis, the role of tryptophan in ETp is rationalized by charge tunneling across a heterogeneous energy barrier, via electronic states of alanine and tryptophan, and by relatively efficient direct coupling of tryptophan to a Au electrode. These results reveal a controlled way of modulating the electrical properties of molecular junctions by tailormade "building block" peptides. oligopeptide | electron transport | self-assembled monolayer | inelastic electron tunneling spectroscopy | doping E lectron transfer (ET) processes taking place between prosthetic groups across the polypeptide matrices of proteins (1-3) have been extensively explored by, e.g., time-resolved photolysis (4, 5), pulse radiolysis (6, 7), scanning tunneling microscopy (8, 9), electrochemical methods (10-12), and by theoretical studies (13-16). The surprisingly fast and efficient ET over considerable distances (up to ∼25 Å) (17) via peptide matrices in proteins suggests possible development of peptide-and protein-based bioelectronics with diverse functionality and relative ease of modification (18,19). Studying electron transport (ETp) via solid-state molecular junctions represents an approach, bridging the study of basic ET-related phenomena and electronic devices, where measuring ET rates as a function of an electrochemical driving force is replaced by measuring current across molecular junctions as a function of an applied electrical voltage (20). Combining the concepts and methods of molecular electronics such as currentvoltage (I-V) line-shape analysis (21, 22), temperature-dependent measurements (23, 24), and electronic spectroscopy techniques (25-27) may yield new insights into the mechanism of ETp across the peptide matrix of proteins (28-30) and pave the road to peptide-and protein-based electronic devices for switching, rectification, and memory (18, 31).ETp via homopeptides has been investigated, probing the roles of specific amino acid residues, their protonation, and secondary structure (29,32). Synthetic heteropeptides with defined compositi...

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Ambipolar transition voltage spectroscopy: Analytical results and experimental agreement

Cited by 143 publications

References 32 publications

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

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

Experimental and Theoretical Analysis of Nanotransport in Oligophenylene Dithiol Junctions as a Function of Molecular Length and Contact Work Function

Tuning electronic transport via hepta-alanine peptides junction by tryptophan doping

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