Interpretation of Transition Voltage Spectroscopy

Huisman, E. H.; Guedon, Constant M.; Wees, B. J. van; Molen, Sense Jan van der

doi:10.1021/nl9021094

Cited by 220 publications

(350 citation statements)

References 37 publications

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“…[13][14][15][16]23,65,66 In most cases the evidence for hole tunneling is based on transport across relatively short alkyl chains, up to C12, and is indirect. An exception is the measurement of thermo-power (Seebeck coefficient), where the positive coefficient was taken as direct evidence for hole / HOSO-mediated tunneling.…”

Section: Resultsmentioning

confidence: 99%

“…22 In spite of this apparent discrepancy, HOMOdominated transport is the prevailing concept for such junctions. [13][14][15][16]23,24 In the present study we challenge this concept and find that transport is dominated by the energy difference between the Fermi level and the lowest unoccupied molecular orbital (LUMO) of the molecules.…”

Section: Introductionmentioning

confidence: 80%

“…This finding agrees with complementary spectroscopic measurements of the samples without Hg contact, but challenges the prevailing concept of HOMO-dominated transport. [13][14][15][16]23,24 Highly doped n ++ -and p ++ -Si-C n H 2n+1 /Hg junctions (n = 2, 14,16,18) were prepared by alkylation of freshly etched P-or B-doped (N d/a ≈ 10 19 cm −3 ) Si(1 1 1) surfaces. Detailed descriptions of the preparation and characterization of both 'long' (C14-C18) and 'short' alkyl chain (C2) samples can be found elsewhere 26,27,69 …”

Section: Introductionmentioning

confidence: 99%

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Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Yaffe

Scheres

et al. 2012

Phys. Rev. B

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We compare the charge transport characteristics of heavy doped p ++ -and n ++ -Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS) results for the molecule-Si band alignment at equilibrium show the Fermi level to LUMO energy difference to be much smaller than the corresponding Fermi level to HOMO one. This result supports the conclusion we reach, based on negative differential resistance in an analogous semiconductor-inorganic insulator/metal junction, that for both p ++ -and n ++ -type junctions the energy difference between the Fermi level and LUMO, i.e., electron tunneling, controls charge transport. The Fermi level-LUMO energy difference, experimentally determined by IPES, agrees with the non-resonant tunneling barrier height deduced from the exponential length-attenuation of the current.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

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Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Yaffe

Scheres

et al. 2012

Phys. Rev. B

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“…At V = +0.5 V, rates of charge tunneling follow (qualitatively) the Simmons equation (eq 1); in addition, values of tunneling current across SAMs of the full set of nalkanethiolates (SC n , with n = 1−18) fall within the operative range of our electrometer (105 mA to 0.1 nA). At voltages > +0.5 V (< −0.5 V), resonances of the Fermi levels of the electrodes with molecular or interfacial electronic states lead to nonlinear variation of J 0 with V, 54 and the approximate Simmons equation does not describe charge tunneling adequately. In this paper we do not explore the high-bias regime.…”

Section: 19mentioning

confidence: 99%

Defining the Value of Injection Current and Effective Electrical Contact Area for EGaIn-Based Molecular Tunneling Junctions

et al. 2013

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Analysis of rates of tunneling across self-assembled monolayers (SAMs) of n-alkanethiolates SC n (with n = number of carbon atoms) incorporated in junctions having structure Ag TS -SAM//Ga 2 O 3 /EGaIn leads to a value for the injection tunnel current density J 0 (i.e., the current flowing through an ideal junction with n = 0) of 10 3.6±0.3 A·cm −2 (V = +0.5 V). This estimation of J 0 does not involve an extrapolation in length, because it was possible to measure current densities across SAMs over the range of lengths n = 1−18. This value of J 0 is estimated under the assumption that values of the geometrical contact area equal the values of the effective electrical contact area. Detailed experimental analysis, however, indicates that the roughness of the ). A comparison of the characteristics of conical Ga 2 O 3 / EGaIn tips with the characteristics of other top-electrodes suggests that the EGaIn-based electrodes provide a particularly attractive technology for physical-organic studies of charge transport across SAMs. ■ INTRODUCTIONMeasurements, using a number of techniques, of rates of charge transport by tunneling across self-assembled monolayers (SAMs) of n-alkanethiolates on silver and gold substrates show an interesting, puzzling, and unresolved mixture of consistency and inconsistency. Rates of tunneling across these SAMs follow the simplified Simmons equation,( 1) with the falloff in current density J(V) (A·cm ). Using mercury drops as top-electrodes, measurements of rates of tunneling across n-alkanes anchored to heavily doped silicon surfaces led to β = 0.9 ± 0.2 nC −1 , similar to the values observed for nalkanethiolates on Au and Ag substrates. , observed in large-area junctions using, as top-electrodes, conductive polymers, 13 Hg-drops supporting an insulating organic film (Hg-SAM), 14−16 and Ga 2 O 3 /EGaIn tips. 17−20 Why is there high consistency in values of β, but broad inconsistency in values of J 0 (V) within these systems?A priori, at least four factors might contribute to differences in J 0 (V) among methods of measurements:(i) In large-area junctions, assuming that the effective electrical contact area (A elec )the area through which current actually passescoincides with the geometrical contact area (A geo ) estimated by optical microscopy could result in errors in the conversions of values of current into current densities. Contact between surfaces occurs only through asperities distributed on the surfaces, which are always rough to some extent; in addition, only a fraction of the true, physical contact area is conductive.21−24 Estimations of the effective contact area from measurements of adhesion and friction between surfaces indicate that values of A elec /A geo vary in the range 10 −2 −10 −4 , depending on the hardness of the materials, the heights, widths, and number of asperities on both surfaces, and loads applied to the contacts. 22,23,25−27

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“…6 Only within the molecular transport picture, V trans can be directly scaled with Φ B , thus giving valid information on molecular energy levels. Therefore, our findings from length-dependent TVS measurements provide additional verification of the molecular junction formation by CAFM.…”

Section: 4mentioning

confidence: 99%

Charge Transport in Metal-Molecule-Metal Junctions Probed by Conducting Atomic Force Microscopy

Lee¹,

Song

2013

Bulletin of the Korean Chemical Society

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Interpretation of Transition Voltage Spectroscopy

Cited by 220 publications

References 37 publications

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Defining the Value of Injection Current and Effective Electrical Contact Area for EGaIn-Based Molecular Tunneling Junctions

Charge Transport in Metal-Molecule-Metal Junctions Probed by Conducting Atomic Force Microscopy

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