Single Molecule Conductance, Thermopower, and Transition Voltage

Guo, Shaoyin; Zhou, Gang; Tao, Nongjian

doi:10.1021/nl4021073

Cited by 83 publications

(110 citation statements)

References 34 publications

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“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 To end this section, we briefly compare our present results for Au-OPD-Au junctions with existing reports in the literature. [56][57][58][59][60] Here, it is important to distinguish between the magnitude of the currents (conductances) and the transition voltages. The currents measured by us are up to two order of magnitudes larger than those found for electromigrated junctions 56 …”

Section: Non-linear Bias Range (|V|>01 V); Tvs and Analysis Of The Hmentioning

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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Section: Non-linear Bias Range (|V|>01 V); Tvs and Analysis Of The Hmentioning

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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“…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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“…[2][3][4][5] Measuring the conductance of an individual molecule seems at first glance a rather simple task, since one only has to apply a voltage difference across both ends of the molecule and measure the current flowing through it. The problem is that, due to the small size of the molecule, it is very hard to connect it to macroscopic electrical contacts.…”

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confidence: 99%

Research Update: Molecular electronics: The single-molecule switch and transistor

et al. 2014

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In order to design and realize single-molecule devices it is essential to have a good understanding of the properties of an individual molecule. For electronic applications, the most important property of a molecule is its conductance. Here we show how a single octanethiol molecule can be connected to macroscopic leads and how the transport properties of the molecule can be measured. Based on this knowledge we have realized two single-molecule devices: a molecular switch and a molecular transistor. The switch can be opened and closed at will by carefully adjusting the separation between the electrical contacts and the voltage drop across the contacts. This single-molecular switch operates in a broad temperature range from cryogenic temperatures all the way up to room temperature. Via mechanical gating, i.e., compressing or stretching of the octanethiol molecule, by varying the contact's interspace, we are able to systematically adjust the conductance of the electrode-octanethiol-electrode junction. This two-terminal single-molecule transistor is very robust, but the amplification factor is rather limited.

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Single Molecule Conductance, Thermopower, and Transition Voltage

Cited by 83 publications

References 34 publications

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

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

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

Research Update: Molecular electronics: The single-molecule switch and transistor

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