Adventures in molecular electronics: how to attach wires to molecules

Haynie, Brendan C.; Walker, Amy V.; Tighe, Timothy B.; Winograd, Nicholas

doi:10.1016/s0169-4332(02)00695-5

Cited by 78 publications

(117 citation statements)

References 7 publications

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“…Early devices utilized vapor-deposited titanium as an adhesion layer for further metal deposition, in part to form a Ti-C bond which prevented penetration of metals into the monolayer. [14,59,123] Later work reported that Ti reacts with a SAM [124] or L-B film, [125] with possibly severe structural changes. In addition, Ti can oxidize during deposition, resulting in a molecule/TiOx/Ti (TiOx ¼ titanium oxide) structure with different properties from that of a molecule/metal device.…”

Section: Progress With Ensemble Molecular Junctionsmentioning

confidence: 99%

“…[6,49] A detailed study of metal deposition on SAMs revealed that penetration channels were formed through lateral motion of the thiolate molecules such that after deposition, the vapor-deposited metal was observed to be located on the substrate, with thiolate molecules re-adsorbing on top of the deposited metal. [124,130,131] Unfortunately, the same lateral restructuring of a thiolate SAM that permits a high degree of ordering to be obtained during assembly also permits metal penetration and causes relatively low thermal stability. Au readily penetrates L-B structures as well, although a soft deposition technique involving a cooled sample and an Ar backpressure to thermalize evaporated atoms has proven successful for Au, [132][133][134] Pb, and Al top contacts.…”

Section: Progress With Ensemble Molecular Junctionsmentioning

confidence: 99%

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Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

2009

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Molecular electronics seeks to incorporate molecular components as functional elements in electronic devices. There are numerous strategies reported to date for the fabrication, design, and characterization of such devices, but a broadly accepted example showing structure-dependent conductance behavior has not yet emerged. This progress report focuses on experimental methods for making both single-molecule and ensemble molecular junctions, and highlights key results from these efforts. Based on some general objectives of the field, particular experiments are presented to show progress in several important areas, and also to define those areas that still need attention. Some of the variable behavior of ostensibly similar junctions reported in the literature is attributable to differences in the way the junctions are fabricated. These differences are due, in part, to the multitude of methods for supporting the molecular layer on the substrate, including methods that utilize physical adsorption and covalent bonds, and to the numerous strategies for making top contacts. After discussing recent experimental progress in molecular electronics, an assessment of the current state of the field is presented, along with a proposed road map that can be used to assess progress in the future.

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Section: Progress With Ensemble Molecular Junctionsmentioning

confidence: 99%

Section: Progress With Ensemble Molecular Junctionsmentioning

confidence: 99%

Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

2009

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“…For instance, migration of metal atoms from the surface of one electrode to the second electrode may result in a highly conductive pathway (or filament) between the electrodes through which electrons can travel (Haynie et al 2003). In the case of SAMs of n-alkanethiolates, step edges and grain boundaries in the metal surface probably result in 'thin areas' of the SAM, where the molecules are not trans-extended and the top electrode contacts a disordered region of the SAM; this type of defect may result in a reduced length of the through-bond pathway between the electrodes and increased current (compared with that through the all-trans molecules).…”

Section: Reproducibility Of Measurements Of Charge Transportmentioning

confidence: 99%

The study of charge transport through organic thin films: mechanism, tools and applications

Weiss

Kriebel

Rampi

et al. 2007

Phil. Trans. R. Soc. A.

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In this paper, we discuss the current state of organic and molecular-scale electronics, some experimental methods used to characterize charge transport through molecular junctions and some theoretical models (superexchange and barrier tunnelling models) used to explain experimental results. Junctions incorporating self-assembled monolayers of organic molecules-and, in particular, junctions with mercury-drop electrodes-are described in detail, as are the issues of irreproducibility associated with such junctions (due, in part, to defects at the metal-molecule interface).

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“…The electrical transport through self-assembled monolayers of alkanedithiols was studied in large-area molecular junctions and described by the Simmons model [ [7][8][9] and theoretically (10)(11)(12)(13)(14)(15). Theoretical descriptions of electrical transport through molecular wires show that contacts, coupling of contacts to molecules, interface geometries, and vibrations are important in single-molecule experiments (16)(17)(18)(19)(20)(21).…”

mentioning

confidence: 99%

Electron tunneling through alkanedithiol self-assembled monolayers in large-area molecular junctions

Akkerman

Naber

Jongbloed

et al. 2007

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

179

222

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The electrical transport through self-assembled monolayers of alkanedithiols was studied in large-area molecular junctions and described by the Simmons model [Simmons JG (1963) J Appl Phys 34:1793-1803 and 2581-2590] for tunneling through a practical barrier, i.e., a rectangular barrier with the image potential included. The strength of the image potential depends on the value of the dielectric constant. A value of 2.1 was determined from impedance measurements. The large and well defined areas of these molecular junctions allow for a simultaneous study of the capacitance and the tunneling current under operational conditions. Electrical transport for octanedithiol through tetradecanedithiol self-assembled monolayers up to 1 V can simultaneously be described by a single effective mass and a barrier height. There is no need for additional fit constants. The barrier heights are in the order of 4 -5 eV and vary systematically with the length of the molecules. Irrespective of the length of the molecules, an effective mass of 0.28 was determined, which is in excellent agreement with theoretical predictions. and consist of a saturated carbon backbone with one (or two) thiol end groups. Experimentally, the tunneling current through a monolayer of alkane(di)thiols was shown to be temperatureindependent and to decrease exponentially with increasing molecular length (4, 5). The transport has been interpreted in terms of the classical tunneling model through a thin insulating film as provided by Simmons (24,25). In this model the tunneling current depends on the mean value of the barrier height, allowing for a simplification of the problem of an arbitrarily shaped potential barrier to that of a rectangular barrier. This model has been applied to junctions based on SAMs (4, 26), but an extra fit parameter ␣ is needed to obtain a fit to the measured data. However, as already explained by Simmons (24, 25), for a practical tunnel junction the image potential has to be taken into account. This effect has been neglected in the literature so far.The system studied in this article is a tunnel junction with an alkanedithiol SAM as the insulating film, a bottom gold electrode, and a highly conducting polymer as a top contact. The polymeric top contact allows for the fabrication of devices with a yield of almost unity for areas up to 100 m in diameter (5). The highly conducting polymer used is PEDOT:PSS, a waterbased suspension of poly(3,4-ethylenedioxythiophene) stabilized with poly(4-styrenesulfonic acid). The polymer acts as a cushion for the thermally evaporated metal atoms to land on and prevents the metal atoms from penetration into the molecular layer. Consequently, the formation of electrical shorts is prevented (27). Simmons ModelThe tunneling current density J through a rectangular potential barrier with height 0 is given by (4, 24, 26):wherewhere ⌬s is the barrier width at the Fermi level of the electrodes, here equal to the total length s of the tunneling path between the electrodes, m e is the bare electron mass, V is th...

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Adventures in molecular electronics: how to attach wires to molecules

Cited by 78 publications

References 7 publications

Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

The study of charge transport through organic thin films: mechanism, tools and applications

Electron tunneling through alkanedithiol self-assembled monolayers in large-area molecular junctions

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