Contact Resistance in Metal−Molecule−Metal Junctions Based on Aliphatic SAMs:  Effects of Surface Linker and Metal Work Function

Beebe, Jeremy M.; Engelkes, Vincent B.; Miller, Larry L.; Frisbie, C. Daniel

doi:10.1021/ja0268332

Cited by 371 publications

(416 citation statements)

References 19 publications

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“…[24] Transport across alkyl (di) thiols contacted by varying metals showed that b is independent of the metal while J C varies logarithmically with it. [50] For direct binding to Si we found that changing SiÀCÀ to SiÀOÀCÀ [88] or ÀPO 3 ÀR to ÀSR, [140] alters the tunneling transport so that both J C and b (see Eq. (6a)) are larger with CÀSi than with CÀOÀSi, or with SÀGaAs than with PO 3 ÀGaAs.…”

Section: The Effect Of Contactsmentioning

confidence: 99%

“…His solar cell interests led to work hybrid molecular/non-molecular materials, which evolved into his other present activities, understanding electronic transport across (bio)molecules, exploring how molecules can control such transport, looking for novel science in such systems and for possible relevance to solar cells. changes in molecular energy levels upon contacting [47][48][49][50][51][52] and effects due to intermolecular interactions [21,[53][54][55] is accumulating. Such effects need to be clarified to isolate unique molecular contributions, be they purely molecular ones or due to interactions with the environment.…”

Section: Why Alkanes? Insulating Versus Conjugated Moleculesmentioning

confidence: 99%

“…Contacts can completely dominate net transport via: molecular tilt, packing monolayer dynamics [32,168] (see Section 6, temperature effect); alignment of molecular energy levels, with respect to the substrate Fermi level, via a substrate-molecule bond dipole across them [50][51][52]113] (see Section 3.3); electronic coupling between molecules and electrode, which can be expressed as the contact transmission probability. [21,23] In how far can we carry these understandings over to MOMS?…”

Section: The Effect Of Contactsmentioning

confidence: 99%

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Molecules on Si: Electronics with Chemistry

et al. 2009

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Basic scientific interest in using a semiconducting electrode in molecule‐based electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics. Semiconductors, especially Si, present an important experimental test‐bed for assessing electronic transport behavior of molecules, because they allow varying the critical interface energetics without, to a first approximation, altering the interfacial chemistry. To investigate semiconductor‐molecule electronics we need reproducible, high‐yield preparations of samples that allow reliable and reproducible data collection. Only in that way can we explore how the molecule/electrode interfaces affect or even dictate charge transport, which may then provide a basis for models with predictive power.To consider these issues and questions we will, in this Progress Report, review junctions based on direct bonding of molecules to oxide‐free Si. describe the possible charge transport mechanisms across such interfaces and evaluate in how far they can be quantified. investigate to what extent imperfections in the monolayer are important for transport across the monolayer. revisit the concept of energy levels in such hybrid systems.

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Section: The Effect Of Contactsmentioning

confidence: 99%

Section: Why Alkanes? Insulating Versus Conjugated Moleculesmentioning

confidence: 99%

Section: The Effect Of Contactsmentioning

confidence: 99%

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Molecules on Si: Electronics with Chemistry

et al. 2009

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“…The effect of changing the group (which we call the "anchoring group") that links the SAM to the metal substrate has not been explored in detail; 9,10 only a few studies have approached this issue at the single-molecular level using scanning tunneling microscopy [11][12][13][14] or conducting atomic force microscopy. 15 …”

Section: Studies Of Charge Tunneling Through Self-assembled Monolayermentioning

confidence: 99%

Replacing Ag^TSSCH₂‐R with Ag^TSO₂C‐R in EGaIn‐Based Tunneling Junctions Does Not Significantly Change Rates of Charge Transport

et al. 2014

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Abstract:This paper compares rates of charge transport by tunneling across junctions with the structures Ag TS X(CH 2 ) 2n CH 3 //Ga 2 O 3 /EGaIn (n = 1 -8 and X = -SCH 2 -and -O 2 C-); here Ag TS was template-stripped silver, and EGaIn is the eutectic alloy of gallium and indium. Its objective was to compare the tunneling decay coefficient (β, Å -1 ) and the injection current (J 0 , A/cm 2 ) of the junctions comprising SAMs of n-alkanethiolates and n-alkanoates.

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“…In a previous study, 34 our group estimated a value of the specific resistance (i.e., the resistance per unit area) of the Ga 2 4 times lower than that of a SAM composed of SC 9 , the shortest molecule studied at that time. 19 We thus concluded that, for medium-length SAMs (n = 9−18), the values of J(V) were determined by the SAM; this inference did not automatically apply to short-chain SAMs (which were not examined in previous studies).…”

Section: ■ Introductionmentioning

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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Contact Resistance in Metal−Molecule−Metal Junctions Based on Aliphatic SAMs: Effects of Surface Linker and Metal Work Function

Cited by 371 publications

References 19 publications

Molecules on Si: Electronics with Chemistry

Molecules on Si: Electronics with Chemistry

Replacing Ag^TSSCH₂‐R with Ag^TSO₂C‐R in EGaIn‐Based Tunneling Junctions Does Not Significantly Change Rates of Charge Transport

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

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Contact Resistance in Metal−Molecule−Metal Junctions Based on Aliphatic SAMs: Effects of Surface Linker and Metal Work Function

Cited by 371 publications

References 19 publications

Molecules on Si: Electronics with Chemistry

Molecules on Si: Electronics with Chemistry

Replacing AgTSSCH2‐R with AgTSO2C‐R in EGaIn‐Based Tunneling Junctions Does Not Significantly Change Rates of Charge Transport

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

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Replacing Ag^TSSCH₂‐R with Ag^TSO₂C‐R in EGaIn‐Based Tunneling Junctions Does Not Significantly Change Rates of Charge Transport