Characterizing the Metal–SAM Interface in Tunneling Junctions

Bowers, Carleen M.; Liao, Kung-Ching; Żaba, Tomasz; Rappoport, Dmitrij; Baghbanzadeh, Mostafa; Breiten, Benjamin; Krzykawska, Anna; Cyganik, Piotr; Whitesides, George M.

doi:10.1021/nn5059216

Cited by 42 publications

(87 citation statements)

References 50 publications

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“…Since the value of J 0 reflects the characteristics of the interfaces between the SAM and the electrodes, rather than the shape of the most insulating part of the tunneling barrier, significant differences in values of injection current densities, J 0 , and indistinguishable values of tunneling decay, β, for SAMs of n-alkanethiolates with n odd and n even imply that the odd−even effect is influenced by some property of the interfaces (e.g., Au/S or SAM//Ga 2 O 3 ). We suggest that a determining contribution of the SAM//Ga 2 O 3 interface to odd−even effects is more plausible than one for the Au/S interface for two reasons: (i) Our previous studies, 10,47 and the current study (Figure 4a), showed that changing the bottom interface does not significantly influence the tunneling current densities. (ii) Results of this study indicate that changing the terminal group from CH 3 to CH 2 CH 3 correlates with a change in the injection current density (Figures 2b and 4b).…”

Section: ■ Conclusionmentioning

confidence: 72%

Odd–Even Effects in Charge Transport across n-Alkanethiolate-Based SAMs

et al. 2014

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This paper compares rates of charge transport across self-assembled monolayers (SAMs) of n-alkanethiolates having odd and even numbers of carbon atoms (n odd and n even ) using junctions with the structure M TS /SAM//Ga 2 O 3 /EGaIn (M = Au or Ag). Measurements of current density, J(V), across SAMs of n-alkanethiolates on Au TS and Ag TS demonstrated a statistically significant odd−even effect on Au TS , but not on Ag TS , that could be detected using this technique. Statistical analysis showed the values of tunneling current density across SAMs of n-alkanethiolates on Au TS with n odd and n even belonging to two separate sets, and while there is a significant difference between the values of injection current density, J 0 , for these two series (log|J 0Au,even | = 4.0 ± 0.3 and log|J 0Au,odd | = 4.5 ± 0.3), the values of tunneling decay constant, β, for n odd and n even alkyl chains are indistinguishable (β Au,even = 0.73 ± 0.02 Å ). A comparison of electrical characteristics across junctions of n-alkanethiolate SAMs on gold and silver electrodes yields indistinguishable values of β and J 0 and indicates that a change that substantially alters the tilt angle of the alkyl chain (and, therefore, the thickness of the SAM) has no influence on the injection current density across SAMs of n-alkanethiolates.

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Section: ■ Conclusionmentioning

confidence: 72%

Odd–Even Effects in Charge Transport across n-Alkanethiolate-Based SAMs

et al. 2014

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“…Changes to the interface that cause a disruption in the delocalization of the HOMO appear to raise the height of the barrier at the interface, inducing an increase in β. The interesting trend that is emerging from these and related studies 5,48 is that the introduction of groups that decreases the strength of the interactions, and thus increases the height of the barrier, at either interface increases β and increases J 0 .…”

Section: V) Error Associated With the Extrapolation Of The Best Fit Lmentioning

confidence: 75%

“…Our previous investigations on the influence of the Metal/SAM interface on rates of charge transport considered alkyl-based SAMs having different anchoring groups (e.g., S, C≡C, and O 2 C). 11,48 This study suggested-based on indistinguishable values of β and J 0 -that the interface between the metal and the SAM was not important in determining rates of charge transport. The current study analyzes conjugated molecular systems where the HOMO extends beyond the anchoring group and onto the phenyl rings.…”

Section: V) Error Associated With the Extrapolation Of The Best Fit Lmentioning

confidence: 94%

Tunneling across SAMs Containing Oligophenyl Groups

et al. 2016

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This paper describes rates of charge tunneling across self-assembled monolayers (SAMs) of compounds containing oligophenyl groups, supported on gold and silver, using Ga 2 O 3 /EGaIn as the top electrode. It compares the injection current, J 0 , and the attenuation constant, β, of the simplified Simmons equation, across oligophenyl groups (R = Ph n ; n = 1, 2, 3), with three different anchoring groups (thiol, HSR; methanethiol, HSCH 2 R; and acetylene, HC≡CR) that attach R to the template-stripped gold and silver substrates. The results demonstrate that the structure of the molecules between the anchoring group (-S-or -C≡C-) and the oligophenyl moiety significantly influences charge transport. SAMs of SPh n , and C≡CPh n on gold show similar values of β and log|J 0 | (β = 0.28 ± 0.03 Å -1 and log|J 0 | = 2.7 ± 0.1 for Au/SPh n ; β = 0.30 ± 0.02 Å -1 and log|J 0 | = 3.0 ± 0.1 for Au/C≡CPh n ). The introduction of a single intervening methylene (CH 2 ) group, between the anchoring sulfur atom and the aromatic units to generate SAMs of SCH 2 Ph n , increases β to ~0.6 Å -1 on both gold and silver substrates. (For nalkanethiolates on gold the corresponding values are β = 0.76 Å -1 and log|J 0 | = 4.2). As a generalization, based on this and other work, it seems that increasing the height of the tunneling barrier in the region of the interfaces increases β, and may decrease J 0 ; by contrast, it appears that lowering the height of the barrier at these interfaces has little influence on β or J 0 .

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“…(19) SAMs on template-stripped gold (Au TS ) were prepared according to protocols reported previously. (18,25) Detailed surface analyses indicate that SAMs of Cys(Gly) n are ordered:…”

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Charge Tunneling along Short Oligoglycine Chains

et al. 2015

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This work examines charge transport (CT) through self‐assembled monolayers (SAMs) of oligoglycines having an N‐terminal cysteine group that anchors the molecule to a gold substrate, and demonstrate that CT is rapid (relative to SAMs of n‐alkanethiolates). Comparisons of rates of charge transport‐using junctions with the structure AuTS/SAM//Ga2O3/EGaIn (across these SAMs of oligoglycines, and across SAMs of a number of structurally and electronically related molecules) established that rates of charge tunneling along SAMs of oligoglycines are comparable to that along SAMs of oligophenyl groups (of comparable length). The mechanism of tunneling in oligoglycines is compatible with superexchange, and involves interactions among high‐energy occupied orbitals in multiple, consecutive amide bonds, which may by separated by one to three methylene groups. This mechanistic conclusion is supported by density functional theory (DFT).

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Characterizing the Metal–SAM Interface in Tunneling Junctions

Cited by 42 publications

References 50 publications

Odd–Even Effects in Charge Transport across n-Alkanethiolate-Based SAMs

Odd–Even Effects in Charge Transport across n-Alkanethiolate-Based SAMs

Tunneling across SAMs Containing Oligophenyl Groups

Charge Tunneling along Short Oligoglycine Chains

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