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Correlation of breaking forces, conductances and geometries of molecular junctions.

Yoshida K, Pobelov IV, Manrique DZ, Pope T, Mészáros G, Gulcur M, Bryce MR, Lambert CJ, Wandlowski T - Sci Rep (2015)

Bottom Line: Correlations between forces, conductances and junction geometries demonstrate that aromatic tolanes bind between electrodes as single molecules or as weakly-conductive dimers held by mechanically-weak π - π stacking.In contrast with the other anchors that form only S-Au or N-Au bonds, the pyridyl ring also forms a highly-conductive cofacial link to the gold surface.Binding of multiple molecules creates junctions with higher conductances and mechanical strengths than the single-molecule ones.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.

ABSTRACT
Electrical and mechanical properties of elongated gold-molecule-gold junctions formed by tolane-type molecules with different anchoring groups (pyridyl, thiol, amine, nitrile and dihydrobenzothiophene) were studied in current-sensing force spectroscopy experiments and density functional simulations. Correlations between forces, conductances and junction geometries demonstrate that aromatic tolanes bind between electrodes as single molecules or as weakly-conductive dimers held by mechanically-weak π - π stacking. In contrast with the other anchors that form only S-Au or N-Au bonds, the pyridyl ring also forms a highly-conductive cofacial link to the gold surface. Binding of multiple molecules creates junctions with higher conductances and mechanical strengths than the single-molecule ones.

No MeSH data available.


Related in: MedlinePlus

Representative structures (a, d), coordinate axes (a), theoretical loading force F (b, e) and logarithm of the normalised conductance log(G/G0) (c, f) of single (a–c) and double (d–f) molecule junctions of PY2 as a function of the electrode separation zAu–Au.The vertical dotted lines mark positions corresponding to the structures S1–S4 and D1–D5, and transitions between configurations with different type of coupling. The thick parts of the force traces illustrate the elastic stages of junction elongation. The horizontal dashed lines in the conductance panels indicate the positions of experimental borders between the high/medium (GHM) and the medium/low (GML) conductance ranges.
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f4: Representative structures (a, d), coordinate axes (a), theoretical loading force F (b, e) and logarithm of the normalised conductance log(G/G0) (c, f) of single (a–c) and double (d–f) molecule junctions of PY2 as a function of the electrode separation zAu–Au.The vertical dotted lines mark positions corresponding to the structures S1–S4 and D1–D5, and transitions between configurations with different type of coupling. The thick parts of the force traces illustrate the elastic stages of junction elongation. The horizontal dashed lines in the conductance panels indicate the positions of experimental borders between the high/medium (GHM) and the medium/low (GML) conductance ranges.

Mentions: For PY2, Figs 4a–4c show the theoretical loading force F and logarithm of the normalised conductance log(G/G0) of a single-molecule (S) junction as a function of the electrode separation zAu–Au (the distance between the centres of the apex atoms of opposing gold pyramids). The computed absolute distance scale zAu–Au is approximately related to the experimental relative distance scale Δz by zAu–Au = Δz + 0.5 nm, where 0.5 nm is a typical snap-back distance of the electrodes after breaking of the Au-Au contact22. Figure 4a illustrates four characteristic configurations of the PY2-S junctions labeled S1 to S4. The computed loading force F and conductance traces are shown in Fig. 4b and 4c. At low zAu–Au, the molecule is attached by the π-systems of the pyridyl rings to the surface of at least one gold pyramid (π-Au coupling), as illustrated by structures S1 and S2. As the junction evolves, a molecule in a stable configuration experiences an elastic elongation with /F/ increasing linearly with electrode separation, as shown by parts of force trace marked by a thicker line in Fig. 4b. At small zAu–Au, this sliding produces saw-tooth-like features in F. Upon reaching a certain force threshold (position S2), the junction experiences an inelastic deformation and adopts a new stable geometry. Structurally, the π-system(s) of PY2 slide across the gold pyramids without losing contact. As zAu–Au approaches the molecular length, the molecule jumps into the gap and binds to the apex atoms of both pyramids forming coordination bonds between the nitrogen atoms of the pyridyl groups and the gold atoms (N-Au coupling). Further pulling of this configuration leads to a relatively long elastic stage until one Au-N bond dissociates (structure S4). Breaking of the junction results in a rapid decrease of the conductance and the relaxation of the loading force towards zero. The observed residual conductance is attributed to through-vacuum tunnelling.


Correlation of breaking forces, conductances and geometries of molecular junctions.

Yoshida K, Pobelov IV, Manrique DZ, Pope T, Mészáros G, Gulcur M, Bryce MR, Lambert CJ, Wandlowski T - Sci Rep (2015)

Representative structures (a, d), coordinate axes (a), theoretical loading force F (b, e) and logarithm of the normalised conductance log(G/G0) (c, f) of single (a–c) and double (d–f) molecule junctions of PY2 as a function of the electrode separation zAu–Au.The vertical dotted lines mark positions corresponding to the structures S1–S4 and D1–D5, and transitions between configurations with different type of coupling. The thick parts of the force traces illustrate the elastic stages of junction elongation. The horizontal dashed lines in the conductance panels indicate the positions of experimental borders between the high/medium (GHM) and the medium/low (GML) conductance ranges.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4355744&req=5

f4: Representative structures (a, d), coordinate axes (a), theoretical loading force F (b, e) and logarithm of the normalised conductance log(G/G0) (c, f) of single (a–c) and double (d–f) molecule junctions of PY2 as a function of the electrode separation zAu–Au.The vertical dotted lines mark positions corresponding to the structures S1–S4 and D1–D5, and transitions between configurations with different type of coupling. The thick parts of the force traces illustrate the elastic stages of junction elongation. The horizontal dashed lines in the conductance panels indicate the positions of experimental borders between the high/medium (GHM) and the medium/low (GML) conductance ranges.
Mentions: For PY2, Figs 4a–4c show the theoretical loading force F and logarithm of the normalised conductance log(G/G0) of a single-molecule (S) junction as a function of the electrode separation zAu–Au (the distance between the centres of the apex atoms of opposing gold pyramids). The computed absolute distance scale zAu–Au is approximately related to the experimental relative distance scale Δz by zAu–Au = Δz + 0.5 nm, where 0.5 nm is a typical snap-back distance of the electrodes after breaking of the Au-Au contact22. Figure 4a illustrates four characteristic configurations of the PY2-S junctions labeled S1 to S4. The computed loading force F and conductance traces are shown in Fig. 4b and 4c. At low zAu–Au, the molecule is attached by the π-systems of the pyridyl rings to the surface of at least one gold pyramid (π-Au coupling), as illustrated by structures S1 and S2. As the junction evolves, a molecule in a stable configuration experiences an elastic elongation with /F/ increasing linearly with electrode separation, as shown by parts of force trace marked by a thicker line in Fig. 4b. At small zAu–Au, this sliding produces saw-tooth-like features in F. Upon reaching a certain force threshold (position S2), the junction experiences an inelastic deformation and adopts a new stable geometry. Structurally, the π-system(s) of PY2 slide across the gold pyramids without losing contact. As zAu–Au approaches the molecular length, the molecule jumps into the gap and binds to the apex atoms of both pyramids forming coordination bonds between the nitrogen atoms of the pyridyl groups and the gold atoms (N-Au coupling). Further pulling of this configuration leads to a relatively long elastic stage until one Au-N bond dissociates (structure S4). Breaking of the junction results in a rapid decrease of the conductance and the relaxation of the loading force towards zero. The observed residual conductance is attributed to through-vacuum tunnelling.

Bottom Line: Correlations between forces, conductances and junction geometries demonstrate that aromatic tolanes bind between electrodes as single molecules or as weakly-conductive dimers held by mechanically-weak π - π stacking.In contrast with the other anchors that form only S-Au or N-Au bonds, the pyridyl ring also forms a highly-conductive cofacial link to the gold surface.Binding of multiple molecules creates junctions with higher conductances and mechanical strengths than the single-molecule ones.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.

ABSTRACT
Electrical and mechanical properties of elongated gold-molecule-gold junctions formed by tolane-type molecules with different anchoring groups (pyridyl, thiol, amine, nitrile and dihydrobenzothiophene) were studied in current-sensing force spectroscopy experiments and density functional simulations. Correlations between forces, conductances and junction geometries demonstrate that aromatic tolanes bind between electrodes as single molecules or as weakly-conductive dimers held by mechanically-weak π - π stacking. In contrast with the other anchors that form only S-Au or N-Au bonds, the pyridyl ring also forms a highly-conductive cofacial link to the gold surface. Binding of multiple molecules creates junctions with higher conductances and mechanical strengths than the single-molecule ones.

No MeSH data available.


Related in: MedlinePlus