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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.


2D histograms of log(G/G0) versus Δz (left) and 1D histograms of log(G/G0) (right) constructed from all data points of the measured elongation traces for the molecular junctions formed by BT2 and PY2.The occurrence of data points in the 2D (size 0.01 nm × 0.1) and 1D (size 0.1) bins is given by the colour scale and by the solid lines, respectively. The dashed ellipses in the 2D histograms and letters in 1D histograms mark features of molecular junctions with high (H), medium (M) and low (L) conductance as well as features of the baseline conductance (B). The latter are separated from the molecule-specific features by a dotted horizontal line. The dashed horizontal lines correspond to the positions of borders between the conductance ranges log(GHM/G0), log(GML/G0) for PY2, as well as log(GHL/G0) for BT2 (Supplementary Table 2).
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f2: 2D histograms of log(G/G0) versus Δz (left) and 1D histograms of log(G/G0) (right) constructed from all data points of the measured elongation traces for the molecular junctions formed by BT2 and PY2.The occurrence of data points in the 2D (size 0.01 nm × 0.1) and 1D (size 0.1) bins is given by the colour scale and by the solid lines, respectively. The dashed ellipses in the 2D histograms and letters in 1D histograms mark features of molecular junctions with high (H), medium (M) and low (L) conductance as well as features of the baseline conductance (B). The latter are separated from the molecule-specific features by a dotted horizontal line. The dashed horizontal lines correspond to the positions of borders between the conductance ranges log(GHM/G0), log(GML/G0) for PY2, as well as log(GHL/G0) for BT2 (Supplementary Table 2).

Mentions: Figure 2 shows 1D and 2D histograms of log(G/G0) constructed from all measured traces for the highly stable BT2 and PY2 junctions. All traces were aligned in a common distance scale by setting the first point with the conductance G < 0.1 G0 to the Δz = 0. The corresponding plots for NH22, CN2, SH2 and SH1 are presented in Supplementary Fig. 3. All histograms display a region of high data density at Δz < 0 and log(G/G0) > 0 (2D), as well as sharp peaks at log(G/G0) ≈ 0 (1D). These features are characteristic of the formation and breaking of (single-atom) Au-Au contacts33. Horizontally aligned clouds (2D) in the range log(G/G0) < −5.5 and broad peaks with a maximum at log(G/G0) ≈ −6 (1D) correspond to the “baseline” conductance (B) measured in the absence of an electrical contact between the two gold electrodes, i.e. when the junction is completely broken. Conductance values in the interval −5.5 < log(G/G0) < −0.5 reflect the properties of specific molecular junctions.


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)

2D histograms of log(G/G0) versus Δz (left) and 1D histograms of log(G/G0) (right) constructed from all data points of the measured elongation traces for the molecular junctions formed by BT2 and PY2.The occurrence of data points in the 2D (size 0.01 nm × 0.1) and 1D (size 0.1) bins is given by the colour scale and by the solid lines, respectively. The dashed ellipses in the 2D histograms and letters in 1D histograms mark features of molecular junctions with high (H), medium (M) and low (L) conductance as well as features of the baseline conductance (B). The latter are separated from the molecule-specific features by a dotted horizontal line. The dashed horizontal lines correspond to the positions of borders between the conductance ranges log(GHM/G0), log(GML/G0) for PY2, as well as log(GHL/G0) for BT2 (Supplementary Table 2).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: 2D histograms of log(G/G0) versus Δz (left) and 1D histograms of log(G/G0) (right) constructed from all data points of the measured elongation traces for the molecular junctions formed by BT2 and PY2.The occurrence of data points in the 2D (size 0.01 nm × 0.1) and 1D (size 0.1) bins is given by the colour scale and by the solid lines, respectively. The dashed ellipses in the 2D histograms and letters in 1D histograms mark features of molecular junctions with high (H), medium (M) and low (L) conductance as well as features of the baseline conductance (B). The latter are separated from the molecule-specific features by a dotted horizontal line. The dashed horizontal lines correspond to the positions of borders between the conductance ranges log(GHM/G0), log(GML/G0) for PY2, as well as log(GHL/G0) for BT2 (Supplementary Table 2).
Mentions: Figure 2 shows 1D and 2D histograms of log(G/G0) constructed from all measured traces for the highly stable BT2 and PY2 junctions. All traces were aligned in a common distance scale by setting the first point with the conductance G < 0.1 G0 to the Δz = 0. The corresponding plots for NH22, CN2, SH2 and SH1 are presented in Supplementary Fig. 3. All histograms display a region of high data density at Δz < 0 and log(G/G0) > 0 (2D), as well as sharp peaks at log(G/G0) ≈ 0 (1D). These features are characteristic of the formation and breaking of (single-atom) Au-Au contacts33. Horizontally aligned clouds (2D) in the range log(G/G0) < −5.5 and broad peaks with a maximum at log(G/G0) ≈ −6 (1D) correspond to the “baseline” conductance (B) measured in the absence of an electrical contact between the two gold electrodes, i.e. when the junction is completely broken. Conductance values in the interval −5.5 < log(G/G0) < −0.5 reflect the properties of specific molecular junctions.

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.