Suppression of single-molecule conductance fluctuations using extended anchor groups on graphene and carbon-nanotube electrodes

Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance fluctuations, which inhibit their development as reproducible functional units. We demonstrate that single molecules with planar anchor groups attached to carbon-based electrodes are more resilient to atomic-scale variation in the contacts and exhibit significantly lower conductance fluctuations. We examine the conductance of a 2,6-dibenzylamino core-substituted naphthalenediimide chromophore attached to carbon electrodes by either phenanthrene anchors or more extended anchor groups, which include oligophenylene ethynylene spacers. We demonstrate that for the more spatially extended anchor groups conductance fluctuations are significantly reduced. The current-voltage characteristic arising from long-range tunneling is found to be strongly nonlinear with pronounced conductance suppression below a threshold voltage of approximately 2.5 V.

Figure 1

The studied molecule with an NDI functioning group, OPE spacers, and phenanthrene anchor groups on the top of the CNT junction (shown in light gray).

Figure 2

Projections of the contact area to the $x-z$ plane, viewed from above and from the side. The gray shading represents the molecule above it. The gap and the middle section of the molecule are shrunk to fit the figure.

Figure 3

Transport probability as a function of the energy and room-temperature current as a function of the applied bias voltage. The current is presented on a logarithmic scale and also on a linear scale in the inset. The black curve corresponds to perfect electrodes, dark gray to CNTs with a few defects, and light gray to CNTs with many defects. Note the threshold voltage below 3 V.