Anomalous length dependence of the conductance of graphene nanoribbons with zigzag edges

Abstract

Charge transport through two sets of symmetric graphene nanoribbons with zigzag shaped edges in a two-terminal device has been investigated, using density functional theory combined with the nonequilibrium Green's function method. The conductance has been explored as a function of nanoribbon length, bias voltage, and the strength of terminal coupling. The set of narrower nanoribbons, in the form of thiolated linear acenes, shows an anomalous length dependence of the conductance, which at first exhibits a drop and a minimum, followed by an evident rise. The length trend is shown to arise because of a gradual transformation in the transport mechanism, which changes from being governed by a continuum of out-of-plane π type and in-plane state channels to being fully controlled by a single, increasingly more resonant, occupied π state channel. For the set of nanoribbons with a wider profile, a steady increase is observed across the whole length range, owing to the absence of the former transport mechanism. The predicted trends are confirmed by the inclusion of self-interaction correction in the calculations. For both sets of nanoribbons the replacement of the strongly coupling thiol groups by weakly bonding phenathroline has been found to cause a strong attenuation with the length and a generally low conductance.

First-principles studies on transport properties and contact effects of Cu(111)/ZnO-nanobelt(101̄0)/Cu(111) systems

“…[17][18][19][20] There are extensive reports on the transport properties of molecular junctions, carbon nanotubes, semiconductor nanowires and graphene. [21][22][23][24][25][26] Comparing to the large amount of experimental studies on the transport behavior of ZnO nanostructures, only a few theoretical reports have been found in recent years. Yang et al 27 observed clearly rectifying current-voltage characteristics in ZnO nanowires coupled by aluminum electrodes.…”

Tailoring highly conductive graphene nanoribbons from small polycyclic aromatic hydrocarbons: a computational study

“…This leads to two additional possibilities: pyrene-1,2,6,7-tetrathiol (PTT) and 2,3,7,8-PTT. Other combinations, such as 1,3,6,8-PTT, are not considered because the additional separation between the thiols would make double attachment to the terminals impossible, while 3,4,8,9-PTT has been treated elsewhere [21] very recently.…”

“…As a consequence, the occupied peak just below the Fermi level in the 1,2,6,7-PTT transmission spectrum is substantially amplified, resulting in a higher low bias conductance than any of the PDT isomers. However, as in the case of 3,4,8,9-PTT [21], the benefits of the reduced contact resistance are rather limited, because the two thiol groups at each terminal are connected to the same C ring. This is a poor design since it does not qualitatively change the charge flow pathway.…”