Conductance saturation in a series of highly transmitting molecular junctions

Abstract

Note:The published version in Nature Materials contains an extended manuscript and comprehensive supplementary information. . One of the primary experimental methods to reveal the mechanisms behind electronic transport through metal-molecule interfaces is the study of conductance as a function of molecule length in molecular junctions [4][5][6][7][8][9][10][11][12][13][14] . Previous studies focused on transport governed either by coherent tunneling or hopping, both at low conductance. However, the upper limit of conductance across molecular junctions has not been explored, despite the great potential for efficient information transfer, charge injection and recombination processes at high conductance. Here, we study the conductance properties of highly transmitting metal-molecule-metal interfaces, using a series of single-molecule junctions based on oligoacenes with increasing length. We find that the conductance saturates at an upper limit where it is independent of molecule length. Furthermore, we show that this upper limit can be controlled by the character of the orbital hybridization at the metal-molecule interface. Using two prototype systems, in which the molecules are contacted by either Ag or Pt electrodes, we reveal two different origins for the saturation of conductance. In the case of Ag-based molecular junctions, the conductance saturation is ascribed to a competition between energy level alignment and level broadening, while in the case of Pt-based junctions, the saturation is attributed to a band-like transport. The results are explained by an intuitive model, backed by ab-initio transport calculations. Our findings shed light on the mechanisms that constrain the conductance at the high transmission limit, providing guiding principles for the design of highly conductive metal-molecule interfaces.In order to study the conductance characteristics of highly transmitting molecular junctions, strong electronic coupling is required between the molecule and the electrodes, as well as within the molecule itself 10,11,15,16 . These conditions are achieved in this work by direct hybridization between the π-orbitals of the oligoacene molecules and the frontier orbitals of the metal electrodes, without employing anchoring groups such as thiols that can act as spacers between the orbitals of the molecular backbone and the frontier orbitals of the metal 13,15 . The oligoacenes (Fig. 1a) are linear π-conjugated molecules that can be viewed as short graphene nanoribbons 17 , whose electronic structure is subject to an ongoing research 18 . We study the evolution of conductance as a function of molecule length and compare the conductance characteristics of

Tuning electronic transport via hepta-alanine peptides junction by tryptophan doping

“…We postulate that for W-7 contact/overlap between the Au's spillover electron density and the indole ring's π-electrons is sufficient to decrease the effective transport barrier (63). Such sensitivity of the energy levels to mere physical proximity to the metallic contact was not observed for thiol-terminated polyphenyls (62), from another hand indicating that actual chemical bonding can act to buffer coupling, rather than enhance it, possibly via electron localization in the bond (64,65). In addition, the separation into Γ g and « 0 reveals that the slightly lower current via W-4 compared with W-1 (Fig.…”

Effects of the Backbone and Chemical Linker on the Molecular Conductance of Nucleic Acid Duplexes

“…[47][48] 14 Summary: Table 1 shows the most probable conductance values for the high (G H ) and medium (G M ) conductance modes observed in this study, as well as the ratios of the conductance of the high mode to medium mode. much shorter than the 30 angstrom PNA duplex studied here.…”

GW in the Gaussian and Plane Waves Scheme with Application to Linear Acenes

“…Remarkably, the HOMO-LUMO gap oscillations in acenes on the level of closed-shell PBE 76 have not been reported before Ref. 67 despite of the intensive research on the electronic groundstate properties of acenes [77][78][79][80][81][82][83][84] , which is driven by organic electronics [85][86][87][88][89] and photovoltaics [90][91][92][93][94] . In Ref.…”