Critical roles of metal-molecule contacts in electron transport through molecular-wire junctions

Abstract

We study the variation of electron transmission through Au-S-benzene-S-Au junctions and related systems as a function of the structure of the Au:S contacts. For junctions with semi-infinite flat Au(111) electrodes, the highly coordinated in-hollow and bridge positions are connected with broad transmission peaks around the Fermi level, due to a broad range of transmission angles from transverse motion, resulting in high conductivity and weak dependence on geometrical variations. In contrast, for (unstable) S-adsorption on top of an Au atom, or in the hollow of a 3-Au-atom island, the transmission peaks narrow up due to suppression of large transmission angles. Such more one-dimensional situations may describe more common types of contacts and junctions, resulting in large variations in conductivity and sensitivity to bonding sites, tilting and gating. In particular, if S is adsorbed in an Au vacancy, sharp spectral features appear near the Fermi level due to essential changes of the level structure and hybridization in the contacts, admitting order-of-magnitude variations of the conductivity. Possibly such a system, can it be fabricated, will show extremely strong non-linear effects and might work as uni-or bi-directional voltage-controlled 2-terminal switches and non-linear mixing elements. Finally, density-functional-theory (DFT) based transport calculations seem relevant, being capable of describing a wide range of transmission peak structures and conductivities. Prediction and interpretation of experimental results probably require more precise modeling of realistic experimental situations.

Interference effects in phtalocyanine controlled by H-H tautomerization: Potential two-terminal unimolecular electronic switch

“…Figure 4 indeed provides a nice illustration of Fano resonances and interference in resonance transmission involving a narrow and a broad (continuum) resonance, [47][48][49][50][51] showing the whole range of line shapes from a pure window resonance (interference minimum) [ Fig. 4(a), V = 0] to strongly asymmetric resonances with pronounced interference minima [ Fig.…”

Cumulene molecular wire conductance from first principles

“…10 Core electrons were modeled with Troullier-Martins 13 soft norm-conserving pseudopotentials and the valence electrons were expanded in a basis set of local orbitals. 14 The transmission spectrum, which gives the probability for electrons with incident energy E to be transferred from the left to the right electrode, is calculated from 15 …”

“…A system of a cumulene wire coupled to Au͑111͒-͑3 ϫ 3͒ surface electrodes via thiolate bonds was fully optimized. 14 The adsorption geometry has been determined by positioning thiolate capped cumulenes above four adsorption sites, on top, bridge, fcc, and hcp on Au surfaces at a favorable Auu S bonding distance. 18 During relaxation sulfur atoms move to the bridge sites.…”

Tuning the thermal conductance of molecular junctions with interference effects

“…Theoretically this topic has been explored extensively in the last two decades [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] . In particular, special attention has been devoted to the role of Fano resonances [28][29][30][31][32] and to the determination of general rules governing the appearance of quantum interference effects in molecules with extended π-electron systems [33][34][35][36] . Also different experimental reports in recent years have convincingly shown the influence of the quantum interference on electronic transport of molecular junctions, as illustrated by measurements of linear conductances and current-voltage characteristics [37][38][39][40][41][42][43][44][45][46][47][48] .…”