Tuning Rectification in Single-Molecular Diodes

Abstract

We demonstrate a new method of achieving rectification in single molecule devices using the high-bias properties of gold-carbon bonds. Our design for molecular rectifiers uses a symmetric, conjugated molecular backbone with a single methylsulfide group linking one end to a gold electrode and a covalent gold-carbon bond at the other end. The gold-carbon bond results in a hybrid gold-molecule "gateway" state pinned close to the Fermi level of one electrode. Through nonequilibrium transport calculations, we show that the energy of this state shifts drastically with applied bias, resulting in rectification at surprisingly low voltages. We use this concept to design and synthesize a family of diodes and demonstrate through single-molecule current-voltage measurements that the rectification ratio can be predictably and efficiently tuned. This result constitutes the first experimental demonstration of a rationally tunable system of single-molecule rectifiers. More generally, the results demonstrate that the high-bias properties of "gateway" states can be used to provide additional functionality to molecular electronic systems.

Large Spatially Resolved Rectification in a Donor–Acceptor Molecular Heterojunction

“…2(d)) are orders of magnitude larger than in the C 60 /Cu(111) region with values approaching or 1000 for 0.4 V ≤ V B ≤ 1.3 V, significantly larger than rectification reported for single-molecule systems. 14,[16][17][18]20 Interestingly, the preferred path for electrons -from acceptor to donor -is opposite to the path found in most single-molecule rectifiers. 9 As explained below, this is due to the unique electronic structure of our system.…”

“…12 Following theoretical models, 10,11 efforts towards the synthesis and characterization of more efficient molecular diodes can be divided into attempts to (1) increase the electron rich/poor characters of the donor/acceptor moieties, 13 (2) decrease their conjugation, 14,15 and (3) imbalance their coupling to the electrodes. 7,[16][17][18][19][20] The experimental poor performance of these single-molecule diodes -with the notable exception of environment-induced diodes 21 -suggests that these physical parameters tend to be mutually exclusive in most molecular systems. 22,23 In this Letter, inspired by thin-film organic photovoltaic devices, 24 we simultaneously optimize parameters (1-3) by assembling a bilayer heterojunction (HJ) of pentacene (Pn) and C 60 -archetypal donor and acceptor molecules (respectively) -that weakly interact through van der Waals interactions.…”

Controlling the direction of rectification in a molecular diode

“…The shape of the electrostatic potential profile in a molecular junction has been thoroughly investigated theoretically [33][34][35][36][37] but has not been measured directly due to technical limitations. As discussed above, Z V parameterises the electrostatic potential profile within the molecule on which R directly depends, among other factors (for example, level broadening, intrinsic coupling asymmetries, and so on).…”

HOMO–LUMO coupling: the fourth rule for highly effective molecular rectifiers

“…4 The performance of a rectifier is quantified by its rectification ratio (RR), defined as the absolute current through the device at bias V versus the current at −V . Most unimolecular rectifiers have reported rectification ratios in the low single digits [5][6][7][8] . Capozzi and co-workers reported achieving a rectification ratio greater than 200 for thiophene derivatives in a scanning tunneling microscope based break junction.…”