Signatures of Cooperative Effects and Transport Mechanisms in Conductance Histograms

Abstract

We present a computational investigation into the line shapes of peaks in conductance histograms, finding that they possess high information content. In particular, the histogram peak associated with conduction through a single molecule elucidates the electron transport mechanism and is generally well-described by beta distributions. A statistical analysis of the peak corresponding to conduction through two molecules reveals the presence of cooperative effects between the molecules and also provides insight into the underlying conduction channels. This work describes tools for extracting additional interpretations from experimental statistical data, helping us better understand electron transport processes.

Molecular Electronics: From Single‐Molecule to Large‐Area Devices

“…From CV measurements, dense monolayers in the NMJs give a broadening of the voltammograms (FWHM=110 mV) as expected for intermolecular electrostatic coupling, while less dense, diluted, monolayers in the NMJs have a narrow CV peak (FWHM=40 mV). Similarly, conductance histograms for the dense monolayers clearly exhibited an asymmetric distribution with a tail towards the low conductance values (Figure a) as predicted by Reuter et al ., while a classical log‐normal distribution was observed for diluted monolayers (Figure b). Ultra‐High‐Vacuum Scanning Tunneling Microscopy (UHV‐STM) was used to resolve the supramolecular organization of the dense monolayer (Figure c), which was used as the model for DFT calculations of t. To fit the conductance histograms, the previously proposed model with 2 molecules was extended to a network of 11x11 molecules more relevant considering the size of the NMJs (about 150 molecules).…”

“…Similarly, conductance histograms for the dense monolayers clearly exhibited an asymmetric distribution with a tail towards the low conductance values (Figure a) as predicted by Reuter et al ., while a classical log‐normal distribution was observed for diluted monolayers (Figure b). Ultra‐High‐Vacuum Scanning Tunneling Microscopy (UHV‐STM) was used to resolve the supramolecular organization of the dense monolayer (Figure c), which was used as the model for DFT calculations of t. To fit the conductance histograms, the previously proposed model with 2 molecules was extended to a network of 11x11 molecules more relevant considering the size of the NMJs (about 150 molecules). Good fits (Figure d) of the asymmetric histograms were obtained with t ∼ 30–35 meV, in very good agreement with the calculated DFT values for these NMJs.…”

“…Recently, Reuter et al . suggested that such cooperative effects induce asymmetrical conductance histogram spectra (i. e. no longer log‐normal distributed), and they proposed a simple toy model with two π‐conjugated molecules in parallel between electrodes . An experimental proof requires several conditions : (i) an easy way to record conductance histograms (a solid statistical analysis requires thousands of molecular junctions), (ii) a method to control/monitor the intermolecular interactions.…”

Forty years of molecular electronics: Non‐equilibrium heat and charge transport at the nanoscale

“…Suppose that two molecules are caught in the junction at the same time: Is the current going through the two molecules the same as twice the current through a single molecule? Previous theoretical studies have shown that the transport through two or more molecules connected in parallel (which interact via their joint linkage to the electrodes, or directly with each other) can result in transport that is larger than, equal to, or smaller than twice the transport through a single molecule. This effect can be understood in analogy with an optical double‐slit experiment, where quantum coherence can mix the transport paths, giving twice the conductance for complete constructive interference and close to zero for complete destructive interference.…”

A Toolbox for Controlling the Energetics and Localization of Electronic States in Self‐Assembled Organic Monolayers

“…In many instances, a convenient way for tuning the characteristics of such interfaces is by using molecular (mono)layers. These can even adopt the role of functional elements in devices, for example, in highly efficient organic monolayer transistors1, 2 or as self‐assembled monolayer (SAM) based devices in the field of molecular electronics 3, 4, 5, 6, 7, 8, 9, 10, 11. The spatial localization and energetics of the electronic states in these layers play a crucial role, as the states serve as “channels” for the electrical current 12, 13.…”