Charge Transport in Single Au|Alkanedithiol|Au Junctions: Coordination Geometries and Conformational Degrees of Freedom

TL;DR

This study investigates charge transport in Au|alkanedithiol|Au junctions, revealing multiple conductance features linked to different molecular conformations and coupling geometries, with implications for experimental analysis.

Contribution

It provides an in-depth analysis combining STM measurements and quantum chemistry to clarify conductance features and conformational effects in molecular junctions.

Findings

Multiple conductance series correspond to different junction configurations.

Certain sulfur-gold couplings and conformations drive conductance variations.

Conductance histograms may mask microscopic diversity when conformations are correlated.

Abstract

Recent STM molecular break-junction experiments have revealed multiple series of peaks in the conductance histograms of alkanedithiols. To resolve a current controversy, we present here an in-depth study of charge transport properties of Au|alkanedithiol|Au junctions. Conductance histograms extracted from our STM measurements unambiguously confirm features showing more than one set of junction configurations. Based on quantum chemistry calculations, we propose that certain combinations of different sulfur-gold couplings and trans/gauche conformations act as the driving agents. The present study may have implications for experimental methodology: whenever conductances of different junction conformations are not statistically independent, the conductance histogram technique can exhibit a single series only, even though a much larger abundance of microscopic realizations exists.