The Role of Oligomeric Gold-Thiolate Units in Single Molecule Junc-tions of Thiol-Anchored Molecules

TL;DR

This study reveals that oligomeric gold-thiolate units significantly influence conductance in thiol-anchored molecular junctions, providing new insights into their structural role and clarifying conductance behavior of certain molecules.

Contribution

The paper demonstrates the presence and impact of Au(RS)2 oligomeric units in molecular junctions, a structural motif previously observed only on gold nanoparticle surfaces.

Findings

Au(RS)2 units are incorporated at contacts in molecular junctions.

Distinct conductance plateau groups correspond to different structural motifs.

Clarifies the conductance characteristics of 1,4-benzenedithiol on gold.

Abstract

Using the break junction (BJ) technique we show that Au(RS)2 units play a significant role in thiol-terminated molecular junctions formed on gold. We have studied a range of thiol-terminated compounds, either with the sulfur atoms in direct conjugation with a phenyl core, or bonded to saturated methylene groups. For all molecules we observe at least two distinct groups of conductance plateaus. By a careful analysis of the length behavior of these plateaus, comparing the behavior across the different cores and with methyl sulfide anchor groups, we demonstrate that the lower conductance groups correspond to the incorporation of Au(RS)2 oligomeric units at the contacts. These structural motifs are found on the surface of gold nanoparticles but they have not before been shown to exist in molecular-break junctions. The results, while exemplifying the complex nature of thiol chemistry on gold, moreover clarify the conductance of 1,4-benzenedithiol on gold. We show that true Au-S-Ph-S-Au junctions have a relatively narrow conductance distribution.