Electronically transparent Ag-C(sp3) contacts result in low conductance junctions

Chemical groups capable of connecting molecules physically and electrically between electrodes are of critical importance in molecular-scale electronics, influencing junction conductance, variability, and function. While the development of such linkage chemistries has focused on interactions at gold, the distinct reactivity and electronic structure of other electrode metals provides underexplored opportunities to characterize and exploit new binding motifs. In this work we show that 𝛼,ω-alkanedibromides spontaneously form well-defined junctions using silver, but not gold, electrodes. Through application of the glovebox-based scanning tunneling microscope-based break junction method, we find that the same junctions form when using different halide, or trimethyltin, terminal groups, suggestive of an electronically transparent silver-carbon(sp3) contact chemistry. However, the conductance of these junctions is ~30× lower than for analogous junctions formed on gold and does not align with predictions based on first-principles calculations. Through insights provided from prior temperature-programmed desorption studies and a robust series of atomistic simulations and control experiments, we propose that in these experiments we measure alkoxide-terminated junctions formed through the reaction of unstable silver-alkyl species with adsorbed surface oxygen. This study, in demonstrating that high conductance contact chemistries established using model gold electrodes may not be readily transferred to other metals, underscores the need to directly characterize the interfacial electronic properties and reactivity of electrode metals of wider technological relevance.