Electric Field Breakdown in Single Molecule Junctions

Here we study the stability and rupture of molecular junctions under high voltage bias at the single molecule/single bond level using the scanning tunneling microscope-based break-junction technique. We synthesize carbon-, silicon-, and germanium-based molecular wires terminated by aurophilic linker groups and study how the molecular backbone and linker group affect the probability of voltage-induced junction rupture. First, we find that junctions formed with covalent SAu bonds are robust under high voltage and their rupture does not demonstrate bias dependence within our bias range. In contrast, junctions formed through donoracceptor bonds rupture more frequently, and their rupture probability demonstrates a strong bias dependence. Moreover, we find that the junction rupture probability increases significantly above similar to 1 V in junctions formed from methylthiol-terminated disilanes and digermanes, indicating a voltage-induced rupture of individual SiSi and GeGe bonds. Finally, we compare the rupture probabilities of the thiol-terminated silane derivatives containing SiSi, SiC, and SiO bonds and find that SiC backbones have higher probabilities of sustaining the highest voltage. These results establish a new method for studying electric field breakdown phenomena at the single molecule level.