Efficient Molecular Rectification in Metal-Molecules-Semimetal Junctions

Molecular rectification is expected to be observed in metal-molecule-metal tunnel junctions in which the resonance levels responsible for their transport properties are spatially localized asymmetrically with respect to the leads. Yet, effects such as electrostatic screening and formation of metal induced gap states reduce the magnitude of rectification that can be realized in such junctions. Here we suggest that junctions of the form metal-molecule(s)-semimetal mitigate these interfacial effects. We report current rectification in junctions based on the semimetal bismuth (Bi) with high rectification ratios (>10²) at 1.0 V using alkanethiols, molecules for which rectification has never been observed. In addition to the alleviation of screening and surface states, the efficient rectification is argued to be related to symmetry breaking of the applied bias in these junctions because of a built-in potential within the Bi lead. The significance of this built-in potential and its implications for the future and other applications are discussed.