Towards molecular electronics with large-area molecular junctions

Abstract

The use of molecular electronics is a much-discussed alternative to conventional silicon devices: the prospect of such tiny components has obvious implications for miniaturization. One approach is to replace the conventional semiconductor with a single molecular layer that self-organizes between two electrodes. Molecular tunnel junctions have been made in such systems, but they tend to be hard to reproduce, unstable and limited to small diameters. Now Akkerman et al. have developed a relatively simple way of producing stable, reproducible molecular junctions with large areas from self-assembled monolayers of alkanethiols. The process is compatible with standard integrated circuit technologies and could offer a cheap way forward in the quest for practical molecular electronics. A relatively simple method to fabricate stable, reproducible molecular junctions with large areas from self-assembled monolayers of alkanethiols has been developed — this approach could offer a cheap and promising way forward for molecular electronics. Electronic transport through single molecules has been studied extensively by academic1,2,3,4,5,6,7,8 and industrial9,10 research groups. Discrete tunnel junctions, or molecular diodes, have been reported using scanning probes11,12, break junctions13,14, metallic crossbars6 and nanopores8,15. For technological applications, molecular tunnel junctions must be reliable, stable and reproducible. The conductance per molecule, however, typically varies by many orders of magnitude5. Self-assembled monolayers (SAMs) may offer a promising route to the fabrication of reliable devices, and charge transport through SAMs of alkanethiols within nanopores is well understood, with non-resonant tunnelling dominating the transport mechanism8. Unfortunately, electrical shorts in SAMs are often formed upon vapour deposition of the top electrode16,17,18, which limits the diameter of the nanopore diodes to about 45 nm. Here we demonstrate a method to manufacture molecular junctions with diameters up to 100 µm with high yields (> 95 per cent). The junctions show excellent stability and reproducibility, and the conductance per unit area is similar to that obtained for benchmark nanopore diodes. Our technique involves processing the molecular junctions in the holes of a lithographically patterned photoresist, and then inserting a conducting polymer interlayer between the SAM and the metal top electrode. This simple approach is potentially low-cost and could pave the way for practical molecular electronics.