1. Materials Science Centre, University of Groningen, Nijenborgh 4, NL-9747 AG, Groningen, The Netherlands
2. Philips Research Laboratories, High Tech Campus 4, NL-5656 AA, Eindhoven, The Netherlands

Correspondence to: Bert de Boer¹ Correspondence and requests for materials should be addressed to B.d.B. (Email: b.de.boer@rug.nl).

Abstract

Electronic transport through single molecules has been studied extensively by academic^{1, 2, 3, 4, 5, 6, 7, 8} and industrial^{9, 10} research groups. Discrete tunnel junctions, or molecular diodes, have been reported using scanning probes^{11, 12}, break junctions^{13, 14}, metallic crossbars⁶ and nanopores^{8, 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 electrode^{16, 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 m 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.

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