Synthesis and electrical properties of fullerene-based molecular junctions on silicon substrate

TL;DR

This study synthesizes fullerene-based molecular junctions on silicon, examining their electrical properties and how alkyl chain length influences electron transport, with potential applications in molecular electronics.

Contribution

It introduces new synthesis routes for fullerene junctions on silicon and analyzes how alkyl chain length modulates electronic transport properties.

Findings

The fullerene LUMO - metal Fermi energy offset can be tuned from ~0.2 eV to ~1 eV.

Different synthesis routes affect the physico-chemical properties of the monolayers.

The alkyl chain length controls the electron tunneling barrier and energy level alignment.

Abstract

We report the synthesis and the electrical properties of fullerene-based molecular junctions on silicon substrate in which the highly \pi-conjugated molecule C60 (\pi quantum well) is isolated from the electrodes by alkyl chains (\sigma tunnel barriers). Initially, the Si/SiO2/\sigmaC60 architecture was prepared either by sequential synthesis (3 different routes) or by direct grafting of the presynthesized C60-\sigma-Si(OEt)3 molecule. We described the chemical synthesis of these routes and the physico-chemical properties of the molecular monolayers. Then, the second \sigma tunnel barrier was added on the Si/SiO2/\sigma C60 junction by applying a hanging mercury drop electrode thiolated with an alkanethiol monolayer. We compared the electronic transport properties of the Si/SiO2/\sigma C60//Hg and Si/SiO2/\sigma C60//\sigmaHg molecular junctions, and we demonstrated by transition voltage spectroscopy that the fullerene LUMO - metal Fermi energy offset can be tailored from ~ 0.2 eV to ~ 1 eV by changing the length of the alkyl chain between the C60 core and the Hg metal electrode (i. e. from direct C60//Hg contact to 14 carbon atoms tunnel barrier).