Towards molecular electronic devices based on ‘all-carbon’ wires

Abstract

Nascent molecular electronic devices based on linear ‘all-carbon’ wires attached to gold electrodes through robust and reliable C–Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me₃Si–(CC)₄–SiMe₃ (1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|CCCCCCCCSiMe₃ (Au|C₈SiMe₃). In the second stage, treatment of Au|C₈SiMe₃ with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer Au|CCCCCCCCH (Au|C₈H). The reactive terminal CC–H moiety in Au|C₈H can be modified by ‘click’ reactions with (azidomethyl)ferrocene (N₃CH₂Fc) to introduce a redox probe, to give Au|C₆C₂N₃HCH₂Fc. Alternatively, incubation of the modified gold substrate supported monolayer Au|C₈H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon–Au σ-bond, to give structures Au|C₈|GNP in which the monolayer of linear, ‘all-carbon’ C₈ chains is sandwiched between two macroscopic gold contacts. The covalent carbon–surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C–H bond is confirmed by surface-enhanced Raman scattering (SERS). The integrity of the carbon chain in both Au|C₆C₂N₃HCH₂Fc systems and after formation of the gold top-contact electrode in Au|C₈|GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal–monolayer–metal devices Au|C₈|GNP featuring ‘all-carbon’ molecular wires were characterised by sigmoidal I–V curves, indicative of well-behaved junctions free of short circuits.