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

© The Royal Society of Chemistry. 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, AuCCCCCCCCSiMe3 (AuC8SiMe3). In the second stage, treatment of AuC8SiMe3 with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer AuCCCCCCCCH (AuC8H). The reactive terminal CC-H moiety in AuC8H can be modified by ‘click' reactions with (azidomethyl)ferrocene (N3CH2Fc) to introduce a redox probe, to give AuC6C2N3HCH2Fc. Alternatively, incubation of the modified gold substrate supported monolayer AuC8H 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 AuC8GNP 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 AuC6C2N3HCH2Fc systems and after formation of the gold top-contact electrode in AuC8GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal-monolayer-metal devices AuC8GNP featuring ‘all-carbon' molecular wires were characterised by sigmoidal I-V curves, indicative of well-behaved junctions free of short circuits.