We report on a new highly reproducible route to recognitive self-assembly of molecular-scale circuits using sulfur-terminated subnanometer diameter Mo6S9-xIx (MoSIx) molecular nanowires. We demonstrate solution-processed attachment of MoSIx connecting leads to gold nanoparticles (GNPs). We also show that naked nanowires have the potential to bind thiolated proteins such as green fluorescent protein directly, thus providing a universal construct to which almost any protein could be attached. We further demonstrate three-terminal branched circuits with GNPs, opening a self-assembly route to multiscale complex molecular-scale architectures at the single-molecule level.

Longitudinal resistivity measurements on single Mo6S9−xIx (x = 4.5, 6 and 7) molecular nanowire bundles ranging in diameter from d = 7 nm to 1 µm are performed to investigate the longitudinal transport properties of individual bundles. Different contacting methods are used to study diverse nanocircuit manufacturing technologies that can be used for interconnects based on Mo6S9−xIx. The measurements show ubiquitously linear I–V characteristics with Pd, Au, Ag and Ti contact metals. The highest room-temperature conductivity achieved is σ0∼10 S m−1 using Ag contacts. The critical current densities typically achieved are Jc∼104 A cm−2. The observed metallic behaviour at room temperature is consistent with the band structure calculated using density functional theory (DFT). At low temperatures, the conductivity is found to decrease, following variable range hopping (VRH) behaviour of the form σ = σ0exp−(T0/T)β reasonably well, but the exponent β changes upon annealing. From fits to the temperature dependence of the conductivity, a change from β∼1/4 to β∼1/2 is observed, which may be explained by a change in dimensionality from 3D-like VRH to 1D-like VRH following the removal of intra-bundle interstitial iodine.

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The field emission (FE) properties of nanowires made from the recently synthesized nanowire material Mo6S3I6 are reported. A single nanowire was mounted on an indium-coated nickel holder by dielectrophoresis in isopropyl alcohol. A careful activation or conditioning in a vacuum of 10−7 mbar was shown to be indispensable in order to extract relatively stable FE currents in excess of 1 µA originating from only a few sites at the end of the nanowire. Measurements were performed in an FE microscope with an additional plane mesh, which enables us to record I–U characteristics in diode mode, or to observe the emission patterns in triode mode. With FE currents around 5–7 µA the emitter degrades gradually, and to some extent irreversibly. The degradation mechanism is not a reversal of the instant site build-up.

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