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.

Charge transport measurements on flexible Mo 6 S 3 I 6 ͑MoSI͒ nanowires with different diameters in highly imperfect two-terminal circuits reveal systematic power-law behavior of the conductivity ͑T , V͒ as a function of temperature and voltage. On the basis of measurements on a number of circuits we conclude that the behavior in thin wires can be most convincingly described by tunneling through Tomonaga-Luttinger liquid segments of MoSI wire, which is in some cases modified by environmental Coulomb blockade. The latter are proposed to arise from deformations or imperfections of the MoSI wires, which-in combination with their recognitive terminal sulfur-based connectivity properties-might be useful for creating subnanometer scale interconnects as well as nonlinear elements for molecular electronics.

Mo6S3I6 nanowire networks of interest are found to change their resistance in response to the presence of analyte vapors. The vapor sensing behavior is quantitatively described very well phenomenologically in terms of the concentration of adsorbed analyte molecules in the contact tunneling junctions, and an expression is derived for the dynamics and sensor resistance in terms of analyte vapor pressure. The time response of the sensor is observed to follow simple adsorption–desorption kinetics. The network sensor shows very clear selectivity, whereby the response is related to the dipole moment of the analyte. The response function favors rapid detection of small analyte concentrations.

We report on a new highly reproducible route to recognitive self‐assembly of molecular‐scale circuits using sulfur‐terminated subnanometer diameter Mo6S9–x Ix (MoSIx) molecular nanowires.We demonstrate solutionprocessed 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. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)