Conductivity of single Mo₆S_9−<i>x</i>I_<i>x</i>molecular nanowire bundles

Abstract

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.