Electrical transport study of individually-wired colloidal nano-rods

Colloidal semiconducting nano-particles can be fabricated with fine control over size, shape and composition. They have been studied extensively by optical techniques, but very few attempts have been made to wire such particles into an electrical circuit. This work presents a study of wiring individual CdSe and CdS nano-rods, 30-70 nm long and of 4-5 nm diameter, by applying the Electron-Beam-Induced-Deposition (EBID) technique. EBID is based on electron-bean dissociation of precursor molecules and allows the single-step in-situ deposition of thin (< 10 nm) metallic lines onto a substrate. The resulting devices are measured at T = 4-300K. At 4K many of the devices exhibit smooth I(V) curves with no sharp onset features, which remarkably fit a field-effect (Fowler-Nordheim) tunneling model. All devices exhibit an anomalous exponential temperature dependence, of the form I ~ exp(T/To). This highly irregular behavior, which can not be explained by any hopping or activation model, is interpreted by accounting for the lowering of the conduction band due to lattice dilation and phonon-coupling.