Observation of Step-like Conductance Plateaus in a Molecular Film

We explore the transport properties of a film made of a Ru-complex displaying memristive response where the switching in film conductance is controlled by the ligand redox states of the film molecules, while the counter ions account for the hysteresis. As temperature is lowered, the hysteresis in J(V) gradually decays below 145K till ~5K where it completely quenches. In the temperature range of 135K to 110K, we observe well resolved conductance plateaus at different applied bias with sharp transition in between them. The number of plateaus N in the J(V) follows the empirical rule of N= d[nm]/5 where d is the film thickness in nm. The conductance plateaus correspond to a correlation of [J₀]^N, with J₀ = current of the first plateau. Each of the plateaus are characterized by in-situ Raman spectroscopy as well as photoluminescence (PL) measurement which scale as N x I₀, where I₀ is the PL/Raman intensity of the first plateau. These observations indicate a layer by layer electron doping in the film where layers of around 5 nm get doped sequentially. By reducing the van der Wall radius of the counterion this step can be reduced to a single layer ~ 1.5nm! This is an unprecedented result in an amorphous film which might have significant implication in neuromorphic computing.