Programmable Conductance Switching and Negative Differential Resistance in Nanoscale Organic Films

Thin (12-nm) self-assembled films of the insulating molecule 11-mercaptoundecanoic acid (MUA) were contacted by gold electrodes in a sandwich structure. Current-voltage scans of the resulting devices revealed symmetric negative differential resistance (NDR) with peaks at ±3 V and large peak current densities of up to 10 A/cm. Devices could be programmed reversibly into nonvolatile highand low-conductance states by applying 1-ms voltage pulses of 4 V and 10 V, respectively; this conductance could be probed non-destructively with voltages below 2.5 V. A conductance ratio of 10 between the highand low-conductance states was measured. The NDR is attributed to the dynamic alteration of the device conductivity as the voltage is scanned. Devices fabricated with one gold and one aluminum electrode displayed NDR only for positive bias on the gold electrode, which supports a model in which the observed programming and NDR is due to the movement of gold in the film leading to the formation and destruction of conductive pathways through the insulating layer.