Arrays of Au/NiOx/Ni/Au nanowires with a diameter of 50 nm were characterized by conductive atomic force microscopy, which was used to probe the electrical behavior of single nanowires still included in the array. A bipolar switching of the single Au/NiOx/Ni/Au nanowires is demonstrated and is attributed to the choice of an asymmetric couple of electrode materials and, possibly, to a non-uniform Ni oxidation profile inside the NiOx segments. An analysis of the conduction mechanism in a single nanowire is presented to further support this conclusion.
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A very rough estimation of the order of magnitude of the SET resistance can be obtained considering that the reset voltage has been found to be almost constant in unipolar NiO-based cells (Ref. 22) around a value of 1 V. Then, if this empirical rule held true also in the present case, one should expect a reset voltage dropping on the nanowire of about 1 V when we apply 5 V to the entire voltage divider composed of nanowire and contact resistance. Considering a total resistance of 35 kΩ, we obtain a nanowire SET resistance of about 7 kΩ and a tip-sample contact resistance of 28 kΩ.
