Reliable multilevel resistive switching in nanoscale cells is desirable for the wide adoption of resistive random access memory as the next-generation nonvolatile memory. We designed NiO-based cells in arrays of multilayered NiO/Pt nanowires to explore multilevel memory effects. Nonpolar resistive switching reproducibly occurs with significantly reduced switching voltages, narrow switching voltage distributions and a robust multilevel memory effect. A high resistance ratio (B10 5 ) between the highand low-resistance states in nanoscale cells enables stable multilevels that can be induced easily by a series of pulsed voltage. The existence of intermediate resistance states in NiO/Pt nanowire arrays can be well explained by the binary-resistor model combined with energy perturbations induced by the pulse voltage. We also verified that the conduction mechanism in multilayered NiO/Pt nanowires is dominated by the hopping of holes. Our bottom-up approach and proposed mechanism explain the controllable multilevel memory effect and facilitate sound device design to encourage their universal adoption.

Fabrication of a nanosize metal aperture for a near field scanning optical microscopy sensor using photoresist removal and sputtering techniques This paper presents an innovative approach for directly forming surface microstructures at submicrometer scale on the cylindrical surface of a metal roller. This roller can then serve as a roller mold in roller imprinting processes for large-area micro/nanofabrication. In the proposed approach, a novel contact printing method is used to transfer a patterned metal film from a planar soft mold to a thin photoresist (PR) layer coated on the roller surface. The pattern definition capability can easily reach submicrometer scale over a large patterning area. Subsequent ultraviolet light exposure and PR developing processes then form a layer of patterned PR microstructures on the cylindrical surface. Finally, patterned microfeatures are directly formed on the roller's surface by an additive (metal deposition) approach. The overall system design, experimental procedures, and experimental results are systematically discussed.