Enhancement of resistive switching under confined current path distribution enabled by insertion of atomically thin defective monolayer graphene.

Resistive random access memory (ReRAM) devices have been extensively investigated resulting in significant enhancement of switching properties. However fluctuations in switching parameters are still critical weak points which cause serious failures during 'reading' and 'writing' operations of ReRAM devices. It is believed that such fluctuations may be originated by random creation and rupture of conducting filaments inside ReRAM oxides. Here, we introduce defective monolayer graphene between an oxide film and an electrode to induce confined current path distribution inside the oxide film, and thus control the creation and rupture of conducting filaments. The ReRAM device with an atomically thin interlayer of defective monolayer graphene reveals much reduced fluctuations in switching parameters compared to a conventional one. Our results demonstrate that defective monolayer graphene paves the way to reliable ReRAM devices operating under confined current path distribution.

Ultra-thin resistive switching oxide layers self-assembled by field-induced oxygen migration (FIOM) technique.

High-performance ultra-thin oxide layers are required for various next-generation electronic and optical devices. In particular, ultra-thin resistive switching (RS) oxide layers are expected to become fundamental building blocks of three-dimensional high-density non-volatile memory devices. Until now, special deposition techniques have been introduced for realization of high-quality ultra-thin oxide layers. Here, we report that ultra-thin oxide layers with reliable RS behavior can be self-assembled by field-induced oxygen migration (FIOM) at the interface of an oxide-conductor/oxide-insulator or oxide-conductor/metal. The formation via FIOM of an ultra-thin oxide layer with a thickness of approximately 2-5 nm and 2.5% excess oxygen content is demonstrated using cross-sectional transmission electron microscopy and secondary ion mass spectroscopy depth profile. The observed RS behavior, such as the polarity dependent forming process, can be attributed to the formation of an ultra-thin oxide layer. In general, as oxygen ions are mobile in many oxide-conductors, FIOM can be used for the formation of ultra-thin oxide layers with desired properties at the interfaces or surfaces of oxide-conductors in high-performance oxide-based devices.

Confining grains of textured Cu2O films to single-crystal nanowires and resultant change in resistive switching characteristics.

By confining columnar grains of textured oxide film using anodized aluminum oxide template, we could obtain a grain-boundary-free (GB-free) cuprous oxide (Cu(2)O) nanowire arrays with a narrow diameter distribution and a high density under the same electrochemical deposition condition. A two-terminal device fabricated using an individual GB-free nanowire and Au/Cr electrodes exhibits bipolar resistive switching contrary to the unipolar one of a textured film, and Schottky-like conduction. On the other hand, a nanowire device with Pt electrodes reveals non-switching behavior and Ohmic conduction. Thus, we can propose that the bipolar switching of a nanowire device with Au/Cr electrodes may result from the modulation of Schottky barrier at the interface by migration of oxygen vacancies while the unipolar one of a textured film may be defined as the bulky filamentary switching along the GBs in the GB-embedded texture films.

Agarose and gellan as morphology-directing agents for the preparation of selenium nanowires in water.

Commercially available polysaccharides, agarose and gellan, were used as morphology-directing agents for the synthesis of t-Se nanowires in water at room temperature in the presence of ascorbic acid as reducing agent. The nanostructures were characterized using XRD, SEM, and TEM. The diameter of the nanowires varied from 100 to 208 nm for nanowires obtained in the presence of agarose and from 51 to 145 nm for nanowires from gellan, as evidenced by SEM and TEM. Agarose and gellan have then a potential as environmentally acceptable morphology-directing agents to generate Se nanostructures in water.