Yongai Zhang

Highly reproducible memory effect of organic multilevel resistive-switch device utilizing graphene oxide sheets/polyimide hybrid nanocomposite

The functionalization of graphene oxide (GO) sheets with polyimide (PI) enables the layer-by-layer fabrication of a GO-PI hybrid resistive-switch device and leads to high reproducibility of the memory effect. The current-voltage curves for the as-fabricated device exhibit multilevel resistive-switch properties under various reset voltages. The capacitance-voltage characteristics for a capacitor based on GO-PI nanocomposite indicate that the electrical switching may originate from the charge trapping in GO sheets. The high device-to-device uniformity and unique memory properties of the device make it an attractive candidate for applications in next-generation high-density nonvolatile flash memories.

Structural, Optical, and Improved Field-Emission Properties of Tetrapod-Shaped Sn-Doped ZnO Nanostructures Synthesized via Thermal Evaporation

High-quality tetrapod-shaped Sn-doped ZnO (T-SZO) nanostructures have been successfully synthesized via the thermal evaporation of mixed Zn and Sn powder. The effects of the Sn dopant on the morphology, microstructure, optical, and field-emission (FE) properties of T-SZO were investigated. It was found that the growth direction of the legs of T-SZO is parallel to the [0001] crystal c-axis direction and that the incorporation of Sn in the ZnO matrix increases the aspect ratio of the tetrapods, leads to blue shift in the UV region, and considerably improves the FE performance. The results also show that tetrapod cathodes with around a 0.84 atom % Sn dosage have the best FE properties, with a turn-on field of 1.95 V/μm, a current density of 950 μA/cm2 at a field of 4.5 V/μm, and a field-enhancement factor as high as 9556.

Recoverable electrical transition in a single graphene sheet for application in nonvolatile memories

The electrical properties of a resistive-switching memory based on a single graphene sheet suspended on a patterned indium-tin-oxide electrode pair were investigated. Current-voltage measurements on the planar device showed a large ON/OFF ratio (∼106) and excellent retention ability in ambient conditions. Data storage of the device can be realized by applying voltage bias and rewritten after simple heat treatment. Switching mechanisms for the graphene-based memory device were found to be related to the local oxidation of graphene sheet at the graphene/electrode interface.