Negative resistance behavior and reproducible resistance switching were found in polycrystalline NiO films deposited by dc magnetron reactive sputtering methods. Oxygen to argon gas ratio during deposition was critical in deciding the detailed switching characteristics of either bi-stable memory switching or mono-stable threshold switching. Both metallic nickel defects and nickel vacancies influenced the negative resistance and the switching characteristics. We obtained a distribution of low resistance values which were dependent on the compliance current of high-to-low resistance switching. At 200°C, the low-resistance state kept its initial resistance value while the high-resistance state reached 85% of its initial resistance value after 5×105s. We suggested that the negative resistance and the switching mechanism could be described by electron conduction related to metallic nickel defect states existing in deep levels and by small-polaron hole hopping conduction.

Otherwise identical regions of supported graphene can be distinguished by changes in friction with sliding direction.

The graphene/SiO₂ system is a promising building block for next-generation electronic devices, integrating the high electromagnetic performance of graphene with the mature technology of Si-based electronic devices. It is well known that the electromagnetic performance of graphene/SiO₂ is dramatically reduced by structural defects, such as wrinkles and folding, which are suspected to result from water droplets. Therefore, understanding water diffusion between graphene and SiO₂ is required for controlling structural defects and thus improving the electromagnetic performance of this system. Although the behavior of water between graphene and atomically flat mica has been investigated, the characteristics and effects of diffused water between graphene and SiO₂ remain unidentified. We have investigated water diffusion between monolayer graphene and SiO₂ under high humidity conditions using atomic force microscopy. For a relative humidity of over 90%, water diffuses into graphene/SiO₂ and forms an ice-like structure up to two layers thick. Liquid-like water can further diffuse in, stacking over the ice-like layer and evaporating relatively easily in the air causing graphene to wrinkle and fold. By similarly investigating water diffusion between graphene and mica, we argue that water-induced wrinkle formation depends on the hydrophilicity and roughness of the substrate.