Multilevel Resistive Switching in Planar Graphene/SiO₂ Nanogap Structures

We report a planar graphene/SiO₂ nanogap structure for multilevel resistive switching. Nanosized gaps created on a SiO₂ substrate by electrical breakdown of nanographene electrodes were used as channels for resistive switching. Two-terminal devices exhibited excellent memory characteristics with good endurance up to 10⁴ cycles, long retention time more than 10⁵ s, and fast switching speed down to 500 ns. At least five conduction states with reliability and reproducibility were demonstrated in these memory devices. The mechanism of the resistance switching effect was attributed to a reversible thermal-assisted reduction and oxidation process that occurred at the breakdown region of the SiO₂ substrate. In addition, the uniform and wafer-size nanographene films with controlled layer thickness and electrical resistivity were grown directly on SiO₂ substrates for scalable device fabrications, making it attractive for developing high-density and low-cost nonvolatile memories

Goos-Hänchen Shift and Even–Odd Peak Oscillations in Edge-Reflections of Surface Polaritons in Atomically Thin Crystals

Two-dimensional surface polaritons (2DSPs), such as graphene plasmons, exhibit various unusual properties, including electrical tunability and strong spatial confinement with high Q-factor, which can enable tunable photonic devices for deep subwavelength light manipulations. Reflection of plasmons at the graphene’s edge plays a critical role in the manipulation of 2DSP and enables their direct visualization in near-field infrared microscopy. However, a quantitative understanding of the edge-reflections, including reflection phases and diffraction effects, has remained elusive. Here, we show theoretically and experimentally that edge-reflection of 2DSP exhibits unusual behaviors due to the presence of the evanescent waves, including an anomalous Goos-Hänchen phase shift as in total internal reflections and an unexpected even–odd peak amplitude oscillation from the wave diffraction at the edge. Our theory is not only valid for plasmons in graphene but also for other 2D polaritons, such as phonon polaritons in ultrathin boron nitride flakes and exciton polariton in two-dimensional semiconductors

Graphene Edge Lithography

Fabrication of graphene nanostructures is of importance for both investigating their intrinsic physical properties and applying them into various functional devices. In this paper, we report a scalable fabrication approach for graphene nanostructures. Compared with conventional lithographic fabrication techniques, this new approach uses graphene edges as the templates or masks and offers advantage in technological simplicity and capability of creating small features below 10 nm scale. Moreover, mask layers used in the fabrication process could be simultaneously used as the dielectric layers for top-gated devices. The as-fabricated graphene nanoribbons (GNRs) are of high quality with the carrier mobility ∼400 cm²/(V s) for typical 15 nm wide ribbons. Our technique allows easy and reproducible fabrication of various graphene nanostructures, such as ribbons and rings, and can be potentially extended to other materials and systems by use of their edges or facets as templates