Interface-Engineered Resistive Switching: CeO₂ Nanocubes as High-Performance Memory Cells

We reported a novel and facile approach to fabricate self-assembled CeO₂ nanocube-based resistive-switching memory device. The device was found to exhibit excellent bipolar resistive-switching characteristics with a high resistance state (HRS/OFF) to low resistance state (LRS/ON) ratio of 10⁴, better uniformity, and stability up to 480 K. The presence of oxygen vacancies and their role was discussed to explain the resistive-switching phenomenon in the fabricated devices. Further, the effect of the film thickness on carrier concentrations and estimated electric field strength with the switching (OFF/ON) ratio were also discussed

Highly Efficient and Selective Cu/MnO_<i>x</i> Catalysts for Carbon Dioxide Reduction

Catalytic reduction of carbon dioxide (CO₂) to chemical and energy feedstocks is of great importance to both environmental improvement and energy regeneration. Herein, a Cu decorated MnO_<i>x</i> nanowirebased heterogeneous catalyst was rationally designed via a facile hydrothermal method toward the optimization of their performance in CO₂ reduction. The synthesized Cu/MnO_<i>x</i> combines well-dispersed Cu nanoparticles on MnO_<i>x</i> nanowires, exhibiting a nearly complete conversion efficiency and 100% selectivity toward reverse water gas shift to produce CO under mild reaction conditions (425 °C). It is found that Cu/MnO_<i>x</i> with Cu/Mn molar ratio of 1:1 with a strong interaction between metal and support possessed rich surface oxygen vacancies and lattice strain, resulting in the optimal activity with CO₂ conversion rate of 13.8 μmol g_cat^–1 s^–1 and TOF of 4.32 mol mol_cat^–1 h^–1. The strategy to optimize the metal–support interaction in this work has opened a new avenue for the design of advanced noble-metal-free catalysts for more heterogeneous catalytic applications

Interfacial Redox Reactions Associated Ionic Transport in Oxide-Based Memories

As an alternative to transistor-based flash memories, redox reactions mediated resistive switches are considered as the most promising next-generation nonvolatile memories that combine the advantages of a simple metal/​solid electrolyte (insulator)/​metal structure, high scalability, low power consumption, and fast processing. For cation-based memories, the unavailability of in-built mobile cations in many solid electrolytes/​insulators (e.g., Ta₂O₅, SiO₂, etc.) instigates the essential role of absorbed water in films to keep electroneutrality for redox reactions at counter electrodes. Herein, we demonstrate electrochemical characteristics (oxidation/​reduction reactions) of active electrodes (Ag and Cu) at the electrode/​electrolyte interface and their subsequent ions transportation in Fe₃O₄ film by means of cyclic voltammetry measurements. By posing positive potentials on Ag/Cu active electrodes, Ag preferentially oxidized to Ag⁺, while Cu prefers to oxidize into Cu²⁺ first, followed by Cu/Cu⁺ oxidation. By sweeping the reverse potential, the oxidized ions can be subsequently reduced at the counter electrode. The results presented here provide a detailed understanding of the resistive switching phenomenon in Fe₃O₄-based memory cells. The results were further discussed on the basis of electrochemically assisted cations diffusions in the presence of absorbed surface water molecules in the film

Synthesis of Au and Pt Hollow Capsules with Single Holes via Pickering Emulsion Strategy

Au and Pt hollow capsules with single holes were synthesized via a Pickering emulsion strategy. Pickering emulsions provided particles with oil–water interfaces as asymmetric platform for anisotropic structure sculpture. Reactive Cu₂O particles were utilized not only as emulsifier to prepare Pickering emulsions but also as sacrificed hard template for the consequent asymmetric galvanic reaction at the oil–water interfaces, resulting in the formation of open-mouthed Au and Pt hollow capsules. The opened hollow structure can facilitate the diffusion of reactants to inner side of the shell wall, thus effectively activating the catalytic activity of the inner shell wall of the hollow capsules. The obtained open-mouthed Au hollow capsules show much higher catalytic performance than that of intact Au hollow capsules

Threshold Switching Induced by Controllable Fragmentation in Silver Nanowire Networks

Silver nanowire (Ag NW) networks have been widely studied because of a great potential in various electronic devices. However, nanowires usually undergo a fragmentation process at elevated temperatures due to the Rayleigh instability that is a result of reduction of surface/interface energy. In this case, the nanowires become completely insulating due to the formation of randomly distributed Ag particles with a large distance and further applications are hindered. Herein, we demonstrate a novel concept based on the combination of ultraviolet/ozone irradiation and a low-temperature annealing process to effectively utilize and control the fragmentation behavior to realize the resistive switching performances. In contrast to the conventional fragmentation, the designed Ag/AgO_<i>x</i> interface facilitates a unique morphology of short nanorod-like segments or chains of tiny Ag nanoparticles with a very small spacing distance, providing conduction paths for achieving the tunneling process between the isolated fragments under the electric field. On the basis of this specific morphology, the Ag NW network has a tunable resistance and shows volatile threshold switching characteristics with a high selectivity, which is the ON/OFF current ratio in selector devices. Our concept exploits a new function of Ag NW network, i.e., resistive switching, which can be developed by designing a controllable fragmentation

High-Performance Nanocomposite Based Memristor with Controlled Quantum Dots as Charge Traps

We report a novel approach to improve the resistive switching performance of semiconductor nanorod (NR) arrays, by introducing ceria (CeO₂) quantum dots (QDs) as surface charge trappers. The vertically aligned zinc oxide (ZnO) (NR) arrays were grown on transparent conductive glass by electrochemical deposition while CeO₂ QDs were prepared by a solvothermal method. Subsequently, the as-prepared CeO₂ QDs were embedded into a ZnO NR array by dip coating to obtain a CeO₂–ZnO nanocomposite. Interestingly, such a device exhibits excellent resistive switching properties with much higher ON/OFF ratios, better uniformity, and stability over the pure ZnO and CeO₂ nanostructures. The origin of resistive switching was studied and the role of heterointerface was discussed

Interface Thermodynamic State-Induced High-Performance Memristors

A new class of memristors based on long-range-ordered CeO₂ nanocubes with a controlled degree of self-assembly is presented, in which the regularity and range of the nanocubes can be greatly improved with a highly concentrated dispersed surfactant. The magnitudes of the hydrophobicity and surface energy components as functions of surfactant concentration were also investigated. The self-assembled nanostructure was found to demonstrate excellent degradation in device threshold voltage with excellent uniformity in resistive switching parameters, particularly a set voltage distribution of ∼0.2 V over 30 successive cycles and a fast response time for writing (0.2 μs) and erasing (1 μs) operations, thus offering great potential for nonvolatile memory applications with high performance at low cost

Engineering Silver Nanowire Networks: From Transparent Electrodes to Resistive Switching Devices

Metal nanowires (NWs) networks with high conductance have shown potential applications in modern electronic components, especially the transparent electrodes over the past decade. In metal NW networks, the electrical connectivity of nanoscale NW junction can be modulated for various applications. In this work, silver nanowire (Ag NW) networks were selected to achieve the desired functions. The Ag NWs were first synthesized by a classic polyol process, and spin-coated on glass to fabricate transparent electrodes. The as-fabricated electrode showed a sheet resistance of 7.158 Ω □^–1 with an optical transmittance of 79.19% at 550 nm, indicating a comparable figure of merit (FOM, or Φ_TC) (13.55 × 10^–3 Ω^–1). Then, two different post-treatments were designed to tune the Ag NWs for not only transparent electrode but also for threshold resistive switching (RS) application. On the one hand, the Ag NW film was mechanically pressed to significantly improve the conductance by reducing the junction resistance. On the other hand, an Ag@AgO_<i>x</i> core–shell structure was deliberately designed by partial oxidation of Ag NWs through simple ultraviolet (UV)-ozone treatment. The Ag core can act as metallic interconnect and the insulating AgO_<i>x</i> shell acts as a switching medium to provide a conductive pathway for Ag filament migration. By fabricating Ag/Ag@AgO_<i>x</i>/Ag planar structure, a volatile threshold switching characteristic was observed and an on/off ratio of ∼100 was achieved. This work showed that through different post-treatments, Ag NW network can be engineered for diverse functions, transforming from transparent electrodes to RS devices

Liquid-Metal Solvents for Designing Hierarchical Nanoporous Metals at Low Temperatures

Metallic nanoarchitectures hold immense value as functional materials across diverse applications. However, major challenges lie in effectively engineering their hierarchical porosity while achieving scalable fabrication at low processing temperatures. Here we present a liquid-metal solvent-based method for the nanoarchitecting and transformation of solid metals. This was achieved by reacting liquid gallium with solid metals to form crystalline entities. Nanoporous features were then created by selectively removing the less noble and comparatively softer gallium from the intermetallic crystals. By controlling the crystal growth and dealloying conditions, we realized the effective tuning of the micro-/nanoscale porosities. Proof-of-concept examples were shown by applying liquid gallium to solid copper, silver, gold, palladium, and platinum, while the strategy can be extended to a wider range of metals. This metallic-solvent-based route enables low-temperature fabrication of metallic nanoarchitectures with tailored porosity. By demonstrating large-surface-area and scalable hierarchical nanoporous metals, our work addresses the pressing demand for these materials in various sectors