High-Speed Optoelectronic Nonvolatile Memory Based on van der Waals Heterostructures.

High-performance optoelectronic nonvolatile memory is promising candidate for next-generation information memory devices. Here, a floating-gate memory is constructed based on van der Waals heterostructure, which exhibits a large storage window ratio (≈75.5%) and an extremely high on/off ratio (107 ), as well as an ultrafast electrical writing/erasing speed (40 ns). The enhanced performance enables as-fabricated devices to present excellent multilevel data storage, robust retention, and endurance performance. Moreover, stable optical erasing operations can be achieved by illuminating the device with a laser pulse, showcasing outstanding optoelectronic storage performance (optical erasing speed ≈ 2.3 ms). The nonvolatile and high-speed characteristics of these devices hold significant potential for the integration of high-performance nonvolatile memory.

An anomalous Hall effect in edge-bonded monolayer graphene.

An anomalous Hall effect (AHE) is usually presumed to be absent in pristine graphene due to its diamagnetism. In this work, we report that a gate-tunable Hall resistance Rxy can be obtained in edge-bonded monolayer graphene without an external magnetic field. In a perpendicular magnetic field, Rxy consists of a sum of two terms: one from the ordinary Hall effect and the other from the AHE (RAHE). Plateaus of Rxy ∼ 0.94h/3e2 and RAHE ∼ 0.88h/3e2 have been observed while the longitudinal resistance Rxx decreases at a temperature of 2 K, which are indications of the quantum version of the AHE. At a temperature of 300 K, Rxx shows a positive, giant magnetoresistance of ∼177% and RAHE still has a value of ∼400 Ω. These observations indicate the existence of a long-range ferromagnetic order in pristine graphene, which may lead to new applications in pure carbon-based spintronics.

In-situelectrochemical polymerization of aniline on flexible conductive substrates for supercapacitors and non-enzymatic ascorbic acid sensors.

Polyaniline, as a kind of conductive polymer with commercial application prospects, is still under researches in its synthesis and applications. In this work, polyaniline was fabricated on flexible substrates including carbon cloths and polyethylene naphthalate byin situelectropolymerization method. The synthesized flexible electrodes were characterized by scanning electron microscopy, High resolution transmission electron microscope, atomic force microscope, Fourier transform infrared, x-ray diffraction, and x-ray photoelectron spectroscopy. Owing to the conductivity and the reversible redox property, the polyaniline/carbon cloth electrodes show excellent properties such as decent supercapacitor performance and good detection capability toward ascorbic acid. As supercapacitors, the electrodes exhibit a specific capacitance as high as 776 F g-1at a current density of 1 A g-1and a long cycle life of 20 000 times in the three-electrode system. As ascorbic acid sensors, the flexible electrodes demonstrate stable response to ascorbic acid in the range of 1-3000µM with an outstanding sensitivity (4228µA mM-1cm-2), low detection limit (1µM), and a fast response time. This work holds promise for high-performance and low-cost flexible electrodes for both supercapacitors and non-enzymatic ascorbic acid sensors, and may inspire inventions of self-powered electrochemical sensor.

Extremely Low Program Current Memory Based on Self-Assembled All-Inorganic Perovskite Single Crystals.

Memory devices based on lead halide perovskite have attracted great interests because of their unique current-voltage hysteresis. However, current memory devices based on polycrystalline perovskites usually suffer from large intrinsic electronic current and parasitic leakage current due to the existence of grain boundaries, which further leads to high power consumption. Here, a low-power resistance switching random-access memory device is demonstrated by assembling single-crystalline CsPbBr3 on Ag electrodes. The assembled structure serves as a bipolar nonvolatile resistance switching memory device with a low program current (∼10 nA), good endurance, long data retention (>103 S), and big on/off ratio of ∼103. The low program current results in a power of ∼3 × 10-8 W, which is much lower than that of polycrystalline perovskite-based devices (10-1-10-6 W). It is found that the formation and annihilation of Ag and bromide vacancy conductive filaments contribute to the significant resistive switching effect. At a low resistive state, the conductive filaments originate from the accumulation of Br- ions at the drain. Furthermore, the conductive filaments are proved to be a cone shape, shrinking from the drain to the source.