Chalcogenide phase-change materials (PCMs), in particular, the flagship Ge2Sb2Te5 (GST), are leading candidates for advanced memory applications. Yet, GST in conventional devices suffer from high power consumption, because the RESET operation requires melting of the crystalline GST phase. Recently, we have developed a conductive-bridge scheme for low-power phase-change application utilizing a self-decomposed Ge-Sb-O (GSO) alloy. In this work, we present thorough structural and electrical characterizations of GSO thin films by tailoring the concentration of oxygen in the phase-separating GSO system. We elucidate a two-step process in the as-deposited amorphous film upon the introduction of oxygen: with increasing oxygen doping level, germanium oxides form first, followed by antimony oxides. To enable the conductive-bridge switching mode for femtojoule-level RESET energy, the oxygen content should be sufficiently low to keep the antimony-rich domains easily crystallized under external electrical stimulus. Our work serves as a useful example to exploit alloy decomposition that develops heterogeneous PCMs, minimizing the active switching volume for low-power electronics.
Quasi-two-dimensional (quasi-2D) perovskites are promising materials for potential application in light-emitting diodes (LEDs) due to their high exciton binding energy and efficient emission. However, their luminescent performance is limited by the low-n phases that act as quenching luminescence centers. Here, a novel strategy for eliminating low-n phases is proposed based on the doping of strontium bromide (SrBr2) in perovskites, in which SrBr2 is able to manipulate the growth of quasi-2D perovskites during their formation. It was reasonably inferred that SrBr2 readily dissociated strontium ions (Sr2+) in dimethyl sulfoxide solvent, and Sr2+ was preferentially adsorbed around [PbBr6]4− through strong electrostatic interaction between them, leading to a controllable growth of quasi-2D perovskites by appropriately increasing the formation energy of perovskites. It has been experimentally proved that the growth can almost completely eliminate low-n phases of quasi-2D perovskite films, which exhibited remarkably enhanced photoluminescence. A high electroluminescent efficiency matrix green quasi-2D perovskite-LED (PeLED) with a pixel density of 120 pixels per inch fabricated by inkjet printing technique was achieved, exhibiting a peak external quantum efficiency of 13.9%, which is the most efficient matrix green quasi-2D PeLED so far to our knowledge.
Carbon, as an indispensable chemical element on Earth, has diverse covalent bonding ability, which enables construction of extensive pivotal carbon-based structures in multiple scientific fields. The extraordinary physicochemical properties presented by pioneering synthetic carbon allotropes, typically including fullerenes, carbon nanotubes, and graphene, have stimulated broad interest in fabrication of carbon-based nanostructures and nanomaterials. Accurate regulation of topology, size, and shape, as well as controllably embedding target spn-hybridized carbons in molecular skeletons, is significant for tailoring their structures and consequent properties and requires atomic precision in their preparation. Scanning probe microscopy (SPM), combined with on-surface synthesis strategy, has demonstrated its capabilities in fabrication of various carbon-based nanostructures and nanomaterials with atomic precision, which has long been elusive for conventional solution-phase synthesis due to realistic obstacles in solubility, isolation, purification, etc. More intriguingly, atom manipulation via an SPM tip allows unique access to local production of highly reactive carbon-based nanostructures. In addition, SPM provides topographic information of carbon-based nanostructures as well as their characteristic electronic structures with unprecedented submolecular resolution in real space. In this review, we overview recent exciting progress in the delicate application of SPM in probing low-dimensional carbon-based nanostructures and nanomaterials, which will open an avenue for the exploration and development of elusive and undiscovered carbon-based nanomaterials.
Scanning probe microscopy (SPM) allows the spatial imaging, measurement, and manipulation of nano and atomic scale surfaces in real space. In the last two decades, numerous advanced and functional SPM methods, particularly atomic force microscopy (AFM), have been developed and applied in various research fields, from mapping sample morphology to measuring physical properties. Herein, we review the recent progress in functional AFM methods and their applications in studies of two-dimensional (2D) materials, particularly their interfacial physical properties on the substrates. This review can inspire more exciting application works using advanced AFM modes in the 2D and functional materials fields.
Flash memory with high operation speed and stable retention performance is in great demand to meet the requirements of big data. In addition, the realisation of ultrafast flash memory with novel functions offers a means of combining heterogeneous components into a homogeneous device without considering impedance matching. This report proposes a 20 ns programme flash memory with 108 self-rectifying ratios based on a 0.65 nm-thick MoS2-channel transistor. A high-quality van der Waals heterojunction with a sharp interface is formed between the Cr/Au metal floating layer and h-BN tunnelling layer. In addition, the large rectification ratio and low ideality factor (n = 1.13) facilitate the application of the MoS2-channel flash memory as a bit-line select transistor. Finally, owing to the ultralow MoS2/h-BN heterojunction capacitance (50 fF), the memory device exhibits superior performance as a high-frequency (up to 1 MHz) sine signal rectifier. These results pave the way toward the potential utilisation of multifunctional memory devices in ultrafast two-dimensional NAND-flash applications.
We report the synthesis of ordered mesoporous ceria (mCeO2) with highly crystallinity and thermal stability using hybrid polymer templates consisting of organosilanes. Those organosilane-containing polymers can convert into silica-like nanostructures that further serve as thermally stable and mechanically strong templates to prevent the collapse of mesoporous frameworks during thermal-induced crystallization. Using a simple evaporation-induced self-assembly process, control of the interaction between templates and metal precursors allows the co-self-assembly of polymer micelles and Ce3+ ions to form uniform porous structures. The porosity is well-retained after calcination up to 900◦C. After the thermal engineering at 700 ◦C for 12 h (mCeO2-700-12 h), mCeO2 still has a specific surface area of 96 m2 g-1 with a pore size of 14 nm. mCeO2 is demonstrated to be active for electrochemical oxidation of sulfite. mCeO2-700-12 h with a perfect balance of crystallinity and porosity shows the fastest intrinsic activity that is about 84 times more active than bulk CeO2 and 5 times more active than mCeO2 that has a lower crystallinity.
Detection of ppb-level NO2 gas under atmosphere is urgent to meet the requirements of the rapidly developing internet of things. Compared with traditional sensing methods, light illumination has been considered as a key approach for excellent gas sensor performance under moderate conditions. Herein, we developed a green-light-assisted gas sensor based on cadmium sulfide nanowires (CdS NWs) that has good NO2 sensing capability at ambient temperature. The response values of NO2 are 236% and 11% to 10 ppm and 12.5 ppb, respectively. Furthermore, the CdS NWs sensor has a high selectivity for NO2 over a variety of interference gases, as well as good stability. The cleaning light activation and the sulfur vacancy-trapped charge behavior of CdS NWs are observed, which suggest a light-assisted sensing mechanism. These results suggest that light-induced charge separation behavior might significantly improve gas-sensing characteristics.
Since being rediscovered as an emerging 2D material, black phosphorus (BP), with an extraordinary energy structure and unusually strong interlayer interactions, offers new opportunities for optoelectronics and photonics. However, due to the thin atomic body and the ease of degradation with water and oxides, BP is highly sensitive to the surrounding environment. Therefore, high-quality engineering of interfaces and surfaces plays an essential role in BP-based applications. In this review, begun with a review of properties of BP, different strategies of interface and surfaces engineering for high ON-OFF ratio, enhanced optical absorption, and fast optical response are reviewed and highlighted, and recent state-of-the-art advances on optoelectronic and photonic devices are demonstrated. Finally, the opportunities and challenges for future BP-related research are considered.
Perovskite quantum dots (PeQDs) are considered potential display materials due to their high color purity, high photoluminescence quantum yield (PLQY), low cost and easy film casting. In this work, a novel electroluminescence (EL) device consisting of the interface layer of long alkyl-based oleylammonium bromide (OAmBr), which passivates the surface defects of PeQDs and adjusts the carrier transport properties, was designed. The PLQY of the OAmBr/PeQD bilayer was significantly improved. A high-performance EL device with the structure of indium tin oxide/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)/OAmBr/PeQDs/2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1H benzimidazole)/LiF/Al was constructed using a spin-coating method. A peak external quantum efficiency (EQE) of 16.5% at the emission wavelength of 646 nm was obtained. Furthermore, an efficient matrix EL device was fabricated using an inkjet printing method. A high-quality PeQD matrix film was obtained by introducing small amounts of polybutene into the PeQDs to improve the printing process. The EQE reached 9.6% for the matrix device with 120 pixels per inch and the same device structure as that of the spin-coating one.