2D Reconfigurable Memory Device Enabled by Defect Engineering for Multifunctional Neuromorphic Computing.

In this era of artificial intelligence and Internet of Things, emerging new computing paradigms such as in-sensor and in-memory computing call for both structurally simple and multifunctional memory devices. Although emerging two-dimensional (2D) memory devices provide promising solutions, the most reported devices either suffer from single functionalities or structural complexity. Here, this work reports a reconfigurable memory device (RMD) based on MoS2/CuInP2S6 heterostructure, which integrates the defect engineering-enabled interlayer defects and the ferroelectric polarization in CuInP2S6, to realize a simplified structure device for all-in-one sensing, memory and computing. The plasma treatment-induced defect engineering of the CuInP2S6 nanosheet effectively increases the interlayer defect density, which significantly enhances the charge-trapping ability in synergy with ferroelectric properties. The reported device not only can serve as a non-volatile electronic memory device, but also can be reconfigured into optoelectronic memory mode or synaptic mode after controlling the ferroelectric polarization states in CuInP2S6. When operated in optoelectronic memory mode, the all-in-one RMD could diagnose ophthalmic disease by segmenting vasculature within biological retinas. On the other hand, operating as an optoelectronic synapse, this work showcases in-sensor reservoir computing for gesture recognition with high energy efficiency.

Precursor-Confined Chemical Vapor Deposition of 2D Single-Crystalline SexTe1-x Nanosheets for p-Type Transistors and Inverters.

Two-dimensional (2D) tellurium (Te) is emerging as a promising p-type candidate for constructing complementary metal-oxide-semiconductor (CMOS) architectures. However, its small bandgap leads to a high leakage current and a low on/off current ratio. Although alloying Te with selenium (Se) can tune its bandgap, thermally evaporated SexTe1-x thin films often suffer from grain boundaries and high-density defects. Herein, we introduce a precursor-confined chemical vapor deposition (CVD) method for synthesizing single-crystalline SexTe1-x alloy nanosheets. These nanosheets, with tunable compositions, are ideal for high-performance field-effect transistors (FETs) and 2D inverters. The preformation of Se-Te frameworks in our developed CVD method plays a critical role in the growth of SexTe1-x nanosheets with high crystallinity. Optimizing the Se composition resulted in a Se0.30Te0.70 nanosheet-based p-type FET with a large on/off current ratio of 4 × 105 and a room-temperature hole mobility of 120 cm2·V-1·s-1, being eight times higher than thermally evaporated SexTe1-x with similar composition and thickness. Moreover, we successfully fabricated an inverter based on p-type Se0.30Te0.70 and n-type MoS2 nanosheets, demonstrating a typical voltage transfer curve with a gain of 30 at an operation voltage of Vdd = 3 V.

Integration of fine-tuned chiral donor with hybrid long/short-range charge-transfer for high-performance circularly polarized electroluminescence.

The synergistic integration of a fine-tuned chiral donor with a hybrid long/short-range charge-transfer mechanism offers an accessible pathway to construct highly efficient circularly polarized emitters. Consequently, a notable dissymmetry factor of 1.6 × 10-3, concomitantly with a record-setting maximum external quantum efficiency of 37.4%, is synchronously realized within a single embodiment.

A 2D Heterostructure-Based Multifunctional Floating Gate Memory Device for Multimodal Reservoir Computing.

The demand for economical and efficient data processing has led to a surge of interest in neuromorphic computing based on emerging two-dimensional (2D) materials in recent years. As a rising van der Waals (vdW) p-type Weyl semiconductor with many intriguing properties, tellurium (Te) has been widely used in advanced electronics/optoelectronics. However, its application in floating gate (FG) memory devices for information processing has never been explored. Herein, an electronic/optoelectronic FG memory device enabled by Te-based 2D vdW heterostructure for multimodal reservoir computing (RC) is reported. When subjected to intense electrical/optical stimuli, the device exhibits impressive nonvolatile electronic memory behaviors including ≈108 extinction ratio, ≈100 ns switching speed, >4000 cycles, >4000-s retention stability, and nonvolatile multibit optoelectronic programmable characteristics. When the input stimuli weaken, the nonvolatile memory degrades into volatile memory. Leveraging these rich nonlinear dynamics, a multimodal RC system with high recognition accuracy of 90.77% for event-type multimodal handwritten digit-recognition is demonstrated.

Pure Polycyclic Aromatic Hydrocarbon Isomerides with Delayed Fluorescence and Anti-Kasha Emission: High-Efficiency Non-Doped Fluorescence OLEDs.

Pure polycyclic aromatic hydrocarbons (PAHs) consisting solely of carbon-hydrogen or carbon-carbon bonds offer great potential for constructing durable and cost-effective emitters in organic electroluminescence devices. However, achieving versatile fluorescence characteristics in pure PAHs remains a considerable challenge, particularly without the inclusion of heteroatoms. Herein, an efficient approach is presented that involves incorporating non-six-membered rings into classical pyrene isomerides, enabling simultaneous achievement of full-color emission, delayed fluorescence, and anti-Kasha emission. Theoretical calculations reveal that the intensity and distribution of aromaticity/anti-aromaticity in both ground and excited states play a crucial role in determining the excited levels and fluorescence yields. Transient fluorescence measurements confirm the existence of thermally activated delayed fluorescence in pure PAHs. By utilizing these PAHs as emitting layers, electroluminescent spectra covering the entire visible region along with a maximum external quantum efficiency of 9.1% can be achieved, leading to the most exceptional results among non-doped pure hydrocarbon-based devices.

Surfactant-Free Ultrasonication-Assisted Synthesis of 2d Tellurium Based on Metastable 1T'-MoTe2.

Elemental 2D materials (E2DMs) have been attracting considerable attention owing to their chemical simplicity and excellent/exotic properties. However, the lack of robust chemical synthetic methods seriously limits their potential. Here, a surfactant-free liquid-phase synthesis of high-quality 2D tellurium is reported based on ultrasonication-assisted exfoliation of metastable 1T'-MoTe2 . The as-grown 2D tellurium nanosheets exhibit excellent single crystallinity, ideal 2D morphology, surfactant-free surface, and negligible 1D by-products. Furthermore, a unique growth mechanism based on the atomic escape of Te atoms from metastable transition metal dichalcogenides and guided 2D growth in the liquid phase is proposed and verified. 2D tellurium-based field-effect transistors show ultrahigh hole mobility exceeding 1000 cm2  V-1  s-1 at room temperature attributing to the high crystallinity and surfactant-free surface, and exceptional chemical and operational stability using both solid-state dielectric and liquid-state electrical double layer. The facile ultrasonication-assisted synthesis of high-quality 2D tellurium paves the way for further exploration of E2DMs and expands the scope of liquid-phase exfoliation (LPE) methodology toward the controlled wet-chemical synthesis of functional nanomaterials.

Uncovering the Role of Crystal Phase in Determining Nonvolatile Flash Memory Device Performance Fabricated from MoTe2-Based 2D van der Waals Heterostructures.

Although the crystal phase of two-dimensional (2D) transition metal dichalcogenides (TMDs) has been proven to play an essential role in fabricating high-performance electronic devices in the past decade, its effect on the performance of 2D material-based flash memory devices still remains unclear. Here, we report the exploration of the effect of MoTe2 in different phases as the charge-trapping layer on the performance of 2D van der Waals (vdW) heterostructure-based flash memory devices, where a metallic 1T'-MoTe2 or semiconducting 2H-MoTe2 nanoflake is used as the floating gate. By conducting comprehensive measurements on the two kinds of vdW heterostructure-based devices, the memory device based on MoS2/h-BN/1T'-MoTe2 presents much better performance, including a larger memory window, faster switching speed (100 ns), and higher extinction ratio (107), than that of the device based on the MoS2/h-BN/2H-MoTe2 heterostructure. Moreover, the device based on the MoS2/h-BN/1T'-MoTe2 heterostructure also shows a long cycle (>1200 cycles) and retention (>3000 s) stability. Our study clearly demonstrates that the crystal phase of 2D TMDs has a significant impact on the performance of nonvolatile flash memory devices based on 2D vdW heterostructures, which paves the way for the fabrication of future high-performance memory devices based on 2D materials.

Electronic/Optoelectronic Memory Device Enabled by Tellurium-based 2D van der Waals Heterostructure for in-Sensor Reservoir Computing at the Optical Communication Band.

Although 2D materials are widely explored for data storage and neuromorphic computing, the construction of 2D material-based memory devices with optoelectronic responsivity in the short-wave infrared (SWIR) region for in-sensor reservoir computing (RC) at the optical communication band still remains a big challenge. In this work, an electronic/optoelectronic memory device enabled by tellurium-based 2D van der Waals (vdW) heterostructure is reported, where the ferroelectric CuInP2 S6 and tellurium channel endow this device with both the long-term potentiation/depression by voltage pulses and short-term potentiation by 1550 nm laser pulses (a typical wavelength in the conventional fiber optical communication band). Leveraging the rich dynamics, a fully memristive in-sensor RC system that can simultaneously sense, decode, and learn messages transmitted by optical fibers is demonstrated. The reported 2D vdW heterostructure-based memory featuring both the long-term and short-term memory behaviors using electrical and optical pulses in SWIR region has not only complemented the wide spectrum of applications of 2D materials family in electronics/optoelectronics but also paves the way for future smart signal processing systems at the edge.

Preparation of Dye Molecule-Intercalated MoO3 Organic/Inorganic Superlattice Nanoparticles for Fluorescence Imaging-Guided Catalytic Therapy.

Intercalation of organic molecules into the van der Waals gaps of layered materials allows for the preparation of organic/inorganic superlattices for varying promising applications. Herein, the preparation of a series of dye molecule/MoO3 organic/inorganic superlattice nanoparticles by aqueous intercalation of several dye molecules into layered MoO3 for fluorescence imaging-guided catalytic therapy is reported. The long MoO3 nanobelts are treated by ball milling and subsequent aqueous intercalation followed by a cation ion exchange to obtain the dye molecule-intercalated MoO3 organic/inorganic superlattices. Importantly, because of the activation induced by organic intercalation, the Nile blue (NB)-intercalated MoO3-x (NB-MoO3-x ) nanoparticles show excellent catalytic activity for the generation of reactive oxygen species, that is, hydroxyl radical (·OH) and superoxide anion (·O2- ), through catalyzing H2 O2 and O2 , respectively. Moreover, the intense fluorescence of the intercalated NB molecules endows NB-MoO3-x with the in vivo fluorescence imaging capability. Thus, the polyvinylpyrrolidone-modified NB-MoO3-x nanoparticles can be used for tumor-specific catalytic therapy to realize efficient cancer cell elimination in vitro and fluorescence imaging-guided tumor ablation in vivo.

Growth of Tellurium Nanobelts on h-BN for p-type Transistors with Ultrahigh Hole Mobility.

The lack of stable p-type van der Waals (vdW) semiconductors with high hole mobility severely impedes the step of low-dimensional materials entering the industrial circle. Although p-type black phosphorus (bP) and tellurium (Te) have shown promising hole mobilities, the instability under ambient conditions of bP and relatively low hole mobility of Te remain as daunting issues. Here we report the growth of high-quality Te nanobelts on atomically flat hexagonal boron nitride (h-BN) for high-performance p-type field-effect transistors (FETs). Importantly, the Te-based FET exhibits an ultrahigh hole mobility up to 1370 cm2 V-1 s-1 at room temperature, that may lay the foundation for the future high-performance p-type 2D FET and metal-oxide-semiconductor (p-MOS) inverter. The vdW h-BN dielectric substrate not only provides an ultra-flat surface without dangling bonds for growth of high-quality Te nanobelts, but also reduces the scattering centers at the interface between the channel material and the dielectric layer, thus resulting in the ultrahigh hole mobility .

Activating Layered Metal Oxide Nanomaterials via Structural Engineering as Biodegradable Nanoagents for Photothermal Cancer Therapy.

Layered metal oxides including MoO3 and WO3 have been widely explored for biological applications owing to their excellent biocompatibility, low toxicity, and easy preparation. However, they normally exhibit weak or negligible near-infrared (NIR) absorption and thus are inefficient for photo-induced biomedical applications. Herein, the structural engineering of layered MoO3 and WO3 nanostructures is first reported to activate their NIR-II absorption for efficient photothermal cancer therapy in the NIR-II window. White-colored micrometre-long MoO3 nanobelts are transformed into blue-colored short, thin, defective, interlayer gap-expanded MoO3-x nanobelts with a strong NIR-II absorption via the simple lithium treatment. The blue MoO3-x nanobelts exhibit a large extinction coefficient of 18.2 L g-1 cm-1 and high photothermal conversion efficiency of 46.9% at 1064 nm. After surface modification, the MoO3-x nanobelts can be used as a robust nanoagent for photoacoustic imaging-guided photothermal therapy to achieve efficient cancer cell ablation and tumor eradication under irradiation by a 1064 nm laser. Importantly, the biodegradable MoO3-x nanobelts can be rapidly degraded and excreted from body. The study highlights that the structural engineering of layered metal oxides is a powerful strategy to tune their properties and thus boost their performances in given applications.

Preparation of novel catalyst-free Fe3C nanocrystals encapsulated NCNT structured catalyst for continuous catalytic wet peroxide oxidation of phenol.

Novel nitrogen-doped carbon nanotubes encapsulating Fe3C nanocrystals coated paper-like sintered stainless steel fibers (PSSF) structured catalyst (Fe3C@NCNT/PSSF) was designed for continuous catalytic wet peroxide oxidation of phenol. Firstly, Fe3C@NCNT/PSSF was fabricated by directly growing the Fe3C encapsulated NCNTs onto the three-dimensional PSSF substrate through CVD method using melamine as precursor, the monolithic PSSF substrate served as a self-catalyzing agent for catalyst preparation. Secondly, the surface morphology and structure of Fe3C@NCNT/PSSF were investigated to optimize the synthesis condition. Then Fe3C@NCNT/PSSF was employed as a structured catalyst for continuous CWPO of phenol, effect of operating conditions was studied. Catalytic results showed that the encapsulated Fe3C nanoparticles significantly enhanced the degradation efficiency of phenol, and catalytic performance was improved with the increase of temperature. However, catalytic performance appeared unusual when residence time was considered, due to the effect of strongly polar surface of NCNTs on the contact efficiency between pollutants and hydroxyl radicals. Reusability experiments showed that catalytic performance of catalyst was improved with the increase of reusability cycles although the iron leaching concentration decreased, attributing to enhanced reaction within internal channel of Fe3C@NCNT. The fourth reaction run achieved a stable phenol conversion of 90%, TOC conversion around 41% under optimized conditions.

Great enhancement in phosphate uptake onto lanthanum carbonate grafted microfibrous composite under a low-voltage electrostatic field.

Removal of phosphorus from water via cost-effective measures becomes important for water industry mainly due to eutrophication in waterbody. In our lab, a novel lanthanum carbonate-microfibrous composite (LC-MC) with good performance was previously synthesized for the removal of phosphorus. In this study, we further improved our technology by applying the electrostatic field (direct current, DC) to the adsorption system. It was showed that the applied DC can greatly improve the adsorption of phosphate in particular the adsorption capacity. Better removal was seen in the pH range of 5-9 at a higher temperature. The maximum adsorption capacity of 47.57 mg-PO43- g-1 was achieved, which was 1.4 times of that operated in the absence of applied DC. The adsorption equilibrium was established at the contact time of 240 min; the adsorption history was well described by the intraparticle surface diffusion model. The negative effect from oxygen-containing anions on the phosphate uptake followed the decreasing sequence of: humic acid > carbonate > nitrate > sulfate; on the other hand, the halogen anions had almost no influence on it. Finally, the mechanism study by XPS, XRD, and IR demonstrated that the ligand exchange played an important role in the electro-assisted phosphate uptake process.

Synthesis of graphene with different layers on paper-like sintered stainless steel fibers and its application as a metal-free catalyst for catalytic wet peroxide oxidation of phenol.

Different layers of graphene (Gr) films are prepared on the paper-like sintered stainless steel fibers (PSSF) support with three-dimensional structure by CVD method. The effects of acetylene flow rate, deposition time, and deposition temperature on the properties of PSSF-Gr are investigated by EDS, AFM, SEM, TEM, and Raman spectroscopy, respectively. Then, the catalytic performances of PSSF-Gr with different layers of Gr films as metal-free catalysts for catalytic wet peroxide oxidation (CWPO) of phenol are assessed in the continuous fixed-bed reactor. The catalytic results demonstrate that the PSSF-Gr catalyst with single layer graphene film achieves the best catalytic performance (phenol and TOC removal efficiency reach 99% and 73%, respectively) after continuously operating for 6 h. Under the treatment of the PSSF-Gr catalyst with single-layer graphene, total phenol oxidation and excellent TOC removal (maintain about 71%) have been achieved for the long-term operation (38 h). Moreover, the phenol conversion of blank experiment (without catalyst) and PSSF are around 40%, which are caused by thermal degradation and thus, the excellent catalytic activity of PSSF-Gr is ascribed to graphene. Like other Fenton's catalysts, the catalytic mechanism of PSSF-Gr catalyst in phenol degradation is also a ·OH mechanism.

Iron-loaded carbon nanotube-microfibrous composite for catalytic wet peroxide oxidation of m-cresol in a fixed bed reactor.

A kind of novel iron-loaded carbon nanotube-microfibrous composite (Fe2O3-CNT-MF) catalyst is prepared and tested for fixed bed m-cresol catalytic wet peroxide oxidation (CWPO) reaction. Results show that the Fe2O3-CNT-MF can significantly decline the pressure drop of the fixed bed. Higher temperature, lower feed flow rate, higher catalyst bed height, and higher H2O2 dosage are beneficial to m-cresol degradation. Lower pH can also improve m-cresol degradation, but it will cause severe iron leaching. The highest m-cresol removal (over 99.5%) and total organic carbon (TOC) removal (53.6%) can be observed under condition of 2 cm bed height, flow rate of 2 mL/min, reaction temperature of 70 °C, 6 g/L H2O2, and initial pH = 1. Meanwhile, the Fe2O3-CNT-MF catalyst shows good stability with less than 10% decrease in m-cresol conversion and 7% decrease in TOC conversion after 24-h reaction and less than 2 mg/L iron leaching is observed in all conditions except for strong acid condition. Two probable pathways of m-cresol degradation process are presented. Under most conditions, m-cresol will first be turned into methylhydroquinone, followed by oxidation to p-toluquinone. In basic condition, some m-cresol will first be changed into 4-methylpyrocatechol. These aromatic intermediates will then be oxidized into some small molecular acids and finally be mineralized to CO2 and H2O.

Graphene as efficient and robust catalysts for catalytic wet peroxide oxidation of phenol in a continuous fixed-bed reactor.

Monolayer graphene film (Gr) as a metal-free catalyst was synthesized on the paper-like sintered stainless steel fibers (PSSF) with three-dimensional net structure by chemical vapor deposition (CVD) technique. The prepared PSSF-Gr was characterized by SEM, EDS, XRD, AFM, TEM, and Raman spectroscopy. Then, the optimum reaction conditions for catalytic wet peroxide oxidation (CWPO) of phenol in a continuous reactor using PSSF-Gr catalysts were explored by analyzing the effects of reaction temperature, feed flow rate, and catalyst bed height on catalytic performance. Moreover, the long-term stability of PSSF-Gr catalyst was investigated and demonstrated complete phenol oxidation and dramatic TOC removal (values ranging between 80.7% and 91.0%) after continuously operating for 72 h under optimum condition. Finally, a reasonable reaction mechanism for CWPO of phenol was proposed by analyzing the HPLC results and evolution of aromatic intermediates content. From these results, seldom toxic aromatic intermediates were observed on account of the production of short-chain organic acids by opening of aromatic ring, which subsequently mineralized to CO2 and H2O. The simple preparation method, unique structure, extraordinary catalytic activity and stability of the graphene-based material would provide a new potential catalyst for environmental catalysis.

Uncovering two kinetic factors in the controlled growth of topologically distinct core-shell metal-organic frameworks.

Constructing core-shell metal-organic frameworks (MOFs) based on two topologically distinct MOFs is a great way to increase MOF material complexity and explore their new functions. However, such a nucleation process is energetically less favored compared to epitaxial growth due to mismatched unit cell parameters. Here, two kinetic factors, nucleation kinetics and dissolution kinetics, are revealed to be two key factors in overcoming this challenge. Through kinetic control, we demonstrate the growth of 4 types of Zr/Hf-MOF shells uniformly and contiguously on 7 different core MOFs including ZIF-8, an acid labile core. Taking advantage of the modular synthesis of Zr-MOFs, we demonstrate that post-synthetic covalent surface modification on a non-functionalizable MOF surface can be made possible through core-shell construction. We also demonstrated that the size selective catalytic behavior can be systematically tuned through changing either the ligand length or ligand functionality.