Adaptive Memory of a Neuromorphic Transistor with Multi-Sensory Signal Fusion

One of the ultimate goals of artificial intelligence is to achieve the capability of memory evolution and adaptability to changing environments, which is termed adaptive memory. To realize adaptive memory in artificial neuromorphic devices, artificial synapses with multi-sensing capability are required to collect and analyze various sensory cues from the external changing environments. However, due to the lack of platforms for mediating multiple sensory signals, most artificial synapses have been mainly limited to unimodal or bimodal sensory devices. Herein, we present a multi-modal artificial sensory synapse (MASS) based on an organic synapse to realize sensory fusion and adaptive memory. The MASS receives optical, electrical, and pressure information and in turn generates typical synaptic behaviors, mimicking the multi-sensory neurons in the brain. Sophisticated synaptic behaviors, such as Pavlovian dogs, writing/erasing, signal accumulation, and offset, were emulated to demonstrate the joint efforts of bimodal sensory cues. Moreover, associative memory can be formed in the device and be subsequently reshaped by signals from a third perception, mimicking modification of the memory and cognition when encountering a new environment. Our MASS provides a step toward next-generation artificial neural networks with an adaptive memory capability

Metal Doping Effect of the M–Co₂P/Nitrogen-Doped Carbon Nanotubes (M = Fe, Ni, Cu) Hydrogen Evolution Hybrid Catalysts

The enhancement of catalytic performance of cobalt phosphide-based catalysts for the hydrogen evolution reaction (HER) is still challenging. In this work, the doping effect of some transition metal (M = Fe, Ni, Cu) on the electrocatalytic performance of the M–Co₂P/NCNTs (NCNTs, nitrogen-doped carbon nanotubes) hybrid catalysts for the HER was studied systematically. The M–Co₂P/NCNTs hybrid catalysts were synthesized via a simple in situ thermal decomposition process. A series of techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrometry, transmission electron microscopy, and N₂ sorption were used to characterize the as-synthesized M–Co₂P/NCNTs hybrid catalysts. Electrochemical measurements showed the catalytic performance according to the following order of Fe–Co₂P/NCNTs > Ni–Co₂P/NCNTs > Cu–Co₂P/NCNTs, which can be ascribed to the difference of structure, morphology, and electronic property after doping. The doping of Fe atoms promote the growth of the [111] crystal plane, resulting in a large specific area and exposing more catalytic active sites. Meanwhile, the Fe^δ+ has the highest positive charge among all the M–Co₂P/NCNTs hybrid catalysts after doping. All these changes can be used to contribute the highest electrocatalytic activity of the Fe–Co₂P/NCNTs hybrid catalyst for HER. Furthermore, an optimal HER electrocatalytic activity was obtained by adjusting the doping ratio of Fe atoms. Our current research indicates that the doping of metal is also an important strategy to improve the electrocatalytic activity for the HER

Controlling Fundamental Fluctuations for Reproducible Growth of Large Single-Crystal Graphene

The controlled growth of graphene by the chemical vapor deposition method is vital for its various applications; however, the reproducibility remains a great challenge. Here, using single-crystal graphene growth on a Cu surface as a model system, we demonstrate that a trace amount of H₂O and O₂ impurity gases in the reaction chamber is key for the large fluctuation of graphene growth. By precisely controlling their parts per million level concentrations, centimeter-sized single-crystal graphene is obtained in a reliable manner with a maximum growth rate up to 190 μm min^–1. The roles of oxidants are elucidated as an effective modulator for both graphene nucleation density and growth rate. This control is more fundamental for reliable growth of graphene beyond previous findings and is expected to be useful for the growth of various 2D materials that are also sensitive to trace oxidant impurities

Reactive Adsorption Desulfurization on Cu/ZnO Adsorbent: Effect of ZnO Polarity Ratio on Selective Hydrogenation

The desulfurization activity and selective hydrogenation of Cu/ZnO adsorbents on the different polarity ratios of ZnO as supports was investigated in reactive adsorption desulfurization. The ZnO particles were synthesized by the hydrothermal process, and CuO/ZnO adsorbents were synthesized by incipient impregnation method. The structure and morphology of the ZnO and CuO/ZnO were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, X-ray photoelectron spectra (XPS), scanning electron microscope/selected area electron diffraction (SEM/SAED), transmission electron microscopy (TEM), and temperature-programmed reduction (TPR). The surface area and polarity ratio of ZnO supports were controlled by the calcination temperature and concentration of P₁₂₃, respectively. More reactive activity sites were provided by the high surface area of ZnO supports, thus improving the desulfurization activity. The polarity ratio of ZnO may strongly influence the hydrogenation reactions of olefins. The selective hydrogenation increased with the value of polarity ratios

Conjugated Polymers of Rylene Diimide and Phenothiazine for n‑Channel Organic Field-Effect Transistors

A series of new n-type copolymers based on perylene diimide (PDI) or naphthalene diimide (NDI) and phenothiazine (PTZ) with different side chain length and molecular weight have been designed and synthesized by Pd-catalyzed Suzuki coupling polymerization with or without phase-transfer catalyst Aliquat 336. The effects of main chain, side chain, and molecular weight on the thermal, optical, electronic, and charge transport properties of the polymers have been investigated. Aliquat 336 improves molecular weight as well as reduces polydispersity index of the polymers. All the polymers exhibit a broad absorption extending from 300 to 900 nm. The main chain and side chain structure and molecular weight have minor effects on the HOMO (−5.8 to −5.9 eV) and LUMO (−3.7 to −3.8 eV) levels of the polymers. n-Channel field-effect transistors with bottom-gate top-contact geometry based on these copolymers exhibit electron mobilities as high as 0.05 cm² V^–1 s^–1 and on/off ratios as high as 10⁵ in nitrogen, which are among the best reported for rylene diimide-based polymers under the same test conditions

One-Pot Self-Assembled Three-Dimensional TiO₂‑Graphene Hydrogel with Improved Adsorption Capacities and Photocatalytic and Electrochemical Activities

We reported the development of a new type of multifunctional titanium dioxide (TiO₂)-graphene nanocomposite hydrogel (TGH) by a facile one-pot hydrothermal approach and explored its environmental and energy applications as photocatalyst, reusable adsorbents, and supercapacitor. During the hydrothermal reaction, the graphene nanosheets and TiO₂ nanoparticles self-assembled into three-dimensional (3D) interconnected networks, in which the spherical nanostructured TiO₂ nanoparticles with uniform size were densely anchored onto the graphene nanosheets. We have shown that the resultant TGH displayed the synergistic effects of the assembled graphene nanosheets and TiO₂ nanoparticles and therefore exhibited a unique collection of physical and chemical properties such as increased adsorption capacities, enhanced photocatalytic activities, and improved electrochemical capacitive performance in comparison with pristine graphene hydrogel and TiO₂ nanoparticles. These features collectively demonstrated the potential of 3D TGH as an attractive macroscopic device for versatile applications in environmental and energy storage issues

Highly Active CoMoS/Al₂O₃ Catalysts ex Situ Presulfided with Ammonium Sulfide for Selective Hydrodesulfurization of Fluid Catalytic Cracking Gasoline

An improved ex situ presulfidation method for the preparation of the CoMoS/γ-Al₂O₃ catalyst was developed with ammonium sulfide as the sulfiding agent, and the prepared catalysts were evaluated in selective hydrodesulfurization (HDS) of fluid catalytic cracking (FCC) gasoline. The selectivity of the ex situ presulfided catalysts was more than 4 times of that of the in situ presulfided catalysts. The characterization by XRD, HRTEM, XPS, TPR, and FT-IR indicated that ammonium sulfide effectively reacted with the supported Mo oxide to form ammonium tetrathiomolybdate as intermediate, thus realizing the more complete sulfidation of Mo oxide. However, the supported Co oxide could not be sulfided by ammonium sulfide, and the delayed sulfidation would not hinder the easy growth of MoS₂ particles, subsequently lead to the significantly longer slab lengths of MoS₂ particles than that of the in situ presulfided catalyst, which effectively decreased the number of active sites for olefins, thus inducing much higher HDS selectivity

Self-Templated Synthesis of Triphenylene-Based Uniform Hollow Spherical Two-Dimensional Covalent Organic Frameworks for Drug Delivery

Constructing two-dimensional covalent organic frameworks (2DCOFs) with a desirable crystalline structure and morphology is promising but remains a significant challenge. Herein, we report self-templated synthesis of uniform hollow spherical 2DCOFs based on 2,3,6,7,10,11-hexakis(4-aminophenyl) triphenylene. A detailed time-dependent study of hollow sphere formation reveals an intriguing transformation from initial homogeneous solid spheres into uniform hollow spheres with the Ostwald ripening mechanism. Impressively, the resultant spherical 2DCOFs are composed of high crystallinity nanosheets and even hexagonal single crystals, as demonstrated by transmission electron microscopy. Thanks to its uniform morphology and high crystallinity, the pore volume of the obtained 2DCOFs is up to 1.947 cm3 g–1, which makes it function as superior nanocarriers for efficient controlled drug delivery. This result provides an avenue for improving COFs’ performance by regulating their morphology

Solution-Processed and Air-Stable n‑Type Organic Thin-Film Transistors Based on Thiophene-Fused Dicyanoquinonediimine (DCNQI) Deriatives

π-Conjugated systems <b>2a</b> and <b>2b</b> containing thiophene-fused DCNQI with long alkyl and trifluoromethylphenyl groups were synthesized as potential active materials for solution-processed and air-stable n-type organic thin-film transistors (OTFTs). The electrochemical measurements revealed that the lowest unoccupied molecular orbital (LUMO) of the compounds have an energy level less than −4.0 eV, indicating air stable n-type materials. The long alkyl groups endowed the compounds good solubility and solution-processability. X-ray diffraction measurements revealed the difference of the molecular arrangement depending on the alkyl groups, which were also observed in the UV–vis absorptions of the films. A relatively good mobility up to 0.003 cm² V^–1 s^–1 for <b>2a</b> by spin-coating was obtained with good air stability

N‑Alkylation <i>vs</i> O‑Alkylation: Influence on the Performance of a Polymeric Field-Effect Transistors Based on a Tetracyclic Lactam Building Block

Lactam-containing conjugated molecules are important building blocks for conjugated polymers for high performance organic field-effect transistors (OFETs). The alkylation on conjugated lactam building blocks may preferably produce either O-alkylated or N-alkylated isomers, which might have different influences on the HOMO/LUMO energy levels, π–π stacking patterns and crystallinity of the corresponding polymers. However, the influence of O-alkylation and N-alkylation on the OFET performance of the resultant polymers has not been reported. Here, with an improved synthetic strategy, we prepared the N-alkylated isomer of dibenzonaphthyridinedione (DBND), a tetracyclic lactam building block that used to give O-alkylated product preferably, which gave us a chance to compare the influence of N-alkylated DBND (<i>N</i>-DBND) and O-alkylated DBND (<i>O</i>-DBND) on the OFET performance of the corresponding polymers. It was found that the polymer based on <i>N</i>-DBND exhibits a much higher hole mobility (0.55 cm² V^–1 s^–1), almost 100 times greater than the one based on <i>O</i>-DBND (0.006 cm² V^–1 s^–1). The reasons for such a huge difference were thoroughly investigated theoretically and experimentally. It was found that repeating unit in the polymer based on <i>N</i>-DBND exhibits a much higher dipole moment (1.56 D) than that based on <i>O</i>-DBND (0.49 D), which results in a much stronger intermolecular binding energy (−57.2 vs −30.0 kcal mol^–1). Although both polymers exhibits very similar coplanarity and crystalline patterns, stronger intermolecular interaction of the polymer based on <i>N</i>-DBND leads to shorter π–π stacking distance (3.63 vs 3.68 Å), which results in a film with higher crystallinity and highly interconnected fibrillar domains, and accounts for its high charge carrier mobility, as evidenced by 2D-GIXD and AFM analysis. We come to the conclusion that the more polar amide bond in <i>N</i>-DBND is the major factor which governs the charge transport properties, which overwhelms the side-chain engineering effect that O-alkylation might bring in (the branching point of the side-chain of an <i>O</i>-DBND-based polymer is one more atom away from the polymer backbone and results in less steric hindrance)