Bottom-Up Synthesis of Covalent Organic Frameworks with Quasi-Three-Dimensional Integrated Architecture via Interlayer Cross-Linking

Developing strategies to enhance the structural robustness of covalent organic frameworks (COFs) is of great importance. Here, we rationally design and synthesize a class of cross-linked COFs (^CCOFs), in which the two-dimensional (2D) COF layers are anchored and connected by polyethylene glycol (PEG) or alkyl chains through covalent bonds. The bottom-up fabrication of these ^CCOFs is achieved by the condensation of cross-linked aldehyde monomers and tritopic amino monomers. All the synthesized ^CCOFs possess high crystallinity and porosity, and enhanced structural robustness surpassing the typical 2D COFs, which means that they cannot be exfoliated under ultrasonication and grinding due to the cross-linking effect. Furthermore, the cross-linked patterns of PEG units are uncovered by experimental results and Monte Carlo molecular dynamics simulations. It is found that all ^CCOFs are dominated by vertical cross-layer (interlayer) connections (clearly observed in high-resolution transmission electron microscopy images), allowing them to form quasi-three-dimensional (quasi-3D) structures. This work bridges the gap between 2D COFs and 3D COFs and provides an efficient way to improve the interlayered stability of COFs.

Resistance-switchable conjugated polyrotaxane for flexible high-performance RRAMs

A representative closely packed conjugated polyrotaxane (CPR1) is synthesized by threading polyaniline (PAN) into β-cyclodextrin (CD) macrocycles and utilized for the first time to construct an RRAM device that exhibits an outstanding resistive switching capability. The CPR1 RRAM device displays remarkable nonvolatile memory performance with an extremely high ON/OFF ratio of 10⁸, the ultra-fast response of 29 ns, excellent reliability and reproducibility, and long-term stability (more than 1 year). The mechanism underlying this resistive switching behavior is understood according to the electric-field-induced proton doping of the PAN core by the CD sheath through hydrogen bonding interactions. More impressively, the favorable solubility and intrinsic flexibility of CPR1 allow for large-scale fabrication of flexible CPR1 RRAM device arrays by full-printing technology with endurance of 1000 bending cycles at the minimum bending radius of 3 mm, higher ON/OFF ratio of 10⁸, and relatively lower operating voltage of 1.8 V. This work shows the potential of CPR materials in highly stable memory devices for next-generation flexible and wearable electronics.

Tunable Control of the Hydrophilicity and Wettability of Conjugated Polymers by a Postpolymerization Modification Approach

A facile method to prepare hydrophilic polymers by a postpolymerization nucleophillic aromatic substitution reaction of fluoride on an emissive conjugated polymer (CP) backbone is reported. Quantitative functionalization by a series of monofunctionalized ethylene glycol oligomers, from dimer to hexamer, as well as with high molecular weight polyethylene glycol is demonstrated. The length of the ethylene glycol sidechains is shown to have a direct impact on the surface wettability of the polymer, as well as its solubility in polar solvents. However, the energetics and band gap of the CPs remain essentially constant. This method therefore allows an easy way to modulate the wettability and solubility of CP materials for a diverse series of applications.

Novel polymeric microspheres: Synthesis, enzyme immobilization, antimutagenic activity, and antimicrobial evaluation against pathogenic microorganisms

New polymeric microspheres containing azomethine (1a-1c and 2a-2c) were synthesized by condensation to compare the enzymatic properties of the enzyme glucose oxidase (GOx) and to investigate antimutagenic and antimicrobial activities. The polymeric microspheres were characterized by elemental analysis, infrared spectra (FT-IR), proton nuclear magnetic resonance spectra, thermal gravimetric analysis, and scanning electron microscopy analysis. The catalytic activity of the glucose oxidase enzyme follows Michaelis-Menten kinetics. Influence of temperature, reusability, and storage capacity of the free and immobilized glucose oxidase enzyme were investigated. It is determined that immobilized enzymes exhibit good storage stability and reusability. After immobilization of GOx in polymeric supports, the thermal stability of the enzyme increased and the maximum reaction rate (V_max ) decreased. The activity of the immobilized enzymes was preserved even after 5 months. The antibacterial and antifungal activity of the polymeric microspheres were evaluated by well-diffusion method against some selected pathogenic microorganisms. The antimutagenic properties of all compounds were also examined against sodium azide in human lymphocyte cells by micronuclei and sister chromatid exchange tests.

Novel carbazole-based donor-isoindolo[2,1-a]benzimidazol-11-one acceptor polymers for ternary flash memory and light-emission

Three novel donor-acceptor polymers (PCz0, PCz2 and PCz4) based on 9-(9-heptadecanyl)-9H-carbazole and isoindolo[2,1-a]benzimidazol-11-one with fluorine substituents (0, 2 and 4) on the acceptor unit were prepared by Suzuki polymerization. The synthesized polymers were studied by theoretical calculation, and optical and electrochemical characterizations to further investigate the performance of memory storage and light-emission. The memory devices of the three polymers all exhibited obvious ternary flash behavior with total ON/OFF state current ratio around 104 and threshold voltages below 3.0 V, with no other blending or doping. Bright emissions of an electroluminescence device based on PCz0 was obtained at 556 nm, the maximum brightness was 2006 cd m-2 with EQE of 0.21%. The results suggested that polymers with the structure of carbazole-based donor as backbone and isoindolo[2,1-a]benzimidazol-11-one segment as acceptor could be excellent materials for memory storage and light-emitting applications with further investigation and could be used for further design of other new polymer systems.

Organic and hybrid resistive switching materials and devices

This review presents a timely and comprehensive summary of organic and hybrid materials for nonvolatile resistive switching memory applications in the “More than Moore” era, with particular attention on their designing principles for electronic property tuning and flexible memory performance.

Development of Conjugated Polymers for Memory Device Applications

This review summarizes the most widely used mechanisms in memory devices based on conjugated polymers, such as charge transfer, space charge traps, and filament conduction. In addition, recent studies of conjugated polymers for memory device applications are also reviewed, discussed, and differentiated based on the mechanisms and structural design. Moreover, the electrical conditions of conjugated polymers can be further fine-tuned by careful design and synthesis based on the switching mechanisms. The review also emphasizes and demonstrates the structure-memory properties relationship of donor-acceptor conjugated polymers for advanced memory device applications.

Synthesis and optical and electrochemical memory properties of fluorene–triphenylamine alternating copolymer

A fluorene–triphenylamine copolymer (PF–TPA) was designed and synthesized under Suzuki coupling reaction conditions in this work. It exhibited a typical electrical conductance switching behavior and non-volatile flash memory effects.

Convertible resistive switching characteristics between memory switching and threshold switching in a single ferritin-based memristor

The coexistence and inter-conversion between threshold and memory resistance switching in a ferritin memristor makes it a promising candidate for physiological applications.

Nonvolatile memory devices based on poly(vinyl alcohol) + graphene oxide hybrid composites

The performance of the ITO/PVA + GO/Al device was effectively enhanced by the introduction of GO into the PVA matrix.

Organic Electronic Memory Devices

With the rapid development of the electronics industry in recent years, information technology devices, such as personal computers, mobile phones, digital cameras and media players, have become an essential part of our daily life. From both the technological and economic points of view, the development of novel information storage materials and devices has become an emergent issue facing the electronics industry. Due to the advantages of good scalability, flexibility, low cost, ease of processing, 3D-stacking capability and high capacity for data storage, organic-based electrical memory devices have been promising alternatives or supplementary devices to conventional inorganic semiconductor-based memory technology. The basic concepts and historical development of electronic memory devices are first presented. The following section introduces the structures and switching mechanisms of organic electronic memory devices classified as transistors, capacitors and resistors. Subsequently, the progress in the field of organic-based memory materials and devices is systematically summarized and discussed. Finally, the challenges posed to the development of novel organic electronic memory devices are summarized.

Impact of program/erase operation on the performances of oxide-based resistive switching memory

Further performance improvement is necessary for resistive random access memory (RRAM) to realize its commercialization. In this work, a novel pulse operation method is proposed to improve the performance of RRAM based on Ti/HfO2/Pt structure. In the DC voltage sweep of the RRAM device, the SET transition is abrupt under positive bias. If current sweep with positive bias is utilized in SET process, the SET switching will become gradual, so SET is current controlled. In the negative voltage sweep for RESET process, the change of current with applied voltage is gradual, so RESET is voltage controlled. Current sweep SET and voltage sweep RESET shows better controllability on the parameter variation. Considering the SET/RESET characteristics in DC sweep, in the corresponding pulse operation, the width and height of the pulse series can be adjusted to control the SET and RESET process, respectively. Our new method is different from the traditional pulse operation in which both the width and height of program/erase pulse are simply kept constant which would lead to unnecessary damage to the device. In our new method, in each program or erase operation, a series of pulses with the width/height gradually increased are made use of to fully finish the SET/RESET switching but no excessive stress is generated at the same time, so width/height-controlled accurate SET/RESET can be achieved. Through the operation, the uniformity and endurance of the RRAM device has been significantly improved.

Organic memory effect from donor–acceptor polymers based on 7-perfluorophenyl-6H-[1,2,5]thiadiazole[3,4-g]benzoimidazole

A novel D–A polymer is designed for resistance memory devices with a large off ratio, good endurance, and long retention time.

Well-defined star-shaped donor–acceptor conjugated molecules for organic resistive memory devices

Solution processable star-shaped donor–acceptor conjugated molecules are explored for the first time as charge storage materials for resistor-type memory devices with a triphenylamine (donor) core, and three 1.8-naphthalimide (acceptors) end-groups.

Retracted Article: Light-controlled resistive switching memory of multiferroic BiMnO3 nanowire arrays

Ferroelectricity can be controlled by white-light illumination, thus offering a light-controlled resistive switching memory device using a Ag/BiMnO₃/Ti structure.