Solution-processable poly(N-vinylcarbazole)-covalently grafted MoS2 nanosheets for nonvolatile rewritable memory devices

Donor-acceptor-type poly[chalcogenoviologen-alt-triphenylamine] for synaptic biomimicking and neuromorphic computing

Polymer memristors are preeminent candidates for low-power edge computing paradigms. Poly[chalcogenoviologen-alt-triphenylamine] (PCVTPA) has been synthesized by direct coupling of chalcogeno-viologen as electron acceptor and 4-(bromomethyl)-N-(4-(bromo-methyl)phenyl)-N-phenylaniline as electron donor. The introduction of chalcogen atoms (S, Se, Te) into viologen scaffolds can greatly improve electrical conductive, electrochemical, and electrochromic properties of the materials when compared with the conventional viologens. Taking PTeVTPA as an example, the as-fabricated electronic device with a configuration of Al/PTeVTPA/ITO exhibits excellent multilevel storage and history-dependent memristive switching performance. Associated with the unique memristive behavior, the PTeVTPA-based device can not only be used to emulate the synaptic potentiation/depression, the human's learning and memorizing functions, and the transition from short-term synaptic plasticity to long-term plasticity but also carry out decimal arithmetic operations as well. This work will be expected to offer a train of new thought for constructing high-performance synaptic biomimicking and neuromorphic computing system in the near future.

Fast Polymeric Functionalization Approach for the Covalent Coating of MoS2 Layers

We present the covalent coating of chemically exfoliated molybdenum disulfide (MoS₂) based on the polymerization of functional acryl molecules. The method relies on the efficient diazonium anchoring reaction to provoke the in situ radical polymerization and covalent adhesion of functional coatings. In particular, we successfully implement hydrophobicity on the exfoliated MoS₂ in a direct, fast, and quantitative synthetic approach. The covalent functionalization is proved by multiple techniques including X-ray photoelectron spectroscopy and TGA-MS. This approach represents a simple and general protocol to reach dense and homogeneous functional coatings on 2D materials.

Flexible Nonvolatile Bioresistive Random Access Memory with an Adjustable Memory Mode Capable of Realizing Logic Functions

In this study, a flexible bioresistive memory with an aluminum/tussah hemolymph/indium tin oxide/polyethylene terephthalate structure is fabricated by using a natural biological material, tussah hemolymph (TH), as the active layer. When different compliance currents (Icc) are applied to the device, it exhibits different resistance characteristics. When 1 mA is applied in the positive voltage range and 100 mA is applied in the negative voltage range, the device exhibits bipolar resistive switching behavior. Additionally, when 1 mA is applied in both the positive- and negative-voltage ranges, the device exhibits write-once-read-many-times (WORM) characteristics. The device has good endurance, with a retention time exceeding 10⁴ s. After 10⁴ bending cycles, the electrical characteristics remain constant. This memory device can be applied for “AND” and “OR” logic operations in programmable logic circuits. The prepared flexible and transparent biomemristor made of pure natural TH provides a promising new approach for realizing environmentally friendly and biocompatible flexible memory, nerve synapses, and wearable electronic devices.

Bistable non-volatile resistive memory devices based on ZnO nanoparticles embedded in polyvinylpyrrolidone

The resistive random access memory (RRAM) devices based on polyvinylpyrrolidone (PVP) and PVP:PVP:zinc oxide nanoparticle (ZnO NP) active layers have bistable electrical switching behavior. Herein, via a series of storage performance tests, it was proved that the ITO/PVP:ZnO/Al device has a higher ON/OFF current ratio and better memory performance than the ITO/PVP/Al device. Moreover, at 13 wt% concentration of ZnO NPs, optimal storage performance was obtained, the switch state current ratio significantly increased, and the threshold voltage obviously decreased. The conduction mechanism of the devices was further discussed. The device having inorganic nanoparticles embedded in the polymer has excellent storage performance, which has potential application value in data storage.

The resistive random access memory (RRAM) devices based on polyvinylpyrrolidone (PVP) and PVP:PVP:zinc oxide nanoparticle (ZnO NP) active layers have bistable electrical switching behavior.

Coordination-Driven Hierarchical Assembly of Hybrid Nanostructures Based on 2D Materials

2D materials have received tremendous scientific and engineering interests due to their remarkable properties and broad-ranging applications such as energy storage and conversion, catalysis, biomedicine, electronics, and so forth. To further enhance their performance and endow them with new functions, 2D materials are proposed to hybridize with other nanostructured building blocks, resulting in hybrid nanostructures with various morphologies and structures. The properties and functions of these hybrid nanostructures depend strongly on the interfacial interactions between 2D materials and other building blocks. Covalent and coordination bonds are two strong interactions that hold high potential in constructing these robust hybrid nanostructures based on 2D materials. However, most 2D materials are chemically inert, posing problems for the covalent assembly with other building blocks. There are usually coordination atoms in most of 2D materials and their derivatives, thus coordination interaction as a strong interfacial interaction has attracted much attention. In this review, recent progress on the coordination-driven hierarchical assembly based on 2D materials is summarized, focusing on the synthesis approaches, various architectures, and structure-property relationship. Furthermore, insights into the present challenges and future research directions are also presented.

Decade of 2D-materials-based RRAM devices: a review

Two dimensional (2D) materials have offered unique electrical, chemical, mechanical and physical properties over the past decade owing to their ultrathin, flexible, and multilayer structure. These layered materials are being used in numerous electronic devices for various applications, and this review will specifically focus on the resistive random access memories (RRAMs) based on 2D materials and their nanocomposites. This study presents the device structures, conduction mechanisms, resistive switching properties, fabrication technologies, challenges and future aspects of 2D-materials-based RRAMs. Graphene, derivatives of graphene and MoS2 have been the major contributors among 2D materials for the application of RRAMs; however, other members of this family such as hBN, MoSe2, WS2 and WSe2 have also been inspected more recently as the functional materials of nonvolatile RRAM devices. Conduction in these devices is usually dominated by either the penetration of metallic ions or migration of intrinsic species. Most prominent advantages offered by RRAM devices based on 2D materials include fast switching speed (<10 ns), less power losses (10 pJ), lower threshold voltage (<1 V) long retention time (>10 years), high electrical endurance (>108 voltage cycles) and extended mechanical robustness (500 bending cycles). Resistive switching properties of 2D materials have been further enhanced by blending them with metallic nanoparticles, organic polymers and inorganic semiconductors in various forms.

Two-dimensional MoS2: a platform for constructing three-dimensional structures using RAFT polymerization

Controlled and straightforward functionalization are relevant strategies to obtain MoS₂ platforms with defined functionality and improved processability.

Facile Synthesis of Ti3C2Tx-Poly(vinylpyrrolidone) Nanocomposites for Nonvolatile Memory Devices with Low Switching Voltage

MXenes, an emerging class of two-dimensional (2D) transition-metal carbide materials, have received increasing attention for their interesting physiochemical properties. For not only MXenes but also other 2D materials, delamination is a requisite step for the exploitation of their unique properties. In this work, a facile method for exfoliating Ti₃C₂T_x MXene to nanosheets of small size with the aid of poly(vinylpyrrolidone) (PVP) is designed, which has never been reported to our knowledge. Since both hydrophobic methylene groups and hydrophilic amide groups are provided with PVP, this method is applicable in a wide range of solvents, such as ethanol, water, and chloroform. Considering the charge detrapping and trapping behavior of 2D transition-metal materials in PVP dielectric, a memory device with the configuration of reduced graphene oxide (rGO)/Ti₃C₂T_x-PVP/Au is directly fabricated with these well-dispersed Ti₃C₂T_x-PVP composites by the solution process technique. Interestingly, the resultant device exhibits a typical bistable electrical switching, ultralow switching voltage (∼0.9 V), and a nonvolatile rewritable memory effect with the function of flash. This work might pave the way of using MXenes for future data storage, which is an indispensable field nowadays.

Redox gated polymer memristive processing memory unit

Memristors with enormous storage capacity and superior processing efficiency are of critical importance to overcome the Moore’s Law limitation and von Neumann bottleneck problems in the big data and artificial intelligence era. In particular, the integration of multifunctionalities into a single memristor promises an essential strategy of obtaining a high-performance electronic device that satisfies the nowadays increasing demands of data storage and processing. In this contribution, we report a proof-of-concept polymer memristive processing-memory unit that demonstrates programmable information storage and processing capabilities. By introducing redox active moieties of triphenylamine and ferrocene onto the pendants of fluorene skeletons, the conjugated polymer exhibits triple oxidation behavior and interesting memristive switching characteristics. Associated with the unique electrochemical and electrical behavior, the polymer device is capable of executing multilevel memory, decimal arithmetic operations of addition, subtraction, multiplication and division, as well as simple Boolean logic operations.

Though designing conductive polymers for memory devices is attractive for future low-cost flexible electronics, a proof-of-concept device has yet to be realized. Here, the authors report a redox-gated polymer memristive processing unit with programmable multilevel storage and logic functionalities.

Recent Progress in Two-Dimensional Nanomaterials for Laser Protection

The Nobel Prize in Physics 2018, “For groundbreaking inventions in the field of laser physics”, went to Arthur Ashkin and Gérard Mourou and Donna Strickland. Their inventions have revolutionized laser physics and greatly promoted the development of laser instruments, which have penetrated into many aspects of people’s daily lives. However, for the purpose of protecting human eyes or optical instruments from being damaged by both pulsed and continuous wave laser radiation, the research on laser protective materials is of particular significance. Due to the intriguing and outstanding physical, chemical, and structural properties, two-dimensional (2D) nanomaterials have been extensively studied as optical limiting (OL) materials owing to their broadband nonlinear optical (NLO) response and fast carrier relaxation dynamics that are important for reducing the laser intensity. This review systematically describes the OL mechanisms and the recent progress in 2D nanomaterials for laser protection.

Directed Assembly of Hybrid Nanomaterials and Nanocomposites

Hybrid nanomaterials are molecular or colloidal-level combinations of organic and inorganic materials, or otherwise strongly dissimilar materials. They are often, though not exclusively, anisotropic in shape. A canonical example is an inorganic nanorod or nanosheet sheathed in, or decorated by, a polymeric or other organic material, where both the inorganic and organic components are important for the properties of the system. Hybrid nanomaterials and nanocomposites have generated strong interest for a broad range of applications due to their functional properties. Generating macroscopic assemblies of hybrid nanomaterials and nanomaterials in nanocomposites with controlled orientation and placement by directed assembly is important for realizing such applications. Here, a survey of critical issues and themes in directed assembly of hybrid nanomaterials and nanocomposites is provided, highlighting recent efforts in this field with particular emphasis on scalable methods.

Recent Advances in RAFT Polymerization: Novel Initiation Mechanisms and Optoelectronic Applications

Reversible addition-fragmentation chain transfer (RAFT) is considered to be one of most famous reversible deactivation radical polymerization protocols. Benefiting from its living or controlled polymerization process, complex polymeric architectures with controlled molecular weight, low dispersity, as well as various functionality have been constructed, which could be applied in wide fields, including materials, biology, and electrology. Under the continuous research improvement, main achievements have focused on the development of new RAFT techniques, containing fancy initiation methods (e.g., photo, metal, enzyme, redox and acid), sulfur-free RAFT system and their applications in many fields. This review summarizes the current advances in major bright spot of novel RAFT techniques as well as their potential applications in the optoelectronic field, especially in the past a few years.

An all-in-one memory cell based on a homopolymer with a pyrene side chain and its volatile and nonvolatile resistive switch behaviors

Memory devices based on PMPPE exhibit a rewritable ternary memory behaviour (0, 1, 2, three conductivity states).

Digital to analog resistive switching transition induced by graphene buffer layer in strontium titanate based devices

Resistive switching behaviour can be classified into digital and analog switching based on its abrupt and gradual resistance change characteristics. Realizing the transition from digital to analog switching in the same device is essential for understanding and controlling the performance of the devices with various switching mechanisms. Here, we investigate the resistive switching in a device made with strontium titanate (SrTiO₃) nanoparticles using X-ray diffractometry, scanning electron microscopy, Raman spectroscopy, and direct electrical measurements. It is found that the well-known rupture/formation of Ag filaments is responsible for the digital switching in the device with Ag as the top electrode. To modulate the switching performance, we insert a reduced graphene oxide layer between SrTiO₃ and the bottom FTO electrode owing to its good barrier property for the diffusion of Ag ions and high out-of-plane resistance. In this case, resistive switching is changed from digital to analog as determined by the modulation of interfacial resistance under applied voltage. Based on that controllable resistance, potentiation and depression behaviours are implemented as well. This study opens up new ways for the design of multifunctional devices which are promising for memory and neuromorphic computing applications.

Conjugated polymer covalently modified graphene oxide quantum dots for ternary electronic memory devices

Zero dimensional graphene oxide (GO) quantum dots (GOQDs) have been expected to play an important role in the development of new memory materials. When the size of GO was reduced to that of GOQDs, both the electron affinity and ionization potential of GO were found to be decreased, and this was followed by the elevation of lowest energy unoccupied molecular orbital (LUMO) energy level. This implies that the electron withdrawing ability of GOQDs is weaker than that of GO. In this work, a novel arylamine-based polyazomethine covalently functionalized graphene oxide quantum dots (TPAPAM-GOQDs), which was synthesized using an amidation reaction, was for the first time used to fabricate a ternary memory device with a configuration of gold/TPAPAM-GOQDs/indium tin oxide. The current ratio of OFF : ON-1 : ON-2 was found to be 1 : 60 : 3000. Its conductive nature was also revealed using an in situ conductive atomic force microscopy technique. This memory device could potentially increase the memory capacity of the device from the conventional 2ⁿ to 3ⁿ when compared to binary memory devices.