Memory devices using a mixture of MoS₂ and graphene oxide as the active layer

Compositional effects of hybrid MoS2-GO active layer on the performance of unipolar, low-power and multistate RRAM device

Currently, 2D nanomaterials-based resistive random access memory (RRAMs) are explored on account of their tunable material properties enabling fabrication of low power and flexible RRAM devices. In this work, hybrid MoS2-GO based active layer RRAM devices are investigated. A facile hydrothermal co-synthesis approach is used to obtain the hybrid materials and a cost-effective spin coating method adopted for the fabrication of Ag/MoS2-GO/ITO RRAM devices. The performance of the fabricated hybrid active layer RRAM device is analysed with respect to change in material properties of the synthesized hybrid material. The progressive addition of 0.5, 1.5, 2.5 and 4.5 weight % of GO to MoS2, results in a hybrid active layer with higher intermolecular interaction, in the case of Ag/MoS2-GO4.5/ITO RRAM device, resulting in a unipolar resistive switching RRAM behavior with low SET voltage of 1.37 V and highIon/Ioffof 200 with multilevel resistance states. A space charge limited conduction mechanism is obtained during switching, which may be attributed to the trap states present due to functional groups of GO. The increased number of conduction pathways on account of both Ag+ions and oxygen vacancies (Vo2+), participating in the formation of conducting filament, results in higherIon/Ioff. This is the first report of unipolar Ag/MoS2-GO/ITO RRAM devices, which are particularly important in realizing high density crossbar memories for neuromorphic and in-memory computing as well as enabling flexible 2D nanomaterials-based memristor applications.

Artificial visual perception neural system using a solution-processable MoS2-based in-memory light sensor

Optoelectronic devices are advantageous in in-memory light sensing for visual information processing, recognition, and storage in an energy-efficient manner. Recently, in-memory light sensors have been proposed to improve the energy, area, and time efficiencies of neuromorphic computing systems. This study is primarily focused on the development of a single sensing-storage-processing node based on a two-terminal solution-processable MoS₂ metal-oxide-semiconductor (MOS) charge-trapping memory structure-the basic structure for charge-coupled devices (CCD)-and showing its suitability for in-memory light sensing and artificial visual perception. The memory window of the device increased from 2.8 V to more than 6 V when the device was irradiated with optical lights of different wavelengths during the program operation. Furthermore, the charge retention capability of the device at a high temperature (100 °C) was enhanced from 36 to 64% when exposed to a light wavelength of 400 nm. The larger shift in the threshold voltage with an increasing operating voltage confirmed that more charges were trapped at the Al₂O₃/MoS₂ interface and in the MoS₂ layer. A small convolutional neural network was proposed to measure the optical sensing and electrical programming abilities of the device. The array simulation received optical images transmitted using a blue light wavelength and performed inference computation to process and recognize the images with 91% accuracy. This study is a significant step toward the development of optoelectronic MOS memory devices for neuromorphic visual perception, adaptive parallel processing networks for in-memory light sensing, and smart CCD cameras with artificial visual perception capabilities.

2D materials: increscent quantum flatland with immense potential for applications

Quantum flatland i.e., the family of two dimensional (2D) quantum materials has become increscent and has already encompassed elemental atomic sheets (Xenes), 2D transition metal dichalcogenides (TMDCs), 2D metal nitrides/carbides/carbonitrides (MXenes), 2D metal oxides, 2D metal phosphides, 2D metal halides, 2D mixed oxides, etc. and still new members are being explored. Owing to the occurrence of various structural phases of each 2D material and each exhibiting a unique electronic structure; bestows distinct physical and chemical properties. In the early years, world record electronic mobility and fractional quantum Hall effect of graphene attracted attention. Thanks to excellent electronic mobility, and extreme sensitivity of their electronic structures towards the adjacent environment, 2D materials have been employed as various ultrafast precision sensors such as gas/fire/light/strain sensors and in trace-level molecular detectors and disease diagnosis. 2D materials, their doped versions, and their hetero layers and hybrids have been successfully employed in electronic/photonic/optoelectronic/spintronic and straintronic chips. In recent times, quantum behavior such as the existence of a superconducting phase in moiré hetero layers, the feasibility of hyperbolic photonic metamaterials, mechanical metamaterials with negative Poisson ratio, and potential usage in second/third harmonic generation and electromagnetic shields, etc. have raised the expectations further. High surface area, excellent young's moduli, and anchoring/coupling capability bolster hopes for their usage as nanofillers in polymers, glass, and soft metals. Even though lab-scale demonstrations have been showcased, large-scale applications such as solar cells, LEDs, flat panel displays, hybrid energy storage, catalysis (including water splitting and CO2 reduction), etc. will catch up. While new members of the flatland family will be invented, new methods of large-scale synthesis of defect-free crystals will be explored and novel applications will emerge, it is expected. Achieving a high level of in-plane doping in 2D materials without adding defects is a challenge to work on. Development of understanding of inter-layer coupling and its effects on electron injection/excited state electron transfer at the 2D-2D interfaces will lead to future generation heterolayer devices and sensors.

2D Materials and Primary Human Dendritic Cells: A Comparative Cytotoxicity Study

Human health can be affected by materials indirectly through exposure to the environment or directly through close contact and uptake. With the ever-growing use of 2D materials in many applications such as electronics, medical therapeutics, molecular sensing, and energy storage, it has become more pertinent to investigate their impact on the immune system. Dendritic cells (DCs) are highly important, considering their role as the main link between the innate and the adaptive immune system. By using primary human DCs, it is shown that hexagonal boron nitride (hBN), graphene oxide (GO) and molybdenum disulphide have minimal effects on viability. In particular, it is evidenced that hBN and GO increase DC maturation, while GO leads to the release of reactive oxygen species and pro-inflammatory cytokines. hBN and MoS₂ increase T cell proliferation with and without the presence of DCs. hBN in particular does not show any sign of downstream T cell polarization. The study allows ranking of the three materials in terms of inherent toxicity, providing the following trend: GO > hBN ≈ MoS₂ , with GO the most cytotoxic.

High-yield production of mono- or few-layer transition metal dichalcogenide nanosheets by an electrochemical lithium ion intercalation-based exfoliation method

Transition metal dichalcogenide (TMD) nanomaterials, especially the mono- or few-layer ones, have received extensive research interest owing to their versatile properties, ranging from true metals (e.g., NbS2 and VSe2) and semimetals (e.g., WTe2 and TiSe2) to semiconductors (e.g., MoS2 and We2) and insulators (e.g., HfS2). Therefore, the reliable production of these nanomaterials with atomically thin thickness and laterally uniform dimension is essential for their promising applications in transistors, photodetectors, electroluminescent devices, catalysis, energy conversion, environment remediation, biosensing, bioimaging, and so on. Recently, the electrochemical lithium ion intercalation-based exfoliation method has emerged as a mature, efficient and promising strategy for the high-yield production of mono- or few-layer TMD nanosheets; monolayer MoS2 (yield of 92%), monolayer TaS2 (yield of 93%) and bilayer TiS2 (yield of 93%) with lateral dimensions of ~1 µm (refs. 1-3). This Protocol describes the details of experimental procedures for the high-yield synthesis of mono- or few-layer TMDs and other inorganic nanosheets such as MoS2, WS2, TiS2, TaS2, ZrS2, graphene, h-BN, NbSe2, WSe2, Sb2Se3 and Bi2Te3 by using the electrochemical lithium ion intercalation-based exfoliation method, which involves the electrochemical intercalation of lithium ions into layered inorganic crystals and a mild sonication process. The whole protocol takes 26-38 h for the successful production of ultrathin inorganic nanosheets.

Bipolar Resistive Switching Behavior of PVP-GQD/HfOx/ITO/Graphene Hybrid Flexible Resistive Random Access Memory

We have investigated highly flexible memristive devices using reduced graphene oxide (RGO) nanosheet nanocomposites with an embedded GQD Layer. Resistive switching behavior of poly (4-vinylphenol):graphene quantum dot (PVP:GQD) composite and HfOx hybrid bilayer was explored for developing flexible resistive random access memory (RRAM) devices. A composite active layer was designed based on graphene quantum dots, which is a low-dimensional structure, and a heterogeneous active layer of graphene quantum dots was applied to the interfacial defect structure to overcome the limitations. Increasing to 0.3–0.6 wt % PVP-GQD, V_f changed from 2.27–2.74 V. When negative deflection is applied to the lower electrode, electrons travel through the HfOx/ITO interface. In addition, as the PVP-GQD concentration increased, the depth of the interfacial defect decreased, and confirmed the repetition of appropriate electrical properties through Al and HfOx/ITO. The low interfacial defects help electrophoresis of Al⁺ ions to the PVP GQD layer and the HfOx thin film. A local electric field increase occurred, resulting in the breakage of the conductive filament in the defect.

Heteroepitaxial Growth of High Optical Quality, Wafer-Scale van der Waals Heterostrucutres

Transition metal dichalcogenides (TMDs) are materials that can exhibit intriguing optical properties like a change of the bandgap from indirect to direct when being thinned down to a monolayer. Well-resolved narrow excitonic resonances can be observed for such monolayers although only for materials of sufficient crystalline quality and so far mostly available in the form of micrometer-sized flakes. A further significant improvement of optical and electrical properties can be achieved by transferring the TMD on hexagonal boron nitride (hBN). To exploit the full potential of TMDs in future applications, epitaxial techniques have to be developed that not only allow the growth of large-scale, high-quality TMD monolayers but also allow the growth to be performed directly on large-scale epitaxial hBN. In this work, we address this problem and demonstrate that MoSe2 of high optical quality can be directly grown on epitaxial hBN on an entire 2 in. wafer. We developed a combined growth theme for which hBN is first synthesized at high temperature by metal organic vapor phase epitaxy (MOVPE) and as a second step MoSe2 is deposited on top by molecular beam epitaxy (MBE) at much lower temperatures. We show that this structure exhibits excellent optical properties, manifested by narrow excitonic lines in the photoluminescence spectra. Moreover, the material is homogeneous on the area of the whole 2 in. wafer with only ±0.14 meV deviation of excitonic energy. Our mixed growth technique may guide the way for future large-scale production of high quality TMD/hBN heterostructures.

Nanomaterials and their applications on bio-inspired wearable electronics

Wearable electronics featuring conformal attachment, sensitive perception and intellectual signal processing have made significant progress in recent years. However, when compared with living organisms, artificial sensory devices showed undeniable bulky shape, poor adaptability, and large energy consumption. To make up for the deficiencies, biological examples provide inspirations of novel designs and practical applications. In the field of biomimetics, nanomaterials from nanoparticles to layered two-dimensional materials are actively involved due to their outstanding physicochemical properties and nanoscale configurability. This review focuses on nanomaterials related to wearable electronics through bioinspired approaches on three different levels, interfacial packaging, sensory structure, and signal processing, which comprehensively guided recent progress of wearable devices in leveraging both nanomaterial superiorities and biorealistic functionalities. In addition, opinions on potential development trend are proposed aiming at implementing bioinspired electronics in multifunctional portable sensors, health monitoring, and intelligent prosthetics.

Periodic nanostructures: preparation, properties and applications

Periodic nanostructures, a group of nanomaterials consisting of single or multiple nano units/components periodically arranged into ordered patterns (e.g., vertical and lateral superlattices), have attracted tremendous attention in recent years due to their extraordinary physical and chemical properties that offer a huge potential for a multitude of applications in energy conversion, electronic and optoelectronic applications. Recent advances in the preparation strategies of periodic nanostructures, including self-assembly, epitaxy, and exfoliation, have paved the way to rationally modulate their ferroelectricity, superconductivity, band gap and many other physical and chemical properties. For example, the recent discovery of superconductivity observed in "magic-angle" graphene superlattices has sparked intensive studies in new ways, creating superlattices in twisted 2D materials. Recent development in the various state-of-the-art preparations of periodic nanostructures has created many new ideas and findings, warranting a timely review. In this review, we discuss the current advances of periodic nanostructures, including their preparation strategies, property modulations and various applications.

Polyvinylalcohol (PVA)-Assisted Exfoliation of ReS2 Nanosheets and the Use of ReS2-PVA Composites for Transparent Memristive Photosynapse Devices

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant attention for their outstanding optoelectrical properties. Unlike most TMDs with layer-dependent photoresponsivity, rhenium disulfide (ReS₂) shows excellent thickness-independent photoresponsivity. Herein, we show a surfactant-free polyvinyl alcohol (PVA)-assisted exfoliation method for 2D-TMDs in aqueous solution and a transparent photosensitive memristor synapse device based on ReS₂ nanosheets composited with PVA. ReS₂ nanosheets are obtained via PVA-assisted exfoliation. After exfoliation, the ReS₂-PVA dispersion solution is spin-coated on a substrate and dried to form a nanocomposite film without additional processing. Transparent memristors are then fabricated on plastic or glass substrates to demonstrate the applicability of the ReS₂-PVA film. The devices show "write once, read many" memory behavior with a high ON/OFF current ratio (1.0 × 10⁴ at 0.5 V) during electrical operation. In the high resistive state, synaptic functions with long-term memory behavior are successfully mimicked by applying photonic stimuli to the transparent ReS₂-PVA memristors. The excitatory postsynaptic current stimulated by the photosignal is gradually reduced by electric stimuli. The proposed PVA-assisted exfoliation method is cost-effective, environmentally friendly, and applicable to various TMD nanomaterials. Furthermore, the ReS₂-PVA nanocomposite film obtained via a simple solution-based process demonstrates excellent photosynaptic behavior.

Two-Dimensional Near-Atom-Thickness Materials for Emerging Neuromorphic Devices and Applications

Two-dimensional (2D) layered materials and their heterostructures have recently been recognized as promising building blocks for futuristic brain-like neuromorphic computing devices. They exhibit unique properties such as near-atomic thickness, dangling-bond-free surfaces, high mechanical robustness, and electrical/optical tunability. Such attributes unattainable with traditional electronic materials are particularly promising for high-performance artificial neurons and synapses, enabling energy-efficient operation, high integration density, and excellent scalability. In this review, diverse 2D materials explored for neuromorphic applications, including graphene, transition metal dichalcogenides, hexagonal boron nitride, and black phosphorous, are comprehensively overviewed. Their promise for neuromorphic applications are fully discussed in terms of material property suitability and device operation principles. Furthermore, up-to-date demonstrations of neuromorphic devices based on 2D materials or their heterostructures are presented. Lastly, the challenges associated with the successful implementation of 2D materials into large-scale devices and their material quality control will be outlined along with the future prospect of these emergent materials.

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.

Memristive devices based on emerging two-dimensional materials beyond graphene

With the explosion of data in the information universe and the approaching of fundamental limits in silicon-based flash memories, the exploration of new device architectures and alternative materials is necessary for next-generation memory technology. Accordingly, emerging two-dimensional (2D) material-based memristive devices have attracted increasing attention due to their unique properties and great potential in flexible and wearable devices, and even neuromorphic computing systems. Herein, we provide an overview of the recent progress on memristive devices based on 2D materials beyond graphene. The device structures and choice of active materials and electrodes materials are summarized for various types of 2D material-based memristive devices. Following the discussion and classification on the device performances and mechanisms, the challenges and perspectives on future research based on 2D materials are also presented.

A Robust Nonvolatile Resistive Memory Device Based on a Freestanding Ultrathin 2D Imine Polymer Film

Here, the synthesis of a wafer-scale ultrathin 2D imine polymer (2DP) film with controllable thickness from simple benzene-1,3,5-tricarbaldehyde (BTA) and p-phenylenediamine (PDA) building blocks is reported using a Schiff base polycondensation reaction at the air-water interface. The synthesized freestanding 2DP films are porous, insulating, and more importantly, covalently linked, which is ideally suited for nonvolatile memristors that use a conductive filament mechanism. These devices exhibit excellent switching performance with high reliability and reproducibility, with on/off ratios in the range of 10² to 10⁵ depending on the thickness of the film. In addition, the endurance and data retention capability of 2DP-based nonvolatile resistive memristors are up to 200 cycles and 8 × 10⁴ s under constant voltage stress at 0.1 V. The intrinsic flexibility of the covalent organic polymer enables the fabrication of a flexible memory device on a polyimide film, which exhibits as reliable memory performance as that on the rigid substrate. Moreover, the 2DP-based memory device shows outstanding thermal stability and organic solvent resistance, which are desirable properties for applications in wearable devices.

Electrical transportation mechanisms of molybdenum disulfide flakes-graphene quantum dots heterostructure embedded in polyvinylidene fluoride polymer

In the interest of the trend towards miniaturization of electronic gadgets, this study demonstrates a high-density data storage device with a very simple three-stacking layer consisting of only one charge trapping layer. A simple solution-processed technique has been used to fabricate the tristable non-volatile memory. The three-stacking layer was constructed in between two metals to form a two-terminal metal-insulator-metal structure. The fabricated device showed a large multilevel memory hysteresis window with a measured ON/OFF current ratio of 10⁷ that might be attributed to the high charge trapped in molybdenum disulphide (MoS₂) flakes-graphene quantum dots (GQDs) heterostructure. Transmission electron microscopy was performed to examine the orientation of MoS₂-GQD and mixture dispersion preparation method. The obtained electrical data was used further to speculate the possible transport mechanisms through the fabricated device by a curve fitting technique. Also, endurance cycle and retention tests were performed at room temperature to investigate the stability of the device.

Flexible Molybdenum Disulfide (MoS2) Atomic Layers for Wearable Electronics and Optoelectronics

Flexible, stretchable, and bendable materials, including inorganic semiconductors, organic polymers, graphene, and transition metal dichalcogenides (TMDs), are attracting great attention in such areas as wearable electronics, biomedical technologies, foldable displays, and wearable point-of-care biosensors for healthcare. Among a broad range of layered TMDs, atomically thin layered molybdenum disulfide (MoS₂) has been of particular interest, due to its exceptional electronic properties, including tunable bandgap and charge carrier mobility. MoS₂ atomic layers can be used as a channel or a gate dielectric for fabricating atomically thin field-effect transistors (FETs) for electronic and optoelectronic devices. This review briefly introduces the processing and spectroscopic characterization of large-area MoS₂ atomically thin layers. The review summarizes the different strategies in enhancing the charge carrier mobility and switching speed of MoS₂ FETs by integrating high-κ dielectrics, encapsulating layers, and other 2D van der Waals layered materials into flexible MoS₂ device structures. The photoluminescence (PL) of MoS₂ atomic layers has, after chemical treatment, been dramatically improved to near-unity quantum yield. Ultraflexible and wearable active-matrix organic light-emitting diode (AM-OLED) displays and wafer-scale flexible resistive random-access memory (RRAM) arrays have been assembled using flexible MoS₂ transistors. The review discusses the overall recent progress made in developing MoS₂ based flexible FETs, OLED displays, nonvolatile memory (NVM) devices, piezoelectric nanogenerators (PNGs), and sensors for wearable electronic and optoelectronic devices. Finally, it outlines the perspectives and tremendous opportunities offered by a large family of atomically thin-layered TMDs.

Nonvolatile Memories Based on Graphene and Related 2D Materials

The pervasiveness of information technologies is generating an impressive amount of data, which need to be accessed very quickly. Nonvolatile memories (NVMs) are making inroads into high-capacity storage to replace hard disk drives, fuelling the expansion of the global storage memory market. As silicon-based flash memories are approaching their fundamental limit, vertical stacking of multiple memory cell layers, innovative device concepts, and novel materials are being investigated. In this context, emerging 2D materials, such as graphene, transition metal dichalcogenides, and black phosphorous, offer a host of physical and chemical properties, which could both improve existing memory technologies and enable the next generation of low-cost, flexible, and wearable storage devices. Herein, an overview of graphene and related 2D materials (GRMs) in different types of NVM cells is provided, including resistive random-access, flash, magnetic and phase-change memories. The physical and chemical mechanisms underlying the switching of GRM-based memory devices studied in the last decade are discussed. Although at this stage most of the proof-of-concept devices investigated do not compete with state-of-the-art devices, a number of promising technological advancements have emerged. Here, the most relevant material properties and device structures are analyzed, emphasizing opportunities and challenges toward the realization of practical NVM devices.

Highly flexible memristive devices based on MoS2 quantum dots sandwiched between PMSSQ layers

This paper reports a facile, cost effective method that uses an aqueous hydrothermal process for synthesizing two-dimensional molybdenum disulphide (MoS2) monolayer quantum dots (QDs) and their potential applications in flexible memristive devices. High-resolution transmission electron microscopy and atomic force microscopy images confirmed that the diameters of the synthesized MoS2 QDs with irregular shapes were in the range between 3 and 6 nm; their thicknesses were confirmed to lie between 1.0 and 0.8 nm, a clear indication that a monolayer of MoS2 QDs had been synthesized. Photoluminescence (PL) and time-resolved PL spectra of the MoS2 QDs revealed a strong emission in the blue region with a slower decay constant. Memristive devices fabricated by incorporating MoS2 QDs between poly(methylsilsesquioxane) ultrathin layers, which had been deposited on poly(ethylene terephthalate), demonstrated a high ON-OFF current ratio of ∼104, stable retention, and excellent endurance in the relaxed state; these devices were also demonstrated to function properly during bending and in a bent state. The flexible memristive devices demonstrated an OFF state with a very low current of 10-6 A. These results clearly show that ultrathin two-dimensional QDs have promising applications in high-performance flexible memristive devices.

Versatile and Scalable Strategy To Grow Sol-Gel Derived 2H-MoS2 Thin Films with Superior Electronic Properties: A Memristive Case

Transition metal dichalcogenides, such as molybdenum disulfide (MoS₂), show peculiar chemical/physical properties that enable their use in applications ranging from micro- and nano-optoelectronics to surface catalysis, gas and light detection, and energy harvesting/production. One main limitation to fully harness the potential of MoS₂ is given by the lack of scalable and low environmental impact synthesis of MoS₂ films with high uniformity, hence setting a significant challenge for industrial applications. In this work, we develop a versatile and scalable sol-gel-derived MoS₂ film fabrication by spin coating deposition of an aqueous sol on different technologically relevant, flexible substrates with annealing at low temperatures (300 °C) and without the need of sulfurization and/or supply of hydrogen as compared to cutting-edge techniques. The electronic and physical properties of the MoS₂ thin films were extensively investigated by means of surface spectroscopy and structural characterization techniques. Spatially homogenous nanocrystalline 2H-MoS₂ thin films were obtained exhibiting high chemical purity and excellent electronic properties such as an energy band gap of 1.35 eV in agreement with the 2H phase of the MoS₂, and a density of states that corresponds to the n-type character expected for high-quality 2H-MoS₂. The potential use of sol-gel-grown MoS₂ as the candidate material for electronic applications was tested via electrical characterization and demonstrated via the reversible switching in resistivity typical for memristors with a measured ON-OFF ratio ≥10². The obtained results highlight that the novel low-cost fabrication method has a great potential to promote the use of high-quality MoS₂ in technological and industrial-relevant scalable applications.

Photocatalytic Reduction of Graphene Oxide-TiO2 Nanocomposites for Improving Resistive-Switching Memory Behaviors

Graphene oxide (GO)-based resistive-switching (RS) memories offer the promise of low-temperature solution-processability and high mechanical flexibility, making them ideally suited for future flexible electronic devices. The RS of GO can be recognized as electric-field-induced connection/disconnection of nanoscale reduced graphene oxide (RGO) conducting filaments (CFs). Instead of operating an electrical FORMING process, which generally results in high randomness of RGO CFs due to current overshoot, a TiO2 -assisted photocatalytic reduction method is used to generate RGO-domains locally through controlling the UV irradiation time and TiO2 concentration. The elimination of the FORMING process successfully suppresses the RGO overgrowth and improved RS memory characteristics are achieved in graphene oxide-TiO2 (Go-TiO2 ) nanocomposites, including reduced SET voltage, improved switching variability, and increased switching speed. Furthermore, the room-temperature process of this method is compatible with flexible plastic substrates and the memory cells exhibit excellent flexibility. Experimental results evidence that the combined advantages of reducing the oxygen-migration barrier and enhancing the local-electric-field with RGO-manipulation are responsible for the improved RS behaviors. These results offer valuable insight into the role of RGO-domains in GO memory devices, and also, this mild photoreduction method can be extended to the development of carbon-based flexible electronics.

Group 6 transition metal dichalcogenide nanomaterials: synthesis, applications and future perspectives

Group 6 transition metal dichalcogenides (G6-TMDs), most notably MoS₂, MoSe₂, MoTe₂, WS₂ and WSe₂, constitute an important class of materials with a layered crystal structure. Various types of G6-TMD nanomaterials, such as nanosheets, nanotubes and quantum dot nano-objects and flower-like nanostructures, have been synthesized. High thermodynamic stability under ambient conditions, even in atomically thin form, made nanosheets of these inorganic semiconductors a valuable asset in the existing library of two-dimensional (2D) materials, along with the well-known semimetallic graphene and insulating hexagonal boron nitride. G6-TMDs generally possess an appropriate bandgap (1-2 eV) which is tunable by size and dimensionality and changes from indirect to direct in monolayer nanosheets, intriguing for (opto)electronic, sensing, and solar energy harvesting applications. Moreover, rich intercalation chemistry and abundance of catalytically active edge sites make them promising for fabrication of novel energy storage devices and advanced catalysts. In this review, we provide an overview on all aspects of the basic science, physicochemical properties and characterization techniques as well as all existing production methods and applications of G6-TMD nanomaterials in a comprehensive yet concise treatment. Particular emphasis is placed on establishing a linkage between the features of production methods and the specific needs of rapidly growing applications of G6-TMDs to develop a production-application selection guide. Based on this selection guide, a framework is suggested for future research on how to bridge existing knowledge gaps and improve current production methods towards technological application of G6-TMD nanomaterials.

Tunable Nonvolatile Memory Behaviors of PCBM-MoS2 2D Nanocomposites through Surface Deposition Ratio Control

Efficient preparation of single-layer two-dimensional (2D) transition metal dichalcogenides, especially molybdenum disulfide (MoS₂), offers readily available 2D surface in nanoscale to template various materials to form nanocomposites with van der Waals heterostructures (vdWHs), opening up a new dimension for the design of functional electronic and optoelectronic materials and devices. Here, we report the tunable memory properties of the facilely prepared [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM)-MoS₂ nanocomposites in a conventional diode device structure, where the vdWHs dominate the electric characteristics of the devices for various memory behaviors depending on different surface deposition ratios of PCBM on MoS₂ nanosheets. Both nonvolatile WORM and flash memory devices have been realized using the new developed PCBM-MoS₂ 2D composites. Specially, the flash characteristic devices show rewritable resistive switching with low switching voltages (∼2 V), high current on/off ratios (∼3 × 10²), and superior electrical bistability (>10⁴ s). This research, through successfully allocating massive vdWHs on the MoS₂ surface for organic/inorganic 2D nanocomposites, illustrates the great potential of 2D vdWHs in rectifying the electronic properties for high-performance memory devices and paves a way for the design of promising 2D nanocomposites with electronically active vdWHs for advanced device applications.

Interface Engineering with MoS2 -Pd Nanoparticles Hybrid Structure for a Low Voltage Resistive Switching Memory

Metal oxide-based resistive random access memory (RRAM) has attracted a lot of attention for its scalability, temperature robustness, and potential to achieve machine learning. However, a thick oxide layer results in relatively high program voltage while a thin one causes large leakage current and a small window. Owing to these fundamental limitations, by optimizing the oxide layer itself a novel interface engineering idea is proposed to reduce the programming voltage, increase the uniformity and on/off ratio. According to this idea, a molybdenum disulfide (MoS₂ )-palladium nanoparticles hybrid structure is used to engineer the oxide/electrode interface of hafnium oxide (HfO_x )-based RRAM. Through its interface engineering, the set voltage can be greatly lowered (from -3.5 to -0.8 V) with better uniformity under a relatively thick HfO_x layer (≈15 nm), and a 30 times improvement of the memory window can be obtained. Moreover, due to the atomic thickness of MoS₂ film and high transmittance of ITO, the proposed RRAM exhibits high transparency in visible light. As the proposed interface-engineering RRAM exhibits good transparency, low SET voltage, and a large resistive switching window, it has huge potential in data storage in transparent circuits and wearable electronics with relatively low supply voltage.

Preparation of 2D material dispersions and their applications

A comprehensive review on the exfoliation of layer materials into 2D materials, their assembly, and applications in electronics and energy.

Nonvolatile ternary resistive switching memory devices based on the polymer composites containing zinc oxide nanoparticles

Nonvolatile ternary memory devices were fabricated from the composites polymer blends containing zinc oxide (ZnO) nanoparticles.

Large Lateral Photovoltage Observed in MoS2 Thickness-Modulated ITO/MoS2/p-Si Heterojunctions

Molybdenum disulfide (MoS₂), as a typical two-dimensional (2D) material, has attracted extensive attention in recent years because of its fascinating optical and electric properties. However, the applications of MoS₂ have been mainly in photovoltaic devices, field-effect transistors, photodetectors, and gas sensors. Here, it is demonstrated that MoS₂ can be found another important application in position sensitive detector (PSD) based on lateral photovoltaic effect (LPE) in it. The ITO/MoS₂(3, 5, 7, 9, 10, 20, 50, 100 nm)/p-Si heterojunctions were successfully prepared with vertically standing nanosheet structure of MoS₂. Because of the special structure and the strong light absorption of the relatively thick MoS₂ film, the ITO/MoS₂/p-Si heterojunction exhibits an abnormal thickness-dependent LPE, which can be ascribed to the n- to p-type transformation of MoS₂. Moreover, the LPE of ITO/MoS₂/p-Si structure improves greatly because of forward enhanced built-in field by type transformation in a wide spectrum response ranging from visible to near-infrared, especially the noticeable improvement in infrared region, indicating its great potential application in infrared PSDs. This work not only suggest that the ITO/MoS₂/p-Si heterojunction shows great potential in LPE-based sensors, but also unveils the importance of type transformation of MoS₂ in MoS₂-based photoelectric devices besides strong light absorption and suitable bandgap.

Work Function Tuning in Two-Dimensional MoS2 Field-Effect-Transistors with Graphene and Titanium Source-Drain Contacts

Based on the first principles calculation, we investigate the electronic band structures of graphene-MoS₂ and Ti-MoS₂ heterojunctions under gate-voltages. By simultaneous control of external electric fields and carrier charging concentrations, we show that the graphene’s Dirac point position inside the MoS₂ bandgap is easily modulated with respect to the co-varying Fermi level, while keeping the graphene’s linear band structure around the Dirac point. The easy modulation of graphene bands is not confined to the special cases where the conduction-band-minimum point of MoS₂ and the Dirac point of graphene are matched up in reciprocal space, but is generalized to their dislocated cases. This flexibility caused by the strong decoupling between graphene and MoS₂ bands enhances the gate-controlled switching performance in MoS₂-graphene hybrid stacking-device.

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

A novel nonvolatile rewritable memory device based on the soluble poly(N-vinylcarbazole)-chemically modified MoS₂ nanosheets (MoS₂-PVK) was fabricated with the configuration of Au/MoS₂-PVK/ITO. This is the first example of polymer covalently modified MoS₂ nanosheet-based memory devices. As expected, this device exhibited a typical storage performance of nonvolatile rewritable memory, with a turn-on voltage of -1.54 V and an ON/OFF current ratio of 4 × 10². After annealing at 80 °C for 1 h under a nitrogen atmosphere, a high ON/OFF current ratio (up to 3 × 10⁴) and a lower turn-on voltage (-1.31 V), which are among the best reported for MoS₂-based polymer/organic memory devices, were achieved due to enhanced crystallization of PVK, which induced a more efficient intramolecular charge transfer effect between PVK and MoS₂ during the annealing process. The effect of film thickness on the current-voltage characteristics of the MoS₂-PVK-based devices and the memory performance of the MoS₂/PVK blends-based devices have also been explored.

Recent Advances in Synthesis and Biomedical Applications of Two-Dimensional Transition Metal Dichalcogenide Nanosheets

During recent decades, a giant leap in the development of nanotechnology has been witnessed. Numerous nanomaterials with different dimensions and unprecedented features have been developed and provided unimaginably wide scope to solve the challenging problems in biomedicine, such as cancer diagnosis and therapy. Recently, two-dimensional (2D) transition metal dichalcogenide (TMDC) nanosheets (NSs), including MoS₂ , WS₂ , and etc., have emerged as novel inorganic graphene analogues and attracted tremendous attention due to their unique structures and distinctive properties, and opened up great opportunities for biomedical applications, including ultrasensitive biosensing, biological imaging, drug delivery, cancer therapy, and antibacterial treatment. A comprehensive overview of different synthetic methods of ultrathin 2D TMDC NSs and their state-of-the-art biomedical applications, especially those that have appeared in the past few years, is presented. At the end of this review, the future opportunities and challenges for 2D TMDC NSs in biomedicine are also discussed.

Abnormal Multiple Charge Memory States in Exfoliated Few-Layer WSe2 Transistors

To construct reliable nanoelectronic devices based on emerging 2D layered semiconductors, we need to understand the charge-trapping processes in such devices. Additionally, the identified charge-trapping schemes in such layered materials could be further exploited to make multibit (or highly desirable analog-tunable) memory devices. Here, we present a study on the abnormal charge-trapping or memory characteristics of few-layer WSe₂ transistors. This work shows that multiple charge-trapping states with large extrema spacing, long retention time, and analog tunability can be excited in the transistors made from mechanically exfoliated few-layer WSe₂ flakes, whereas they cannot be generated in widely studied few-layer MoS₂ transistors. Such charge-trapping characteristics of WSe₂ transistors are attributed to the exfoliation-induced interlayer deformation on the cleaved surfaces of few-layer WSe₂ flakes, which can spontaneously form ambipolar charge-trapping sites. Our additional results from surface characterization, charge-retention characterization at different temperatures, and density functional theory computation strongly support this explanation. Furthermore, our research also demonstrates that the charge-trapping states excited in multiple transistors can be calibrated into consistent multibit data storage levels. This work advances the understanding of the charge memory mechanisms in layered semiconductors, and the observed charge-trapping states could be further studied for enabling ultralow-cost multibit analog memory devices.

Resistive Switching in All-Printed, Flexible and Hybrid MoS2-PVA Nanocomposite based Memristive Device Fabricated by Reverse Offset

Owing to the increasing interest in the nonvolatile memory devices, resistive switching based on hybrid nanocomposite of a 2D material, molybdenum disulphide (MoS2) and polyvinyl alcohol (PVA) is explored in this work. As a proof of concept, we have demonstrated the fabrication of a memory device with the configuration of PET/Ag/MoS2-PVA/Ag via an all printed, hybrid, and state of the art fabrication approach. Bottom Ag electrodes, active layer of hybrid MoS2-PVA nanocomposite and top Ag electrode are deposited by reverse offset, electrohydrodynamic (EHD) atomization and electrohydrodynamic (EHD) patterning respectively. The fabricated device displayed characteristic bistable, nonvolatile and rewritable resistive switching behavior at a low operating voltage. A decent off/on ratio, high retention time, and large endurance of 1.28 × 102, 105 sec and 1000 voltage sweeps were recorded respectively. Double logarithmic curve satisfy the trap controlled space charge limited current (TCSCLC) model in high resistance state (HRS) and ohmic model in low resistance state (LRS). Bendability test at various bending diameters (50-2 mm) for 1500 cycles was carried out to show the mechanical robustness of fabricated device.

Structural Phase Transition Effect on Resistive Switching Behavior of MoS2 -Polyvinylpyrrolidone Nanocomposites Films for Flexible Memory Devices

The 2H phase and 1T phase coexisting in the same molybdenum disulfide (MoS2 ) nanosheets can influence the electronic properties of the materials. The 1T phase of MoS2 is introduced into the 2H-MoS2 nanosheets by two-step hydrothermal synthetic methods. Two types of nonvolatile memory effects, namely write-once read-many times memory and rewritable memory effect, are observed in the flexible memory devices with the configuration of Al/1T@2H-MoS2 -polyvinylpyrrolidone (PVP)/indium tin oxide (ITO)/polyethylene terephthalate (PET) and Al/2H-MoS2 -PVP/ITO/PET, respectively. It is observed that structural phase transition in MoS2 nanosheets plays an important role on the resistive switching behaviors of the MoS2 -based device. It is hoped that our results can offer a general route for the preparation of various promising nanocomposites based on 2D nanosheets of layered transition metal dichalcogenides for fabricating the high performance and flexible nonvolatile memory devices through regulating the phase structure in the 2D nanosheets.

Few-layered MoS2 nanosheets wrapped ultrafine TiO2 nanobelts with enhanced photocatalytic property

Photocatalytic materials comprised of semiconductor nanostructures have attracted tremendous scientific and technological interest over the last 30 years. This is due to the fact that these photocatalytic materials have unique properties that allow for an effective direct energy transfer from light to highly reactive chemical species which are applicable in the remediation of environmental pollutants and photocatalytic hydrogen generation. Heterostructured photocatalysts are a promising type of photocatalyst which can combine the properties of different components to generate a synergic effect, resulting in a high photocatalytic activity. In this work, a heterostructured photocatalyst comprised of few-layered MoS2 nanosheets coated on a TiO2 nanobelts surface was synthesized through a simple hydrothermal treatment. The hybrid heterostructures with enhanced broad spectrum photocatalytic properties can harness UV and visible light energy to decompose organic contaminants in aqueous solutions as well as split water to hydrogen and oxygen. The mechanism of the enhancement is that the MoS2/TiO2 nanobelts heterostructure can enhance the separation of the photo-induced carriers, which results in a higher photocurrent due to the special electronic characteristics of the graphene-like layered MoS2 nanosheets. This methodology is potentially applicable to the synthesis of a range of hybrid nanostructures with promising applications in photocatalysis and other relevant areas.

Hybrid Flexible Resistive Random Access Memory-Gated Transistor for Novel Nonvolatile Data Storage

Here, a single-device demonstration of novel hybrid architecture is reported to achieve programmable transistor nodes which have analogies to flash memory by incorporating a resistive switching random access memory (RRAM) device as a resistive switch gate for field effect transistor (FET) on a flexible substrate. A high performance flexible RRAM with a three-layered structure is fabricated by utilizing solution-processed MoS2 nanosheets sandwiched between poly(methyl methacrylate) polymer layers. Gate coupling with the pentacene-based transistor can be controlled by the RRAM memory state to produce a nonprogrammed state (inactive) and a programmed state (active) with a well-defined memory window. Compared to the reference flash memory device based on the MoS2 floating gate, the hybrid device presents robust access speed and retention ability. Furthermore, the hybrid RRAM-gated FET is used to build an integrated logic circuit and a wide logic window in inverter logic is achieved. The controllable, well-defined memory window, long retention time, and fast access speed of this novel hybrid device may open up new possibilities of realizing fully functional nonvolatile memory for high-performance flexible electronics.

Memristive Behavior and Ideal Memristor of 1T Phase MoS2 Nanosheets

Memristor, which had been predicted a long time ago (Chua, L. O. IEEE Trans. Circuit Theory 1971, 18, 507), was recently invented (Strukov, D. B.; et al. Nature 2008, 453, 80). The introduction of a memristor is expected to open a new era for nonvolatile memory storage, neuromorphic computing, digital logic, and analog circuit. Furthermore, several breakthroughs were made for memristive phenomena and transistors with single-layer MoS2 (Sangwan, V. K.; et al. Nat. Nanotechnol. 2015, 10, 403. van der Zande, A. M.; et al. Nat. Mater. 2013, 12, 554. Liu, H.; et al. ACS Nano 2014, 8, 1031. Bessonov, A. A.; et al. Nat. Mater. 2015, 14, 199. Yuan, J.; et al. Nat. Nanotechnol. 2015, 10, 389). Herein, we demonstrate that 2H phase of bulk MoS2 possessed an ohmic feature, whereas 1T phase of exfoliated MoS2 nanosheets exhibited a unique memristive behavior due to voltage-dependent resistance change. Furthermore, an ideal odd-symmetric memristor with odd-symmetric I-V characteristics was successfully fabricated by the 1T phase MoS2 nanosheets via combining two asymmetric switches antiserially.

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.

CO oxidation by MoS2-supported Au19 nanoparticles: effects of vacancy formation and tensile strain

The mechanism of the catalytic oxidation of CO activated by MoS₂-supported Au₁₉ nanoparticles (NPs) was studied using density functional theory calculations.

Mechanically-induced reverse phase transformation of MoS2from stable 2H to metastable 1T and its memristive behavior

The reverse phase transformation of MoS₂from stable 2H to metastable 1T could be mechanically induced by ball-milling. Furthermore, the mechanically generated 1T MoS₂exhibited memristive behavior.

Preparing non-volatile resistive switching memories by tuning the content of Au@air@TiO2-h yolk-shell microspheres in a poly(3-hexylthiophene) layer

Crystalline hybrid microspheres, encapsulating a Au nanocore in the hollow cavity of a hairy semiconductor TiO2 shell (Au@air@TiO2-h microspheres) were prepared using template-assisted synthesis methods. The as-prepared microspheres are dispersed into a poly(3-hexylthiophene) (P3HT) matrix and used as a memory active layer. The electrical rewritable memory effects of Al/[Au@air@TiO2-h + P3HT]/ITO sandwich devices can be effectively and exactly controlled by tuning the microsphere content in the electroactive layer. To clarify the switching mechanism, different components in the device, such as P3HT and the microspheres, have been investigated. And it was determined that the switching mechanism can be attributed to the formation and rupture of oxygen vacancy filaments. These results suggest that the Au@air@TiO2-h microspheres are potentially capable of high density data storage. In addition, this finding could provide important guidelines for the reproducibility of nanocomposite-based memory devices and is helpful to demonstrate the switching mechanism of these devices.

Two-dimensional molybdenum disulphide nanosheet-covered metal nanoparticle array as a floating gate in multi-functional flash memories

Semiconducting two-dimensional materials appear to be excellent candidates for non-volatile memory applications. However, the limited controllability of charge trapping behaviors and the lack of multi-bit storage studies in two-dimensional based memory devices require further improvement for realistic applications. Here, we report a flash memory consisting of metal NPs-molybdenum disulphide (MoS2) as a floating gate by introducing a metal nanoparticle (NP) (Ag, Au, Pt) monolayer underneath the MoS2 nanosheets. Controlled charge trapping and long data retention have been achieved in a metal (Ag, Au, Pt) NPs-MoS2 floating gate flash memory. This controlled charge trapping is hypothesized to be attributed to band bending and a built-in electric field ξbi between the interface of the metal NPs and MoS2. The metal NPs-MoS2 floating gate flash memories were further proven to be multi-bit memory storage devices possessing a 3-bit storage capability and a good retention capability up to 10(4) s. We anticipate that these findings would provide scientific insight for the development of novel memory devices utilizing an atomically thin two-dimensional lattice structure.

Synthesis of Large-Area Highly Crystalline Monolayer Molybdenum Disulfide with Tunable Grain Size in a H2 Atmosphere

Large-area and highly crystalline monolayer molybdenum disulfide (MoS2) with a tunable grain size was synthesized in a H2 atmosphere. The influence of introduced H2 on MoS2 growth and grain size, as well as the corresponding mechanism, was tentatively explored by controlling the H2 flow rate. The as-grown monolayer MoS2 displays excellent uniformity and high crystallinity evidenced by Raman and high-resolution transmission electron microscopy. The Raman results also give an indication that the quality of the monolayer MoS2 synthesized in a H2 atmosphere is comparable to that synthesized by using seed or mechanical exfoliation. In addition, the electronic properties and dielectric inhomogeneity of MoS2 monolayers were also detected in situ via scanning microwave microscopy, with measurements on impedance and differential capacitance (dC/dV). Back-gated field-effect transistors based on highly crystalline monolayer MoS2 shows a field-effect mobility of ∼13.07 cm2 V(-1) s(-1) and an Ion/Ioff ratio of ∼1.1×10(7), indicating that the synthesis of large-area and high-quality monolayer MoS2 with H2 is a viable method for electronic and optoelectronic applications.

Aptamer loaded MoS2 nanoplates as nanoprobes for detection of intracellular ATP and controllable photodynamic therapy

In this work we designed a MoS2 nanoplate-based nanoprobe for fluorescence imaging of intracellular ATP and photodynamic therapy (PDT) via ATP-mediated controllable release of (1)O2. The nanoprobe was prepared by simply assembling a chlorine e6 (Ce6) labelled ATP aptamer on MoS2 nanoplates, which have favorable biocompatibility, unusual surface-area-to-mass ratio, strong affinity to single-stranded DNA, and can quench the fluorescence of Ce6. After the nanoprobe was internalized into the cells and entered ATP-abundant lysosomes, its recognition to ATP led to the release of the single-stranded aptamer from MoS2 nanoplates and thus recovered the fluorescence of Ce6 at an excitation wavelength of 633 nm, which produced a highly sensitive and selective method for imaging of intracellular ATP. Meanwhile, the ATP-mediated release led to the generation of (1)O2 under 660 nm laser irradiation, which could induce tumor cell death with a lysosomal pathway. The controllable PDT provided a model approach for design of multifunctional theranostic nanoprobes. These results also promoted the development and application of MoS2 nanoplate-based platforms in biomedicine.

Electrical and Optical Characterization of MoS2 with Sulfur Vacancy Passivation by Treatment with Alkanethiol Molecules

We investigated the physical properties of molybdenum disulfide (MoS2) atomic crystals with a sulfur vacancy passivation after treatment with alkanethiol molecules including their electrical, Raman, and photoluminescence (PL) characteristics. MoS2, one of the transition metal dichalcogenide materials, is a promising two-dimensional semiconductor material with good physical properties. It is known that sulfur vacancies exist in MoS2, resulting in the n-type behavior of MoS2. The sulfur vacancies on the MoS2 surface tend to form covalent bonds with sulfur-containing groups. In this study, we deposited alkanethiol molecules on MoS2 field effect transistors (FETs) and then characterized the electrical properties of the devices before and after the alkanethiol treatment. We observed that the electrical characteristics of MoS2 FETs dramatically changed after the alkanethiol treatment. We also observed that the Raman and PL spectra of MoS2 films changed after the alkanethiol treatment. These effects are attributed to the thiol (-SH) end groups in alkanethiols bonding at sulfur vacancy sites, thus altering the physical properties of the MoS2. This study will help us better understand the electrical and optical properties of MoS2 and suggest a way of tailoring the properties of MoS2 by passivating a sulfur vacancy with thiol molecules.

Porous hollow carbon spheres decorated with molybdenum diselenide nanosheets as anodes for highly reversible lithium and sodium storage

Porous hollow carbon spheres (PHCS) decorated with MoSe2 nanosheets (MoSe2@ PHCS) are synthesized via a three-step process. Uniform and conformal MoSe2 nanosheets are firmly attached to PHCS according to the characterization of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption/desorption measurements. Enhanced electrochemical performance of MoSe2@PHCS is investigated in lithium-ion and sodium-ion storage. The MoSe2@PHCS deliver a reversible lithium storage capacity of 681 mA h g(-1) for 100 discharge/charge cycles. In Na-ion batteries, it manifests a reversible sodium capacity of 580 mA h g(-1) after 100 cycles. Three synergic effects can be attributed to the enhanced electrochemical performance of MoSe2@PHCS: (1) both the sheet structure of the MoSe2 and the mechanically robust carbon sphere supporter can accommodate stress from cycling; (2) the porous hollow carbon spheres matrix in the MoSe2@PHCS offers a beneficial conductivity environment; (3) uniform and conformal MoSe2 nanosheets attachment shortens the electronic lithium-ion and sodium-ion pathway during cycling. The MoSe2@PHCS have a great potential as an anode for lithium and sodium batteries.

Surface Plasmon-Enhanced Photodetection in Few Layer MoS2 Phototransistors with Au Nanostructure Arrays

2D Molybdenum disulfide (MoS2 ) is a promising candidate material for high-speed and flexible optoelectronic devices, but only with low photoresponsivity. Here, a large enhancement of photocurrent response is obtained by coupling few-layer MoS2 with Au plasmonic nanostructure arrays. Au nanoparticles or nanoplates placed onto few-layer MoS2 surface can enhance the local optical field in the MoS2 layer, due to the localized surface plasmon (LSP) resonance. After depositing 4 nm thick Au nanoparticles sparsely onto few-layer MoS2 phototransistors, a doubled increase in the photocurrent response is observed. The photocurrent of few-layer MoS2 phototransistors exhibits a threefold enhancement with periodic Au nanoarrays. The simulated optical field distribution confirms that light can be trapped and enhanced near the Au nanoplates. These findings offer an avenue for practical applications of high performance MoS2 -based optoelectronic devices or systems in the future.