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.

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

The Future of Memristors: Materials Engineering and Neural Networks

Resistive random access memory (RRAM) devices are receiving increasing extensive attention due to their enhanced properties such as fast operation speed, simple device structure, low power consumption, good scalability potential and so on, and are currently considered to be one of the next-generation alternatives to traditional memory. In this review, an overview of RRAM devices is demonstrated in terms of thin film materials investigation on electrode and function layer, switching mechanisms and artificial intelligence applications. Compared with the well-developed application of inorganic thin film materials (oxides, solid electrolyte and two-dimensional (2D) materials) in RRAM devices, organic thin film materials (biological and polymer materials) application is considered to be the candidate with significant potential. The performance of RRAM devices is closely related to the investigation of switching mechanisms in this review, including thermal-chemical mechanism (TCM), valance change mechanism (VCM) and electrochemical metallization (ECM). Finally, the bionic synaptic application of RRAM devices is under intensive consideration, its main characteristics such as potentiation/depression response, short-/long-term plasticity (STP/LTP), transition from short-term memory to long-term memory (STM to LTM) and spike-time-dependent plasticity (STDP) reveal the great potential of RRAM devices in the field of neuromorphic application.

https://www.mdpi.com/2079-4991/10/8/1437/pdf

Advances of RRAM Devices: Resistive Switching Mechanisms, Materials and Bionic Synaptic Application.

A Review of Resistive Switching Devices: Performance Improvement, Characterization, and Applications

https://www.tandfonline.com/doi/pdf/10.1080/14686996.2020.1730236

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

The photoluminescence increment in chloride doped all-inorganic rubidium lead iodide (RbPbI3) perovskite has been reported. The pristine RbPbI3 perovskite was synthesized by a simple sol gel method and the crystals are found to be polycrystalline in nature having orthorhombic symmetry. Whereas, an increase in diffracting angles and band gap could be observed upon insertion of chloride in the perovskite structure. Moreover, the photoluminescence (PL) characteristics of the pristine perovskite demonstrated near band edge emission with poor intensity. But, an increasing trend of the PL intensity was observed for chloride doped crystals. Interestingly, an emission intensity more than 102 in order was observed when the chloride concentration was 30% with respect to the iodide. Thus, the increment in band gap due to chloride doping makes the RbPbI3 more flexible for wide range of optoelectronic devices. Further, the enhanced emission characteristics of the chloride doped perovskite enriches its implication in optoelectronic devices. Finally, we conclude that the RbPbI3 perovskite could be utilized in various application via optimized incorporation of chloride.

Enhanced photoluminescence in chloride doped all-inorganic rubidium lead iodide perovskite

Organic–inorganic halide perovskite (OIHP) materials have become the focus of attention in the photovoltaic and other electronic/optoelectronic applications since past few years. The exceptional and fundamental properties of these materials pave the desired state-of-the-art in the perovskite based applications. However, the associated issue of stability must be solved for commercialization. The critical weakness of the OIHPs against moisture originates mainly from the hygroscopic organic cations in the structure. In this work, rubidium (Rb) has been partially substituted at the A-site of formamidinium lead iodide (FAPbI3) structure and found to be suitable for moisture-tolerance. The incorporation of Rb, induced the absorption over the entire visible window, which may lead to various long-term applicability in solar cells, photocatalysis and other optoelectronic devices.

Incorporation of Rubidium in the Organic–Inorganic FAPbI 3 Structure for Stabilizing the Optically Active Perovskite Phase

Resistive switching properties of tungsten disulfide (WS2) as a functional material arereported. The WS2 film was grown over Pt/Ti/SiO2/Si substrate by chemical vapor deposition method inside a horizontal tube furnace. X-ray diffraction pattern of as-deposited WS2 layer confirms the crystalline nature of the film. The current-voltage measurements of the Al/WS2/Pt device reveled typical bipolar resistive switching characteristic with high on/off ratio. Moreover, the multilevel capability of the Al/WS2/Pt device promises its potential as a high density data storage device along with significant retention upto 104 sec.

Ujjal Das

Papers

Enhanced photoluminescence in chloride doped all-inorganic rubidium lead iodide perovskite

Incorporation of Rubidium in the Organic–Inorganic FAPbI 3 Structure for Stabilizing the Optically Active Perovskite Phase

Multilevel conductance state in chemical vapor deposited WS2 based resistive memory device