Ghayas Uddin Siddiqui

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.

Direct synthesis of graphene quantum dots from multilayer graphene flakes through grinding assisted co-solvent ultrasonication for all-printed resistive switching arrays

Graphene quantum dots (GQD) with diameters as small as ∼2 nm were synthesized by an efficient chemo-mechanical technique. This involved mortar grinding and ultra-sonication as a means of mechanical energy transfer, while N-methyl-pyrrolidone and 1,2-dichlorobenzene were used for exfoliation and breakdown of graphene nanoplatelets. High resolution transmission electron microscopy images showed that the solution-based GQDs were about 2–4 nm in size, and had a crystalline lattice parameter of 0.24 nm. The technique proved useful for extracting GQDs of the desired size. XRD, Raman and FTIR spectroscopy were used to analyze the quality of the graphene structure within the GQDs. The UV responsive GQDs had a band-gap of 2.6 eV and stronger photoluminescence at 350 nm compared to lower wavelengths of laser excitation. An all-printed 2 × 2 array of memristors based on a GQD embedded polymer matrix fabricated on a flexible PET substrate showed an OFF/ON ratio of just over 7 when read at 100 mV, stable retention despite a high compliance current for ∼100 switching cycles, and a robustness of 200 bending cycles up to 1.5 cm bending diameter without compromise on resistive switching states.

A two-dimensional hexagonal boron nitride/polymer nanocomposite for flexible resistive switching devices

Organic–inorganic hybrid nanocomposites are an attractive choice for various electronic device applications. Owing to the unique characteristics of hybrid nanocomposites, we have explored the memory effect in a device, based on a 2D material: boron nitride (BN) and a polymer, polyvinyl alcohol (PVOH). This memory device has been fabricated on a flexible ITO coated PET substrate by using an all printed approach including electrohydrodynamic atomization (EHDA) and reciprocating head (RPC). The fabricated device displayed nonvolatile, rewritable and characteristic bipolar resistive switching at a low current compliance and small operating voltage. The conduction mechanism was deduced to be conductive filamentary and verified by the effect of temperature and device size on switching characteristics. Raman, FTIR and UV/Vis spectroscopies were employed in studying the optical properties of as-deposited hBN/PVOH thin films. The morphological characteristics were analyzed by FESEM and AFM techniques. A bendability test at various bending diameters (50–4 mm) for 1500 cycles was carried out to show the mechanical robustness of the fabricated device. The remarkably stable and repeatable results of electrical and mechanical characterization make this hybrid nanocomposite a potential candidate for future flexible, robust and low power nonvolatile memory devices.

Hybrid Surface Acoustic Wave- Electrohydrodynamic Atomization (SAW-EHDA) For the Development of Functional Thin Films

Conventional surface acoustic wave - electrostatic deposition (SAW-ED) technology is struggling to compete with other thin film fabrication technologies because of its limitation in atomizing high density solutions or solutions with strong inter-particle bonding that requires very high frequency (100 MHz) and power. In this study, a hybrid surface acoustic wave - electrohydrodynamic atomization (SAW-EHDA) system has been introduced to overcome this problem by integrating EHDA with SAW to achieve the deposition of different types of conductive inks at lower frequency (19.8 MHZ) and power. Three materials, Poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV), Zinc Oxide (ZnO), and Poly(3, 4-ethylenedioxythiophene):Polystyrene Sulfonate (PEDOT:PSS) have been successfully deposited as thin films through the hybrid SAW-EHDA. The films showed good morphological, chemical, electrical, and optical characteristics. To further evaluate the characteristics of deposited films, a humidity sensor was fabricated with active layer of PEDOT:PSS deposited using the SAW-EHDA system. The response of sensor was outstanding and much better when compared to similar sensors fabricated using other manufacturing techniques. The results of the device and the films’ characteristics suggest that the hybrid SAW-EHDA technology has high potential to efficiently produce wide variety of thin films and thus predict its promising future in certain areas of printed electronics.

Resistive switching phenomena induced by the heterostructure composite of ZnSnO3 nanocubes interspersed ZnO nanowires

The resistive switching effect of various materials has been investigated because of their promising advantages such as high scalability, low cost, simple structure and less power consumption of such memory devices. In this study, the resistive switching effect in nanocomposites of zinc oxide nanowires (ZnO NWs) and zinc stannate nanocubes (ZnSnO3 NCs) has been explored. The device was fabricated on a flexible poly(ethylene terephthalate) substrate on which highly conductive (0.3 Ω cm) patterns of silver (Ag) were deposited as bottom electrodes using a reverse offset printing technique. Vertically aligned and highly dense ZnO NWs were grown on the Ag patterns using hydrothermal synthesis followed by spraying of ZnSnO3 NCs using an electrohydrodynamic atomization (EHDA) technique. Finally, the top Ag electrode was patterned using an EHD patterning technique to complete the fabrication of the device. The fabricated device exhibited bipolar and rewritable characteristics, and had a nonvolatile resistive switching memory with an off/on ratio of 5.8 × 102 and a retention time of 104 s at a small operating voltage (1.2 V). The electrical results obtained with the Ag–ZnO/ZnSnO3–Ag memory device were remarkable and they showed significant repeatability. The significantly stable, highly durable and promising results obtained with the ZnO NWs–ZnSnO3 NCs heterostructure make this semiconductive nanocomposite a potential candidate for use in future flexible memory devices.

All-printed highly sensitive 2D MoS 2 based multi-reagent immunosensor for smartphone based point-of-care diagnosis

Immunosensors are used to detect the presence of certain bio-reagents mostly targeted at the diagnosis of a condition or a disease. Here, a general purpose electrical immunosensor has been fabricated for the quantitative detection of multiple bio-reagents through the formation of an antibody-antigen pair. The sensors were fabricated using all printing approaches. 2D transition metal dichalcogenide (TMDC) MoS2 thin film was deposited using Electrohydrodynamic atomization (EHDA) on top of an interdigitated transducer (IDT) electrode fabricated by reverse offset printing. The sensors were then treated with three different types of antibodies that were immobilized by physisorption into the highly porous multi-layered structure of MoS2 active layer. BSA was used as blocking agent to prevent non-specific absorption (NSA). The sensors were then employed for the targeted detection of the specific antigens including prostate specific antigen (PSA), mouse immunoglobulin-G (IgG), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). IgG was then selected to test the sensors for point of care (POC) diagnosis through a specially designed electronic readout system for sensors and interfacing it with a smartphone using Bluetooth connection. The sensors showed promising performance in terms of stability, specificity, repeatability, sensitivity, limit of detection (LoD), and range of detection (RoD).

3D printing for soft robotics – a review

Abstract Soft robots have received an increasing attention due to their advantages of high flexibility and safety for human operators but the fabrication is a challenge. Recently, 3D printing has been used as a key technology to fabricate soft robots because of high quality and printing multiple materials at the same time. Functional soft materials are particularly well suited for soft robotics due to a wide range of stimulants and sensitive demonstration of large deformations, high motion complexities and varied multi-functionalities. This review comprises a detailed survey of 3D printing in soft robotics. The development of key 3D printing technologies and new materials along with composites for soft robotic applications is investigated. A brief summary of 3D-printed soft devices suitable for medical to industrial applications is also included. The growing research on both 3D printing and soft robotics needs a summary of the major reported studies and the authors believe that this review article serves the purpose.