227 research outputs found

    Metal-Ion Intercalation Mechanisms in Vanadium Pentoxide and Its New Perspectives

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    The investigation into intercalation mechanisms in vanadium pentoxide has garnered significant attention within the realm of research, primarily propelled by its remarkable theoretical capacity for energy storage. This comprehensive review delves into the latest advancements that have enriched our understanding of these intricate mechanisms. Notwithstanding its exceptional storage capacity, the compound grapples with challenges arising from inherent structural instability. Researchers are actively exploring avenues for improving electrodes, with a focus on innovative structures and the meticulous fine-tuning of particle properties. Within the scope of this review, we engage in a detailed discussion on the mechanistic intricacies involved in ion intercalation within the framework of vanadium pentoxide. Additionally, we explore recent breakthroughs in understanding its intercalation properties, aiming to refine the material’s structure and morphology. These refinements are anticipated to pave the way for significantly enhanced performance in various energy storage applications

    A Contribution Towards Intelligent Autonomous Sensors Based on Perovskite Solar Cells and Ta2O5/ZnO Thin Film Transistors

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    Many broad applications in the field of robotics, brain-machine interfaces, cognitive computing, image and speech processing and wearables require edge devices with very constrained power and hardware requirements that are challenging to realize. This is because these applications require sub-conscious awareness and require to be always “on”, especially when integrated with a sensor node that detects an event in the environment. Present day edge intelligent devices are typically based on hybrid CMOS-memristor arrays that have been so far designed for fast switching, typically in the range of nanoseconds, low energy consumption (typically in nano-Joules), high density and endurance (exceeding 1015 cycles). On the other hand, sensory-processing systems that have the same time constants and dynamics as their input signals, are best placed to learn or extract information from them. To meet this requirement, many applications are implemented using external “delay” in the memristor, in a process which enables each synapse to be modeled as a combination of a temporal delay and a spatial weight parameter. This thesis demonstrates a synaptic thin film transistor capable of inherent logic functions as well as compute-in-memory on similar time scales as biological events. Even beyond a conventional crossbar array architecture, we have relied on new concepts in reservoir computing to demonstrate a delay system reservoir with the highest learning efficiency of 95% reported to date, in comparison to equivalent two terminal memristors, using a single device for the task of image processing. The crux of our findings relied on enhancing our capability to model the unique physics of the device, in the scope of the current thesis, that is not amenable to conventional TCAD simulations. The model provides new insight into the redox characteristics of the gate current and paves way for assessment of device performance in compute-in-memory applications. The diffusion-based mechanism of the device, effectively enables time constants that have potential in applications such as gesture recognition and detection of cardiac arrythmia. The thesis also reports a new orientation of a solution processed perovskite solar cell with an efficiency of 14.9% that is easily integrable into an intelligent sensor node. We examine the influence of the growth orientation on film morphology and solar cell efficiency. Collectively, our work aids the development of more energy-efficient, powerful edge-computing sensor systems for upcoming applications of the IOT

    Atomistic simulations of nanoscale molecular and metal oxide junctions

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    The push to continually improve computing power through the further miniaturisation of electronic devices has led to an explosion of "post-Moore" technologies such as molecular electronics and quantum computing. The downscaling of electronic devices has enhanced the importance of quantum effects. As a result to aid in the understanding and development of new devices, accurate and efficient atomistic material modelling methods are crucial for guiding experiments. In this thesis first principle material modelling (e.g Density Functional Theory) is combined with the atomistic Non Equilibrium Green’s Function quantum transport method to study how the electronic structure of two interesting junction systems relate to the electron transport through the junction. These two types of junctions, molecular and metal oxide, have crucial roles to play in the development of molecular based memories and superconducting quantum computing respectively. The first half of this thesis shows how the electronic structure of Polyoxometalate molecules dominate their electron transport properties whilst their redox ability makes them promising for memory applications. The results of the simulations reveal how the charge-balancing counterions of Polyoxometalates increase the conductance of the molecular junctions by stabilisation of unoccupied states, this is a key discovery as the effect of counterions are typically ignored. Polyoxometalates can be altered easily by changing the identity of the central caged atom, enhancing device engineering possibilities. The IV characteristics and capacitance are computed for Polyoxometalates with different caged atoms, the results show how the charge transport and storage can be engineered by choice of caged species and redox state. In the second half of this work, the archetypal Josephson junction, Al/AlOx/Al is explored. The goal was to understand from an atomistic point of view how the nature of the amorphous barrier influences the electron transport. The calculations provide evidence that the oxide concentration of the amorphous barrier significantly influences the resistance of the junction, it is found that oxygen deficient barriers lead to higher than expected critical currents. Unexpectedly the simulations here fail to show an exponential relationship between barrier length and resistance of the device. It is argued that there is an effective barrier length smaller than the physical barrier length due to thinner regions of the barrier. This highlights how important an understanding of the atomic structure of these junctions are for designing high quality junctions for superconducting qubits

    Chalcogenide and metal-oxide memristive devices for advanced neuromorphic computing

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    Energy-intensive artificial intelligence (AI) is prevailing and changing the world, which requires energy-efficient computing technology. However, traditional AI driven by von Neumann computing systems suffers from the penalties of high-energy consumption and time delay due to frequent data shuttling. To tackle the issue, brain-inspired neuromorphic computing that performs data processing in memory is developed, reducing energy consumption and processing time. Particularly, some advanced neuromorphic systems perceive environmental variations and internalize sensory signals for localized in-senor computing. This methodology can further improve data processing efficiency and develop multifunctional AI products. Memristive devices are one of the promising candidates for neuromorphic systems due to their non-volatility, small size, fast speed, low-energy consumption, etc. In this thesis, memristive devices based on chalcogenide and metal-oxide materials are fabricated for neuromorphic computing systems. Firstly, a versatile memristive device (Ag/CuInSe2/Mo) is demonstrated based on filamentary switching. Non-volatile and volatile features are coexistent, which play multiple roles of non-volatile memory, selectors, artificial neurons, and artificial synapses. The conductive filaments’ lifetime was controlled to present both volatile and non-volatile behaviours. Secondly, the sensing functions (temperature and humidity) are explored based on Ag conductive filaments. An intelligent matter (Ag/Cu(In, Ga)Se2/Mo) endowing reconfigurable temperature and humidity sensations is developed for sensory neuromorphic systems. The device reversibly switches between two states with differentiable semiconductive and metallic features, demonstrating different responses to temperature and humidity variations. Integrated devices can be employed for intelligent electronic skin and in-sensor computing. Thirdly, the memristive-based sensing function of light was investigated. An optoelectronic synapse (ITO/ZnO/MoO3/Mo) enabling multi-spectrum sensitivity for machine vision systems is developed. For the first time, this optoelectronic synapse is practical for front-end retinomorphic image sensing, convolution processing, and back-end neuromorphic computing. This thesis will benefit the development of advanced neuromorphic systems pushing forward AI technology

    Nanoscale Ferroic Materials—Ferroelectric, Piezoelectric, Magnetic, and Multiferroic Materials

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    Ferroic materials, including ferroelectric, piezoelectric, magnetic, and multiferroic materials, are receiving great scientific attention due to their rich physical properties. They have shown their great advantages in diverse fields of application, such as information storage, sensor/actuator/transducers, energy harvesters/storage, and even environmental pollution control. At present, ferroic nanostructures have been widely acknowledged to advance and improve currently existing electronic devices as well as to develop future ones. This Special Issue covers the characterization of crystal and microstructure, the design and tailoring of ferro/piezo/dielectric, magnetic, and multiferroic properties, and the presentation of related applications. These papers present various kinds of nanomaterials, such as ferroelectric/piezoelectric thin films, dielectric storage thin film, dielectric gate layer, and magnonic metamaterials. These nanomaterials are expected to have applications in ferroelectric non-volatile memory, ferroelectric tunneling junction memory, energy-storage pulsed-power capacitors, metal oxide semiconductor field-effect-transistor devices, humidity sensors, environmental pollutant remediation, and spin-wave devices. The purpose of this Special Issue is to communicate the recent developments in research on nanoscale ferroic materials

    CsPbX3 Nanoparticle Synthesis Via Nonpolar Solvent Choice and Microwave Heating, Growth Mechanism and CsPb(Br/I)3 Stabilization by Halide Exchange

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    Perovskites are a group of crystalline chemicals with ABX3 formula where cations are surrounded by corner-sharing octahedra. Their crystal structure was described by Victor Goldschmidt in 1926, almost a century after the first discovery of the mineral perovskite, CaTiO3, by Gustav Rose in 1839. Organic-inorganic (hybrid) lead halide perovskites became a point of interest when their potential as a visible-light adsorber in solar cells was demonstrated by Kojima et. al. in 2009. All-inorganic perovskites gain traction after their synthesis as colloidal quantum dots in 2014. While there have been numerous studies on the application of perovskite nanoparticles (NP) in optoelectronic devices, lasers and sensors, there is a lot of chemistry to explore to reach their full potential. The focus of this dissertation is on all-inorganic CsPbX3 nanoparticles. In chapter two, a novel microwave assisted method is described to synthesize 2-dimentional (2D) CsPbX3 NPs in benzyl ether. We demonstrated that microwave irradiation provides a feasible and reproducible path to tailor the morphology of these NPs. Then, the NP’s structural features and subsequent optoelectronic properties are explained. To fully understand the effect of the structure and composition on the band gap of these NPs, a comprehensive description of the intrinsic optoelectronic properties of CsPbX3 NPs is reported in chapter one. To elucidate their synthesis path further, we compared them with NPs prepared with a stablished synthesis technique, hot-injection method in 1-octadecene, in chapter three. This comparison shed light on the preference of the NPs to grow in 2D directions in benzyl ether under microwave irradiation. This study was expanded, by monitoring the growth of CsPbBr3 NPs over time at ambient condition as well, which confirmed the role of benzyl ether in the morphology. Other perovskite synthetic methods are also reviewed in chapter one, along with the various mechanisms of orientational growth in CsPbX3 NPs. In addition, we explored the effect of benzyl ether on ionic interactions in the lead halide precursor, in particular, the formation of halo plumbate complexes and their contribution in the 2D growth of the perovskite colloidal seeds were evaluated. In chapter four, the goal was to use a halide exchange technique to stabilize CsPbI3 NPs in colloidal form and in thin film format. In this chapter, the electronic band gap of the CsPbBr3 and I-rich CsPbX3 NPs was measured using cyclic voltammetry. We calculated the energy gap between HOMO and LUMO of the NPs and explain the contribution of atomic orbitals, as well.During this dissertation research, we sought to learn the chemistry of all-inorganic perovskites and became fascinated with their adaptability to the synthesis environment and their dynamic response to the post-synthesis challenges. This ability provides tremendous opportunity for researchers to tailor perovskite NPs for applications that require a semiconductor with any desired band gap that can be formed into nano-, micro- or macro-scale with flexibility

    Reconfigurable Multifunctional van der Waals Ferroelectric Devices and Logic Circuits

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    In this work, we demonstrate the suitability of Reconfigurable Ferroelectric Field-Effect- Transistors (Re-FeFET) for designing non-volatile reconfigurable logic-in-memory circuits with multifunctional capabilities. Modulation of the energy landscape within a homojunction of a 2D tungsten diselenide (WSe2_2) layer is achieved by independently controlling two split-gate electrodes made of a ferroelectric 2D copper indium thiophosphate (CuInP2_2S6_6) layer. Controlling the state encoded in the Program Gate enables switching between p, n and ambipolar FeFET operating modes. The transistors exhibit on-off ratios exceeding 106^6 and hysteresis windows of up to 10 V width. The homojunction can change from ohmic-like to diode behavior, with a large rectification ratio of 104^4. When programmed in the diode mode, the large built-in p-n junction electric field enables efficient separation of photogenerated carriers, making the device attractive for energy harvesting applications. The implementation of the Re-FeFET for reconfigurable logic functions shows how a circuit can be reconfigured to emulate either polymorphic ferroelectric NAND/AND logic-in-memory or electronic XNOR logic with long retention time exceeding 104^4 seconds. We also illustrate how a circuit design made of just two Re-FeFETs exhibits high logic expressivity with reconfigurability at runtime to implement several key non-volatile 2-input logic functions. Moreover, the Re-FeFET circuit demonstrates remarkable compactness, with an up to 80% reduction in transistor count compared to standard CMOS design. The 2D van de Waals Re-FeFET devices therefore exhibit groundbreaking potential for both More-than-Moore and beyond-Moore future of electronics, in particular for an energy-efficient implementation of in-memory computing and machine learning hardware, due to their multifunctionality and design compactness.Comment: 23 pages, 5 figures; Supporting Information: 12 pages, 6 figure

    Chapter 34 - Biocompatibility of nanocellulose: Emerging biomedical applications

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    Nanocellulose already proved to be a highly relevant material for biomedical applications, ensued by its outstanding mechanical properties and, more importantly, its biocompatibility. Nevertheless, despite their previous intensive research, a notable number of emerging applications are still being developed. Interestingly, this drive is not solely based on the nanocellulose features, but also heavily dependent on sustainability. The three core nanocelluloses encompass cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC). All these different types of nanocellulose display highly interesting biomedical properties per se, after modification and when used in composite formulations. Novel applications that use nanocellulose includewell-known areas, namely, wound dressings, implants, indwelling medical devices, scaffolds, and novel printed scaffolds. Their cytotoxicity and biocompatibility using recent methodologies are thoroughly analyzed to reinforce their near future applicability. By analyzing the pristine core nanocellulose, none display cytotoxicity. However, CNF has the highest potential to fail long-term biocompatibility since it tends to trigger inflammation. On the other hand, neverdried BNC displays a remarkable biocompatibility. Despite this, all nanocelluloses clearly represent a flag bearer of future superior biomaterials, being elite materials in the urgent replacement of our petrochemical dependence

    Advance in Composite Gels

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    In the last few decades, various composite gels have been developed. In recent years, further advances have been made in the development of novel composite gels with potential applications in various fields. This reprint offers the latest findings of composite gels by experts throughout the world

    Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors

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    This reprint is a collection of the Special Issue "Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors" published in Nanomaterials, which includes one editorial, six novel research articles and four review articles, showcasing the very recent advances in energy-harvesting and self-powered sensing technologies. With its broad coverage of innovations in transducing/sensing mechanisms, material and structural designs, system integration and applications, as well as the timely reviews of the progress in energy harvesting and self-powered sensing technologies, this reprint could give readers an excellent overview of the challenges, opportunities, advancements and development trends of this rapidly evolving field
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