1,720,966 research outputs found
Sodium-based nano-ionic synaptic transistor with improved retention characteristics
No full textWe propose an all-solid-state Na ion-based synaptic transistor (NST) to overcome the low retention problem of the Li ion-based synaptic transistor (LST). Through our analysis, it was found that the retention instability in an ionic synaptic transistor originated from its high ionic diffusivity. As confirmed by cyclic voltammetry analysis, Na ions have a lower ionic diffusivity than Li ions in the WO(x)layer. The state retention of NST was found to be improved to 20 times that of LST. Furthermore, near-ideal synaptic behaviors, such as linear weight update and linearI-Vcharacteristics, were also obtained by material engineering.11Nsciescopu
Improved Synaptic Characteristics of Oxide-Based Electrochemical Random Access Memory at Elevated Temperatures Using Integrated Micro-Heater
No full textIn this brief, we propose an oxygen-based electrochemical RAM (O-ECRAM) with a micro-heater to enhance the synaptic characteristics. Our findings demonstrate that by accelerating the drift/diffusion of oxygen ions at elevated temperatures, the conductance ON/OFF ratio and weight-update linearity of the O-ECRAM can be improved. To elucidate temperature-dependent synaptic behavior, we fitted weight-update curves using numerical modeling of ion injection from the electrolyte and diffusion within the channel. As a result, the micro-heater-integrated O-ECRAM (WO2.7/HfO1.7) device exhibits an increased training speed and near-ideal synaptic properties. © 1963-2012 IEEE.11Nsciescopu
Highly Scalable (30 nm) and Ultra-low-energy (~5fJ/pulse) Vertical Sensing ECRAM with Ideal Synaptic Characteristics Using Ion-permeable Graphene Electrodes
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Single‐Atom Quantum‐Point Contact Switch Using Atomically Thin Hexagonal Boron Nitride
No full textThe first report of a quantized conductance atomic threshold switch (QCATS) using an atomically-thin hexagonal boron nitride (hBN) layer is provided. This QCATS has applications in memory and logic devices. The QCATS device shows a stable and reproducible conductance quantization state at 1 center dot G(0) by forming single-atom point contact through a monoatomic boron defect in an hBN layer. An atomistic switching mechanism in hBN-QCATS is confirmed by in situ visualization of mono-atomic conductive filaments. Atomic defects in hBN are the key factor that affects the switching characteristic. The hBN-QCATS has excellent switching characteristics such as low operation voltage of 0.3 V, low "off" current of 1 pA, fast switching of 50 ns, and high endurance > 10(7) cycles. The variability of switching characteristics, which are the major problems of switching device, can be solved by reducing the area and thickness of the switching region to form single-atom point contact. The switching layer thickness is scaled down to the single-atom (approximate to 0.33 nm) h-BN layer, and the switching area is limited to single-atom defects. By implementing excellent switching characteristics using single-layer hBN, the possibility of implementing stable and uniform atomic-switching devices for future memory and logic applications is confirmed.11Nsciescopu
Multidimensional Transition Metal Dichalcogenides for Hydrogen Evolution and White Light Emitting Devices Applications
No full textThe aim of this Ph.D. thesis is to synthesize multidimensional TMDs and their heterostructures by chemical vapor deposition (CVD) for light emitting diode (LED) and electrocatalytic hydrogen evolution (HER) applications. In the first part of this thesis, we briefly introduce TMDs. The formation of artificial lateral or vertical heterostructure between two types of TMDs is an effective strategy to tune the electronic and optical property of individual TMDs. The vertical heterostructures formed in TMDs have tremendous future applications in the fields of energy and optoelectronics such as in HER and LED applications. In this connection, we briefly review the underlying mechanism for the formation of vertical heterostructures using TMDs by CVD. In the second part of this thesis, we demonstrate that molybdenum sulfide (MoSx) tetracyanoquinodimethane (TCNQ) hybrid material shows excellent catalytic effects in HER applications. We have found a significant enhancement in the electrocatalytic activity of MoSx when it is grown on carbon cloth treated with TCNQ, where the MoSx is synthesized by thermolysis from the ammonium tetrathiomolybdate ((NH4)2MoS4) precursor at 170 °C. The pyridinic-N and graphitic N-like species on the surface of carbon cloth arising from the TCNQ treatment facilitate the formations of Mo5+ and S22– species in the MoSx, especially with S22– serving as an active site for HER. Also, the smaller particle size of the MoSx grown on the TCNQ-treated carbon cloth reveals a high ratio of the edge sites to the basal plane sites, indicating more adequate reaction sites are created with superior electrocatalytic characteristics. This study provides the fundamental concepts useful in the design and preparation of TMDs, beneficial in the development of clean energy. In the third part of this thesis, we synthesized MoS2 nanosheets on 3D conductive MoO2 via a two-step chemical vapor deposition (CVD) reaction. The 3D MoO2 structure can create structural disorders in MoS2 nanosheets, which lead to superior HER activity by exposing tremendous active sites in the form of terminal disulfur of and utilizing the backbone conductive oxide layer to facilitate the interfacial charge transport for proton reduction. Also, the MoS2 nanosheets could protect the inner MoO2 core from the acidic electrolyte in HER reaction. The high activity of the as-synthesized 3D MoS2/MoO2 hybrid material in HER is attributed to the small onset overpotential of 142 mV, a largest cathodic current density of 85 mA cm-2, a little Tafel slope of 35.6 mV dec-1, and the robust electrochemical durability. In the fourth part of this thesis, we demonstrate the novel vertically stacked heterostructures of p-GaN/p-n MoS2 by chemical vapor deposition (CVD). The as-grown novel hybrid heterostructures were applied to fabricate white light emitting diode (WLED) based on a three-emitter system. We report the electroluminescence (EL) from vertically stacked p-GaN/p-n MoS2 heterojunction LEDs under forward bias. The EL spectra were composed of three emissions centered at 480 nm (from p-GaN), 530 nm (p-MoS2) and 650 nm (n-MoS2) under forward biases, and were dominated by the broad emission at 650 nm from n-MoS2. Our WLED device with the p-GaN/p-n MoS2 structure showed the luminance of 100 cd m−2 at a current density of 2.5 mA cm−2
High polarization and wake-up free ferroelectric characteristics in ultrathin Hf0.5Zr0.5O2 devices by control of oxygen-deficient layer
No full textThe formation of an interfacial layer is believed to affect the ferroelectric properties in HfO2 based ferroelectric devices. The atomic layer deposited devices continue suffering from a poor bottom interfacial condition, since the formation of bottom interface is severely affected by atomic layer deposition and annealing process. Herein, the formation of bottom interfacial layer was controlled through deposition of different bottom electrodes (BE) in device structure W/HZO/BE. The transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy analyses done on devices W/HZO/W and W/HZO/IrO (x) suggest the strong effect of IrO (x) in controlling bottom interfacial layer formation while W/HZO/W badly suffers from interfacial layer formation. W/HZO/IrO (x) devices show high remnant polarization (2P (r)) similar to 53 mu C cm(-2), wake-up free endurance cycling characteristics, low leakage current with demonstration of low annealing temperature requirement as low as 350 degrees C, valuable for back-end-of-line integration. Further, sub-5 nm HZO thicknesses-based W/HZO/IrO (x) devices demonstrate high 2P (r) and wake-up free ferroelectric characteristics, which can be promising for low power and high-density memory applications. 2.2 nm, 3 nm, and 4 nm HZO based W/HZO/IrO (x) devices show 2P (r) values 13.54, 22.4, 38.23 mu C cm(-2) at 4 MV cm(-1) and 19.96, 30.17, 48.34 mu C cm(-2) at 5 MV cm(-1), respectively, with demonstration of wake-up free ferroelectric characteristics.11Nsciescopu
Excellent synaptic behavior of lithium-based nano-ionic transistor based on optimal WO2.7 stoichiometry with high ion diffusivity
No full textIn this study, we introduce a lithium (Li) ion-based three-terminal (3-T) synapse device using WOx as a channel. Our study reveals a key stoichiometry of WO2.7 for excellent synaptic characteristics that is related to Li-ion diffusivity. The open-lattice structure formed by oxygen deficiency promoted Li-ion injection and diffusion. The optimized stoichiometry and improved Li-ion diffusivity were confirmed by x-ray photoelectron spectroscopy analysis and cyclic voltammetry, respectively. Furthermore, the transient conductance change that inevitably occurs in ion-based synaptic transistors was resolved by applying a two-step voltage pulse scheme. As a result, we achieved a symmetric and linear weight-update characteristic with reduced program/erase operation time.11Nsciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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