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Reverse engineering (RE) is one of the major security threats to the semiconductor industry due to the involvement of untrustworthy parties in an increasingly globalized chip manufacturing supply chain. RE efforts have already been successful in extracting device level functionalities from an integrated circuit (IC) with very limited resources. Camouflaging is an obfuscation method that can thwart such RE. Existing work on IC camouflaging primarily involves transformable interconnects and/or covert gates where variation in doping and dummy contacts hide the circuit structure or build cells that look alike but have different functionalities. Emerging solutions, such as polymorphic gates based on a giant spin Hall effect and Si nanowire field effect transistors (FETs), are also promising but add significant area overhead and are successfully decamouflaged by the satisfiability solver (SAT)-based RE techniques. Here, we harness the properties of two-dimensional (2D) transition-metal dichalcogenides (TMDs) including MoS

Realization of wafer-scale single-crystal films of transition metal dichalcogenides (TMDs) such as WS2 requires epitaxial growth and coalescence of oriented domains to form a continuous monolayer. The domains must be oriented in the same crystallographic direction on the substrate to inhibit the formation of inversion domain boundaries (IDBs), which are a common feature of layered chalcogenides. Here we demonstrate fully coalesced unidirectional WS2 monolayers on 2 in. diameter c-plane sapphire by metalorganic chemical vapor deposition using a multistep growth process to achieve epitaxial WS2 monolayers with low in-plane rotational twist (0.09°). Transmission electron microscopy analysis reveals that the WS2 monolayers are largely free of IDBs but instead have translational boundaries that arise when WS2 domains with slightly offset lattices merge together. By regulating the monolayer growth rate, the density of translational boundaries and bilayer coverage were significantly reduced. The unidirectional orientation of domains is attributed to the presence of steps on the sapphire surface coupled with growth conditions that promote surface diffusion, lateral domain growth, and coalescence while preserving the aligned domain structure. The transferred WS2 monolayers show neutral and charged exciton emission at 80 K with negligible defect-related luminescence. Back-gated WS2 field effect transistors exhibited an ION/OFF of ∼107 and mobility of 16 cm2/(V s). The results demonstrate the potential of achieving wafer-scale TMD monolayers free of inversion domains with properties approaching those of exfoliated flakes.

Here we benchmark device-to-device variation in field-effect transistors (FETs) based on monolayer MoS2 and WS2 films grown using metal-organic chemical vapor deposition process. Our study involves 230 MoS2 FETs and 160 WS2 FETs with channel lengths ranging from 5 μm down to 100 nm. We use statistical measures to evaluate key FET performance indicators for benchmarking these two-dimensional (2D) transition metal dichalcogenide (TMD) monolayers against existing literature as well as ultra-thin body Si FETs. Our results show consistent performance of 2D FETs across 1 × 1 cm2 chips owing to high quality and uniform growth of these TMDs followed by clean transfer onto device substrates. We are able to demonstrate record high carrier mobility of 33 cm2 V−1 s−1 in WS2 FETs, which is a 1.5X improvement compared to the best reported in the literature. Our experimental demonstrations confirm the technological viability of 2D FETs in future integrated circuits. Here, the authors perform a benchmark study of field-effect transistors (FETs) based on 2D transition metal dichalcogenides, i.e., 230 MoS2 and 160 WS2 FETs, and track device-to-device variations to gauge the technological viability in future integrated circuits.

In this article, we analyze the characteristics of a recently conceived steep switching device 2-D Strain FET (2D-SFET) and present its circuit implications in the context of 6T-SRAM. We discuss the dependence of 2D-SFET characteristics on key design parameters, showing up to $2.7\times $ larger ON-current and 35% decrease in subthreshold swing when compared to 2D-FET. We analyze the performance of 2D-SFET (as drop-in replacement for standard 2D-FET) in 6T-SRAM for a range of design parameters and compare those to 2D-FET 6T-SRAM. 2D-SFET 6T-SRAM achieves up to 5.7% lower access time, 63% higher write margin, and comparable hold margin, but at the cost of comparable to 11% lower read stability and 16% increase in write time. In Part II of this article, we mitigate the read stability issues of 2D-SFET SRAMs by proposing ${V}_{{\mathrm {B}}}$ -enabled SRAM designs.

Integration of low-power consumer electronics on glass can revolutionize the automotive and transport sectors, packaging industry, smart building and interior design, healthcare, life science engineering, display technologies, and many other applications. However, direct growth of high-performance, scalable, and reliable electronic materials on glass is difficult owing to low thermal budget. Similarly, development of energy-efficient electronic and optoelectronic devices on glass requires manufacturing innovations. Here, we accomplish both by relatively low-temperature (

Memristive crossbar architectures are evolving as powerful in-memory computing engines for artificial neural networks. However, the limited number of non-volatile conductance states offered by state-of-the-art memristors is a concern for their hardware implementation since trained weights must be rounded to the nearest conductance states, introducing error which can significantly limit inference accuracy. Moreover, the incapability of precise weight updates can lead to convergence problems and slowdown of on-chip training. In this article, we circumvent these challenges by introducing graphene-based multi-level (>16) and non-volatile memristive synapses with arbitrarily programmable conductance states. We also show desirable retention and programming endurance. Finally, we demonstrate that graphene memristors enable weight assignment based on k-means clustering, which offers greater computing accuracy when compared with uniform weight quantization for vector matrix multiplication, an essential component for any artificial neural network., Designing efficient and low power memristors-based neuromorphic systems remains a challenge. Here, the authors present graphene-based multi-level (>16) and non-volatile memristive synapses with arbitrarily programmable conductance states capable of weight assignment based on k-means clustering.

Transition-metal dichalcogenides (TMDCs) with atomic thickness are promising materials for next-generation electronic and optoelectronic devices. Herein, we report uniform growth of triangular-shaped (∼40 μm) monolayer WS2 using the atmospheric-pressure chemical vapor deposition (APCVD) technique in a hydrogen-free environment. We have studied the optical and electrical behaviors of as-grown WS2 samples. The absorption spectrum of monolayer WS2 shows two intense excitonic absorption peaks, namely, A (∼630 nm) and B (∼530 nm), due to the direct gap transitions at the K point. Photoluminescence (PL) and fluorescence studies reveal that under the exposure of green light, monolayer WS2 gives very strong red emission at ∼663 nm. This corresponds to the direct band gap and strong excitonic effect in monolayer WS2. Furthermore, the efficacy of the synthesized WS2 crystals for electronic devices is also checked by fabricating field-effect transistors (FETs). FET devices exhibit an electron mobility of μ ∼ 6 cm2 V-1 s-1, current ON/OFF ratio of ∼106, and subthreshold swing (SS) of ∼641 mV decade-1, which are comparable to those of the exfoliated monolayer WS2 FETs. These findings suggest that our APCVD-grown WS2 has the potential to be used for next-generation nanoelectronic and optoelectronic applications.

A defect-controlled approach for the nucleation and epitaxial growth of WSe2 on hBN is demonstrated. The WSe2 domains exhibit a preferred orientation of over 95%, leading to a reduced density of inversion domain boundaries (IDBs) upon coalescence. First-principles calculations and experimental studies as a function of growth conditions and substrate pretreatment confirm that WSe2 nucleation density and orientation are controlled by the hBN surface defect density rather than thermodynamic factors. Detailed transmission electron microscopy analysis provides support for the role of single-atom vacancies on the hBN surface that trap W atoms and break surface symmetry leading to a reduced formation energy for one orientation of WSe2 domains. Through careful control of nucleation and extended lateral growth time, fully coalesced WSe2 monolayer films on hBN were achieved. Low-temperature photoluminescence (PL) measurements and transport measurements of back-gated field-effect transistor devices fabricated on WSe...

We demonstrate that atomically thin layered two-dimensional (2D) semiconductors are promising candidates for space electronics owing to their inherent and extraordinary resilience to radiation damage from energetic heavy charged particles. In particular, we found that ultrathin MoS2 nanosheets can easily withstand proton and helium irradiation with fluences as high as ∼1016 and ∼1015 ions/cm2, respectively, corresponding to hundreds or thousands of years of unshielded exposure to radiation in space. While radiation effects on 2D material-based field effect transistors have been reported in the recent past, none of these studies could isolate the impact of irradiation on standalone ultrathin 2D layers. By adopting a unique experimental approach that exploits the van der Waals epitaxy of 2D materials, we were able to differentiate the effects of radiation on the 2D semiconducting channel from that of the underlying dielectric substrate, semiconductor/substrate interface, and metal/semiconductor contact interface, revealing the ultimate potential of these 2D materials. Furthermore, we used a statistical approach to evaluate the effect of radiation damage on critical device and material parameters, including threshold voltage, subthreshold slope, and carrier mobility. The statistical approach lends additional credence to the general conclusions drawn from this study, overcoming a common drawback of methods applied in this area of research. Our findings do not only offer exciting prospects for the operation of modern electronics in space, but may also benefit electronics applications in high-altitude flights, military aircraft, satellites, nuclear reactors, particle accelerators, and other high-radiation environments. Additionally, they highlight the importance of evaluating the impact of damage to the substrate and surrounding materials on electrical characteristics during future radiation studies of 2D materials.

Scalable substitutional doping of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is a prerequisite to developing next-generation logic and memory devices based on 2D materials. To date, doping efforts are still nascent. Here, we report scalable growth and vanadium (V) doping of 2D WSe2 at front-end-of-line (FEOL) and back-end-of-line (BEOL) compatible temperatures of 800 {\deg}C and 400 {\deg}C, respectively. A combination of experimental and theoretical studies confirm that vanadium atoms substitutionally replace tungsten in WSe2, which results in p-type doping via the introduction of discrete defect levels that lie close to the valence band maxima. The p-type nature of the V dopants is further verified by constructed field-effect transistors, where hole conduction becomes dominant with increasing vanadium concentration. Hence, our study presents a method to precisely control the density of intentionally introduced impurities, which is indispensable in the production of electronic-grade wafer-scale extrinsic 2D semiconductors.

In passive seismic and microseismic monitoring, identifying and characterizing events in a strong noisy background is a challenging task. Most of the established methods for geophysical inversion are likely to yield many false event detections. The most advanced of these schemes require thousands of computationally demanding forward elastic-wave propagation simulations. Here we train and use an ensemble of Gaussian process surrogate meta-models, or proxy emulators, to accelerate the generation of accurate template seismograms from random microseismic event locations. In the presence of multiple microseismic events occurring at different spatial locations with arbitrary amplitude and origin time, and in the presence of noise, an inference algorithm needs to navigate an objective function or likelihood landscape of highly complex shape, perhaps with multiple modes and narrow curving degeneracies. This is a challenging computational task even for state-of-the-art Bayesian sampling algorithms. In this paper, we propose a novel method for detecting multiple microseismic events in a strong noise background using Bayesian inference, in particular, the Multimodal Nested Sampling (MultiNest) algorithm. The method not only provides the posterior samples for the 5D spatio-temporal-amplitude inference for the real microseismic events, by inverting the seismic traces in multiple surface receivers, but also computes the Bayesian evidence or the marginal likelihood that permits hypothesis testing for discriminating true vs. false event detection.

Surface functionalization of metallic and semiconducting 2D transition metal dichalcogenides (TMDs) have mostly relied on physi- and chemi-sorption at defect sites, which can diminish the potential applications of the decorated 2D materials, as structural defects can have substantial drawbacks on the electronic and optoelectronic characteristics. Here, we demonstrate a spontaneous defect-free functionalization method consisting of attaching Au single atoms to monolayers of semiconducting MoS2(1H) via S-Au-Cl coordination complexes. This strategy offers an effective and controllable approach for tuning the Fermi level and excitation spectra of MoS2 via p-type doping and enhancing the thermal boundary conductance of monolayer MoS2, thus promoting heat dissipation. The coordination-based method offers an effective and damage-free route of functionalizing TMDs and can be applied to other metals and used in single-atom catalysis, quantum information devices, optoelectronics, and enhanced sensing.

Among several non-volatile memories (NVMs), ferroelectric (FE) based memories show distinct advantages due to electric field ( E )-driven low-power write [1] - [2] . However, there are other concerns in FE based NVMs (such destructive read in FERAMs [3] , gate leakage in FEFETs with floating inter-layer metal (ILM) [5] and traps and depolarization fields in FEFETs without ILM [4] ). To overcome such issues while retaining the useful features of FE, we propose a Polarization-induced Strain coupled TMD FET (PS FET) [ Fig. 1(a) ] that features (a) polarization-based non-volatile bit-storage (b) E-driven write and (c) coupling of piezoelectricity with dynamic bandgap (EG) tuning of 2D Transition Metal Dichalcogenides (TMDs) for read [ Fig. 1(b) ].

Silicon CMOS technology has fueled the phenomenal growth in semiconductor electronics over the past several decades. The miniaturization of a transistor, the basic tenet of technology scaling, is at the core of this revolution. Despite several challenges, the innovations in materials, processes, and device architecture have ensured that Moore’s law is still alive and going strong, with 7-nm silicon FinFET technology in volume production. However, over the past couple of decades, there has been a realization that the silicon CMOS technology may reach the end of scaling unless it is augmented and complemented by other semiconductors. For instance, there has been a substantial effort in the research community to integrate other bulk semiconductors such as germanium and III-Vs, into silicon technology.

Industrially relevant substrates, such as amorphous oxides and metallic substrates, typically cannot withstand the elevated temperatures (>800 °C) required for metalorganic chemical vapor deposition (MOCVD), thus limiting the applicability of these substrates for the realization of electronic-grade 2D materials. This work demonstrates MOCVD of crystalline MoS2 on multicomponent glass at temperatures ranging from 400 to 600 °C. Incorporated to understand the effects of ions in the glass on 2D layer growth, nitrogen plasma treatment of the glass surface enables increased domain size and minimized the effects of low temperature on electronic characteristics. Trends of growth morphology, crystalline quality, and film stoichiometry are examined as a function of glass chemistry, growth temperature, and degree of surface treatment. It is found that glass surface chemistry and growth temperature are the dominant factors in controlling domain size, which is improved with increasing plasma treatment, introducing alkali-containing glass, and growth temperature. While crystalline quality is improved with higher temperature, the films no longer remain stoichiometric. Finally, we demonstrate that glass surface chemistry has important impacts on electronic transport properties.

Structural defects govern various physical, chemical, and optoelectronic properties of two-dimensional transition-metal dichalcogenides (TMDs). A fundamental understanding of the spatial distribution and dynamics of defects in these low-dimensional systems is critical for advances in nanotechnology. However, such understanding has remained elusive primarily due to the inaccessibility of (a) necessary time scales via standard atomistic simulations and (b) required spatiotemporal resolution in experiments. Here, we take advantage of supervised machine learning, in situ high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) simulations to overcome these limitations. We combine genetic algorithms (GA) with MD to investigate the extended structure of point defects, their dynamical evolution, and their role in inducing the phase transition between the semiconducting (2H) and metallic (1T) phase in monolayer MoS2. GA-based structural optimization is used to identify the long-range structure of randomly distributed point defects (sulfur vacancies) for various defect densities. Regardless of the density, we find that organization of sulfur vacancies into extended lines is the most energetically favorable. HRTEM validates these findings and suggests a phase transformation from the 2H-to-1T phase that is localized near these extended defects when exposed to high electron beam doses. MD simulations elucidate the molecular mechanism driving the onset of the 2H to 1T transformation and indicate that finite amounts of 1T phase can be retained by increasing the defect concentration and temperature. This work significantly advances the current understanding of defect structure/evolution and structural transitions in 2D TMDs, which is crucial for designing nanoscale devices with desired functionality.

This work has been supported by the Shell Projects and Technology. The Wilkes high performance GPU computing service at the University of Cambridge has been used in this work.

Given increasing demand and importance of rare earth elements (REE), exploration is underway to find alternatives to ore-extracted product. With REE concentrations varying between 270 and 1480 ppm, coal ash has been deemed as one such potential source. A number of research groups are exploring technologies to separate REEs from coal ash and supercritical extraction has emerged as a high yield contender. Estimating the economic viability of this lab-scale process at the industrial scale is both important and challenging. In this study we estimate industrial scale cost and revenues of production of REEs from coal ash by combining prior laboratory results, scaling models, combinatorial scenarios and sensitivity analysis. The processing cost of extracting REEs from one ton of coal ash using supercritical CO2 and tributylphosphate (TBP) is found to vary between $380 and $1200 for 550 g of REE. The value of REE oxides that may be obtained per ton of ash is estimated to vary between $6 and $557, with a median of $250. Scandium is the most expensive REE and can account for up to 90% of the value of the yield. The results suggest that factors critical to the economic viability of the process include scandium content & yield, reagent use, and processing time.

This work reports the development of a novel bilayered Zn Ni/Ni Co SiC nanocomposite coating on mild steel (MS) by electrodeposition. The top Ni-Co-SiC nanocomposite layer, when deposited directly on MS (monolayer) shows a hardness of 734 HV and a corrosion current density of ∼28μA/cm2 in 3.5 wt% NaCl. However, the lack of adherence of the coating with MS results in poor wear and scratch resistance. Mild steel is anodic to Ni Co SiC nanocomposite and any kind of discontinuity in the coating may lead to severe galvanic corrosion. This problem has been successfully overcome with the incorporation of an anodic (with respect to mild steel)Zn 12%Ni under-layerin between the electrodeposited Ni Co SiC nanocomposite coating and MS, which is adherent to both the materials. This bilayer coating has a hardness of 760 HV and corrosion current density of ∼19μA/cm2 in 3.5 wt% NaCl which are slightly better than that of the monolayer. Further, the bilayer coating assembly exhibits exceptionally low volume loss under wear (∼350 mm3) compared to bare mild steel (∼1700 mm3). This Zn Ni/Ni Co SiC nanocomposite bilayercoating has the potential to emerge as hard, wear resistant and anti-corrosive coating which is essential in the field of heavy duty machines.

Physics of monolayer and few-layer transition metal dichalcogenides (TMDs) and chemistry of few-layer TMDs have been well studied in recent years in the context of future electronic, optoelectronic, and energy harvesting applications. However, what has escaped the attention of the scientific community is the unique chemistry of monolayer TMDs. It has been demonstrated that the basal plane of multilayer TMDs is chemically inert, whereas edge sites are chemically active. In this article, we experimentally demonstrate that the edge reactivity of the TMDs can be significantly impeded at the monolayer limit through monolayer/substrate interaction, thus making the monolayers highly resistant to electrooxidation and corrosion. In particular, we found that few-layer flakes of MoS2 and WS2 exfoliated on conductive TiN substrates are readily corroded beyond a certain positive electrode potential, while monolayer remnants are left behind unscathed. The electrooxidation resistance of monolayers was confirmed using a ...

A facile electrophoretic deposition technique is developed to prepare composite films of ZnFe2O4 (ZFO) and different carbonaceous materials such as carbon nanotubes and reduced graphene oxide for stable lithium-ion battery anode. The as-deposited films exhibit superior cycling stability with no capacity fade and good rate capability. High reversible capacities of 840 and 870 mAhg−1 were obtained after 100 cycles at 0.5 Ag−1 for ZFO-CNT and ZFO-RGO electrodes, respectively. The contribution of capacitive charge storage in the electrochemical performance is analyzed.

This article demonstrates the applicability of electrophoretically fabricated CuO-carbon black (CB) film as negative electrodes for lithium and sodium-ion rechargeable cells. CuO powder is derived from a thermally decomposed copper metal-organic framework (MOF) template. Electrophoretic deposition (EPD) of CuO-CB electrode has been carried out from a stable CuO-CB suspension, which is prepared in isopropanol medium containing polyacrylic acid and nickel nitrate as dispersant and charging agent respectively. The obtained EPD films are found to be porous and strongly adherent to underlying current collector, with a uniform distribution of CB and CuO. These films are observed to retain a reversible specific capacity of 500 mA h g−1 at 0.5 A g−1 and 256 mA h g−1 at 0.1 A g−1 after 100 cycles as Li-ion battery and Na-ion battery anode respectively. The uniformly dispersed CuO within the conductive network of CB particles is found to sustain the high-rate battery operations efficiently and exhibit a specific capacity of 265 mA h g−1 at 5 A g−1 (LIB) and 140 mA h g−1 at 3 A g−1 (SIB). Owing to the simple and cost-effective route for fabricating these negative electrodes, electrophoretically deposited CuO-CB porous film proves to be a suitable candidate for high-rate Li-ion and Na-ion batteries.

We report the use of nickel ferrite (NFO) with different morphologies as a superior anode material for lithium-ion batteries. The NFO nanoparticles are synthesized using simple auto-combustion process (CNFO) and micron-sized faceted particles are synthesized through pyrolysis of a nickel and iron metal-organic framework (MOF-NFO). Facile electrophoretic deposition (EPD) technique is employed to fabricate electrodes from a stable suspension of the active material (NFO) and conducting carbon-black. The EPD grown electrodes are uniform, porous and well adhered to the copper current collector. The CNFO and MOF-NFO electrodes retain a reversible capacity of 560 and 650 mAhg−1, respectively, after 150 cycles at a specific current of 0.5 Ag−1. Such EPD grown electrodes exhibit excellent rate capability delivering a capacity of 150 and 275 mAhg−1 at a high specific current of 8 Ag−1 for CNFO and NFO-MOF electrodes, respectively. The role of pseudocapacitance in enhancing the rate performance has been explained with the help of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. It is observed that even with significantly different particle size and morphology, the method of electrode fabrication plays a key role in accommodating the large volumetric changes during cycling and thereby improves the electrochemical properties of the electrode.

In this paper, we report high-performance monolayer thin-film transistors (TFTs) based on a variety of two-dimensional layered semiconductors such as MoS2, WS2, and MoSe2 which were obtained from their corresponding bulk counterparts via an anomalous but high-yield and low-cost electrochemical corrosion process, also referred to as electro-ablation (EA), at room temperature. These monolayer TFTs demonstrated current ON–OFF ratios in excess of 107 along with ON currents of 120 μA/μm for MoS2, 40 μA/μm for WS2, and 40 μA/μm for MoSe2 which clearly outperform the existing TFT technologies. We found that these monolayers have larger Schottky barriers for electron injection compared to their multilayer counterparts, which is partially compensated by their superior electrostatics and ultra-thin tunnel barriers. We observed an Anderson type semiconductor-to-metal transition in these monolayers and also discussed possible scattering mechanisms that manifest in the temperature dependence of the electron mobility. ...

This article provides a comprehensive review of recent advances in heterostructures of two-dimensional (2-D) layered materials for future electronic and optoelectronic applications. We also discuss the progress in capping heterostructures, where an inert 2-D material serves as a passivation layer and provides environmental stability to the relatively unstable 2-D material. Such capping of heterostructures often enhances the electronic properties (e.g., the carrier mobility) of the active 2-D layer by orders of magnitude. Finally, we elucidate the progress in large-area growth of these heterostructures using various state-of-the-art techniques.

Neurotransmitter release in chemical synapses is fundamental to diverse brain functions such as motor action, learning, cognition, emotion, perception, and consciousness. Moreover, improper functioning or abnormal release of neurotransmitter is associated with numerous neurological disorders such as epilepsy, sclerosis, schizophrenia, Alzheimer’s disease, and Parkinson’s disease. We have utilized hysteresis engineering in a back-gated MoS2 field effect transistor (FET) in order to mimic such neurotransmitter release dynamics in chemical synapses. All three essential features, i.e., quantal, stochastic, and excitatory or inhibitory nature of neurotransmitter release, were accurately captured in our experimental demonstration. We also mimicked an important phenomenon called long-term potentiation (LTP), which forms the basis of human memory. Finally, we demonstrated how to engineer the LTP time by operating the MoS2 FET in different regimes. Our findings could provide a critical component toward the design ...

The recent decline in energy, size and complexity scaling of traditional von Neumann architecture has resurrected considerable interest in brain-inspired computing. Artificial neural networks (ANNs) based on emerging devices, such as memristors, achieve brain-like computing but lack energy-efficiency. Furthermore, slow learning, incremental adaptation, and false convergence are unresolved challenges for ANNs. In this article we, therefore, introduce Gaussian synapses based on heterostructures of atomically thin two-dimensional (2D) layered materials, namely molybdenum disulfide and black phosphorus field effect transistors (FETs), as a class of analog and probabilistic computational primitives for hardware implementation of statistical neural networks. We also demonstrate complete tunability of amplitude, mean and standard deviation of the Gaussian synapse via threshold engineering in dual gated molybdenum disulfide and black phosphorus FETs. Finally, we show simulation results for classification of brainwaves using Gaussian synapse based probabilistic neural networks., Designing large-scale hardware implementation of Probabilistic Neural Network for energy efficient neuromorphic computing systems remains a challenge. Here, the authors propose an hardware design based on MoS2/BP heterostructures as reconfigurable Gaussian synapses enabling EEG patterns recognition.

Incorporating CH-groups into WS2 can tailor its opto-electronic properties, inducing p-type conduction and reducing its bandgap., Chemical doping constitutes an effective route to alter the electronic, chemical, and optical properties of two-dimensional transition metal dichalcogenides (2D-TMDs). We used a plasma-assisted method to introduce carbon-hydrogen (CH) units into WS2 monolayers. We found CH-groups to be the most stable dopant to introduce carbon into WS2, which led to a reduction of the optical bandgap from 1.98 to 1.83 eV, as revealed by photoluminescence spectroscopy. Aberration corrected high-resolution scanning transmission electron microscopy (AC-HRSTEM) observations in conjunction with first-principle calculations confirm that CH-groups incorporate into S vacancies within WS2. According to our electronic transport measurements, undoped WS2 exhibits a unipolar n-type conduction. Nevertheless, the CH-WS2 monolayers show the emergence of a p-branch and gradually become entirely p-type, as the carbon doping level increases. Therefore, CH-groups embedded into the WS2 lattice tailor its electronic and optical characteristics. This route could be used to dope other 2D-TMDs for more efficient electronic devices.

Practical application of antimony alloy based electrodes in alkali-ion secondary batteries are viable due to their low-cost and widespread abundance. Employing unique nanostructuring strategies is vital for significantly improving their electrochemical performance while simultaneously addressing their inherent drawbacks. In this study, we report a simple microwave-hydrothermal approach for preparing antimony and tin-antimony alloy nanorods for the first time. Detailed X-ray diffraction and transmission electron microscopy measurements reveal that the preferential adsorption of cetrimonium bromide molecules on the (1 1 0) planes of the precursor alloy nanoparticles results in the formation of self-assembled nanorods with an average aspect ratio of 6. When mixed with nitrogen-doped graphene flakes, these nanorods deliver reversible discharge capacities of 500 mAh g−1 and 350 mAh g−1 at the end of 200 cycles in Li+ and Na+ half-cell configurations, respectively. When coupled with a LiNi0.5Mn1.5O4 cathode, the resulting Li+ full-cell delivers a nominal working voltage of 4.3 V, a high energy density of 344 Wh kg−1full-cell, and an 87.5% capacity retention after 200 cycles. Similarly, when coupled with a Prussian blue analog cathode, the resulting Na+ full-cell also delivers a nominal working voltage of 2.5 V, an energy density of 250 Wh kg−1full-cell, and an 82.5% capacity retention after 100 cycles.

In this work, we demonstrate the advantage of introducing extrinsic pseudocapacitance behavior in the active material for designing low-cost, high energy, and power density sodium-ion full cells. Here, tin and antimony based alloy nanopowder is synthesized via microwave assisted hydrothermal process (MAHP) for use as a negative electrode. Ex-situ x-ray diffraction studies reveal that the alloy nanopowder stores Na+ via a diffusion-controlled alloying mechanism. Extrinsic pseudocapacitance behavior is subsequently introduced by sandwiching the alloy nanopowder between nitrogen doped reduced graphene oxide nanosheets via MAHP. When coupled with a diffusion-controlled positive electrode comprising of an iron-based prussian blue analog, the resulting full cell demonstrates a high energy density of 262.5 Wh kg−1 at 1C rate with 85.7% capacity retention at the end of 100 cycles. Detailed cyclic voltammetry and electrochemical impedance studies provide insight into the effect of extrinsic pseudocapacitance in improving the electrochemical performance of the full cell.

Dilute magnetic semiconductors (DMS), achieved through substitutional doping of spin‐polarized transition metals into semiconducting systems, enable experimental modulation of spin dynamics in ways that hold great promise for novel magneto–electric or magneto–optical devices, especially for two‐dimensional (2D) systems such as transition metal dichalcogenides that accentuate interactions and activate valley degrees of freedom. Practical applications of 2D magnetism will likely require room‐temperature operation, air stability, and (for magnetic semiconductors) the ability to achieve optimal doping levels without dopant aggregation. Here, room‐temperature ferromagnetic order obtained in semiconducting vanadium‐doped tungsten disulfide monolayers produced by a reliable single‐step film sulfidation method across an exceptionally wide range of vanadium concentrations, up to 12 at% with minimal dopant aggregation, is described. These monolayers develop p‐type transport as a function of vanadium incorporation and rapidly reach ambipolarity. Ferromagnetism peaks at an intermediate vanadium concentration of ~2 at% and decreases for higher concentrations, which is consistent with quenching due to orbital hybridization at closer vanadium–vanadium spacings, as supported by transmission electron microscopy, magnetometry, and first‐principles calculations. Room‐temperature 2D‐DMS provide a new component to expand the functional scope of van der Waals heterostructures and bring semiconducting magnetic 2D heterostructures into the realm of practical application., Room‐temperature ferromagnetism is achieved in semiconducting vanadium‐doped tungsten disulfide monolayers. A reproducible and atmospheric pressure film sulfidation growth method yields doping concentration tunability in air‐stable samples. These monolayers develop p‐type transport as a function of vanadium incorporation and rapidly reach ambipolarity. The ferromagnetic behavior in this dilute semiconductor is modeled and understood through first‐principles calculations.

Reliable, controlled doping of 2D transition metal dichalcogenides will enable the realization of next-generation electronic, logic-memory, and magnetic devices based on these materials. However, to date, accurate control over dopant concentration and scalability of the process remains a challenge. Here, a systematic study of scalable in situ doping of fully coalesced 2D WSe2 films with Re atoms via metal-organic chemical vapor deposition is reported. Dopant concentrations are uniformly distributed over the substrate surface, with precisely controlled concentrations down to

Digital holography has found applications in many walks of life, from medicine to metrology, due to its ability to measure complex fields. Here, we use the power of digital holography to quantitatively image two-dimensional Transition Metal Dichalcogenides (TMDs) such as MoS2 and WS2 placed on a SiO2/Si substrate and determine their complex refractive indices or layer thicknesses. By considering the different refractive indices of the TMDs as they are thinned down from bulk to monolayers and by holographically capturing both the amplitude and the phase of reflected light, single atomic layers of TMDs, about 0.7 nm thick, can be resolved. Using holography, we also predict the number of layers contained within a thick TMD flake, which shows agreement with results obtained using Atomic Force Microscopy (AFM). A Bland–Altman analysis was performed to compare our experimental results with the standard AFM measurements, yielding a limit of agreement

Two-dimensional (2D) layered materials demonstrate their exquisite properties such as high temperature superconductivity, superlubricity, charge density wave, piezotronics, flextronics, straintronics, spintronics, valleytronics, and optoelectronics, mostly, at the monolayer limit. Following initial breakthroughs based on micromechanically exfoliated 2D monolayers, significant progress has been made in recent years toward the bottom-up synthesis of large-area monolayer 2D materials such as MoS2 and WS2 using physical vapor deposition and chemical vapor deposition techniques in order to facilitate their transition into commercial technologies. However, the nucleation and subsequent growth of the secondary, tertiary, and greater numbers of vertical layers poses a significant challenge not only toward the realization of uniform monolayers but also toward maintaining their consistent electronic and optoelectronic properties which change abruptly when transitioning from the monolayer to multilayer form. Chemica...

The 2D Electrostrictive FET (2D EFET) is a steep switching device that operates on the principle of dynamic bandgap (Eo) modulation of 2D channel enabled by voltage induced strain transduction [1]. However, the steep switching comes with its own overheads such as increased capacitance. Further, 2D-EFETs offer distinct features, such as a back terminal with unique control of device characteristics. To overcome the limitations of 2D EFETs, their unique behavior needs to be judiciously capitalized. In this work, we propose a 2-Transistor Schmitt Trigger (ST) based on 2D-EFETs utilizing the dynamic $E_{G}$ reduction and the resultant drive strength modulation driven by $V_{B}$ . (Fig. 1). We show the significance of circuit-driven device optimization to enable 2D-EFET based ST employing just two transistors.

Numerous advancements have allowed continuous aggressive dimensional scaling of CMOS to the current state of the art 10nm node but none are solutions to the fundamental Boltzmann statistics limits which have stalled Dennard voltage scaling. The semiconductor industry has invested heavily in disruptive, "steep slope" transistor technologies which promise lower operating voltages and dramatically reduced power consumption. While many of these technologies show great promise such as Tunnel FETs, Phase Change FETs, and even nanomechanical switches, all are far from commercialization and large-scale integration due to issues ranging from poor ON currents, limited switching ranges and reliability[4, 5].

Over the past decade, the field of two-dimensional (2D) layered materials has surged, promising a new platform for studying diverse physical phenomena that are scientifically intriguing and technologically relevant. Contacts are the communication links between these 2D materials and the three-dimensional world for probing and harnessing their exquisite electronic properties. However, fundamental challenges related to contacts often limit the ultimate performance and potential of 2D materials and devices. This article provides a comprehensive overview of the basic understanding and importance of contacts to 2D materials and various strategies for engineering and improving them. In particular, we elucidate the phenomenon of Fermi level pinning at the metal/2D contact interface, the Schottky versus Ohmic nature of the contacts and various contact engineering approaches including interlayer contacts, phase engineered contacts, and basal versus edge plane contacts, among others. Finally, we also discuss some of the relatively under-addressed and unresolved issues, such as contact scaling, and conclude with a future outlook.

In this paper, multi-layer feed forward neural networks are used to predict the lower heating value of gas (LHV), lower heating value of gasification products including tars and entrained char (LHVp) and syngas yield during gasification of municipal solid waste (MSW) during gasification in a fluidized bed reactor. These artificial neural networks (ANNs) with different architectures are trained using the Levenberg-Marquardt (LM) back-propagation algorithm and a cross validation is also performed to ensure that the results generalise to other unseen datasets. A rigorous study is carried out on optimally choosing the number of hidden layers, number of neurons in the hidden layer and activation function in a network using multiple Monte Carlo runs. Nine input and three output parameters are used to train and test various neural network architectures in both multiple output and single output prediction paradigms using the available experimental datasets. The model selection procedure is carried out to ascertain the best network architecture in terms of predictive accuracy. The simulation results show that the ANN based methodology is a viable alternative which can be used to predict the performance of a fluidized bed gasifier., Comment: 34 pages, 11 figures

In a recent paper, we presented an intelligent evolutionary search technique through genetic programming (GP) for finding new analytical expressions of nonlinear dynamical systems, similar to the classical Lorenz attractor's which also exhibit chaotic behaviour in the phase space. In this paper, we extend our previous finding to explore yet another gallery of new chaotic attractors which are derived from the original Lorenz system of equations. Compared to the previous exploration with sinusoidal type transcendental nonlinearity, here we focus on only cross-product and higher-power type nonlinearities in the three state equations. We here report over 150 different structures of chaotic attractors along with their one set of parameter values, phase space dynamics and the Largest Lyapunov Exponents (LLE). The expressions of these new Lorenz-like nonlinear dynamical systems have been automatically evolved through multi-gene genetic programming (MGGP). In the past two decades, there have been many claims of designing new chaotic attractors as an incremental extension of the Lorenz family. We provide here a large family of chaotic systems whose structure closely resemble the original Lorenz system but with drastically different phase space dynamics. This advances the state of the art knowledge of discovering new chaotic systems which can find application in many real-world problems. This work may also find its archival value in future in the domain of new chaotic system discovery., Comment: 103 pages, 169 figures, Applied Mathematical Modelling, 2018

In this paper we provide insight into an anomalous corrosion process, referred to as electroablation (EA), which converts multilayer flakes of transition metal diselenides like MoSe2 into their corresponding monolayers when micromechanically exfoliated on a conductive electrode and subsequently subjected to a high anodic potential inside a conventional electrochemical cell. Photoluminescence intensity maps and scanning transmission electron microscopy (STEM) images confirmed the single crystalline nature and 2H-hexagonal lattice structure of the remnant monolayer MoSe2 flakes, indicating the superior corrosion stability of the monolayers compared to that of the bulk counterpart. It is noted that the EA technique is a low-cost alternative for high-yield synthesis of single crystalline monolayer MoSe2 at room temperature. We also found that the dynamics of such an electro-oxidation-mediated and self-limiting corrosion process differs significantly for MoSe2 and WSe2. While we were able to engineer the corro...

Plants monitor their surrounding environment and control their physiological functions by producing an electrical response. We recorded electrical signals from different plants by exposing them to Sodium Chloride (NaCl), Ozone (O3) and Sulfuric Acid (H2SO4) under laboratory conditions. After applying pre-processing techniques such as filtering and drift removal, we extracted few statistical features from the acquired plant electrical signals. Using these features, combined with different classification algorithms, we used a decision tree based multi-class classification strategy to identify the three different external chemical stimuli. We here present our exploration to obtain the optimum set of ranked feature and classifier combination that can separate a particular chemical stimulus from the incoming stream of plant electrical signals. The paper also reports an exhaustive comparison of similar feature based classification using the filtered and the raw plant signals, containing the high frequency stochastic part and also the low frequency trends present in it, as two different cases for feature extraction. The work, presented in this paper opens up new possibilities for using plant electrical signals to monitor and detect other environmental stimuli apart from NaCl, O3 and H2SO4 in future.

The generation of thermal currents in a miniaturized device modeled as a channel connected to reservoirs maintained at different temperatures and coupled to a periodic THz driving source is reported in this letter. Primarily, we show that while thermally activated electrons can be pumped from the hot reservoir into the cold side, the quantum of charge flow increases in the presence of the periodic source. We explain this phenomenon by taking recourse to the Floquet theory guided rearrangement of the energy levels under periodic driving, which, in turn, augments the electron injection into the channel. The calculations uncover a useful feature whereby the strength of such a thermally-pumped current is amenable through a joint control of the amplitude and frequency of the signal, offering an additional experimentally-adjustable set of tools to regulate their flow. In the final part, the Seebeck coefficient and the thermoelectric figure-of-merit for this setup are analytically determined. Results are shown for classes of materials defined by linear and quadratic dispersion.

We study a thermal gradient induced current $\left(I_{th}\right)$ flow in potassium-doped two-dimensional anisotropic black phosphorus (BP) with semi-Dirac dispersion. The prototype device is a BP channel clamped between two contacts maintained at unequal temperatures. The choice of BP lies in the predicted efficient thermolectric behaviour. A temperature-induced difference in the Fermi levels of the two contacts drives the current (typified by the electro-thermal conductance) which we calculate using the Landauer transport equation. The current shows an initial rise when the device is operated at lower temperatures. The rise stalls at progressively higher temperatures and $I_{th}$ acquires a plateau-like flat profile indicating a competing effect between a larger number of transmission modes and a corresponding drop in the Fermi level difference between the contacts. The current is computed for both \textit{n}- and \textit{p}-type BP and the difference thereof is attributed to the particle-hole asymmetry. The utility of such calculations lie in conversion of the heat production and an attendant temperature gradient in miniaturized devices to useful electric power and a possible realization of solid-state Peltier cooling. Unlike the flow of $I_{th}$ that removes heat, the ability of a material to maintain a steady temperature is reflected in its heat capacity which is formulated in this work for BP via a Sommerfeld expansion. In the concluding part, we draw a microscopic connection between the two seemingly disparate processes of heat removal and absorption by pinning down their origin to the underlying density of states. Finally, a qualitative analysis of a Carnot-like efficiency of the considered thermoelectric engine is performed drawing upon the previous results on thermal current and heat capacity., Comment: 9 pages, 7 figures. An amended version of this manuscript has been published in Journal of Chemical Physics

A novel approach is presented for fast generation of synthetic seismograms due to microseismic events, using heterogeneous marine velocity models. The partial differential equations (PDEs) for the 3D elastic wave equation have been numerically solved using the Fourier domain pseudo-spectral method which is parallelizable on the graphics processing unit (GPU) cards, thus making it faster compared to traditional CPU based computing platforms. Due to computationally expensive forward simulation of large geological models, several combinations of individual synthetic seismic traces are used for specified microseismic event locations, in order to simulate the effect of realistic microseismic activity patterns in the subsurface. We here explore the patterns generated by few hundreds of microseismic events with different source mechanisms using various combinations, both in event amplitudes and origin times, using the simulated pressure and three component particle velocity fields via 1D, 2D and 3D seismic visualizations., 13 pages, 23 figures

Iron-based perovskites LaFe0.5M0.5O3, with the orthorhombic (S.G. Pbnm) and rhombohedral (S.G. R-3c) structure for M=Co and Ni, respectively were synthesized using the sol–gel method, in contrast to the literature results. Magnetic investigations reveal that LaFe0.5Co0.5O3 is a canted antiferromagnet and reaches a magnetic transition of 370 K, i.e., much above the 300 K value observed by previous authors, whereas LaFe0.5Ni0.5O3 is antiferromagnetic at low temperature. The sol–gel synthesized LaFe0.5Co0.5O3 perovskite to be stabilized at room temperature with a pure orthorhombic phase. The magnetization behavior reveals the perovskite is canted antiferromagnet at low temperature.

This article proposes a disruptive device concept which meets both low power and high performance criterion for post-CMOS computing and at the same time enables aggressive channel length scaling. This device, hereafter refer to as two-dimensional electrostrictive field effect transistor or 2D-EFET, allows sub-60 mV/decade subthreshold swing and considerably higher ON current compared to any state of the art FETs. Additionally, by the virtue of its ultra-thin body nature and electrostatic integrity, the 2D-EFET enjoys scaling beyond 10 nm technology node. The 2D-EFET works on the principle of voltage induced strain transduction. It uses an electrostrictive material as gate oxide which expands in response to an applied gate bias and thereby transduces an out-of-plane stress on the 2D channel material. This stress reduces the inter-layer distance between the consecutive layers of the semiconducting 2D material and dynamically reduces its bandgap to zero i.e. converts it into a semi-metal. Thus the device operates with a large bandgap in the OFF state and a small or zero bandgap in the ON state. As a consequence of this transduction mechanism, internal voltage amplification takes place which results in sub-60 mV/decade subthreshold swing (SS).

We report the discovery of an electrochemical process that converts two dimensional layered materials of arbitrary thicknesses into monolayers. The lateral dimensions of the monolayers obtained by the process within a few seconds time at room temperature were as large as 0.5 mm. The temporal and spatial dynamics of this physical phenomenon, studied on MoS2 flakes using ex-situ AFM imaging, Raman mapping and photoluminescence measurements trace the origin of monolayer formation to a substrate-assisted self-limiting electrochemical ablation process. Electronic structure and atomistic calculations point to the interplay between three essential factors in the process: (1) strong covalent interaction of monolayer MoS2 with the substrate; (2) electric-field induced differences in Gibbs free energy of exfoliation; (3) dispersion of MoS2 in aqueous solution of hydrogen peroxide. This process was successful in obtaining monolayers of other 2D transition metal dichalcogenides, like WS2 and MoTe2 as well.

Mobility is a critical parameter that is routinely used for benchmarking the performance of field-effect transistors (FETs) based on novel nanomaterials. In fact, mobility values are often used to champion nanomaterials since high-performance devices necessitate high mobility values. The current belief is that the contacts can only limit the FET performance and hence the extracted mobility is an underestimation of the true channel mobility. However, here, such misconception is challenged through rigorous experimental effort, backed by numerical simulations, to demonstrate that overestimation of mobility occurs in commonly used geometries and in nanomaterials for which the contact interface, contact doping, and contact geometry play a pivotal role. In particular, dual-gated FETs based on multilayer MoS2 and WSe2 are used as case studies in order to elucidate and differentiate between intrinsic and extrinsic contact effects manifesting in the mobility extraction. The choice of 2D layered transition metal dichalcogenides (TMDCs) as the semiconducting channel is motivated by their potential to replace and/or coexist with Si-based aging FET technologies. However, the results are equally applicable to nanotube- and nanowire-based FETs, oxide semiconductors, and organic-material-based thin-film FETs.

The field of two-dimensional (2D) materials has witnessed several significant advancements in a short period of time. There have been extensive research efforts dedicated to this field and an expanding community of researchers built around the same. The focus of this review article is on the most recent milestones in several aspects of 2D materials with emphasis on transition metal dichalcogenides, such as improved synthesis and property engineering, approaching this from both experimental and theoretical viewpoints. There is also an attempt at highlighting some emerging material properties that are of interest and use of these 2D materials in several electronic applications.