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The continued miniaturization of chips demands highly thermally conductive materials and effective thermal management strategies. Particularly, the high‐field transport of the devices built with 2D materials is limited by self‐heating. Here a systematic control of heat flow in single‐side fluorinated graphene (FG) with varying degrees of fluorination is reported, revealing a superior room‐temperature thermal conductivity as high as 128 W m−1 K−1. Monolayer graphene/FG lateral heterostructures with seamless junctions are approached for device fabrication. Efficient in‐plane heat removal paths from graphene channel to side FG are created, contributing significant reduction of the channel peak temperature and improvement in the current‐carrying capability and power density. Molecular dynamics simulations indicate that the interfacial thermal conductance of the heterostructure is facilitated by the high degree of overlap in the phonon vibrational spectra. The findings offer novel design insights for efficient heat dissipation in micro‐ and nanoelectronic devices. [ABSTRACT FROM AUTHOR]

A new kind of perylene‐based 2D covalent organic framework (COF) is designed and synthesized based on the C2 + C2 topological diagram. The perylene‐based COF is constructed via the condensation reaction using 2,5,8,11‐tetrakis((4‐formylphenyl) perylene (TFPPer) and 2,5,8,11‐tetrakis(4‐aminophenyl) perylene (TAPPer) as building blocks. The resulting TFPPer‐TAPPer‐COF features high crystallinity, excellent stability, intrinsic porosity, and an electron‐rich skeleton. Significantly, the electrical performance of the COF can be enhanced through the encapsulation of fullerene (C60) into the 1D channels via donor–acceptor interaction. Compared to the pristine COF, the electrical conductivity of C60@TFPPer‐TAPPer‐COF can be greatly increased from 8.98 × 10−8 to 1.59 × 10−5 S cm−1, meanwhile the carrier mobility rises from 1.04 × 10−3 to 4.23 × 10−2 cm2 V−1 s−1. The improvement in electrical performance stems from the strong donor–acceptor interaction between perylene and C60. These results provide insights into the rational construction of conductive COFs through donor–acceptor interaction and demonstrate their great potential in related application fields. [ABSTRACT FROM AUTHOR]

Multichip silicon carbide (SiC) power modules with Kelvin-source connections are commonly used in applications requiring large capacity. As a result of the parasitic effect induced by the interconnections in module packaging, the dynamic current mismatch among paralleled dies limits the available capacity of power modules. This article presents a general analysis on the mechanism of layout-dominated dynamic current balancing in multichip SiC power modules, utilizing a coupled parasitic network model. Focusing on the interrelation of parasitic parameters in the power module, a coupled parasitic network model is developed specially for switching transients, and the dynamic current balancing equations are derived. For the multichip power modules with two different layouts, the parasitic parameters pertaining to the proposed model are extracted by the finite-element analysis (FEA). The acquired parasitic parameters considering magnetic coupling are utilized to calculate and verify the dynamic current balancing equations. Moreover, based on these parasitic parameters, the electromagnetic coupling simulation is performed to evaluate the dynamic current sharing. Furthermore, for the validation of the proposed model and equations, experiments are conducted with the fabricated power module prototypes. [ABSTRACT FROM AUTHOR]

This letter presents a partial-bootstrap gate driver circuit for switching loss reduction and crosstalk mitigation. The proposed circuit is simple and no additional power supply or control is needed. The circuit structure and operating principles of the proposed gate driver are introduced. Three different operating modes of the proposed gate driver are presented. Finally, the experimental results are presented to validate the proposed gate driver. It is found that the proposed gate driver can greatly accelerate the switching process and reduce switching loss. The proposed gate driver can also generate a gradually decaying negative voltage during the turn-off process to suppress crosstalk. [ABSTRACT FROM AUTHOR]

This article presents quick analytical prediction methods of switching loss, turn-on/off overvoltage, di/dt, and dv/dt for SiC metal–oxide–semiconductor field-effect transistor based on device datasheet. First, the switching process is analyzed and the simplification principles are discussed based on charge conservation and flux conservation. Second, the analytical equations of switching loss, turn-on/off overvoltage, di/dt, and dv/dt are derived. Third, experimental results under different operating conditions are presented to validate the proposed methods. It is found that the average prediction error is 10.11%. Finally, relationships between switching performance and different parameters, such as parasitic capacitance, parasitic inductance, dc-voltage, and load current, are analyzed and summarized based on the proposed prediction methods. [ABSTRACT FROM AUTHOR]

Flexible fast-charging sodium ion storage devices are poised to transform the future wearable electronics industry, if the materials used to build such devices can present a versatile integration. Herein, inspired by ferroconcrete, nonwoven graphene fiber (GF) fabric reinforced electrodes were successfully demonstrated in flexible sodium ion capacitors (SICs). For the fabrics, the functionalities of fast electron transport and an ion permeation network, a highly compatible electrode material host, an efficient capacity contributor, and a robust flexible framework are synergistically integrated. These were provided by the high conductivity of the graphene sheets, the tunable porosity of the GF, and the interlocked structure, compatibility with materials, and the surface capacitive contribution of the fabrics. The nonwoven fabrics hosted multi-dimensional active materials as the ferroconcrete electrode exhibits exceptional electrochemical and mechanical properties individually. The SICs can complete an entire charge–discharge process within 15 s. A digital LED and watch powered using the flexible SICs with superior volumetric performances (12 mW h cm−3@37 mW cm−3, and 6 mW h cm−3@1.9 W cm−3) proved the practical capability of our design. We believe that the proposed nonwoven GF fabrics and the ferroconcrete electrode structure will become a universal design, and shed new light on flexible fast-charging sodium ion storage devices. [ABSTRACT FROM AUTHOR]

Inorganic metal halide (IMH) perovskites have recently emerged as highly promising optoelectronic materials due to their excellent material properties, including tunable direct bandgap, long carrier diffusion length, high carrier mobility and outstanding environmental stabilities. However, the performance of photodetectors fabricated from IMH perovskites so far is limited as compared to their counterparts based on organic–inorganic hybrid perovskites. In this work, we demonstrate a high performance ultraviolet–visible (UV–Vis) dual-band photodetector based on a Cs2SnI6/ZnO heterojunction structure. By adjusting the polarity of the applied bias voltage, the photodetector can switch between two operation modes: (1) UV–Vis dual-band detection mode and (2) visible-blind UV detection mode. High detectivity in both the UV (1.39 × 1012 Jones) and visible (5.88 × 1011 Jones) regions is achieved. In addition, this photodetector demonstrated a fast response speed with a rise and fall time on the order of milliseconds and a large linear dynamic range of 119 dB. The excellent performance of this photodetector originates from efficient charge separation at the heterojunction interfaces, which will be discussed in detail in terms of the energy band diagrams and carrier dynamics of the device. Our study demonstrates the great application potential of inorganic vacancy-ordered perovskites in high-performance heterojunction photodetectors. [ABSTRACT FROM AUTHOR]

A heterojunction photodiode was fabricated from Bi doped Cs2SnCl6 nanoparticles (Cs2SnCl6:Bi NPs) spin-coated on an epitaxially grown GaN substrate. With the back illumination configuration, the heterojunction photodiode demonstrated excellent narrow-band UV sensing capability with a full wavelength of half maximum of 18 nm and a maximum detectivity of 1.2 × 1012 jones, which is promising for biomedical applications. In addition to the excellent narrow band UV sensitivity, the device also demonstrated a large linear dynamic range of 71 decibels (dB) and a fast photoresponse speed (a rise time of 0.75 μs and a fall time of 0.91 μs). The excellent performance is attributed to excellent carrier separation efficiency at the heterojunction interface and improved carrier collection efficiency through the multi-walled carbon nanotube (MWCNT) network. All the above advantages are of great importance for commercial deployment of perovskite-based photodetectors. [ABSTRACT FROM AUTHOR]

Abstract: Transparent and flexible supercapacitors (TFSCs) as indispensable components for future transparent and flexible electronics have attracted significant interests. The Ag nanowires/poly(ethylene terephthalate) (PET) transparent conductive electrodes (TCEs) exhibit strong competitiveness applied in the TFSCs due to the exceptional conductivity and transparency. However, the environmental tolerance of Ag nanowires such as oxidation and sulfurization limits the reliability. Herein, electric‐double‐layer TFSCs based on Ag nanowires/PET TCEs as current collectors are reported. More importantly, a seamless, uniform, and flexible graphene layer behaves as armored and active components simultaneously for the TFSCs, by a facile electrodeposition process. On the one hand, the flexible graphene layer can isolate the Ag nanowires away from the oxidation well, particularly in the condition of electrolyte. On the other hand, the laminated graphene layer with wrinkles can store electrons, and the copercolating network of graphene layer and Ag nanowires can transport the electrons efficiently, cyclically accomplishing the operation of storage and transport, by which the synergistic effect endows the TFSCs with decent optical and electrochemical performances. The interfacial capacitance is evaluated to discuss the relationship between the structure of graphene layer and the measured capacitance. This facile process provides a rational architecture and insights into TFSCs. [ABSTRACT FROM AUTHOR]

Nanocrystalline UO2+ x powders are prepared by high-energy ball milling and subsequently consolidated into dense fuel pellets (>95% of theoretical density) under high pressure (750 MPa) by spark plasma sintering at low sintering temperatures (600°C-700°C). The grain size achieved in the dense nano-ceramic pellets varies within 60-160 nm as controlled by sintering temperature and duration. The sintered fuel pellets are single phase UO2+ x with hyper-stoichiometric compositions as derived by X-ray diffraction, and micro-Raman measurements indicate that random oxygen interstitials and Willis clusters dominate the single phase nano-sized oxide pellets of UO2.03 and UO2.11, respectively. The thermal conductivities of the densified nano-sized oxide fuel pellets are measured by laser flash, and the fuel stoichiometry displays a dominant effect in controlling thermal transport properties. A reduction in thermal conductivity is also observed for the dense nano-sized pellets as compared with micron-sized counterparts reported in the literature. The correlation among the SPS sintering parameters-microstructure control-properties is established, and the nano-sized UO2+ x pellets with controlled microstructure can serve as the model systems for fundamental understandings of fuel behaviors and obtaining critical experimental data for multi-physics MARMOT model validation. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid lead-based perovskites experience significant environmental instability under ambient moist air and are not environmentally benign due to the usage of toxic Pb. Here, we report a new approach to synthesize lead-free all inorganic perovskites (Cs2SnIxCl6−x) using hydriodic acid (HI) demonstrating greatly enhanced environmental stability and tunable optical properties by controlling the I−/Cl− ratios. Single phase perovskites can be achieved with a low iodine or chlorine content, and a phase separation occurs in the binary system with closer iodine and chlorine dopings. UV-vis diffuse reflectance and photoluminescence measurements reveal tunable band gaps of Cs2SnIxCl6−x perovskites from the UV to the infrared region. The mixed halide perovskite with a lower chloride content shows significantly higher photoluminescence intensity. The thermal stability of mixed halide all-inorganic perovskites is continuously improved as the Cl content increases. The synthesis of Sn-based perovskites with tunable optical properties and environmental stability represents one step further toward the realization of the stable lead-free all inorganic perovskites. [ABSTRACT FROM AUTHOR]

Pb9.85(VO4)6I1.7, a potential waste form for long-lived I-129 immobilization, experiences phase decomposition and thus iodine loss at an elevated temperature above 400°C, presenting a significant challenge for effective management of radioactive iodine. In this work, we report low-temperature consolidation of dense iodoapatite pellets with above 95% theoretical density by spark plasma sintering (SPS) at temperatures as low as 350°C for 20 min without iodine loss. Microstructure analysis indicates a nanocrystalline ceramic with an average grain size less than 100 nm. Grain growth dominates the sintered microstructure at higher temperatures and longer durations. The dense nanoceramics have significantly-improved fracture toughness as compared with bulk coarsened grain structures. The effects of sintering temperatures (350°C, 400°C, 500°C, and 700°C) and durations (0-20 min) on microstructure, density, fracture morphology, and mechanical properties including Young's modulus and hardness of bulk samples were investigated. Low temperature densified iodoapatites suggest immense potential of SPS as an advanced materials fabrication technology for the development of waste forms for immobilization of volatile radionuclides including radioactive iodine. [ABSTRACT FROM AUTHOR]

Chemical doping of nitrogen into graphene can significantly enhance the reversible capacity and cyclic stability of the graphene-based lithium ion battery (LIB) anodes, and first principles calculations based on density functional theory suggested that pyridinic-N shows stronger binding with Li with reduced energy barrier for Li diffusion and thus is more effective for Li storage than pyrrolic and graphitic-N. Here, we report a novel and rapid (∼30 seconds) process to fabricate nitrogen-doped graphene (NGr) by simultaneous thermal reduction of graphene oxide with ammonium hydroxide. The porous NGr with dominant pyridinic N atoms displays greatly enhanced reversible capacities, rate performance and exceptional cyclic stability as compared with pristine graphene. The reversible discharge capacity of the NGr electrode cycled between 0.01–3 V can reach 453 mA h g−1 after 550 cycles at a charge rate of 2 A g−1 (∼5.4 C), and 180 mA h g−1 after 2000 cycles at a high charge rate of 10 A g−1 (∼27 C) without any capacity fading. When charged within 0.01–1.5 V, the NGr anode still exhibits high reversible capacities of 224 mA h g−1 and 169 mA h g−1 after 700 cycles and 800 cycles at a charge rate of 1 A g−1 and 5 A g−1, respectively. Ex situ X-ray photoelectron spectroscopy (XPS) analysis of the NGr electrode upon lithiation and delithiation indicated that the pyridinic-N dominates the capacity enhancement at 3 V, while the pyrrolic-N contributes primarily to Li ion storage below 1.5 V. [ABSTRACT FROM AUTHOR]

Abstract: Charge transfer complex (CTC) has been formed between photoluminescent graphene oxide (GO) as electron acceptor and N-methylpyrrolidone (NMP) as electron donor. Studies of UV absorption and photoluminescence (PL) suggest that the formation of CTC results in a red-shift of absorption and a new PL emission. Decay dynamics was described by time-resolved PL spectra and a clear ultrafast charge-transfer process was observed from the PL rise times. The PL of the CTC was sensitive to external components, allowing molecular detection of 7,7,8,8-tetracyanoquinodimethane and 1,3,5-trinitrobenzene up to hundred nanomolar concentration levels through the photoluminescence signals. [Copyright &y& Elsevier]

Graphene fibers are fabricated by wet-spinning an aqueous large-size and small-size graphene oxide (GO) dispersion in a rotating Me3N(C16H33)Br or CaCl2 coagulation bath. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides like MoS 2 have been considered as crucial channel materials beyond silicon to continuously advance transistor scaling down owing to their two-dimensional structure and exceptional electrical properties. However, the undesirable interface morphology and vibrational phonon frequency mismatch between MoS 2 and the dielectric layer induce low thermal boundary conductance, resulting in overheating issues and impeding electrical performance improvement in the MoS 2 field-effect transistors. Here, we employed hybrid high- k dielectric layers of Al 2 O 3 /HfO 2 to simultaneously reduce the interfacial thermal resistance and improve device electrical performance. The enhanced contact, greater vibrational phonon overlapping region, and stronger interfacial bonding force between the top Al 2 O 3 layer and MoS 2 promote the heat removal efficiency across the interface to the substrate. Under the same input power density, the temperature profile of the MoS 2 transistor on the Al 2 O 3 /HfO 2 has been largely reduced compared to that of the device on HfO 2 , with a maximum reduction of 49.5 °C. In addition, the field-effect mobility and current of MoS 2 devices on the Al 2 O 3 /HfO 2 high- k dielectric layers have been significantly improved, attributed to the depressed electron scattering and trap states at the interface. The design of the hybrid high- k dielectric layers provides an efficient solution to simultaneously improve the thermal and electrical performance of the two-dimensional devices.

Thermally conductive and electrically insulating thermal interface materials (TIMs) are highly desired for electronic cooling. To improve heat transfer efficiency, thermally conductive fillers with a high loading content have been incorporated into the polymer-based TIMs. However, this is usually at the expense of the interfacial thermal resistance reduction and reliability. In this study, vertically aligned boron nitride nanosheet films (VBNFs) have been prepared by a scalable microfluidic spinning process and template-assisted chemical vapor deposition conversion method. A further high-temperature annealing was applied to achieve high crystallinity. VBNFs have been applied as fillers to fabricate TIMs and achieve a superior through-plane thermal conductivity of 6.4 W m -1 K -1 and low modulus of 2.2 MPa at low BN loading of 9.85 vol %, benefitting from the well-aligned vertical sheet structure and high crystallinity. In addition, the fabricated TIMs present high-volume resistivity and breakdown strength, satisfying the electrical insulation demands. The high thermal conductivity and low modulus contribute an outstanding cooling performance to the TIMs in the heat dissipation application for high-power LEDs. This template-assisted conversion technology for the fabrication of orientated BN nanosheets structure and the prepared high-performance TIMs pave the way for efficient thermal management of high-power electronics.

Fluorochemicals are persistent, bioaccumulative, and toxic compounds that are widely tributed in the environment. Developing efficient biodegradation strategies to decompose the fluorochemicals via breaking the inert C-F bonds presents a holistic challenge. As a promising biodegradation enzyme candidate, fluoroacetate dehalogenase (FAcD) has been reported as the only non-metallic enzyme to catalyze the cleavage of the strong C-F bond. Here, we systematically investigated the catalytic actions of FAcD toward its natural substrate fluoroacetate using molecular dynamics simulations and quantum mechanism/molecular mechanism calculations. We propose that the enzymatic transformation involves four elementary steps, (I) C-F bond activation, (II) nucleophilic attack, (III) C-O bond cleavage, and (IV) proton transfer. Our results show that nucleophilic attack is the rate-determining step. However, for difluoroacetate and trifluoroacetate, C-F bond activation, instead of nucleophilic attack, becomes the rate-determining step. We show that FAcD, originally recognized as α-fluorocarboxylic acid degradation enzyme, can catalyze the defluorination of difluoroacetate to glyoxylate, which is captured by our high-resolution mass spectrometry experiments. In addition, we employed amino acid electrostatic analysis method to screen potential mutation hotspots for tuning FAcD's electrostatic environment to favor substrate conversion. The comprehensive understanding of catalytic mechanism will inform a rational enzyme engineering strategy to degrade fluorochemicals for benefits of environmental sustainability.

Low thermal transport behavior along the radial direction of nuclear fuel pellets and pellet-cladding mechanical interaction significantly impact fuel performance and the safety of current nuclear energy systems. Here we report a new strategy of advanced fuel design in which highly thermally-conductive and mechanically-robust graphene nanoplatelets are incorporated into UO 2 fuel matrix to improve fuel thermal-mechanical properties. The 2D geometry of the graphene nanoplatelets enables a unique lamellar structure upon fuel consolidation by spark plasma sintering. The thermal conductivity along the radial direction of the sintered fuel pellets at room temperature reaches 12.7 and 19.1 wm -1 K -1 at 1 wt.% and 5 wt.% loadings of the graphene nanoplatelets, respectively, representing at least 74% and 162% enhancements as compared to pure UO 2 fuel pellets. Indentation testing suggests great capability of the 2D graphene nanoplatelets to deflect and pin crack propagation, drastically improving the crack propagation resistance of fuel matrix. The estimated indentation fracture toughness reaches 3.5 MPa·m 1/2 by 1 wt.% loading of graphene nano-platelets, representing a 150% improvement over 1.4 MPa·m 1/2 for pure UO 2 fuel pellets. Isothermal annealing of the composite fuel indicates that the graphene nano-platelet is able to retain its structure and properties against reaction with UO 2 matrix up to 1150 °C.

The performance of graphene field-effect transistors is limited by the drastically reduced carrier mobility of graphene on silicon dioxide (SiO2) substrates. Here we demonstrate an ultrasensitive ultraviolet (UV) phototransistor featuring an organic self-assembled monolayer (SAM) sandwiched between an inorganic ZnO quantum dots decorated graphene channel and a conventional SiO2/Si substrate. Remarkably, the room-temperature mobility of the chemical-vapor-deposition grown graphene channel on the SAM is an order-of-magnitude higher than on SiO2, thereby drastically reducing electron transit-time in the channel. The resulting recirculation of electrons (in the graphene channel) within the lifetime of the photogenerated holes (in the ZnO) increases the photoresponsivity and gain of the transistor to ∼10(8) A/W and ∼3 × 10(9), respectively with a UV to visible rejection ratio of ∼10(3). Our UV photodetector device manufacturing is also compatible with current semiconductor processing, and suitable for large volume production.

We report fabrication of a flexible, thorn-like ZnO-multiwalled carbon nanotube (MWCNT) hybrid paper with high aspect ratio for efficient ultraviolet (UV) sensing and photocatalyst applications. The thorn-like ZnO-MWCNT hybrid paper was synthesized via atomic layer deposition (ALD) of a uniform ZnO thin film on the outside surface of the MWCNT followed by hydrothermal growth of ZnO branches. The hybrid paper achieved very high surface to volume ratio, which is favorable for photodetector and photocatalyst applications. A photodetector fabricated from the hybrid paper demonstrates a high sensitivity to UV light with a maximum photoresponsivity of 45.1 A W(-1) at 375 nm, corresponding to an external quantum efficiency as high as 14927%. The rise time and fall time of the UV photodetector are 29 ms and 33 ms, respectively, indicating fast transient response characteristics for the device. The high photoresponsivity and fast transient response are attributed to efficient carrier transport and collection efficiency of the hybrid paper. Besides, the thorn-like ZnO-MWCNT hybrid paper demonstrates excellent photocatalytic performance under UV irradiation, enabling photo-degradation of organic dyes such as Rhodamine B (RhB) within 90 minutes, with good recyclability.

Uniform amorphous vanadium oxide films were coated on graphene via atomic layer deposition and the nano-composite displays an exceptional capacity of ~900 mA h g(-1) at 200 mAg(-1) with an excellent capacity retention at 1 A g(-1) after 200 cycles. The capacity contribution (1161 mA h g(-1)) from vanadium oxide only almost reaches its theoretical value.

Organic phase change materials (PCMs) have been utilized as latent heat energy storage and release media for effective thermal management. A major challenge exists for organic PCMs in which their low thermal conductivity leads to a slow transient temperature response and reduced heat transfer efficiency. In this work, 2D thermally annealed defect-free graphene sheets (GSs) can be obtained upon high temperature annealing in removing defects and oxygen functional groups. As a result of greatly reduced phonon scattering centers for thermal transport, the incorporation of ultralight weight and defect free graphene applied as nanoscale additives into a phase change composite (PCC) drastically improve thermal conductivity and meanwhile minimize the reduction of heat of fusion. A high thermal conductivity of the defect-free graphene-PCC can be achieved up to 3.55 W/(m K) at a 10 wt % graphene loading. This represents an enhancement of over 600% as compared to pristine graphene-PCC without annealing at a comparable loading, and a 16-fold enhancement than the pure PCM (1-octadecanol). The defect-free graphene-PCC displays rapid temperature response and superior heat transfer capability as compared to the pristine graphene-PCC or pure PCM, enabling transformational thermal energy storage and management.

An ultraviolet (UV) photodetector is fabricated by sandwiching a nanocomposite active layer between charge-selective semiconducting polymers. The nanocomposite active layer composed of TiO2 nanoparticles (NPs) blended with 1,3-bis(N-carbazolyl)benzene (mCP), which acts as a "valve" controller that enables hole injection into the device upon UV illumination. The UV photodetector demonstrated a high photocurrent to dark current ratio (∼10(4)), a large linear dynamic range of 60 dB, and a remarkable external quantum efficiency (∼8.5 × 10(4)%) for the UV light at 351 nm. In addition to discussing the performance of the UV photodetector, a general strategy for design and fabrication of high-performance UV photodetectors with hole injection operation mode is suggested.