The development of biocompatible, efficient energy harvesters is essential for next-generation wearable, implantable, and self-powered bioelectronics. Silk fibroin is a piezoelectric biomaterial; however, its moderate response limits its output performance. Here, we report a comparative study of silk fibroin-based piezoelectric nanogenerators (PENGs) reinforced with MAX phase (Ti3AlC2) and MXene (Ti3C2Tx) under identical processing conditions. Incorporation of fillers enhances piezoelectric output, achieving similar to 2.5-fold voltage improvement over pristine devices. Structural and interfacial analyses reveal that MAX phase enhances performance via mechanical confinement and interfacial polarization, while MXene operates through nanoscale networks and hydrogen-bonding-induced polarization stabilization. Silk/MXene PENGs exhibit similar to 12.4 V and 269.02 mu A, while silk/MAX devices show similar to 11.0 V and 256.62 mu A. Impedance matching indicates low internal resistance (similar to 10 k Omega) and peak power densities of similar to 96.49 mu W/cm & sup2; and 87.80 mu W/cm & sup2;, respectively. Notably, silk/MAX devices retain similar to 88-98% performance of MXene systems, highlighting MAX phase as a scalable alternative.

The increasing need for small, portable, and Internet of Things (IoT) devices requires exploring alternatives to conventional power sources. We present a flexible and self-sustainable piezoelectric nanogenerator composed of 2D organic-inorganic halide perovskite, namely guanidium lead iodide (GA2PbI4) and polyvinylidene fluoride (PVDF) composite. By systematically incorporating optimized concentration of GA2PbI4 into the PVDF matrix, the electroactive phase content of the composite could be substantially enhanced to a maximum value of 90% for a 4 wt.% loading of the perovskite. The piezoelectric coefficient consequently increases from similar to 7.46 pC/N for pure PVDF to similar to 39.5 pC/N for the 4% filler loading in the PVDF matrix. The optimized device generates an open circuit voltage of similar to 60 V and a short circuit current of 6.4 mu A. The device delivers a power density of similar to 8.58 mu W/cm2 across a 12 M Omega load, sufficient to power small capacitors and an array of LEDs. In addition to the remarkable energy harvesting capability, the composite demonstrates appreciable photosensitivity under light irradiation, acting as a potential self-powered photodetector. The fabricated self-powered photodetector exhibits an increase in the short circuit current under light illumination, highlighting the potential of GA2PbI4/PVDF composites as wearable energy harvesting devices and real-time, wireless, IoT-enabled self-powered photodetectors.

MXenes have attracted attention in recent years owing to their 2D layered structures with various functionalities. To open a new application field for MXenes in the realm of electronic devices, such as ultrahigh-integrated magnetic memory, a spin-orbit torque (SOT) bilayer structure with MXene of Cr2N is developed: substrate//Cr2N/[Co/Pt]3/MgO using the magnetron sputtering technique. Field-free current-induced magnetization switching in the bilayer structure is demonstrated, regardless of the charge current directions with respect to the mirror symmetry lines of Cr2N crystal. This is a specific characteristic for the 2D MXene-based SOT-devices. As the SOT efficiency increases with increasing the Cr2N thickness, the first-principles calculations predict an intrinsic orbital-Hall conductivity with the dominant out-of-plane component, comparing to the spin-Hall conductivity in the Cr2N. X-ray magnetic circular dichroism reveals the out-of-plane uncompensated magnetic moment of Cr ( m Cr UC . $m_{{\mathrm{Cr}}}^{{\mathrm{UC}}.}$ ) in the Cr2N layer at the interface, induced by contact with the Co in the [Co/Pt]3 ferromagnetic layer. Therefore, the intrinsic bulk orbital-Hall effect in MXene and the interfacial contribution such as spin-filtering-like effect owing to m Cr UC . $m_{{\mathrm{Cr}}}^{{\mathrm{UC}}.}$ are considered as possible major mechanisms for the unconventional out-of-plane SOT in the device, rather than a crystal symmetry and/or an interlayer exchange coupling.

Harnessing self-powered and photoresponsive biomechanical activity sensors by exploring the piezo-phototronic effect in lead-free layered halide perovskite/PVDF composites.

MXenes have attracted considerable attention in recent years owing to their two-dimensional (2D) layered structures with various functionalities similar to those of graphene and transition metal dichalcogenides. To open a new application field for MXenes in the realm of electronic devices, such as ultrahigh-integrated magnetic memory, we have developed a spin-orbit torque (SOT) bilayer structure comprising bare MXene of Cr2N: substrate//Cr2N/[Co/Pt]3/MgO using the magnetron sputtering technique. We demonstrated field-free current-induced magnetization switching (CIMS) in the bilayer structure, regardless of the charge current directions with respect to the mirror symmetry lines of Cr2N crystal. This is a specific characteristic for the 2D MXene-based SOT-devices, originating from an unconventional out-of-plane SOT. As the SOT efficiency increases with increasing the Cr2N thickness, the first-principles calculations predict an intrinsic orbital-Hall conductivity with the dominant out-of-plane component, comparing to the spin-Hall conductivity in the Cr2N. X-ray magnetic circular dichroism reveals the out-of-plane uncompensated magnetic moment of Cr in the Cr2N layer at the interface, induced by contact with the Co in the [Co/Pt]3 ferromagnetic layer. Therefore, the intrinsic bulk orbital Hall effect in MXene and the interfacial contribution such as spin-filtering-like effect owing to uncompensated magnetic moment of Cr are considered as possible major mechanisms for the unconventional out-of-plane SOT in the device, rather than a crystal symmetry and/or an interlayer exchange coupling.

Two-dimensional transition metal dichalcogenides (TMDs) have drawn immense interest due to their strong spin-orbit coupling and unique layer number dependence in response to spin-valley coupling. This leads to the possibility of controlling the spin degree of freedom of the ferromagnet (FM) in thin film heterostructures and may prove to be of interest for next-generation spin-based devices. Here, we experimentally demonstrate the odd-even layer dependence of WS2 nanolayers by measurements of the ultrafast magnetization dynamics in WS2/Co3FeB thin film heterostructures by using time-resolved Kerr magnetometry. The fluence (photon energy per unit area) dependent magnetic damping (alpha) reveals the existence of broken symmetry and the dominance of inter- and intraband scattering for odd and even layers of WS2, respectively. The higher demagnetization time, tau m, in 3 and 5 layers of WS2 is indicative of the interaction between spin-orbit and spin-valley coupling due to the broken symmetry. The lower tau m in even layers as compared to the bare FM layer suggests the presence of a spin transport. By correlating tau m and alpha, we pinpointed the dominant mechanisms of ultrafast demagnetization. The mechanism changes from spin transport to spin-flip scattering for even layers of WS2 with increasing fluence. A fundamental understanding of the two-dimensional material and its odd-even layer dependence at ultrashort timescales provides valuable information for designing next-generation spin-based devices. Odd-even WS2 layer number dependent ultrafast demagnetization and damping are studied by varying the pump fluence.

In the quest to improve energy efficiency and design better thermal insulators, various engineering strategies have been extensively investigated to minimize heat transfer through a material. Yet, the suppression of thermal transport in a material remains elusive because heat can be transferred by multiple energy carriers. Here, the realization of Anderson localization of phonons in a random 3D elastic network of graphene is reported. It is shown that thermal conductivity in a cellular graphene aerogel can be drastically reduced to 0.9 mW m-1 K-1 by the application of compressive strain while keeping a high metal-like electrical conductivity of 120 S m-1 and ampacity of 0.9 A. The experiments reveal that the strain can cause phonon localization over a broad compression range. The remaining heat flow in the material is dominated by charge transport. Conversely, electrical conductivity exhibits a gradual increase with increasing compressive strain, opposite to the thermal conductivity. These results imply that strain engineering provides the ability to independently tune charge and heat transport, establishing a new paradigm for controlling phonon and charge conduction in solids. This approach will enable the development of a new type of high-performance insulation solutions and thermally superinsulating materials with metal-like electrical conductivity. This work demonstrates hierarchical cellular graphene aerogels with superior thermal insulation properties and high electrical conductivity. The thermal conductivity of the aerogels is highly tunable by strain, resulting in the complete inhibition of the phonon heat transport at high strains, a phenomenon known as Anderson localization of phonons, yet providing excellent electric current carrying capacity. image

Sustainable energy harvesting is the need of the hour, and piezoelectric nanogenerators (PENG) offer tremendous opportunities in this field. We have investigated the mechanical energy harvesting applications of a nanocomposite comprising a low-dimensional halide perovskite (HP) and polyvinylidene fluoride (PVDF). Cs4PbBr6 HP was prepared using mechanochemical synthesis, and a composite film of PVDF with Cs4PbBr6 was utilized as the PENG to scavenge energy from day-to-day human biomechanical activities. The properties and output results of the fabricated devices with changing weight percentages (wt.%) of HP used as nanofillers in the PVDF matrix are compared to those of a pure PVDF. A 6 wt.% concentration of Cs4PbBr6 induces the composite's electroactive β-phase to around 87%. The polarization hysteresis (P-E) loop measurement reveals a remanent polarization of 0.31 µC/cm2. The measured piezoelectric coefficient (d33) is about ⁓12 pm/V, and the piezoelectric amplitude is ∼500 pm for the optimized PENG at the maximum applied bias of ±30 V. The device shows an instantaneous output voltage of ⁓90 V, a current of ⁓3.8 μA, and power of ⁓80 µW across a 5 MΩ resistor. Simple daily human activities like finger tapping, leg-toe pressing, finger bending, heel pressing, and walking are used to generate output voltages using PENG with prospective usage in powering portable electronic devices. The output AC voltage of the device is employed to charge a 10 µF capacitor up to ∼3.5 V and shows exceptional stability over long cycles. The output power generated is adequate for lighting commercial LEDs without any external input. The Cs4PbBr6/PVDF composite films thus demonstrate significant potential to be deployed as high-performance, portable, and wearable mechanical energy harvesting devices.

AbstractThe increasing utilization of terahertz (THz) bandwidth in both industrial and private sectors highlights the significance of efficient terahertz shielding and absorption devices. These devices play a crucial role in safeguarding electronic components from disruptive effects and rendering objects less detectable by radar systems. However, the limited availability of materials and devices hinders progress in this field. In this study, a strain engineering route is presented for the active control of terahertz shielding and absorption properties in 3D graphene through the application of mechanical strain. A straintronic modulator based on 3D graphene is demonstrated, capable of modulating absorption and reflection of THz radiation in real‐time over a wide range of 0.1–3 THz. The modulator can be tuned to exhibit either shielding capability with a specific shielding effectiveness of 0.3 × 105 dB cm2 g−1 or stealth characteristics with an average reflection loss of 25 dB and 99.4% absorption. These findings open new avenues for leveraging 2D materials in their 3D porous form, where strain‐induced changes in interlayer interactions enable control over the properties of these materials. This discovery unveils vast unexplored physical phenomena with immense potential for advanced THz imaging, radar, and electromagnetic applications.

Supercapacitors are crucial in renewable energy integration, satellite power systems, and rapid power delivery applications for mitigating voltage fluctuations and storing excess energy. Aqueous electrolytes offer a promising solution for low-cost and safe supercapacitors. However, they still face limitations in cycle life and wide-temperature range performance. Here, we present a symmetric supercapacitor utilizing activated carbon electrodes and a "water-in-salt" electrolyte (WiSE) based on lithium perchlorate. The WiSE electrolyte exhibits an expanded electrochemical stability window, endowing the aqueous supercapacitor with remarkable stability and long cycle life of over 100,000 cycles at 500 mA g-1 with more than 91 % capacity retention. Moreover, the supercapacitor demonstrates good rate capability and wide temperature operability ranging from -20 to 80 °C. The use of high concentrations of salt in the aqueous electrolyte contributes not only to the enhancement of supercapacitor performance and cycle life but also to the temperature stability range, enabling all-season operability.

Organic-inorganic halide perovskites (OIHPs) have attracted tremendous attention from researchers because of their diverse applications in optoelectronics, sensing, catalysis, memory, photodetectors, and medical diagnostics. The presence of inherent ferroelectricity in these perovskite materials facilitates the separation of photogenerated electron-hole pairs. Here, we report a large phosphonium cation-based methyl triphenyl phosphonium lead bromide (MTPLB) perovskite-like semiconductor with a direct band gap of 3.49 eV, which shows ferroelectricity in both nanoscale and bulk at room temperature. The material exhibits a phase transition temperature of 477 K, a polarization saturation of 0.26 mu C/cm2, and a d 33 of 5.2 pC/N. MTPLB displays a robust piezoelectric response, as confirmed via advanced piezoresponse force microscopy (PFM). Further, we have fabricated nanogenerator devices with varying ratios of MTPLB and poly(vinylidene fluoride) (PVDF) composites for mechanical and biomechanical energy harvesting. We report an enhanced piezoresponse in all devices with the best response in the device with a 2% MTPLB loading in the PVDF matrix due to the triggering of the electroactive phases in PVDF. The improved output response, operational durability, and flexibility of the composite-based devices underscore their potential for advanced technological applications in electronics, actuators, sensors, and mechanical energy-harvesting processes.

We use terahertz and multi-terahertz spectroscopy to investigate optical properties of three-dimensional (3D) graphene across a wide frequency range of 0.15-10 THz. We explore the electromagnetic shielding, stealth, and absorber capabilities of 3D graphene samples annealed at various temperatures up to 1300 degrees C. We show that the tradeoff between the transmitted, absorbed and reflected power of the materials can be controlled by the annealing temperature through a fine broadband tuning of the refractive and absorptive indices of the material. This ultralight system (with a specific mass of similar to 7 mg cm(-3)) is capable of acting as a stealth element (non-annealed sample, R < 1%), THz absorber (annealing at 750 C, A > 85%) or a shielding coating (annealing at 1300 degrees C, T < 0.1%) within an ultrabroadband range of 0.2-7 THz. All these properties can be combined by stacking these materials on top of each other, which provides unique opportunities for THz applications.

Lead-free halide perovskites have gained immense popularity in photovoltaic and energy harvesting applications because of their excellent optical and electrical attributes with minimal toxicity. We synthesized composite films of lead-free Cs3Bi2Br9 perovskite embedded in the polyvinylidene fluoride (PVDF) matrix and have investigated their piezoelectric energy harvesting. Five PVDF@Cs3Bi2Br9 composite films were fabricated with varying wt% of the perovskite in the PVDF. The composite with a 4 wt% of the perovskite shows 85% activation of the electroactive β-phase of PVDF. Additionally, this composite exhibits a maximum polarisation of ∼0.1 μC cm-2 and the best energy storage density of ∼0.8 mJ cm-3 at an applied field of ∼16 kV cm-1 among all the synthesized composites. A nanogenerator fabricated using 4 wt% loading in the composite film produced an instantaneous output voltage of ∼40 V, an instantaneous current of ∼4.1 μA, and a power density of ∼17.8 μW cm-2 across 10 MΩ resistance when repeatedly hammered by the human hand. The nanogenerator is further employed to light up several LEDs and to charge capacitors with a small active area demonstrating significant promise for prospective wearables and portable devices and paving the way for high-performance nanogenerators using lead-free halide perovskites. Density functional theory calculations were performed to understand the interaction of the electroactive phase of the PVDF with different perovskite surface terminations to unravel the various interaction mechanisms and their ensuing charge transfer properties.

The production of highly stable, defect-free, and electrically conducting 3D graphene structures from graphene oxide precursors is challenging. This is because graphene oxide is a metastable material whose structure and chemistry evolve due to aging. Aging changes the relative composition of oxygen functional groups attached to the graphene oxide and negatively impacts the fabrication and properties of reduced graphene oxide. Here, we report a universal strategy to reverse the aging of graphene oxide precursors using oxygen plasma treatment. This treatment decreases the size of graphene oxide flakes and restores negative zeta potential and suspension stability in water, enabling the fabrication of compact and mechanically stable graphene aerogels using hydrothermal synthesis. Moreover, we employ high-temperature annealing to remove oxygen-containing functionalities and repair the lattice defects in reduced graphene oxide. This method allows obtaining highly electrically conducting graphene aerogels with electrical conductivity of 390 S/m and low defect density. The role of carboxyl, hydroxyl, epoxide, and ketonic oxygen species is thoroughly investigated using X-ray photoelectron and Raman spectroscopies. Our study provides unique insight into the chemical transformations occurring during the aging and thermal reduction of graphene oxide from room temperature up to 2700 °C.

Terahertz steady-state and time-resolved conductivity and permittivity spectra were measured in 3D graphene networks assembled in free-standing covalently cross-linked graphene aerogels. Investigation of a transition between reduced-graphene oxide and graphene controlled by means of high-temperature annealing allowed us to elucidate the role of defects in the charge carrier transport in the materials. The THz spectra reveal increasing conductivity and decreasing permittivity with frequency. This contrasts with the Drude- or Lorentz-like conductivity typically observed in various 2D graphene samples, suggesting a significant contribution of a relaxational mechanism to the conductivity in 3D graphene percolated networks. The charge transport in the graphene aerogels exhibits an interplay between the carrier hopping among localized states and a Drude contribution of conduction-band carriers. Upon photoexcitation, carriers are injected into the conduction band and their dynamics reveals picosecond lifetime and femtosecond dephasing time. Our findings provide important insight into the charge transport in complex graphene structures.

Materials with high spin–orbit coupling (SOC) are a prerequisite for the realization of spin–orbit torque-based magnetic memories. Transition metal dichalcogenides (TMDs) are an apt choice for such applications due to their high SOC strength. In this work, we have investigated the spin pumping phenomenon at the interface between thin tungsten disulphide (WS2) films and Co2FeAl (CFA) Heusler alloy films by performing ferromagnetic resonance (FMR) measurements on WS2/CFA heterostructures capped with the 4 nm thin Al film. While Raman spectroscopy conclusively proves the number of monolayers in the WS2 films, atomic force microscopy and x-ray reflectivity measurements were used to quantify the smoothness of the grown interfaces (<0.4 nm) as well as the individual layer thicknesses in the heterostructure stacks. Here, we vary the WS2 layer numbers and CFA thicknesses to quantify the spin pumping parameters such as spin mixing conductance, and spin transparency. FMR measurements revealed that damping enhancement reached ∼41% with a monolayer of WS2. Interfacial effective spin mixing conductance and spin transparency of the WS2/CFA interface are found to be 7.47 ± 0.97 nm−2 and 73.35 ± 9.52%, respectively. Thus, high-quality TMDs can be used as efficient materials for magnetic memory device applications.

We report on the facile emulsion approach to synthesize zero-dimensional inorganic Cs4PbBr6 samples and explore their structural and luminescence properties. Crystallinity and morphological characterizations are performed, and the band gap is evaluated to be around 2.29 eV. The photoluminescence spectra of Cs4PbBr6 perovskite exhibit peaks in the green region. Cathodoluminescence (CL) spectroscopy was executed to investigate the emission properties of the sample as well as its structural integrity under exposure to high-energy electron beams. The time-dependent CL study under exposure to electron beam reveals no apparent degradation even after 60 min and establishes the stability of the material.

We report a high voltage Zn–graphite dual-ion battery based on Zn(ClO 4 ) 2 water-in-salt (WiS) electrolyte with a wide electrochemical window of 2.80 V and high oxidative stability of 2.60 V vs. Zn/Zn 2+ .

Anion intercalated graphite has achieved tremendous attention for the application as cathode materials in dual-ion batteries due to their high working potentials, reversibility, and low cost. However, the process of anion intercalation into graphite requires high oxidative stability of the electrolytes and high reaction potentials above 1.4 V vs. Ag/AgCl (4.5 V vs. Li (+)). Reaching such high potentials is difficult with conventional aqueous electrolytes due to their limited electrochemical window. Here, we demonstrate a highly concentrated "water-in-salt " electrolyte of aluminum perchlorate that demonstrates a wide electrochemical stability window of 4.0 V. The "water-in-salt " electrolyte suppresses the dissociation of water at high potentials, facilitating a stable and reversible perchlorate (ClO4-) anion intercalation into the graphite with a Coulombic efficiency of over 95% for more than 2000 cycles. The structural and chemical changes of the anion-intercalated graphite are studied by Operando Raman, Operando X-ray diffraction, and X-ray photoelectron spectroscopy. Our study provides an insight into ClO4- anion intercalation into graphite in the supersaturated aluminum perchlorate "water-in-salt " electrolyte, demonstrating a suitable platform for future high-voltage aqueous energy storage systems. (c) 2021 Elsevier Ltd. All rights reserved.