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Three complementary methods are used for studying the resulting changes in the CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) microstructure. Soft x-ray resonant magnetic scattering and transmission electron microscopy are used for showing a roughening of the magnetic interfaces of the MTJ free layer and also the changes in the CoFeB and MgO to a lattice-matched polycrystalline form.

Annealing is necessary to achieve giant tunneling magnetoresistance (TMR) values in sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). In this study three complementary techniques were used to study the resulting changes in junction microstructure. The as-deposited TMR was modest, 5%, but rose to 101% after annealing at 325 °C for 1 h, corresponding to the tunneling spin polarization rising from 16% to 58%. Soft x-ray resonant magnetic scattering showed a roughening of the magnetic interfaces of the MTJ free layer, confirmed by transmission electron microscopy, which also showed the changes in the CoFeB and MgO to a lattice-matched polycrystalline form. [ABSTRACT FROM AUTHOR]

Understanding the underlying principles of contact electrification is critical for more efficient triboelectric nanogenerator (TENG) development. Herein, we use ReaxFF molecular dynamics simulations in conjunction with a charge equilibration method to investigate the contact electrification mechanism in polyisoprene (PI), a natural rubber polymer, when it comes into contact with copper (Cu) and polytetrafluoroethylene (PTFE). The simulations reveal that the charge transfer directions in the PI/Cu and PI/PTFE contact models are opposite, and the amount of charge transfer in the former is substantially less than that in the latter, which are consistent with our TENG measurements. Contact electrification is revealed to be a spontaneous process that occurs to lower electrostatic energy, and the electrostatic energy released during contact electrification of PI/PTFE is greater than that of PI/Cu, which can be correlated with the relative strength of triboelectric charging observed for the two systems. A compression simulation of the PI/Cu contact model reveals that the quantity of charge transfer grows exponentially as compressive strain increases. Despite increasing the total energy of the system due to densification and distortion of the polymer structure, the applied deformation results in an energetically more stable electrostatic arrangement. We also find that the incorporation of a carbonaceous material into a polyisoprene matrix causes a faster increase in the amount of charge transfer with compressive strain, which is governed by a steeper electrostatic energy profile. This study provides an alternative perspective on the contact electrification mechanism, which could be beneficial for the development of energy harvesting devices., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

In this study, we investigated the humidity sensing properties of TiO 2 -based ceramics doped with tantalum pentoxide (Ta 2 O 5 ) and indium tin oxide (ITO). Pure TiO 2 , 1%Ta-doped TiO 2 (1%TTO), 1%ITO-doped TiO 2 (1%ISTO), and 1%(Ta 2 O 5  + ITO) co-doped TiO 2 (1%ISTTO) ceramic samples were obtained by sintering at 1200 °C for 3 h. The rutile phase was observed in all samples. The lattice parameters of the single and co-doped samples were larger than those of pure TiO 2 , confirming the substitution of dopants. Porosity was observed in all ceramics. The mean grain sizes of all doped samples were significantly reduced compared to undoped TiO 2 . A homogeneous element dispersion was observed in the 1%TTO and 1%ISTTO ceramics, while segregation particles of related In-rich elements was observed in the 1%ISTO ceramic. Giant dielectric properties were not achieved in any samples due to the porosity. Nevertheless, excluding the undoped TiO 2 , the dielectric properties of all porous ceramics varied significantly with changes in humidity. The 1%ISTTO ceramic demonstrated superior humidity sensing properties, including a low maximum hysteresis error of 3.6% at 10 2  Hz. In contrast, the 1% TTO and 1% ISTO ceramics showed higher maximum hysteresis errors of 7.2% and 19.8%, respectively. Notably, the response and recovery times were 7.05 ± 0.18 and 2.48 ± 0.39 min, respectively, with good repeatability. This improvement is likely due to the synergistic effect of oxygen vacancies and Ta Ti · defects on the surface, enhancing the humidity sensing properties of the 1% ISTTO ceramic, coupled with its optimal microstructure due to its lowest porosity and grain size., (© 2024. The Author(s).)

Carbon nanostructures derived from human hair biowaste are incorporated into polyvinylidene fluoride (PVDF) polymer to enhance the energy conversion performance of a triboelectric nanogenerator (TENG). The PVDF filled with activated carbon nanomaterial from human hair (AC-HH) exhibits improved surface charge density and photoinduced charge generation. These remarkable properties are attributed to the presence of graphene-like nanostructures in AC-HH, contributing to the augmented performance of PVDF@AC-HH TENG. The correlation of surface morphologies, surface charge potential, charge capacitance properties, and TENG electrical output of the PVDF composites at various AC-HH loading is studied and discussed. Applications of the PVDF@AC-HH TENG as a power source for micro/nanoelectronics and a movement sensor for detecting finger gestures are also demonstrated. The photoresponse property of the fabricated TENG is demonstrated and analyzed in-depth. The analysis indicates that the photoinduced charge carriers originate from the conductive reduced graphene oxide (rGO), contributing to the enhanced surface charge density of the PVDF composite film. This research introduces a novel approach to enhancing TENG performance through the utilization of carbon nanostructures derived from human biowaste. The findings of this work are crucial for the development of innovative energy-harvesting technology with multifunctionality, including power generation, motion detection, and photoresponse capabilities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Cellulose nanocrystal (CNC) is an abundant biopolymer possessing high strength and biodegradability. In the present work, the extraction of CNCs from Napier grass stems was carried out. The CNCs were subsequently modified by maleic anhydride, called M-CNC, before being incorporated into the epoxidized natural rubber (ENR). The compounds were later cured by ultraviolet (UV) irradiation under various conditions. The obtained optimum condition was then used to fabricate the biocomposites filled with various CNC and M-CNC loadings for triboelectric nanogenerator (TENG) performance measurements. Output voltage and current increased continuously with increasing filler loading. Regardless of the filler type, an increase in filler loading enhanced TENG output. ENR/M-CNC exhibited a superior TENG output to ENR/CNC due to the greater electron transfer capability of the biocomposites, as proven by the reduction in the ionization potential (IP) value obtained from the quantum calculation. In this study, ENR/M-CNC5 exhibited the maximum output voltage (80.3 V), current (7.4 μA), and power density (1.32 W/m 2 ) at a load resistance of 9 MΩ., Competing Interests: Declaration of competing interest There is no conflict of interests to declare., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Green and sustainable power sources for next-generation electronics are being developed. A cellulose paper-based triboelectric nanogenerator (TENG) was fabricated to harness mechanical energy and convert it into electricity. This work proposes a novel approach to modify cellulose paper with natural dyes, including chlorophyll from spinach, anthocyanin from red cabbage, and curcumin from turmeric, to enhance the power output of a TENG. All the natural dyes are found to effectively improve the energy conversion performance of a cellulose paper-based TENG due to their photogenerated charges. The highest power density of 3.3 W/m 2 is achieved from the cellulose paper-based TENG modified with chlorophyll, which is higher than those modified with anthocyanin and curcumin, respectively. The superior performance is attributed not only to the photosensitizer properties but also the molecular structure of the dye that promotes the electron-donating properties of cellulose.

Increasing energy demands and growing environmental concerns regarding the consumption of fossil fuels are important motivations for the development of clean and sustainable energy sources. A triboelectric nanogenerator (TENG) is a promising energy technology that harnesses mechanical energy from the ambient environment by converting it into electrical energy. In this work, the enhancement of the energy conversion performance of a natural rubber (NR)-based TENG has been proposed by using modified activated carbon (AC). The effect of surface modification techniques, including acid treatments and plasma treatment for AC material on TENG performance, are investigated. The TENG fabricated from the NR incorporated with the modified AC using N 2 plasma showed superior electrical output performance, which was attributed to the modification by N 2 plasma introducing changes in the surface chemistry of AC, leading to the improved dielectric property of the NR-AC composite, which contributes to the enhanced triboelectric charge density. The highest power density of 2.65 mW/m 2 was obtained from the NR-AC (N 2 plasma-treated) TENG. This research provides a key insight into the modification of AC for the development of TENG with high energy conversion performance that could be useful for other future applications such as PM2.5 removal or CO 2 capture.

CaCu 3 -x Ni x Ti 4 O 12 /CaTiO 3 ceramic composites were fabricated using initial Ca 2 Cu 2- x Ni x Ti 4 O 12 compositions ( x  = 0, 0.05, 0.10, and 0.20) to improve the dielectric properties (DPs) of the CaCu 3 Ti 4 O 12 ceramics. CaCu 3 Ti 4 O 12 and CaTiO 3 phases were confirmed. Microstructural analysis and Rietveld refinement showed that the Ni 2+ dopant might substitute the Cu 2+ sites of the CaCu 3 Ti 4 O 12 structure. The average grain sizes of CaCu 3 Ti 4 O 12 (4.1-5.6 μm) and CaTiO 3 (1.2-1.4 μm) changed slightly with the Ni 2+ doping concentration. The best DPs were obtained for the CaCu 3 -x Ni x Ti 4 O 12 /CaTiO 3 with x  = 0.2. The loss tangent was significantly reduced by an order of magnitude compared to that of the undoped composite, from tanδ∼0.161 to ∼0.016 at 1 kHz, while the dielectric permittivity slightly decreased from ε'∼5.7 × 10 3 to ∼4.0 × 10 3 . Furthermore, the temperature dependence of ε' could be improved by doping with Ni 2+ . The improved DPs were caused by the enhanced electrical responses of the internal interfaces, which resulted in enhanced non-Ohmic properties. The largest nonlinear coefficient (α∼7.6) was obtained for the CaCu 3 -x Ni x Ti 4 O 12 /CaTiO 3 with x  = 0.05. Impedance spectroscopy showed that the CaCu 3 -x Ni x Ti 4 O 12 /CaTiO 3 composites consisted of semiconducting and insulating components. The DPs of CaCu 3 -x Ni x Ti 4 O 12 /CaTiO 3 were explained based on the space-charge polarization at the active-interfaces., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (© 2023 The Authors.)

The triboelectric nanogenerator (TENG) is a newly developed energy harvesting technology that can convert mechanical energy into electricity. The TENG has received extensive attention due to its potential applications in diverse fields. In this work, a natural based triboelectric material has been developed from a natural rubber (NR) filled with cellulose fiber (CF) and Ag nanoparticles. Ag nanoparticles are incorporated into cellulose fiber (CF@Ag) and are used as a hybrid filler material for the NR composite to enhance the energy conversion efficiency of TENG. The presence of Ag nanoparticles in the NR-CF@Ag composite is found to improve the electrical power output of the TENG by promoting the electron donating ability of the cellulose filler, resulting in the higher positive tribo-polarity of NR. The NR-CF@Ag TENG shows significant improvement in the output power up to five folds compared to the pristine NR TENG. The findings of this work show a great potential for the development of a biodegradable and sustainable power source by converting mechanical energy into electricity.

An environmentally friendly triboelectric nanogenerator (TENG) is fabricated from a natural rubber (NR)-Ag nanocomposite for harvesting mechanical energy from human motions. Ag nanoparticles (AgNPs) synthesized with two different capping agents are added to NR polymer for improving dielectric constant that contributes to the enhancement of TENG performance. Dielectric constant is modulated via interfacial polarization between AgNPs and NR matrix. The effects of AgNP concentration, particle size and dispersion in NR composite, and type of capping agents on dielectric properties and electrical output of the NR composite TENG are elucidated. It is found that, apart from AgNPs content in the NR-Ag nanocomposite, cations of CTAB capping agent play important roles not only on the dispersion of AgNPs in NR matrix but also on intensifying tribopositive charges in the NR composite. In addition, the application of the NR-Ag TENG as a shoe insole is also demonstrated to convert human footsteps into electricity to power small electronic devices. Furthermore, with the presence of Ag nanoparticles, the fabricated shoe insole also exhibits antibacterial property against Staphylococcus aureus that causes foot odor.

Cellulose-based materials have recently drawn much interest due to their sustainability, biodegradability, biocompatibility, and low cost. In this present work, cellulose fiber paper (CFP) was fabricated from sugarcane leaves and used as a friction material for a triboelectric nanogenerator (TENG). Fe 3 O 4 was incorporated to CFP triboelectric material to increase the dielectric constant of CFP for boosting power generation of TENG. The Fe 3 O 4 filled CFP was synthesized using a facile one-pot co-precipitation technique. The effect of Fe 3 O 4 content in CFP on dielectric property and TENG performance was investigated and optimized. The CFP filled with Fe 3 O 4 nanoparticles exhibited the improved dielectric constant and possessed a superior TENG performance than pristine CF. The highest power density of 1.9 W/m 2 was achieved, which was able to charge commercial capacitors serving as a power source for small electronic devices.

The growing demand for energy and environmental concern are crucial driving forces for the development of green and sustainable energy. The triboelectric nanogenerator (TENG) has emerged as a promising solution for harvesting mechanical energy from the environment. In this research, a natural rubber (NR)-based TENG has been developed with an enhanced power output from the incorporation of cellulose nanofibers (CNF) and activated carbon (AC) nanoparticles. The highest voltage output of 137 V, a current of 12.1 µA, and power density of 2.74 W/m 2 were achieved from the fabricated NR-CNF-AC TENG. This is attributed to the synergistic effect of the electron-donating properties of cellulose material and the large specific surface area of AC materials. The enhancement of TENG performance paves the way for the application of natural-based materials to convert mechanical energy into electricity, as a clean and sustainable energy source.

The effects of the sintering conditions on the phase compositions, microstructure, electrical properties, and dielectric responses of TiO 2 -excessive Na 1/2 Y 1/2 Cu 3 Ti 4.1 O 12 ceramics prepared by a solid-state reaction method were investigated. A pure phase of the Na 1/2 Y 1/2 Cu 3 Ti 4.1 O 12 ceramic was achieved in all sintered ceramics. The mean grain size slightly increased with increasing sintering time (from 1 to 15 h after sintering at 1070 °C) and sintering temperature from 1070 to 1090 °C for 5 h. The primary elements were dispersed in the microstructure. Low dielectric loss tangents (tan δ~0.018-0.022) were obtained. Moreover, the dielectric constant increased from ε'~5396 to 25,565 upon changing the sintering conditions. The lowest tan δ of 0.009 at 1 kHz was obtained. The electrical responses of the semiconducting grain and insulating grain boundary were studied using impedance and admittance spectroscopies. The breakdown voltage and nonlinear coefficient decreased significantly as the sintering temperature and time increased. The presence of Cu + , Cu 3+ , and Ti 3+ was examined using X-ray photoelectron spectroscopy, confirming the formation of semiconducting grains. The dielectric and electrical properties were described using Maxwell-Wagner relaxation, based on the internal barrier layer capacitor model.

The triboelectric nanogenerator (TENG) has emerged as a novel energy technology that converts mechanical energy from surrounding environments to electricity. The TENG fabricated from environmentally friendly materials would encourage the development of next-generation energy technologies that are green and sustainable. In the present work, a green triboelectric material has been fabricated from natural rubber (NR) filled with activated carbon (AC) derived from human hair. It is found that the TENG fabricated from an NR-AC composite as a tribopositive material and a poly-tetrafluoroethylene (PTFE) sheet as a tribonegative one generates the highest peak-to-peak output voltage of 89.6 V, highest peak-to-peak output current of 6.9 µA, and can deliver the maximum power density of 242 mW/m 2 . The finding of this work presents a potential solution for the development of a green and sustainable energy source.

In this work, the colossal dielectric properties and Maxwell-Wagner relaxation of TiO 2 -rich Na 1/2 Y 1/2 Cu 3 Ti 4+ x O 12 ( x = 0-0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na 1/2 Y 1/2 Cu 3 Ti 4 O 12 is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance ( R gb ). The colossal permittivities of ε ' ~ 0.7-1.4 × 10 4 with slightly dependent on frequency in the frequency range of 10 2 -10 6 Hz are obtained in the TiO 2 -rich Na 1/2 Y 1/2 Cu 3 Ti 4+ x O 12 ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016-0.020 at 1 kHz due to the increased R gb . The semiconducting grain resistance ( R g ) of the Na 1/2 Y 1/2 Cu 3 Ti 4+ x O 12 ceramics increases with increasing x , corresponding to the decrease in Cu + /Cu 2+ ratio. The nonlinear electrical properties of the TiO 2 -rich Na 1/2 Y 1/2 Cu 3 Ti 4+ x O 12 ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO 2 -rich Na 1/2 Y 1/2 Cu 3 Ti 4+ x O 12 ceramics are explained by the Maxwell-Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.

In this research, natural rubber (NR)-TiO 2 nanocomposites were developed for triboelectric nanogenerator (TENG) application to harvest mechanical energy into electrical energy. Rutile TiO 2 nanoparticles were used as fillers in NR material to improve dielectric properties so as to enhance the energy conversion performance of the NR composite TENG. The effect of filler concentration on TENG performance of the NR-TiO 2 composites was investigated. In addition, ball-milling method was employed to reduce the agglomeration of TiO 2 nanoparticles in order to improve their dispersion in the NR film. It was found that the TENG performance was significantly enhanced due to the increased dielectric constant of the NR-TiO 2 composite films fabricated from the ball-milled TiO 2 . The TENG, fabricated from the NR-TiO 2 composite using 24 h ball-milled TiO 2 at 0.5%wt, delivered the highest power density of 237 mW/m 2 , which was almost four times higher than that of pristine NR TENG. Furthermore, the applications of the fabricated NR-TiO 2 TENG as a power source to operate portable electronics devices were also demonstrated.

Flexible dielectric polymer composites have been of great interest as embedded capacitor materials in the electronic industry. However, a polymer composite has a low relative dielectric permittivity (ε' < 100), while its dielectric loss tangent is generally large (tanδ > 0.1). In this study, we fabricate a novel, high-permittivity polymer nanocomposite system with a low tanδ. The nanocomposite system comprises poly(vinylidene fluoride) (PVDF) co-filled with Au nanoparticles and semiconducting TiO 2 nanorods (TNRs) that contain Ti 3+ ions. To homogeneously disperse the conductive Au phase, the TNR surface was decorated with Au-NPs ~10-20 nm in size (Au-TNRs) using a modified Turkevich method. The polar β-PVDF phase was enhanced by the incorporation of the Au nanoparticles, partially contributing to the enhanced ε' value. The introduction of the Au-TNRs in the PVDF matrix provided three-phase Au-TNR/PVDF nanocomposites with excellent dielectric properties (i.e., high ε' ≈ 157 and low tanδ ≈ 0.05 at 1.8 vol% of Au and 47.4 vol% of TNRs). The ε' of the three-phase Au-TNR/PVDF composite is ~2.4-times higher than that of the two-phase TNR/PVDF composite, clearly highlighting the primary contribution of the Au nanoparticles at similar filler loadings. The volume fraction dependence of ε' is in close agreement with the effective medium percolation theory model. The significant enhancement in ε' was primarily caused by interfacial polarization at the PVDF-conducting Au nanoparticle and PVDF-semiconducting TNR interfaces, as well as by the induced β-PVDF phase. A low tanδ was achieved due to the inhibited conducting pathway formed by direct Au nanoparticle contact.

The enhanced dielectric permittivity (ε') while retaining a low loss tangent (tanδ) in silver nanoparticle-(In 1/2 Nb 1/2 ) 0.1 Ti 0.9 O 2 /poly(vinylidene fluoride) (Ag-INTO/PVDF) composites with different volume fractions of a filler ( f Ag-INTO ) was investigated. The hybrid particles were fabricated by coating Ag nanoparticles onto the surface of INTO particles, as confirmed by X-ray diffraction. The ε' of the Ag-INTO/PVDF composites could be significantly enhanced to ~86 at 1 kHz with a low tanδ of ~0.044. The enhanced ε' value was approximately >8-fold higher than that of the pure PVDF polymer for the composite with f Ag-INTO = 0.5. Furthermore, ε' was nearly independent of frequency in the range of 10 2 -10 6 Hz. Therefore, filling Ag-INTO hybrid particles into a PVDF matrix is an effective way to increase ε' while retaining a low tanδ of polymer composites. The effective medium percolation theory model can be used to fit the experimental ε' values with various f Ag-INTO values. The greatly increased ε' primarily originated from interfacial polarization at the conducting Ag nanoparticle-PVDF and Ag-INTO interfaces, and it was partially contributed by the high ε' of INTO particles. A low tanδ was obtained because the formation of the conducting network in the polymer was inhibited by preventing the direct contact of Ag nanoparticles.

The energy conversion performance of the triboelectric nanogenerator (TENG) is a function of triboelectric charges which depend on the intrinsic properties of materials to hold charges or the dielectric properties of triboelectric materials. In this work, Ag nanoparticles were synthesized and used to incorporate into natural rubber (NR) in order to enhance the dielectric constant for enhancing the electrical output of TENG. It was found that the size of Ag nanoparticles was reduced with the increasing CTAB concentration. Furthermore, the CTAB surfactant helped the dispersion of metallic Ag nanoparticles in the NR-insulating matrix, which promoted interfacial polarization that affected the dielectric properties of the NR composite. Ag nanoparticle-incorporated NR films exhibited an improved dielectric constant of up to almost 40% and an enhanced TENG performance that generated the highest power density of 262.4 mW/m 2 .

Cost-effective reduced graphene oxide sheets decorated with magnetite (Fe 3 O 4 ) nanoparticles (Fe 3 O 4 -rGO) are successfully fabricated via a chemical vapor deposition (CVD) technique using iron (III) nitrate as an iron precursor, with glucose and CH 4 as carbon sources, and NaCl as a supporting material. TEM analysis and Raman spectroscopy reveal hierarchical nanostructures of reduced graphene oxide (rGO) decorated with Fe 3 O 4 nanoparticles. Fe K-edge x-ray absorption near edge structure (XANES) spectra confirm that the nanoparticles are Fe 3 O 4 with a slight shift of the pre-edge peak position toward higher energy suggesting that the fabricated Fe 3 O 4 nanoparticles have a higher average oxidation state than that of a standard Fe 3 O 4 compound. The hierarchical Fe 3 O 4 -rGO is found to exhibit an excellent catalytic activity toward the reduction of triiodide to iodide in a dye-sensitized solar cell (DSSC) and can deliver a solar cell efficiency of 6.65%, which is superior to a Pt-based DSSC (6.37%).

In this work, a new approach to modifying poly(dimethylsiloxane) (PDMS) as a negative triboelectric material using graphene oxide (GO) and a sodium dodecyl sulfate (SDS) surfactant was reported. A porous PDMS@GO@SDS composite triboelectric nanogenerator (TENG) could deliver an output voltage and current of up to 438 V and 11 μA/cm 2 , respectively. These values were 3-fold higher than those of the flat PDMS. The superior performance is attributed to the intensified negative charges on PDMS from the oxygen functional groups of GO and anionic head groups of the SDS molecules. The outstanding performance and straightforward, low-cost fabrication process of the PDMS@GO@SDS TENG would be beneficial for the further development of powerful NGs integrated into wearable electronics and self-charging power cells.