Enhanced resonance frequency in Co2FeAl thin film with different thicknesses grown on flexible graphene substrate

The flexible materials exhibit more favorable properties than most rigid substrates in flexibility,weight saving,mechanical reliability,and excellent environmental toughness.Particularly,flexible graphene film with unique mechanical properties was extensively explored in high frequency devices.Herein,we report the characteristics of structure and magnetic properties at high frequency of Co2FeAl thin film with different thicknesses grown on flexible graphene substrate at room temperature.The exciting finding for the columnar structure of Co2FeAl thin film lays the foundation for excellent high frequency property of Co2FeAl/flexible graphene structure.In-plane magnetic anisotropy field varying with increasing thickness of Co2FeAl thin film can be obtained by measurement of ferromagnetic resonance,which can be ascribed to the enhancement of crystallinity and the increase of grain size.Meanwhile,the resonance frequency which can be achieved by the measurement of vector network analyzer with the microstrip method increases with increasing thickness of Co2FeAl thin film.Moreover,in our case with graphene film,the resonance magnetic field is quite stable though folded for twenty cycles,which demonstrates that good flexibility of graphene film and the stability of high frequency magnetic property of Co2FeAl thin film grown on flexible graphene substrate.These results are promising for the design of microwave devices and wireless communication equipment.

Direct fabrication of flexible tensile sensors enabled by polariton energy transfer based on graphene nanosheet films

A fundamental problem in the direct manufacturing of flexible devices is the low melting temperature of flexible substrates,which hinders the development of flexible electronics.Proposed here is an electron-cyclotron-resonance sputtering system that can batch-fabricate devices directly on flexible substrates under a low temperature by virtue of the polariton energy transfer between the plasma and the material.Flexible graphene nanosheet-embedded carbon(F-GNEC)films are manufactured directly on polyimide,polyethylene terephthalate,and polydimethylsiloxane,and how the substrate bias(electron energy),microwave power(plasma flux and energy),and magnetic field(electron flux)affect the nanostructure of the F-GNEC films is investigated,indicating that electron energy and flux contribute to the formation of standing graphene nanosheets in the film.The films have good uniformity of distribution in a large size(17 mm×17 mm),and tensile and angle sensors with a high gauge factor(0.92)and fast response(50 ms)for a machine hand are obtained by virtue of the unique nanostructure of the F-GNEC film.This work sheds light on the quantum manufacturing of carbon sensors and its applications for intelligent machine hands and virtual-reality technology.

Flexible Large-Area Graphene Films of 50-600 nm Thickness with High Carrier Mobility

Bulk graphene nanofilms feature fast electronic and phonon transport in combination with strong light-matter interaction and thus have great potential for versatile applications,spanning from photonic,electronic,and optoelectronic devices to charge-stripping and electromagnetic shielding,etc.However,large-area flexible close-stacked graphene nanofilms with a wide thickness range have yet to be reported.Here,we report a polyacrylonitrile-assisted’substrate replacement’strategy to fabricate large-area free-standing graphene oxide/polyacrylonitrile nanofilms(lateral size~20 cm).Linear polyacrylonitrile chains-derived nanochannels promote the escape of gases and enable macro-assembled graphene nanofilms(nMAGs)of 50-600 nm thickness following heat treatment at 3,000℃.The uniform nMAGs exhibit 802-1,540 cm^(2)V-1s-1carrier mobility,4.3-4.7 ps carrier lifetime,and>1,581 W m^(-1)K^(-1)thermal conductivity(n MAG-assembled 10μm-thick films,mMAGs).nMAGs are highly flexible and show no structure damage even after 1.0×10^(5)cycles of folding-unfolding.Furthermore,n MAGs broaden the detection region of graphene/silicon heterojunction from near-infrared to mid-infrared and demonstrate higher absolute electromagnetic interference(EMI)shielding effectiveness than state-of-the-art EMI materials of the same thickness.These results are expected to lead to the broad applications of such bulk nanofilms,especially as micro/nanoelectronic and optoelectronic platforms.

A Novel Method of Fabricating Flexible Transparent Conductive Large Area Graphene Film

We fabricate flexible conductive and transparent graphene films on position-emission-tomography substrates and prepare large area graphene films by graphite oxide sheets with the new technical process. The multi-layer graphene oxide sheets can be chemically reduced by HNO3 and HI to form a highly conductive graphene film on a substrate at lower temperature. The reduced graphene oxide sheets show a high conductivity sheet with resistance of 476Ω/sq and transmittance of 76% at 550nm （6 layers）. The technique used to produce the transparent conductive graphene thin film is facile, inexpensive, and can be tunable for a large area production applied for electronics or touch screens.

A flexible solid-state supercapacitor based on graphene/polyaniline paper electrodes

The direct coating of graphene sheets obtained by electrochemical exfoliation on commercial paper renders the preparation of highly conductive flexible paper substrate for subsequent deposition of polyaniline (PANi) nanorods via electrochemical polymerization. The deposit ion of PANi can be well-controlled by adjusting the electrochemical polymerization time, leading to the formation of PANi coated graphene paper (PANi-GP). The as-prepared electrode exhibited high areal capacitance of 176 mF cm^-2 in three-electrode system at a current density of 0.2 mA cm^-2 which is around 10 times larger than that of pris-tine graphene paper due to the pseudocapacitive behavior of PANi. In-situ Raman test was used to determine the molecular changes during redox process of PANi. More importantly, all-solid-state symmetric capacitor assembled with two PANi-GP electrodes in a polymer electrolyte delivered an areal capacitanee of 123 mF cm^-2, corresponding to an areal energy density of 17.1 μWh cm^-2 and an areal power density of 0.25 mW cm^-2. The symmetric capacitor held a capacitive retention of 74.8% after 500 bending tests from 0 to 120°, suggesting the good flexibility and mechanical stability. These results showed the great promising application in flexible energy-storage devices.

Large-scale fabrication of re duce d graphene oxide-sulfur composite films for flexible lithium-sulfur batteries

The rapid development of flexible electronic devices requires the design of flexible energy-storage devices. Lithium-sulfur(Li-S) batteries are attracting much interest due to their high energy density. Therefore, flexible Li-S batteries with high areal capacity are desired. Herein, we fabricated freestanding reduced graphene oxide-sulfur(RGO@S) composite films with a cross-linked structure using a blade coating technique, followed by a subsequent chemical reduction. The porous cross-linked structure endows the composite films with excellent electrochemical performance. The batteries based on RGO@S composite films could exhibit a high discharge capacity of 1381 m Ah/g at 0.1 C and excellent cycle stability. Furthermore, the freestanding composite film possesses excellent conductivity and high mechanical strength. Therefore, they can be used as the cathodes of flexible Li-S batteries. As a proof of concept, soft-packaged Li-S batteries were assembled and remained stable electrochemical performance under different bending states.

Graphene-based materials for flexible energy storage devices

The booming developments in portable and wearable electronics promote the design of flexible energy storage systems. Flexible supercapacitors and batteries as promising energy storage devices have attracted tremendous attention. As the key component of both supercapacitors and batteries, electrode materials with excellent flexibility should be considered to match with highly flexible energy storage devices. Owing to large surface area, good thermal and chemical stability, high conductivity and mechanical flexibility,graphene-based materials have been widely employed to serve as promising electrodes of flexible energy storage devices. Considerable efforts have been devoted to the fabrication of flexible graphene-based electrodes through a variety of strategies. Moreover, different configurations of energy storage devices based on these active materials are designed. This review highlights flexible graphene-based two-dimensional film and one-dimensional fiber supercapacitors and various batteries including lithium-ion, lithium–sulfur and other batteries. The challenges and promising perspectives of the graphene-based materials for flexible energy storage devices are also discussed.

Electron-Induced Perpendicular Graphene Sheets Embedded Porous Carbon Film for Flexible Touch Sensors

Graphene-based materials on wearable electronics and bendable displays have received considerable attention for the mechanical flexibility,superior electrical conductivity,and high surface area,which are proved to be one of the most promising candidates of stretching and wearable sensors.However,polarized electric charges need to overcome the barrier of graphene sheets to cross over flakes to penetrate into the electrode,as the graphene planes are usually parallel to the electrode surface.By introducing electron-induced perpendicular graphene(EIPG)electrodes incorporated with a stretchable dielectric layer,a flexible and stretchable touch sensor with"in-sheet-chargestransportation"is developed to lower the resistance of carrier movement.The electrode was fabricated with porous nanostructured architecture design to enable wider variety of dielectric constants of only 50-μm-thick Ecoflex layer,leading to fast response time of only 66 ms,as well as high sensitivities of 0.13 kPa-1 below 0.1 kPa and 4.41 MPa-1 above 10 kPa,respectively.Moreover,the capacitance-decrease phenomenon of capacitive sensor is explored to exhibit an object recognition function in one pixel without any other integrated sensor.This not only suggests promising applications of the EIPG electrode in flexible touch sensors but also provides a strategy for internet of things security functions.

Direct growth of graphene films without catalyst on flexible glass substrates by PECVD

A hydrogen-plasma-etching-based plasma-enhanced chemical vapor deposition(PECVD)synthesis route without metal catalyst for preparing the graphene films on flexible glass is developed.The quality of the prepared graphene films is evaluated by scanning electron microscopy,x-ray photoelectron spectroscopy,high-resolution transmission electron microscopy,ultraviolet-visible spectroscopy,and electrochemical measurements.In a radio frequency(RF)power range of 50 W-300 W,the graphene growth rate increases with RF power increasing,while the intensity ratio of D-to G-Raman peak(I_(D)/I_(G))decreases.When the RF power is higher than 300 W,the I_(D)/I_(G)rises again.By optimizing experimental parameters of hydrogen plasma etching and RF power,the properties of as-prepared flexible graphene on glass are modulated to be able to achieve the graphene's transparency,good electrical conductivity,and better macroscopic uniformity.Direct growth of graphene film without any metal catalyst on flexible glass can be a promising candidate for applications in flexible transparent optoelectronics.

Heterogeneous single-cluster catalysts(Mn_(3),Fe_(3),Co_(3),and Mo_(3))supported on nitrogen-doped graphene for robust electrochemical nitrogen reduction

Electrochemical nitrogen reduction reaction(NRR)is one of the most promising alternatives to the traditional Haber-Bosch process.Designing efficient electrocatalysts is still challenging.Inspired by the recent experimental and theoretical advances on single-cluster catalysts(SCCs),we systematically investigated the catalytic performance of various triple-transition-metal-atom clusters anchored on nitrogen-doped graphene for NRR through density functional theory(DFT)calculation.Among them,Mn_(3)-N4,Fe_(3)-N4,Co_(3)-N4,and Mo_(3)-N4 were screened out as electrocatalysis systems composed of non-noble metal with high activity,selectivity,stability,and feasibility.Particularly,the Co_(3)-N4 possesses the highest activity with a limiting potential of-0.41 V through the enzymatic mechanism.The outstanding performance of Co_(3)-N4 can be attributed to the unique electronic structure leading to strong π backdonation,which is crucial in effective N_(2) activation.This work not only predicts four efficient non-noble metal electrocatalysts for NRR,but also suggest the SCCs can serve as potential candidates for other important electrochemical reactions.

Stress release in high-capacity flexible lithium-ion batteries through nested wrinkle texturing of graphene

Flexible lithium-ion batteries(LIBs)are critical for the development of next-generation smart electronics.Conversion reaction-based electrodes have been considered promising to construct high energy-density flexible LIBs,which satisfy the ever-increasing demand for practical use.However,these electrodes suffer from inferior lithium-storage performance and structural instability during deformation and long-term lithiation/delithiation.These are caused by the sluggish reaction kinetics of active-materials and the superposition of responsive strains originating from the large lithiation-induced stress and applied stress.Here,we propose a stress-release strategy through elastic responses of nested wrinkle texturing of graphene,to achieve high deformability while maintaining structural integrity upon prolonged cycles within high-capacity electrodes.The wrinkles endow the electrode with a robust and flexible network for effective stress release.The resulting electrode shows large reversible stretchability,along with excellent electrochemical performance including high specific capacity,high-rate capability and long-term cycling stability.This strategy offers a new way to obtain high-performance flexible electrodes and can be extended to other energy-storage devices.

Novel Formaldehyde Sensor based on Hydrogen Peroxide/Melamine Modulated Photoluminescence of Nitrogen-doped Graphene Quantum Dots

A modulated photoluminescence nanosensor was developed for the quantitative detection of formaldehyde with nitrogen-doped graphene quantum dots and melamine. The sensing system was based on the different activated effects of melamine and hydrogen peroxide on the photoluminescence intensity of nitrogendoped graphene quantum dots. Under the optimal conditions, the modulated photoluminescence sensing system can be used to detect formaldehyde with a good linear relationship between the nitrogen-doped graphene quantum dots photoluminescence difference and the concentration of formaldehyde. The novel sensing system provided new directions for the detection of formaldehyde with high selectivity and quick response.

Zeolitic imidazolate framework-67 derived Al-Co-S hierarchical sheets bridged by nitrogen-doped graphene:Incorporation of PANI derived carbon nanorods for solid-state asymmetric supercapacitors

Metal sulfides have been widely enticed as battery-type electrodes in supercapacitor devices because of their maximal theoretical capacitance.Nevertheless,their lower conductivity and ion transport kinetics can largely restrict their rate performance,hence the practical usage in fields of demanding high power devices.Therefore,the design of new electrodes with higher energy and power densities remains a highly challenging task.To the best of our knowledge,a novel hierarchical composite of Al-CoS_(2) on nitrogendoped graphene(NG)is prepared based on a zeolite imidazole framework using a simple and scalable hydrothermal process.In this hybrid,ultrathin Al-CoS_(2) nanosheet arrays are vertically orientated on the NG framework to limit self-aggregation,hence increasing the electrical property and cycle stability of composite.It is investigated that the Al/Co feeding ratio plays a crucial role in controlling the obtained hierarchical structure of Al-Co-S sheets and their electrode performance.Also,Al^(3+) can influence remarkably the morphology and electrochemical property of the resultant graphene composite.An effective synergism is noticed between the redox Al-CoS_(2) and NG resulting in fast electron transfer and chargingdischarging processes.Surprisingly,when the as-developed composite is utilized as a positive electrode at an applied current density of 1 A/g,a specific capacitance of 1915.8 F/g is attained with ultra-long cycle stability(96%,10,000 cycles)and an excellent retention rate(~89%).As a consequence,when a solid-state asymmetric supercapacitor(ASC)device is made by combining an Al-CoS_(2) @NG hybrid with a negative electrode made of polyaniline(PANI)derived carbon nanorods(PCNRs),it demonstrates remarkable specific capacitance(188 F/g),energy density(66.9 Wh/kg),and cyclic stability of 92%after 10,000 cycles.This may open the pathway for the application of the next-generation supercapacitors in the future.

Flexible Nanopaper Composed of Wood-Derived Nanofibrillated Cellulose and Graphene Building Blocks

Nanopaper has attracted considerable interest in the fields of films and paper research.However,the challenge of integrating the many advantages of nanopaper still remains.Herein,we developed a facile strategy to fabricate multifunctional nanocomposite paper(NGCP)composed of wood-derived nanofibrillated cellulose(NFC)and graphene as building blocks.NFC suspension was consisted of long and entangled NFCs(10–30 nm in width)and their aggregates.Before NGCP formation,NFC was chemically modified with a silane coupling agent to ensure that it could interact strongly with graphene in NGCP.The resulting NGCP samples were flexible and could be bent repeatedly without any structural damage.Within the NGCP samples,the high aspect ratio of NFC made a major contribution to its high mechanical strength,whereas the sheet-like graphene endowed the NGCP with electrical resistance and electrochemical activity.The mechanical strength of the NGCP samples decreased as their graphene content increased.However,the electrical resistance and electrochemical activity of the NGCP samples both rose with increasing content of graphene.The NGCPs still kept advantageous mechanical properties even at high temperatures around 300℃ because of the high thermal stability of NFCs and their strong entangled web-like structures.In view of its sustainable building blocks and multifunctional characteristics,the NGCP developed in this work is promising as low-cost and high-performance nanopaper.

Flexible Graphene Devices with an Embedded Back-Gate

We show the fabrication of flexible graphene devices with an embedded backgate. The resistance of these devices can be tuned by changing the strain through the bending of the substrate. These devices can be useful for applications requiring a flexible graphene-based field effect transistor in where the graphene channel is not covered (such as biological or chemical sensors and photo-detectors).

Preparation and characterization of colorful graphene oxide papers and flexible N-doping graphene papers for supercapacitor and capacitive deionization

An efficient method that utilizes simple techniques,easy operation,and low-cost production to create flexible graphene-based materials is a worthy practical challenge.A rapid strategy for preparing flexible,functional graphene oxide(GO)is introduced using GO-ethanol dispersion filtration.The filtration process is highly efficient and drying time is significantly reduced by employing ethanol as solvent,due to the fact that ethanol is a volatile liquid.Freestanding GO papers can be harvested with ultralarge size(700 cm2),color variety,and writable characteristics.After reduction,N-doped graphene(NDG)papers still maintain good foldability with improved electric conductivity and porous structure.When used as an electrode for a supercapacitor,the flexible NDG paper device demonstrates good electrochemical performance even with size expansion and extreme double folding.Moreover,this NDG paper capacitor device shows a good electrosorption performance for capacitive deionization of sulfate and chromate in groundwater system.These flexible GO and NDG papers promise potential to facilitate the production of graphene-based materials for practical applications in energy and environmental related fields.

Study on Graphene Based Next Generation Flexible Photodetector for Optical Communication

We report on the efficient photodetection (PD) properties of graphene based p-i-n photodetector, where all the three layers are either single or multilayer graphene sheets. We report the bandwidth and responsivity performance of the device. This simple structure paves the way for the next generation flexible wireless communication systems. A theoretical model is used to study the carrier distribution and current in a graphene based p-i-n photodetector system.

Graphene-Polymer Nanocomposites and Roll-to-Roll (R2R) Compatible Flexible Solid-State Supercapacitor Based on Graphene Nanoplatelets and Ionic Liquid-Polymer Gel

We present the electrical and supercapacitive performance of graphene nanoplatelets in polymer nanocomposites and flexible solid state electrical double layer capacitors (EDLC) respectively. Graphene-doped poly (3,4-ethylenedioxythiophene) (PEDOT) coated polyethylene terephthalate (PET) and glass exhibited transmittance above 95% and electrical conductivity of 2.70 × 10ˉ1 S·cmˉ1 and 9.01 × 10ˉ1 S·cmˉ1 respectively. Graphene loaded polymethyl methacrylate (PMMA) and polystyrene (PS) nanocomposites showed electrical conductivity as high as 2.11 × 10ˉ1 S·cmˉ1 at low loadings of 2 wt%. The use of graphene was necessitated by the need to increase the EDLC capacitance and energy density since it provides high effective surface area. The polymer gel membrane made from polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) and the Ionic Liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate exhibited high porosity which made it suitable for use as separator in the EDLC. The highest recorded specific capacitance was 133.82 F/g which can be attributed to the porosity of the IL containing PVDF-co-HFP membrane and the large surface area of the graphene electrodes. At an operating voltage of 3.5 V the energy density was found to be 56.92 Wh·Kgˉ1. All chemicals were research grade and were obtained from Sigma Aldrich.

Wet-spun poly(ionic liquid)-graphene hybrid fibers for high performance all-solid-state flexible supercapacitors

It is crucial to develop flexible and wearable electronic devices that have attracted tremendous interest due to their merits on compactness,flexibility and high capacitive properties.Herein we report the continuously ordered macroscopic poly(ionic liquid)-graphene fibers by wet spinning method via liquid crystal assembly for supercapacitor application.The fabricated all-solid-state supercapacitors exhibited a high areal capacitance(268.2 mF cm 2)and volumetric capacitance(204.6 F cm 3)with an outstanding areal energy density(9.31μWh cm-2)and volumetric energy density(8.28 mWh cm-3).The fiber supercapacitors demonstrated exceptional cycle life for straight electrodes of about 10,000 cycles(94.2%capacitance retention)and flexibility at different angles(0°,45°,90°,180°)along with a good flexible cycling stability after 6000 cycles(92.7%capacitance retention).To date,such a novel poly(ionic liquid)-graphene fiber supercapacitors would be a new platform in real-time flexible electronics.

Thermoelectric characteristics of flexible reduced graphene oxide/silver selenide nanowire composites prepared by a facile vacuum filtration process

The reduced graphene oxide/silver selenide nanowire(rGO/Ag;Se NW)composite powders were fabricated via a wet chemical approach,and then flexible rGO/Ag;Se NW composite film was prepared by a facile vacuum filtration method combined with cold-pressing treatment.A highest power factor of 228.88μW·m;·K;was obtained at 331 K for the cold-pressed rGO/Ag;Se NW composite film with 0.01 wt%r GO.The rGO/Ag;Se NW composite film revealed superior flexibility as the power factor retained 94.62%after bending for 500 times with a bending radius of 4 mm,which might be due to the interwoven network structures of Ag;Se NWs and pliability of r GO as well as nylon membrane.These results demonstrated that the GO/Ag;Se NW composite film has a potential for preparation of flexible thermoelectric devices.