The results show that no graphene agglomeration is found in the mixed powder. The complex composites prepared by high energy ball milling and powder metallurgy have approximately 4–5 layers of graphene and the thickness of single-layer graphene is approximately 0.334 nm. The final experimental results confirm the formation of compound AlC The preparation technology of this kind of metal composites has gradually matured, including agitation casting, pressure leaching, friction stirring and powder metallurgy3. The strengthening approach of aluminum matrix composites is to add discontinuous hard phase into the matrix in some way. Several popular strengthening phase include ceramic particle, whisker, short fiber and so on4. The addition of hard phase to improve the properties of aluminum matrix composites has attracted more and more attention. Therefore, it is of great significance to study aluminum matrix composites improved by hard phase.Aluminum matrix composites are widely used in many fields, such as aerospace, automotive, military and electronic packaging because of their excellent properties5. With the development of science and technology, graphene is favored by an increasing number of researchers, and its application field is also expanding. This is mainly due to graphene's excellent thermoelectric properties, as well as its tensile strength of 130 GPa. Its Young's modulus is 1 TPa, and it has excellent deformation resistance7. Therefore, graphene has attracted extensive attention in the scientific community. It has been found that graphene is added not only to metallic materials but also to nonmetallic materials. Due to its important influence on the properties of materials, it is widely used in the research and improvement of material properties. Graphene is playing an increasingly important role in the field of materials.With the development of technology, new reinforcement phases are constantly being explored to meet the needs of materials in more fields. Moreover, the desire for some kind of reinforcement can be processed by multidimensional processing technology to enhance the aluminum matrix composite. Since 2004, scientists Geim and Novoselov of the University of Manchester in the United Kingdom have successfully isolated graphene from graphite using micromechanical stripping and described its electronic properties2/g8, which makes graphene easily agglomerate. If graphene is not uniformly distributed in the matrix, it will have an adverse impact on the properties of the material. To this end, different approaches have been tried to improve the problem and achieve the even dispersion of graphene. Wang et al.9 modified aluminum flake powder with mixed graphene oxide nanosheets and polyvinyl alcohol to achieve an effective graphene dispersion in the matrix. The composites are successfully prepared by powder metallurgy and hot extrusion. Xin Gao et al.10 achieved uniform adsorption of graphene sheets on aluminum oxide powder through mutual attraction of dissimilar charges. Aluminum matrix composites reinforced with uniformly dispersed graphene were prepared by powder metallurgy. Some urgent problems and deficiencies still restrict its development and application. For example, reduce the weight of the product and ensure the high temperature resistance, bite resistance and wear resistance of the material at the same time.However, graphene has some limitations in its applications. Graphene has a large specific surface area of up to 2630 cm11 compared the friction properties of aluminum alloy Al6061 with its nanocomposite through different load frictions. Harun Mindivan et al.12 studied the friction properties of different types of aluminum matrix composites reinforced by silicon carbide. As is well known, metal materials are often accompanied by corrosion in a friction environment. For the study of corrosion friction, the composite reinforced material Al-30Fe3O4-20SiC prepared by Negin Ashraf et al.13 improved the corrosion protection efficiency of the matrix to more than 99%. Toptan et al.14 studied the corrosion and tribocorrosion behavior of Al–Si–Cu–Mg alloy and its composites reinforced with B4C particles in 0.05 M NaCl solution. It is found that the matrix material mainly slides on the B4C particles, thus protecting the matrix alloy from serious wear damage. In addition, the strengthening mechanism and microstructure of graphene-reinforced aluminum matrix composites need to be further studied.Herein, it is particularly important to emphasize the fact that there are relatively few studies on the friction corrosion of graphene-reinforced aluminum matrix composites. Most of the research is focused on the friction behavior of aluminum matrix composites. For instance, Manivannan et al.In this work, the graphene reinforced aluminum matrix composites (GAMCs) were prepared by high-energy ball milling (HEBM) and powder metallurgy. The hardness and friction corrosion properties of GAMCs were tested. The friction corrosion of graphene aluminum matrix composites is analyzed in detail. Based on previous work, the strengthening mechanism of the material and the main factors affecting the properties of the material are given. The matrix morphology and the distribution of graphene in the grain boundary are observed carefully and the strengthening effect of graphene on the aluminum matrix composite is comprehensively considered.In this work, Al powder (purity: 99%) was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. The Graphene powder (purity: 96%) came from Qingdao Huagao Graphene Technology Corp. First, uniformly mixed graphene and aluminum powders were prepared by high-energy ball milling at a ball powder ratio of 10:1. The mass of graphene accounts for 0.5%, and the rest is aluminum powder. The milling medium were the stainless-steel ball. HEBM was carried out on a planetary ball mill at a speed of 150 rpm for 2 h. In the second step, 1.5 g of mixed powder was consolidated by cold isostatic pressing. A preform with a diameter of 15 mm and a thickness of 3 mm was formed at a pressure of 750 MPa for 5 min. Finally, the preform is sintered in a vacuum furnace at a heating rate of 4 °C/min to 600 °C, and the holding time is 4 h. After heat preservation, the sample is cooled with the furnace.The friction and corrosion resistance of the material is tested by electrochemical friction and wear coupling test systems. The open circuit potential (OCP) is the relative value between the working electrode and the reference electrode. It will change with the change in the reference electrode and time. When the electrode interface reaction reaches a steady state, the OCP will also tend to be stable. The test system was a three-electrode system, with high-purity graphite as the auxiliary electrode, composite material as the working electrode and a saturated calomel electrode (SCE) as the reference electrode. The friction length is 5 mm, and the frequency is 0.2 Hz. The initial load is 10 N, and the load is controlled by the weight. The test time was 30 min. The OCP was recorded for 5 min before sliding and 20 min for the intermediate sliding test. At the end of sliding, OCP recording lasted for 5 min. Alumina ball, 6 mm in diameter, can be used as the counterpart. The sample is a cylinder with a diameter of 15 mm and a thickness of 3 mm. Metallographic polishing was carried out before the experiment.To characterize the morphology of the powders and sintered samples, microstructural analysis was performed using an FEI Quanta FEG 250 scanning electron microscope (SEM) at 20 kV. The phase composition of the matrix and the carbide or oxide is determined by energy dispersive spectroscopy (EDS) and X-ray diffractometry. The microstructure of the GAMCs was observed by high-resolution transmission electron microscopy  operating at an accelerating voltage of 300 kV. Thin foil samples were carefully prepared by ion beam 6 milling . An MFT-4000 multifunction material surface performance tester is used to test the friction corrosion of the GAMCs.To approximately estimate the tensile strength of Al matrix composites, the Vickers hardness was measured by a microhardness tester (HV-1000). The oxide on the surface of the sample was removed with a polishing machine to make the surface smooth. The sample was observed under 400 times magnification through the micrometer eyepiece of the Vickers hardness tester, and then the point to be tested and loaded was selected. The load is 0.98 N, and the loading time is 10 s.SEM observation was conducted on the mixed powder after grinding, as shown in Fig. Moreover, the surface morphology of the prepared GAMCs is observed, as shown in Fig. Figure 3 : ,,2), it cmentclass2pt{minim10. As mentioned in the previous section, graphene has payload transfer during frictional etching and slows down the destruction speed of the matrix surface.Figure To further study the fine microstructure structure, the high-resolution transmission at the grain boundary is shown in Fig. 22. On the one hand, these frictions are conducive to smooth work. They affect the service life of metal materials, production cost and resource utilization14. The working environment of most metal materials is exposed to moist air or direct contact with liquid. The flow of air and liquid not only produces friction on the material but also carries out continuous corrosion on it. Due to friction and wear, new contact surfaces are constantly produced on the metal surface, and the contact surface is involved in the corrosion caused by the atmosphere or liquid, which aggravates the wear process. The synergy increases the surface damage rate of metal materials and seriously affects the service life of metal materials22.In the process of preparing and improving aluminum matrix composites, the wear resistance and corrosion resistance of the materials are important indexes to characterize the properties of the materials. Certain metal materials cannot avoid friction and wear during service, such as bearings, cutting tools, drilling equipment and certain precision structuresTherefore, to study the friction and corrosion properties of materials, electrochemical friction and wear coupling test systems were used. The friction corrosion process of GAMCs (graphene accounts for 0.5 wt%) is comprehensively analyzed. Figure 23. This film can be used as the surface strengthening layer, which is the source point of staggered enrichment and increases the internal stress of the material24. The strengthening layer on the initial material surface is not continuous. The friction coefficient tends to rise under the influence of load. As the friction continues, work hardening occurs on the surface of aluminum matrix composites, and the hardening area expands with time14. The load action promotes surface strengthening to accumulate more energy, and friction and wear require a greater load. Under the condition of constant load, the friction coefficient of this experiment will be relatively reduced, and the friction coefficient can be as low as 0.10 or below. When the surface energy accumulates to a certain level, corrosion is more likely to occur26. Tribo-corrosion acts on the material surface to promote surface damage, so that the friction coefficient will be increased again for the next work of hardening. In the case of constant load, frictional corrosion is repeated, and the friction coefficient fluctuates slightly over time, but the average friction coefficient is relatively low.A schematic diagram of frictional corrosion is shown in Fig. 14. Changes in OCP are influenced by this process. A significant decrease in electric potential is observed at the start of the slide as the tribo-etched surface becomes more active under higher normal loads, resulting in lower OCP. In this process, the changes in the surface energy and friction coefficient make the OCP fluctuate slightly throughout the whole process. During the friction phase, the average CPO is approximately − 0.76 V. At the end of tribological corrosion, OCP will have a rising fluctuation due to the formation of a tribological film and the decrease in surface energy.Frictional corrosion is the joint action of mechanical and chemical friction. Tribological corrosion is defined as degradation due to mechanical wear and corrosion electrochemical etching11. The graphene at and near the grain boundary rapidly transfers the load to the substrate near the surface28. The plastic deformation near the crack results in the crack being deformed and squeezed, and then the crack is filled and repaired. The repaired crack prevents the electrolyte from entering the matrix, making the frictional corrosion stay only locally, slowing down the corrosion process and reducing the friction coefficient on the material surface. The reciprocating friction of GAMCs is nearly 20,000 times in 30 min. By analyzing the friction data, the friction coefficient and OCP potential of graphene/Al composite materials tend to be stable as a whole. GAMCs do not form in the whole process, which indicates that the material has good friction-corrosion resistance. Graphene is distributed at the grain boundary, which enhances the corrosion and friction resistance of the material because it promotes load transfer and self-repair of the matrix.Repeated friction of the surface from the alumina ball tends to generate a thin oxide film on the surface, resulting in stress concentration under load. In addition, the action of the corrosion solution causes microcracks in the oxide film area, as shown in Fig. In this study, the Vickers hardness of pure aluminum was 36 Hv, while that of GAMCs was 61.8 Hv, an increase of 41.7%. The corresponding tensile strength is 211 MPa. During the sintering process, a higher sintering temperature is conducive to nucleation, grain growth, atomic amplitude expansion, atomic diffusion velocity and plastic flow at grain boundaries. The holding time of 4 h makes the atoms at the grain boundary enter the range of atomic force, which strengthens the bonding degree of the grain boundary and obviously improves the strength of the composite.29, thermal mismatch strengthening30, Orowan strengthening1, and shear lag strengthening31. This paper will analyze the strengthening effect of GAMCs from the following strengthening mechanisms.At present, the strengthening mechanisms of GAMCs are mainly as follows: fine grain strengthening29 formula is used to calculate the strengthening effect of fine grain strengthening on aluminum matrix composites. The expression is as follows:32).Based on previous studies, the preparation of GAMCs and the binding of graphene at the grain boundary can effectively inhibit grain growth and hinder grain boundary expansion. Hall–Petch–6 K−1, while the coefficient of thermal expansion of aluminum is 23 × 10–6 K−1, which is an order of magnitude difference. The intensification caused by the expansion difference between graphene and the aluminum base is calculated by using the model formula proposed by Arsenault et al.33:4 MPa34) and K is the constant maturity factor (0.535). b represents the Boggs vector (0.286 nm), and ρ represents the dislocation density. The following formula gives the calculation process of density.The enhancement of thermal mismatch is due to the difference in the thermal expansion coefficient between the reinforcement and the matrix when the temperature changes. The effect of this thermal mismatch is more obvious between the normal direction perpendicular to graphene and the matrix, due to the unique two-dimensional structure of graphene. This results in residual thermal stress at the interface between the reinforcement and the matrix, accompanied by the generation of height dislocations. The coefficient of thermal expansion of graphene is 1.1 × 1036:37:Accordingly, Orowan strengthening is also known as second phase strengthening. The graphene is distributed in the matrix as a fine second phase, which can act as a hindrance to dislocation movement. When the matrix is subjected to applied stress, graphene hinders dislocation movement, and the dislocation is bent to form a dislocation ring, thus playing a strengthening role. In this paper, the reinforcement value is calculated using the following model31. The yield strength value of GAMCs is calculated by using this model, which is expressed as follows:1) and s is the aspect ratio of graphene.The shear lag model proposed that the strengthening mechanism of graphene-enhanced aluminum matrix composites is that the external load is transferred and dispersed through interfacial shear force. It is believed that the amount of graphene addition and the aspect/diameter ratio of graphene added to the composite material affect the properties of the compositesThe calculation results of each enhancement effect are shown in Table 38 is used to calculate the yield strength. To further illustrate the reliability of the reinforcement mechanism, the shear-lag model modified by Nardone and PrewoReferring to the relevant values, the yield strength of the material calculated by the modified model is 227.75 MPa. Compared with Formula , this va3 in the microstructure, and its diffraction spot index is (According to the experimental results, high-energy ball milling is an effective method to prevent agglomeration of graphene. The complex composites prepared by high-energy ball milling and powder metallurgy have approximately 4–5 layers of graphene and the thickness of single-layer graphene is approximately 0.334 nm. The final experimental results confirm the formation of compound AlCThe maximum friction coefficient is 0.126, and the average friction coefficient is 0.027, suggesting good wear resistance and corrosion resistance. Surface payload transfer and plastic deformation improve the corrosion resistance to a certain extent. The obtained results indicate that the distribution of graphene at grain boundaries plays a role in effective load transfer.The hardness of aluminum matrix composites strengthened by 0.5 wt% graphene prepared by high-energy ball grinding and powder metallurgy reached 61.8 Hv, which is improved by 41.7% compared with pure aluminum, and the strengthening effect is obvious.The strengthening mechanisms of GAMCs are analyzed, and the strengthening effects are calculated. In the calculation process, the distribution of graphene in the matrix is idealized. The thermal expansion coefficients of graphene and aluminum are significantly different, so the thermal mismatch strengthening effect of the calculation is more significant. The yield strength of the material calculated by the modified model is very close to the actual value.In the current study, graphene reinforced aluminum matrix composites were successfully prepared by a powder metallurgy method. In particularly, the typical microstructure, tribological corrosion properties and strengthening mechanism of this kind of composite are analyzed in depth. The interesting and meaningful innovative results are as follows:


Febrile neutropenia secondary to chemotherapy is one of the most critical complications in cancer treatment. The aim of this study was to determine if an increase in the percentage of immature platelet fraction (IPF%) might predict early neutrophil recovery following cytostatic-dependent aplasia. A retrospective cohort study compared serial complete blood counts and the level of C-reactive protein (CRP) following induction chemotherapy for Ewing sarcoma and Non-Ewing sarcoma patients. The measurements were taken on a Sysmex XE-2100 instrument. A total of 287 paired samples from 28 children after the first cycle of chemotherapy were analyzed to test if an increase in the IPF% anticipated the CRP peak and recovery of neutrophil count. The chemotherapy associated nadir of neutrophils, reticulocytes and platelets was reached at 9.7 ± 1.5, 11.0 ± 1.7 and 11.9 ± 0.9 days (mean ± SD) respectively, in Ewing sarcoma patients. Still in severe neutropenia, IPF% was the first parameter that significantly increased and anticipated the CRP peak . The IPF% continuously increased  and peaked at 12.2 ± 1.4 days (mean ± SD) after commencement of chemotherapy. Compared to neutrophil recovery , the IPF% peak was anticipated by 2.4 days (p = 0.0085). Although variably treated, in non-Ewing sarcoma patients the effect was similar and the IPF% peak anticipated neutrophil recovery by 6.8 ± 4.7 days (p < 0.01). IPF% increased significantly at > 48 h before neutrophil recovery in patients treated with chemotherapy. IPF% is an inexpensive parameter and may be valuable in the management of febrile neutropenia. Severe myelosuppression puts patients at risk of opportunistic and often fatal life-threatening infection, and is one of the major reasons for dose modifications, dose delays, or discontinuation of therapy2.Myelotoxicity—including neutropenia, thrombocytopenia and anemia—is the most frequent side-effect of chemotherapy in cancer patients4. When the neutrophil count remains low, controversy exists over whether antibiotic therapy should be stopped5. Discontinuation at uncertain blood culture results may put the patient at risk for sepsis progression with possibly fatal outcome. This is clearly of more concern than avoidance of drug-related adverse events or drug resistance6. Therefore, additional clinical parameters are urgently required for the management of antibiotic treatment.In the case of febrile neutropenia, early empirical antibiotic therapy is mandatory to avoid progression to sepsis. Antibiotics are continued until the patient is afebrile and clear signs of bone marrow recovery are detected7. Immature platelets remain undetected in the traditional manual microscopic method. However, they can be measured by flow cytometry-based hematology analyzers8. The fact that the immature platelet fraction (IPF%) is high in patients with immune thrombocytopenia is already used to distinguish thrombocytopenia in acute lymphoblastic leukemia9. Although this value can be extrapolated to other scenarios, data on IPF% recovery after treatment with chemotherapy in children are sparse.Recent progress in understanding bone marrow physiology has identified immature platelets as a parameter of imminent bone marrow recovery after chemotherapyThe aim of this study is to evaluate early IPF% recovery as an earlier indicator of absolute neutrophil recovery in the myelosuppressive phase of pediatric cancer patients in order to decide and control the length and intensity of a preemptive antibiotic therapy.2 at day 1; ifosfamide 3.0 g/m2, doxorubicin 20 mg/m2 and etoposide 150 mg/m2, given on days 1, 2 and 3; the interval between two VIDE cycles was 21 days) and for 17 non-Ewing sarcoma patients with different diagnoses and treated with different protocols  with newly diagnosed cancer and treated at our institution  between January 2016 and July 2021 were recruited for the study. Fortyfive patients with the diagnosis of acute leukemia  were excluded from this study, because of severe bone marrow infiltration by tumor cells (27–99%) and chemotherapy was administered irrespective of white blood recovery (which is the standard practice in the induction phase). All other patients were monitored clinically for signs of infection at inpatient stay between the first and second cycle of chemotherapy. Complete blood sample and level of C-reactive protein (CRP) were drawn on a daily basis. The assignment to “febrile neutropenia” was fulfilled if a neutrophil count < 0.5 G/L and the presence of a single temperature > 38.3 °C or a sustained temperature of ≥ 38.0 degrees Celsius for more than one hour was present. Accordingly, three patients were excluded, because they did not fulill the criteria of “febrile neutropenia”. Finally, we collected data for 11 patients , count of immature platelets (IPF#), and CRP level. Immediate and automatic measurement of immature platelets was performed using the Sysmex XE-2100 blood cell counter. Recovery of relative reticulocyte values was defined as levels > 2‰, recovery of neutrophils as levels > 0.5 G/L.Descriptive statistics were performed for all variables of interest, giving means, standard deviations, minimum and maximum ranges, and absolute and relative frequencies for qualitative variables. The chi-squared test was used for categorical variables and the Mann–Whitney U test for continuous variables. Data visualization and analysis was performed using GraphPad Prism, version 8.4, IBM SPSS Statistics, version 26, and Excel.This study was performed in line with the principles of the Declaration of Helsinki. The Ethics Committee of the Medical University of Innsbruck approved the retrospective evaluation (EC No. AN2016-0059 360/4.10). All data were obtained from medical records. Waiver of informed consent given by Ethics Committee of the Medical University of Innsbruck.IPF% reference values were collected on the basis of 416 healthy children and adolescents. The included probands were normally distributed between gender groups. The analysis included distribution of values and calculation of percentiles in various age groups as defined by the WHO classification of age groups  as compared to pre-school/primary school age children  and adolescents . Compared to children of pre-school/primary school age, adolescents showed slightly higher IPF# values, which differed from the two other age groups  during and after her first VIDE cycle  and were equally distributed for sex and age  guidelines in very large study populations and result in IPF% values between 0.5–3.2% and 0.4–3%20. In pediatrics, large studies in different age groups are missing. One single study limits the analysis to the neonatal period and attributes distinct values to different gestational ages, with the values differing between 1.5 and 5.9%19. Another study limits the IPF% values (0.7–5.7%) to 100 children between 6 months and 18 years of age and includes samples from patients with a wide variety of different diagnoses9. Our analysis of IPF% in 416 healthy children shows that IPF% is sex-independent and differs concerning the age (Table 9. It is known that thrombopoietin has higher concentration levels in this age group, which translates to increased activity of megakaryocytes and production of thrombocytes22.Although we anticipate that more data on this topic are necessary, a much broader investigation of the normal levels of IPF% is needed. Numerous studies limit the analysis of IPF% to healthy and adult patients and show values between 0.3 and 17.8%12, it has long been claimed to have its value in predicting neutrophil regeneration after chemotherapy23. After observing the course of cell count in an individual case, we analyzed 11 uniformly treated patients diagnosed with Ewing sarcoma. The nadir of neutrophil, reticulocyte and platelet count resulted early after initiation of chemotherapy and was immediately paralleled by a simultaneous rise in IPF%. Interestingly, in our study the IPF% peak occurred almost simultaneously with the CRP peak (Fig. 25. In this sense IPF% has been proposed as a biomarker for the prediction of sepsis diagnosis and severity28.Considering that IPF% is a useful diagnostic parameter for identifying the production of thrombocytesNonetheless, the findings presented and discussed here must be interpreted with caution and a number of limitations should be borne in mind. Most of the studies, including ours, were performed retrospectively and possibly include a biased selection of controls. Our and other studies may underestimate the IPF% values, as this parameter appears very quickly and disappears at the same time. Furthermore, IPF% measurement is not standardized and is performed with different devices. The only way to overcome these limitations is to perform a prospective clinical study with a large number of subjects, well-defined methods and precisely formulated aims.32.We conclude that analysis of IPF% may give helpful data on neutrophil activity and kinetics in the post-chemotherapy period in children. Considering these data may help determine timing and the need for antibiotic therapy in phases of aplasia. We suggest that this method be included in routine report of blood differential in pediatric oncology, as the barriers to integrate IPF% are minimal—it is not expensive, readily available and it is a precise method for estimating bone marrow kinetics. Finally, prediction of bone marrow recovery can facilitate overall survival, as a more rapid application of chemotherapy is associated with improved survivalSupplementary Table 1.


Via near-field coupling, broadband PIT can be produced through the interference between different modes. Based on different arrangements of graphene positions, not only can we achieve electrical switching of the amplitude of broadband PIT, but can also realize modulation of the bandwidth of the transparent window. Simultaneously, both the capability and region of slow light can be dynamically tunable. This work provides schemes to manipulate PIT with more degrees of freedom, which will find significant applications in multifunctional THz modulation.A hybrid metal–graphene metamaterial (MM) is reported to achieve active control of broadband plasmon-induced transparency (PIT) in the THz region. The unit cell consists of one cut wire (CW), four U-shaped resonators (USRs) and monolayer graphene sheets under the USRs.  A hybrid metal–graphene metamaterial (MM) is reported to achieve active control of broadband plasmon-induced transparency (PIT) in the THz region. Besides, the EIT effect is mainly observed in the optical frequency range due to the limited energy interval for transitions of quantum states, which makes it hard to produce EIT in the terahertz (THz) region.4 Recently, as an EIT analogue in a plasmonic system, plasmon-induced transparency (PIT) has been proposed and widely realized in the THz band based on metamaterials (MMs).5 The metal meta-resonators of such MMs, including split-ring resonators (SRRs),6,7 U-shape resonators (USRs)8,9 and cut wires (CWs),10,11 can support electromagnetic resonances in the THz region. Via near-field coupling of meta-resonators, PIT can be realized from the destructive interference between the bright and dark mode.12 Nowadays, MMs-based PIT has been found a wide range of applications in THz switch,13–15 slow light devices16 and sensors.17Electromagnetically-induced transparency (EIT) is a quantum phenomenon coming from the interference between two different excitation pathways in a three-level atomic system,18 and utilizing photoconductive silicon island, an on-to-off switch of PIT also can be realized.19 However, these modulation schemes suffer from relative slow response time . As a two-dimension (2D) material, graphene has drawn more attention owing to the superior photoelectric modulation performance. Due to the high mobility of graphene electrons, the Fermi energy of graphene can be tuned via electrical gating or chemical doping. According to Kubo formula,20 the graphene surface conductivity will be changed flexibly. The corresponding response time is on the order of picosecond, promising for the ultrafast switching.21 So far, plenty of works have concentrated on proposing PIT with tunable transparent position based on graphene nanopattern MMs22,23 or graphene complementary MMs24,25 in THz regime. Nevertheless, extra noises will be involved at adjacent frequency spectra during such manipulation process. Recently, the hybrid metal–graphene MMs are introduced to achieve active control of the transparency window amplitude.26,27 However, these works only focus on switching the amplitude of a narrowband PIT. The modulation with more degrees of freedom need to be demonstrated.Although PIT can be tuned by changing geometric parameters of MMs, it's essential to propose a dynamic tunable PIT in practice. Superconductor is used to obtain temperature modulation of transparent window position,Via near-field coupling, broadband PIT will be produced through the destructive interference of modes, which can be theoretically explained by the plasmonic hybridization model (PHM). Most importantly, based on different graphene positions, not only can we achieve on/off switching of broadband PIT, but also can manipulate the bandwidth of the transparent window by electrically tuning the Fermi energy of graphene sheet. Such PIT with tunable bandwidth is introduced for the first time so far as we know. Simultaneously, both the capability and region of slow light can be dynamic tunable. This work makes possible the PIT modulation with more degrees of freedom, which will find significant applications in multifunctional modulators, switches and buffers for future THz wireless interconnects.In this paper, we report a hybrid metal–graphene MM to achieve the active control of the broadband PIT in THz region. The unit cell consists of one CW, four USRs and monolayer graphene sheets. 2.z direction) and front (from y direction) view for the unit cell of the proposed hybrid metal–graphene MM are shown in x and y direction.The top  and will be transferred onto the quartz substrate by dry transfer technique. Next, the graphene sheet is fabricated into strips by electron beam lithography (EBL) and oxygen plasma etching (OPE). Then, the aluminum layer is deposited on the top of the existing structure. Finally, utilizing EBL and OPE, both the metal resonant elements and metal electrode pairs can be manufactured.The Fermi energy of graphene can be tuned by external voltage, which can be realized based on gate electrodes.x and y directions and perfectly matched layer (PML) in the z direction, moderate mesh grid is employed to ensure the accuracy: dx = dy = 500 nm, dz = 200 nm. A THz source with x-direction polarization is put on the top of the MM and propagates along the z direction, a monitor is set at the bottom of substrate to detect the transmitted power.The finite-difference time-domain (FDTD) solution is utilized for simulating features of introduced device with periodical boundary conditions in the 3.x-direction polarization, a symmetric Lorenz-type resonance appears around 1 THz as exhibited in 34 The inductive–capacitive (LC) resonance can be supported by the USR35 but cannot be efficiently excited by such polarized light as depicted in 12 As an analogue of a three-level atomic EIT system, there will be a destructive interference between the bright and dark mode,26 PIT will come out near the common resonant frequency of two modes as shown in At first, three kinds of MMs without graphene are simulated to investigate the mechanism of PIT, the unit cell of each MM only consists of a CW, a USR and a CW coupled with one USR, respectively. The corresponding transmission spectrum and electric field distributions are shown in via electromagnetic interaction, which can be explained by the PHM.36 The two supermodes are extremely close in resonant frequencies, consequently forming a relatively broadband PIT. Same procedure can be applied when USR pair are on the left side as shown in The transmission spectrum of MM composed of one CW coupled with four USRs  is introduced:T0 is the transmission of the transparent window center when Fermi energy is at 0.05 eV, ΔT is the central transmission change compared with T0, and the corresponding details are collected in Next, two monolayer graphene strips are integrated under the USR pairs respectively as shown in τg:26ψ(ω) stands for the transmission phase shift from the light source to the monitor. As shown in As one of the most important applications of PIT, slow light is also investigated under different Fermi energy. The slow light can be qualified by the delay time 38 As electric fields on USR pairs fade, the destructive interference between bright and dark mode will be cancelled, finally there will be only bright mode at 0.45 eV as shown in The electric field distributions of the unit cell at different Fermi energy are shown in via integrating monolayer graphene under one of USR pairs as depicted in F0 is the FWHM of the transparent window when Fermi energy is at 0.05 eV, ΔF is the change of FWHM relative to F0, the details are shown in 37Furthermore, 39 consequently the slow light capability is enhanced. However, the PIT peak value and bandwidth are smaller compared with the spectrum given in 40 not only the narrowband PIT can be switched from on to off state, but also the amplitude and bandwidth of the transparent window can be controlled simultaneously at the same MM.The corresponding electric field distributions at different Fermi energy are shown in Via the electric control, the transmission of light can be modulated. Besides, the delay time and bandwidth of slow light can also be dynamically tunable. Simultaneously, this device possesses the ultrafast response time owing to the characteristics of graphene.21The potential applications of the proposed PIT metamaterial include electro-optic modulators and slow-light devices. 4.In summary, we propose a metal–hybrid MM to realize broadband PIT with electrical tunable amplitude and bandwidth of the transparent window. The function can be achieved under different arrangements of graphene positions or applying different independent voltages on each graphene strip. The simulation results show that such MM not only has a significant performance on depth and width modulation of PIT, but also can electrically control both the capability and frequency region of slow light. Obviously, this device will play an important role in THz filtering, sensing, buffering and switching for future THz interconnects.The authors declare no conflict of interest.


To facilitate the rapid development of van der Waals materials and heterostructures, scanning probe methods capable of nondestructively visualizing atomic lattices and moiré superlattices are highly desirable. Lateral force microscopy (LFM), which measures nanoscale friction based on the commonly available atomic force microscopy (AFM), can be used for imaging a wide range of two-dimensional (2D) materials, but imaging atomic lattices using this technique is difficult. Here, we examined a number of the common challenges encountered in LFM experiments and presented a universal protocol for obtaining reliable atomic-scale images of 2D materials under ambient environment. By studying a series of LFM images of graphene and transition metal dichalcogenides (TMDs), we have found that the accuracy and the contrast of atomic-scale images critically depended on several scanning parameters including the scan size and the scan rate. We applied this protocol to investigate the atomic structure of the ripped and self-folded edges of graphene and have found that these edges were mostly in the armchair direction. This finding is consistent with the results of several simulations results. Our study will guide the extensive effort on assembly and characterization of new 2D materials and heterostructures. In recent years, atomically thin layers and heterostructures of van der Waals (vdW) materials prepared via chemical vapor deposition (CVD) or mechanical exfoliation/stacking have been intensively studied because of their unique properties and potential applications in quantum electronics and nanophotonics ,2,3,4. BDifferent atomic-scale microscopy techniques provide complementary information and capabilities. Scanning tunneling microscopy (STM) is capable of obtaining information on electronic band structures but requires a conducting substrate and ultra-high vacuum environment. Transmission electron microscopy (TEM) offers chemical identification capabilities. However, TEM experiments require an elaborate sample preparation process ,27 and oA number of challenges, however, have prevented the wide application of LFM in obtaining accurate images of the atomic lattices of 2D materials routinely ,36,37. L2 and MoSe2) and graphene. By selecting appropriate scan parameters, the geometric distortions in the LFM raw images decreased, and the signal-to-noise ratio in the raw FFT images improved significantly. The protocol allows one to successfully identify and interpret the crystallographic structures of the torn and self-folded edges of graphene. This demonstrated that this protocol can be used successfully to determine the crystalline axes of folded graphene nanoribbons.In this paper, we demonstrated a protocol capable of obtaining atomic lattice images of 2D materials by LFM under ambient conditions. The protocol is based on an in-depth understanding of how feedback loops of an AFM and various parameters such as scan rate, scan size, and gain can influence the LFM raw (unflatten and unfiltered) images in the presence of drifts. In addition, we discussed the effects of load and substrate roughness on the accuracy and sharpness of atomic lattice images of 2D materials. We drew examples from TMD monolayers . Graphene and MoSe2 were prepared by exfoliation using a scotch tape. Each sample thus prepared was attached to a metal disk with a double-sided carbon tape. The carbon tape was squeezed to minimize the viscoelastic behavior of the polymer adhesive to avoid associated imaging artifacts [We purchased a piece of SiOrtifacts ,53.The LFM technique is commonly used to measure the friction between the AFM tip and the sample by recording the lateral deflection signal from the backside of the cantilever. The higher the friction, the more the torsion of the cantilever. An image with 128 × 128 pixels was obtained from a clean Si sample without moving the AFM tip  to evaluate the noise floor. The RMS roughness of this image, calculated using XEI version 4.3.0 , was ~38 pm for the main NX 10 AFM . A noise floor between 30 and 60 pm is considered typical . 2 or MoS2) and multilayer graphene with a Si cantilever (NSC36) under ambient conditions  using the NX10 AFM. The NSC36 series probes  have three beam-shaped cantilevers with different spring constants on one side of the holder chip. Usually, we use the cantilever with the lowest normal spring constant (NSC36C) among them: the lower the normal spring constant of the rectangular cantilever is, the better the lateral force difference can be detected. More precisely, the force sensitivity of the LFM is determined by the torsional spring constant, which is proportional to the normal spring constant for a given rectangular cantilever geometry [2 at a scan rate of 7 Hz and a load of about 10 nN) [We obtained the atomic-scale LFM images of TMDs  ,61,62,63−1. For the cantilever with a normal spring constant of 1.43 Nm−1 (having the lowest LFM force sensitivity among the cantilevers used in our experiments), the torsional spring constant calculated with the dimensions provided by the company was 14.87–23.01 Nm−1 (the range results from the uncertainty of the given tip height) and the lateral optical lever sensitivity obtained from the NX10 following the wedge method using the NT-MDT TGG1 silicon grating was 80.9–112.8 nNV−1 [−1, since the smallest radius of the curvature measured in the experiment is approximately 52.3 nm [−1 Si tip and the reference Si substrate at the load of 10.3 nN (RH: 23% ± 2%) was estimated to be 240.9 Nm−1 according to the Hertz model when the tip was medium sharp , which was proportional to the friction at the tip−sample contact . The lat2 trace image before and after the color range adjustment. To visualize the atomic lattice structure clearly without these black bands, we recommend applying a minimum of 20% overscan (the overscan is an overscanned area that is not used for sampling image data) when acquiring images with a scan size of less than 5 nm. We applied 5−20% overscan throughout the work. Black bands appear on the left of the atomic-scale images, when the color range was adjusted. The origin of the bands is initial sticking . Figure http://gwyddion.net/ (accessed on 10 April 2022) for our analysis. We performed 2D FFT to analyze the atomic-scale LFM images of MoSe2, graphene, and MoS2. The inverse FFT images accurately revealed the respective honeycomb lattices and yielded the expected lattice constants of MoSe2, graphene, and MoS2.We used Gwyddion software from 2 is presented in 2 monolayer  along the fast-scan direction  requires a certain amount of time ∆t, it takes a duration of 2N × ∆t for the tip to cover the equal distance in the slow-scan direction (the y-axis). Therefore, it is important to extract crystallographic information such as lattice constants or crystal orientation from the fast-scan direction which involves negligible distortion. The hexagonal lattice structure in −1). The magnitude of friction is known to change with scan speed [So far, we have investigated the effects of the scan size and the scan rate separately. However, these two scan parameters are related to one another as scan speed = 2 × scan size × scan rate, when the tip moves in a raster fashion during imaging. Thus, it is possible to produce more accurate lattice images by LFM, as long as the scan speed is set high enough to compensate for the drift effect. LFM lattice images obtained from the graphene and monolayer MoSan speed . HoweverNext, we investigated the effect of feedback gain using the example of LFM images taken from multilayer graphene at 19 Hz. For a proper comparison between images, we equally set the maximum/minimum limits of each color bar. Counterintuitively, the image sharpness tended to decrease with the increasing gain a–c. Each2 taken at various setpoints to study the effect of the load  to avoid this type of distortion in the atomic lattice imaging of 2D materials. However, the corrugation of the potential energy surface reduce with the load; thus, the stick−slip contrast can disappear at very low loads (in the adhesive regime) [We compared LFM images of MoSthe load a–c. In othe load a–c. In athe load a–c. We cthe load d–f. Six the load d. In conthe load f. This c regime) . In thisLastly, we investigated the influence of the substrate roughness. We acquired dozens of images from monolayer graphene and multilayer graphene on the same Si substrate (roughness: 0.3–0.4 nm) using a single AFM tip with various combinations of scan parameters following the protocol. A representative atomic lattice image of monolayer graphene is presented in We summarized the protocol established through a series of experiments presented above in 2, and MoS2 using different commercial AFMs (2 and MoS2 monolayers and their FFT images are reported in 2 was taken at 12.9 Hz with a scan size of 300 Å and a gain of 1 (2 was collected at 17.0 Hz with a scan size of 250 Å and a gain of 0.51 (2 (2 lattice (To demonstrate this protocol, we collected several atomic lattice images from graphene, MoSeial AFMs . The LFMial AFMs b and theial AFMs c, confirain of 1 d, while  of 0.51 h using t 0.51 (2 f,g and M lattice i,j-relatWe applied our protocol to another case. One of the most compelling applications of graphene-based materials is to enable control of their physical properties through edge engineering . Thus, aWe found that self-folding and ripping occurred primarily in the armchair direction. Out of four self-folding events, three occurred along the armchair direction, and one along the zigzag direction (solid lines; In conclusion, we have developed a protocol to obtain high-quality atomic lattice images of 2D materials using an AFM operated under the ambient environment. The challenges caused by inevitable thermal drift can be mitigated to a large extent by properly selecting several parameters, including the scan size, scan rate, and gain as well as by disenabling the XY feedback loop. The optimal values for these scan parameters varied with the drift velocity specific to a laboratory. In addition, we found that the load and the substrate roughness influenced the accuracy and the sharpness of the atomic lattice image, respectively, and we estimated the contact area and the stiffness between the AFM tip and the Si substrate using the Hertz model so that others can adapt the proposed protocol readily. Using this protocol, we have demonstrated that the atomic structure of self-folded and torn edges of graphene can be determined. Accurate atomic-scale images can be used to identify local strains and twist angle variations and guide the extensive effort to improve the quality of vdW heterostructures and 2D materials such as graphene, hBN, TMDs, MXenes, and perovskite oxides.


Q) without changing the mutual inductance and footprint of coil at high frequency. The AC resistance of the double-layer coil method can be greatly reduced compared with the general method through simulation and experiment. The work efficiency of WPT system is increased by 4.3%, which verifies the accuracy and flexibility of theoretical analysis.Circular planar spiral coils are wildly used for the magnetic coupling system in a high-frequency wireless power transfer system. The loss of the magnetic coupling system usually takes dominance in the whole system. This paper built the calculation model of magnetic field strength and coil loss, the proposed calculation model can effectively consider the mutual influence between the transmitter and receiver coil and accurately calculated the AC loss of WPT coils. Then, the effect of turn spacing on the AC resistance of coil is analyzed. It reveals that the proximity effect loss is greater when the coil is tightly wound, and the AC loss can be optimized by designing the turn spacing. Based on the above analysis, a double-layer coil method is proposed. This method can reduce the AC loss and improve the quality factor ( It can avoid the disadvantages of using wires and sockets8. The characteristics of the magnetic coupling systems (MCS), including gain, transfer distance, efficiency, and stability, can affect the operating performance of the whole WPT system. And its loss occupies 30% to 50% of the WPT system loss11. Thus, its optimization technique is extremely important to improve the efficiency of WPT system. The magnetic core is not usually used in long transfer distance and high-frequency applications. As a result, the air planar spiral coil optimization becomes increasingly important in the WPT MCS’s design.The magnetic resonant WPT technology is the most widely studied and applied because of its transfer distance and power gradeQ value. In12, the influence of coil turns and turn spacing on self-inductance and AC resistance is analyzed. An optimal design of limited-size wireless power transmission coil is proposed. The optimal Q value is obtained by changing the turns and turn spacing in the case of constant coil size. In13, a method for optimizing the ratio of mutual inductance M and the AC resistance of coils Rac is proposed. This method can obtain the maximum value M/Rac by designing the turns and turn spacing. However, keeping the coil inductance, footprint, and turns constant is difficult in these methods.For the turn spacing optimization of the solid coil, the current method mainly aims to improve the 15, the variable winding width scheme is proposed to reduce the high-frequency AC loss. However, changing the width of each turn for a solid wire coil is impractical. The connection of adjacent turns requires welding, and the welding resistance between adjacent turns cannot be ignored. Double-layer and multilayer coils have been designed for medical implants17. They can provide a high-power efficiency in a limited space by stacking layers of coils together rather than enlarging the coil diameter. However, the coil is a PCB structure, and the traditional AC resistance calculation model of PCB coil is one dimension and unsuitable for double-layer and multilayer coils. The loss of double-layer coil in current schemes usually be obtained by simulation. At the same time, the current double-layer coil structure mainly improves Q by increasing inductance instead of reducing the AC resistance of the coil. In18, a double spiral coil is proposed, and it can improve the coupling coefficient of the WPT system by increasing the interlayer distance. When the interlayer distance is large enough, the quality factor can be improved. However, the too large interlayer distance may lead to an increase in coil volume.The variable winding width scheme and multiple-layer structure coil have been widely studied to optimize printed circuit board (PCB) coil. In19. However, Litz wire has many stranded wires and thin strands, which results in the proximity effect loss of Litz wire being larger than the solid wire in high-frequency applications21. If the frequency exceeds several hundred kHz, the proximity effect will be greatly enhanced and the coil loss will greatly increase.To reduce the skin effect loss of MCS coil, the Litz wire is usually used to improve the efficiency of the WPT system instead of solid coilThe current is distributed to the conductor surface at high frequency due to the interaction of magnetic field between two adjacent conductors, thereby increasing the proximity effect loss. The turn spacing of a tightly wound coil is extremely small, resulting in a greater proximity effect and AC resistance to the coil. Thus, the efficiency of WPT system can be improved by designing the turn spacing of MCS coil.This paper analyzes the AC resistance of the single-turn coil, then deduces the planar spiral coil's AC resistance model and proposes the coil's AC resistance model, which can take the mutual influence between the transmitter and the receiver coil into consideration. Based on the model, a double-layer coil structure is proposed to reduce the winding loss of MCS and improve the WPT system's efficiency without changing the mutual inductance and footprint of coil. Finally, it verifies the correctness of the theoretical analysis by comparing the simulation and experimental results.The rest of this paper is organized as follows. "r-z coordinate system is shown in Fig. Each turn of the air planar spiral coil in the WPT system can be simplified as a concentric circle coil, and its two-dimensional (2D) model in the Rin, outer diameter Rout, and transmission distance h. And the transmitter coil parameters include wire gauge 2r0, turn spacing d0, the radius of the concentric circle of the i-th turn Rp(i) and turns Np, respectively. Moreover, the receiver coil parameters include wire gauge 2r1, turn spacing d1, the radius of the concentric circle of the i-th turn Rs(i) and turns Ns, respectively.The size of the MCS includes inner diameter I in the coil and the external magnetic field strength H in Fig. In the WPT system, the coil loss is related to current I in the coil will result in the skin effect loss, and the external magnetic field H of the coil will result in the proximity effect loss.Firstly, this paper analyzed the loss model of single-turn air planar spiral coil. Furthermore, the high frequency eddy current model of single-turn planar spiral coil is shown in Fig. I from the inside to the outside of the screen, and × represents the oppsite direction compared to ·.In Fig. JE(r0) and the proximity current density JN(r0) can be calculated in Eq. (JE(r0) is only related to current I and JN(r0) is only related to the external magnetic field H.μ0 and σ are the magnetic permeability and the conductivity of the conductor, respectively. fs is the operation frequency, δ is the skin depth and R(i) is the radius of i-th turn coil. ber and bei are Kelvin functions, while J1 and J0 are Bessel functions.According to Bessel and Kelvin functions, the skin current density d in Eq. . And thed in Eq.  that JE turns transmitter coils has only the ez component Hpz(i), which can be expressed as:In accordance with the model of WPT coil in Fig. Ns turns receiver coils has the ez component Hsz(i) and the eρ component Hsρ(i), which can be expressed as:m is obtained by Rs(m) ≤ Rp(i) < Rs(m + 1).The magnetic field strength generated by the Hadd is found.When the turn spacing is small, the proximity effect is larger, resulting in the uneven current distribution in the coil. An additional magnetic field strength JN(r0) is equivalent to two current sources I1 and I2 with the same value and opposite direction in solving Hadd. The direction of I1 is from the outside to the inside of the screen, while the direction of I2 is opposite to I1, as shown in Fig. Ao is the distance between the equivalent current sources and the center of the conductor. It can be solved using Eqs. (ing Eqs.  and 9)  JN(r0) iHadd(i) in the i-th turn coil can be expressed as Eq. ..9). Thusd as Eq. .10\documH(i) in the i-th turn coil can be solved using the process in Fig. The magnetic field strength i0 is the number of iterations, and δ is the maximum error of |H(i)|.H(i)| of the model in Fig. Hpz(i)|, |Hsz(i)|, and |Hsρ(i)| can be further improved by using the process in Fig. Hpz(i)i0|, |Hsz(i)i0|, and |Hsρ(i)i0| can be obtained in accordance with the superposition theorem:For the solution of |r0 = 1.2 mm), the turn spacing will change by changing the radius of the coil outside along the x-axis when the radius of the coil inside is determined . This condition results in different magnetic field strengths in the coil inside, as shown in Fig. For a two-turn coil with a fixed wire gauge | can be solved in accordance with Eqs. ..D0 and DRac with single-layer and double-layer coils are shown in Fig. Rin = 0.1 m, Rout = 0.15 m, N = 20, r0 = 1.18 mm).The calculation results of AC resistance The moving distance should not be extremely large. The moving distance d0 = 0.272 mm.The turn spacing of the single-layer coil is Z0 = 2r0, the turn spacings of the interlaced double-layer coil are D0 = 1.175 mm and D1 = 2.904 mm. The turn spacings of parallel double-layer coil are D0 = 2.983 mm and D1 = 2.903 mm.When the moving distance Z0 = 3r0, the turn spacings of the interlaced double-layer coil are D0 = 2.051 mm and D1 = 2.904 mm. The turn spacings of parallel double-layer coil are D0 = 3.983 mm and D1 = 2.903 mm.When the moving distance In accordance with Eqs. , 13), a, a13), aRac, and the optimization effect is more obvious with the increase in frequency and Z0. The moving distance Z0 is restricted by coil volume and transmission distance. Thus, the moving distance cannot be extremely large. Coil with three or multiple layers can be used. However, the thickness of the coil increases with the increase in the number of coil layers.As shown in Fig. The circuit model of the S/S compensation topology WPT system is shown in Fig. Uin is the DC voltage source, M is the mutual inductance, Cf is the filter capacitor, and R0 is the load resistance. Lp, Rp, Cp, and ip are the transmitter coil's self-inductance, AC resistance, compensation capacitor, and currents. Ls, Rs, Cs, and is are the receiver coil's self-inductance, AC resistance, compensation capacitor, and currents.The MCS is shown in Fig. Comparison case.Three different schemes are adopted for comparison.(2)Optimal case 1.The 2D model of the coil is shown in Fig. (3)Optimal case 2.The coils are designed as interlaced double-layer coils, and the moving distances of the transmitter and receiver coil are 1.2 and 2.36 mm, respectively.The coils are designed as parallel double-layer coils, and the moving distances of the transmitter and receiver coil are 1.2 and 2.36 mm, respectively.Tables As shown in Tables Rin = 0.1 m, Rout = 0.15 m) are the same in different schemes, the mutual inductance M of MCS coils is only related to the product of Np and Ns. So, the mutual inductance M of MCS coils is the same in the three schemes. The consistency of the simulation and measured mutual inductance M values in the three schemes are excellent, and the maximum error between the measured M values is below 0.3% in accordance with Tables Uin and load resistance R0 are the same.When the coil sizes  to analyze the optimization effect of the double-layer coil on the WPT system. Furthermore, the efficiency curves at different input voltage and load resistance are shown in Fig. η is always higher than the comparison case with Uin increases when MCS coils use double-layer coils. It can be seen in Fig. The curve in Fig. This paper analyzes the AC resistance of the single-turn coil, then deduces the planar spiral coil's AC resistance model and proposes the coil's AC resistance model, which can take the mutual influence between the transmitter and the receiver coil into consideration.The affecting factors are analyzed based on the loss model. The proximity effect is obvious with the decrease in turn spacing, and the coil loss increases. The AC resistance of the coil can be reduced by optimizing the turn spacing.A new scheme to optimize MCS coils is proposed-a double-layer coil structure. This scheme can greatly reduce the coil AC resistance and improve the quality factor without changing the coil turns, wire gauge, and footprint.Compared with the air planar spiral coil with a one-layer structure, the parallel double-layer coils can reduce the AC resistance of the coil by more than 40% and the system efficiency of optimized MCS coils is increased by 4.3%.This study proposes the optimized double-layer coil structure for the solid planar spiral coil. The conclusions are summarized as follows:


These values exceed that for a standard platinum thermistor. The Gpl and Gcvd sensors showed the least dependence on relative humidity, which is attributable to the number of oxygen groups in their structures.Four different graphene-based temperature sensors were prepared, and their temperature and humidity dependences were tested. Sensor active layers prepared from reduced graphene oxide (rGO) and graphene nanoplatelets (Gnp) were deposited on the substrate from a dispersion by air brush spray coating. Another sensor layer was made by graphene growth from a plasma discharge (Gpl). The last graphene layer was prepared by chemical vapor deposition (Gcvd) and then transferred onto the substrate. The structures of rGO, Gnp, and Gpl were studied by scanning electron microscopy. The obtained results confirmed the different structures of these materials. Energy-dispersive X-ray diffraction was used to determine the elemental composition of the materials. Gcvd was characterized by X-ray photoelectron spectroscopy. Elemental analysis showed different oxygen contents in the structures of the materials. Sensors with a small flake structure, i.e., rGO and Gnp, showed the highest change in resistance as a function of temperature. The temperature coefficient of resistance was 5.16 Since the isolation of graphene in 2004, this material has been extensively studied, and many experiments have been carried out . GraphenGraphene is produced in many different ways, but two major approaches have been defined: top-down (TD) and bottom-up (BU) methods . TD methOne of the many fields where graphene is studied and used in experiments is active sensor materials. The main differences in the relevant research articles are the production/preparation mechanism and graphene active layer of the sensors, which correspond to different material structures. The production aspect is related to BU versus TD methods. The vast majority of authors report that fabricated temperature sensors are characterized by resistance with a negative temperature coefficient (NTC), but some, e.g., Mahmoud et al.  and Kim 2O3; the devices not only showed hysteresis-free behavior and reproducible device characteristics when stored and operated under ambient conditions for weeks but also possessed stable and reproducible doping levels after thermal treatment and exposure to chemicals [Temperature sensors are manufactured to meet certain requirements. The main requirements are measurement accuracy, a good response time , and consistent performance under varying environmental conditions (mainly humidity). Because of graphene’s sensitivity toward humidity, it has been utilized by many authors as a humidity sensor, and its parameters have been tested. In 2020, Zhu et al. fabricated a flexible humidity sensor with laser-induced graphene electrodes . Graphenhemicals . In 2018hemicals . In 2017In this work, four types of graphene-based temperature sensors were prepared. The materials differed in the graphene production method: two of the materials were made by the TD method, and the other two were made by the BU method. In addition to the dependences that characterize temperature sensors, their humidity dependences were measured. This paper aims to compare these four graphene-based materials in terms of their temperature and humidity responses because the structure of the formed graphene affects these properties of the sensor. Moreover, a comparison of several types of graphene in terms of the effect of humidity on the function of the temperature sensor and temperature dependence has not been found in the scientific literature. Based on the scientific literature and the obtained results, we describe and clarify the basic mechanisms related to these sensor dependences.The first two materials used as the active layers of the tested sensors, reduced graphene oxide (rGO) supplied by Graphenea  and graphene nanoplatelets (Gnp) from Nanografi , were prepared from graphene powder. In both cases, graphene powder was deposited as a dispersion, which was prepared by mixing 1 mg of graphene powder with 1 mL of dimethyl acetamide (DMAC). The mixtures were treated for 6 h in an ultrasonic bath to break graphene agglomerates and thus ensure better homogeneity of the dispersion. Next, the dispersions were centrifuged at 10,000 rpm for 45 min to remove agglomerates that had failed to break during sonication. The active sensor layers were deposited from the prepared dispersions using air-brush spray coating. An alumina plate with gold interdigital electrodes (IDEs) was used as a substrate for the temperature sensors. The width of the electrode fingers was the same as the gap between them, namely, 100 μm see . The che2 atmosphere [Two other types of graphene active sensor layers were prepared by growing graphene on the substrate. Graphene grown from a plasma (Gpl) was prepared by the plasma discharge method, which uses ethanol as the source of carbon atoms and an argon atmosphere, according to the literature . The lasmosphere . Finallymosphere .–9 mbar. A monochromatic Al Kα radiation source with a spot size of 1 mm2 was used to excite the electrons. The pass energy of the electron energy analyzer was set at 50 eV. The take-off angle between the analyzed photoelectrons and the substrate surface was 90°. EDS could not be used to determine the oxygen content of Gcvd, because this material is only one atomic layer in thickness, precluding the effective use of EDS.The graphene layers based on rGO, Gnp, and Gpl were analyzed by scanning electron microscopy (SEM) to verify their structure. A Phenom ProX G6  SEM instrument was used, and images of the layers were created using a backscattered electron detector with an electron beam accelerating voltage of 15 kV at a magnification of 10,000. Then, in conjunction with SEM, energy-dispersive X-ray diffraction spectroscopy (EDS) was used for elemental analysis to determine the amount of oxygen in the graphene structure. A Phoibos 150  spectrometer was used to collect XPS (X-ray Photoelectron Spectroscopy) spectra of Gcvd to obtain information about the amount of oxygen in the structure. The XPS measurements were performed at base pressures lower than 10R (Ω) is the sensor resistance at the maximum value of the parameter under investigation , and R0 (Ω) is the sensor resistance at the minimum value of the parameter under investigation .All temperature tests were performed in a small in-house-developed measuring chamber. The temperature was controlled by the two Peltier elements in a cascade, which allowed the temperature to be adjusted from −10 °C to 120 °C. During the measurement, the sensors were tightly connected over the entire surface of the sensor substrate to the Peltier cell to obtain the fastest possible response to temperature changes. The humidity inside the chamber during measurements was kept at 40 ± 1% relative humidity (RH) to simulate a standard operating environment. The temperature tests for all sensors were carried out from 0 °C to 100 °C with a 10 °C step change, and each step lasted 10 min. A climatic chamber  was used to determine the humidity dependence of the prepared temperature sensors. The RH inside the chamber gradually increased from 20% to 90% with a rate of 0.5% per minute, and the temperature was maintained at 25 °C during the whole test. The humidity test was performed at two constant temperatures, 20 °C and 50 °C, to observe how humidity affects the properties of graphene sensors at different temperatures. The electrical resistance was continuously measured during all tests by an E4980A LCR meter . The sensors were contacted via spring test probes connected to the LRC meter using a 4-wire method. The AC signal voltage was 0.25 Vrms at a frequency of 1000 Hz. The resulting changes in the resistance of the sensors during testing with varying temperature and humidity were converted to a relative change in resistance so that the individual sensors could be compared with each other. The formula for the relative change in resistance is as follows:3/2 and Cu 2p1/2 at binding energies of approximately 933 eV and 952.5 eV, respectively, we can determine the surface atomic content of the material. At approximately 284.5 eV, there is a typical C 1s peak. The typical O 1s peak is very small in the energy spectrum and can be found at approximately 531.5 eV. The surface atomic contents of these three elements were determined assuming a homogeneous distribution of atoms and a Scofield photoionization cross-section. The resulting percentage contents of these elements on the surface are as follows: Cu 2p = 58.96%, which is attributed to the substrate; C 1s = 40.39%, which are the carbon atoms that make up graphene; and O 1s = 0.35%, the oxygen atoms in the graphene structure forming defects. After elimination of the copper substrate, the percentage of carbon in the structure of Gcvd is 99.14%, and that of oxygen is 0.86%. The amount of oxygen in the Gcvd structure is negligible in comparison with the amount of oxygen atoms in the other graphene-based materials.Gcvd was characterized after formation on a copper foil before the transfer process. Most of the peaks in the binding energy spectrum belong to copper see d. From tThe sensor measurements were first performed under different constant DC bias voltages  to verify the effect of the bias voltage on the sensor response. The results of the temperature test are shown in R is the resistance at temperature T, R0 is the resistance at infinite temperature, aE is the activation energy, and bk is the Boltzmann constant. For this type of dependence, a linear relationship between ln(R) and 1/T is assumed. This linearity is confirmed by the dependences presented in 2) is higher than 0.99 for all sensors, which shows good linear dependence. The activation energy was calculated for all sensors, and the obtained values were 40.1, 63.9, 116.5, and 124 meV for Gpl, Gcvd, rGO, and Gnp, respectively. These values are comparable to the activation energies of this type of material reported in the literature [While Gcvd behaves like a metal, the other materials investigated in this study exhibit behavior typical of semiconductor materials. This is mainly due to the material structure, which is determined by the graphene preparation method. Pristine graphene in one or a few atomic layers with a minimal number of defects has a zero bandgap. This is reflected in the fact that in certain cases, pristine graphene behaves as a semimetal. In our case, semimetal-like behavior was observed for Gcvd, where the electron–phonon scattering effect dominates in the temperature dependence of resistance . As the terature ,30. The 90t. The evaluated response time is defined for the temperature change from 20 °C to 30 °C that occurred in the 20th minute of the measurement. A detail of the temperature change area for all tested sensors and the 90t value labeling is shown in 90t of the temperature change (from 20 °C to 30 °C) in the measuring chamber was 59 s.The response time of a sensor is defined as the time it takes to reach 90% of the maximum change in resistance for the variable change between two stable levels . This time is referred to as TCR), which is described by the following equation:R0 is the initial resistance at initial temperature T0 (10 °C) and R is the resistance at temperature T (100 °C). The calculated TCR values for all types of temperature sensors are shown in TCR value, namely, 5.16−3·K−1, and the Gpl sensor has the lowest value, namely, 1.68−3·K−1. For comparison, a typical platinum temperature sensor has a TCR of 3.92−3·K−1. The TCR parameter indicates the temperature sensitivity of a sensor. The sensitivity of the tested graphene sensors is comparable to that of a conventional platinum sensor; notably, the sensitivities of two of the tested sensors exceed that of the conventional sensor. Furthermore, TCR.The characteristic parameter of temperature sensors is the temperature coefficient of resistance , which serves as a charge carrier. The motion of the charge between water molecules is mediated by the Grotthuss mechanism of proton jumps between adjacent water molecules [Despite the fact that Gpl contains oxygen atoms (24%) in its graphene structure, the resistance of the active layer decreases with increasing humidity. This effect is associated with the continuous structure of plasma-prepared graphene and the different charge transfer mechanism in this case. At low RH, water molecules bind to oxygen side groups by physisorption. These molecules are usually bound by a double hydrogen bond, which can occur between hydrogen-terminated groups and oxygen in Holecules . The resolecules .T. The material with the highest temperature sensitivity and thus the highest TCR was Gnp. However, it also had the highest response to humidity at 20 °C, which is due to the number of oxygen groups in its structure. In general, graphene with a flake structure showed a better temperature response. In contrast, the material with the fewest oxygen groups (Gcvd) had the least sensitivity to humidity. This material also exhibited semimetallic behavior due to its uniform continuous structure, which is the reason for its inverse dependence of resistance on temperature compared to those of the other materials. Graphene is a suitable material for temperature sensors for new applications in electronics, such as flexible, stretchable, and wearable electronics, where, among other things, the mechanical properties of graphene are important.Four different graphene-based temperature sensors were successfully prepared, and dissimilarities in their structures were confirmed by SEM characterization, except in the case of Gcvd. Based on the EDS and XPS results, the contents of oxygen and other substances in structures of the tested materials were determined. The temperature dependences of sensor resistance were analyzed by the Arrhenius model, where all sensors showed a linear relationship between ln(R) and 1/


Moreover, by means of centrifugation, the graphene cells were arranged by their diameter, and a gradient, open-cell graphene structure was first fabricated. Based on this unique structure, an amazing microwave absorption value of −62.58 dB was reached on a condition of ultra-low graphene content of 0.53 wt%. In our opinion, such excellent microwave absorption performance results from multiple reflection and well-matched impedance brought by the open-cell and gradient structure, respectively. In addition, the structural strength of the OCGA is greatly improved with a maximum increase of 167% due to the introduction of cell structure. Therefore, the OCGAs with the gradient structure can be an excellent candidate for lightweight, efficient microwave absorption materials.Development of high-performance graphene-based microwave absorbing materials with low density and strong absorption is of great significance to solve the growing electromagnetic pollution. Herein, a controllable open-cell structure is introduced into graphene aerogels by the graphene oxide (GO) Pickering emulsion. The open-cell graphene aerogel (OCGA) with multiple microstructures shows a significantly enhanced microwave absorption ability without any additions. A high microwave absorption performance with the minimum value of reflection loss (RL In recent years, emerging technologies such as Internet of Things, 5G communication and satellite networks bring about kinds of electromagnetic waves in our environment, which are harmful to human health, electronic devices, aerospace, information security, etc. Therefore, in order to solve above problems, the development for high-performance electromagnetic absorbing materials with low reflection, wide absorption band and small density becomes an urgent need. Graphene aerogels have been widely studied in the electromagnetic absorption applications because of their excellent electrical properties, lightness and high specific surface area. However, their poor matching impedance and single attenuation mechanism lead to unsatisfactory absorption performance . So varimin of graphene aerogels can be reduced to below −60 dB by above methods, a large thickness (about 5 mm) or high fill rate (0.74 wt%) is necessary [In order to meet the demands for light weight and high efficiency, researchers focus on microstructural adjustment of graphene aerogels. Various methods including mechanical compression, oriented structure and changing porosity have been applied to improve microwave absorption performance of aerogels ,16,17,18ecessary ,21. Thismin of −51.22 dB, whose density was only 4.81 mg/cm3. To improve the microwave absorption properties further, the OCGA with a gradient cell diameter structure (OCGA-G) was designed and prepared. This gradient aerogels without any additional phase showed a maximum effective absorption bandwidth  of 8.55 GHz and a RLmin of −62.58 dB at the thickness of 3.2 mm and ultra-low fill rate (0.53 wt%). In our opinion, the multiple, gradient structure of OCGA-G greatly increases the microwave transmission path, strengthens multiple reflection loss and provides an excellent impedance matching characteristic, so that OCGA-G achieves the ultra-light, broadband and strong microwave absorption.Herein, to obtain the strong microwave absorption performance, an open-cell structure was introduced into graphene aerogels via the self-assembly and freeze-drying process. The OCGA with multiple microstructures exhibited an enhanced RL2H4·H2O (80%) was obtained from Yiweian Chemical Technology . Sliced paraffin (54~56 °C) was obtained from Shanghai hushi chemical reagent and analysis instrument Co., Ltd. .Pristine graphite  and diphenyl ether  were obtained from Shanghai Aladdin Bio-Chem Technology Co., Ltd. . Concentrated sulfuric acid (98%), hydrogen peroxide (30%) and Potassium permanganate were obtained from J&K Scientific. N2H4·H2O vapor at 100 °C for 18 h. Finally, the OCGAs were obtained by heating at 110 °C for 2 h in a vacuum oven to eliminate the residual N2H4·H2O.GO solution was prepared from graphite powder through an improved Hummer’s method as reported in our previous paper ,23. A miThe Pickering emulsions prepared at different rotation speeds were mixed together in equal proportion and centrifuged at 2000 rpm for 5 min. The centrifuged emulsion was extracted carefully and frozen dried to obtain gradient GO aerogels. After the reduction treatment in the same way of OCGA, the OCGA-G was prepared.−1 to 4000 cm−1 to obtain the FTIR spectra. Raman spectroscopy was carried out with an inVia confocal Raman microscope  using the 514.5 nm laser excitation with an objective magnification of 50× (10 mV spot diameter: 1 μm). The X-ray diffraction  patterns were recorded with a scanning rate of 1° per minute in a 2θ range from 5° to 80° with Cu Kα radiation (λ = 1.5418 Å) to characterize the inter layer spacing . The compression properties of aerogels were tested by RGM-4100 type microcomputer controlled universal material testing machine produced by Shenzhen Regal Instrument Co., Ltd. .Scanning electron microscopic (SEM) images were taken on a Zeiss Ultra Plus  field emission microscope  was employed to analyze the of functional groups and GO and graphite pellets were prepared using KBr and the samples were scanned in the range from 400 cm1), and the other part infiltrates into the absorber (2). If R1 and R2 meet the conditions of interference cancellation, then extinction effect can be obtained, leading to a dissipation of them at the air-absorber interface and resulting in enhanced microwave absorption performance. At this time, the reflected microwave energy will reach the lowest value and the reflection loss reach the peak.The principle of transmission line calculates the input impedance and reflection loss of single-layer microwave absorbing material with a metal backplate. As shown in the figure below, when an incident wave hits on the surface of absorber, it is divided into two parts, one part reflects from the surface into air (Rabsorber a. The abrε = ε′ − jε″) and relative complex permeability (rμ = μ′ − jμ″) of OCGAs were measured on a vector network analyzer  at 2–18 GHz , pε″ is the imaginary part corresponding to the relaxation polarization, and cε″ is the imaginary part corresponding to the conductivity loss.The enhancement of the complex permittivities can be interpreted by Debye relaxation theory as expressed in the following equations :(3)ε′(ω)mt) with peak frequency (mf) are described by the following equations [rε| and |rμ| are the modulus of measured rε and rμ at mf.The quarter-wavelength matching model is used in this study, in which the relationship of absorbers thickness (quations :(5)tm=nc2H4·H2O vapor. Through the above process, a series of OCGAs was prepared by adjusting the concentration of GO solution, the volume ratio of GO solution to DE and the rotational speed.−1 and 2500 cm−1 in the IR spectrum [−1 is attributed to C=O stretch of carboxyl group [−1 corresponds to C-OH stretch of alcohol group [−1 is attributed to C-O stretching vibrations of C-O-C [−1 is attributed to C=C stretches from unoxidized graphitic domain [2H4·H2O successfully reduced graphene oxide. However, all peaks did not disappear, which indicates that the GO was not completely reduced and suggests the presence of some functional groups.In order to explore the preparation process of aerogel, we carried out scanning morphology analysis, infrared spectrum analysis, Raman spectrum analysis and XRD analysis. Through SEM analysis, we found that the micro morphology of aerogel gel is a three-dimensional network structure composed of interconnected open-celled microspheres a. FT-IR spectrum ,29. The yl group  while 12of C-O-C  and the c domain . All thec domain . This su−1, respectively. Additionally, the intensity ratio of the two peaks (D and G) in the Raman spectrum of graphene is higher than that of graphene oxide [2 carbon atoms in graphene is higher than that of sp3 carbon atoms, which means that the average size of the sp hybridized carbon planes in graphene is larger than that of graphene oxide. This shows that when graphene oxide is reduced under the present experimental conditions, only part of its sp3 carbon atoms are reduced to sp2 carbon atoms.Raman spectra has long been considered as the simplest and non-invasive tool to characterize the structure of carbon . Figure ne oxide ,35, indi3, 4.81 mg/cm3 and 7.22 mg/cm3 were prepared using the GO solution with the concentration of 5 mg/mL, 10 mg/mL and 15 mg/mL, respectively. The volume ratio of GO solution to DE was 4:1, and the rotational speed was 15k rpm. The obtained OCGA with low, medium and high densities were named OCGA-L, OCGA-M and OCGA-H, respectively.It is well known that the density of graphene aerogels could affect the framework character, which is the usual way to adjust microwave absorption properties. The relationship between the microwave absorption performance of OCGA and its density was investigated at first. OCGAs with densities of 2.43 mg/cmε′ and ε″ decrease with the increasing frequency. As the graphene content increases, a significant enhancement is achieved in ε′ and ε″ (ε′ and ε″ is explained as follow. According to Equation (3), ε′ is related to the amount of polarization, which represents the ability to store electrical energy from the electric field. Aerogels containing much graphene can produce more dipole-like orientational polarization and interfacial polarization. Therefore, the increase in density of OCGA is responsible for the enhancement of ε′. In addition, according to Equation (4), the increase in ε″ is not only attributed to enhanced polarization loss, but also to conduction loss. As the content of graphene increases, the conduction of aerogel. This promotes more electron migration between graphene cells and leads to an increase of the conduction loss. Therefore, ε′ and ε″ both significantly enhance with the increasing graphene content. Furthermore, because the OCGAs are composed of pure graphene without any magnetic component, all samples show μ′ and μ″ at around 1 and 0, indicating a negligible magnetic loss for incident electromagnetic wave [The framework morphology of OCGAs with different density was observed using SEM. As shown in ′ and ε″ d,e, whictic wave .min. For OCGA-H with higher dielectric loss, most microwaves cannot enter inside this dense aerogel due to the mismatched impedance. Proper dielectric loss and good impedance matching , 0, 0.125, 0.250 and 0.375 at the same rotational speed. The obtained graphene aerogels were named GA, OCGA-DE1, OCGA-DE2 and OCGA-DE3, respectively.The cell number was regulated by the ratio of DE to GO solution during emulsion preparation process. The OCGAs with a growing number of cells were fabricated using Pickering emulsion with increased DE/GO solution ratios  was placed on different graphene aerogel. As shown in The compressive strength of graphene aerogels is also obviously improved when the cell structure is introduced. The compression performance of GA and OCGAs with different cell sizes was tested. The results show that compression strength of GA without cell structure is 3.6 kPa. When the cell structure exists, the compressive strength of OCGAs increases obviously, and its maximum value reaches 9.5 kPa of OCGA-20K with a 167% increase a. Based 3) and GO solution (1.01 g/cm3), the DE microspheres in Pickering emulsion can be accelerated to settle by the simple centrifugation treatment , ρ′ is the density of the continuous phase (GO aqueous solution in this study), and η is the shear viscosity of the continuous phase. Based on this, the Pickering emulsions containing DE microspheres with different sizes were centrifuged to obtain a gradient distribution. The OCGA-G with gradient cell size cell was first prepared using this centrifugated emulsion through the process of freeze-drying, vapor ejection and chemical reduction in turn. Furthermore, as comparison groups, the OCGAs using the same Pickering emulsions after mixing (OCGA-m) and precipitating for 2 h (OCGA-P) were also prepared, respectively.Here, The SEM of OCGA-G shows an obvious gradient structure along thickness direction b–d. At tmin for OCGA-m (min decreases slightly to −42.88 dB. Furthermore, the peak shifts towards the high frequency region (min is declined dramatically to −62.58 dB at 14.73 GHz, and the matching thickness is also reduced to 3.2 mm. Furthermore, the maximum value of EAB reaches 8.55 GHz in OCGA-G at a matching thickness of 3.7 mm (The distribution state of the cells has a significant effect on the electromagnetic parameters  and micrr OCGA-m e is −35.y region f. For OCf 3.7 mm g,h. It iWe consider that these outstanding performances of OCGA-G root in its gradient structure, and the different positions in aerogels play different roles in the microwave absorption. Firstly, the large opening cells at the bottom of OCGA-G can improve the impedance matching between the surface and the air and reduce the reflection of microwave, which make large amounts of microwave enter the aerogels . Then, wmin reached −62.58 dB at a thickness of only 3.2 mm, and the EAB was as wide as 8.55 GHz. In addition, the structural strength of the OCGA was greatly improved with a maximum increase of 167% due to the introduction of cell structure. Thus, this work provides an inspiration for the design and preparation of ultralight, efficient microwave absorption materials using multiple structures.In summary, OCGAs with open-cell structures were prepared using the GO Pickering emulsion, which is a meaningful way to fabricate large-size aerogels for practical applications. The cell structures including number and size could be changed by the ratio of DE to GO solution and rotational speed, respectively. By means of the changeable multiple microstructures, OCGAs had adjustable impedance matching and attenuation characteristics, which will greatly optimize microwave absorption properties without any additional phase. Moreover, a gradient design for diameter distribution of cells was first described, and the OCGA-G with gradient structure showed surprising electromagnetic performance that RL