Graphene nano-electromechanical resonant sensors have wide application in areas such as seawater desalination, new energy, biotechnology, and aerospace due to their small size, light weight, and high sensitivity and resolution. This review first introduces the physical and chemical properties of graphene and the research progress of four preparation processes of graphene. Next, the principle prototype of graphene resonators is analyzed, and three main methods for analyzing the vibration characteristics of a graphene resonant sheet are described: molecular structural mechanics, non-local elastic theory and molecular dynamics. Then, this paper reviews research on graphene resonator preparation, discussing the working mechanism and research status of the development of graphene resonant mass sensors, pressure sensors and inertial sensors. Finally, the difficulties in developing graphene nano-electromechanical resonant sensors are outlined and the future trend of these sensors is described. As the core device in measurements, silicon micro-resonant sensors play an important role in atmospheric parameter measurement system, aerospace ground test system, industrial automation production, consumer electronic products, etc. ,2,3,4,5.3, which is lower than that of single crystal silicon. When graphene has a size of micron, its fundamental frequency can reach megahertz [In 2004, Konstantin Novoselov and Andre Geim of Manchester University used mechanical exfoliation to exfoliate a single-layer graphene sheet (SLGS) from graphite , triggeregahertz . In receegahertz ,19,20,21egahertz ,24,25,26egahertz  and chemegahertz ,29, predegahertz ,36,37,38Because graphene has excellent crystallinity, the preparation process of single-layer and multi-layer graphene has been rather mature. There are mainly four preparation methods: micromechanical exfoliation , SiC epiThe present review focuses on the application of graphene in nano-electromechanical resonators. Herein, the birth of graphene and its physical and chemical properties are introduced, and the principle prototype of graphene resonators is presented. Three theoretical model of graphene sheets: molecular structural mechanics, non-local elastic theory and molecular dynamics. The preparation of graphene resonators is reviewed, followed by the application of graphene resonant mass, pressure and inertial sensors. This paper highlights high-performance graphene resonators, paving the way for future research on graphene nano-electromechanical resonant sensors.2 insulating layer with shallow grooves through intermolecular van der Waals force to form a double-clamped beam. Gold electrodes are arranged at both ends of the SiO2 layer, which can vibrate the resonator in MHz through electrical excitation. The frequency of a single-layer graphene resonator is 70.5 MHz, detected by optical interferometry, and the quality factor Q is about 78 in the experiment. This frequency is much larger than the resonant frequency when graphene is natural bending, indicating the presence of internal tension in the resonator. This result may be due to the friction between the graphene and the substrate during device preparation [After the emergence of the SLGS in 2004, the prototype of the nanoelectromechanical resonator is produced by Bunch with single-layer and multi-layer graphene sheets in 2007, providing an important experimental and theoretical basis for designing and examining graphene resonators . The sinparation .In In 2009 a single-layer graphene resonator with electrical signal output is shown in The resonator with suspended the graphene sheet on the surface of the SU-8 rubber substrate is shown in The above explorations of the structural design, signal detection, and additional factors of the graphene resonator prototype have laid an important foundation for the subsequent application of graphene resonators in the field of sensing technology. In order to examine the resonant characteristics of graphene in depth, researchers have carried out comprehensive research from multiple perspectives such as the simulation and experiment of graphene resonant beams, graphene resonator processing, and applications of graphene resonators.Graphene resonators mostly use a single-layer graphene beam as sensitive element. The measured state can be reflected by the change of the output frequency of graphene beams. The thickness of single-layer graphene is only 0.335 nm. The establishment of the ultra-thin material graphene resonant beam model and the choice of analysis method affect the design of the graphene resonator structure and the experimental structural analysis. In this section, we will introduce three main analysis methods of graphene resonant sheets.Single-layer graphene is at the magnitude of microscopic atom and molecule. Molecular structural mechanics equates atoms to individual nodes. Using Cauchy-Born rule, the force between atoms is equivalent to that between nodes, and the vibration potential energy between atoms is converted to the strain energy in mechanics. Structural mechanical equations are established to obtain mechanical parameters, and molecular structural mechanics first needs to determine the model for graphene modeling.In 2008, Juan et al. approximated a single graphene sheet to an elastic thin plate using the continuous elastic theory. The equilibrium shape and motion equation of the graphene sheet under external forces were derived. The static and dynamic responses of defect-free quadrilateral supported graphene were studied, and the formula for calculating the resonant frequency was deduced .In 2009, Scarpa et al. proposed a truss-type analysis model and studied the in-plane linear elastic properties of graphene monolayers based on the theory of cell material mechanics. This study provids not only information about the mechanical properties of an SLGS, but also the results of the equivalent mechanical deformation mechanism when an SLGS is subjected to uniaxial small strain and pure shear load. Pure shear load exerts a tensile effect on the carbon-carbon bond of an SLGS . In 2011In 2013, Sakhacee et al. used molecular structural mechanics to simulate the vibration behavior of flawless SLGS at a constant temperature. The fundamental frequencies of the zigzag and armchair SLGS with different chiral configurations were obtained under the cantilever and fixed-support boundary conditions by simulating the carbon atoms in graphene lattices with equivalent structure beams and centralized mass units . In 2013Non-local elastic theory, an extension of classical continuum theory proposes that the conservation laws of mass, energy, and momentum are valid for an object as a whole, but that arbitrarily small voxels divided by the object may not hold. Additionally, the stress component of an arbitrarily small voxel as a reference point x depends on the strain components at position x, at all the other points of the object . This thIn 2009, Murmu et al. studied the vibration characteristics of monolayer graphene sheets, using non-local elastic theory. The theory takes into account the small size effect introduced in the nanoscale structure. With a small size of an SLGS, it is found that the resonant fundamental frequency of an SLGS is rather sensitive to size changes . In 2011In 2014, Chang et al. explored the possibility of using peripherally clamped double-layer circular graphene as a nano-mechanical resonator based on non-local elastic theory. The frequency equation of the resonant cavity with attached mass at any position was derived and the influence of the parameters on the vibration frequency and sensitivity of the resonator was studied. The results show that the farther the attachment mass is from the center of the resonator, the higher the frequency and the lower the sensitivity, that the frequency and sensitivity of the double-layer graphene resonator decrease with the increase of the aspect ratio, and that the sensitivity increases with the increase of the local nano-meter parameters . In 2016Molecular dynamics is an analytical method based on classical mechanics. The object of molecular dynamics is atoms, and this model is composed of several atoms. The core idea of molecular dynamics is to calculate the positions and trajectories of all atoms in the simulation system, using statistical analysis to obtain the macroscopic physical quantities of the system. Statistical physics holds that macro physical phenomena are intrinsically related to the movement of microscopic particles, and that the macroscopic quantity is equal to the statistical average of the microscopic quantities. Therefore, by knowing the relevant laws and trajectories of all atoms in the system, macroscopic physical quantities can be obtained.Molecular dynamics examines atoms, and its model is composed of several atoms. The core idea of molecular dynamics is to calculate the positions and trajectories of all atoms in a simulation system, and obtain the macroscopic physical quantities of the system with statistical analysis. According to statistical physics, macro physical phenomena are intrinsically related to the movement of microscopic particles, and the macroscopic quantity is equal to the statistical average of microscopic quantities. Therefore, knowledge of the relevant laws and trajectories of all atoms in a system can generate macroscopic physical quantities.With molecular dynamics, Kwon et al. studied a nano-scale graphene-nanoribbon-resonator in 2012, finding that the resonant frequency of graphene is greatly affected by driving force and axial strain, and that the tunable range of resonant frequency decreases exponentially with the increase of axial strain or driving force, as shown in In 2013, Kang et al. studied suspended graphene nanoribbons resonators using molecular dynamics. The simulation results show that the resonant frequency of graphene nanoribbons depends on the average tension on both sides of the ribbons. The tension comes from two aspects. One is the deformation caused by the electrostatic force generated by the grid voltage; the other is the initial strain caused by the mismatch between the negative thermal expansion coefficient of graphene and the positive thermal expansion coefficient of the substrate when the ambient temperature changes. As the initial strain increases, the tunability and frequency tuning range of the graphene nanoribbons decrease. Therefore, if the axial tension can be changed by pending measurement, the graphene resonator will have the potential for the measurement of physical quantities such as high sensitivity mass, acceleration and pressure .In 2013, Kim et al. used classical molecular dynamics simulation to study the mechanical response of nano-scale graphene resonators . In 2014In 2016, Zhang used molecular dynamics simulation to study the vibration characteristics of an SLGS, including its free vibration resonant frequency and mode, and the effect of boundary conditions on the resonant frequency, such as size, initial strain, initial displacement, aspect ratio and chirality. It is found that the fundamental frequency of single graphene nanoribbons can reach GHz. When the size of graphene is small, there is a non-linear relationship between the resonant frequency and the size. With the increase of the size, the resonant frequency changes approximately linearly with the size. The strain change of graphene has greater influence on the fundamental frequency while the width and chirality of graphene have less influence on the change of the resonant fundamental frequency ,75.At present, there is no perfect theoretical model for the research on the resonant characteristics of graphene. Among the existing models, molecular dynamics is used to simulate the movement of molecules or atoms, and the result is closer to the experimental data. However, this method is usually used for nano-scale structure. For micron-sized structure, calculation is extremely time-consuming and complex, so it is necessary to find new solutions.For multilayer graphene, macroscopic continuum theory can be used to approximate the model by using thin plate, shell and other continuous media models. Then the mechanical behavior and mechanical properties of graphene such as bending, stretching and vibration can be analyzed by Euler beam theory, Timoshenko plate and shell theory, etc. . The numThe results of the above-mentioned studies show that for small size graphene sheets, the resonant frequency calculated by the classical continuous model is higher than that calculated by molecular dynamics or non-local elastic theory. This is because the small-scale effect of graphene is not taken into account by classical mechanical model. A comparison of molecular dynamics and non-local elastic theory shows that the small-scale effect of graphene depends on the boundary conditions and vibration modes of graphene, and that the small-scale effect has the least influence on the resonant frequency under the four-sided clamping. Thus, graphene nanoribbons with an appropriate size, aspect ratio, and boundary conditions are expected to be used to make high-sensitivity sensors detecting weak pressure, acceleration, and additional nano-mass.The research of graphene resonator technology is the key to ensuring stable output of graphene resonators and their quantitative production. In recent years, the preparation process of graphene and graphene resonators has also been extensively studied.In 2008, Jeremy et al. pioneered the preparation of large-scale and few-layer reduced graphene oxide sheets through oxidation and exfoliation, and the drum-shaped graphene resonator is produced, as shown in A method is reported to fabricate a large-scale double-clamped suspended epitaxy single-layer graphene resonator by wet chemical etching, providing experimental and theoretical basis for the implementation of graphene resonator array. The size of the double-clamped graphene beam in In 2010, Paul L. McEuen et al. produced large scale single-layer graphene sheets by CVD, and fabricated suspended graphene resonator array, as shown in 2 film has been developed by CVD. The quality of the prepared graphene has been significantly improved, the size of the substrate is not limited, the cost is greatly reduced, and the transfer is easy to achieve [2 under the metal electrode contact will be removed, resulting in mechanical structural instability in the process of using buffered hydrofluoric acid (BHF) to remove part of the SiO2. The manufacturing process of suspended graphene devices by using LOR etchant effectively solves this problem. The polymer under the graphene layer was effectively removed by using organic solvents irresponsive to inorganic materials such as metals and insulators, and a desirable effect and a stable mechanical structure have been obtained [The above-mentioned literature on the method for fabricating graphene resonators seldom discusses how to fabricate high-quality graphene sheets. In recent years, growing single-layer or multi-layer graphene on the surface of metal Cu and Ni foil or SiO achieve . The Ins achieve . Among t achieve . Howeverobtained .These preparation and transfer technologies have opened up possibilities for manufacturing various graphene devices with unique configurations and enhanced performance.As soon as the graphene resonator was developed, research on its application to sensors has been reported. As early as 2007, Bunch et al. pointed out the great potential of graphene resonators in quality and mechanical quantity detection during the experimental study of graphene nano-electromechanical resonant sensors (NEMS) . In thisThe fundamental vibrational frequency of micron-level single-layer graphene has reached MHz , and anyIn 2008, using molecular structural mechanics, Sakhaee et al. studied the influence of single-point mass and atomic dust on the resonant frequency of an SLGS. The numerical results show that the SLGS is sensitive to adsorption mass, and that the sensitivity of mass detection is as high as 10–21 g. For the same size of the additional mass, the frequency offset of a graphene sheet increases with the increase of the length-width ratio of the sheet .In 2013, Kwon et al. used molecular dynamics simulation method to study the relationship between the fundamental frequency and additional mass of a double-clamped suspended graphene resonator, as shown in In 2014, Fazelzadeh et al. studied a nano-size mass sensor based on an SLGS in a thermal environment, using rectangular nano-sheets simply supported on four sides as structural model. The non-local slab model and Galerkin numerical calculation method were used to derive the analytical solution of the frequency deviation of the SLGS with respect to variables such as nanoparticles , temperature, and nanoparticle position. Numerical calculation shows that the relative frequency deviation of the SLGS increases with the increase of temperature, the sensitivity also increases. The closer the additional nanoparticles are to the center of the sheet, the greater the relative frequency shift becomes . In 2015In 2013, Natsuki et al. studied the feasibility of simply supported double-layer graphene sheets for mass sensing. The frequency-additional mass response of single-layer and double-layer graphene sheets is compared and analyzed by the continuum model, as shown in In 2019, Xiao studied the relationship between the resonant frequencies of peripherally supported graphene sheets and the adsorption mass by molecular dynamics simulation. The effects of different high-order modes, the size and the position of the adsorption mass were studied, and a mass solution method based on high-order modes was proposed . In 2021Taken together, single or double-layer graphene resonators have the potential for ultra-high sensitivity of mass detection. However, current research mainly involves theoretical analysis and simulation calculation, lacking necessary experimental data. This will pose difficulties for practical application of the graphene resonant mass sensor.Pressure sensors are one of the most widely used sensors in industry, and many physical quantities of these sensors are shown by pressure. Graphene is a sensitive element in graphene resonant pressure sensors, and has two main shapes: drum shape and beam shape. When subjected to pressure, graphene changes its resonant frequency, and detecting this change can help measure pressure. The difference of the theoretical model lies in the modal analysis of peripheral fixed support and double-clamped of graphene. In the design of drum-shaped graphene resonant pressure sensors, Raj eliminated parasitic capacitance with high-resistance sapphire (resistivity > 1014 Ωm) substrate. Through direct radio frequency drive and detection, the resonant frequency of the multilayer graphene sheet becomes as high as 200 MHz and the mechanical quality factor is close to 500, as shown in For graphene resonant pressure sensors with a double-clamped beam structure, the secondary sensitivity method has been mostly used to avoid direct contact between the graphene beam and the medium, mainly in the stage of finite element simulation. The structure designed by Jiang employed the concept of classic silicon micro-resonant pressure sensor compound sensitivity. The square silicon diaphragm was used as the primary sensitive element to directly sense the measured pressure. This pressure acted on the silicon diaphragm to deform the silicon diaphragm, causing the axial strain and stress change of the graphene beam, while the rectangular graphene beam suspended above the cavity acted as a secondary sensitive element to indirectly sense the pressure as shown in The experiment and simulation of the structure of graphene resonant pressure sensors enable the detection of a series of physical quantities that can be output through changes in force. On this basis, inertial force and Coriolis force have been effectively expressed.Inertia is the inherent property of all objects. They have inertia whether they are solid, liquid or gas, and whether they are moving or stationary. Inertial measurement is to detect the state of an object by using inertial sensitive elements such as gyroscope and accelerometer to determine the relative position and state of an object. This measurement is used in many fields such as navigation positioning, consumer electronics, and motion carrier control. Inertial sensors are divided into two categories: angular velocity gyroscope and accelerometer. The detection principle of the gyroscope is mainly based on: Coriolis effect and Sagnac effect. For Coriolis effect, Coriolis force is proportional to the input angular rate; for Sagnac effect, phase difference is proportional to the input angular rate. The detection principle of the accelerometer is mainly based on Newton’s second law, in which the magnitude of the acceleration of an object is proportional to the force and inversely proportional to the mass of the object, and the direction of acceleration is the same as that of the force. Graphene resonant inertial sensors can achieve high sensitivity signal output due to the mechanical property of graphene, but the structure design of the sensor itself is the basis for effective, reliable and high-quality signal detection.2 substrate through intermolecular van der Waals force. This adhesion is also reflected in the proof mass of graphene to SiO2/Si, which can realize the adhesion of small mass at the bottom of suspended graphene [After 2007, Bunch et al. examined graphene resonators, through experimental analysis, and proved that graphene has a strong adhesion to the surface of SiOgraphene ,100,101.In 2012, Kang et al. designed a graphene nanoribbon acceleration sensor, as shown in 2 insulating film. The layer is polished by CMP method and the graphene sheet is transferred on the layer, and then the periphery of the graphene film is fixed on the SU-8 resist substrate to form a drum resonator. On this basis, the cylindrical SU-8 resist proof mass is placed at the center of the graphene sheet. The proof mass senses the acceleration to change the deflection of the graphene sheet and change the conductivity of the graphene sheet. The acceleration value is obtained by measuring the change of conductivity. Although the detection method is non-resonant, the preparation method of drum resonator provides a reference process route for preparing graphene resonant accelerometer [In 2015, Lee et al. combined graphene drum resonator and SU-8 resist proof mass to create a graphene accelerometer, as shown in erometer ,104.2 insulating layer. Under the action of external acceleration, the additional mass senses the inertial force and causes the deformation of the graphene sheet, resulting in the change of the resonant frequency of the graphene sheet [In 2017, Jie et al. simulated and analyzed the sensitivity of the graphene resonator to acceleration by using COMSOL Multiphysics finite element software. The sensitive structure is shown in ne sheet . In 2018ne sheet .In the design of a graphene resonant acceleration sensor, sensitive mass block is usually introduced as a sensitive element for acceleration detection to change the vibration state of graphene. This introduction enables graphene to generate residual stress during the transfer of graphene to the mass block. In 2020, Fan uses SOI wafer to release the process flow of mass block by sacrificially removing the box layer, combining dry etching with steam HF etching. The weight of sensitive mass block Si is three orders of magnitude greater than that of SU-8 , six ordIn 2021, Lu et al. designed a graphene resonant gyroscope structure with direct output frequency. The variation law of resonant frequency of graphene with different structure parameters and angular velocities is calculated by finite element simulation. The ultra-high sensitivity of diagonal velocity can realize the sensitivity to extremely weak angular velocity .In summary, the graphene resonator can realize the detection of mass, force and other physical quantities based on the measured modulation law of the vibration characteristics of graphene sheets. The preparation technology of graphene materials and related resonators has achieved great progress and has made corresponding progress in the fields of quantum effects and optoelectronic devices ,25,26,37(1)Process. It is still difficult to prepare high-quality graphene with a regular shape, but it is easy to introduce initial stress and strain in the process of graphene matrix transfer. This affects the tunability of graphene resonators. In addition, the effect of electrostatic force, temperature and other interference factors should be fully considered.(2)Overall structure design. The existing literature mainly studies the effect of sensing on graphene resonators from the perspective of the graphene resonator itself, but the research related to the overall structure modeling and optimization analysis of the sensor is not sufficient. A perfect structure is helpful in improving the measurement sensitivity and measurement range of the sensor, and is thus convenient for the design of device processing technology. Overall structure design of graphene resonant NEMS sensors needs to adequately consider the reasonable processing technology, boundary conditions and actual working conditions, reasonably using the theoretical and simulation analysis methods.This paper has reviewed the properties of single-layer graphene, four common graphene material preparation technologies, and the development of graphene resonators from the perspectives of experiments, vibration characteristic analysis and preparation process. This review focuses on the application of graphene resonators in mass, pressure and inertial measurements. Since the research on graphene nano-electromechanical resonant sensors is still in its infancy, two main challenging problems remain to be solved before the fabrication of graphene resonant sensor products:In addition, the graphene resonant sensor works in a resonant state, so the realization of closed-loop self-excited system and weak signal detection are also the key to technical issues. Graphene resonant sensor cannot replace MEMS sensor at the current level of processing and detectionTo sum up, graphene plays an important role in the field of nano-electromechanical resonators, and graphene resonators has developed rapidly due to their high quality with preparation optimization and high sensitivity detection. In the future, graphene nano-electromechanical resonant sensors will have broader prospects in such fields as biological detection, energy and chemical industry, and inertial navigation.


With the research and the development of graphene-based materials, new sensors based on graphene compound materials are of great significance to scientific research and the consumer market. However, in the past ten years, due to the requirements of sensor accuracy, reliability, and durability, the development of new graphene sensors still faces many challenges in the future. Due to the special structure of graphene, the obtained characteristics can meet the requirements of high-performance sensors. Therefore, graphene materials have been applied in many innovative sensor materials in recent years. This paper introduces the important role and specific examples of sensors based on graphene and its base materials in biomedicine, photoelectrochemistry, flexible pressure, and other fields in recent years, and it puts forward the difficulties encountered in the application of graphene materials in sensors. Finally, the development direction of graphene sensors has been prospected. For the past two years of the COVID-19 epidemic, the detection of the virus sensor has been investigated. These new graphene sensors can complete signal detection based on accuracy and reliability, which provides a reference for researchers to select and manufacture sensor materials. A sensor is a kind of detection device that can convert the received information into an electrical signal or other signal output. In this era of intelligence, digitization, and networking, sensors, as “electrical facial features”, have become the main way and means of obtaining information. The requirements for sensor sensitivity and application range are also higher and higher. The sensitive element of the sensor is very important for the performance of the sensor, which directly affects the accuracy, sensitivity, and detection range of the sensor. The applications of sensors in biomedicine, flexible pressure, and photoelectrochemistry introduced in this paper have penetrated all aspects of our life and made indisputable contributions to the development of modernization.Graphene is a single-layer planar film with a hexagonal honeycomb lattice composed of carbon atoms. Graphene material has excellent electrical and mechanical properties due to its special structure, which has attracted extensive attention in the engineering field. The sensor is considered to be one of the most promising applications of graphene . At pres2 and NH3. Although carbon nanotubes as electrochemical sensors are still in their infancy, they have also shown great potential [Carbon nanotubes and graphene belong to graphite materials. Structurally, carbon nanotubes are helical, while graphene is a flake, but they all have some common characteristics of graphite, such as excellent conductivity. Therefore, due to the small size, large specific area, different bond states on the surface and inside the particles, and incomplete coordination of surface atoms, carbon nanotubes have also become an ideal additive for conductive materials. As an electrode material, carbon nanotubes have better electrochemical properties than traditional carbon electrodes and can be used to detect a variety of gases such as NOotential . After cotential . The vibotential ; The defotential . Therefootential . The autGraphene is a single atom thick honeycomb structure formed by a two-dimensional carbon atom monolayer, so it forms a large surface volume ratio, making it suitable for ultrasensitive detection applications ,13,14,15The fundamental reason for graphene’s conductivity is that it has unbound free electrons (π electrons) . The bioIn the past few years, a large number of nanomaterials have been used as signal amplification species . GraphenMolecularly imprinted polymer (MIP) is a promising technology. The GSCR-MIP sensor can be used to detect amino acids for the early detection of cancer diseases in the blood . High coAnother graphene biosensor to be introduced is the SPR (Surface Plasmon Resonance) sensor. The SPR sensor has the ability of real-time, accurate, and minimally invasive concentration analysis, label-free, high-precision detection, and monitoring ,38. The Graphene is considered to be a promising material due to its excellent electrical conductivity . Some reAn important type of physical sensor is the pressure sensor. Graphene material has important applications in pressure sensors, and with the development of intelligence, flexible pressure sensors have attracted much attention. As a new type of electronic product, the flexible pressure sensor has better application prospects in the fields of biomedicine, robot touch, and human–computer interaction than ordinary rigid sensors. The flexible pressure sensor is becoming more and more important; it is the main way of modern electronic products input and control ,49. At tThe research of flexible pressure sensors mainly changes the microstructure of the conductive layer of the sensor to improve the sensing performance of the sensor ,55. The Due to the rapid development of laser direct writing technology, more researchers use laser-assisted technology to obtain graphene on flexible carbon substrate . Among vSome researchers improved the sensitivity based on a wide detection range and designed a PDMS double-layer graphene flexible pressure sensor with a conical microstructure . The desAnother researcher developed a flexible electronic skin based on graphene film. This electronic skin is an array of pressure sensors. The picture of the sensor is shown in These experimental results show that graphene material has good flexibility, conductivity, and sensitivity, and it can realize the function of the pressure sensor. It provides ideas and methods for making flexible pressure sensors in the future and has development potential.The application of graphene in flexible pressure sensors involves many other fields. For example, a flexible dual-mode sensing system is designed to synchronously monitor the pressure and inertia information of finger movement ; A wearaGraphene is a kind of new material with a single-layer two-dimensional lattice structure, which is closely packed by SP2 hybrid-connected carbon atoms . The oriThere is a metal-coated graphene optical fiber probe sensor for nitrate sensor . The tip3) was obtained by diluting 100 ppm NH3 in wet air at 20 °C [3), lower production cost, and better structural stability and durability than the traditional metal oxide or catalytic metal ammonia sensor (NH3) [In recent years, a new type of composite sensor has emerged, that is, the PPy layer is electrodeposited on CVD-grown graphene. This composite sensor has good performance in ammonia monitoring and sensing . First, at 20 °C . The resat 20 °C . From thor (NH3) .Some researchers prepared graphene films by chemical vapor deposition and transferred them to the silicon substrate by PMMA transfer technology. One-dimensional ZnO nanostructures were prepared and grown on the top surface of graphene. The graphene/ZnO nanostructured gas sensor has good sensitivity and repeatability for hydrogen in a certain range. This is attributed to the high specific area of nano ZnO and the p-n heterojunction formed between ZnO and graphene . As showApplying different bias voltages to graphene can change its Fermi level, so the optical properties of the resonator will also change. Some researchers use this adjustable property of graphene to improve the performance of the sensor and change the resonance wavelength to study fingerprint detection . The resThis paper summarizes the important role of graphene in biosensors, physical sensors, and chemical sensors, and it lists several application examples, which provides a basis for researchers to develop sensor materials in corresponding fields. From the above introduction, we can see that graphene has become an ideal sensor material due to its superior conductivity, biocompatibility, and uniform distribution of active groups .(a)Improve the sensitivity of the sensor and shorten the response time;(b)Combined with flexible materials, it can be extended to a large area.The role of graphene in sensor materials can be summarized as follows:However, most graphene-based sensors are still in the experimental stage and have not been commercialized. The main reason is that the preparation of graphene film cannot achieve large-scale and high-quality production. At present, the main preparation methods of graphene films and their advantages and disadvantages are shown in Liquid phase stripping (LPE) is also a widely used two-dimensional material preparation method. Although this method has great potential, the yield is still not high. When studying the changes in ultrasonic-assisted LPE, some researchers found that the low yield was due to the balance between the angular removal of nanosheets and flocculation of nanosheets during ultrasonic treatment . FindingAt present, the graphene sensor for COVID-19 detection has also been developed. It will detect viruses faster and more accurately, which will provide a great convenience for epidemic prevention and control. Graphene has great potential in liquid biopsy biosensors because of its excellent properties. The development of diagnostic technology is very important for the management of the COVID-19 epidemic. Efforts are being made to improve the detection of COVID-19, and a variety of targeted biosensors ,76,77 haThis paper introduces the basic structure information and characteristics of graphene materials, expounds on the role of graphene materials in biomedical sensors, flexible pressure sensors, and photoelectrochemical sensors, and lists application examples in various fields. Finally, various preparation methods of graphene materials are compared, the difficulties encountered in the commercialization of graphene sensors are put forward, and some suggestions for the future development of graphene sensors are given.


Then, the migration of SiO2 nanoparticles to ethanol as a food simulant was evaluated. Subsequently, curcumin was added to the nanocomposite formulation to sense the pH changes. Finally, the cytotoxicity of the developed packaging system was investigated. With increasing nanoparticle concentration, the film thickness, water solubility, and water vapor permeability decreased and mechanical performance of the films improved. SSPS/SiO2 nanocomposite did not show antibacterial activity. SEM analysis showed that SiO2 nanoparticles are uniformly distributed in the SSPS matrix; however, some outstanding spots can be observed in the matrix. A very homogeneous surface was observed for neat SSPS film with Ra and Rq values of 3.48 and 4.26, respectively. With the incorporation of SiO2 (15%) into SSPS film, Ra and Rq values increased to 5.67 and 5.98, respectively. Small amount of SiO2 nanoparticles was released in food simulant. The nanocomposite incorporated with curcumin showed good physical properties and antibacterial activity. A strong positive correlation was observed between TVBN content of shrimp and a* values of the films during storage time (Pearson's correlation = 0.985).In the present work, the effect of various concentrations of SiO 2 nanocomposites. Only a small amount of nanoparticles could release into a food simulant. Incorporation of SiO2 nanoparticles improved the physicochemical properties of SSPS*‐based films. Incorporation of SiO2 nanoparticles imparts antimicrobial activity of SSPS*‐based films *Soluble soybean polysaccharide (SSPS).Neither cytotoxicity nor antimicrobial activity was observed for the SSPS/SiO It has been reported that this polysaccharide can be used as a thickener, stabilizer, and emulsifying agent  was obtained from Fuji Oil Company . All the chemicals used in the present research were purchased from Sigma‐Aldrich. SiO2.22.2.12 nanocomposites was carried out as follows:2 with different concentrations was dispersed in hot water (80°C) under magnetic stirring for 2 hr.To prepare nanoparticle suspensions, SiOThe SSPS (2.4 g) was dispersed in distilled water (40 ml) under mechanical stirring , followed by storage at 4°C for overnight.The glycerol (35 wt%) as plasticizer was incorporated into polymer solution under magnetic stirring and then sonicated for 10 min.The prepared nanoparticle suspensions were incorporated into the resulting solution and homogenized for 15 min.The resulting dispersions were cast on petri dishes, dried at 25°C for 24 hr, and kept at zip kips for further evaluation.Preparation of SSPS/SiO2.2.2SSPS powder (2.4 g) was dispersed in distilled water (40 ml) at 25°C and then kept at 4°C overnight to be hydrated completely. Curcumin (5 mg) was dissolved in 2 ml ethanol (95%) containing Tween 80 under vortexing for 3 min, followed by solvent evaporation with rotary evaporator. The curcumin solution was added to the SSPS dispersion with flow rate of 1 ml/min and vortexed for 5 min. Finally, the resulting solution was cast on petri dishes, dried at 25°C for 20 hr, peeled, and stored at zip kips until further evaluations . Afterward, the dried samples were immersed in 50 ml distilled water at 25°C for 6 hr and the remaining pieces were taken out and dried (at 105°C) until they reached to a constant weight (W1). WS was computed as follows:The films were cut into 2.0 × 2.0 cmTo determine moisture content (MC) of the films, they were heated at 105°C for 24 hr to reach a constant weight. MC values were calculated using the following formula , the film thickness (mm), and the film surface area (m2).WVP was determined following ASTM E96/E96M‐16 standard test ASTM, . Briefly2.2.4Fmax, Amin, Lmax, and L0 represent the maximum load, the cross‐sectional area, the extension at rupture point, and the original length of the specimen, respectively.The mechanical characteristics of the films were analyzed by an M350‐10CT Machine  at a cross‐head speed of 10 mm/min at 25°C. The test was undertaken as described by ASTM D2.2.5SEM analysis was carried out on the surfaces and cross sections of the specimens. Before the analysis, the nanocomposite surface was coated by gold layer with a sputter coater. The analysis was conducted using an accelerating voltage of 20.0 kV.2.2.62 nanoparticles. The surface parameters of the films including root‐mean‐square roughness (Rq) and average roughness (Ra) were determined according to ASME B46.1 2009 Standard (1995).AFM was employed to investigate the topological properties of neat SSPS film and the film incorporated by different concentrations of SiO2.2.72 nanoparticles into ethanol were evaluated after dipping nanocomposite films in simulant solution. The Si content in the applied food simulant was determined using ASTM D 4754‐11 method. The concentration of Si in ethanol was measured using inductively coupled plasma optical emission spectrometry (ICP‐OES) , Bacillus subtilis PTCC 1,023 , and Staphylococcus epidermidis PTCC 1,114  and DSMZ 3,270. SSPS solution with distinct concentration (16 mg/ml) and predetermined concentration of SiO2 , SSPS/SiO2, and SSPS/SiO2/curcumin nanocomposites, and various concentration of curcumin were incorporated into sterilized Mueller Hinton Broth (MHB) and then incubated to perform in vitro antibacterial screening. Culture media and media plus bacterial strain were employed as negative and positive controls, respectively. Antimicrobial parameters of the tested samples including minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were measured as earlier reported protocol  was employed to observe the photographs of smart films after 30‐min contacting with media with various pHs. Color changes were monitored using a colorimeter. ImageJ software was used to determine color properties of the films  content of the shrimps was determined during storage period by stream distillation method as described by Cai et al. .The experimental results were analyzed using complete randomized design using SPSS software . In order to compare the mean values, Duncan's test was used  is a key factor that must be considered when designing food packaging systems  and elongation at break of the SSPS films increased significantly. The improved TS of the films incorporated with SiO2 nanoparticles may be related to the strong interaction between the nanoparticles and SSPS structure by covalent bond  and SSPS/SiO2 nanocomposites without curcumin did not show clear antibacterial activity against Staphylococcus aureus PTCC 1,112 (ATCC 6538p), Bacillus subtilis PTCC 1,023 , Staphylococcus epidermidis , and Staphylococcus epidermidis PTCC 1,114   (data not shown).SSPS (16 mg/ml) and different concentrations of SiO3.1.42 nanoparticles that could show cytotoxicity was far greater than those employed in the tested nanocomposites. Therefore, these nanocomposites do not have potential of carcinogenicity. This result is in agreement with the result reported by Salarbashi et al. . The result demonstrated that the concentration of SiOi et al.  who demo3.1.52 nanoparticles into the 10% ethanol was evaluated to determine the safety of fabricated nanocomposites. The concentration of Si in the solvent containing pure SSPS was below the method's detection limit (MDL). On the other hand, the final content of Si in 10% ethanol containing SSPS/SiO2 (15%) was found to be 7.08 ± 0.03 ppm, demonstrating the migration of nanoparticles from the developed nanocomposite. It has been reported that the small amount of Si released from nanocomposite may be due to the strong interaction between SiO2 nanoparticles and SSPS , and then, physical and antimicrobial properties and cytotoxicity of the developed films were examined. Finally, the color change in the developed films exposing liquid with different pHs was tested.Based on the previous studies, curcumin has strong antimicrobial and antioxidant activities. Furthermore, the films loaded by curcumin are sensitive to pH changes and thus can be used to sense the food quality. Therefore, in the present study, first curcumin was incorporated into the film constructed at optimal concentration of SiO3.2.12 (15%) and SSPS/SiO2 (15%) nanocomposite films is given in Table Melissa officinalis seed gum /curcumin nanocomposite films (0.14 × 10−6 gm−1 s−1 pa−1) was higher than those reported for synthetic‐based films such as cellophane (8.4 10–11 g/m s–1 Pa–1), LDPE (3.6 10–13 g/m s–1 Pa–1), and PVDC (2.2 10–13 g/m s–1 Pa–1) [25]. But, the WVP of SSPS/SiO2 (15%)/curcumin nanocomposite films was lower than most of the biopolymer‐based films. Accordingly, the developed films can be suggested as appropriate candidate for application in packaging industry.Several attempts have been conducted on the improvement of polysaccharide‐based films. The use of hydrophobic compounds in film formulation is one of the most effective approaches to decrease water solubility. The effect of curcumin addition on physical properties of SSPS/SiO3.2.22 (15%)/curcumin nanocomposites are shown in Table E. coli. In another study, Liu et al. /curcumin nanocomposite films can be used as packaging system to delay or prevent the bacterial growth.Antibacterial activity of curcumin has been well documented in the literature /curcumin nanocomposites on the cell lines  were evaluated. Curcumin and SSPS/SiO2 (15%)/curcumin nanocomposites showed cytotoxicity on the cancerous cells evaluated  at high dose /curcumin nanocomposite films exposing acidic, neutral, and alkaline medium is depicted in Figure Curcumin is a pH‐sensitive compound that can inform consumer the freshness of food product. For instance, in the animal‐based protein, the bacterial spoilage leads to producing TVBN that increases the medium pH /curcumin film and TVBN content produced over storage time was investigated. As shown in Figure a* (redness) as a function of storage period is shown in Figure a* values of the films during storage time. A strong positive correlation was observed between TVBN content of shrimp and a* values of the films during storage time (Pearson's correlation = 0.985). Thus, SSPS/SiO2/curcumin can be introduced as a promising intelligent packaging system to monitor the shrimp freshness.It has been documented that the major reason for the spoilage of animal‐based protein foods is microorganisms. Total volatile basic nitrogen (TVBN) is produced during spoilage of seafood. TVBN content is known as a chemical indicator for determining the extent of spoilage of seafood. In the present work, the correlation between color changes in SSPS/SiO42 nanoparticles were fabricated for freshness monitoring of shrimp. The water solubility, moisture content, and water vapor permeability of the nanocomposite decreased when the curcumin was incorporated into film formulation. The films incorporated with curcumin had good antibacterial activity that makes it good candidate to apply as antimicrobial packaging system. The developed smart packaging system could successfully sense the changing pH and therefore can be used to detect the pH change occurred as a result of basic spoilage. Curcumin/SSPS/SiO2 nanoparticle films exhibited distinctive color change to indicate spoilage of shrimp during storage. In conclusion, SSPS/curcumin/SiO2 nanoparticle films with high antibacterial activity and capability to detect the pH change of packaged foods have a high potential for active and intelligent packaging.The pH colorimetric indicator films based on curcumin/SSPS/SiOWe declare that there are no conflicts of interest.


In recent years, polaritons in two-dimensional (2D) materials have gained intensive research interests and significant progress due to their extraordinary properties of light-confinement, tunable carrier concentrations by gating and low loss absorption that leads to long polariton lifetimes. With additional advantages of biocompatibility, label-free, chemical identification of biomolecules through their vibrational fingerprints, graphene and related 2D materials can be adapted as excellent platforms for future polaritonic biosensor applications. Extreme spatial light confinement in 2D materials based polaritons supports atto-molar concentration or single molecule detection. In this article, we will review the state-of-the-art infrared polaritonic-based biosensors. We first discuss the concept of polaritons, then the biosensing properties of polaritons on various 2D materials, then lastly the impending applications and future opportunities of infrared polaritonic biosensors for medical and healthcare applications. The mid-infrared (mid-IR) is part of the electromagnetic spectrum with the wavelength range of 3–50 μm, in which the unique and strong fundamental movements in terms of rotational and vibrational transitions will take place for many molecules. Mid-IR molecular absorption fingerprint lines are approximately three orders of magnitude higher than those in the near-IR or visible wavelengths, hence it is particularly promising for a wide range of applications in the fields of medicine, basic science, energy, environmental monitoring, and pharmaceutical industry. Moreover, bio-chemical structure analysis and non-intrusive measurement have gained great development with the help of mid-IR spectroscopy ,2,3,4,5.Over the last few decades, researchers have demonstrated various biosensors using noble metal nano-particles (NPs). In comparison, graphene and related 2D materials have attracted significant attention for biosensing applications due to high surface-to-volume ratio, excellent biocompatibility, surface charge, outstanding fluorescence-quenching ability, broadband light absorption, ultrafast carrier mobility, and flexibility . RecentlPolaritons are hybrid quasiparticles that form because of strong coupling of photons with electric dipoles of the material. There are three types of polariton modes that have been experimentally observed, including exciton-polaritons (EPs), plasmon-polaritons (PPs) and phonon-polaritons (PhPs) ,14,15,16The plasmonic biosensing is based on the polaritonic mechanism, where the light confinement and enhancement emerges at the interface between two media with opposite sign permittivity, typically metal and dielectric interfaces, which are highly sensitive to the surrounding refractive index ,28,29,30Taking graphene as an example, extremely confined and electrically tunable plasmon-polaritons were comprehensively studied theoretically and experimentally, opening exciting prospects and providing more opportunities for plasmonic biosensing applications . In addiIn this review, we first give a brief introduction about the polaritons in 2D materials, including the launching and visualizing of polaritons, various polaritonic modes in 2D materials, the dispersion mechanism of polaritons in graphene and their applications. Thereafter, we discuss two types of biosensors based on three typical 2D materials systems, i.e., plasmon-polaritonic biosensors based on graphene and graphene–metal composites, phonon-polaritonic biosensors based on hexagonal boron nitride (h-BN), and the infrared biosensing mechanisms are illustrated comprehensively. Lastly, we conclude this review by proposing some impending challenges and future opportunities of infrared polaritonic biosensors for further medical and healthcare applications.3, exciton-polaritons in MoS2 and WSe2, Cooper pair-polaritons in cuprates, FeSe, and RuCl, and magnon-polaritons in Cr2, Ge2 and Te6 ferromagnets [Two-dimensional materials are atomically thin materials in which electrons can move freely in two dimensions and because of quantum confinement the light-matter interactions can be significantly enhanced. The quantum coupling mode of photons with various excited electric dipoles is called polariton. The emergence of 2D materials makes it possible for the polaritonic imaging within atomically thin materials as they provide ideal platform for polaritonic to confine, harness and manipulate light at such dimensions. When illuminated, light is restricted at nanoscale of such materials, much smaller than the incident optical wavelength, demonstrating an enrichment in the correlative electric field strength, which leads to enhanced light-matter interaction ,44,45,46omagnets ,49,50,51SPPs are polaritons constituted by electromagnetic modes confined in a plane interface between dielectric and metal b 13,52,,54,55,56p is significantly more than the characteristic length of the electron de Broglie wave λF should be considered for such model. The oscillation frequency of the plasmon electrons ωp and the phase velocity νΨ of the plasmon wave together determine the plasmon wavelength λp, meanwhile, the optical response of graphene can be traced back to its in-plane conductivity σ, which is mainly controlled by electron-hole pair excitations. Therefore, we refer to two equations to explain the graphene plasmonic [p represents the polariton wavelength, kp means the in-plane polariton wavevector (kp = ωp/νΨ), σ indicates the in-plane conductivity, ω is the incident light frequency, and εa represents the permittivity of the environment.The graphene plasmonic can be considered as the ultra-short-range SPPs where the light will be constrained to approximately three orders of magnitude smaller than that of the incident free-space optical wavelength. A classical plasmon wave whose wavelength λlasmonic ,54.λp =f−1 is the damping time, Sf and Sb represent the spectral weight and they can be different in different materials, ωb is the phonon/exciton frequency. The spectral weight Sf of graphene can be described as (e/ħ2)EF, where ħ represents the Planck constant, e refers to the charge on the electron and EF is Fermi energy.The in-plane conductivity (σ) can be represented by Equation (2) as:0/λp = (εa/α)(ħ/2EF) (λ0 is the incident light wavelength) is extraordinarily high in graphene. Furthermore, compared with metal plasmonic, the carrier density of graphene plasmonic can be optically, chemically, and electrically tuned. Graphene plasmonic polaritons operates in the terahertz to mid-infrared frequencies, hence opening its infrared applications, while metal plasmon-polaritons are usually observed in the visible frequencies.Based on these equations, it is clear that the light confinement ratio λ2Te3, etc., that support similar plasmonic polaritons, which are also potential candidates for these applications [As summarized in ications ,62,63,64ications ,65,66,67As compared with traditional noble metal materials, the IR response of graphene is featured by long-lasting SPPs that can be dynamically tuned by electrostatic gating. Additionally, unparalleled spatial confinement of the electromagnetic fields in graphene via SPPs makes it promising for the future integrated mid-IR photonic applications. Notably, the strong confinement of IR light in graphene and tuneability of its SPPs offer great opportunities for mid-IR based light detection, modulation and biochemical sensing applications ,69.g). A significant resonance condition related to the localized surface plasmon (LSP) on the graphene nanoribbons can be observed. Even though the thickness of the double layer of protein molecule is only in nanometer scale, the plasmonic resonance frequency shifts to 200 cm−1 because of the change in the refractive index at the sensor surface. More importantly, the appearance of two almost undetectable spectral dips at 1550 cm−1 and 1660 cm−1, which are far away from the plasmonic resonance  becomes increasingly intensive with larger spectral overlap . The spectral positions of them are consistent with the amide I and amide II bands, respectively, which clearly shows the existence of protein compounds in a label-free chemical specific way. Furthermore, in order to show the advantages of graphene biosensor, metal local surface plasmon resonance (LSPR) biosensor composed of gold dipole nanoantenna is employed for comparison, its noteworthy that by calculating the percentage of near-field strength limited to a given distance from the structure  has also been proposed as an efficient way to develop mid-IR biosensing applications and it has been proved that LSPR can be probed in NMG without the need of external chemical doping, induced potential or even thick reflective metallic layers . The synInspired by works mentioned above, many studies about graphene for plasmonic biosensing have been carried out. However, large momentum mismatch between plasmons and photons has always impeded direct light absorption in graphene, which limits its potential in mid-IR biosensing application.To overcome the extremely large momentum mismatch between incident photons and plasmon polaritons, many approaches have been proposed to enhance the IR light absorption in terms of coupling efficiency. For instance, one can introduce dielectric beads onto graphene to tackle this problem . More spMany reports have introduced the employment of only graphene or metal to excite SPPs to strengthen the mid-IR based biomolecular fingerprint . There ir) shifted to lower wavenumbers and demonstrated a detection range from 2 nM to 20 mM (r) is shifted due to the boric acid with an empty orbital extract electron from graphene resulting in p-doped graphene initially, and this reaction is weakened when combined with glucose molecules. The plasmonic resonance (ωr) shift for various configurations  as a function of glucose concentration are illustrated in r| were observed when the biosensor was washed with fresh buffer solution and exposing it to the glucose with high concentration, indicating that such biosensor could detect the decrease and increase of glucose concentration due to the reversibility of glucose boric acid binding , thermophotovoltaic (TPV) cells, photothermal therapy (PTT) and nonlinear optics. Furthermore, suitable band gap, high surface-to-volume ratio, excellent biocompatibility, high carrier mobility, and excellent stability make the 2D antimonene extremely suitable for biosensing applications.2D antimonene exfoliated from Sb has superior physicochemical performance than other typical 2D materials . When co−17 M). These results show that the combination of 2D antimonene and SPR structure provides an ultra-sensitive detection method for miRNA and manifests as a new way for early diagnosis, staging and monitoring of cancer.Various expression levels can be detected by microRNA (miRNA) in cancer, which can have an influence on metastasis, carcinogenesis and cellular transformation. Fluorescence methods with dye molecule labels are widely utilized for miRNA detection. Label-free quantification of miRNA in molecular level remains to be developed. To meet this challenge, a unique surface plasmon resonance (SPR) biosensor based on 2D antimonene has been proposed . Figure Following this research work, 2D antimonene has also been explored in DNA sensing . Nowaday2 layer has been reported [2 layer are 224.26°/RIU and 178.76°/RIU, respectively. Here, TiO2 acts as a thin oxide layer with high refractive index, it can combine with plasmonic metal materials to form bimetallic layer and enhance SPR signal. These research works pave new way for exploring more antimonene-based composites in biosensing applications.Based on the research works mentioned above, recently, a MXene/antimonene composite based SPR biosensor with an adhesive TiOreported . The senN-carbazolyl)-1,1-biphenyl (CBP) on a CaF2 substrate. The CBP molecules were chosen for their distinct vibrational modes in the h-BN nanoribbons. Additionally, CBP can be uniformly deposited by simple thermal evaporation, and the thickness of the layer can be adjusted at sub-nanometer scale. After the device fabrication, real-space observation has also been carried out by using scattering-type scanning near-field optical microscopy (s-SNOM) to launch phonon-polaritons in a h-BN layer above CBP , which comes from the Heisenberg uncertainty principle . EnhanciMoreover, from the perspective of materials, it is still challenging to obtain large-area and high-quality single-layer 2D materials. Among the various synthesis strategies, CVD is the most outstanding way to solve this problem, especially in the fabrication of graphene and its various composites. The size and quality of 2D materials depend largely on the precursor, substrate, pressure, and temperature kept in the CVD growth process. It is necessary to carefully choice these parameters for mass fabrication and controllable synthesis of high-quality 2D materials for biosensing applications. Additionally, decorating 2D materials with plasmonic metal NPs or depositing them on the substrate, improves excellent interface contact and is favorable to energy transfer, charge shift, plasmon coupling, and ultimately improves the sensing properties and enhance sensitivity. vdW force and electrostatic interaction are two main routes to combine 2D materials and the substrates, resulting in inferior stability of the device. By contrast, 2D materials with a large number of free radicals can covalently combine with the matrix and metal NPs. Hence, it is of great significance to treat the surface grafted free radicals of 2D materials for the preparation of polaritonic biosensors.In the future, more efforts are expected to explore novel biosensors based on phonon-polaritons because of their long polaritonic mode lifetimes and slow speeds, which are especially advantageous for enhancing local emitters, molecular vibrational modes, and strengthening applications requiring strong light-matter interactions. Besides, exciton-based polaritonic biosensors may be exploited for their long-lived feature which enables further observation of their condensation and superfluidity at relatively high temperatures. Furthermore, the combination of 2D metamaterials and quantum plasmonics has great potential to provide enhancing phase-change sensitivity for improving limit of detection.


The photocurrent is retained after light withdrawal when positive gate voltage is applied to the device. The device exhibits distinct conductance states, modulated by different parameters of incident light, such as pulse width and number of pulses. The conductance state can be retained for 104 s, indicating long term potentiation (LTP), similar to biological synapses. By using optical and electrical pulses, the device shows optical potentiation and electrical LTD repeatably, implying their applicability in neural networks for pattern recognition.Optoelectronic synapses combine the functionalities of a non-volatile memory and photodetection in the same device, paving the path for the realization of artificial retina systems which can capture, pre-process, and identify images on the same platform. Graphene/Ta In biological brains, neuron and synapses are the smallest units of learning and memory. To do neuromorphic computing, the realization of neurons and synapses is necessary. Memristors have reached an advance stage of exploration for mimicry electronic synapses8. However, since most of the information sensed and stored by the brain comes from the eyes, a pure electrical synapse is not sufficient; an optoelectronic synapse is going to fulfill more necessities in the internet of things (IoT) and big-data era. For example, Chen et al.10, have shown an avalanche photodetector in the mid-wavelength infrared region (MWIR), which is important for remote sensing and defense11 because of its transparency in the Earth’s atmosphere; employing this type of photodetectors on optoelectronic synapses can improve the way for future pattern recognition applications. For the realization of an artificial retina, platforms integrating diffractive optics are required but chromatic aberration is a problem when using diffractive optics in such small scales. The work by Ou et al.12, shows an achromatic metasurface in the MWIR wavelengths compatible with CMOS platform13. By proper material engineering, the integration of this metasurfaces can help with the realization of artificial retina systems. Such multifunctional devices can perform photodetection and store the information carried by light signals, such as wavelength and intensity, as conductance states.The miniaturization of digital components is reaching the limits predicted by Moore’s law, and new methodologies and devices that can collect, store and process information have been pursued. Motivated by the brain’s ability to store, process, and memorize information, neuromorphic computing rises as an active candidate to solve the miniaturization problem. Neuromorphic computing contrasts with traditional von Neumann architecture due to the well-suited interaction with sensory data in humanlike ways18. Graphene is another 2D material with unique optoelectronic properties that has not been fully explored for optoelectronic synapse applications. Graphene is a gapless two-dimensional (2D) material which exhibits an absorption spectrum from ultra-violet to terahertz wavelengths; it shows very large mobility and ambipolar characteristics23. Single-layer graphene absorbs only ~ 2.3% in visible and infrared regions and because of the zero band-gap behavior on the energy diagram, it leads to short lifetime of exciton in pure graphene; the high carrier mobility (electrons and holes) comes with the price of low light absorption, which gives low responsivity values  on a 32. Graphene-based optoelectronic synapse is also obtained by using 2D perovskite/graphene structure33. However, there has not been much exploration on the use of graphene/oxide interface for optoelectronic synapse which is important because it can get integrated easily with CMOS technology.Realization of optoelectronic synaptic devices have been possible using 2D materials such as 2O5/graphene heterostructure to demonstrate optoelectronic synapses. Ta2O5 has shown good platform on CMOS technology35. It also has a high energy bandgap of ~ 4 eV which facilitates the realization of optoelectronic synaptic characteristics in the visible spectrum36. It has been shown that Ta2O5 deposited by e-beam instead of RF sputtering gives a narrow gap of visible light absorption37. which is the mechanism used for deposition in this work. Graphene can show different mechanism for the change in current with light; photo-induced bolometric effect and photovoltaic22. In order to decouple these two effects, we used a Si/SiO2 substrate with 285 nm thick dielectric as opposed to Freitag et al.19 where the thickness of the dielectric is 90 nm. Probing the top graphene layer, we observe gate-controlled long-term potentiation (LTP) in these devices. A positive gate voltage is essential to enhance carrier lifetime, elongating the retention of photoconductance. The device exhibits distinct conductance states as a function of light pulse width and the number of light pulses applied. The device demonstrates LTP for 4 s. It can be optically potentiated and electrically depressed to obtain its conductance weight update curves, essential for use in neural networks for pattern recognition.In this work, we use a graphene/Ta2O5/graphene device schematic is shown in Fig. R vs. VG characteristics of the bottom and top graphene films with the gate voltage applied through the Si substrate which we are going to refer as the global back gate voltage. Refer to methods for the thickness and doping of substrate. The hole mobility of the bottom graphene film in dark is calculated to be in the range of 1000–2272 cm2/V-s and the contact resistance in the range of 281–717 Ω for 10 devices. Figure 38:0 ~ εrεVg/te and at the charge neutrality point 39.The graphene/TaVCNP of the top graphene layer is lower than that of the bottom graphene layer. This indicates that the bottom graphene film is more p-doped than the top graphene film, given that the effective electric field reaching the bottom graphene is higher than the top graphene because of the additional Ta2O5 layer between the two graphene layers. Upon illumination with light of wavelength 405 nm, with a power of 100 mW, the VCNP of both the top and bottom graphene layers shift positively. Figure Itunnel) as a function of voltage applied across the two graphene layers, both in dark and under illumination, indicating the tunneling of carriers from one layer to the other across the Ta2O5 barrier. The tunneling current is enhanced upon illumination. During illumination, the bottom graphene layer generates electron–hole pairs. Since the bottom graphene layer has a higher charge neutrality point VCNP than the top graphene layer in dark, implying a higher hole doping in the bottom graphene layer, the photogenerated holes tunnel into the top graphene layer. The photogenerated electrons from the top graphene layer can also tunnel into the bottom graphene layer. The accumulation of electrons in the bottom graphene layer leads to a photogating effect, shifting the VCNP of the top graphene layer to more positive voltages. This enhances the photocurrent in the top graphene layer significantly, as indicated by the decreased resistance of the top graphene layer upon illumination. Because of the large spot area of the laser light it could also mean that near the graphene/metal interface causes a bolometric effect which in turn increases the photo-generated current. The mechanism of enhanced carrier generation due to the presence of a tunneling barrier between the top and bottom graphene layers is illustrated through the band diagram in Fig. VCNP of both bottom and top graphene layers under illumination can also be associated to the adsorption of water molecules in the Gr/Ta2O5 interface. This behavior is not observed in Liu et al., since RF sputtering creates a zero absorption Ta2O5 film37.The 2O5/graphene device. The light pulses are 125 ms long. The back gate voltage VG is held at 0 V. The bottom graphene is kept floating. A drain-source voltage of VTGr = 0.1 V is applied to the top graphene layer. The dimensions of the bottom graphene layer is Figure mentclass2pt{minimIph = Ilight – Idark, where Idark is the current through the top graphene layer in dark, and Ilight is the current after illumination with each light pulse  of the device. Figure VGy0 is the offset, τ1 and τ2 are time constants for a fast and slow decay, respectively, and A1 and A2 are pre-exponentials. We observe that for all gate voltages, there is a fast (within ~ 3 s) decay in photocurrent. However, for positive gate voltages, there is a slow decay of conductance following that. The device is able to retain the conductance state for > 100 s. The photocurrent increases with increasing gate voltage, and the conductance retention increases as well. This is because, the positive back gate voltage helps in the trapping of electrons at the graphene/dielectric interfaces, leading to accumulation of holes in the top graphene layer. Figure 2 reaching infinity for the pulse widths of 31 and 35 ms. The fitted time constants are plotted in Fig. 2O5/Graphene devices can exhibit optically stimulated long term memory.The photocurrent is given by 2O5/Graphene device, as the number of light pulses is varied from 4 to 40. The gate voltage is held at + 80 V, and the photocurrent is measured from the top graphene layer held at a drain-source voltage (VTGr) of 0.1 V. Figure 4 s after the application of 40 light pulses, each of duration 125 ms. The measured current through top graphene layer is shown in Fig. 3 s for use in neural networks. Thus, our graphene/Ta2O5/graphene device is fit for practical implementation in neural networks for learning and inference tasks.An electronic synapse shows multiple conductance states when subjected to electrical pulses. Similarly, a device behaves as an optoelectronic synapse when multiple non-volatile conductance states can be extracted as a function of number of incident optical pulses. Figure 2O5/graphene optoelectronic synapses, we use 20 optical pulses of duration 125 ms to potentiate the device, and 20 electrical pulses at the gate electrode to depress the device. While optically potentiating the device, the gate voltage VG is held at + 80 V for inducing a condition of maximum conductance retention. To depress the device, the light pulses are withdrawn, and VG is pulsed from + 80 to + 70 V, with a 125 ms on time and 125 ms off time. The top graphene drain-source voltage VTGr is held at 0.1 V throughout the measurement. The reduction of the gate voltage using pulses releases trapped electrons in gradual steps and reduces the conductance of the device gradually. Thus, the conductance weight update curve is obtained, as shown in Fig. A synaptic device’s conductance tuning curve is of utmost importance for its use in the training of a neural network. Linearity and symmetry in conductance weight update determine the accuracy of the neural network. For obtaining the weight update of the graphene/Ta2O5/Graphene heterostructures acting as optoelectronic synapses. These devices show enhanced photocurrent due to photogating effect caused by selective tunneling of photogenerated carriers from one graphene layer to the other. The devices exhibit LTP, modulated by the gate voltage. The conductance states can be modulated by the light pulse width and the number of light pulses applied. The device retains its conductance state for 104 s. Optical potentiation and electrical depression can be repeatably used to generate conductance weight update curves for these devices, to be used for the training of neural networks for pattern recognition tasks.In summary, we report Graphene/Ta2 (285 nm) substrate, which acts as the global back gate, by standard photolithography technique, and deposit Ni/Au (60/20 nm) by electron beam evaporation followed by lift-off. A monolayer of graphene film, grown by chemical vapor deposition (CVD) on Cu foil is wet-transferred onto this substrate40, followed by annealing in forming gas  for 3 h at 400 °C. The bottom graphene layer is patterned and etched in O2 plasma to form graphene strips. Next, 5 nm of Ta2O5 is patterned and deposited by e-beam evaporation. A second monolayer of CVD-grown graphene is wet-transferred on the substrate, patterned and etched into strips aligned with the bottom graphene layer. Ni/Au electrodes are patterned and deposited as contacts to the top graphene layer. Finally, the devices are annealed again in forming gas for 3 h at 300 °C.We first pattern the bottom graphene electrodes on a p-Si/SiO2O5 film to be 5 nm. Figure 42. All electrical measurements were performed at room temperature on a probe station, using HP 4145B Semiconductor Parameter Analyzer and B1500A Semiconductor Device Analyzer. To measure the transfer characteristics after illumination of light, we use a cw laser diode light source in the visible spectrum radiation (The optical image of a representative device with 5 terminals is shown in Fig. Supplementary Figures.


Terahertz waves are expected to be used in next-generation communications, detection, and other fields due to their unique characteristics. As a basic part of the terahertz application system, the terahertz detector plays a key role in terahertz technology. Due to the two-dimensional structure, graphene has unique characteristics features, such as exceptionally high electron mobility, zero band-gap, and frequency-independent spectral absorption, particularly in the terahertz region, making it a suitable material for terahertz detectors. In this review, the recent progress of graphene terahertz detectors related to photovoltaic effect (PV), photothermoelectric effect (PTE), bolometric effect, and plasma wave resonance are introduced and discussed. The terahertz (THz) wave is an electromagnetic wave in a particular band having a frequency range of 0.1–10 THz (wavelength within 30–3000 microns) . More inThe THz detectors mainly include bolometer, pyroelectric detector, Golay cell, Schottky diode detector, nanometric field-effect transistor (NFET), etc. . The bolThe nature of the materials and their structures have a significant impact on the performance THz detector . For exaIt had been Geim and Novoselov, who used mechanical exfoliation to develop graphene, a single-atomic-layer graphite structure . Graphentructure ,44,45. Ttructure ,47,48. Ttructure .The most commonly used THz detectors have some limitations for specific applications. For example, the response speed of the pyroelectric detectors and Golay cell is low, and it is difficult to respond in real time to ultra-short THz pulse signals in the order of picoseconds ,50. SchoIn general, most of the graphene non-zero bias detectors are graphene bolometers. A bolometer is a device that uses the bolometer effect to detect the intensity of the radiation power. The bolometer is based on an electrical resistance’s temperature dependency. More specifically, the working mechanism of the bolometer is to convert absorbed terahertz radiation energy to a changing temperature value by absorbing a photon and increasing the electron temperature from Ryzhii et al.  report aeviously . This woYan et al.  designedThe conventional approach of using electrical transport as a readout detector can hardly realize the supervisory characteristic of graphene for making high-sensitivity THz detectors. A thermionic electron detector based on noise readout also has been reported . The temWith very weak coupling and high-speed thermal response, graphene could act as a highly sensitive bolometer. Fong et al.  introducMiao et al.  reportedIn graphene zero-bias detectors, a built-in electric field is formed inside the material after absorbing THz radiation, so it can realize zero-bias detection. The built-in electric field can be enhanced by local mixing or the use of contact asymmetry. The working principle of graphene zero-bias detector mainly includes a photovoltaic effect, photo-thermoelectric effect, plasma wave resonance, etc. ,68. ComppW/Hz1/2 . AccordiThe detection mechanism of the photovoltaic effect means that when electromagnetic waves are irradiated on the detector, the electrons in the valence band of the photoelectric material absorb the energy according to the equation of The photodetector usually combines the effect of the PV and the PTE, but their role during the detection can be far different ,72. DeglTemperature-dependent resistance in bilayer graphene is important in graphene detectors that use the photothermoelectric effect and must work at low temperatures ,65. Cai The structure of the coupling antenna for the PTE THz detector can also considerably improve the detector’s performance. Guo et al.  used ult antenna , the detAnother significant parameter to improve the characteristic of the THz detector is reducing the device resistance . In 2019In addition, there are many studies on the performance of THz detectors. Metamaterials are an effective way to enhance the performance of graphene photodetectors ,79. The In 1993, Dyakonov and Shur proved that the electron behavior in a short channel field effect transistor (FET) is similar to that in shallow water, which provides a new mechanism to detect THz ,85. The  density , the con density ,91. A br density . The eleIn 2007, Echtermeyer et al.  reportedThe working frequency of the THz detector is related to the size of the device. Therefore, to detect the higher frequency THz waves, large size graphene is needed ,99. TongQin et al.  reportedMittendorff et al.  investigThe plasmonic wave detection requires the asymmetrical coupling of source and drain. The non-linear rectification of the carrier transmission is a direct detection, and the detection by the PTE is realized by asymmetric contact . Liu et The structure parameters of the antenna also played an important role in the performance of the FET. In 2020, Viti et al.  encapsulIn order to increase the absorption of graphene, many effective ways such as quantum dot enhancement, antenna coupling enhancement, and plasmonic enhancement can be used ,106,107.The interference of plasma oscillations in the channel of the field-effect transistors can be used to measure radiation polarization . Sergey The antenna will be coupled with the rectifying device by GFET, but the detector performance was affected by the rectifying of the parasitic capacitance. Gregory et al.  fabricatThe responsivity of the traditional FET is affected by the channel conductivity, and the transconductance is limited by n et al.  developeThe development of ways to manufacture graphene increases graphene application, which is an exciting occurrence. The reason is that the methods of making graphene are different, and their properties determine the application. In addition to the mechanical exfoliation method where graphene was first discovered, there are liquid exfoliation methods, molecular beam epitaxy , chemicaal value . The graal value .Geim and Novoselov reported mechanical exfoliation for the first time in 2004 . More sp2Si-Al2O3 core–shell nanowires as a self-aligned top gate to fabricate graphene transistors [2Si-Al2O3 core–shell nanowires are aligned with the graphene by the physical dry transfer method. Finally, a layer of metal is deposited on the structure. Hence, the nanowire acts as a mask, forming a self-aligned source and drain electrodes on both sides. The graphene transistor produced by this method has lower access resistance and less impurities introduced in the manufacturing process; the carrier mobility can reach 20,000 The graphene–dielectric integration process will introduce substantial defects into pristine graphene lattices, which reduce the mobility in graphene. In addition, an immature manufacturing process leads to large access resistance. These two points lead to the poor performance of graphene THz detectors compared to other mature FET detectors ,122,123.nsistors . The graVicarelli et al.  used sinPackaging graphene with standard dry skin technology can provide the cleanest environment for graphene . BanduriUnder high temperatures and certain conditions, carbon atoms are deposited on the metal surface using a mixture of methane and hydrogen or other carbon sources to form large-area graphene film ,128. Ches at 2 K . This CVZak et al. explored the use of CVD-grown graphene for the detection of THz signals . They tr2O3 gate and then make the source and drain, as shown in However, the fabrication process of the device will introduce impurities in the graphene, which will affect the performance of the detector. In order to solve this problem, Generalov et al.  used CVDA graphene layer can be formed on the silicon or carbon surface of the SiC wafer by sublimating the Si atoms on the surface of the SiC (0001) wafer and annealing the remaining C atoms to graphitize them ,137. Witcm2/V·s , which cAn FET made of SiC epitaxial growth graphene was reported by Bianco . The detQin et al.  fabricatRama et al. fabricated a THz detector coupled with a split-bow-tie antenna on a 4H-SiC (0001) substrate . The phoThe resistance of the epitaxial growth graphene on SiC varies greatly with temperature due to quantum containment, so it has a high response rate ,142. Abdvelength .Although many scholars have made progress on graphene THz detectors, there are still great challenges. For the preparation of graphene, the methods mentioned above have their limitations. The graphene produced by mechanical exfoliation has high quality, but the process is hard to control, and the produced graphene can hardly be mass-produced (with different areas and different layers), while large-area graphene also can hardly be produced. These limitations make it difficult to make the graphene THz detectors. The graphene synthesized by CVD can be controlled by changing the carbon source gas, deposition time, temperature, and other factors to control the size and layers of graphene . Althoug2O3 or diamond instead of SiO2 as the substrate or encapsulating graphene with hBN may be employed in the future to develop GFET [There are also many challenges in the making of the graphene THz detector. For example, the detector is usually coupled with a metal antenna, but this will inevitably introduce some parasitic capacitance and increase the access resistance. When designing a specific antenna, scientists not only need to consider the size and type of the antenna but also need to take care of the impedance matching problem. Impedance mismatch will increase the NEP and RC time constants of the detection circuit . When prlop GFET . In addiDespite the challenges, there has been continuous progress in this field. CVD can prepare graphene materials with a large area and consistent performance with a single crystal and can use the direct transfer layer method to achieve clean and non-destructive transfer of graphene . In addiIn this review, we introduce the recent developments in graphene THz detectors. The review discussed the methods reported by researchers to improve the performance of THz detectors, which are based on graphene made by different methods. The performances of the detectors mentioned in the article are shown in Although the graphene THz detector has made a lot of progress in the laboratory, and they show many promising prospects comparing to traditional detectors, there is still a long way to go to achieve commercialization application. Moreover, the working range of these THz detectors is mostly at low-frequency THz waves, and high-frequency THz detectors are still difficult to achieve. These THz detectors with low equivalent noise power and high responsivity need to be realized in a low-temperature environment, and room temperature detectors still need to be further studied.


The influence of multi-pass cold drawing on the evolution of microstructure, texture, and properties of Cu matrix composite, reinforced by in situ grown graphene, has been systematically investigated. Under continuous and severe plastic deformation, the grains in the composite were continuously refined to nanoscale. In addition, graphene in the composite could be gradually refined, exfoliated, and redispersed. Interestingly, dynamic recrystallization of the composite was formed after 80% drawing reduction and its formation mechanism was discussed. The texture of the as-drawn composite comprised a mixture of fiber textures with dominated <111> and minor <100> orientation after 99.7% severe drawing reduction. The tensile properties and electrical conductivity of the as-drawn composites were also investigated. This work provides a better guideline on the plastic deformation behavior of the advanced graphene/metal nanocomposite. Metal matrix composites reinforced by graphene (Gr/MMCs) have recently attracted considerable attention and researchers strive to improve its structural or functional properties ,2,3,4,5.As a result, the plastic deformation of composites is the next step. In addition, it is crucial to the realization of the transformation from blank materials to semi-manufactured products. Commonly, several plastic deformation methods, such as extrusion , rollingHerein, graphene/Cu composite wires were prepared by in situ grown graphene on Cu powders, spark plasma sintering (SPS), hot-extrusion, and multi-pass cold drawing. During the process of cold drawing, grains in the composite could be continuously refined to nanoscale and the homogeneity of microstructure was improved. Moreover, graphene in the composite was found to be gradually refined, exfoliated, and redispersed. Interestingly, after severe plastic deformation, the recrystallization of composites was formed. The underlying deformation mechanism was discussed. As a result, the composites showed an improvement of mechanical properties and electrical conductivity after cold drawing. This work provides a deep understanding of the plastic deformation process of Gr/MMCs and can be a guide for the preparation of Gr/MMCs with high performance.2 (17 mL/min)/Ar (83 mL/min) mixture. Thereafter, in situ grown graphene on Cu composite powders could be achieved.Commercial flake Cu powders (purity of 99.9%) with a diameter of 30~50 μm and solid molecular naphthol ) were used for the raw Cu matrix and carbon source, respectively. The typical growth process of graphene, which was systematically studied in our recent investigation , can be The as-prepared composite powders were first sintered using SPS  . Then, a rod (Φ9.5 × 40 mm) was cut from the as-sintered composite. Subsequently, the rod was extruded at 750 °C (extrusion ratio of 7.4:1). The as-extruded composite (diameter of 3.5 mm) was drawn by the multi-pass process at room temperature and the reduction of each single pass was less than 10%. Finally, the as-drawn composites with different diameters were obtained. The area reduction is calculated as the drawing reduction, and 3 (5 wt%) to remove Cu. The composites for TEM analysis were prepared by several steps of mechanical grinding to obtain a foil (thickness of 50~60 μm), and ion thinning technique. The C content of graphene in Cu matrix is tested by carbon and sulfur analyzer . The room temperature tensile properties of block composites were studied by an Instron-1186 tensile testing machine. In addition, the tensile speed, gauge length, and gauge width were 0.5 mm/min, 15 and 2 mm, respectively. The tensile properties of as-drawn composites (length of 20 mm) were measured on a tensile machine  with a speed of 0.5 mm/min. The resistance of the samples was tested on a low resistance instrument based on the four-wire measurement method . The electron backscatter diffraction  of the composites was carried to investigate the microstructure of the composite. The EBSD system is HKL Nordlys , and the data processing software is Channel5. The samples for EBSD investigation were prepared by the cross section ion polishing instrument . For SEM and EBSD test, the observation positions of as-extruded and as-drawn composites were investigated on the transverse direction–normal direction (TD–ND) plane.The microstructure was carried on scanning electron microscopy  and transmission electron microscope . Prior to the SEM investigation of individual graphene in graphene/Cu composite powders, the composite powders were first etched by HNO−1), G band (1603 cm−1), and 2D band (2300~3000 cm−1) of the graphene. The ID/IG (intensity ratio of D to G band) of the as-grown graphene is calculated as 0.89, indicating a low defect density of the graphene [In graphene . All of W) and length (dL) of the grains are counted as 1.88 and 3.9 μm, respectively. Nevertheless, The dispersibility of graphene is one of the most challenging difficulties for the preparation of composite. Nevertheless, this problem can be easily solved by the graphene in situ growth method. Therefore, the as-obtained composites can be a model material for the study of plastic deformation mechanism. As shown in Typical SEM-BSE images of the as-drawn composites are shown in EBSD was used to study the microstructure evolution of the composites during the drawing process, including the evolution of grain size, grain boundaries (GBs), recrystallization, microstrain, and texture. To investigate the characteristics of GBs in the composites, the type and misorentation angle distribution of GBs are presented in Furthermore, Since the composites are drawn at room temperature, how does the mechanism of the dynamic recrystallization form? The underlying reasons are discussed as follows: (i) Initially, for the matrix, the GBs in the initial as-extruded composite are dominated by HAGBs see c. The reDuring the drawing deformation of FCC metals, the <100> and <111> orientation will parallel to the axis direction, and form a mixture of <100> and <111> fiber textures. Among them, the <111> fiber texture is considered to be a stable texture, while the <100> fiber texture is a transitional texture. In addition, the <100> fiber texture is mainly attributed to the recrystallization during deformation ,52. As s6 S/m when the drawing reduction is 99.7%, indicating that the as-drawn composite still has good electrical conductivity. There are complicated factors affecting the EC of the as-drawn composites. First, the increasing number of interfaces resulting from the refinement of grain size and graphene lead to the intensification of electron scattering [attering , which wattering . TherefoIn this work, the cold drawing behavior of in situ grown graphene/Cu nanocomposite, including the evolution of microstructure, graphene, texture, and properties, have been systematically investigated. Graphene sheets were homogeneously distributed in Cu matrix during the cold drawing process. Furthermore, the refinement and exfoliation of graphene could be clearly found with the increasing drawing reductions. The grain of the composite could be continuously refined to nanoscale and the homogeneity of microstructure was improved after severe drawing deformation. In addition, recrystallization of composites after 80% reduction can be formed, which was affected by a synergistic effect of matrix and graphene. The final fiber texture of the as-drawn composite was a mixture of fiber textures with dominated <111> and minor <100> fiber textures. After cold drawing, the composites presented an enhancement of tensile strength and showed excellent electrical conductivity.


The Covid-19 pandemic has had a deep impact on the lives of the entire world population, inducing a participated societal debate. As in other contexts, the debate has been the subject of several d/misinformation campaigns; in a quite unprecedented fashion, however, the presence of false information has seriously put at risk the public health. In this sense, detecting the presence of malicious narratives and identifying the kinds of users that are more prone to spread them represent the first step to limit the persistence of the former ones. In the present paper we analyse the semantic network observed on Twitter during the first Italian lockdown (induced by the hashtags contained in approximately 1.5 millions tweets published between the 23rd of March 2020 and the 23rd of April 2020) and study the extent to which various discursive communities are exposed to d/misinformation arguments. As observed in other studies, the recovered discursive communities largely overlap with traditional political parties, even if the debated topics concern different facets of the management of the pandemic. Although the themes directly related to d/misinformation are a minority of those discussed within our semantic networks, their popularity is unevenly distributed among the various discursive communities. The Covid-19 pandemic has had a deep impact on nearly every human activity; as such, it is not surprising that it has generated a widespread online debate which, in turn, attracted the interest of scholars from different disciplines . Due to super-spreaders.Indeed, the already prolific research on the diffusion of d/misinformation –18 was eThe comparison of several platforms is also the research target of : Gab, FaAcross the entire literature overview, a limited attention is paid to identify the narratives shared by the various users. In this sense, the contribution of , 20 is tnot encoded into the constraints ,,NEMtropyIn the present manuscript, we analysed the narratives emerged on Twitter during the Covid-19 epidemic in Italy. Our data set covered a period of one month (from the 23rd of March 2020 to the 23rd of April 2020) and included approximately 1.5 millions of tweets. As observed in previous studies , even inNEMtropy and described in [In the present paper, we have refined the partition in communities obtained in  by usingribed in , insteadWe represent it as a bipartite network of users and hashtags, where a link connects a user to an hashtag if the former one has used the latter one at least once during the observation period. Then, using a bipartite entropy-based null-model  as a benmediated events stimulate the discussions on Twitter more in DX and FI community: by looking at the temporal evolution of the communities of the semantic network, we were able to identify these events, as TV-appearances of politicians.As observed in , 20, theConfirming other previous studies , the comEven if the literature is limited to a few studies, it has been shown that often non trivial correlations between offline and online behaviours occur –71. In t