The combination of graphene and a metasurface holds great promise for dynamic manipulation of the electromagnetic wave from low terahertz to mid-infrared. The optical response of graphene is significantly enhanced by the highly-localized fields in the meta-atoms, and the characteristics of meta-atoms can in turn be modulated in a large dynamic range through electrical doping of graphene. Graphene metasurfaces are initially focused on intensity modulation as modulators and tunable absorbers. In this paper, we review the recent progress of graphene metasurfaces for active control of the phase and the polarization. The related applications involve, but are not limited to lenses with tunable intensity or focal length, dynamic beam scanning, wave plates with tunable frequency, switchable polarizers, and real-time generation of an arbitrary polarization state, all by tuning the gate voltage of graphene. The review is concluded with a discussion of the existing challenges and the personal perspective of future directions. Metasurfaces significantly reduce the size of optical devices with comparable or even unavailable novel functionalities, such as a metalens with close-to-unity numerical aperture and a planar profile [The electromagnetic response of an optical device, from basic lenses and mirrors to advanced metasurface alternatives, is governed by two factors: material and structure. Beam engineering in conventional optics relies on separate contributions from the material refractive index ta-atoms ,2,3. Met profile ,5,6, pol profile ,8,9,10,  profile ,12,13, a profile ,15, to nActively-tunable or reconfigurable responses are highly desired in practical applications including dynamic wavefront shaping, adaptive optics, and single-pixel detection, which can be facilitated by including functional materials in the metasurfaces with dynamic modulation. Graphene, a single layer of carbon atoms arranged in a honey-comb lattice, is an outstanding candidate with extraordinary electrical and optical properties ,17, as iCompared to metasurfaces employing other active materials with different tuning mechanisms, such as electrically-tuned liquid crystals ,19, therThe development of graphene metasurfaces starts from intensity modulation. In 2011, the intensity modulation of the THz wave in graphene micro-ribbon array was reported , followeThe paper is organized as follows. The optical response of graphene is governed fundamentally by its surface conductivity. Since the intuitive optical characterization is usually done through the permittivity or the mode index, we summarize in this section the conductivity, the effective permittivity, and the mode index of the surface plasmon (SP) wave supported by graphene, so as to perceive the transformation of optical response with Fermi level and in different frequency bands.e is the electron charge, ℏ is the reduced Planck constant, and T is the temperature. n is related to the Fermi level by n with The surface conductivity of graphene can be modeled by the well-known Kubo formula derived with the random phase approximation (RPA) theory ,37,38.σinted is considered, the effective permittivity of graphene relative to the vacuum permittivity is defined as:If the thickness ation as ,43:(5)nsIn In the THz to mid-IR band b, the moWhen  and ϵr″ c, both i of 2.3% .The variation of key material properties from sub-THz to near-IR is summarized in Metasurfaces have been applied with great success for complicated wavefront shaping because of their compactness and flexibility when compared to conventional bulky devices. Dynamic wavefront shaping is a highly-desirable feature towards practical applications including, but not limited to adaptive optics and satellite communication. Ideally, the phase shifters should cover the complete In 2012, Min’s group experimentally demonstrated terahertz switching  by attacnstrated  in a bilWhen graphene itself is patterned as a phase shifter, such as a graphene ribbon or a graphene patch, it only provides a dynamic phase range of esonance d. In facfocusing . The phaRecently, the geometric phase has been utilized widely in metasurfaces for wavefront shaping by rotating the asymmetric inclusions ,50. In FAs the geometric phase does not change with the Fermi level, the active tunability of the device is limited to intensity modulation at a fixed frequency. In more scenarios, one wants to tune the focal point or the steering angle dynamically with the maximum possible intensity. For this purpose, Wang’s group proposed a strategy in 2017 to achieve a transmissive metalens with a dynamically-tunable focal length . The expWhen a metallic mirror is introduced to the active phase shifter with a dielectric spacer, the phase modulation range can be significantly enlarged. The whole structure can be considered as an asymmetric Fabry–Perot resonator, where the large phase range is gained from the multi-path propagation between the top and bottom layers. In other words, the electric current circulating between the top metasurface and the bottom plate forms a magnetic resonance with In order to access the The above design works at sub-THz, where graphene is a lossy surrounding medium, as analyzed in Alternatively, graphene resonators can replace the graphene–metallic resonator structure in the top layer for reflective phase modulation, as summarized in When the graphene ribbons are separately biased, more degrees of freedom are gained for controlling the functionality temporally and spatially ,59. Figuk to use d. It leaSimilar to the transmission cases, uniform biasing of either monolayer graphene or graphene ribbons is promising for fabrication, but limited to efficiency modulation or on-off switching of a specific function. In contrast, individual biasing of each ribbon is extremely difficult to implement in device integration, although at-will wavefront shaping is theoretically possible in real time with satisfactory efficiency. A compromise solution utilizes both the geometric phase and resonance phase with a similar configuration as In addition, the metasurface is endowed with increased power when more complicated graphene elements and the corresponding gate configuration are considered. For example, when two graphene patches are combined in a unit cell in-plane  or stackApart from wavefront shaping in free space, control of the SP waves propagating along the graphene surface holds significant promises towards minimization of the photonic integrated circuits. Compared to the noble metal counterparts, graphene plasmonics show low loss and strong confinement together with the tunability via electrical or chemical doping. As will be shown in the following literature, in-plane and out-of-plane beam shaping focus on applications in the THz to mid-IR frequencies taking advantage of the spatially- and temporally-tunable Fundamentally, the plasmonic wavefront is manipulated via a nonuniform conductivity pattern along graphene. Several ways are proposed to achieve such a conductivity pattern . Figure On the other hand, the strong mismatch of the wave vectors in the plasmonic wave and free space wave causes a great obstacle in exciting and leaking the SP waves in graphene. Different mechanisms have been reported to excite the strongly-localized SP waves in graphene through diffraction gratings , sharp tThe above leaky wave scanning is limited to one plane. Scanning in arbitrary directions in the full space is more difficult, as pixel-by-pixel biasing makes the configuration a huge challenge for device integration. Polarization manipulation, usually achieved by birefringence materials, total internal reflection, optical gratings, and the Faraday effect, is instrumental in a wide range of optical applications, such as telecommunications , imagingThe quarter-wave plate (QWP) converts a linear polarization into a circular one, by engineering the two orthogonal eigenmodes with equal amplitude and  1% from ) once a spersion . VariatiThe form birefringence of the graphene grating is further enhanced in Half-wave plates (HWPs) as the cross-polarization converter require  degrees , and almThe first three designs ,86,87 in designs  also gain effect . The Fern effect , where tThe lattice size is apparently one or two orders of magnitude smaller than the vacuum wavelength taking advantage of the strong localization of graphene plasmons. As the localization increases with frequency, the lattice size is smaller in higher frequency designs. Due to such a small feature size, all the proposed designs are very robust to the variation of the incidence angle up to  or more ,90,93,94Finally, the dynamic tunability of the graphene-based HWP through the electrical control of the Fermi level is discussed in the last column of signs in ,89,94 shIn addition to engineering the phase retardation of the two eigenmodes, graphene metasurfaces can be tailored to filter selectively one eigenmode while eliminating the orthogonal one so as to be a polarizer, or in other words a polarization-selective surface. A straightforward example is an anisotropic graphene resonator such as Besides the switchable function, graphene endows the polarizer with frequency tunability and the active controllable isolation depth of the polarization states with the elaborate designs in The chiral metamaterials have been studied with enhanced circular dichroism (CD)  and optiIn general, the output beam through graphene metasurfaces may exhibit elliptical polarization, where the tilt angle and/or the ellipticity can be actively engineered with the variation of the graphene Fermi level. Multiple polarization states are flexibly switchable with proper biasing voltage at high modulation speed in a single structure, which is highly demanding for polarization encoding and multiplexing.In 2017, Shvets’ group experimentally demonstrated an active graphene metasurface that converts a linear polarization into an elliptical one with controllable tilt angle and ellipticity . The conSimilarly, by utilizing another anisotropic metasurface, namely the rectangle slot array in ectively f. The th 1.2 THz , taking If the metasurfaces are classified as two categories: graphene-integrated metallic resonator array and patterned graphene resonator array, most of the experimental validations until now fall into the first case. This is not only because of the relatively mature transfer technique  of graphThe relaxation time of carriers in most of the CVD-grown graphene layer is around 10∼30 fs when transferred to different substrates ,56,100. d before . It is pd before ,89,90. Td before  or the bd before .The development of graphene metasurfaces is generally following the track of metallic metasurfaces. The initially-proposed monolayer metallic metasurfaces usually suffer from poor efficiency and limited phase response range. The introduction of the back mirror enhances the interaction of light with the metallic resonators for efficient wavefront shaping in reflection mode. The geometric phase is then successfully used for wideband phase manipulation, and the layered configuration is helpful to improve the efficiency in transmission mode. All of these progresses have been witnessed in the development of graphene metasurfaces. However, most of the graphene configurations stay at the stage of dynamic phase shifters. To continue following the track of metallic metasurfaces, we envision graphene designs with spatially- and temporally-variant phase profiles for complicated wavefront shaping beyond focusing and bending, such as dynamic hologram imaging and reconfigurable structured beam generation, where the static metallic counterparts have been widely studied.With the recent trend from plasmonic to dielectric metasurfaces due to programmable electric and magnetic responses, graphene-dielectric hybrid design has become one of the most promising directions for active wave engineering with improved efficiency and increased flexibility. Initial studies include enhanced transmission modulation ,107, tunIn summary, the recent progress of graphene metasurfaces is overviewed with emphasis on the active phase and polarization control by relating the basic material property to the tunable device functionality. With the introduction of graphene, the metasurface is vested with tunable operation frequency, controllable efficiency, or switchable multiple functionalities. Additionally, graphene also extends the operation frequency of metallic metasurfaces into the sub-THz regime where metals as perfect electric conductors do not interact much with light, and even the near-IR and visible region where the interband transition dominates the conductivity . Althoug


The pore size of the adsorption and desorption in the 3D zz‐PS/GR/PU is also reduced from 354 and 352 Å to 34 and 33 Å. The 3D zz‐PS/GR/PU satisfies the requirement of high‐demanding superhydrophobic materials, like a low‐cost fabrication process, reusability, and tunability. This strategy can trigger large‐scale production with a controlled morphology.Superhydrophobic 3D robust materials are introduced for the separation of hexane and water. For the first time, novel 3D zigzag polystyrene on graphene‐incorporated polyurethane (3D zz‐PS/GR/PU) is prepared using exclusively natural sunlight without any chemical initiator. The zigzag polystyrene growth is accomplished by polymerizing the styrene vapors. The natural sunlight provides a compact 3D zz‐PS/GR/PU material with superoleophilic and hydrophobic channels that allow for the rapid passage of oil, whereas water is entirely prevented from passing. The 3D zz‐PS/GR/PU compact channels are transformed into the compressible material by treating them with toluene without affecting the hydrophobicity of the material. The 3D zz‐PS/GR/PU displays a high‐water contact angle of approximately 150°. The developed materials are characterized by FTIR, SEM, and BET. The graphene incorporation makes surface area of the 3D zz‐PS/GR/PU substantially large compared with PU. It is improved from 15 to 67 m Oil spillage incidents have become common due to the frequent oil movements across the world. In history, the Deep‐water Horizon oil spill 2010) in Mexico was considered to be a major oil spillage accident in marine water. Five million barrels of oil were released, and the deaths of 11 people were reported due to this accident. Another incident in North Dakota, the USA in 2016 caused the release of 4200 barrels of oil.0 in MexiOil–water separation is of great interest to the researchers due to its economic, social, and environmental significance.3O4) and the graphene/reduced graphene oxide (rGO). The introduction of magnetic properties into foam facilitates the facile movement and removal of foam after oil absorption.Recently, 2D graphene and its derivatives have received extraordinary attention due to their unique physicochemical properties. Graphene and its derivatives are extensively used to improve the chemical, electrical, mechanical, and thermal behavior of materials.In most of the cases, rGO is obtained from the GO. The synthesis and the handling of the GO are easy, cost effective and it can be produced at large scale.To overcome this drawback, the rGO and polystyrene 3D network synthesized on polyurethane using natural sunlight initiated polymerization in a confined glass reactor for oil and water separation. The rGO in the material is not enough to impart superhydrophobic behavior due to the preservation of the oxygen functionalities in the reduction process. Herein, efforts are made to construct a 3D superhydrophobic porous network with the help of polyurethane and polystyrene. Polystyrene is a good hydrophobic material but the introduction of the porous network into the polystyrene is a challenging task. In this work, the porous 3D network of polystyrene and graphene was synthesized through a green methodology that displayed excellent mechanical stability with a superhydrophobic behavior. The polymerization process was carried out under natural sunlight which provided a green, nonhazardous and cost‐effective route for the bulk production of the superhydrophobic material with a better uniform controlled morphology. A zigzag‐shaped growth of polystyrene on the surface of the GR/PU was observed which might be helpful to provide a better surface area for the efficient separation of oil from water. The synthesized porous superhydrophobic material can be shown to be a better choice for the removal of the bulk contamination of nonpolar organic solvents and oils from water.22.1The synthesized hydrophobic material 3D zz‐PS/GR/PU is a combination of graphene, polystyrene, and polyurethane. The incorporation of graphene into the polyurethane network provided a large surface area and also contributed to improving the mechanical properties of the material. The midway hanging of the GR/PU into the glass reactor assisted with achieving uniform growth of PS in 3D zz‐PS/GR/PU. The glass reactor played a crucial role in the formation of the 3D zz‐PS/GR/PU. The glass reactor walls were transparent and permitted the sunlight radiation to enter the reactor through it. The synthesis process of 3D zz‐PS/GR/PU was completed in two steps. The styrene liquid cannot approach directly to the GR/PU because it is hanging midway in the middle of the reactor. The sunlight radiation entered into the transparent glass reactor that provided the heat to vaporize the volatile styrene and might also have established equilibrium between the styrene vapors and the liquid styrene in the reactor. Vapors can move freely in the free space of the reactor and some of them stayed and passed through the porous network of the GR/PU. Simultaneously, the second step of polymerization was started. During this step, the polymerization process of styrene was initiated by the natural light. In this polymerization step, the styrene vapors started to convert into polystyrene and further stimulated the styrene liquid to vaporize. This process was continued until the polymerization process was completed.Step 1: VaporizationStep 2: PolymerizationFigureThe critical observation was made, after the polymerization of polystyrene on the pure polyurethane, that the interior of the PS/PU became fragile. It was shattered into small pieces by touching its surface. However, the incorporation of graphene into PU enhanced the growth of the polystyrene and the surface was more mechanically stable. The growth of polystyrene from the vapors of styrene is more interesting and provided a particular zigzag pattern of polystyrene that was porous in nature. This methodology might provide a better opportunity to combine the intrinsic characteristics of the polyurethane, graphene and the polystyrene for efficient utilization in various targeted fields. The fabrication process for the 3D macro zigzag architecture of graphene‐reinforced polystyrene is illustrated in 2.2−1. During the reduction process of GO, some oxygen‐containing functionalities were retained, which generally appeared in the FTIR spectra of the rGO. The absorption bands of oxygen‐containing functionalities such as carboxy —C—O stretching (ν = 1391 cm−1), alkoxy —C—O stretching (ν = 1027 cm−1), and hydroxyl group (ν = 3438 cm−1) absorption bands appeared in the FTIR spectra of graphene. The TEM study revealed either one or only a few layered graphenes. The FTIR and the TEM study have shown that graphene was successfully synthesized. The typical Raman spectrum of the graphene was determined. The D band appeared at 1350 cm−1 and G band appeared at 1580 cm−1. The D band was appeared due to the defects in the graphene sheets. The G band was appeared due to the in‐plane vibration of the sp2 bonded carbon atoms. In the Raman spectra of the graphene, the intensity of the G band was more compared with the D band, which is an indication of the partial restoration of the conjugation network. The ID/IG ratio was found 0.91 which is less than 1. If ID/IG ratio is large it is an indication that the reduction process generated more defects in the obtained grapheneFigureFigureThe synthesized materials were characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), and Fourier transfer infrared spectroscopy (FTIR). The synthesized graphene was characterized by the FTIR and the TEM. The FTIR spectra have shown the characteristic absorption band of aromatic carbon–carbon double bond (—C=C—) at 1633 cmFigure−1 was assigned to —N—H stretching and —N—H deforming, respectively. The —CH2 symmetric and asymmetric stretching vibrational bands appeared at 2866 and 2970 cm−1, respectively. The absorption band appeared at 1450 cm−1 and was assigned to the —CH2 bending vibration band. The band appeared at 1714 cm−1 in the spectra was assigned to the C=O vibrational band.The pure polyurethane FTIR spectra Figure4a disp−1 was absent. The absence of the absorption band at 2270 cm−1 revealed that after polymerization there were no free NCO functionalities.−1 was assigned to the stretching of C—O—C.In the FTIR spectra of the polyurethane, the asymmetric stretching vibrational band of the NCO at 2270 cm−1 (3D zz‐PS/GR/PU). This interaction of the PU surface with the graphene and the polystyrene might be responsible for the change in the C—O—C band intensity and band position. Apart from this, band shifts in the absorption bands of some functionalities were also observed. For example, a red shift in the —CH2 symmetric and asymmetric band of the PS/GR/PU was observed as the bands shifted from 2866 to 2859 and 2970 to 2927 cm−1, respectively. A blue shift in the —N‐H deforming band was observed and it was shifted from 1541 to 1542 cm−1. The carbonyl band that appeared in the pure polyurethane became considerably unclear in the PS/PU and PS/GR/PU FTIR spectra  and 100 g of sodium nitrate (NaNO3). The resulting solution was stirred for 30 min at 5 °C in an ice‐bath. After that, potassium permanganate  powder (15 g) was added slowly to the flask, and the mixture was heated to 35–40 °C and stirred for another 30 min. Distilled water (200 mL) was then added to the above mixture over a period of 25 min. Finally, 30% H2O2 was added to the mixture until the formation of a yellowish solid product. The mixture was then kept under stirring. The powder was separated in a centrifuge and washed several times by HCl solution and then by water. The obtained GO was then reduced by sodium. After that, GO was reduced by using ascorbic acid. Around 20 g of ascorbic acid was introduced to the dispersed GO under stirring at 70 °C for 4 h. The obtained material was allowed to cool and then separated in a centrifuge. The obtained reduced graphene was characterized.Fabrication of 3D zz‐PS/GR/PU: A fine dispersion of 0.5 mg mL−1 graphene was prepared by sonicating the graphene in ethanol for 1 h. After sonication, a piece of PU was dipped into the ethanol dispersed graphene. After that, it was removed from the ethanol dispersed graphene. It was dried and cured for 12 h in an oven at 60 °C. The obtained graphene‐coated polyurethane was described as GR/PU. After the curing process, the GR/PU was transferred into a glass reactor. The glass reactor contained 3 mL styrene monomer. In the glass reactor, the GR/PU was suspended almost in the middle to prevent it from touching the styrene liquid. Similarly, the PU without graphene coating was also prepared in another glass reactor for performance comparison. The glass reactors contained pure PU and the GR/PU was exposed to the natural sunlight until the styrene liquid disappeared. The zigzag growth of the polystyrene on the GR/PU surface could be noted. After the polystyrene growth, the black color of the GR/PU was changed to blackish white. The achieved architecture of the 3D zigzag polystyrene/graphene‐incorporated polyurethane was described as 3D zz‐PS/GR/PU. The 3D tzz‐PS/GR/PU was obtained by instantly dipping and then removing it from the pure toluene. After this toluene treatment, it was dried at room temperature.Experiment for Hexane/Water Separation: The experimental setup was designed for the hexane and water separation. The glass reactor in which the 3D zz‐PS/GR/PU was synthesized was made open from both ends. It was directly fixed on the opening of the suitable funnel to establish an experimental setup. The hexane and water mixture was prepared by mixing 100 mL hexane and 300 mL water in a reagent bottle. The mixture was introduced through the separation setup. For the absorption experiment, the synthesized material was dipped into hexane and taken out for weight measurement.The authors declare no conflict of interest.SupplementaryClick here for additional data file.


Liquid-phase exfoliated graphene sheets are promising candidates for printing electronics. Here, a high-performance printed 2.4 GHz graphene-based antenna is reported. Graphene conductive ink prepared by using liquid-phase exfoliation process is printed onto a water-transferable paper by using blade printing technique, which is then patterned as dipole antenna and transferred onto a target substrate. The fabricated dipole antenna (43 × 3 mm), exhibiting typical radiation patterns of an ideal dipole antenna, achieves −10 dB bandwidth of 8.9% and a maximum gain of 0.7 dBi. The printed graphene-antennas satisfy the application requirements of the Internet of Things and suggest its feasibility of replacing conventional metallic antennas in those applications.  It haGraphene is a type of two-dimensional (2D) materials, in which carbon atoms are arranged in a honeycomb to form a single carbon layer. The high charge mobility of graphene yields its high conductivity. Moreover, its conductivity is frequency independent up to the microwave region ,25, whicThere are a few recent reports on printed graphene-based antennas, showing potentials for practical applications ,8,30–36.In this work, we report a new process to fabricate printed graphene-based antenna with a high gain and small dimensions. The graphene-based antenna is printed on a water-transferable paper by blade printing and then transferred onto the surface of a target substrate. The fabricated dipole antenna with small dimensions achieves −10 dB bandwidth of 2.297–2.510 GHz (8.9%) with a maximum gain of 0.7 dBi. Such performance of our antenna satisfies its potential applications in the field of IoT.2.The graphene-based dipole antenna was designed and simulated using HFSS (High-Frequency Structure Simulator). Each pole of the antenna has the length of 20 mm and a width of 3 mm. The gap between the two poles is 3 mm .10.1080/insitu immediately with the infrared drier to volatilize the solvent. The heating temperature and time were set to 100°C and 30 min. The water-transferable paper with printed graphene layer was sculpted into the designed antenna pattern. Then, it was soaked into deionized water for 5 min to let the printed graphene layer separate from the paper substrate and transferred onto the surface of a target substrate. Thickness of the printed graphene layer was measured by using a profiler Bruker DektakXT  and sheet resistance was measured by using a Hall effect system .To prepare the graphene ink for blade printing , ethyl c11) of the graphene-based antenna. The radiation patterns of the antenna were measured in an anechoic chamber. The graphene antenna on the glass slide was fixed on a rotary table, with a horn antenna HD-26SGAH15N  on another rotary table as the receiver antenna. Measurements were performed once per degree in rotation.To perform antenna performance measurements, a coaxial wire with Subminiature Version A connector was attached to the poles using silver conductive paste to feed power into the graphene-based antenna. We integrated a folded balun with the coaxial wire to offset the current resulting from the outer conductor of the coaxial wire. A vector network analyzer Rohde & Schwarz ZNB20  was employed to measure reflection coefficient , Bluetooth, and ANT operate at 2.4 GHz, our dipole antenna is designed to operate at this frequency. Thus, each pole of the antenna has the length of 20 mm and a width of 3 mm, and the gap between the two poles is 3 mm . The simBy exploiting blade printing, we can easily produce thick and quite uniform films, which is depicted in 11) of our graphene-based antenna and it is found that the measured S11 has the minimum value of −13.79 dB at 2.407 GHz   which ha4.We have demonstrated the fabrication of high-performance 2.4 GHz graphene-based antenna by printing and using water-transferrable paper. Such a low-temperature and environment-friendly process is suitable for scalable production of graphene-based antennas. Our small-sized graphene dipole antenna has −10 dB bandwidth of 2.297–2.510 GHz (8.9%) with a maximum gain of 0.7 dBi. The performance of our graphene antenna satisfies the application requirements of IoT sensing and suggests its feasibility of replacing conventional metallic antennas in those applications.


Graphene has unique properties which make it an ideal material for photonic and optoelectronic devices. However, the low light absorption in monolayer graphene seriously limits its practical applications. In order to greatly enhance the light absorption of graphene, many graphene-based structures have been developed to achieve perfect absorption of incident waves. In this review, we discuss and analyze various types of graphene-based perfect absorption structures in the visible to terahertz band. In particular, we review recent advances and optoelectronic applications of such structures. Indeed, the graphene-based perfect absorption structures offer the promise of solving the key problem which limits the applications of graphene in practical optoelectronic devices. Graphene is a novel two-dimensional 2D) material, which has been studied widely due to its unique properties. Graphene has the ultrabroad absorption spectrum , the ultD materiaIn order to profoundly enhance the light absorption of graphene, many graphene-based perfect absorption structures have been developed. In the microwave, the absorption of graphene can be easily tuned by controlling the carrier density of graphene, and perfect absorption of graphene has been experimentally realized by combing a graphene capacitor with a metallic surface  or by emIn the application aspect, graphene-based perfect absorption structures have great potential in optoelectronic devices. Graphene-based perfect absorption structures can effectively enhance the responsivity of graphene photodetectors ,45 and iIn this paper, we will give a comprehensive review of graphene-based perfect absorption structures in the visible to THz band. Firstly, we will introduce the theory of perfect absorption. Secondly, we discuss and analyze various types of graphene-based perfect absorption structures in the mid-IR to THz band and in the visible to near-IR band, respectively. The recent progress of those structures will also be introduced. Still next, we review the optoelectronic applications of graphene-based perfect absorption structures. Finally, we will highlight the perspectives and challenges of graphene-based perfect absorption structures.Perfect absorption phenomenon has been studied for many years, here we will introduce the perfect absorption theory by using two simple structures. The first structure is a single mode resonator with one-side input wave, and the resonator can perfectly absorb the input wave when the critical coupling condition is satisfied. The second structure consists of an ultra-thin absorbing sheet  and a dielectric spacer on top of a thick metal layer, and perfect absorption can be realized by matching the impedance of the structure to that of vacuum.It’s well known that the resonant effect can effectively enhance the optical absorption of materials due to the local field enhancement, and resonant structures have been widely utilized to realize perfect absorption of an incident wave. In the following, we will discuss the perfect absorption conditions for a single mode resonator.A normal single mode resonator with one-side input wave, as shown in In order to get perfect absorption (Q factor) of the resonator should be controlled carefully, since it determines the mode leakage rate Q resonator is needed and the graphene should be away from the place with high field intensity. Conversely, we should concentrate the mode field near the graphene and reduce the Q factor of the resonator.When a perfect absorption structure is designed by integrating graphene with a resonator illuminated from one side, a back mirror is needed to completely block the transmission. In order to satisfy the critical coupling condition  with a distance According to the boundary conditions for the ultra-thin sheet under normal incidence condition, we can get the following Equation: For perfect absorption, R) and reactance (X) of the impedance for PIMS (ZS = R − iX) can be obtained from Equation (4). The values of R and X as a function of the spacer thickness d are plotted in n is chosen as 1.45 (corresponding to refractive index of silica in the IR) and rm is chosen as −1(corresponding to reflection coefficient of perfect electric conductor).The resistance (ZS = 1/σ2D(ω), σ2D(ω) is the conductivity of graphene) in the visible to near-IR band cannot satisfy Equation (4), since the real part of the graphene conductivity in this band is close to 6.08 × 10−5 Ω−1 [Considering graphene as the absorbing sheet in 10−5 Ω−1 ,81. Howe10−5 Ω−1  and the 10−5 Ω−1  in the TPlasmons are collective density oscillations of free electrons in metals and semiconductors. Doped graphene can support plasmons in the mid- and far-IR to THz band, and graphene plasmons have many advantages over plasmons in metals ,84,85. FGraphene plasmons can greatly enhance the near-field of graphene, which can be utilized to enhance the absorption  or realiUntil now, single-band ,89,90, dNevertheless, the graphene plasmons induced perfect absorption discussed above is normally band-limited or narrowband, which is restricted in some broadband applications. In the following, we will discuss graphene-based broadband perfect absorption structures.Broadband graphene-based perfect absorption is highly desirable for some applications, such as imaging and photodetection. In order to achieve broadband perfect absorption in the mid-IR to THz band, various approaches have been investigated. One effective method is using two layers or multi-layers patterned graphene to increase the absorption bandwidth ,108,109.Another effective method to achieve broadband absorption is using multi-resonances of patterned monolayer graphene ,114,115.Meanwhile, monolayer-graphene-based broadband perfect absorption structures were demonstrated by using the impedance matching concept ,116,117.The broadband absorption structures discussed above are based on patterned graphene which will result in some edge effects, thus rendering it difficult to realize perfect absorption in reality. In order to avoid the edge effects, broadband perfect absorption structures based on unpatterned graphene are put forward ,118,119.In addition, broadband perfect absorption structures based on the periodic structures with graphene-based hyperbolic metamaterials , graphenGenerally, there is a fundamental trade-off between the operational bandwidth and the attainable absorption, which means it is hard to improve the absorbance and the bandwidth simultaneously. Consequently, most of the broadband perfect absorption structures are based on 90% absorption, and the bandwidth will drop dramatically when trying to obtain higher absorbance. Hence, the broadband absorption structure with higher absorbance needs to be further investigated. The absorption structure in A normal perfect absorption structure just has one port, which means the structure is illuminated from one side by the incident wave. However, perfect absorption can be also achieved in a structure illuminated from both sides, and this two-port absorption is called “coherent perfect absorption” (CPA) . CPA wasIn 2014, J. Zhang et al. demonstrated that both CPA and coherent perfect transparency (CPT) can be realized in a patterned monolayer graphene in the mid-IR . The schIn 2015, H. Xiao et al. utilized split-ring graphene to realize CPA in the THz regime, and the calculated response time of the device was about 36 ps . MeanwhiThe main advantage of CPA is that optical absorption can be modulated simply by varying the relative phase of the coherent beams. The realization of CPA in graphene may lead to further demonstration of new types of optoelectronic devices such as coherent graphene photodetectors, phase-based sensors or all-optical logical devices.In the visible and near-IR band, the light absorption of suspended monolayer graphene under normal incidence is only 2.3%, and graphene can hardly support plasmon resonances due to the limit of doping level. Thus, the absorption of graphene was normally enhanced by coupling the graphene with metallic or dielectric resonant structures. In the following, we will firstly discuss the perfect absorption structures realized by coupling graphene with metallic nanostructures and with dielectric-mode structures, respectively. We will discuss a chip-integrated graphene-based perfect absorption structure afterwards.Metallic nanostructures can support localized surface plasmon resonances (SPRs) in the visible and near-IR band, and graphene absorption can be effectively enhanced by coupling graphene with metallic nanostructures due to the near-field enhancement. In 2013, S. Song et al. designed a graphene photodetector by coupling graphene with a metamaterial perfect absorber, perfect absorption of the whole structure was realized and the absorption of graphene can be enhanced to above 40% at wavelength around 1500 nm . SimilarIn 2015, F. Xiong et al. demonstrated graphene-based ultrabroadband absorption by exciting localized plasmons in the metallic structures, and simulation results show that the absorption of monolayer graphene is over 30% in the wavelength range from 780 to 1760 nm . GraphenIn addition, dual-band or multiband perfect absorption structures were designed by coupling graphene with metallic nanostructues ,41,42.Q factors of localized SPRs of metallic nanostructures are relatively low, and at the same time, the SPRs can effectively enhance the field intensity in graphene, so the absorption bandwidth of those structures could be broad. Secondly, the frequencies of the SPRs excited by incident waves are normally insensitive to the incident angle, so this kind of perfect absorption structures could have high incident angular tolerance [Graphene-based perfect absorption structures designed by coupling graphene with metallic nanostructures have some advantages. Firstly, the olerance ,39. Howeolerance . TherefoIn order to reduce the undesirable optical loss, graphene based perfect absorption structures were designed by coupling graphene with dielectric-mode structures, and in the following we will introduce those structures.Perfect absorption structures realized by coupling graphene with dielectric-mode structures can minimize the undesired optical loss in metals, and even 100% absorption in graphene can be achieved. In 2012, A. Ferreira et al. and M. Furchi et al. demonstrated that by integrating graphene with two Fabry-Pérot cavities  or a FabAlthough many perfect absorption structures have been designed, the experimental realization of monolayer-graphene-based perfect absorption in the optical range is still challenging. In 2014, Y. Liu et al. measured peak absorption of 85% at near-IR from monolayer graphene coupled with 2D silicon photonic crystals on top of a back mirror . In 20152 layer and a 1D polymethy1-methacrylate (PMMA) grating, and a thick gold layer is coated on the back side of the SiO2 layer. A scanning electron microscope (SEM) image of a fabricated structure and measured absorption spectra of absorption structures with different grating periods for TE polarization are also shown in In 2016, C.-C. Guo et al. experimentally demonstrated total absorption over 99% in the near-IR for monolayer-graphene-based subwavelength structures, which convincingly confirms the theoretical prediction of graphene-based perfect absorption in the optical range . The schThe graphene-based perfect absorption structures discussed above are based on free space incidence, which cannot be used for on-chip devices. In 2015, W. Xu et al. proposed a chip-integrated graphene-based near perfect absorption structure through waveguide-cavity (covered by graphene)-waveguide (WCW) system . In orde2.The theoretical work discussed above may provide an effective way to enhance the performance of chip-integrated graphene photodetectors. However, so far there is no experimental demonstration. Besides, the concept of chip-integrated perfect absorption structure is not limited to graphene and nanobeam cavity, which could also be extended to other WCW systems and other two-dimensional material such as MoSGraphene-based perfect absorption structures provide the opportunity to solve the key problem which limits the applications of graphene in practical optoelectronic devices, so they have been applied widely in advanced graphene optoelectronic devices. Here, we briefly summarize some optoelectroinc applications of graphene-based perfect absorption structures.Graphene is a promising material for photodetectors since it has ultra high carrier mobility and ultrabroad absorption band. Graphene photodetectors can potentially operate at speeds over 500 GHz , and manBy employing graphene-based perfect absorption structures, we can greatly enhance the responsivity without compromising the operational speed of the graphene photodetectors.In 2012, A. Ferreira et al. designed a graphene-based photodetector with two Fabry-Pérot cavities, and the peak absorption can reach near 100% . In 2012The optical absorption in graphene can be controlled by tuning the Fermi energy of graphene with electrostatic gating . Based o−1 can be tuned from 24.8% to 96.9%, with a modulation depth of 95.9% (13.9 dB) in reflection.Graphene-based perfect absorption structures can greatly enhance the modulation depth of graphene modulators. In 2014, Y. Yao et al. demonstrated graphene spatial modulators at mid-IR by using metasurface perfect absorption structures, and a modulation depth of 95% (13 dB) with modulation speed about 20 GHz was achieved . Figure In addition to photodetectors and modulators, tunable optical filters, polarizers and sensors were also demonstrated by utilizing graphene-based perfect absorption structures. The performances of those devices have been greatly enhanced compared with normal graphene-based devices.The emergence of graphene-based perfect absorption structures could solve the key problem which limits the applications of graphene in practical optoelectronic devices. Until now, a lot of graphene-based perfect absorption structures have been developed in the visible to THz band, and some applications of those structures have been demonstrated by experiments.Although a lot of works have been done and dramatic progresses have been made in the field of graphene-based perfect absorption structures, the real applications of those structures are still at the early stage. Graphene-based perfect absorption structures have some challenges that need be overcome in the practical device applications. The first challenge is how to simplify the structure which designed to achieve perfect absorption. The fabrication will be a big issue if a designed structure is complicated, and it will be hard to apply the structure in the real devices. In the real applications, unpatterned few-layer structures or planar patterned structures with big feature sizes are preferable, since those structures can be easily fabricated. The second challenge is how to realize near 100% optical absorption in the reality and minimize the undesirable optical loss in the same time. It’s not hard to get perfect absorption in the simulation, but the realization of perfect absorption in the reality is not easy work. For this issue, the designed perfect absorption structure should have relatively high fabrication tolerance and incident angular tolerance. On the other hand, the undesirable optical loss should be minimized. In the visible and near-IR band, the metal attenuation cannot be ignored, so the optical field intensity near the metal should be reduced as much as possible. The third challenge is how to control the wavelength and bandwidth of the perfect absorption. Broad absorption bandwidth is highly desired for photodetection and imaging, and narrow absorption bandwidth with tunable working wavelength is very important for optical filters, spectrally selective photodetectors and sensors. In the mid-IR to THz band, perfect absorption structures based on unpatterned graphene are preferable, in order to avoid the edge effects and simplify the fabrication processes. In the visible and near-IR band, perfect absorption structures realized by combing graphene with dielectric structures are preferable in many cases, since the undesirable optical loss can be minimized. However, the absorption bandwidths of those structures are normally narrow, which are not suitable for broadband applications. The surface mode or surface wave  in dieleIn summary, graphene-based perfect absorption structures can greatly enhance the optical absorption in graphene and the light-graphene interaction. We believe their potential is still not fully reached. Besides the applications of photodetectors, modulators, filters and polarizers, graphene-based perfect absorption structures could be also of valuable applications in light emitting devices, photovoltaic devices, nonlinear photonic devices and so on. Graphene has been demonstrated to be a good candidate for light emitters ,137, how


Background: Fatigue is a common symptom in patients with sarcoidosis. Despite lacking evidence on whether high-intensity interval training (HIIT) will aggravate fatigue, moderate-intensity exercise is often recommended. This study aimed to investigate whether a single session of HIIT would affect fatigue differently from a single session of moderate-intensity continuous training (MICT). Methods: Forty-one patients with pulmonary sarcoidosis were recruited to a cross-over study. All patients completed one treadmill session of HIIT (85% of peak heart rate (HRpeak)) and one of MICT (70% of HRpeak). Fatigue was assessed with the Visual Analogue Scale 0–100 mm, before (T0), after (T1), and 24 hours after (T2) each exercise session. Paired sample t-test was used to compare changes in fatigue from T0 to T1 and from T0 to T2 between HIIT and MICT. Results: No statistically significant difference in fatigue levels was found between HIIT and MICT, either at T1 (3.6 (13.5) and 1.4 (13.5)) or at T2 (8.2 (17.0) and 2.1 (17.1)). Conclusions: A single session of HIIT did not affect fatigue differently than a single session of MICT. These preliminary findings support the need for further research on the long-term effect of HIIT on fatigue in patients with sarcoidosis. Sarcoidosis is a multisystem granulomatous disorder affecting any organ. The lung is involved in more than 90% of the patients . Up to 8ClinicalTrials.gov (NCT02735161) before the first patient was included. The study had a crossover design with a convenience sample of patients with pulmonary sarcoidosis recruited from LHL Hospital Gardermoen, a national pulmonary rehabilitation (PR) clinic in Norway. Patients >18 years) with pulmonary sarcoidosis diagnosed in accordance with accepted guidelines [8 years w2peak) was assessed by a cardiopulmonary exercise test (CPET) (Ganshorn Schiller CS-200/ Vyntus CPX) on a treadmill, using a modified Bruce Protocol with reference values from a Norwegian population [Information about medical history was collected from the pulmonary physician’s medical report. Body composition and lung function tests were performed according to international guidelines  and refepulation . Submaxipulation ,22 and cpulation . All bacAll 41 patients in this crossover study performed two supervised exercise sessions on a treadmill , i.e., one HIIT session and one MICT session. As the patients primarily were participants in a four-week PR program, the choice of two sessions separated by a week was due to practical considerations. The HIIT session was performed the first week, and the MICT session was performed the second week. The two exercise sessions were conducted at the same time of the day to avoid the influence of individually daily variations of fatigue. The HIIT session consisted of a 6 min warm-up, four intervals of 3 min (4 × 3 min), active pauses of 2 min between each interval, and a 2 min cooldown with a total duration of 26 min. The target intensity of the 3 min intervals was >85% of peak heart rate (HRpeak) based on the obtained HRpeak from the CPET and/or perceived exertion of breathlessness ≥5 (severe) on the Borg CR10 scale . During The target intensity of the MICT session was 70% of HRpeak; HR was monitored and controlled during the entire session by a Polar sport watch. To keep the intensity constant, the treadmill function “Constant Pulse Rate” was used. The treadmill then automatically adjusted speed and/or elevation during the session to maintain the target intensity of 70% of HRpeak. Equal energy expenditure  was used to equate the HIIT and MICT sessions, and warm-up was included in both sessions, estimated by the Polar V800 watch. The MICT session lasted until the patient had consumed the same amount of individual kcal as in the HIIT session. The Polar V800 “Smart calories” function is based on the following individual parameters: gender, date of birth, bodyweight, height, HRpeak, resting HR, VO2peak, and a grading of how hard/often they usually exercise (hours per week). The Polar V800 has shown to be the most accurate sport watch for estimating kcal during aerobic activities in healthy individuals . The wasSeveral studies have failed to identify physiological biomarkers which correlate with sarcoidosis-related fatigue as a response to exercise in sarcoidosis ,26,27, sTo monitor the intensity of the two exercise sessions, HR and perceived breathlessness were used. HR was monitored continuously using the sport watch Polar V800. Breathlessness was assessed with the Borg CR10 scale . This isp values of <0.05 were considered as statistically significant. All relevant variables were tested for normal distribution by visual inspection of the histograms, Q-Q plots, and test of normality. Because of the cross-over design, paired sample t-tests were used to detect statistically significant changes in fatigue from T0 to T1 and from T0 to T2 within and between the HIIT and the MICT sessions. All statistical analysis was performed with SPSS version 22 .Power calculation was based on a change in MCID of 10 mm for VAS-F , an alphThe sample was evenly divided in females and males with normal lung function and slightly reduced exercise capacity. Thirty-nine of the 41 patients (95%) had fatigue FAS score > 22 points .p = 0.326) nor at T2 (8.2 (17.0) vs 2.1 (17.1), p = 0.106). VAS-F increased slightly following both the HIIT and the MICT exercise session, with a statistically significant increase in VAS-F from 22.6 (18.8) mm to 30.9 (21.9) mm, p = 0.003 only at T2 after the HIIT session  mm vs 1.4 (13.5) mm,  session . p = 0.550.All 41 patients were able to complete the 26 min HIIT session. The target intensity of 85% of HRpeak was obtained by 33 of 41 patients (80%), and the perceived exertion of breathlessness Borg CR10 > 5 was obtained by 40 of 41 patients (98%) . One patp = 0.280) (p < 0.0001)  kcal) and MICT (187 (65) kcal) was met, (= 0.280) . The mea 0.0001) . No adveTo our knowledge, this is the first study that has examined the development of sarcoidosis-related fatigue after two exercise sessions with different intensities but with the same total amount of energy expended in patients with pulmonary sarcoidosis. There was no statistically significant difference in fatigue levels between one session of HIIT and one session of MICT, either immediately after (T1), or 24 h after exercise (T2). Our findings are in line with a comparable study by Sandler et al.  who compWhen exploring the effects on sarcoidosis-related fatigue in the context of exercise, we have to be aware of the influence of acute exercise-induced fatigue due to physiological stress which increases with increasing exercise intensity . The patBecause of the need for establishing an optimal training program  for patients with pulmonary sarcoidosis , the secA review recommends the exercise intensity for patients with sarcoidosis to be personalized and adjusted for daily fluctuations of fatigue . The samThe HIIT protocol of 4 × 3 min in this study is a modified version of a 4 × 4 min protocol which has shown to be feasible for patients with several other diseases, such as coronary heart diseases, metabolic syndrome, and heart failure ,42,43. OOne method used when comparing two exercise sessions with different intensity is to equate the total work performed by energy expenditure  ,42,43. TBecause of the small numbers of patients with sarcoidosis attending PR in Norway with an annual number of 30, a cross-over study was considered as the most appropriate and feasible design. Both sessions were supervised, and regular monitoring of heart rate and perceived exertion ensured the target intensity was reached and contributed to quality assurance of the results. The location of an in-patient PR clinic made it possible to customize the project schedule in relation to the PR schedule, to avoid inflicting additional stress on the participants. However, there are some limitations to this study. Firstly, the absence of a random allocation. Randomization was considered but found difficult to implement, as the two sessions were matched by energy expenditure. If randomized, the MICT protocol must have had a defined duration as well. The caloric consumption after a fixed duration of the MICT session could have resulted in an interruption of the HIIT before completing the 26 min, due to the challenges described in the section above. As feasibility of HIIT was a secondary aim, we considered a random allocation not to be suitable. Secondly, as daily variation of fatigue is reported in patients with sarcoidosis, this could potentially have influenced our results. Measures of VAS fatigue on days without exercise could have been added to control for this bias. Thirdly, the design with only one session of HIIT is a limitation to predict the long-term effects of high-intensity exercise training on fatigue. Finally, since we do not know how exercise of any modalities affects the immunological, muscular, or respiratory functions in sarcoidosis, we cannot preclude that there are differential effects of MICT and HIIT on these systems.The results from this study show that patients with pulmonary sarcoidosis are able to safely perform a single session of HIIT without worsening of sarcoidosis-related fatigue. The change in fatigue was comparable to those seen following an MICT session. These preliminary findings support the need for further research on the long-term effects of HIIT on fatigue in patients with sarcoidosis.


The soluble interleukin 2 receptor (sIL-2R) has been proposed as a marker of disease activity in patients with sarcoidosis. However, no studies have evaluated whether serum sIL-2R measurement is of use in establishing the diagnosis of sarcoidosis in patients who are suspected of sarcoidosis among other diseases.A cohort study was conducted, consisting of new patients who visited the immunology outpatient clinic and whose serum sIL-2R levels were available before a definitive diagnosis was established between February 2011 and February 2016. All patients underwent standard diagnostic testing for sarcoidosis . This resulted either in the diagnosis of sarcoidosis or the exclusion of sarcoidosis with the diagnosis of another disease. Results of sIL-2R and angiotensin-converting enzyme (ACE) levels, radiographic and nuclear imaging and histology results were collected and definitive diagnoses were recorded. Sensitivity, specificity, the concordance statistic from the receiver operating characteristic curve and Youden’s Index were calculated to assess the performance of sIL-2R in the diagnosis of sarcoidosis and were compared to ACE, currently one of the most used diagnostic biomarkers in the diagnosis of sarcoidosis.In total 983 patients were screened for inclusion, of which 189 patients met the inclusion criteria. A total of 101 patients were diagnosed with sarcoidosis after diagnostic workup, of whom 79 were biopsy-proven. In 88 patients a diagnosis other than sarcoidosis was made. The sensitivity and specificity of serum soluble interleukin 2 receptor levels to detect sarcoidosis were 88% and 85%. The sensitivity and specificity of ACE were 62% and 76%. Receiver operating characteristic curve analysis revealed that sIL-2R receptor is superior to ACE (p<0.0001).Serum sIL-2R is a sensitive biomarker and superior to ACE in establishing the diagnosis of sarcoidosis and can be used to rule out sarcoidosis in patients suspected of sarcoidosis. Sarcoidosis is a multisystem disease of unknown origin, characterized by non-caseating granulomas, which can affect almost any organ system. The diagnosis of sarcoidosis is based on clinical and radiographic manifestations and histopathologic detection of non-caseating granulomas in the affected organ, after exclusion of other diseases that may present similarly.  Diagnost+ T-helper (Th)1 cells at sites of active disease. Reviewers' comments:Reviewer's Responses to QuestionsComments to the Author1. Is the manuscript technically sound, and do the data support the conclusions?The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: YesReviewer #2: Partly**********2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: YesReviewer #2: Yes**********3. Have the authors made all data underlying the findings in their manuscript fully available?PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.The Reviewer #1: YesReviewer #2: No**********4. Is the manuscript presented in an intelligible fashion and written in standard English?PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.Reviewer #1: YesReviewer #2: Yes**********5. Review Comments to the AuthorPlease use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. Reviewer #1: Sarcoidosis is a systemic granulomatous disease of unknown etiology. The polarization into T helper type-1 response and its associated cytokines have been reported to play key roles in pathogenesis of this disease. Until now, the diagnosis of sarcoidosis is still difficult and sometimes very problematic, almost bases on a combination of clinical and imaging findings, histological demonstration and exclusion of other capable diseases. So, exploring a marker with high sensitivity and specificity for diagnosis of sarcoidosis is very interesting and meaning with clinical practices. However, serum level of sIL-2R is not a new marker for sarcoidosis with many research studies before in which sensitivity and correlation between this serum level with disease activity and other diagnosis parameters were already confirmed. Because this serum correlates with the level of T-cell activation, identification for the specificity of sIL-2R required a bigger survey from many other diseases and I have a few questions that I would like to discuss below.1. The new information from your study is identification for the specificity of sIL-2R that required a bigger survey from many non-sarcoidosis diseases. In your manuscript, the number patient is small, they are not representative for the disease populations. If you increase these numbers, your study may be more convincing.2. In Figure 3, please change the format box-plot to dot-plot, and add the number of each group. It will help to recognize the number of patients involved in this study.3. In the result 3.3: correlation of sIL-2R with diagnostic parameter, the author showed the significant correlation between sIL-2R and chest radiograph stage, but R=0.27 is not difference. May you check it? And it might be better if you show these data by correlation chart.Reviewer #2: Review comment PONE-D-19-207The authors examined the diagnostic utility of sIL-2R and ACE in patients with suspected sarcoidosis patients, and concluded that sIL-2R was useful for such biomarkers. Although the manuscript basically well written, this reviewer feels that there is serious concern that should be addressed.Major1. Study population:To consider sensitivity and specificity of biomarker, study subjects  are very important.A) Suspected of sarcoidosis patients: As mentioned in the introduction, sarcoidosis is systemic disease. Thus, there were many courses in suspected sarcoidosis patients . Were all the patients who have lung sarcoidosis in the present study? The authors should clearly define the patients who suspected sarcoidosis. To clarify study subject who suspected sarcoidosis, how about the authors consider to limit the study subjects who have lung sarcoidosis or lung disease.B) As shown in Figure 2, patients with immunosuppressive medication <2 weeks before sIL-2R measurement or ACE inhibitors < 1 month before ACE were excluded. Are there any backgrounds in this setting period? This reviewer feels that all patients who prescribed immunosuppressive medication should be excluded in the study subjects.C) In Figure 4, to examine sensitivity and specificity of sIL-2R and ACE, which subjects  did the authors use?2. Results Figures 1 and 2Please consider combine Figures 1 and 2, to easy to understand for readers.Minor3. Figure 3Please add the numbers of each group in Figure 3.**********what does this mean?). If published, this will include your full peer review and any attached files.6. PLOS authors have the option to publish the peer review history of their article  digital diagnostic tool,  16 Sep 2019Dear editor,Thank you for the opportunity to clarify the message of our manuscript. We have answered the remarks of the reviewers, and we feel that the manuscript, after applying the suggested changes, has improved significantly. In addition to this, we noticed that the objective of our study was not stated clearly enough. Therefore, in addition to our replies and corrections based on the advice of the reviewers, we have shifted the focus of the manuscript slightly to highlight our study population and our objective more clearly. Consequently, we have changed the title to “Sensitivity and specificity of serum soluble interleukin 2 receptor in a population of patients suspected of sarcoidosis”. We hope you will find the manuscript sufficiently improved and suitable for publishing in PlosOne. Reviewer #1: Sarcoidosis is a systemic granulomatous disease of unknown etiology. The polarization into T helper type-1 response and its associated cytokines have been reported to play key roles in pathogenesis of this disease. Until now, the diagnosis of sarcoidosis is still difficult and sometimes very problematic, almost bases on a combination of clinical and imaging findings, histological demonstration and exclusion of other capable diseases. So, exploring a marker with high sensitivity and specificity for diagnosis of sarcoidosis is very interesting and meaning with clinical practices. However, serum level of sIL-2R is not a new marker for sarcoidosis with many research studies before in which sensitivity and correlation between this serum level with disease activity and other diagnosis parameters were already confirmed. Because this serum correlates with the level of T-cell activation, identification for the specificity of sIL-2R required a bigger survey from many other diseases and I have a few questions that I would like to discuss below.1. The new information from your study is identification for the specificity of sIL-2R that required a bigger survey from many non-sarcoidosis diseases. In your manuscript, the number patient is small, they are not representative for the disease populations. If you increase these numbers, your study may be more convincing.Thank you for your comment. We agree that increasing the number of patients, thus patients who got a definitive diagnosis of sarcoidosis or another disease than sarcoidosis, in our study would add statistical power and value to our study. Therefore, we did go back into the dataset and now added patients in whom a diagnosis (sarcoidosis or another disease) was now established .In total, we added 9 additional patients, of whom 4 got the definitive diagnosis of sarcoidosis and 5 patients who were diagnosed with another disease. The addition of these extra patients to our study implied recalculations for the whole manuscript, so you will find that all of our numbers have changed slightly, although not significantly. With the addition of these patients, the total number of patients in the revised manuscript now is 189. Prior to the analysis of this study, we have performed a power calculation, with a power of 80% and a confidence interval of approximately 5% on either side, with a modest estimated effect difference of 10%. This yielded a suggested sample size of 200 patients. The number of patients included in this study (189), is close to the suggested sample size. Importantly, since the effect difference appeared larger than the estimated effect difference used in the initial power calculations, it is easier to detect significant differences. Therefore, we feel our study is adequately powered for our primary outcome. Adding more patients from another population to add power for our secondary outcomes might induce bias to this study. In this study, we selected all patients from the same pool: patients whose sIL-2R had been assessed because sarcoidosis was part of the differential diagnosis. Therefore, we are limited in the number of patients we can include by our population pool of patients that at that time of serum sIL-2R measurement had a differential diagnosis that included sarcoidosis among other diseases. If we would have selected patients from other departments, such as Rheumatology for example with high suspicion of rheumatoid arthritis yet without any suspicion of sarcoidosis to add to the non-sarcoidosis patient group, we include patients who were never suspected of sarcoidosis. For example, a female patient with a family history of rheumatoid arthritis, with a symmetrical polyarthritis of the hands, morning stiffness and a positive rheumatoid factor or anti-citrullinated protein antibody, would in practice never be tested for sarcoidosis. As the aim of our study was to explore whether serum sIL-2R measurements could be of added value to diagnose sarcoidosis in patients that present at the clinic with features that can be associated with sarcoidosis, as well as other diseases, we feel it would not be statistically sound to include serum the sIL-2R from patients who never have been suspected of sarcoidosis. This would clearly not reflect the daily clinical practice where we want to apply serum sIL-2R measurements in patients who are suspected of having sarcoidosis. Furthermore, it would not answer the research question: can sIL-2R be used in case of suspicion of sarcoidosis? Therefore, we only used this pool of patients suspected of sarcoidosis whose sIL-2R was assessed. 2. In Figure 3, please change the format box-plot to dot-plot, and add the number of each group. It will help to recognize the number of patients involved in this study.We agree with the reviewer and have changed the initial box-plot into a dot-pot and added the group sizes to make this figure more insightful.3. In the result 3.3: correlation of sIL-2R with diagnostic parameter, the author showed the significant correlation between sIL-2R and chest radiograph stage, but R=0.27 is not difference. May you check it? And it might be better if you show these data by correlation chart.We thank the reviewer for addressing this point. Indeed, a correlation of 0.27, even though it might be statistically significant (P < 0.05) is not a strong correlation and presumably of low clinical value. Therefore, we have changed our wording in that paragraph to ‘There is a statistically significant, weak correlation between sIL-2R and chest radiograph stage’ and we have commented on this in the discussion as well. Since this finding is of low clinical value, we feel it might not be appropriate to use an additional graph for this finding. Reviewer #2: Review comment PONE-D-19-207The authors examined the diagnostic utility of sIL-2R and ACE in patients with suspected sarcoidosis patients, and concluded that sIL-2R was useful for such biomarkers. Although the manuscript basically well written, this reviewer feels that there is serious concern that should be addressed.Major1. Study population:To consider sensitivity and specificity of biomarker, study subjects  are very important.A) Suspected of sarcoidosis patients: As mentioned in the introduction, sarcoidosis is systemic disease. Thus, there were many courses in suspected sarcoidosis patients . Were all the patients who have lung sarcoidosis in the present study? The authors should clearly define the patients who suspected sarcoidosis. To clarify study subject who suspected sarcoidosis, how about the authors consider to limit the study subjects who have lung sarcoidosis or lung disease.Thank you for this insightful comment. As you mentioned, there are many localizations of sarcoidosis and sarcoidosis patients may present with a broad variety of symptoms. This directly translates into a difficulty describing the suspicion of sarcoidosis. In our study, we included a wide range of patients who were diagnosed with sarcoidosis after the diagnosis workup, and not only those presenting with lung complaints. On the one hand, including only those patients presenting only with lung complaints, would have resulted in the inclusion of a more homogenous group. On the other hand, including all patients suspected of sarcoidosis, who eventually were diagnosed with sarcoidosis of any organ, enabled us to include more patients, . Importantly, this also better reflects the usefulness of sIL-2R in establishing the diagnosis of sarcoidosis, since not all patients suspected of sarcoidosis will initially present themselves to the clinician with lung complaints. Sarcoidosis was suspected when a patient was referred to the Immunology department with one or more of these criteria: 1) lung complaints i.e. shortness of breath, persistent dry cough or chest pains 2) uveitis or inflammation of the lacrimal glands 3) skin disorders i.e. erythema nodosum, lupus pernio, infiltration of scars or tattoos4) neurological complaints i.e. hearing loss, facial nerve palsy or epilepsy5) polyarthritis6) incidental finding of lymphadenopathy on imagingWe have added these criteria to the manuscript to clearly describe our study population. B) As shown in Figure 2, patients with immunosuppressive medication <2 weeks before sIL-2R measurement or ACE inhibitors < 1 month before ACE were excluded. Are there any backgrounds in this setting period? This reviewer feels that all patients who prescribed immunosuppressive medication should be excluded in the study subjects.Thank you for this astute observation. We agree that patients who were prescribed immunosuppressive medication should be excluded from this study. To assess immunosuppressive medication use, the list of medication at first visit to the department was screened. The referral letter was also screened for use of any immunosuppressive medication. We cannot know whether the patient had any immunosuppressive medication prior to the referral letter. For example, one patient might have had corticosteroids prescribed to them by their general practitioner. If this medication has been stopped just before the referral and the referral letter, we might not be aware of this use. Therefore, we defined the immunosuppressive use as two weeks before the first visit and sIL-2R determination, since this is the minimum waiting time between referral and visit to the immunology department. Within this time frame, we are certain that patients have not used any immunosuppressive medication. However, for most patients, the time between the referral letter and the first visit to our clinic is longer, and thus increases the interval of time of which we are sure that they did not use immunosuppressive medication. With regards to the use of ACE-inhibitors, we were able to employ a broader strategy. Since this medication is prescribed for long periods of time, and not in short courses as corticosteroids are, we were able to use data not only from the list of medication at first visit and the referral letter, but also from letters from other departments of our Medical Centre, such as the cardiology or ophthalmology department. Therefore we were able to achieve the certainty that patients did not use ACE-inhibitors one month prior to ACE measurement. C) In Figure 4, to examine sensitivity and specificity of sIL-2R and ACE, which subjects  did the authors use?Thank you for your comment. In this figure, we examined the sensitivity and specificity of sIL-2R and ACE in included patients (n = 189) that had a suspicion of sarcoidosis in the differential diagnosis. We choose to use this specific population, since this is the population who, in clinical practice, would undergo diagnostic testing for sarcoidosis. We feel that, if we include healthy controls as well, sIL-2R would over-perform in this setting and would not give realistic values that are applicable for the current medical practice. To clarify, we now have added the numbers patient to this Figure. 2. Results Figures 1 and 2Please consider combine Figures 1 and 2, to easy to understand for readers.We welcome this helpful comment and we have merged Figure 1 and 2 into one figure. Minor3. Figure 3Please add the numbers of each group in Figure 3.We have added the group size to make this figure more insightful. 2 Oct 2019Sensitivity and specificity of serum soluble interleukin-2 receptor for diagnosing sarcoidosis in a population of patients suspected of sarcoidosisPONE-D-19-20768R1Dear Dr. Eurelings,We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.Within one week, you will receive an e-mail containing information on the amendments required prior to publication. 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We theoretically demonstrate that tunable exceptional points (EPs) can be realized by using graphene-embedded one-dimensional (1D) photonic crystals with optical pumping in the terahertz (THz) frequency range. By tuning the Fermi level of graphene sheet, the energy band are altered significantly and the EP appears. In particular, multiple EPs at different frequencies can be selectively produced via subtly adjusting the band structure. Furthermore, topological features of these EPs, such as crossing and anti-crossing of the real and imaginary parts of the eigenvalues, have been analyzed in detail. We expect that tunable EPs can provide an instructive method to design active optical devices based on photoexcited graphene sheets in the THz frequency range. Beyond some non-Hermiticity threshold, typically called the exceptional point (EP), the PT-symmetry is broken, and the system experiences an abrupt phase transition with eigenvalues becoming complex. The EP represents spectral singularity for the non-Hermitian Hamiltonian, where the eigenvalues and their corresponding eigenvectors coalesce simultaneously2. Inspired by the unique property, a lot of attentions have been paid to the PT-symmetric quantum systems5 and the concept of PT-symmetry has been successfully extended to wave optics. Photonic platforms are well-suited for constructing structures that satisfy the conditions of balanced gain and loss required by PT-symmetry22. In the PT-symmetric systems with EPs, a great variety of interesting optical phenomena have been discovered, such as asymmetric light propagation10 and invisibility12, Bloch oscillation of energy13, coherent perfect laser absorber18, single-mode laser20 and loss-induced suppression and revival of lasing22. While, the EP sustained in the previous investigation is fixed once the geometry and non-Hermitian parameters are determined. The EPs that can be tailored have many potential applications, such as controllable unidirectional invisibility and adjustable single-mode laser. However, the tunable EPs based on external fields are still rare.Since the pioneering work of Bender 24, graphene has sparked keen interest and remained in the scientific limelight for over a decade, resulting in a rapid development of the field of graphene plasmonics. For example, the nanopatterned graphene sheet can be used as an active medium for infrared electro-optic devices26. Moreover, embedding graphene in the photonic crystal allows the system to exhibit desirable optical properties, such as enhanced nonlinear and absorption31. Furthermore, it have been demonstrated theoretically that loss induced amplification of graphene plasmons32 and singularity-enhanced sensing based on the PT-graphene metasurface33 are characteristics of EP behaviors. In addition, the utilization of the tunable graphene layer to control EPs has been rarely studied35. Motivated by the above investigations, the problem is whether or not the tunable EPs can be obtained in a quasi-PT symmetrical system, which is made up of the incorporation of graphene sheets into a one-dimensional photonic crystal with the PT symmetry.On the other hand, due to the high-performance electric, thermal, mechanic and optical propertiesIn this work, we explore the possibility to tailor EPs in 1D graphene-embedded photonic crystals with optical pumping in the THz frequency range. By investigating the evolution of the complex band structures of the system, we find that the energy band can be effectively modified by tuning the Fermi level of graphene sheet and the EPs in THz frequency region emerge. Particularly, these EPs have topological features, such as the crossing and anti-crossing behaviors around them. In addition, many EPs at different frequencies are realized by altering only the Fermi level of the graphene sheet.2 and A2) and loss (B1 and A1) dielectrics with corresponding dielectric constants being 1 (A2) and B1 (B2) are taken to be dA and dB. We can clearly figure out that the system presented in Fig. 37. The optical properties of the graphene layer can be described by the equivalent permittivity εg,eq, and the relationship between εg,eq and the complex surface conductivity of the graphene σg is expressed as38λ is the wavelength of the incident wave in the air. The surface conductivity of the monolayer graphene consists of two parts: the intraband conductivity σraint and the interband conductivity σerint, which can be approximately expressed as (in the THz frequency)39:e represents the charge, kB is the Boltzmann constant, v is the frequency of the incident wave), τ is the intra-band transition time, and Ef denotes the quasi-Fermi energy level of electrons and holes at temperature T. The energy splitting of the quasi-Fermi levels Ef is expressed as40vF is the Fermi-velocity of charge carriers in the graphene, τr is the recombination time for electron-hole pairs and I describes the intensity of the photo-doping pump source. It can be seen that Ef is highly tunable via the external pumping strength I, thereby affecting the optical properties of graphene. Motivated by the above characteristic, we study the evolution of the complex band structure by tuning the Fermi level of graphene sheet in such a general non-Hermitian system and explore whether the tunable EPs can be gained.The systems considered to realize the control of the EPs are 1D graphene-embedded photonic crystals, composed of the multi-layered unit cell that satisfies the quasi-PT symmetric condition with the tunable graphene layer. Here, we only show one of the systems we studied, and the other structures have similar results . As shown schematically in Fig. 41, in order to calculate the complex band structures of the non-Hermitian system, we should utilize the transfer matrix method to calculate the dispersion relation of the corresponding Hermitian part firstly, where the gain and loss of the photonic crystal are chosen to be zero. Then, the Hamiltonian for the non-Hermitian system can be set up by using the Bloch states of a fixed k (the Bloch wave vector) for the corresponding Hermitian part as a basis. The same method was used to investigate the band structure (TE mode) of the graphene-embedded 1D photonic crystal in this work.According to ref.42. It can be expressed as:an and bn are the amplitudes of the field propagating in the forward and backward directions in the medium layer marked with n , k is the Bloch wave vector, a is the lattice constant, and pn for the unit cell43. Here, um(x) is obtained from Eq. . Substituting this expansion into Helmholtz equation, we arrive at the corresponding model Hamiltonian for this non-Hermitian system:Cl,m, c is the speed of light in vacuum, Firstly, the eigen equation for the 1D photonic crystal in the absence of gain or loss can be obtained by using the transfer matrix method with the consideration of the boundary condition and the periodicity of the structure44, and other parameters are taken as: lmax = 25. As shown in Fig. The eigenvalue of the above non-Hermitian system is generally complex, and the real and imaginary parts correspond to the energy and linewidth of the Bloch mode, respectively. The calculated complex band structures for the real and imaginary parts are depicted in Fig. Ef < EfEP , such as Ef > EfEP), the red curves intersect, but the blue curves reopen.In order to clearly see the process of the emergence and disappearance of the EP, we present the complex band structures with different Fermi levels in Fig. From the above results, we find that the EPs can be gained by subtly adjusting the Fermi level of graphene sheet in the graphene-embedded 1D photonic crystal. It is very significant that the Fermi level can be controlled expediently by only tuning the external electric field. This is in contrast to the case without graphene, in which the EPs can only be obtained by changing the geometry (such as the thickness of the media) or dielectric parameters (such as loss and gain) of the system. Such a switching effect is very beneficial to the optical devices based on EPs.The results illuminated in Fig. EfEP (Fig. We study the transition between crossing and anti-crossing by only changing the Fermi level of the graphene sheet. The real part of the complex band structures in the vicinity of the EP are plotted in Fig. fEP Fig. . In addiThe above results only focus on the case with the EP formed around the 8th and 9th bands. In fact, many EPs emerged around other frequency ranges can also be obtained by precisely adjusting the Fermi level of the graphene sheet. In this part, we studied the lowest 12 bands of the 1D photonic crystal. Six EPs at different frequencies and normalized Bloch wave vectors are realized by altering the Fermi level of the graphene sheet.The real and imaginary parts of the eigenfrequencies of different EPs are plotted in Fig. 47. According to refs47, the phase rigidity is defined as:48. They can be expressed as:48Dl,m is the element in the eigenvector 41. During the process away from the EP, the phase rigidity gradually increases and is close to 1 at the position of the maximum width of the bifurcation. When the non-Hermiticity parameters are nonexistent, meaning that the system becomes Hermitian, the phase rigidity takes the maximum value of 145. For the above 6 EPs, the corresponding phase rigidities are all calculated, as shown in Fig. In order to further analyze the behavior of these EPs, we also calculate the phase rigidity. The phase rigidity is the quantitative measurement of the ratio between the orthogonality and the bi-orthogonality of the eigenstates, which has been discussed in detail in refsIt is worthy to note that the above results are only for the photonic crystal with a certain geometry and non-Hermitian potential. In fact, if we change the thickness and the relative permittivity of the dielectric layer and keep the multi-layered unit cell satisfies the quasi-PT-symmetric condition, EPs can always be found by tuning the Fermi level of the graphene sheet. In addition, we want to point out that the geometric structure shown in Fig. In conclusion, using the non-Hermitian transfer matrix method based on the basis expansion with the results in the Hermitian potential, the band spectrum of a 1D graphene-embedded photonic crystal was obtained, exhibiting the EP in higher-order mode. The characteristics of the Riemann sheet structure and the phenomenon of crossing and anti-crossing of the eigenvalues adjacent to the EP were also studied. Furthermore, the behaviors of EPs have been disclosed by calculating the phase rigidity in the vicinity of the EPs. In particular, many EPs were gained at different frequencies by only tuning the Fermi level of graphene sheet. This means that we can tailor the EPs by using the external fields, which is very beneficial for the designs of optical functional devices based on the EPs.sp


This excellent performance is the result of the effect of ZnO and graphene that combines two Li+ accommodation sites, and the contribution of graphene pyramids, which provides more available sites to favor lithium storage capacity. Hence, this anode may be a promising electrode material for lithium-ion batteries.A three-dimensional (3D) printer was utilised for the three-dimensional production of graphene-based pyramids and an efficient hydrothermal procedure for ZnO growth. In particular, the 3D-printed graphene pyramids were forwarded in Pyrex glass bottles with autoclavable screw caps filled with 50 mL of an aqueous solution of zinc nitrate hexahydrate and hexamethylenetetramine for 1 h at 95 °C; sufficient enough time to deposit well-dispersed nanoparticles. X-ray diffraction patterns were in accordance with a Raman analysis and presented the characteristic peaks of graphite along with those of wurtzite ZnO. Different positions on the sample were tested, confirming the uniform dispersion of ZnO on graphene pyramids. From the electrochemical studies, it was found that the charging and discharging processes are affected by the presence of ZnO, indicating one well-defined plateau for each process compared to the previously reported bare graphene pyramids. In total, the material shows a value of 325 mAh g ToA h g−1) ,12,13. HA h g−1) ,15.−1 after 100 cycles at 200 mA g−1 [−1 at 200 mA g−1 [−1 after 100 cycles [The exceptional conductivity, abundant adsorption sites and short diffusion paths associated with graphene are expected to further enhance the transport processes within the oxide nanomaterials . A major0 mA g−1 , a high 0 mA g−1  and a reIn this work, ZnO is deposited on three-dimensional (3D)-printed graphene  using thCommercially available PLA (polylactic acid)-graphene filaments  with a volume resistivity of 0.6 ohm⋅cm, compatible with typical FDM (Fused Deposition Modeling) 3D printers, were used. As reported elsewhere , the dev3)2·6H2O and HMTA at 95 °C. The HMTA acts asa reducing agent in the hydrothermal synthesis of ZnO [2O to produce OH− and promote the precipitation reaction. Since the oxidation state of Zn in ZnO and Zn(NO3)2·6H2O is 2, the role of the reducing agent is in the nucleation and growth rate processes of ZnO materials instead of the reduction ofZn2+ ions [2O, dried in air at 95 °C, and characterized using the techniques described below. The growth temperature was carefully controlled with thermometers inside the oven and the Pyrex glass bottles during the whole growth period.The 3D-printed PLA-graphene pyramids (as presented in ) were fos of ZnO . In partn2+ ions . After 1n2+ ions ,23,25. TThe surface morphology of the samples was determined using a field emission scanning electron microscope  with a magnification of 100×.The crystal structure of all ZnO/3D-printed graphene samples was studied by X-ray diffraction  with Cu Kα (λ = 1.5406 Å). Raman measurements were carried out using a Horiba LabRAM HR  via a 532 nm solid state laser with an output power of 100 mW .−1 at potential ranging from −1.0 V to +0.5 V. Galvanostatic measurements were obtained in the range −0.5 V to +0.5 V under a specific current of 40 mA g−1.Electrochemical analysis of the materials was performed in an electrochemical cell  using PtA typical XRD pattern of ZnO/3D-printed graphene samples is presented in −1 are the characteristic ones for carbon materials, the so-called G and D peaks. According to the literature associated with Raman analysis of graphene [−1 (E2g mode (G band) of graphite) is related to the vibration of sp2-bonded carbon atoms. Additionally, the peak at 1356 cm−1 is associated with the vibration of carbon atoms (D band). Accordingly, the phonon frequencies of the Raman spectra attributed to ZnO are: 332 cm−1 (multiple-phonon scattering processes), 379 cm−1 (A1(TO)), 438 cm−1 (E2(high)), 483 cm−1 (2LA), 574 cm−1 (A1(LO)), and 663 cm−1 (TA+A1(LO)); which are in agreement with the literature [−1 exhibitingthe strongest intensity. The rest peaks shown in the Raman spectrum of −1 can be assigned to the C–CH3 stretching mode, whereas the one at 871 cm−1 to the C–COO stretching of the polymer unit [A typical Raman spectrum of ZnO/3D-printed graphene samples is presented in graphene ,32, the terature ,33,34,35mer unit ,37. The −1. The voltammogram for the first scan shows two cathodic humps at −0.60 V/−0.19 V and two respective anodic humps at −0.54 V/+0.05 V. Additionally, it may be seen that the anodic humps shift to higher potentials, whereas the cathodic humps to lower values after 2500 scans. Nevertheless, the curves are stable and overlap in subsequent scans, indicating that the material presents high electrochemical reversibility and stability after a prolonged period. The high resistivity of the cyclic voltammograms may be due to the low conductivity of the electrolyte solution or the graphene pyramids. Work on the electrochemical study of the material is currently in progress using a higher concentration of electrolyte solution and developing graphene pyramids on a conductive substrate.−1 and a potential range of −0.50 V to +0.50 V are shown in −1 and a capacitance retention factor of 92% after 5000 scans (+ accommodation sites [+ + C6 + xe− <-> LixC6 [The chronopotentiometric (CP) curves of the ZnO/3D-printed graphene for the first and the 5000th scan at 40 mA g00 scans b. This eon sites . In parton sites ,39. Acco-> LixC6 . In Tabl2@C hollow spheres (≈45%) [−1, 80 mA g−1, 100 mA g−1, and 200 mA g−1 as presented in −1 under a specific current of 200 mA g−1. Furthermore, it delivered a value of 322 mAh g−1 when the specific current returned to 40 mA g−1, suggesting high reversibility of the electrode.The anode material exhibited a coulombic efficiency of 100% that dropped to 85% after 5000 scans as shown in s (≈45%)  and carbs (≈45%) , showing−1 and a capacitance retention factor of 92% after 5000 scans. This excellent performance is due to the combination of two Li+ accommodation sites from ZnO and graphene along with the contribution of graphene pyramids facilitating more available sites. Considering these outcomes, the proposed anode material may significantly contribute to the fabrication of battery materials technology.Hydrothermally grown ZnO on 3D-printed graphene was accomplished at 95 °C for 1 h. The materials were crystalline and the ZnO was uniformly dispersed on graphene pyramids. The presence of both ZnO and 3D-printed graphene pyramids affected the electrochemical behavior of the anode, indicating a specific discharge capacity of 325 mAh g