Different from previous work, in which only DMS was tested and under pure nitrogen conditions, we measured DMS mixed by common air to establish the actual atmospheric measurement environment. Moreover, we used tunable laser absorption spectroscopy with spectral fitting to enable multi-species  measurement simultaneously. Meanwhile, we used empirical mode decomposition and greatly reduced the interference of optical fringes and noise. The sensor performances were evaluated with atmospheric mixture in laboratory conditions. The sensor’s measurement uncertainties of DMS, CH4, and H2O were as low as 80 ppb, 20 ppb, and 0.01% with an integration time 1 s, respectively. The sensor possessed a very low detection limit of 9.6 ppb with an integration time of 164 s for DMS, corresponding to an absorbance of 7.4 × 10−6, which showed a good anti-interference ability and stable performance after optical interference removal. We demonstrated that the sensor can be used for DMS measurement, as well as multi-species atmospheric measurements of DMS, H2O, and CH4 simultaneously.This paper presents a mid-infrared dimethyl sulfide (CH However, it was balanced by pure nitrogen and only DMS was detected, rather than a real air condition. Although spectral interference has been considered comprehensively during spectra investigation, practically, the sensitivity of the sensor is deteriorated by the strong spectral interference from H2O and CH4 when working in practical air condition; there is no other method of data processing for reducing the interference of optical fringes and noise; and the accuracy is affected by internal optical path.Recently, a Mid-Infrared (MIR) spectral DMS sensor was developed by our group . The senν1/ν8-band of DMS, and deduced the concentration of DMS, as well as atmospheric interference CH4 and H2O simultaneously by Multi-Component Spectral Fitting (MCSF). Moreover, we reduced the interference from noise and optical fringes by performing Empirical Mode Decomposition (EMD) and reconstruction to the recorded spectral data. The sensor’s performances were evaluated with common air mixture in laboratory conditions.Moreover, based on our previous investigation, the atmospheric DMS concentration is about 28 ppb around a sewage treatment tower and about 500 ppb near an instant noodle factory. Thus, in this paper, to develop a DMS sensor with strong anti-interference capability and stable performances to detect polluted atmosphere in those factories and the surrounding environment, we utilized another candidate spectrum with wavelength of 3336.7 nm located at the The remainder of this paper is arranged in three sections:  sensor cA < 0.05, according to Beer-Lambert absorption law and optically thin condition, absorption coefficient ωt and can be expanded as a Fourier cosine series:a is the modulation amplitude, which is the wavelength modulation of the laser generated by sinusoidal modulation; ω is the modulation frequency; kH are Fourier series; and k is the harmonic order. Because the second harmonic signal 2f is closely related to the absorption and free of background, typically k = 2 is used in Wavelength Modulation Spectroscopy (WMS). Thus, for the mixed second harmonic signal of n types of gases, they can be expressed as follows:P is the pressure, L is the length of optical path, iχ is the mole fraction of the ith absorbing species, and ijS and ijφ are the line strength and line shape function of the jth line of the ith absorbing species, respectively. Referring to Equation (2), if the pressure and temperature remain constant, we can ignore the variations of line profile, and it can be expressed as:ith absorbing species in per unit volume concentration, and the magnitude of the absorption-based 2f signal, 2fS is the 2f signal that is measured by a lock-in amplifier, G is the electro-optical gain of the measurement system, oI is average intensity of the laser at frequency 2f_i_perS is the 2f signal of ith absorbing species in per unit volume concentration. Therefore, 2fS of a mixture theoretically equals the sum of the product of each component’s concentration and its 2f signal in per unit volume concentration.We developed a DMS sensor based on wavelength modulation spectroscopy, whose theoretical basis is the Beer-Lambert absorption law ,30,31,32ribed as :(4)S2f≈ν14/ν18-bandwidth wavelength of 3367.3 nm was preferred, and the strong absorption made the sensor possess much higher measurement sensitivity than other spectral lines.The MIR fundamental absorption spectra of DMS were investigated in detail in our previous work . By compWe reexamined the spectral line of DMS based on minimum interference principle, including relatively less interference lines and distant interference spectral lines, and the absorbance of absorption line is relatively large. Thus, another spectral range of DMS was preferred based on the Pacific Northwest National Laboratory (PNNL) and High Resolution Transmission (HITRAN) databases. The 5 ppm×m DMS within the range of 3333–3371 nm is presented in ν1/ν8-band to be measured. Detailed analysis is presented in ν1/ν8-band between 3333.7 and 3337.8 nm, and the ν1/ν8-band of 3336.710 nm suffers much lower interference than ν14/ν18-band of 3367.229 nm, including the magnitude of interference and distance between the absorption line and the interference line. Thus, we chose 3333.7–3337.8 nm as our ultimate selection for DMS measurement with comprehensive consideration. Furthermore, although CH4 and H2O have less interference in the absorption of DMS, they are located at the working range of the laser. At the same time, the absorption spectra of methane and water overlap each other, thus it is necessary to obtain the concentration of three gases simultaneously by using the MCSF.The absorption peak wavelength and strength of DMS candidate regions are listed as well as the spectral information of possible interferences from air absorptions. In f signal was processed by MCSF program to obtain the target gas concentration.We developed a DMS gas sensor based on our instrument development platform ,33,34,35f demodulation signal from the data acquisition software.We carefully set all the working parameters of the sensor, including the optical path, gas flow, modulation amplitude, temperature, and so on. The instantaneous line width, dynamic tuning rate, and slope efficiency of ICLs have been reported to be suitable for precision spectroscopy measurements . The lasf signal [f signal, modulation amplitude of 0.27 cm−1 was chose as our optimized selection. Thus, the modulation amplitude of 0.27 cm−1 was preferred to improve the Signal-to-Noise Ratio (SNR) and measurement accuracy.We optimized the modulation amplitude of the DFB-ICL to enable measurement of multi-species spectra without overlap. We optimized the modulation amplitude according to Spectral Discrimination (SD) and normalized amplitude of the DMS WMS-2f signal . Traditif signal  can no lA MCSF algorithm to reduce spectral interference was developed in our previous work , as showAs for the wide-band characteristics of the MIR fingerprint absorption, the measurement sensitivity and accuracy are always deteriorated by overlap with adjacent spectrum, optical fringes, and noise. A solution by EMD and reconstruction to the recorded spectral data was developed in our previous work , as showf signal of each component is normalized, the initialization concentration parameters of each component are estimated, and the 2f signals of single component concentration and mixed concentrations participating in the fitting are produced. If the algorithm converges, the best fitting parameters are obtained. In our simulation, the results of the algorithm basically did not depend on the initial concentration. When the concentration of DMS is within the range of 1–20 ppm, the algorithm always converges.The algorithm includes two parts: (1) EMD is used to decompose and reconstruct the measured spectral data for reducing the optical fringes and noise; and (2) the 2The initialization concentrations of DMS, methane, and water were set as 1 ppm, 1 ppm, and 1%, respectively. Each component used 370 points to participate in fitting, and the program usually cycles fewer than 100 times. Once the algorithm converges, the best fitting parameters are determined.4, and H2O for the MCSF algorithm of the sensor with elaborately planned experiments. The HWG was filled with N2 first and then with a reference gas, therefore, the difference between the 2f signals of the reference gas and N2 could be used as reference signal. The reference signals of DMS and CH4 were obtained using reference gases with concentrations of 20.2 ppm and 3 ppm, respectively. In contrast, the reference signal of H2O was obtained using high humidity air that subtracted air background, and the high humidity air was obtained by a humidifier. With the EMD method [f signal of each component with less optical fringe and noise between 3333.7 and 3337.8 nm of DMS, CH4, and H2O are shown in We obtained superior reference signals of DMS, CHD method , we reduf signals of the mixture and reconstructing them with the EMD method. Take the mixture of H2O (0.14%)-CH4 (0.19 ppm)-DMS (10.1 ppm) as an example: about four IMF components were obtained. Thus, according to the signal characteristics of correlation coefficient, amplitude, and symmetry, the signal was reconstructed, as shown in We reduced the interference from noise and optical fringes by decomposing the measured 2Noise signals usually possess the characteristics of small amplitude and high frequency, while optical fringes are similar to the profile of sinusoidal signal, and all of them have a very low correlation coefficient relative to the absorption signal. Thus, IMF 1 in The detection ability of sensor was usually limited by noise and optical fringes ,37. Thus−6, which is sufficient to satisfy the needs of human health. Although the detection limit is much lower than the 2.8 ppb mentioned in Reference [A comparison was made for the sensitivity and detection limit before and after fringe removal. In eference , it is beference .4 and H2O), prepared with a homemade high-precision gas mixer [4 and H2O in the air were tested beforehand by absolute measurement of direct absorption spectroscopy. The initial concentrations of DMS, CH4, and H2O were 20.2 ppm, 1.9 ppm, and 1.4%, respectively. Thus: (1) in the first group, the concentration of DMS ranged from 2.02 to 10.1 ppm , while the concentration of CH4 and H2O remained at 0.95 ppm and 0.7%, respectively; and (2) the concentration of CH4 ranged from 0.19 to 0.95 ppm (in 0.19 ppm), the concentration of H2O ranged from 0.14% to 0.7% , and the volume of DMS remained at 10.1 ppm in the second group. All of the concentration settings were realized by adjusting the three-channel volumetric flow rate settings in Two groups of DMS concentration gradient experiments with air mixture  for DMS, CH4, and H2O. The measured accuracy of DMS, CH4, and H2O were 0.3%, 1.9%, and 2.8%, respectively. The standard deviations could primarily be attributed to the uncertainty of the mass flow controller and the fluctuation of H2O in the air over time. Although because of the concentration gradient, the O2 and N2 concentrations in the experiment are different from their actual concentrations in air, they have no absorption in the spectrum that we chose and have less influence on our measurement.The concentration of DMS, CH4, and 0.7% H2O. The results are shown in Sixty measurements with 1 s intervals were performed to verify the stability and accuracy of the sensor with the flowing gas mixture of 10.1 ppm DMS, 0.95 ppm CH4, and H2O were 10.10 ± 0.08 ppm, 0.96 ± 0.02 ppm, and 0.7 ± 0.01% with a sampling interval of 1 s, respectively. Therefore, the measurement uncertainties of DMS, CH4, and H2O were 80 ppb, 20 ppb, and 0.01%, respectively, which shows that the sensor has an excellent performance.In 4, and H2O. The sensor’s working wavelength located at 3336.7 nm, i.e., the ν1/ν8-band, was chosen to measure atmospheric DMS, which could avoid serious spectral interference from atmospheric CH4 and H2O. Multiple techniques were specified for wide-band spectra measurement, including modulation amplitude optimization, MCSF, and removal of optical fringes and noise by EMD, which enhanced the performances of the sensor. Experimental results indicate that the measurement accuracy of DMS was raised to 0.3%, and the measurement uncertainties of DMS, CH4, and H2O were improved to 80 ppb, 20 ppb, and 0.01%, respectively. Furthermore, detection limit as low as 9.6 ppb with an integration time of 164 s was obtained, thus the sensor can be applied in monitoring the atmosphere around food processing plants and chemical plants. Future work can concentrate on adjusting the structure of optical path and lengthening the HWG, which will further improve the stability and detection limit of the sensor.In summary, we demonstrated a high-sensitivity and multi-species sensor of atmospheric DMS, CH


Our results suggest the adsorption ability of the epitaxial graphene towards divalent Lead ions is concentration-dependent and tends to saturate at higher concentrations. To elucidate the mechanisms responsible for Pb adsorption, we performed DFT calculations and estimated the solvent-mediated interaction between Lead species in different oxidative forms and graphene. Our results provide central information regarding the energetics and structure of Pb-graphene interacting complexes that underlay the adsorption mechanisms of neutral and divalent Lead species. Such a holistic understanding favors design and synthesis of new sensitive materials for water quality monitoring.Deep understanding of binding of toxic Lead (Pb) species on the surface of two-dimensional materials is a required prerequisite for the development of next-generation sensors that can provide fast and real-time detection of critically low concentrations. Here we report atomistic insights into the Lead behavior on epitaxial graphene (Gr) on silicon carbide substrates by thorough complementary study of voltammetry, electrical characterization, Raman spectroscopy, and Density Functional Theory (DFT). It is verified that the epitaxial graphene exhibits quasi-reversible anode reactions in aqueous solutions, providing a well-defined redox peak for Pb species and good linearity over a concentration range from 1 nM to 1 µM. The conductometric approach offers another way to investigate Lead adsorption, which is based on the formations of stable charge-transfer complexes affecting the  The RSD of Pb determination with six repetitions was 3.5%.To monitor the dependence of the analytic signal on the concentration of the Lead ions in solution, we performed more effective SWASV analysis  for Pb in the concentration range between 102+) are initially adsorbed on the inert electrode surface and then they are reduced to neutral Lead species  at a constant potential. At the second stage, Pb0 species are re-oxidized to Pb2+ and desorbed back to the solution in the oxidized state. During the stripping of Lead species accumulated onto the epitaxial graphene surface, Pb0 adatoms lose 2 electrons, thereby contributing to the generation of the stripping current. It is important to note that the resulting stripping current is proportional to the concentration of the adsorbed species. This means that the preconcentration process predominantly defines the sensitivity of the epitaxial graphene towards Pb. Indeed, the more Pb2+ ions will be plated as neutral Pb species on the electrode, the more will be re-oxidized and thus the stronger the striping peak current is expected. Therefore, a knowledge about the interaction between elemental Lead species and graphene in the presence of water is a key to understanding the sensing mechanism at the atomistic level. For this aim we performed comprehensive DFT calculations focusing on the nature of this interaction. Since the van der Waals (vdW) forces are expected to play a fundamental role in the adsorption of elemental metals on graphene [0 on graphene nanofragment are summarized in To gain deep insight into the adsorption mechanism, it is very important to clarify the fundamental principle of generation of the stripping current observed in our experiment. Generally, SWASV comprises two stages: (i) preconcentration step and (ii) stripping step. During the first preconcentration step, Lead divalent ions . According to B3LYP results, binding height of Pb adatom is 4.36 Å see . By consions see  without ions see c. Howeveions see b, we notz-direction (perpendicular to the graphene plane). Therefore, consideration of the vdW correction is a key for gaining insight into the interaction between elemental Pb and graphene and, consequently, for correct explanation of the adsorption mechanism.Furthermore, an important role of London dispersion forces in interaction between Pb and graphene is also evidenced by the spatial redistribution of electron wavefunctions describing frontier molecular orbitals see d. In parD peak, we further investigate the Raman spectra of epitaxial graphene after electrodeposition of the Pb to ensure that adsorption capacity is high enough to provide the appropriate stripping response. Detailed analysis of the Pb electrodeposition on epitaxial graphene was performed in our previous work [D-line. Since the D-mode was not present before electrodeposition process, it is reasonable to assume that its appearance is due to the formation of Pb-C bonds.To gain deeper insight into the interaction between elemental Pb and graphene, we also performed Raman mapping. Bearing in mind that as-grown epitaxial graphene exhibits no defect-related ous work . TherefoD peak intensity distribution suggests that the perturbation related to adsorption of Pb species has local character, most likely restricted to the vicinity of the adsorbed species. Since large Pb clusters are weakly bonded to graphene [D peak. To summarize this section, one can conclude that epitaxial graphene provides enough available electroactive sites for oxidation-reduction reactions during stripping analysis.Furthermore, the observed non-uniform graphene , it is m2+ ions will influence the band structure of graphene and, consequently, the electron transport through graphene. It means that real-time monitoring of the resistance of the epitaxial graphene as a function of time under exposure to injected liquid containing Pb2+ ions will allow estimation of how the epitaxial graphene interacts with divalent Lead ions dissolved in water. As was mentioned before we used epitaxial graphene as a lateral resistor for measurement of the conductometric response. Schematic representation of the device is depicted in 2+ at different molar concentrations within the range from 0.125 μM to 500 μM. The graphene resistor exhibits a good response to Pb2+ and reproducibility even after several repeated cycles. The initial resistance of the epitaxial graphene changed with the Pb2+ solution injected into the flow chamber. It can be understood that the presence of Pb2+ ions dissolved in aqueous solution enhances the conductivity of graphene, as evidenced by the resistance drop during each cycle. The relative variation of the resistance was calculated by equation ΔR = (RPb − REG)/REG, where RPb and REG represent the resistances of the epitaxial graphene after injection of Pb-containing liquid and the initial resistance of the epitaxial graphene, respectively. We noticed that the increase in Lead concentration causes an increase of the differential resistance value, suggesting that the adsorption of Pb2+ metal ions on the epitaxial graphene follows the Langmuir isotherm  in the presence of solvent (water in our case). It was found that the hollow site  is the most favorable adsorption site of Pb2+ ion on graphene  and is very interesting from a practical point of view. As was mentioned before the difference between interaction energy and adsorption energy can be regarded as a degree of deformation of the sp2-plane adsorption event. With this knowledge in mind, we estimated the deformation energy for all considered adsorption geometries. This parameter was found to increase with increasing number of adsorbates, indicating that more energy penalty needs to be paid to accommodate larger number of adsorbates at the graphene surface. Independently of the kind of adsorption configuration, divalent ions always act as typical acceptors, which extract electrons from graphene resulting in the increase in hole concentration. As a result, LUMO is strongly hybridized and shared between graphene and Pb2+ ion b, implyi2+ ion, respectively. As shown in 2+ ions near the adsorption site. Therefore, hole doping effect is caused by the formation of a hybrid charge-transfer complex. It should also be noted that the charge-transfer value obtained using the vdW-corrected functional is very close to that calculated without vdW correction (To visualize the charge-transfer mechanism, we calculated the charge density difference by using the following equation:rrection . This su2+ ion on graphene is very stable and the strong Cation-π interaction helps the Pb2+ ions to remain in the chemisorbed state on the graphene surface. In other words. Pb2+@graphene complex did not collapse with time. Such a dynamical stability will lead to reproducible resistance-time characteristics, which we observed in the experiment.To verify the stability of Cation-π bonding in the presence of water we performed ADMP simulations at room temperature. The potential energy trajectory represented in sp2-bonded carbon network. Our results indicated that Pb2+/Pb0 redox system at the graphene electrode surface is quasi-reversible. The results revealed a strong stripping response of Pb2+ with slope of linear regression of 2.3 × 103 A·cm−2·mole−1·L and good linearity within concentration range between 10−10 M to 10−6 M. The adsorption behavior of Lead was further investigated with Raman spectroscopy. By monitoring of defect-related D-mode of graphene induced by Pb adsorption it was established that epitaxial graphene is an appropriate template providing high adsorption capacity towards Pb. The conductometric approach was found to be an effective tool for monitoring the presence of Lead ions in aqueous solutions, since graphene lateral resistor enables fast response and recovery. It was found that adsorption energy of Lead ions in the regime of low concentrations is higher than that at high concentrations, which is evidenced by the longer recovery time at the nanomolar concentrations. To elucidate the adsorption mechanisms, we also preformed DFT calculations. It was found that the electrochemical response of the epitaxial graphene to Lead is mainly regulated by a van der Waals interaction between neutral Lead atoms and graphene during a redox process, while the conductometric response is governed by the formation of stable charge-transfer complexes, which cause the increase in hole conductivity under Pb accumulation conditions. The current work provides deep insights into the fundamental understanding of the adsorption of Lead in different oxidative forms on epitaxial graphene and is an important step towards development of easy-to-use and portable sensing platform, which enables real-time determination of the toxic Lead in drinking water.In summary, the behavior of Lead species at epitaxial graphene supported by Si-terminated 4H-SiC has been evaluated. By using two independent experimental methods, namely voltammetry and time-resolved electrical characterization we investigate the response of the epitaxial graphene under exposure to Pb-containing aqueous solutions. Raman mapped images provided by confocal Raman spectroscopy confirmed high quality of the epitaxial graphene and low density of point defects, indicating that adsorption events occur at the defect-free


Recent emergence of metasurfaces has enabled the development of ultra-thin flat optical components through different wavefront shaping techniques at various wavelengths. However, due to the non-adaptive nature of conventional metasurfaces, the focal point of the resulting optics needs to be fixed at the design stage, thus severely limiting its reconfigurability and applicability. In this paper, we aim to overcome such constraint by presenting a flat reflective component that can be reprogrammed to focus terahertz waves at a desired point in the near-field region. To this end, we first propose a graphene-based unit cell with phase reconfigurability, and then employ the coding metasurface approach to draw the phase profile required to set the focus on the target point. Our results show that the proposed component can operate close to the diffraction limit with high focusing range and low focusing error. We also demonstrate that, through appropriate automation, the reprogrammability of the metamirror could be leveraged to develop compact terahertz scanning and imaging systems, as well as novel reconfigurable components for terahertz wireless communications. They have led to significant breakthroughs in various fields such as imaging, radar, and wireless communications to name a few4. Metasurfaces, the thin-film planar analogue of metamaterials, are composed of an array of subwavelength resonators, and inherit the unique properties of their three-dimensional counterparts while addressing their issues related to bulkiness, losses, and cost. For this, metasurfaces operating at the microwave8, Terahertz12, or optical14 bands have been widely proposed to achieve attractive features such as negative refraction, cloaking, superlensing, or holographic behavior. A large subset of these designs have been based on the generalization of the Snell’s laws of reflection and refraction15, which provided fundamental understanding on how to achieve precise beam manipulation16, vortex creation17, focusing5 through the drawing of specific phase gradients. Another remarkable advance is the proposal of coding metasurfaces, where the device is built (encoded) using a discrete set of unit cell options (bits or words)19. This provides a powerful and intuitive design perspective while drawing a clear parallelism with information theory, which opens new ways to model, compose, and design advanced metasurfaces21. Several works have exemplified such approach mainly for scattering control22.Metamaterials have drawn a great deal of attention since their conception as they enable unprecedented levels of electromagnetic control23. The resulting reconfigurable metasurfaces can be globally or locally tunable, depending on the specific scheme and, with appropriate control means, they become programmable24. Not coincidentally, the programmable metasurface paradigm has found in the aforementioned coding paradigm a natural match to describe and implement reconfigurability. When built using locally switchable elements such as pin diodes, varactors, or switches, coding metasurfaces can be elegantly described as a bit or state matrix and digitally controlled through reconfigurable logic, e.g. a Field-Programmable Gate Array (FPGA)18. Polarization and focusing control5, beam manipulation16, or holograms7 have been demonstrated in the GHz range, whereas fewer proposals have appeared in the THz regime mostly due to the lack of appropriate means for tuning.Two of the main downturns of most metasurfaces are non-adaptivity and non-reconfigurability as, in most cases, the electromagnetic function and its scope are fixed once the unit cell is designed. In response to these drawbacks, metasurface designs with tunable or switchable elements in the unit cell have emerged26. The reasonably low loss of graphene plasmons at THz frequency band has been the main motivation of several wave steering devices27. The plasmon tunability of graphene is achievable through chemical doping or electrostatic biasing. The tunablity of graphene opens the door to globally reconfigurable metasurfaces with fine-grained control of the amplitude-phase response28, or it can provide switching between diverse electromagnetic functionalities in particular setups29. Plasmon tunability can also be leveraged locally, in which case graphene becomes a natural candidate for the implementation of (re)programmable THz metasurfaces. In spite of their potential, graphene-based programmable designs have remained relatively unexplored, and current proposals are mainly limited to dynamic beam manipulation for diffusion30, encryption31, or vorticity control17.Graphene shows great promise for the implementation of THz metasurfaces. This is due to its widely demonstrated plasmonic properties that provide subwavelength behavior required in the unit cell building blockIn this work, a (re)programmable metamirror is proposed as shown in Figure Figure 15. This approach, however, offers no reconfigurability. In this work, instead, we achieve reconfigurability through changes in the electrostatic bias applied to uniformly sized graphene patches. This modifies the complex conductivity of the graphene sheet and, by extension, the phase of the reflected wave.A reflective metasurface operating as a mirror calls for the use of unit cells with a high reflection amplitude and a wide phase range. Fabry-Pérot resonant structures composed of metallic patches over a square grounded substrate can provide such functionality by adjusting the size or position of the metallic patch to achieve the required phaseMethods section.Figure μc,1 and μc,2, respectively). A quick exploration reveals a complete 2π phase range as well as large design space areas with high reflectivity.Compared to the the single-layer graphene structures, our proposed unit cell based on dual-layer graphene enjoys more flexibility to achieve a wide range of phase response and a high reflection amplitude, simultaneously. The dual layer structure, modeled as two parallel RLC cells, provides an additional degree of freedom as each graphene patch can be biased independently. Figure Nbit is the number of bits. We will see that two bits are enough for our purpose. We choose μc,1 = {0.6, 1.3, 0.1, 0.4} eV and μc,2 = {0, 0.6, 0.1, 0.1} eV corresponding to the bit combinations B = {00, 01, 10, 11}, respectively. As observed in Figure π/2 is maintained over the range of 1.9–2.1 THz with an amplitude close to 0.7. This high reflection amplitude for all states guarantees a high focusing efficiency for the designed metamirror.The coding set is built by picking points with as high amplitude as possible, and phases equal to multiples of θi and azimuth angle φi. It is used to focus the energy in a given point defined by x′, y′) at an arbitrary point on the metamirror can be written asλ0 is the wavelength in free space, k0 is the incident wavevector, and r′ =  is the vector position of an arbitrary point on the metasurface.Consider a reflective metasurface under illumination of an incident plane wave at elevation angle θi = ϕi = 0), Equation x′, y′), and rounding off the phase values to those offered by the closest coding states.When the metamirror is illuminated by a normally incident wave  of the reflected field response when the focal point is scanned in space. Differences in the reflected field response due to the scan of focal point creates the confocal image.Figure Charts (a–l) of Figure et al.32, wherein a single graphene layer is laid over the whole metasurface area and tuned using a single bias source. Such approach only allows to control the focal depth with limited range. Focusing with programmable coding metasurfaces has been only demonstrated in the GHz range with devices that use PIN diodes for reconfiguration. This limits the amount of achievable unit cell states, reducing the precision and focusing range.In this work, we have presented for the first time the design of a fully reprogrammable metamirror that can be used in terahertz confocal imaging. The metamirror acts as a focusing reflectarray that leverages the tunability of graphene to achieve the required phase range and programmability at the unit cell level. At the metasurface level, we adopted a coding metasurface approach that allows to dynamically shift the focal point by adjusting the center and slope of a concentric phase gradient. This is in stark contrast to the design by Huang We demonstrated analytically and numerically that the proposed metamirror can shift the focal point both laterally and in depth. With 2 bits per unit cell and assuming a total size of 9λ × 9λ, energy is focused around the desired focal point with less than 6% deviation in the evaluated points. Moreover, the metamirror can operate close to the diffraction limit as long as the focal point is located around the focal depth and centered with respect to the metasurface. We also showed that the programmability of the focal point can be applied to the development of compact devices for 3D terahertz confocal imaging.τ = 0.6 ps, which is well achievable with Chemical Vapor Deposition (CVD) techniques and encapsulated in hexagonal boron nitride (h-BN)34. Those techniques in fact produce significantly higher relaxation times, which would lead to lower loss and better overall performance. Moreover, considering the electrically thin boron nitride layer has a negligible impact in the simulation results. To mention, when the graphene has a lower relaxation time, the plasmonic losses within the structure increase. Therefore, it results in a device with a lower efficiency. Regarding the biasing scheme, different gate-controllable designs have been simulated35 and experimentally validated36, which could be adapted to local addressing of unit cells. Before actually addressing fabrication, a challenge to be addressed in future work would consist on minimizing the interference imposed by the metallic biasing structure on the response of the metasurface. It is worthy to note that bilayer graphene, a material consisting of two layers of graphene, exists in the various forms such as Bernal-stacked form37. Depending on the relative position of layers, different quantum effects can happen in the spacing. But what we have here is different. In our proposed dual-layer structure, the insulating layer (here HDPE) between two graphene patches is sufficiently large for quantum effects to be negligible38. Therefore, crystallographic alignment is not required, and micrometric precision of current lithographic techniques is enough to achieve the results reported in the paper. Therefore, the process of fabrication of dual-layer metasurface structure is generally similar to one-layer structure; and the existing transfer printing methods could be employed39.As a final note, it is worth highlighting that this work brings the concept close to realization by making reasonable assumptions. First, we consider a graphene quality leading to a relaxation time of 40. The length of the unit cell is du = 20 μm and graphene patches are squared with side dg = 12 μm. The operation frequency is set to 2 THz. We consider bulk silicon as the substrate with relative permittivity εr = 11.9, loss tangent tan(δ) = 2.5 × 10−4, and thickness hsi = 10 μm. The extra layer is composed of a layer of HDPE with relative permittivity εr = 2.37, loss tangent tan(δ) = 0.011, and thickness hHDPE = 4 μm.The unit cell structure shown in in Figure σ(ω) is the frequency-dependent complex conductivity of graphene. The conductivity is given bye, kB are constants corresponding to the charge of an electron, the reduced Planck constant and the Boltzmann constant, respectively41. Variables T, τ and μc correspond to the temperature (T = 300 K in this paper), the relaxation time and the chemical potential of the graphene layer. Note that this expression neglects effects at the graphene edges and considers that the Drude-like intraband contribution dominates, which are experimentally validated assumptions at the sizes and frequencies considered in this work42. In all cases, the relaxation time of graphene τ = 0.6 ps, which is well achievable with current fabrication and encapsulation techniques33. The chemical potential of the top and bottom layers are initially left as parameters for exploration and then fixed to discrete values leading to the adequate amplitude and phase.The graphene layers are modeled as infinitesimally thin sheets with surface impedance 40. For the simulation of unit cells, a Floquet port is applied to excite an x-polarized normal plane wave onto the unit cell and the back-scattered wave is then measured. This way, we obtain the amplitude and phase of the reflection coefficient of the proposed unit cells while taking into consideration mutual coupling between adjacent unit cells. After obtaining the response of individual unit cells, the complete metamirror is modeled as an array of such unit cells with different phases. The metasurface is illuminated by a normal plane wave with x-polarization to obtain the scattered fields above the metasurface and, thus, the field distribution around the focal point. Finally, we simulate the THz imaging device by estimating the scattering response of the spheres in different positions. To this end, we again consider x-polarized normal illumination. To identify the presence of a sphere in the focal point of the metamirror, we compare the far field response of the metamirror with and without the spherical objects. Strong variations indicate the presence of a sphere in the focal point of the metamirror. To note, for the results shown in Figures We implement the unit cells and the complete metasurface in CST Microwave StudioR1, L1, C1; R2, L2, C2) in parallel with equivalent transmission lines representing the HDPE and grounded silicon layers. The values of resistance, inductance, and capacitance of the graphene patches have been extracted from the reflection parameter at the boundary between air and unit cell, which only depend on the chemical potentials of the top and bottom graphene layers for a fixed patch size. For the results shown in Figure R1, L1, C1; R2, L2, C2) are .To gain physical insight into the scattering behavior of the proposed unit cell, an approximate circuit model has been developed. As sketched in Figure Jx on all unit cells. Therefore, we can write the inhomogeneous potential wave equation asr =  and r′ =  are the vector positions of the observation and source points, respectively. The magnetic and electric fields can be found by applying To validate the response of the metamirror around the focal point, we need to use analytical models compatible with near field conditions. Fresnel diffraction theory cannot be used because of the small focal length to lens diameter ratio of our device. Alternatively, we apply the Huygens’ principle to model the currents excited at the metasurface as electrically small sources of radiation. Consider an incident wave polarized along the x-direction that excites an x-directed current density M × N cells asFinally, the metasurface response is obtained by adding the contribution of its


The authors of “The Ready to Reduce Risk (3R) Study for a Group Educational Intervention With Telephone and Text Messaging Support to Improve Medication Adherence for the Primary Prevention of Cardiovascular Disease: Protocol for a Randomized Controlled Trial”  require corrections in relationship to the use of the Morisky Medication Adherence Scale (MMAS-8).The following text was omitted from the Acknowledgements and as a footnote in Table 1 and should be added:Use of the MMAS is protected by US and International copyright laws. Permission for use is required. A license agreement is available from: Donald E Morisky, MMAS Research (MORISKY), 294 Lindura Court, Las Vegas, NV 89138-4632; dmorisky@gmail.com.Two additional references should be cited after reference 37 in the following sentences:In addition, the self-reported 8-item Morisky Medication Adherence Scale (MMAS) was completed at baseline and 12 months. This is an established and validated scale that is commonly used to measure adherence [37].Self-report: 8-item Morisky Medication Adherence Scale (MMAS) [37].Therefore, we have also used a self-reported validated questionnaire (MMAS) [37] and repeat prescription history as supporting outcome measures.The references to be cited are:Berlowitz DR, Foy CG, Kazis LE, Bolin LP, Conroy MB, Fitzpatrick P, SPRINT Research Group. Effect of Intensive Blood-Pressure Treatment on Patient-Reported Outcomes. N Engl J Med 2017 Dec 24;377(8):733-744.Morisky DE, DiMatteo MR. Improving the measurement of self-reported medication nonadherence: Final response. Journal of Clinical Epidemiology 2011 Mar;64(3):262-263.These have become references 50 and 51, respectively, and all subsequent references have been renumbered accordingly.The correction will appear in the online version of the paper on the JMIR website on July 24, 2019, together with the publication of this correction notice. Because this was made after submission to PubMed, PubMed Central, and other full-text repositories, the corrected article also has been resubmitted to those repositories.Authors and journal had to publish this correction due to legal threats by Steven Trubow and Donald Morisky from the company MMAS Research LLC, the copyright holder of the instrument. This is unfortunately not an isolated case, as the developers of this scale are known to comb the literature and ask those who used the scale for research to pay for a retroactive license which may cost thousands or tens of thousands of dollars, and to add references to their work . This isThe Committee on Publication Ethics (COPE) has recently discussed the ethics of this type of behavior by copyright holders of scales (“holding authors to ransom in this way”) and recommends to emphasize “the fact that this is not good for the advancement of scientific knowledge or in the public interest” . As open


Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level. Controllably synthesizing nanocrystals2567Commercially available silicon nitride liquid cell TEM holders have provided the necessary resolution to see and understand a variety of interesting phenomena on the nanoscale91011121314151920Since the thickness of the encapsulating material is one aspect that negatively affects the spatial resolution of the liquid cell experiments, atomically thin, low-Z materials such as graphene would be ideal encapsulating materials222324252628in situ transformations can benefit from employing graphene liquid cell electron microscopy technique. This in situ method is especially valuable for non-equilibrium processes that require visualization during the transformation. One significant drawback of liquid cell TEM techniques is the generation of radiolysis species by the perturbative electron beam3130Figure 1), using an example experiment observing single particle etching of nanocrystals, and hopefully show that graphene liquid cell experiments are possible for almost any group with access to an electron microscope. The protocol will cover graphene coating of grids, liquid cell formation, TEM use for graphene liquid cell etching experiments, and image analysis techniques. Critical steps in making the liquid cells such as the size of the droplet encapsulated, careful consideration of liquid solution contents, and use of only direct transfer graphene will be covered with additional advice on how to avoid repeating the pitfalls of previous researchers. Graphene liquid cell TEM is an emerging technique for nanoscale research, and this article will enable new entrants to begin utilizing this technique.Researchers in chemical, nanomaterial, biological, and other fields desiring spatial resolution of 2 piece of premade graphene-on-copper  which fits around 6 to 8 TEM grids. NOTE: Using 3 - 5-layer graphene instead of single layer graphene encapsulates liquid pockets with higher success rates without losing resolution. Since graphene is an atomically thin, low-Z material, most resolution loss is from liquid thickness for graphene liquid cells.Cut out a roughly 2 cmPlace the graphene-on-copper piece in a glass Petri dish and fill with acetone. NOTE: Acetone is used because PMMA dissolves in acetone.Gently heat the acetone solution (~50 °C) for 5 min, swirling the solution periodically. NOTE: Make sure to watch the acetone and temperature to avoid a fire. This should be done in a fume hood.Remove the graphene-on-copper piece from the acetone wash with tweezers and replace the acetone with new, clean acetone. NOTE: Be careful not to scrape or otherwise damage the graphene surface with the tweezers.Repeat the washing process a total of 3 times.Let the graphene-on-copper air-dry thoroughly before going on to the next step.Clean the graphene using an acetone wash . NOTE: TTable of Materials) are able to properly bond to the graphene surface. Bumps and creases in the graphene-on-copper make it difficult to maintain good contact. Table of Materials) on the bottom glass slide. On top of the wipe, place the graphene-on-copper piece. Finally, place the second glass slide on top. NOTE: Place the graphene-on-copper piece with the graphene side up (touching glass slide) to prevent scratching from the tissue wipe. The folded tissue is used to gradually push out the wrinkles and prevent folding in new creases.Take two clean glass slides and place a folded wipe  down on the graphene with the amorphous carbon in contact with the graphene. NOTE: Be careful not to bend or deform TEM grids when picking them up with the tweezers. Bent TEM grids do not bind properly to the graphene. Picking the grids up by the edge of the grid prevents deformation of the grids. Here, gold TEM grids are used to avoid etching the grids during the step that removes the copper from the graphene-on-copper.Place the holey amorphous carbon support foil-TEM grids  in a second Petri dish. NOTE: The easiest method to transfer the grids involves using a glass slide to pick up the grids and then placing them down in the second Petri dish filled with water. Some grids will fall to the bottom of the Petri dish during the transfer process. This is usually a sign that the graphene on the grid is cracked or otherwise damaged.Remove the floating grids from the solution and place them on top of clean, deionized water ,3 solution in a solution of deionized water with 1.8 µL of HCl per mL water. NOTE: The FeCl3 is the etchant for this etching experiment. Other experiments may add different solutions depending on the experiment being performed.Make a 40 mM FeClMake gold nanorods and concentrate the nanorod sample after cleaning13 in HCl, and 10 µL of nanorods.Mix 0.15 mL of 0.01-0.1 mM Tris Buffer HCl, 0.1 mL of 40 mM FeClPrepare the solution to be encapsulated. NOTE: The solution is specific to the nanocrystal etching experiment. Place ~0.5 µL droplet of solution to be encapsulated on the non-cut graphene-coated TEM grid. Use a tweezers to hold the edge of the TEM grid down while placing the droplet so that the capillary forces do not pick up the TEM grid . NOTE: BQuickly and carefully place the graphene-coated TEM grid with the cut corner on top of the droplet; the goal is to have the second grid come to rest on top of the first grid with no liquid getting squeezed out . NOTE: HWait 5 min to let graphene liquid cell pockets form. NOTE: Some evaporation of the liquid may occur as the pockets are forming, but once a hermetic seal is formed, no additional liquid loss is likely. The relative concentrations of each species in solution should remain constant.Bring the sample to the TEM for imaging. NOTE: The amount of time set aside for sealing varies from researcher to researcher. For etching experiments, less time before bringing the liquid cell to the TEM is desirable to avoid pre-etching.Note:The operation of the Transmission Electron Microscope followed standard procedures found in the user manual. Every TEM will have different alignment procedures.Place the graphene liquid cell in a traditional TEM single tilt holder . NOTE: OLoad the TEM holder into the TEM column. NOTE: Since the graphene liquid cell contains such a small volume of liquid with no reservoir and has separate pockets, there is no need to rigorously check for leaks like silicon nitride liquid cell experiments. Even if a graphene liquid cell pocket burst, only a very small amount of liquid is released and thus would not crash the TEM vacuum system.-/Å2s). In the radiation chemistry community, this is known as the flux density, and dose rate is defined as the amount of energy absorbed per unit area per unit time. Since calculating the amount of energy absorbed by a sample is difficult for complex geometries found in liquid cells, and to maintain consistency with the TEM community, we choose to use dose rate to refer to electrons per unit area per unit time.Turn the TEM filament on at least 20 min prior to calibration to allow it to stabilize for reproducible dose rates; this waiting time may be different depending on the TEM system and electron gun type. NOTE: Election microscopists often use dose rate to refer to the number of electrons delivered per unit area per unit time , and image . Then remove the holder from the beam path and calibrate electron beam dose rate. -/Å2s). NOTE: Keeping the dose rate low prevents the nanoparticles from etching while searching for nanoparticles.Begin searching for nanoparticles in liquid pockets while keeping the dose rate low  to set the condenser lens current for the desired dose rate . NOTE: ABegin collecting a time series of TEM images with metadata of dose rate and time stamps embedded in the image file.After the particle has finished etching, spread the beam and begin looking for other nanoparticles in the liquid pockets.When a sufficient amount of nanoparticle etching videos have been collected, remove the TEM holder from the TEM following standard TEM procedures. Take the graphene liquid cell out of TEM holder. NOTE: A typical imaging session lasts around 2-3 h with approximately 30 videos taken. The number of videos with usable data depends on the quality of the pockets and type of etching experiment.Note: Since TEM videos are 2-dimensional projections of 3-dimensional shapes, careful image analysis needs to be done to extract etching rates or shape changes.Table of Materials).Convert the native DM3 video files to an avi format using ImageJ and import the avi videos into computational software  can be extracted and evaluated further . One ind. Schematic of graphene liquid cell TEM technique. (A) To assemble a graphene liquid cell, a droplet of solution is placed on a graphene-coated holey carbon TEM grid. A second graphene-coated grid is placed on top of the droplet to form a pocket. Note that this image is not to scale and the liquid droplet is about 33% too large. (B) Zoomed-in schematic of a liquid pocket during TEM imaging of gold nanorods. This cartoon is also not to scale. Please click here to view a larger version of this figure.. Process for making graphene coated TEM grids (A) Washing the graphene-on-copper piece in warm acetone (B) Removing macroscopic wrinkles by flattening graphene-on-copper between two glass slides. A tissue is placed beneath the graphene-on-copper piece so as to not fold in new wrinkles. (C) Placing amorphous holey carbon TEM grids on graphene-on-copper with amorphous carbon side of TEM grids touching the graphene. (D) Floating copper/graphene/TEM grids on sodium persulfate etchant. This removes the copper from the grids. (E) Graphene coated TEM grids after etching off copper. The solution is blue and there is no copper left on the graphene-coated grids. For size reference, the diameter of the glass Petri dish is approximately 6 cm and the glass slide is 7.5 cm by 2.5 cm. Please click here to view a larger version of this figure.. Process for making graphene liquid cells (A) Two graphene-coated TEM grids prepared on a glass slide with an edge cut off one of them. The surgical scalpel used to cut the grid is on the top right of the image. (B) Droplet of encapsulating solution on a graphene coated grid. The droplet on the top grid is the right size and has made a nice bead on the graphene. The droplet on the bottom grid has bled through the graphene, possibly due to a crack in the graphene. (C) Second graphene-coated grid placed on top of first grid with droplet of solution. This graphene liquid cell is now ready to load into a TEM. For size reference, the glass slide is 7.5 cm by 2.5 cm. Please click here to view a larger version of this figure.. Loading graphene liquid cell into standard single tilt TEM holder. The graphene liquid cell fits in a standard single-tilt TEM holder in the same way a normal TEM grid fits in the holder. For size reference, the TEM grid has a diameter of 3 mm. Please click here to view a larger version of this figure.. TEM beam control. (A) Condensed electron beam for dose rate calibration viewed using the fluorescent screen. (B) Expanded electron beam for dose rate calibration viewed using fluorescent screen. Intensity decreases as the electrons per area per time decrease which is why the electron beam is very faint. (C) Calibration curve relating the electron beam dose rate to the condenser lens current. This calibration curve is used for controlling the beam dose rate during imaging. (D) Parameters used when collecting TEM videos of nanoparticles in graphene liquid cells. Specific values used for each parameter may change depending on the material being imaged and the resolution needed. Please click here to view a larger version of this figure.. Gold nanorod etching in a graphene liquid cell pocket. Frames of a representative TEM video of a gold nanorod etching under dose rate of 800 e-/Å2s. After an initial period of no etching, the nanorod etches at a constant rate. Please click here to view a larger version of this figure..Method for analyzing frames of video (A) Outlining the nanorod using thresholding in image analysis software.  This separates the nanoparticle from the background and provides a shape for quantitative analysis. (B) Determining the major and minor axes of the nanorod. (C) Extracting each half of the 2-D outline cut along the major axis. Using these outlines, reconstruct the 3-D shape by rotating the outline around the x-axis. Please click here to view a larger version of this figure.Graphene liquid cell electron microscopy can provide mechanistic information about nanocrystal growth and etching with high spatial resolution, but since making graphene liquid cells can be difficult and delicate, the technique requires attention to detail to extract usable data. Even after extensive practice making graphene liquid cells, only about a half to a quarter of made liquid cells successfully encapsulate the liquid solution. The critical step in forming liquid cells is placing the second grid on top of the droplet of liquid. Common errors include getting the tweezers stuck between the two grids, dropping the second grid too far off-center, and starting with a droplet that is too large. Since the assembly of graphene liquid cells is delicate and requires fine motor skills, it usually takes practice to successfully make the liquid pockets. Due to the expense of graphene-coated TEM grids, it is highly recommended that new graphene liquid cell users first practice the liquid cell making process on traditional copper, amorphous carbon TEM grids to save money.Determining the causes of failure for liquid cells can be challenging because a researcher may not know if each step has been successful until imaging the sample at the end, and mistakes, like scratching the graphene, can go unnoticed. The easiest error to identify is an improper assembly because the researcher will immediately see liquid leaking out of the graphene liquid cell. Problems with making the graphene on copper grids, like cracking of the graphene, can be tougher to pinpoint. The quality of the graphene can be checked both before and after coating the TEM grids using Raman spectroscopy, but the graphene usually is unusable after this testing. Additionally, it is important to use direct transfer graphene because the two faces of graphene being put together need to be clean to properly form a seal through Van der Waals forces. Making graphene-coated grids through polymer transfer methods may leave polymer residue on the side of the graphene that is expected to bond together. If the correct procedure is followed using the correct TEM grids, lack of success with the graphene liquid cell is usually due to mishandling of the graphene and grids during assembly and fabrication.Graphene liquid cell TEM advances existing liquid cell TEM techniques by using a much thinner encapsulation material that can used in any traditional TEM holder, making high resolution and facet trajectory tracking experiments much easier. With the resolution of commercial silicon nitride membrane liquid cells, much of the facet and kinetic information that can be attained by etching nanocrystals in the graphene liquid cell would be lost. Graphene liquid cell TEM experiments can also be performed on existing single tilt TEM holders negating the need for expensive new specialized holders. Further, the graphene liquid cell can be put in any holder that accepts standard TEM grid samples allowing for liquid cell experiments to be performed in advanced holders  where silicon nitride liquid cells have not been designed. In addition, graphene liquid cells do not pose the risk of crashing the vacuum of the TEM column if the pockets rupture like other liquid cell TEM techniques. Although the graphene liquid cell is not a ubiquitous technique in nanocrystal fields yet, its ease of use and spatial resolution will make it much more widely used in the future.3, Tris Buffer, and even grapheneex situ reactions in a flask.Even with its many advantages, graphene liquid cell TEM does have limitations on the types of experiments that can be performed. Some liquid does evaporate as pockets form, so it is difficult to exactly determine the concentration of species in solution, even without considering electron beam effects. Graphene liquid cells also have random sizes, heights, and distributions of small pockets, so silicon nitride flow cells have the advantage of more quantifiable pre-beam concentrations and large, uniform liquid layers. As described in this work, only preloaded samples can be viewed using graphene liquid cell in the TEM, so it is not possible to flow in other solutions to trigger chemical reactions. The radiolysis species generated by the interaction of the electron beam with the liquid solution are the only trigger that can be used to start a reaction. Although not demonstrated yet, thermally initiated processes could be triggered in graphene liquid cells using standard heating holders. Electron beam-induced radiolysis effects are still not fully understood and can be difficult to control. Researchers have developed kinetic models to determine the contents of liquid cell pockets after beam interaction31ex situ nanocrystal synthesis and etching experiments will be critical in corroborating the mechanisms seen in liquid cell TEM experiments. Also, researchers have begun working on adding flow capabilities to graphene liquid cell TEMFuture graphene liquid cell experiments will help alleviate some of these concerns while also using new TEM advances to further probe the underlying mysteries of nanocrystals. Correlative The authors have nothing to disclose.


Accumulating behavioral and neurophysiological evidence supports the idea of language being grounded in sensorimotor processes, with indications of a functional role of motor, sensory and emotional systems in processing both concrete and abstract linguistic concepts. However, most of the available studies focused on native language speakers (L1), with only a limited number of investigations testing embodied language processing in the case of a second language (L2). In this paper we review the available evidence on embodied effects in L2 and discuss their possible integration into existing models of linguistic processing in L1 and L2. Finally, we discuss possible avenues for future research towards an integrated model of L1 and L2 sensorimotor and emotional grounding. Amodal system theories of language suggest that cognition is built of abstract amodal representations via formal rules, related to their referents . These tDespite the accumulating evidence, however, the exact functional role of these activations remains debated. One possibility is that embodied mechanisms are indeed an inseparable and functionally crucial part of language processing . OppositFundamental to the hypothesis of language grounding in sensorimotor processes, is the assumption that linguistic and sensorimotor experience develops with similar timings in early developmental stages. While this is mostly the case for a first language (L1), typically it is not for second language (L2) late learners who do not grow up as bilinguals . PulvermSubsequently, word learning is often accompanied by a direct association to objects, actions and properties of their referents in the environment . These sThus, while L1 is acquired in a strong connection to bodily sensations and motor programs and is used daily, L2 is usually learned through symbol manipulation, often based on L1 through analogy or translation and is used in specific settings . However, new concepts might borrow sensorimotor groundings from previously grounded symbols  might overcome this limitation but the available evidence is still insufficient. Evidence on L2 grounding effects induced by abstract words is particularly scarce, possibly as a result of the available contradicting evidence of embodiment in L1 for abstract linguistic concepts . A largeThe semantic aspects of abstract words might depend much more on the context in which they were learned . Thus, sFrom the reviewed evidence, an explicit sensorimotor and emotional grounding approach to L2 has so far been taken only by a limited number of studies. However, it is worth noting that evidence on L1 and L2 outside this particular approach is much more extensive and has produced several competing models and hypotheses regarding the neural bases of L1 and L2. It is worth briefly reviewing them in order to discuss whether and how the embodied cognition evidence might support the existing models.According to the so-called differential hypothesis , differeAccording to these models, if language is indeed embodied and grounded in sensorimotor  processes, then a similar engagement of these systems should be expected regardless of the use of L1 or L2. However, the time course might differ, with later L2 effects . These eSimilar temporal dynamics, on the other hand, would support effects directly produced by L2 linguistic stimuli, not mediated by L1. This would for instance be in line with the Revised Hierarchical Model (RHM) , a languIt is evident that approaching L1 and L2 processing from an embodied point of view is a new and complex area of research. On the one hand, L2 poses a challenge to strong views of embodied cognition: if linguistic concepts are deeply rooted in sensorimotor processes, then this should be true regardless of the use of L1 or L2. On the other hand, the same assumption of a strong link between sensorimotor experience and linguistic concepts, would predict differences between L1 and L2 grounding based on their age of acquisition.Furthermore, when approaching L1 and L2 existing competing models should be taken into account and integrated models should be produced including evidence based on the embodied and grounding hypothesis. In this sense, these models should take into account several parameters, including localization, magnitude and timing of the embodied effects.The use of methodologies with high temporal resolution, such as M/EEG, or allowing focal brain stimulation (TMS), will be crucial for disentangling the time course of effects in L1 and L2. In addition, behavioral measures collected in various tasks, will allow a more complete view of how L1 and L2 linguistic concepts are shared or differentially activated. The possible task-dependency of these effects– an issue already recognized in the embodied language literature – has to be even more carefully addressed when testing L2 as it might either support or conflict with existing strategies used for language acquisition and/or memory retrieval. Such an improved methodological approach would help in clarifying the different functional role of language grounding in L1 and L2.In the same vein, researchers should focus on formalizing the way linguistic experience  can be factored into the experimental design. Finally, the advancement of research on embodiment in L2 will necessary profit from the extension of the stimuli from single nouns or verbs to more complex sentences, as well as towards the use of abstract and emotional stimuli.CG and KK wrote and approved the final version of this manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


N-Methyl pyrrolidone and deionized water to form a homogeneous GO suspension, which was finally added into electroless plating solutions for the reduction process. Copper-coated graphene (Cu@graphene) and nickel-coated graphene (Ni@graphene) were synthesized using this one-step and co-reduction method by mixing salt solutions containing metal ions and GOs into the plating solution. The Cu ions or Ni ions were adsorbed and bonded onto the edges and surfaces of graphene, which was reduced from the GOs using a strong reducing agent of ascorbic acid or sodium borohydride. Crystalline Cu particles with an average size of about 200 nm were formed on the surface of graphene, whereas amorphous or nanocrystalline Ni particles with an average size of 55 nm were formed on the surface of graphene. Distribution of these metal particles on the graphene is homogeneous and highly dispersed, which can effectively improve the sinterability of composite powders. Cohesive energy distribution between graphene and metal interface was analyzed using first-principle calculation method. Formation mechanism of metal coated graphene was identified to be that both the GO and metal ions were simultaneously reduced in the reducing agents and thus a chemical bonding of graphene/metal was formed between the metal particles and graphene.Nanocomposite powders based on metal-coated graphene were synthesized using an in-situ co-reduction method in order to improve wettability and interfacial bonding between graphene and metal. Graphene oxide (GO) of 2~3 atomic layers was synthesized using the Hummer’s method with graphite as a raw material and then dispersed into a dispersing agent solution mixed with  Graphene has excellent physical and mechanical properties owing to its unique structure . In factGraphene is commonly used as a reinforcing material in composites, including metal, polymer and ceramic matrix composites ,12,13,14An efficient method was proposed to pre-coat the surface of graphene with a layer of metal in order to prevent its agglomeration in the matrix ,16. Due Therefore, in the present work, we synthesized Cu@graphene and Ni@graphene using a new and efficient in-situ co-reduction method. The formation mechanism of the metal@graphene composite was analyzed based on various characterization results. The cohesive energy between metal and graphene was calculated and analyzed using the first principle calculation method.2O2 (30%), N-methyl pyrrolidone, NaOH (PH = 11), ammonia (25–28%), KMnO4, were bought from Sinopharm Chemical Reagent Co. Ltd., Shanghai, China. All the chemicals were used directly without further purification.In this work, the raw materials used were flakes of graphite powders . Chemical reagents, such as copper sulfate, nickel sulfate, sodium hydroxide, concentrated sulfuric acid (98%), HCl (37%), H2SO4 and then stirred using an ice-bath (at 0 °C) for 30 min; (b) At room temperature of 25 °C, 20 g of KMnO4 was slowly added into the above mixture and agitated for 120 min; (c) The temperature of above mixture solution was increased to 35 °C during the process; and then 50 mL of deionized water (DI) was gradually added into the above solution; (d) 80 mL of DI water was gradually added into the system; After all the reactions were completed, hydrogen peroxide (30 wt %) was added into the solution until it turned into a yellow color and no bubbles were further produced; (e) The mixture was filtered and washed using HCl (5 wt %) and DI water for ~28 times and then dried at 70 °C for 12 h using a vacuum freeze-drying method. In this paper, we did not perform the recycling of the residual product as reported in Reference [The standard Hummer’s method was employed to synthesize GO ,26,27. AAs illustrated in (a)N-Methyl pyrrolidone and DI mixture solution;20 mg of GO was dispersed into 100 mL dispersing agent solution in an ultrasound bath for 3 h to obtain a homogeneous GO suspension solution (0.2 mg/mL) as shown in (b)The salts , reducing agents  and surfactant agents were mixed together to form an electroless plating solution b;(c)Then the GO suspension solution was added into the electroless plating solution c;(d)The mixed solution was intensively stirred using a magnetic stirrer to disperse the GO suspension solution. The copper plating process was done at 90 °C for 3 h and the nickel plating was done at 30 °C for 30 min. Simultaneously the NaOH solution or ammonia solution was dripped into the mixed solution to adjust the pH value to between 9 and 10 d. The pH(e)The precipitates were separated from the solution after the chemical reactions were completed e. DI watThe detailed electroless plating processes are listed as follows:α radiation at 40 kV and 15 mA was used to analyze the crystalline structures of GO and metal@graphene. The scanning rate was 8°/min and the scanning range of 2θ was 5~65° with a step size of 0.02°. Surface morphology of the GO and metal@graphene was observed using a scanning electron microscope  and chemical element analysis was performed using an energy dispersive X-ray spectrometer . Detailed morphological characteristics of the GO and metal@graphene composites were obtained using a transmission electron microscope . Characterization of samples using Raman spectroscopy  were performed using a laser beam with a wavelength of 532 nm and a SWIFT detector over a range of 500–3500 cm−1 and all the spectra were taken at room temperature (20 °C). Fourier transform infrared (FT-IR) spectra of the GO and metal@graphene were obtained using a TENSOR 27 spectrophotometer  with wavelengths ranging from 500 to 4000 cm−1 at room temperature. Microscale surface morphologies of metal@graphene powders were obtained using an atomic force microscope  in a tapping mode.An X-ray diffractometer  with Cu KFor the graphene system after atomic adsorption, there are defects, grain boundaries and intrinsic atoms formed. The adsorption energy of defects on the graphene is maximum and those of the grain boundary and intrinsic atoms on the graphene are approximately equal. The binding between graphene and metal is generally weaker than a typical covalent bond. In the present study, we focused on analysis of cohesive energies of Cu and Ni atoms with both their (111) surfaces bonded onto a graphene of a few atomic layers. The modeling work only considered the intrinsic atoms and defects adsorption. The first principle calculation was used to evaluate the cohesive energy between graphene and metal interface, as the binding force cannot be obtained using experimental methods easily.k points for the Monkhorst–Packs.The detailed model information is described as follows: firstly, the lattice is established. The lattice constant is set as a = b = 2.46, c = 3.4 and carbon (related to graphene) atoms are added . Then, in order to eliminate the influence of molecular bond between graphene layers, the vacuum layer is expanded to 2 nm on the Z axis direction. Finally, a and b in the supercell are increased to 3 times of original values and the initial configuration of the model is obtained in . The strIn order to check the thickness and microstructure of the GO, TEM and AFM images were obtained and the results are shown in AFM and TEM images of graphene, Cu@graphene and Ni@graphene obtained from the in-situ co-reduction processes are shown in n is 1, λ is the X-ray wavelength of 0.154 nm from the Cu X-ray source, θ is half of the diffraction angle and d is the interlayer spacing. The calculated layer spacing of peak (001) of graphite oxide is ~0.80 nm, which indicates that the GO obtained is nearly a monolayer [The obtained XRD patterns of GO sheets, graphene, Cu@graphene sheets and Ni@graphene sheets are shown in onolayer .For XRD result of Cu@graphene c, there For XRD result of the Ni@graphene sheets d, there In order to verify that the graphene was still maintained after the in-situ co-reduction process, XRD analysis of the prepared composites b shows a−1, which represent the D peak, G peak and 2D peak of the GO. The intensity ratio of D peak and G peak (ID/IG) is often used to characterize the degree of defects in carbon materials [D/IG of GO in this study was measured to be 0.91 and it is similar to those reported in references [Raman spectra of GO, graphene, Cu@graphene and Ni@graphene powders are presented in aterials . The ID/ferences ,37.D/IG data of composites and graphite, we can confirm that the defects are increased after the graphite was oxidized and some of the carbon atoms in the defect structures are combined with the oxygen-containing functional groups [sp2 hybridization into sp3 hybridization. The oxygen-containing functional groups not only cause changes in crystallinity of hexagonal network structures of the graphite but also increase the defects, which causes the G peak to be widened and the strength of D peak to be increased [D/IG is 1.02 as shown in D/IG for the composite indicates that majority of oxygen-containing functional groups were removed during the reduction process, the reason of which has been reported in our previous work [Comparing the Il groups . Formatincreased . Whereasous work ,41.−1 and ~1593.06 cm−1, which represent the D peak and G peak of carbon. The calculated ID/IG values of GO and Cu@graphene are 0.91 and 1.09, respectively. This indicates that the reduction effect will result in the increases of defects, topological disorders and the degree of graphitization; as well as decrease of crystallinity. The Raman spectrum of the Ni@graphene composite  is originated from two phonon and double resonances of laser induced vibration process for carbon. Generally, the 2D peak is an indication if the graphene is single layer or a few layers [−1, whereas that of double-layer graphene is located at 2692.3 cm−1 and that of graphene having more than 10 layers is close to the position of the 2D peak of natural graphite which is located at 2716.5 cm−1. The 2D peak of GO in this study  and (3) [For the FT-IR spectrum of the Ni@graphene d, all th and (3) ,46:(2)4NTEM images of GO and Cu@graphene are shown in TEM image of the Ni@graphene is shown in Based on DFT calculation results, the binding energy of Ni atoms adsorbed onto the graphene is 2.078 eV, whereas the binding energy of Ni atoms adsorbed on the graphene with the defect is 3.214 eV. Meanwhile, the binding energy of Cu atoms adsorbed onto the intrinsic graphene is 1.778 eV, whereas that of Cu atoms adsorbed on the graphene with the defect is 5.114 eV. For both cases, the binding of metal atom and graphene is a chemical process, which verifies the experimental results in the previous sections. Meanwhile, results show that the binding energy of atomic adsorption on defect of graphene is larger than that on the intrinsic graphene, which clearly show that the metal atoms are preferably adsorbed on the defects in the graphene. This result is also consistent with the literature ,54.Pz orbital of carbon atoms and the metal atoms is strong. Therefore, we find that, except for the observed charge transfer between graphene and metal orbitals, a strong coupling is obtained between the band structures of graphene and metal.In order to understand the differences of binding strengths between Cu or Ni and graphene, we further analyzed the electronic coupling across the interfaces. The obtained band structures of graphene-Cu(111) system and graphene-Ni(111) system are plotted in Based on the characterization results, the formation mechanism of metal@graphene is proposed as illustrated in In the second stage, a suitable chemical reagent and a strong reducing agent  are applied depending on the type of metal to be plated and the chemical reduction processes to be initiated.The third step is the most important one which is in-situ and co-reaction process. The copper ions or nickel ions adsorbed on the edge and surfaces of graphene oxide are strongly reduced in the alkaline conditions to obtain metal particles and the specific reactions for copper plating are written in Equations (4)–(7). Those of the nickel plating are written in Equation (8):2OH with the reduction actions of ascorbic acid or sodium borohydride. The reduction reactions can be verified from our FT-IR analysis. The reactions that occur in this process can be expressed as follows:Simultaneously, GO is reduced by the strong reducing agent of ascorbic acid or sodium borohydride to produce a graphene layer. The –COOH functional group on the surface of the GO is reduced to –CHSince the newly formed graphene has a large surface energy, the metal ions in the solution are easily adsorbed onto the surface of the graphene and then deposited onto its surface and the inherent “defects” of the graphene cause the metal ions to form a good chemical bonding . This haIn this work, GO of 2~3 atomic layers were obtained using the Hummer’s method. Using GO, copper sulfate and ascorbic acids (or nickel sulfate and sodium borohydride), the Cu@graphene powders (or Ni@graphene powders) with a homogeneous distribution of metal nanoparticles on the surface of graphene were obtained using an efficient in-situ co-reduction method. The formation mechanism of metal@graphene can be explained: for example, the metal ions and graphene firstly form a chemical bond and the GO and the metal ions are simultaneously reduced by the reducing agents to finally obtain the metal@graphene. The binding of metal atom and graphene is a chemical process which can be verified based on the results from the first-principle calculations.


Lignin graphene oxide was oxidized after Kraft lignin was graphitized by thermal catalytic conversion. The reduced lignin graphene oxide was derived from lignin graphene oxide through thermal reduction treatment. These Kraft lignin, lignin graphite, lignin graphene oxide, and reduced lignin graphene oxide were characterized by scanning electron microscopy, raman microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and thermogravimetric analysis. The results showed lignin graphite converted from Kraft lignin had fewer layers with smaller lateral size than natural graphite. Moreover, lignin graphene oxide was successfully produced from lignin graphite by an oxidation reaction with an hour-long reaction time, which has remarkably shorter reaction time than that of graphene oxide made from natural graphite. Meanwhile, this lignin-derived graphene oxide had the same XRD, FTIR and Raman peaks as graphene oxide oxidized from natural graphite. The SEM, TEM, and AFM images showed that this lignin graphene oxide with 1–3 average layers has a smaller lateral size than that of graphene oxide made from natural graphite. Moreover, the lignin graphene oxide can be reduced to reduced lignin graphene oxide to fabricate graphene-based aerogel, wire, and film for some potential applications. Lignin, as a component in the cell walls of plants, is used to strengthen their structure, and it is the most abundant aromatic biopolymer on Earth . There a2-bonded carbon atoms in a honeycomb crystal lattice structure displaying excellent electrical and mechanical properties [Graphene is an exciting material that has a one-atom-thick 1D planar sheet of spoperties . In receoperties ,10,11,12operties . Howeveroperties . The effoperties . Graphenoperties . This maIn this study, the Kraft lignin, as the carbon source, was used to make few-layered lignin graphite (LG), lignin graphene oxide (LGO) and reduced lignin graphene oxide (RLGO). The morphology, structure, characteristics and properties of LGO and its relative materials  were examined by a scanning electron microscope (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy and thermogravimetric analysis (TGA). The applications of LGO/cellulose nanofibrils (CNF) aerogel, LGO/CNF film, LGO/polyacrylonitrile (PAN) electrical wire, and LGO/PAN fiber sheet fabricated using this synthesized LGO were also developed in this study.3)3·9H2O), tetrahydrofuran (THF), potassium permanganate (KMnO4), and sodium nitrate (NaNO3) were purchased from Sigma-Aldrich ; hydrogen peroxide (H2O2) was obtained from Fisher scientific . Commercial Kraft lignin named Bio-Choice lignin was provided by Domtar Corporation , the specification provided by Domtar showed that the Kraft lignin contained 97.1% lignin and 1.7% sugar with a pH value of 6.2. The content of C, H, and O was 65.9%, 7.5%, and 26.3%, while proximate analysis showed the content of volatile, fixed carbon, and ash as 54.5%, 43,1%, and 2.4%, respectively [Iron(III) nitrate nonahydrate  nitrate was used in this study as metal catalyst source for the catalytic graphitization. Iron with 10% loading in the iron-lignin precursors was prepared at room temperature using a co-precipitation technique. Specifically, lignin solution was prepared by adding 50 g of Kraft lignin to 50 mL tetrahydrofuran (THF) in a 250-mL glass beaker and stirring the mixture for 2 h. Meanwhile, iron nitrate solution was prepared by adding 41 g of iron (III) nitrate nonahydrate to 20 mL DI water in a 100-mL glass beaker and stirring the mixture until the metal salt dissolved completely. Prepared iron nitrate solution drop-like (~10 mL/min) was added to the lignin solution, and the lignin-iron nitrate mixture was stirred for 2 h at 70 °C. The final iron-lignin mixture was kept at room temperature for 24 h, and then transferred to an oven and dried at 150 °C for one day. After drying process, a solid iron-promoted lignin mixture as a precursor was obtained. Then the iron-promoted lignin precursor was loaded in the middle of a 2-inch OD ceramic tubular reactor. The reactor was heated at a rate of 10°C /min to 1100 °C and kept at 1100 °C for 1 h with 50 mL/min argon and 50 mL/min methane. The furnace was naturally cooled down by 10 °C /min to room temperature. The few layers LG sample was collected from the 2-inch OD ceramic tubular reactor for further use.2SO4, and 5.5 g NaNO3 were added into 2000 mL flask with 15 g LG, and the mixture was cooled down to 0 °C in an ice bath and stirred 10 min. Subsequently, 33 g KMnO4 was slowly added and continuously stirred for 30 min. Following this, 1000 mL DI water was added into the flask and the temperature was increased to 75 °C for 20 min. The mixture was then treated with 500 mL 10% H2O2 to terminate the chemical reaction. The total reaction time from LG to LGO was an hour which is noticeably less than that of graphene oxide made from natural graphite [For LGO and purification, a modified Hummers’ method was employed to oxidize LG and remove catalyst from LG to produce LGO . Specifigraphite ,20. The For the RLGO, a simple thermal annealing process was used to produce it from LGO powder. The RLGO powder was obtained by heating LGO powder in an oven at 200 °C in air for 2 h.The morphology of the samples was investigated with a Scanning Electron Microscope (SEM). LG and LGO samples were mounted with conductive carbon tape, sputter coated with gold and imaged using field emission scanning electron microscope (LEO 1530 FESEM) at a 5 mm working distance and a 10 kV accelerating voltage.The morphologies of LG and LGO samples were examined using a JEOL JEM-100CX II Transmission Electron Microscope  operated at an accelerating voltage of 200 kV. All TEM samples were sonicated in ethanol solution for 1 min before transfer to copper grids.The thickness of LGO samples were measured using atomic force microscopy . Samples were diluted to solids consistency of 0.05% and deposited onto clean mica substrates and air dried overnight at room temperature. The samples were imaged by a silicon cantilever in vibrating tapping mode at 160–225 kHz with a radium of the tip curvature less than 10 nm. The thickness and length of samples in the image were measured by Gwyddion software.Thermal degradation and stability of Kraft lignin, LG, LGO, and RLGO was assessed by thermogravimetric analysis . Samples (1–3 mg) were heated from 50 °C to 800 °C with a ramp rate of 5 °C/min under a flowing nitrogen atmosphere (20 mL/min) by thermogravimetric analysis, respectively.X-ray diffraction (XRD) patterns for LG, LGO and RLGO were obtained with a Bruker Discovery 8 diffractometer  using a Cu Kα rotation tube at 50 kV and 1000 μA with scanning over the range of 2θ = 5–60°.Raman spectra of LG, LGO and RLGO were obtained by an Aramis Confocal Raman Microscope  equipped with an excitation laser source emitting at 514 nm and having an incident power around 1 mW on a thin surface.−1 for 64 scans in 500 to 4000 cm−1 range. All powdered samples were pressed against the diamond crystal of the ATR device. Background spectrum obtained by scanning the air was subtracted from the sample spectrum before being converted into transmittance units.The ATR-FTIR spectra of Kraft lignin, LG, LGO, and RLGO samples were recorded with the Thermo Scientific ATR-FTIR spectrometer  at a resolution of 4 cm−1), C=O stretching vibrations (1734 cm−1), C=C from sp2 bonds (1615 cm−1), O–C–O vibrations (1238 cm−1) and C–O vibrations (1068 cm−1) [−1) and C=C from sp2 bonds (1615 cm−1) were observed, and almost all functional groups had been removed through the thermal reduction process. It indicated that LGO can be successfully converted to RLGO through thermal reduction treatment.In 68 cm−1) . However68 cm−1) . For RLGIn −1 is the characteristic peak of sp2 hybrid structure, which represents the symmetry and crystallizability of graphene materials; and the D peak at 1350 cm−1 is the defect peak, which represents the surface defect and disorder of graphite layers [−1 of LG is a second order two phonon process [D/IG from 1.0 of LG to 1.2 of LGO confirms the grafting of oxygen containing functional groups to the graphitic planes. After reduction treatment, ID/IG of RLGO from 1.2 of LGO becomes 1.1, which indicates the removal of most of the oxygen containing functional group. The ID/IG of RLGO is higher than that of LG due to the sp2 domains which are newly formed during reduction and smaller than those of LG [Raman spectroscopy is a very important characterization tool to analyze carbon materials because Raman scattering has a close relationship with the electron structure of the substances. e layers ,29. In Fe layers . The 2D  process , which m process . It indise of LG .2 streaming from the most labile functional group. The result of LGO exhibits another mass loss (28%) in the range of 220 to 800 °C, which has been attributed to the loss of oxygen functional groups. In contrast, the TGA result of the RLGO sample shows higher thermal stability than the LGO sample. The total loss is 27% at temperatures below 800 °C. This lower mass-loss can be attributed to the absence of most oxygen functional groups [In l groups .The excellent dispersibility of LGO makes it a promising candidate to fabricate LGO based composite materials . A 3D bio-aerogel prepared by a synergistic assembly of 50% LGO and 50% cellulose nanofibrils (CNF) through a freeze drying process shows the same appearance and internal structure as an assembly of prepared pure CNF aerogel reported by our previous research . ResultsThe synthetic LGO and its relative materials produced from a new resource (Kraft lignin) have been established by catalytic graphitization, oxidation reaction and thermal reduction process. The experimental results obtained from XRD, FTIR, Raman, SEM, TEM and AFM showed this LGO has similar properties and characteristics to graphene oxide made from natural graphite, while the LGO has a one-hour oxidation reaction time that was remarkably less than that of graphene oxide made from natural graphite. Moreover, the nanoscaled lateral size of LGO that was observed by SEM, TEM and AFM was less than that of graphene oxide made from natural graphite, thus it could be used for some conductivity materials. In addition, the LGO has good dispersibility, and function groups of the LGO can be removed by thermal reduction processes to produce RLGO. Therefore, the LGO can be easily used to fabricate graphene based composites for various applications.