Graphene-covering is a promising approach for achieving an acid-stable, non-noble-metal-catalysed hydrogen evolution reaction (HER). Optimization of the number of graphene-covering layers and the density of defects generated by chemical doping is crucial for achieving a balance between corrosion resistance and catalytic activity. Here, we investigate the influence of charge transfer and proton penetration through the graphene layers on the HER mechanisms of the non-noble metals Ni and Cu in an acidic electrolyte. We find that increasing the number of graphene-covering layers significantly alters the HER performances of Ni and Cu. The proton penetration explored through electrochemical experiments and simulations reveals that the HER activity of the graphene-covered catalysts is governed by the degree of proton penetration, as determined by the number of graphene-covering layers. Graphene-covering technology provides a promising approach for achieving a non-noble-metal-catalyst with corrosion protection and catalytic activity under acidic media. Here, the authors unveil that the electrochemical hydrogen evolution mechanism is governed by the proton penetration phenomenon. Among various H2 generation technologies4, the electrolytic production of H2 from water is a promising method5 because it yields high-purity H2 (>95%) and emits no CO2. Polymer electrolyte membrane (PEM) water electrolysis is likely to be the next-generation technology for H2 production; it is more efficient than alkaline water electrolysis because of its H2 gas purity , faster dynamic response, larger current density , and higher discharge H2 pressure 6.Hydrogen  has frequently been employed as the cathode catalyst because it exhibits a high electrochemical activity and is chemically stable even in strongly acidic environments. However, the scarcity and high cost of noble-metal catalysts limit the use of PEM electrolysers. Given this limitation, it is important to develop cost-efficient, acid-stable, noble-metal-free catalysts that possess high hydrogen evolution reaction (HER) activity comparable to Pt and are chemically tolerant to acidic conditions.10. For example, graphene-encapsulated Ni, Fe, and CoNi alloy nanoparticles have been used in acidic electrolytes13. These encapsulated nanoparticles show sufficient tolerance against corrosion yet maintain their HER performance because the outermost graphene layers become HER-active owing to charge transfer from the underlying metal substrate13. However, regardless of the charge transfer effect, the performance of graphene-covered non-noble metal catalysts seems to be strongly dependent on the underlying metal substrate13. Here, a fundamental question is: how can the HER effectively occur with graphene layer covering, where the covering graphene blocks the catalytically active sites on the surfaces of the non-noble metal catalysts? Although the HER mechanism can be understood by the charge transfer13 and proton penetration through graphene15, this has not been evidenced by experiments. Therefore, it is crucial to determine how both the charge transfer and the proton penetration through graphene affect the HER mechanism of the graphene-covered non-noble metal catalysts.The main source of HER catalyst degradation in acidic media is corrosion. This corrosion can be suppressed through passivation or covering of the catalyst surface with chemically stable graphene layers2) penetrate by bypassing the N-dopant-induced defect sites, which makes the catalysts covered by N-doped graphene electrochemically more active than those covered by non-doped graphene. Our results reveal that the charge transfer effect is not a dominant factor, while the ability of protons to penetrate graphene governs the HER activity of graphene-covered non-noble metal catalysts regardless of morphology and composition. This study provides new insights for the development of non-noble metal catalysts for electrochemical hydrogen production through graphene covering by balancing the contrasting properties of corrosion resistance and catalytic activity in acidic media.In this study, we investigate the HER mechanisms of the proton penetration/charge transfer through the graphene-covering layers and their impact on the catalytic activity of graphene-covered non-noble metal catalysts. We find that protons as well as molecular hydrogen  and N-doped graphene layers (NGLs) Fig. . The gra17. The atomic structures of GLs and NGLs with various layer numbers were observed using high-resolution transmission electron microscopy (HRTEM). The HRTEM image of the monolayer GL (1GL) showed a honeycomb structure comprising six carbon atoms with six-fold symmetry spots assigned to monolayer graphene  induced by N-doping  indicated high 2D-band to G-band (I2D/IG) intensity ratios of 3.8–4.9, suggesting that the monolayer graphene is highly crystalline22  intensity ratios of 0.05–0.08. In contrast, the NGLs exhibited relatively high ID/IG ratios (0.7–1.4), which illustrates that N-doping induced many defects. We interrogated the chemical binding state of GLs and NGLs through XPS , graphitic (0.76 at.%), and oxidic structures (0.36 at.%) in the NGLs24. We observed a very tiny amount of residual Cu metal (≤0.01 at.%) , Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS)ene Fig. . The bilene Fig. , b18,19.2SO4 using a three-electrode system and compared them to those of the bare 3–6NGL samples  as well as the bare Cu and Ni sheets (without graphene-covering). The HER polarization curves of the Cu/3–6NGL samples showed that the overpotential (η10) at the current density 10 mA cm−2, normalized by the electrode surface area, increased with an increasing number of NGLs .We subsequently transferred the graphene layers onto the Cu and Ni sheets with trilayer NGL and hexalayer NGL . These graphene-covered Ni and Cu sheets were sandwiched between Nafion films. We measured the HER activities of the Cu/3–6NGL and Ni/3–6NGL samples in 0.5 M HGLs Fig. . The η10η10 values of the Cu/NGL and Ni/NGL samples should be identical regardless of the catalytic activity of the metal substrates. However, the observed η10 values of the Ni/3NGL and Ni/6NGL samples were 53.3% and 29.7% lower than those of the bare 3NGL and 6NGL samples. The reductions in the η10 values due to the Ni substrate (53.3% for the 3NGL and 29.7% for the 6 NGL) are much larger than the reductions due to the Cu substrate  and observed the generation of Hers Fig. . Raman sers Fig. . Overall−1 at 24 °C25) on both sides. The Nafion/graphene layers/Nafion sandwich membrane was placed on the same Si3N4 chip used for the Raman measurements to isolate the anode and cathode chambers of the H-type cell  between the two chambers that were physically separated by graphene in the H-type cell  characteristics in a two-electrode system. The proton current through the graphene layers was proportional to the bias voltage in the +200 to −200 mV range . This manifests that the proton-penetration resistance arises predominantly from the graphene layers rather than the Nafion. The electrochemical resistance of proton penetration through the graphene layers was further investigated by electrochemical impedance spectroscopy. The results also confirmed the correlation of the proton-penetration resistance and the layer number of graphene . The proton currents, which are defined as the limited current of HER by proton diffusion, through the NGLs were observed to be 1.5 times greater than those through the GLs Fig.  and 7. T14. An Arrhenius-type-fit of the data provides the energy barriers of 0.95 ± 0.03 and 0.87 ± 0.03 eV for 1GL and 1NGL, respectively. In addition, the energy barriers for GLs are almost proportional to the number of GLs (2GL: 1.76 ± 0.04 eV) while the energy barriers for NGLs are not simply proportional to the number of NGLs . These results indicate that the nitrogen dopant-induced defects on the graphene lattice accelerate the proton penetration26. Moreover, the I–V curves of 6NGL demonstrated a non-linear behaviour at a wide voltage range from −3.5 to +3.0 V  from 8 h of CA testing as a function of the overpotential (η10-tot) at the current density of 10 mA cmtot−2, normalized by the total surface area (i.e. the Brunauer-Emmett-Teller (BET) surface area of the catalyst), and the current density at −600 mV vs. RHE for fair catalytic ability comparisons , and NiMo alloy nanoparticle (NiMoNP) catalysts . We plotons Fig. . SurprisQuestions that arise here include: how do NGLs enhance proton penetration compared to GLs, and how does a proton penetrate through multiple graphene layers? To address these questions, we computed the energy barriers for proton penetration through a defect-free 1GL lattice, a 1GL lattice with a 5–7 defect, and several types of NGL lattices using the nudged elastic band (NEB) method. Our calculations reveal energy barriers of 3.16 eV and 2.30 eV for a 1GL lattice with no defects and a 1GL lattice with a 5–7 defect, respectively Fig.  and 10. 2O molecules .The pathway for proton penetration through multiple graphene layers to the non-noble metal surface in the presence of H2 molecules through graphene lattices  , but it must only overcome an energy barrier of <1.0 eV when graphene has nanopores (diameter: 2.5–5.8 Å)  and pyridine  as carbon and nitrogen sources24. The Cu foil was loaded on a corundum boat and inserted into the centre of a quartz tube (φ30 × φ27 × 1000 mm) in a furnace. The tube was heated at 1000 °C for 1 h under an atmosphere of H2  and Ar . Then, GL was grown with an additional flow of CH4  for 30 min, while NGL was grown with an additional flow of CH4 (20 sccm) and pyridine (0.5 m bar). The as-synthesized graphene on Cu foils after Cu dissolution in 0.25 M Fe(NO3)3 solution was manually stacked to prepare graphene-covered Cu and Ni sheets and graphene separating membranes  via a conventional CVD method using CH2, Solid angle 0.26 sr). Raman spectra were performed using a Renishaw InVia Reflex with an incident wavelength of 532 nm. X-ray diffraction (XRD) was carried out using a D2 PHASER . Surface chemical states were studied by X-ray photoelectron spectroscopy  with an Al Ka and X-ray monochromator.Morphology and microstructure of as-synthesized graphene were characterized using a scanning electron microscope , transmission electron microscopes , and equipped energy dispersive spectroscopy  = E(Ag/AgCl) + 0.0591 × pH + 0.197. The pH value of the electrolyte was recorded as 0.5–0.55. The Ag/AgCl reference electrode was calibrated using a Pt wire as the working electrode. The polarization curves were obtained using a sweep rate of 5.0 mV s−1. The electrode potential was automatically iR-compensated with the ohmic resistance.An electrochemical workstation  was used for all electrochemical measurements. Catalytic activities of graphene-covered Cu/Ni sheets and Ni/NiMo nanoparticles samples were performed in a three-electrode system. As-prepared graphene-covered catalysts, a graphite rod, an Ag/AgCl electrode, and Ar-saturated 0.5 M HI–V characteristics and electrochemical impedance spectra were performed in a two-electrode system. The schematic of the homemade H-type cell for electrochemical measurements of proton penetration was shown in Fig. 3N4 chip (window size: 10 × 10 μm) fixed in the centre was used to isolate the anode and cathode chambers filled with 0.5 M H2SO4. The distance between the electrode and separator was 1.0 cm. The size of the Pt plate electrode was 1.0 × 1.0 cm. Electrochemical impedance spectra were recorded with the frequency ranging from 106 to 100 Hz. The CA measurements were carried out in a three-electrode system, in which an Ag/AgCl electrode equipped with a salt bridge was used as the reference electrode. Temperature dependence of proton conductivity experiments for graphene layers were performed over a temperature range of 273–328 K to avoid water freezing and membrane damage due to thermal expansion.The 33. The Becke-Lee-Yang-Parr (BLYP)35 exchange-correlation functional was used. We employed double-zeta valence plus polarization (DZVP) basis sets. The core electrons were described by the Goedecker-Teter-Hutter pseudopotential36. The real-space density cut-off was set to 320 Ry. The van der Waals correction was included via Grimme’s D3 method37. The simulation cell lengths in the x-, y-, and z-directions were 25.56, 24.595, and 50 Å39, respectively. The C–C bond lengths of pristine graphene are 1.42 Å. The 5–7 defect was introduced according to the reported literature40. The nudged elastic band method41 was used with three intermediate states. The calculated barrier heights are independent of calculation methods and consistent with previous reports (Supplementary Tables 42.The DFT calculations were performed via the CP2K programSupplementary InformationPeer Review File


The dataset shows the relationship and valuation of the coastal dunes of the Araucanía region in Chile. The valuation of the local population was surveyed using a questionnaire applied to 49 subjects belonging to Mapuche communities and local government. The data consists of eight tables that show a list of questions, the number of times per year that visit the dunes, cultural practices carried out in the dunes, valuation of ecosystem services provided by the coastal dunes, and knowledge about flora and fauna. Lastly, the original questionnaire and its responses in Spanish and English are included in supplemantary material. This dataset was generated within the framework of the manuscript “Ecosystem services and uses of dune systems of the coast of the Araucanía Region, Chile: a perception study” where 23 leaders of Mapuche communities and 26 representatives of the local government were interviewed. The dataset can be used to compare the valuation of ecosystems by local communities, especially when quantitative data are scarce or do not exist. It also allows comparing local governance in similar contexts.•Data on perception and local knowledge are especially important when there is no other source of data.1The data consists of eight tables in which the perception and local knowledge are collected from the Mapuche communities and representatives of the local government. 2comunas  of Saavedra, Teodoro Schmidt and Toltén on the coast of the Araucanía Region, Chile. The area covered by dunes is 4,349 ha  and the Queule river in the south .The database was built in the dune systems located in the The coast of the Araucanía Region presents the highest percentages of poverty and rural habitation in Chile (CASEN 2015), resulting from high levels of land division , a farming-based economy, and in recent years the impact of forestry plantations Peña-Cortés et al., as a result of which there are few remnant patches of native forest Pincheira-Ulbrich et al.The subsistence farming economy is associated with Mapuche communities and rural inhabitants Peña-Cortés et al. As with the rest of the country, most major decisions are taken centrally in the national capital, Santiago, although a certain level of decision-making occurs at local government level, in the towns of Saavedra, Toltén and Teodoro Schmidt where most public services are concentrated.http://muniteodoro.cl/portal/), Saavedra (http://municipiodesaavedra.cl/Municipio/), and Toltén (http://www.tolten.cl/web/). The selection strategy for the local government group targeted most of the heads of services directly related with the natural system, namely: the Local Development Unit (UDEL), the Community Development Office (DIDECO), the Planning Secretary (SECPLAC), the Territorial Development Programme (PDTI) and the Environment Department. Initial contact with this group was by e-mail, allowing interviews to be coordinated. Local government actors were selected in this way. The participants of the Mapuche group were selected following a non-probabilistic strategy through a “snow-balling” procedure; the first contact was made with the President of the Association of Lafquen Leufu Communities (Saavedra), and a total sample of 23 people was obtained .The study participants were selected using the official lists of Mapuche communities and local government employees. In the case of the Mapuche group (community presidents), the information was provided by the National Indigenous Development Corporation (CONADI), the Local Development Programme (PRODESAL) and the Intercultural Departments of the respective municipality. The information on local government personnel was obtained from the websites of the municipalities of Teodoro Schmidt , five multiple choice (five or six options per question), seven open questions and three using a Likert-type scale. The Likert scale questions used a scale of one to five , covering the full range of values for the item being assessed. Questions of this type included the classification categories proposed by Castro (2015) which are then presented in results rearranged according to Common International Classification of Ecosystem Services (CISES)  (Questions 10). Each section included an explanation of the main concepts of the theme, to ensure correct assessment by the participants.For multiple-choice question in During the interview, efforts were made to maintain openness and non-judgmentality, treating each interviewee fairly and impartially, regardless of their socio-economic status, social status, race, religion or physical appearance. Potential research participants were asked to read the plain language statements and complete a research consent form if they are willing to participate in this project voluntarily. Potential participants were asked to read the research consent form in order to voluntarily express their willingness to participate in this project.Pablo Arévalo-Valenzuela: Conceptualization, Investigation, Application of method, Data analysis; Fernando Peña-Cortés: Supervision, Data discussion; Jimmy Pincheira-Ulbrich: Writing-Original draft preparation, Visualization, Reviewing and Editing, Data analysis.The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article.


A graphene-PbS quantum dot (QD) composite for application in high-performance near-infrared (NIR) photodetectors (PDs) is proposed in this study. A single-layer graphene flake and oleic acid-capped PbS QD composite is fabricated through the conventional sonication process, in hexane solution. Field emission scanning electron microscopy images of the graphene-PbS QD composite dispersed on a glass substrate confirm that the composite contains both aggregated graphene flakes and single-layer graphene with wrinkles; Transmission electron microscopy images reveal close packing with uniform size. The increased absorbance and quenched photoluminescence intensity of the graphene-PbS QD composite supports enhanced photoinduced charge transfer between graphene and the PbS QDs. Moreover, the specific Raman mode of the PbS QDs, embedded in the spectrum, is enhanced by combination with graphene, which can be interpreted by SERS as relevant to the photoinduced charge transfer between the Pbs QDs and graphene. For device application, a PD structure comprised by graphene-PbS QDs is fabricated. The photocurrent of the PD is measured using a conventional probe station with a 980-nm NIR laser diode. In the fabricated PD comprising graphene-PbS QDs, five-times higher photocurrent, 22% faster rise time, and 47% faster decay time are observed, compared to that comprising PbS QDs alone. This establishes the potential of the graphene-PbS QD composite for application in ultrathin, flexible, high-performance NIR PDs. In particular, two-dimensional layered materials and zero-dimensional quantum dots have attracted significant attention for optoelectronic applications because of their excellent optical and electrical properties11. Graphene is a representative metallic layered material consisting of carbon atoms arranged in a hexagonal lattice with strong inplane chemical bonds14. Although graphene has high electron concentration, weak light absorption and fast carrier recombination limit its application in optoelectronics16. PbS colloidal quantum dots (QDs) are promising semiconductors for application as active material in near-infrared optoelectronics because of their small and tunable direct band gap18. Moreover, PbS QDs have outstanding optical and electrical properties due to which their application can be expanded to photodetectors (PDs), light emitting devices, field effect transistors, and photovoltaics22. The different work function and carrier concentration of graphene and the PbS QD enable photoinduced charge transfer when these two materials are in physical contact25. For application in photoresponsive devices, this phenomenon can enhance the photoresponsivity and improve the response time of the PD.Low-dimensional materials are suitable for application in flexible devices because of their atomic-scale dimensions26. Photoinduced charge transfer can be the dominant contribution to the surface-enhanced Raman signal on the semiconductor substrate27. Therefore, the study of the SERS of graphene and PbS QDs is significant for the analysis of the photoinduced charge transfer and Raman spectroscopy.One of primary mechanisms of surface-enhanced Raman scattering (SERS) is chemical enhancement that involves photoinduced charge transfer between inhomogeneous substancesThe hybrid structure comprising graphene and PbS QDs is atomically thin, forming a flexible and transparent device. Furthermore, the fabrication process of this hybrid structure is simple, inexpensive, and large-scale because it is a solution-based process.Herein, we report the fabrication and characterization of a graphene/PbS QD hybrid structure for application in near-infrared PDs. Graphene flakes were dispersed in butylamine and hexane to achieve uniform distribution on a glass substrate. Hexane solution was used to disperse the PbS QDs. Mixtures of graphene flakes and PbS QDs were deposited on a glass substrate using a spin casting machine. Further, the room-temperature photoluminescence, and the Raman and absorption spectra were measured to confirm the optical properties that can be modified by the photoinduced charge transfer of PbS QDs. The surface morphology was evaluated using scanning electron microscopy. The device performance was assessed using the current–voltage curve, photocurrent measurement, and external quantum efficiency.In this study, single-layer graphene and PbS QD composite was dispersed in hexane solution. (See Method section) The single-layer graphene and PbS QD composite was coated on a glass substrate treated with ultraviolet-ozone surface cleaning for 10 min. Figure 28.Figure For the quantitative examination of the graphene-PbS QD composite, energy dispersive spectroscopy (EDS) was employed. Table 29. Note that this increase of absorbance is not mainly induced by absorption of multiple layers of graphene because absorbance of graphene/PbS QD composite is smaller than that of PbS QDs alone in the wavelength range of shorter than 565 nm.  spectroscopies. Figure 30. The PL intensities of the graphene-PbS QD composites with 25% and 50% graphene were lesser by 24.3% and 37.2%, respectively, compared to that of the PbS QDs. The PL intensity represents the number of recombined carriers in the PbS QDs for a unit amount of QDs. These quenched PL intensities are attributed to the enhanced transfer of the photoinduced carriers between graphene and the PbS QDs, which minimizes the charge recombination rate. In addition, Fourier-transform infrared spectroscopy establishes that hexane solution and the glass substrate do not affect the optical properties of the PbS QDs and graphene flakes. . For graphene, three intensive Raman modes are observed at 1,344.8, 1601.3, and 2,701.8 cm−1 , corresponding to the D-band, G-band, and 2D-band, respectively31. In the Raman spectrum of the graphene-PbS QD composite, two Raman modes are observed at 140.3 and 280.8 cm−1, which are associated with the PbS QDs, whereas the Raman spectrum of the PbS QDs does not exhibit a Raman mode32. This is because the specific Raman mode embedded in the spectrum of the PbS QDs is enhanced, which is relevant to the photoinduced charge transfer between the Pbs QDs and graphene, as interpreted by SERS. To verify the enhanced Raman mode of the PbS QDs with graphene, micro-Raman spectroscopy was performed using a 3,000-groove grating for high-spectral resolution, as shown in Fig. −1 is a longitudinal optical (LO) phonon mode corresponding to the 1LO phonon mode of the PbS QD34. The Raman mode at 181.7 cm−1 is attributed to a surface phonon, whose intensity varies depending upon the QD size35. The peak at 140.3 cm−1 is not relevant to the PbS QD. Thus, it can be deduced that the Raman mode of PbS QDs in combination with graphene is enhanced by the photoinduced charge transfer between the two materials.Micro-Raman scattering analysis was performed to examine the photoinduced charge transfer between graphene and the PbS QDs, with a He–Ne laser operating at a wavelength of 632.8 nm. The Raman spectra of the PbS QDs, graphene-PbS QD composite, and glass substrate depicted in Fig. 2 substrate. For a robust metal pad, Au was deposited on the patterned sample using a thermal evaporator  laser diode. In the PD comprising graphene-PbS QD composite, five-times higher photocurrent, 22% shorter rise time, and 47% shorter decay time were observed, compared to that comprising PbS QDs alone. This establishes that the graphene-PbS QD composite has significant potential for application in ultrathin, flexible, high-performance NIR PDs.Single-layer graphene flakes  are fabricated using the modified Hummer’s method. The average diameter and thickness of these graphene flakes ranged between 0.4–0.5 μm and 0.6–1.2 nm, respectively. Single-layer graphene flakes were dispersed in hexane solution (2 mg/ml) through a sonication process for 10 min.37. Subsequently, post-treatment and purification were performed following a published method with some modifications38:All the manipulations for preparing the PbS QDs were performed using the standard Schlenk line technique. Oleic acid-capped PbS QDs (first exciton peak at 950 nm) were prepared as per a previously reported method2 substrate through conventional photolithography and thermal evaporation. A 300-nm thick Au layer was employed as the electrode. Ligand exchanges of the PbS QDs were realized using 1,2-ethanedithiol (EDT) to improve device carrier transportation.Interdigital electrodes were fabricated on an SiOThe absorption spectrum was obtained using a UV–Visible/NIR spectrophotometer (JASCO). PL spectroscopy was performed using a 30-cm monochromator and a charge-coupled device detector excited by a 355-nm diode-pumped solid-state laser. The micro-Raman spectrum was measured with a backscattering geometry using a He–Ne laser (633 nm) for excitation.Supplementary Information.


The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications. The lar.334 nm) . The pre.334 nm) . The mos.334 nm) , which c.334 nm) .+ and OH−. During the process, Li+ entered the layers of the graphite sheets to promote the exfoliation of graphene. OH− was then added to the surface of the graphene to increase its hydrophilicity and dispersion stability in aqueous media. This dispersion theory did not include any surfactants and the entire experimental process was simple, low-cost and environmental-friendly. However, the stable dispersion of the surfactant-free system of graphene in the dispersion was far from that of the surfactant system, and it does not have the potential for the large-scale preparation of graphene [+ salt surfactants have the best wettability for graphene, which can promote the aqueous dispersion of graphene. Therefore, Na+-containing anions and other types of surfactants were selected as dispersants  was purchased from Tsinglube Technology Co., Ltd. , the ionic liquid was obtained from Lanzhou Institute of Chemical Physics , Chinese Academy of Sciences and the other analytical grade reagents were purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd. .The main instruments used in the experiment include: scanning electron microscope (SEM), Carl Zeiss ; atomic force microscope , Oxford Instruments ; Raman, laser model: 532nm, XPOLORA PLUS, JY-HR800 ; Zetasizer Nano ZS .The expanded graphite, which was dried at 80 ± 0.5 °C for 24 h, and a dispersant were added to pure water and magnetically stirred at 60 ± 0.5 °C for 1 h. Subsequently, ultrasonic exfoliation was performed at 60 ± 2.5 °C for 8 h. The mass fraction of the expanded graphite accounts for 0.5 wt.% of the total system mass and that of the dispersant varies at 0.1, 0.3, 0.5 and 1 wt.% of the total system. Except for the NaOH dispersion system, the pH of all dispersant systems was 7.1 ± 0.15. The microscopic mechanism of the 0.5 wt. % dispersant system (SDBS: melamine = 1:1), which was used as a trial basis for the 0.1, 0.3 and 1 wt.% dispersant systems, is shown in The exfoliation grade determines the quality and application value of graphene  in liquid media. The Tyndall phenomenon is a common method for estimating the particle size of the solution in the liquid-phase system after exfoliation. This method relies on the size of the scattering effect of light when parallel light passes through the dispersed phase to evaluate the exfoliation size of graphene in the dispersion. The 0.5 wt.% dispersant system was tested by irradiating parallel light in S value ≤ 0.03). These findings are consistent with the findings of Majid et al. [The volume sedimentation method is one of the simplest and most convenient methods for detecting the stable dispersion of colloids. The smaller the volume ratio of the sediment in the dispersed phase, the higher the concentration of the graphene in the dispersion. The dispersion solution volume ratio is determined as d et al.  and Mated et al. , who repS < 0.05) of the mixed dispersant system (SDBS: melamine = 1:1) was superior to those of single dispersant systems, indicating that the synergistic effect of SDBS and melamine improves the dispersion stability of graphene in pure water. The most excellent dispersion stability was observed when the mass fraction of STAC and CMC in the single dispersant system was 0.3 wt.%. If the mass fraction of the dispersant is excessively high, the dispersant exhibits a micelle phenomenon and loses the ability to stabilize the dispersion. If the mass fraction is extremely low, the dispersion effect cannot be achieved. The solute concentration in each dispersant system was statistically measured in The mass fractions of (SDBS: melamine = 1:1) (PVP: melamine = 1:1) CMC, STAC, SLS and SDBS systems  were varied to further analyzed the graphene dispersion stability in Given the existence of the critical micelle concentrations of the surfactants , the best graphene dispersion effect appears near the micelle concentration. The mass fraction of the dispersants was extremely high due to the intermolecular similarity. The interaction force  shows thAfter the analysis, the chain cationic surfactant STAC was easily electrolyzed to form ammonium ions in the water, which promoted hydrogen bonding with the remaining oxygen-containing groups on the graphene surface after exfoliation . This boThe dispersion stabilities of 0.1 wt.% and 0.3 wt.% SDBS and 0.3 wt.% CMC systems were evident in In non-ionic surfactant systems, although PVP can significantly reduce the surface tension of aqueous dispersion systems, the graphene nanosheets in the water are only affected by the steric hindrance of PVP, which was smaller than the interlayers of the graphene sheets. The van der Waals force cannot promote the stable dispersion of graphene in water. The average zeta potential value was −72.03 mV  and 0.3 wt.% STAC systems in  as seen b,d. Wen The results of the Raman and AFM analyses indicate that the average numbers of graphene nanoflakes in the 0.1 wt.% (SDBS: melamine = 1:1) and 0.3 wt.% STAC systems are approximately 14 and 21, respectively, and a minimum of eight layers of graphene nanoflakes can be exfoliated out.2 hybrid-structured intact expanded graphite. The defect density of graphene in the 0.3 wt.% STAC system is the largest amongst all systems in the experiment (ID/IG = 0.66). The defects, which are generated in the ultrasonic exfoliation process, produce wrinkles. For instance, the point designated by ‘1’ in (1)The electrostatic repulsion force of the charged particles formed by the ionisation of the quaternary ammonium cationic surfactants in water was greater than the steric resistance generated by the non-ionic surfactants. The former also exerts a strong effect on the van der Waals force between the graphene sheets and enhances the exfoliation ability and dispersion stability. The 0.3 wt.% STAC dispersant system exhibited excellent exfoliation ability and dispersion stability and can exfoliate graphene nanosheets with less than eight layers (the average number of layers was less than 14 layers). In addition, the graphene can be stably dispersed in water and no settlement occurred for 13 days.(2)The mixed system of cyclic anionic surfactants and heterocyclic non-ionic surfactants exerts a complex dispersion effect on graphene through electrostatic repulsion and π–π action, which was more stable than that of a single dispersant system. The graphene in the 0.1 wt.% (SDBS: melamine = 1:1) system can remain stable in the storage for 22 days without sedimentation.This study explored the use of a suitable stripping agent in pure water, based on surface energy theory, to overcome the van der Waals force between graphene sheets and prepare graphene. The exfoliation agents must be hydrophilic, heterocyclic and easy to combine with graphene. The graphene surface interacts with a dispersant to prepare few layers of uniformly dispersed aqueous graphene dispersion. The following conclusions were obtained after the experiments:This study used green dispersant to prepare a few layers of stable graphene dispersion in an aqueous system, which is of great significance for the large-scale preparation of such dispersions in practical industrial applications.


ZnO nanoparticles were synthesized by pulsed laser fragmentation in liquid to attain a simple, efficient, ligand-free method for nanoparticle fabrication. By combining simple fabrication processes with a promising device architecture, highly sensitive ZnO nanoparticle/graphene UV photodetectors were successfully demonstrated.By combining the enhanced photosensitive properties of zinc oxide nanoparticles and the excellent transport characteristics of graphene, UV-sensitive, solar-blind hybrid optoelectronic devices have been demonstrated. These hybrid devices offer high responsivity and gain, making them well suited for photodetector applications. Here, we report a hybrid ZnO nanoparticle/graphene phototransistor that exhibits a responsivity up to 4 × 10 The advantages of graphene in sensor applications are numerous, including high mobility >104 cm V1s−1 [22 V1s−1) , excelle2 V1s−1) ,4. While2 V1s−1) ,6, photo2 V1s−1) . Nonethe2 V1s−1) . These p2 V1s−1) , and Ti2etection ). 2 V−1s−1 at room temperature) [Because of its wide band gap (~3.3 eV) and high exciton binding energy (~60 meV), zinc oxide (ZnO) is a promising candidate for ultraviolet (UV)-sensitive hybrid photodetectors . In addierature) , its comerature) ,13,14,15erature) ,17,18,19erature) ,21,22,23erature) . At thisMany different techniques have been utilized to fabricate ZnO nanostructures for hybrid graphene photodetector applications, such as hydrolysis methods for nanoparticle fabrication  and hydrHere, we have demonstrated PLFL for the synthesis of ZnO nanoparticles with a bimodal size distribution (~18 nm and 46 nm). These nanoparticles were integrated into graphene-based hybrid phototransistors, which were then characterized to determine the optical and electrical performance, including wavelength selectivity and responsivity. 2 on the backside of the Si wafer was laser-micromachined to expose the highly conductive Si for device back-gating. Graphene on Cu foils  were spin-coated with poly resulting in a ~600 nm thick layer. The foils were then baked at 100 °C in air for 2 min on a hot plate. The graphene on the backside of the Cu foil was etched by floating the foil on a 10% HNO3 solution for 3 min followed by rinsing with deionized water. The Cu was remove by etching in a ferric chloride solution for 2 h. The remaining PMMA/graphene film was then floated on a dilute 2% HCl solution to remove any particulates introduced during the Cu etching process. The film was rinsed in deionized water before wet transfer. The PMMA/graphene film was then transferred onto the SiO2/Si substrate and allowed to air dry. A small droplet of PMMA was drop casted onto the surface of the PMMA/graphene to encourage flattening of the film, followed by air drying. The PMMA was then removed with acetone, followed by rinsing in isopropanol and then water. After processing the graphene, source and drain electrodes (5 nm Ti/150 nm Au) were deposited via electron beam evaporation using a shadow mask that was laser-micromachined from a thin (75 µm) polyetherimide sheet. After electrode deposition, isolation lines were laser-micromachined around each device on the chip, yielding active device areas of 2 mm × 1 mm.Phototransistor devices were fabricated using standard wet transfer ,36,37,38ZnO nanoparticles were produced using pulsed laser fragmentation in liquid (PLFL) . ZnO powThe optical properties of the fabricated graphene transistors before nanoparticle deposition were characterized via Raman spectroscopy  which revealed the quality of the graphene layer. Optoelectronic characterization was performed using UV illumination that was fiber coupled from a monochromator into a 10× objective, mounted on a probe station. The light intensity was adjusted by a computer-controlled attenuator, maintaining a uniform spot size of ~2 mm for all experiments. Electrical characterization, including the drain and gate sweeps as well as temporal measurements, was conducted using a semiconductor characterization system .Because of the unique properties afforded by nanoscale materials, different methods have been developed for simple and efficient fabrication, including wet chemical synthesis , sol gelThe mechanisms responsible for nanoparticle formation via PLFL and the effect that initial size, concentration and material have on the resulting particle size have been studied extensively ,32,33,34There are several advantages to this technique, including simple experimental set-up and the ability to maintain complex stoichiometries with narrow particle size distributions . The mecsmall/rlarge ≈ 0.42) is potentially advantageous for the final device design because a more efficient packing factor becomes possible compared to the unimodal particle distribution. For bimodal spheres, ideal packing can be efficiently achieved up to a particle size ratio of ~0.41 [Both the original ZnO powder particles before PLFL and the resulting smaller nanoparticles after PLFL can be seen in of ~0.41 , where tof ~0.41 . To give insight into the quality and defect content of the generated nanoparticles, photoluminescence measurements (λ = 343 nm) were conducted. The photoluminescence of ZnO nanoparticles has been studied extensively and typically reveals two distinct emission bands, one in the UV and one in the visible spectrum. The emission peak observed in the UV region is a result of near-band-edge emission which is mediated through exciton–exciton interactions. As the particle size decreases, the fluorescence is blue-shifted due to an increase in transition energy ,56. The The as-received ZnO powders, which can be seen in In addition to the insight into the quality and defect density induced in the nanoparticles during laser processing, the optical transmission spectra of the ZnO nanoparticle solutions were collected to help understand the effect of laser-processing on the particles optical bandgap, which is shown in The mechanism of photoconduction in ZnO nanoparticle/graphene phototransistors is schematically illustrated in 2 up to 1.4 mW/cm2. Drain current as a function of drain voltage can be seen in To understand the photoresponse of the devices, electrical transport properties were measured with UV illumination (λ = 365 nm), from 34 µW/cmThe responsivity and gain as a function of incident UV power were measured to determine the performance of the phototransistors. The responsivity of the devices is the ratio of the measured photocurrent to the UV illumination, where:phI and darkI are the induced photocurrent under UV illumination and the dark current, respectively. The responsivity at a drain current of VD = 5 V with no gate voltage applied can be seen in 4 AW−1, where experimentally at P = 34 µW/cm2, the responsivity is measured to be 2 × 103 AW−1. The photoconductive gain G can be described as the ratio between the number of electrons collected per unit time and the number of absorbed photons per unit time [h is Planck’s constant, c is the speed of light, e is electron charge, and λ is incident wavelength. By fitting the available data, the maximum gain achieved as P approaches zero is Gmax ≈ 1.3 × 105 at VD = 5 V with no applied gate voltage. The gain of the ZnO nanoparticle/graphene phototransistor is a function of the applied optical intensity. The number of electron-hole pairs generated is directly related to the optical intensity applied, where with a higher intensity, more hole trap states are filled at the surface eventually reaching a surface saturation state. Once this occurs, the electron-hole pairs generated do not aid in charge transfer into the graphene layer, thus limiting the efficiency of the hybrid device [Here, nit time ,19:(2)G=d device .In addition to responsivity and gain, the wavelength selectivity of the photodetector is critical because it determines the spectral range. The spectral dependence of responsivity for ZnO nanoparticle/graphene devices can be seen in D = 1 V, with no applied gate voltage (VG = 0 V). The graphene-only phototransistors show no photoresponse when illuminated at 365 µW/cm2 over a time scale of several hundred seconds, which can be seen in 2 can also be seen in 2 can be seen in In order to understand the time-varying behavior of the phototransistors, the photocurrent response was measured as a function of time as the devices were exposed to UV illumination and then subsequently turned off. These temporal measurements were conducted at a drain voltage of VBoth the responsivity and the response times of these ZnO nanoparticle/graphene photodetectors can be optimized by adjusting several experimental parameters. It is well known that the nanoparticle layer is strongly dependent on particle packing in its ability to absorb light and efficiently transfer electrons into the underlying graphene layer . Thus, f4 AW−1 with a maximum gain of 1.3 × 105 and superior spectral selectivity below 400 nm, making them ideal solar-blind UV photodetectors. We have demonstrated the use of pulsed laser fragmentation in liquid (PLFL) as a simple, ligand-free alternative to traditional nanoparticle synthesis techniques for the fabrication of ZnO nanoparticles. Hybrid ZnO nanoparticle/graphene phototransistors were demonstrated, exhibiting a responsivity of up to 4 × 10


Employing density functional theory calculations, we obtain the possibility of fine-tuning the bandgap in graphene deposited on the hexagonal boron nitride and graphitic carbon nitride substrates. We found that the graphene sheet located on these substrates possesses the semiconducting gap, and uniform biaxial mechanical deformation could provide its smooth fitting. Moreover, mechanical tension offers the ability to control the Dirac velocity in deposited graphene. We analyze the resonant scattering of charge carriers in states with zero total angular momentum using the effective two-dimensional radial Dirac equation. In particular, the dependence of the critical impurity charge on the uniform deformation of graphene on the boron nitride substrate is shown. It turned out that, under uniform stretching/compression, the critical charge decreases/increases monotonically. The elastic scattering phases of a hole by a supercritical impurity are calculated. It is found that the model of a uniform charge distribution over the small radius sphere gives sharper resonance when compared to the case of the ball of the same radius. Overall, resonant scattering by the impurity with the nearly critical charge is similar to the scattering by the potential with a low-permeable barrier in nonrelativistic quantum theory. Unfortu2V−1s−1 ,9,10, th2V−1s−1 ,12, mech2V−1s−1 ,14, and 2V−1s−1 ,17,18,192V−1s−1  for deta2V−1s−1 . The mec2V−1s−1 ,24,25,262V−1s−1 ,28 proviIn addition, graphene with a gap in the electronic spectrum in the presence of a multiple-charge impurity is of particular interest. Such a system is similar to the relativistic Coulomb problem . In the symmetry . In the symmetry .Since graphene is an almost ideal planar system, the orbital angular momentum may be quantized fractionally ,33. In aues only . Therefoincluded . TherefoIt has long been known that pure Coulomb potential is an excessive idealization in the three-dimensional problem, which . The emlectrons ,49). In n energy . TherefohBN) and graphitic carbon nitride (gC3N4) substrates under the mechanical biaxial strain in the frame of density functional theory, supplemented by the van der Waals dispersion corrections. It was obtained that the weak van der Waals interlayer interactions, alongside the uniform strain of the graphene sheet on the substrate, leads to the considerable bandgap. Moreover, the value of bandgap increases monotonically with an increasing stretch and vice versa. Note that, due to the remarkable mechanical properties, some substrates allow reversible stretching of graphene up to 30% [hBN or gC3N4 substrate has a crucial role since free-standing graphene does not have an energy gap under uniform mechanical stretching. We discuss a method to smoothly change the electronic properties of graphene, which has a gap in the electronic spectrum by mechanical stretching or compression, which includes tuning the critical value In the presented study, we analyze the electronic behavior of monolayer graphene on the hexagonal boron nitride  and its implementation in the program Quantum ESPRESSO ver. 6.5 ,53. We cesh grid  is used.smearing  techniqusmearing  was appl2 and SiC, as well as more complex systems such as Te2Mo, hBN/Ni(111), or C3B/C3N. At the level of theory used, we obtained that, only quasi-2D hexagonal boron nitride (hBN) and graphitic carbon nitride (gC3N4), opened the band gap in graphene. In all other cases, the “Dirac cone” on the electronic band structure conserved its original shape, and graphene remained a gapless semiconductor, or the Fermi level shifted to the conduction band. Thus, graphene began to exhibit a metallic nature.First, we attempted to select such substrates that would facilitate the opening of an energy gap in graphene without imposing additional conditions, such as an external electric field or mechanical stresses. We examined about fifty different substrates, including the common SiO2 and SiC substrates [hBN and gC3N4 substrates. Peculiarities of the interlayer interactions between the graphene and these substrates lead to the “pure gap” that is characteristic of the narrow-gap semiconductor.Nevertheless, some previous studies revealed that the external electric field could effectively tune the energy gap in graphene on the SiObstrates ,62,63 byhBN and gC3N4 substrates by the hexagonal supercells. In the case of the hBN substrate, the supercell contains eight carbon atoms, and, in the case of the gC3N4 substrate, the graphene sheet inside the supercell is represented by 18 carbon atoms VC. Qualitferences ,42 with +e–-loop. Therefore, the impurity charge screening mechanism specified in Reference [. This moduction , when a eference , accordieference , cannot eference . Therefoperiment .All these conclusions remain valid for the gapless radial Dirac equation in the presence of a supercharged impurity the work , which seference ). Howeve ε¯=−ε>0 .(7)δ0. Therefeference .n-th level with the total angular momentum The critical charge Here, At spectrum , and theollowing ,39.(9)Sg theory , and theThe poles of the scattering matrix The solutions give both the positions Near the top of the valence band As in the nonrelativistic theory of scattering, see Chapter 13 in Reference , quasistThe position of the resonance eference ).+e–-pairs, and the width In the review , resonaneference . Howevermentum J . In the mentum J  for the hBN and gC3N4 substrates by optimizing the supercell parameters as well as atomic positions inside the supercell. For considered samples . In the 3.325 Å ). It shotal data ,79. All hBN and gC3N4 substrates  stretching and shearing as well as inhomogeneous deformation opens the energy gap in free-standing graphene [hBN or gC3N4 substrate makes it possible to tune the bandgap in graphene. In this case, stretching leads to an increase of the gap value, and compression leads to its decrease. For example, uniform stretching of the graphene sheet on the hBN substrate results in the gap of 36.8 meV, and, on the gC3N4 substrate, results in the gap of 36.9 meV (see kBT ~26 meV), which indicates the possibility of maintaining the energy gap at normal conditions. Note that, in real straintronic applications, the limits of strain transfer between graphene and substrate should be considered since biaxial deformation is not always completely transferred from the substrate to graphene [hBN and gC3N4 substrates , where eference  and FiguhBN) and graphitic carbon nitride (gC3N4) substrates, the behavior of the electronic properties of deposited graphene is fundamentally different from the free-standing one. In this case, graphene has an energy gap, which makes it possible to classify it as a narrow-gap semiconductor, whereas the uniform stretching increases the value of the gap. These findings can help to overcome the main barrier to using graphene as an element of nano-electronic and straintronic devices. Moreover, uniform stretching affects the Dirac velocity in graphene on the substrate. Dirac velocity is linear with mechanical tension. It increases with uniform compression and decreases with uniform stretching. The Dirac point, near which the dispersion law is similar to the Einstein dependence of the particle energy on its momentum, corresponds, as usual, to the corner of the Brillouin zone for graphene deposited on the hBN substrate, while, for the gC3N4 substrate, it is located in the center of the zone. However, in both cases, the dynamics of charge carriers near the Dirac points is described by the effective two-dimensional radial Dirac equation for states with the total angular momentum In the presented study, we tried to answer the question of how the choice of the substrate and uniform mechanical stresses can affect the electronic properties in graphene, and, in particular, opens the energy gap and contributes to its fine-tuning. It was found that, when choosing the hexagonal boron nitride (The dependences of the critical charges In addition, the resonant scattering of the holes by the Coulomb potential modified at small distances in states with +e–-pairs exist in the supercritical Coulomb problem. However, calculation of the effective dielectric constant of the considered systems is necessary for the direct comparison of experimental data on the spectra of current-voltage characteristics with the theoretical predictions.Based on such experimental data, it would be possible to conclude whether half-integer orbital angular momenta are realized in the two-dimensional considered systems. In addition, the effective two-dimensional radial Dirac equation with the integer total angular momenta


An acoustic plasmon mode in a graphene-dielectric-metal structure has recently been spotlighted as a superior platform for strong light-matter interaction. It originates from the coupling of graphene plasmon with its mirror image and exhibits the largest field confinement in the limit of a sub-nm-thick dielectric. Although recently detected in the far-field regime, optical near-fields of this mode are yet to be observed and characterized. Here, we demonstrate a direct optical probing of the plasmonic fields reflected by the edges of graphene via near-field scattering microscope, revealing a relatively small propagation loss of the mid-infrared acoustic plasmons in our devices that allows for their real-space mapping at ambient conditions even with unprotected, large-area graphene grown by chemical vapor deposition. We show an acoustic plasmon mode that is twice as confined and has 1.4 times higher figure of merit in terms of the normalized propagation length compared to the graphene surface plasmon under similar conditions. We also investigate the behavior of the acoustic graphene plasmons in a periodic array of gold nanoribbons. Our results highlight the promise of acoustic plasmons for graphene-based optoelectronics and sensing applications. Acoustic graphene plasmons are superior to the graphene surface plasmons in field confinement and normalized propagation length, thus promising for applications. Here, the authors report near-field imaging of acoustic plasmons in high-quality CVD graphene, measure the AGP dispersion and propagation loss, and investigate their behavior in a periodic structure. This mode is supported by a structure comprising of a metal, a dielectric spacer, and a graphene layer, where the image charges in the metal effectively “mirror” the charge density oscillations in the doped graphene layer. The acoustic graphene plasmon (AGP) supported by the structure is mostly confined in the dielectric spacer and does not experience cutoff as the spacer thickness decreases8, thus resembling the fundamental plasmonic mode of a narrow metal gap. The AGP excited at the important MIR frequencies10 does not exhibit significant loss and is detectable even when the spacer is reduced to a single atomic layer of hexagonal boron nitride5. Inside such a narrow dielectric spacer, the AGP wavevector can be about two orders of magnitude larger than that of free space light, which grants access to quantum and non-local phenomena in graphene12, and allows for the AGP localization in nanostructures13 with a stunning mode volume confinement factor4 of ~1010. This ultimate capability to compress MIR light outperforms that of other polaritonic species in van der Waals materials9, including graphene surface plasmon (GSP)15, and is similar to the case of image phonon-polaritons in boron nitride16. For that reason, AGP is promising for applications that require strong light–matter interaction such as molecular sensing20, polaritonic dispersion engineering in van der Waals crystals22, and dynamic light manipulation by graphene-based active metasurfaces26.An acoustic plasmon mode supported by a system of two graphene sheets6. However, the near-field optical probing of AGP, which provides detailed microscopic information about the mode, is yet to be demonstrated.The key advantage of the AGP is its confinement within the dielectric spacer, in contrast to the GSP bound to the graphene layer. Therefore, ohmic losses in graphene are expected to hinder the AGP propagation to a lesser extent compared to GSP. On the other hand, the larger AGP wavevector requires an intermediary structure to alleviate the momentum mismatch under the far-field excitation. So far, structures containing an array of metallic elements have been used to couple far-field radiation to the AGP modeIn this work, we employ a scattering-type scanning near-field optical microscope (s-SNOM) based on an atomic force microscope (AFM) for real-space mapping and analysis of MIR AGP. We directly measure the AGP dispersion, evaluate the mode propagation loss, and investigate its behavior in a periodic structure designed for the far-field coupling. Most importantly, our results reveal a relatively low propagation loss of infrared AGP even when unprotected, CVD-grown, large-area graphene is used at ambient conditions, suggesting a practical route to construct large-area graphene-based optoelectronic devices.Ez, penetrates into the free space above the structure, and hence, can couple to the AFM tip of the s-SNOM effectively acting as a z-oriented electric dipole30  for the structure of interest. Figure De calculated for the range of MIR frequencies and spacer thicknesses, assuming EF = –0.5 eV. Considering that the average tip height above the sample is 40–80 nm, which is approximately equal to the tapping amplitude of the tip32, the most favorable experimental conditions are expected in the frequency window of 1000–1300 cm–1 (where Al2O3 absorption stays sufficiently low), while t > 10 nm.In order to estimate the optimal experimental conditions for the near-field AGP probing by s-SNOM, it is instructive to calculate 2O3 films were fabricated using the template-stripping method34, allowing a sub-nm roughness of substrate surface even when the gold film is patterned6 , wet-transferred on top of the alumina-coated gold substrates, and chemically doped (see Methods section for details).Substrates with gold and Al2O3 substrate reveals an abundance of μm-long edges of monocrystalline areas with AGP interference fringes formed due to its reflection from the graphene termination  is proportional to the amplitude of the z-component of the electric field under the tip30, s ∝ |Ez |, thus it can be numerically calculated by full-wave simulations in a quasi-static approximation36 (see Supplementary Information section 39) corresponds to EF = –0.51 eV and carrier mobility μ = 2000 cm2/V s, consistent with a high-quality CVD graphene7. The roughness-mediated scattering of AGP is neglected in the full-wave simulations. Additional simulations support this assumption, considering the measured root-mean-square (RMS) roughness of 0.5 nm at gold and alumina surfaces , the effective index of the AGP is qAGP = kAGP/k0 = 39.06 + 2.92i (55.96 + 4.17i), where kAGP is the propagation constant of the AGP, and k0 = 2π/λ0 is that of free space light. To quantify the dissipation of plasmonic modes, we use the figure of merit (FOM) defined as the ratio of the plasmon propagation length Lp to its wavelength λp: Lp/λp = lp = Re{kp}/(2πIm{kp}), where lp is the normalized plasmon propagation length in optical cycles. It can be noted that the FOM of AGP lAGP = 2.12 (in both samples) is almost twice larger than the reported value for MIR GSP in exfoliated graphene on an SiO2 substrate41lGSP = 1.18. An analytical solution for GSP in the same graphene on a thick Al2O3 substrate provides qGSP = 23.41 + 2.47i (24.43 + 2.62i), and thus, an expected lGSP ≈ 1.5 in both cases. Therefore, our near-field measurements indicate that, while the observed AGP is ×1.7 (×2.3) times more compressed in terms of the wavenumber, its FOM is 1.4 times higher than that of the GSP in the same graphene sheet. The better FOM of AGP has been predicted8 due to the larger compression factor of the plasmonic wavelength compared to the decrease in the propagation distance. However, dispersion analysis also indicates that the AGP is in general less sensitive to the loss in graphene if considered in local limit42  is shown in Fig. EF = –0.46 eV. The near-field data are obtained from a series of measurements over the same sample area, which makes it possible to compare the spectral dependency of the near-field contrast32sref and φref are the amplitude and phase of the near-field signal over the graphene-free area, respectively. Figure –1 to 46 at 1260 cm–1. Furthermore, the spectral dependency of De , which can provide coupling efficiency exceeding 90% when combined with an optical cavityyer Fig. . Due to λAGP does not depend on the geometry of the structure, thus EF in graphene can be fitted using the AGP dispersion obtained from the near-field imaging (see Supplementary Information section w = 240 nm). Dispersion fit to λAGP at different frequencies  is calculated using a simple model of a planar AGP waveguide with an infinite array of nanogaps, treated as partially reflective “mirrors” with complex transmission and reflection coefficients. Then, the dispersion solution is reduced to the eigenvalue problem for a lossy Bloch state in a 1D periodic medium43. The periodicity of the structure does not lead to the opening of a bandgap or flattening of bands at the center or edges of the Brillouin zone, possibly due to the lossy nature of plasmonic modes  and phase φ obtained at ω = 1200 cm–1 in the sample with P = 230 nm and EF = –0.62 eV; λAGP ≈ 228 nm, so that βAGP = 2π/P. The measured and the numerically calculated profiles of s ∝ |Ez | and φ ∝ arg{Ez} across the nanoribbons  of 30 μm thickness was cut into ribbons and placed inside a CVD quartz tube, stretching between the hottest and the coldest zones inside the tube. Then, cycle annealing was introduced with a thermal gradient along the ribbons. The Cu foil was annealed at 1040 °C for two hours in an atmosphere of 40 sccm hydrogen and 1000 sccm argon gases. Then temperature was decreased to 700 °C during 30 min, and then increased up to 1040 °C during the same time. This process was repeated for four cycles in total, after which we opened the chamber to cool naturally.The gold/alumina layers on a Si substrate were prepared with template stripping as described in Ref. 4, H2, Ar) for graphene synthesis. The graphene flake size is controlled by growth conditions such as the ratio between CH4 and H2 concentrations, the total amount of CH4, and the growth time. Here, we purged 5 sccm of CH4, 30 sccm of H2, and 1000 sccm of Ar for a full coverage of Cu by graphene. Then, Cu ribbons were cut and graphene was wet-transferred from Cu onto the prepared samples, and chemically doped by vapors of HNO3 acid by placing the devices over the acid for 4 min at room temperature in a fume hood.For growing the high-quality graphene, we used low-concentration methane (0.1% in argon) in four stages: ramping, annealing, growth, and cooling. First, the temperature was increased up to 1060 °C during one hour and then kept stable for one hour for annealing, which is necessary for removing organic molecules and enlarging the Cu grain size. Then, we used a mix of three gases , was used for near-field imaging. s-SNOM in AFM tapping mode was used to perform surface scans with 5 nm step and tip oscillation amplitude of ≈70 nm.The near-field scans were obtained by commercial s-SNOM (Neaspec GmbH) coupled with a tunable quantum cascade laser , which illuminates the Pt-coated AFM tip . The background-free interferometric signalα = 0.2 nm, having the effective relative dielectric permittivity εr is the background relative permittivity and σ is the optical conductivity of graphene. Dielectric permittivity of gold was taken from Ref. 45, and that of thin film Al2O3 was taken from Ref. 46. See Supplementary Information for details on full-wave simulations.Commercial finite element method software (COMSOL Multiphysics) was used for full-wave simulations. In our 2D simulations, graphene is implemented as a thin film of finite thickness Supplementary InformationPeer Review File


Mandibular condylar osteochondroma (OC) could lead to facial morphologic and functional disturbances, such as facial asymmetry, malocclusion, and temporomandibular joint dysfunction. However, after condylar OC resection, the inaccurate reposition of the neocondyle still needs to be solved. The purpose of this study was to explore the feasibility of the condylar osteotomy and repositioning guide to reposition the neocondyle in the treatment of patients with severe deformity secondary to condylar OC.Three patients with severe deformity secondary to OC of the mandibular condyle were enrolled in this study. With the aid of condylar osteotomy and repositioning guide, condylar OC resection and repositioning were carried out, and the accuracy and stability of these guides were evaluated. All patients healed uneventfully, and no facial nerve injury and condylar ankylosis occurred. Compared with the computerized tomography scans in centric relation before surgery and 3 days after surgery, the results showed that the facial symmetry was greatly improved in all the patients. Also, after the superimposition of the condylar segments before surgery and 3 days after surgery, the postoperative reconstructed condyles had a high degree of similarity to the reconstruction of the virtual surgical planning. Observed from the sagittal and coronal directions, the measurements of condylar positions were very close to those of virtual surgical planning. Moreover, it also showed stable results after a 1-year follow-up.For patients with severe deformity secondary to condylar OC, condylar osteotomy, and repositioning guide was expected to provide a new option for the improvement of facial symmetry and occlusal relationship. Osteochondroma (OC), a kind of osteocartilaginous exostosis, is considered as the common tumor of long bones, comprising approximately 35 to 50% of all benign bone tumors , 2. The In order to improve the aesthetics and function, different treatment methods are selected according to the degree of dental and maxillofacial deformities secondary to condylar OC. At present, condylar OC resection combined with orthognathic surgery, including mandibular sagittal split ramus osteotomies (SSRO), Le Fort I maxillary osteotomies, and genioplasties is the most frequently used treatment methods . For conFor patients with more severe maxillary and mandibular deviation and worse malocclusion, intraoral condylectomy and contralateral SSRO could not be used to place the residual neocondyle into the fossa to restore the occlusal relationship and TMJ function. To correct the deformities and improve the function, bilateral SSRO must be performed intraorally. Unfortunately, during the follow-up process, we found that this technique may cause ischemic absorption or necrosis of the proximal bone segments of the condylectomy side due to excessive periosteum decollement.Considering the problems mentioned above, for patients with severe asymmetric deformities secondary to condylar OC, we chose a preauricular incision to remove the condylar OC and then performed orthognathic surgery to avoid this situation. Different from the conventional preauricular incision, we innovatively applied the condyle osteotomy and repositioning guides to ensure the accurate position of residual neocondyle with respect to the fossa. Also, the preliminary evaluation was made to investigate its accuracy and stability. This approach could provide a new option for the treatment of severe asymmetric deformities secondary to condylar OC.Three patients with condylar OC accompanying dental maxillofacial deformities were enrolled in this preliminary study at the Department of Oral and Craniomaxillofacial Surgery of Shanghai Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine. Following clinical and radiographic examinations, the patients had no other craniomaxillofacial skeletal syndrome, traumas, or previous orthognathic surgery Fig. . All thePreoperatively, the high-resolution computed tomography (CT) of the craniomaxillofacial skeleton was taken by a GE Medical System LightSpeed CT scanner . All two-dimensional CT images were saved in digital imaging and communications in medicine (DICOM) format and imported into SurgiCase CMF 5.0  for the reconstruction of three-dimensional virtual models of the craniomaxillofacial skeleton. After considering the chief complaint, virtual surgical planning and simulation were created by the surgical team and 3D design engineer according to the clinical physical examinations and three-dimensional malformation analyses. The osteotomies and condylar OC resection were performed virtually by the surgeons so as to achieve an optimal aesthetic appearance. Preoperative virtual condyle osteotomy and repositioning guides were used to ensure accurate positioning of the neocondyle Fig. a–c. The The data of craniomaxillofacial skeleton bone were imported into Unigraphics NX 7.5  for designing of the condylar and other templates. Using the pre-simulated data, skull, maxillary and mandibular stereomodels, condylar osteotomy guide, condylar repositioning guides, and maxillary osteotomy and repositioning guides were manufactured. Condylar guides included condylar osteotomy guide and condylar repositioning guide. The condylar osteotomy guide embraced the neck of the condyle. The position of the condylar osteotomy guide was designed according to the size and position of condylar OC to ensure complete tumor resection. Under the guidance of the osteotomy guide, the osteotomy line was exactly the same as the virtual design. After condylar OC resection, the remaining three holes were placed on the residual bone for the use of a zygomatic-borne condylar repositioning guide. The condylar repositioning guide was divided into two parts: nail hole positioning guide at the root of the zygomatic arch and the zygomatic-borne condylar repositioning guide. The nail hole positioning guide was embraced at the root of the zygomatic arch according to pre-determined virtual design, and the position was unique to ensure the accuracy of the following condylar repositioning. Two holes were also placed on the zygomatic arch for the use of a zygomatic-borne condylar repositioning guide. The zygomatic-borne condylar repositioning guide was fixed on the stationary zygomatic bone. Also, the neocondyle was repositioned using the remaining three holes on the neck of the condyle and two holes on the root of the zygomatic arch. The five holes for fixation screws were carefully placed to avoid damaging the essential tissues and organs while fixing the screws. The zygomatic-borne condylar repositioning guide helped the surgeons to determine the unique optimal site quickly and accurately.The mandible is unstable due to the presence of condylar OC. Hence, the movement of the maxilla was controlled using maxillary osteotomy and repositioning guides to ensure the stability and accuracy of operation. All the guides were made using the three-dimensional printing technique before the operation, and all were tried on the three-dimensional skull, maxillary and mandibular stereomodels to ensure that the guides were placed smoothly Fig. d–f. AfteThe surgery was performed by one team. After adequate exposure of the condylar OC and the neck of the condyle, the articular disc was peeled and perserved intactly without damaging the peripheral anatomic structures. Then, the condylar osteotomy guide was secured to the neck of condyle through designed holes. During the operation, special care was taken to protect the important surrounding tissues, including facial nerve. The osteotomies were performed by referring to the cutting slots to make the condylar OC resection as effectively as in virtual planning Fig. g. After The zygomatic-borne condylar repositioning guide was placed on the bone of the zygomatic arch and the neck of condyle along the holes left by the osteotomy guide and the nail hole positioning guide Fig. i. The fiDue to the instability of condyle, the maxillary movement was determined using 3D printed osteotomy and repositioning guides, after which the surgeon performed BSSRO and repositioned the mandibular segment in the traditional manner to correct the facial asymmetry.A craniomaxillofacial CT scan was taken for each patient at 3 days (T1) and 1 year (T2) postoperatively. The accuracy of the condyle position was assessed by comparing the actual postoperative operation to the virtual planned one (T0). Both postoperative and planned CT data were imported into SurgiCase CMF 5.0, and the deviations were measured by Geomagic Studio 2013 software. Deviations were defined using the following indicators: (1) 3D deviation of the osteotomy, (2) 3D deviation of the condylar segments at 3 days postoperatively. In order to quantitatively compare the accuracy, the following measurements were recorded from the two-dimensional CT images of T0 and T1. For the coronal image, the medial joint space (MJS) and lateral joint space (LJS) were measured from the most prominent medial and lateral condylar points to the glenoid fossa. For the sagittal image, the anterior joint space (AJS), superior joint space (SJS), and posterior joint space (PJS) were measured from the most prominent anterior, posterior, and superior condylar points to the glenoid fossa. The linear measurements of the affected joint spaces in the actual postoperative and virtual planned models were assessed and compared with each other.To observe the stability and accuracy of the condyle repositioning guides, the postoperative CT data (T2) and 3D deviation of the condylar segments were obtained at 1 year postoperatively. The two-dimensional CT images were also acquired to compare the relevant linear indicators mentioned above. The functional and esthetic outcomes were also assessed based on the postoperative dental occlusion, images and clinical examination.The new computer-assisted surgery was performed on three consecutive patients  who required condylar OC resection and orthognathic surgery. The articular discs of the patients in our study were intact with no displacement, rupture, or perforation through observing TMJ MRI before surgery (Additional file After the superimposition of the condylar segments of T0 and T1, the postoperative reconstructed condyles had a high degree of similarity to the reconstruction of the virtual surgical planning Fig. . The 3D To evaluate the stability of condylar position with condylar repositioning guides, the skull and condylar segments were compared with the preoperative virtual ones 1 year after surgery Fig. . The 3D The complications of condylar OC vary with the size of the tumor and its main growth direction , 13. TheCondylectomy or accompanying joint sacrifice and subsequent condylar reconstruction via extraoral incision have been reported in many studies –21. Yet,To achieve the goals mentioned above, individual surgical planning is indispensable. Computed tomography and computer-assisted design could be used to diagnose the lesion, to perform surgical simulation, and to evaluate the accuracy of the technology. With the aid of an endoscope, the condylar OC could be exposed and resected via an intraoral approach , 25. RemIn view of these complications, for patients with severe deformity, the preauricular incision, condylar OC resection, and BSSRO via intraoral incision are necessary. Besides these approaches, maxillary Le Fort I osteotomy or genioplasty or lower border osteotomy might be required in different situations to achieve the goal of correcting deformities and malocclusion . These sIn the present study, we presented a novel condylar osteotomy guide and condylar repositioning guide to solve these problems. In order to overcome the instability of the mandible, maxillary 3D-printed osteotomy and repositioning guides were also simultaneously used to perform orthognathic surgery. Our study demonstrated that this technique could be used to ensure the correct positioning of the neocondyle into fossa after condylar OC resection. The postoperative follow-up results have also shown that the technique could provide clinically acceptable accuracy and stability in repositioning the neocondyle. These guides were designed and made using the CAD/CAM technique based on three-dimensional planning. The condylar osteotomy guide in our surgery could completely guide the condylar OC resection and reduce the additional surgical time and damage caused by repeated grinding. The condylar repositioning guide placed on the predrilled holes of the osteotomy guide could be used for the optimal positioning of the neocondyle with respect to the fossa. The newly designed guides were placed on the fixed zygomatic arch, which eliminated the potential errors caused by the movement of the maxilla or mandible during surgery. Preoperative virtual planning decreased intraoperative changes to ensure the optimal position relationship between neocondyle and fossa and avoid damage that could be caused by anatomical occurrences that were not considered preoperatively. Superimposition of the virtual segments and the actual segments after computer-assisted surgery showed that the mean 3D deviation of the condylar osteotomy guide between T0 and T1 was 0.41 mm; furthermore, the mean 3D deviation of condylar repositioning guide between T0 and T1 was 0.42 mm. The follow-up results demonstrated that the mean 3D deviation of the condylar repositioning guide between T1 and T2 was 0.81 mm. Thus, there is a high degree of similarity between the reconstructed condylar segments and the virtual planned ones. To further evaluate the accuracy and stability of this novel condylar repositioning guide, the distances between the most prominent points to the glenoid fossa in the coronal and sagittal CT images were measured. The results showed that the data of T1 were very close to that of T0 observed from the sagittal and coronal directions. However, compared with the phase of T0 and T1, the condylar position in all dimensions of T2 showed some alterations. However, the facial symmetry and occlusion relationship did not significantly change in any of the patients. It is known that the position and shape of condyle tend to gradually change after surgery . For theThe approach presented in the current study showed certain advantages. First, for patients with severe deformities secondary to condylar OC, the most significant advantage was the use of condylar repositioning guide, which could accurately restore the optimal relationship between neocondyle and fossa. The position and stability of neocondyle were important for maintaining the TMJ function, facial symmetry, and occlusion relationship. Moreover, the design of extraoral incision could avoid ischemic absorption and even necrosis of the proximal bone segment after removing the condylar OC. Another advantage of this computer-assisted surgery was that the condylar osteotomy guide and the repositioning guide used for condyle osteotomies and reposition neocondyle respectively provided a duplication of the preoperative virtual surgical plan and eliminated the need for intraoperative measurement, thus substantially saving time. However, the present study also had some limitations, including the small sample size and short follow-up time, which should be addressed by future studies. Also, the biggest concern related to this technique was extraoral incision resulting in facial nerve injury and scarring. In this study, none of the patients showed any signs of facial nerve injury in the follow-up.Currently, the use of condylar osteotomy and repositioning guide combined with orthognathic surgery in the treatment of asymmetric prognathism caused by condylar OC is still in its infancy. Nevertheless, this surgical technique offers great advantages with no significant complications. The secondary deformities and malocclusion can be corrected by simultaneous orthognathic surgery. Therefore, condylar osteotomy guide and repositioning guide used for condyle OC resection and reposition neocondyle extraorally combined with orthognathic surgery intraorally provide a valuable option for patients with severe jaw deformities secondary to condylar OC.Additional file 1: Figure 1. The evaluation of position and condition through TMJ MRI before surgery. A, B: The TMJ MRI for sagittal view of condylar OC and normal side. C, D: The TMJ MRI for coronal view of condylar OC and normal side.


First isolation of graphene, as a great achievement, opens a new horizon in a broad range of science. Graphene is one of the most promising materials for spintronic fields whose application is limited due to its weak magnetic property. Despite many experimental and theoretical efforts for obtaining ferromagnetic graphene, still, a high degree of magnetization is an unsolved challenge. Even, in most observations, graphene magnetization is reported at extremely low temperatures rather than room temperature. In principle, the magnetic property of graphene is created by manipulation of its electronic structure. Removing or adding bonds of graphene such as creating vacancy defects, doping, adatom, edges, and functionalization can change the electronic structure and the external perturbation, such as external magnetic field, temperature, and strain can either. Recently, single and few-layer graphene have been investigated in the presence of these perturbations, and also the electronic changes have been determined by Raman spectroscopy. Here, we successfully could develop a simple and novel Leidenfrost effect-based method for graphene magnetization at room temperature with the external perturbations which apply simultaneously in the graphene flakes inside the Leidenfrost droplets. Macroscale ferromagnetic graphene particles are produced by this method. Briefly, the graphene is obtained by the liquid-phase exfoliation method in the ethanol solution media and also evaporates on the hot surface as a Leidenfrost droplet in the magnetic fields. Then, the floated graphene flakes circulate inside the droplets. Due to the strain and temperature inside the droplets and external magnetic field (the magnet in heater-stirrer), the electronic structure of graphene is instantly changed. The changes are extremely rapid that the graphene flakes behave as a charged particle and also produce an internal magnetic field during their circulation. The internal magnetic field is measured by sensors. As the main accomplishment of this study, we could develop a simple method for inducing magnetism obtained 0.4 emu/g in the graphene, as magnetization saturation at room temperature, which is higher than the reported values. Another achievement of this work is the detection of the Leidenfrost droplets magnetic field, as an internal one which has obtained for the first time. To investigate magnetic graphene particles, the magnetization process, and the electronic structure of the vibrating sample magnetometer (VSM), magnetic field sensor, and Raman spectroscopy are used, respectively. For example, recent studies indicate that the monolayer graphene is optically transparent and can absorb ~2.3% of the visible light2, and also it is wetting-transparent to substrates such as copper, gold or silicon3. In both cases, transparency is reduced by increasing the number of graphene layers3. Because of the high flexibility of graphene, the folded, wrinkled, and crumpled graphene can be easily created. Consequently, in these structures, the roughness and specific surface area are raised9. Moreover, the results of measuring some properties extremely depend on the measurement conditions, such as temperature, the number of layers, and fabrication method20. Suspended and supported fabrication strategies are two types of developing methods for obtaining the free-standing form of graphene. The suspended form can remarkably enhance its electrical and thermal properties because it can effectively eliminate substrate phonon interaction. Generally, the intrinsic properties of graphene are detected in the suspended form without inconvenience of the substrate. For comparison, the electron mobility of suspended graphene is 200,00012 cm2/Vs and for unsuspended graphene supported by Si/SiO2 substrate is 10,000 cm2/Vs1. Also, the thermal conductivity for suspended monolayer graphene over a trench in Si/SiO2 substrate is 5300 W/mK10 (at room temperature) and is 600 W/mK20 for the supported graphene (near room temperature).Graphene as an ideal material have unique physical properties and extensive usages. The isolation of single-layer graphene in 2004 was a starting point for exploring its structure and properties24. Recently, many methods have been introduced to change the electronic structure and induce magnetization in graphene. For example, unsaturated dangling bond in vacancy defect is responsible for magnetic moment, which is theoretically estimated about 1.12–1.53 μB per atom26. Vacancy defect in graphene and graphite structure is generated by ion  irradiation as well as reduction of graphene oxide31. In addition, adatom such as hydrogen and fluorine can create magnetism in graphene by forming the local magnetic moments37. Recently, low magnetization has been reported for fluorinated graphene (0.2 emu/g at 1.8 K)27, hydrogenated epitaxial one (<30 * 10−7 emu/g)32, and defective one (0.02 emu/g at 2 K)27. Moreover, the zigzag edges in the specific structure of graphene such as graphene nanoribbons have spin-polarized states at the edges which induce magnetism39. Frequently, the graphene oxide is used in the experimental study. The magnetization of ferromagnetic nitrogen-doped graphene created through reduction of graphene oxide in ammonia is 1.66 emu/g 40, and in nitrogen plasma41 is 0.01 emu/g (at room temperature). Using annealing, graphene oxide is reduced in the presence of hydrazine which a magnetization about 0.02 emu/g (at room temperature) was reported by Y. Wang et.al in 200928. The fluorination of the reduced graphene oxide modifies the magnetization up to 2 emu/g at 2 K33. In general, there are limitations in the use of graphene oxide and defective graphene. When graphene is oxidized and reduced, its electrical conductivity is disrupted, and when the defect is created in graphene, in high density of defects, the structural stability become loosed and fragile42. J. Tucek et.al doped graphene by Sulfur and reported its ferromagnetic properties below 62 K (5.5 emu/g) while they observed no ferromagnetic properties at room temperature43. Ultimately, modification of graphene magnetization is followed up by functionalizing with nitrophenyl44. But most of the studies do not achieve suitable ferromagnetic. In general, ferromagnetic graphene is a matter of interest in the spintronic field45. Because the electron structure differs only in the vicinity of the defects, and there are also limitations in the production of these defects, these methods have a low potential for improvement.Among all of these properties, the ferromagnetic property of graphene and graphite is extremely low. The negligible amount of their magnetization relate to defects and impuritiesIn this method, using floated graphene in ethanol droplet during the Leidenfrost effect-based method under the magnetic field at room temperature, the ferromagnetic graphene particles (FGPs) are produced that the magnetization saturation degree is stunningly high in compare to the recent reports. The graphene suspensions are manipulated by Leidenfrost effect. What is important is that the graphene structure is not disrupted by this method.46. Recently, the Leidenfrost droplet has been used to fabricate nanostructures47, create photonic microgranules48, accelerate the chemical reaction49, and used as a chemical reactor51, additionally, many models have been presented for the Leidenfrost droplet54. Despite many studies, dynamics such as vibration, rotation, and internal circulation in the droplet still have not been well understood.When a liquid droplet contact to the hot surface, which the surface temperature is upper than the liquid boiling point, an insulating vapor layer is formed that protects the droplet from boiling rapidly. The droplet floats above its own vapor and become shrinkage during evaporation until the liquid become totally dry. This phenomenon was firstly considered by J.G Leidenfrost in 1756 and known as the Leidenfrost effect55. Adjusting surface tension of solution in the region of 40–50 mN/m is determined as a main parameter for achieving high yield of graphene dispersion56. To adjust surface tension, various liquids and surfactants are used60. In our previous work, the graphene was dispersed in two different surfactants and also their mixture59. In this study, in order to reach the surface tension ~45 mN/m, the ratio of 20:80 ethanol/water was used . In order to control the bouncing of the droplets, the upper plate is drilled. The volume of each hole is about 0.05 ml. As shown in Fig. In recent findings, mechanical control over the electronic structure of graphene is known as “strain engineering”, which affects the magnetic properties of graphene. For more explanation, the pseudo-magnetic field of highly strained nanobubbles of graphene is reported by the N. Levy et.al in 2010. In this study, in addition to strain, other parameters such as temperature and the magnetic fields are applied to graphene flakes by the Leidenfrost effect-based method. Temperature and magnetic field, like strain, can change the electronic structure of graphene flakes and cause magnetic properties in these flakes.61.Raman spectra of single and multilayer graphene indicate useful and prominent features based on the phonon and electronic properties of them. In addition, the changes of lattice vibration and electronic structure in the presence of external perturbations such as magnetic field, strain, and temperature can be determined through the Raman spectroscopy. The three main scattering modes for graphene systems located at ~1340, 1574, and 2707 called D, G  and 2D, respectively. The Raman spectrum of pristine graphite is shown in Fig. 61. Indeed, the frequency of Raman peaks related to temperature62, is raised by isotropic compression and reduced by isotropic tension63. Also, anisotropic stress gives complex features to these peaks (splitting the G mode). In addition, Landau levels can be generated due to the application of an external magnetic field (and in some cases by strain)71, which transition between these levels lead to magneto excitation create72. Resonance, magneto phonon resonances, occurs when the energy between the levels of the Landau and the lattice vibrations of graphene is equal. Other parameters such as number of layers and stacking form can influence Raman spectra. Therefore, we confirm just the change of electronic structure in the graphene by Raman spectra because the graphene flakes inside the droplets feel the non-uniformed perturbation applied in any direction61. The starting point of these changes is observed when the Leidenfrost droplets are placed on the holes. The magnetic field sensor measures the weak magnetic fields for droplets as an internal magnetic field based on the circulation graphene flakes inside the droplets . Here, under the magnetic field, the floated graphene flakes circulate inside the droplet and aggregate during the evaporation. As explained before, the dynamic inside the Leidenfrost droplets is not clear, also, the investigation of the floated graphene inside the droplet is not possible. Therefore, due to these limitations, the probable magnetization process is proposed and interpreted based on the magnetic field measurements. Magnetic field measurement with this procedure detects two sources of magnetic fields. One of them is external, about 420 nT generated by the magnet inside the heater-stirrer, and other is an internal magnetic field in the region of 1–5 nT generated by the circulation of the polarized graphene flakes inside the droplets. Generation of the internal magnetic field contains two steps: (1) the polarization of graphene under the external perturbation when the graphene suspension is injected in the aluminum holes, (2) generation of the internal magnetic field through the circulation of polarized graphene, based on Faraday law.In recent studies, responding of graphene to external factors have been reported such as an alignment of graphene sheets under the external magnetic fieldIn addition, the polarizability of graphene sheets depends on the number of layers and influence the internal magnetic field. To elaborate more, as shown in Fig. Due to high temperature of the heater, measurement of magnetic field faces limitations; therefore, the sensor is located at 30 cm above the heater, as seen in the inset of Fig. 2/gr and 6.2320 m2/g, respectively that are close to each other.Also, high and non-uniform strain is applied on graphene flakes, which creates different shapes and wrinkles on FGPs. Figure H < +10 kOe. Table 24 of graphite investigated by Raman and ICP spectroscopy (Supplementary Table The vibrating sample magnetometer (VSM) was performed for all samples. The (M-H) curve for graphite and graphene shows weak ferromagnetic properties  are purchased from Merck Company. Larger flakes are collected by centrifuge (Hettich EBA20). Set up contains heater stirrer  and two aluminum plates (thickness 2.45 mm). Almost one hundred hole  is drilled in the top plate. The impurities of graphite are measured by ICP spectrometry (ICPS-7000 SHIMADZU). Adjusting surface tension of ethanol solution is performed using Tensiometer (sigma 700 ring mode). Magnetization of FGPs is measured by vibrating sample magnetometer (Kavir IRAN). Magnetic field sensor  is used to detect magnetic fields. Raman spectra are obtained by Raman spectroscopy . The morphologies are investigated by FESEM (TESCAN). UV-Vis (mini 1240) and FTIR (8400S) spectrophotometer analyzes are performed by SHIMADZU instruments. The specific surface area is determined by Micromeritics instrument.Supplementary information.