The high-quality graphene sheets obtained in this work make them suitable for application in many fields such as energy-storage materials and polymer composites.We report an effective method for producing graphene sheets using solvothermal-assisted exfoliation of graphite in a mixed solvent of toluene and oleylamine. The mixed solvent of toluene and oleylamine produces higher yield of graphene than its constituents, oleylamine and toluene. The oleylamine molecules with its long chain enwrap the graphene sheets efficiently, while toluene helps the oleylamine molecules become more flexible and easily intercalate into the edge of graphite. The prepared graphene sheets have a high quality, and the concentration of graphene in the dispersion is as high as 0.128 mg mL The obtained graphene product was dispersed in NMP (30 mL) for UV-visible measurements. By measuring the absorbance of graphene dispersion at 660 nm, the concentration of the exfoliated graphene dispersion was determined from the Lambert-Beer law, using graphene ,23. Rama−1. Thermogravimetric analysis (TGA) was conducted in nitrogen atmosphere at a heating rate of 10°C/min using a TA Hi-Res TGA 2950 thermogravimetric analyzer . X-ray photoelectron spectroscopy (XPS) measurement was performed on an ESCALAB 250Xi photoelectron spectrometer  with Al Kα X-ray radiation as the X-ray source for excitation.Fourier transform infrared (FTIR) spectra were recorded on a FTIR spectrometer  at wavenumbers of 400 to 4,000 cmThe exfoliation of graphite in a mixed solvent using a solvothermal process is depicted in Figure A representative monolayer graphene sheet is shown in Figure The thickness of the prepared graphene sheets was measured by AFM. Figure −1 when the volume ratio of oleylamine/toluene is 5, which is much higher than the reported value (0.01 mg mL−1) for a solvent of NMP [−1), and toluene (1.14 × 10−3 mg mL−1).The concentration of the graphene product at various volume ratios of toluene to oleylamine is shown in Figure t of NMP . This vaDue to the strong ionic interactions between strong acid and oleylamine, the oleylamine molecules readily intercalate into the graphite layers at high temperature and pressure in the solvothermal process. Moreover, with its long chain, oleylamine can prevent the re-aggregation of the graphene sheets effectively, making the graphene suspension more stable.−2 were suggested for the dispersion of carbon nanotubes and graphene [−2, which is lower that the suggested surface tension for the exfoliation of graphite. In view of surface tension, oleylamine and toluene do not seem to be good solvents for the exfoliation of graphite. However, under solvothermal conditions, the oleylamine molecules readily intercalate into the graphite layers, which facilitates the exfoliation of graphite. The addition of toluene into oleylamine makes the oleylamine molecule more flexible, thus increasing the effectiveness of the exfoliation process. Because toluene alone can poorly disperse graphene, the graphene concentration decreases as the toluene content in the mixed solvent increases, i.e., the volume ratio of oleylamine to toluene decreases.For successful exfoliation of graphite, it is necessary to overcome the van der Waals attractions between adjacent graphite layers. One method to reduce the strength of the van der Waals attractions is liquid immersion. By matching the refractive indices of the material and the solvents, the potential energy between adjacent layers which is given by the dispersive London interactions may approach 0. Based on this criterion, solvents with a surface tension of 40 to 50 mJmgraphene ,27. The −1, the G-band at approximately 1,580 cm−1, and the 2D-band at approximately 2,700 cm−1 in both Raman spectra of graphite and graphene product. The D′-band at approximately 1,620 cm−1 is observed in the Raman spectrum of graphene product [ID/ID′) is found to be 1.14. A low value of ID/ID′ indicates that the defects are on-site defects, which describe out-of-plane atoms bonded to carbon atoms  [ID′/IG) is 0.09, indicating that the defects are mostly on sp3 sites, because in the same defect concentration, ID′/IG is higher for vacancies than sp3 sites [D/IG) is found to be 0.11. This ratio is much lower than that of chemically or thermally reduced graphene oxide (approximately 1.2 to 1.5) and graphene prepared by other exfoliation methods, further demonstrating that our graphene product contains a low amount of defects [Raman spectra of the prepared graphene sheets are shown in Figure  product . Low D-bization) . Moreovep3 sites . The int defects -32. An e defects . This in defects ,25,28.Fi−1 is attributed to O-H stretching vibration of adsorbed water molecules and structural OH groups, and a peak at approximately 1,647 cm−1 is ascribed to C=C bending vibrations. Peaks at approximately 1,525 cm−1 reflect the skeletal vibration of graphene [−1 and 2,850 cm−1 which are attributed to stretching of methyl group in oleylamine [−1 which may be attributed to NH2 bending mode [Figure graphene . It is oeylamine -37 and ting mode  indicatiFigure 2) and the second loss around 400°C to 500°C may be attributed to the loss of carboxyl (C=O) and carboxylic groups (O-C=O) [TGA results Figure  reveal t (O-C=O) ,40. The XPS analysis was performed to monitor changes of the structural and chemical composition of the sample during the preparation process. Figure −1 at a volume ratio of oleylamine and toluene of 5. This result is comparable to or higher than previously reported values. An oleylamine molecule with its long chain can intercalate into the edge of graphite during solvothermal process and also wrap the graphene sheets. The addition of toluene, a poor solvent for graphene dispersion, into oleylamine helps oleylamine become more flexible and thus significantly improves the production yield of graphene. High-quality graphene sheets prepared in this work may find their application in many areas from energy-storage materials to polymer composites.In conclusion, we have demonstrated an effective and efficient approach to preparing high-concentration graphene dispersion by solvothermal exfoliation of graphite in a mixed solvent of toluene and oleylamine. The prepared graphene dispersion contains mono or few-layer graphene sheets with a low amount of defects. The graphene concentration in the dispersion is as high as 0.128 mg mL


The prepared LVO NPs-GNs composites displayed high performance as an cathode material for lithium-ion battery, including high reversible lithium storage capacity (237 mA h g−1 after 200 cycles), high Coulombic efficiency (about 98%), excellent cycling stability and high rate capability . Very significantly, the preparation method employed can be easily adapted and may opens the door to complex hybrid materials design and engineering with graphene for advanced energy storage.Lack of high-performance cathode materials has become the major barriers to lithium-ion battery applications in advanced communication equipment and electric vehicles. In this paper, we report a versatile interfacial reaction strategy, which is based on the idea of space confinement, for the synthesis of ultradispersed LiV However, it was also reported that for amorphous one, a maximum amount of 4.5Li+ (ca. 419 mAh g−1) could be demonstrated3O8, more organized arrangements at the subunit level facilitate the inclusion of more lithium ions per unit cell3O8) in lithium-ion batteries are limited by poor electron transport, slow Li-ion diffusion in electrodes, and suffered from fragile surface properties at the interface of electrode/electrolyte at high charge-discharge rates203O8-based materials, such as optimizing particle size22242526−1 have rarely been reported for LiV3O8 cathodes.With the advantages of high energy density, long lifespan and environmental benignity, lithium-ion batteries (LIBs) have become the predominant power source for applications in electric vehicles (EVs), and renewable energy storage in smart grids12345678910Li+ ca. 4 mAh g−1 2 g−1)282930313234363741423O8, which is a promising cathode materials for LIBs.Graphene (G), a monolayer of carbon atoms arranged in a honeycomb network, is one of the most favorable carbonaceous materials for constructing functional composites and/or hybrids because of its unique 2D nanostructure, excellent electron conductivity, good chemical stability, and very high theoretical surface area (2600 m3O8 nanoparticles (~10 nm) and strong coupling on graphene nanosheets (denoted as LVO NPs-GNs) with an unprecedented degree of control on the precise separation and manipulation of nanoparticles nucleation, growth, anchoring, and crystallization on graphene oxide (GO) in a water-in-oil emulsion system over free growth in solution. For comparison LiV3O8 particles were freely grown on graphene sheets in solution via a traditional sol-gel method (denoted as SG-LVO-GNs). Such LVO NPs-GNs composites with the small particle size and uniform distribution of LVO NPs could be controlled with good reproducibility, and anchoring firmly on the GNs is advantageous for inhibiting aggregation and offers a direct short pathway for Li+ diffusion, which are beneficial for high capacity and rate capability. Specifically, this well LVO NPs-GNs composites is able to deliver high reversible capacities with superlative cyclic capacity retention at different current rates for prolonged cycling, and exhibit excellent high-rate performance at a current density as high as 6 A g−1 as an cathode material for LIBs. Very significantly, this facile method may offer an attractive alternative approach for preparation of the graphene-based composites as high-performance electrodes for lithium-ion batteries.Herein, we report a versatile interfacial reaction strategy, which is based on the idea of space confinement, for the synthesis of ultradispersed LiVIn this versatile interfacial reaction design strategy, the unprecedented control of the hybrid materials is achieved by the rational separation and precise manipulation of the synthesis processes  . Firstly3O8. In addition, High-resolution TEM showed the crystal lattice fringes throughout the entire LVO NPs formed on graphene  composites shows the large aggregated nanoparticles and restacked graphene sheets . Diffraction peaks which might appear for graphene are absent, most likely because they are below the limits of detection by XRD or, in the case of the graphene (002) peak, because it is likely to be eclipsed by the LiV3O8 (003) peak. The absence of a reflection peak at approximately 11° indicates that the GO cannot be distinguished, consistent with full or partial reduction to graphene. Raman spectroscopy is a non-destructive approach to characterize graphitic materials, in particular to determine the ordered and/or disordered crystal structure of graphene sheets2g phonons of Csp2 atoms−1) and a broad G band (1590 cm−1) are observed in both samplesD/IG) reflects the graphitization degree of carbonaceous materials and the defect densityD/IG for LVO NPs-GNs (1.37) is much larger than that for GNs (1.26), showing the transformation of graphene sheets from graphene oxide sheets after the thermal treatment. The intensity of the characteristic peak of the D band is slightly stronger than that of the G band, indicating the existence of graphene in the composites. Thermogravimetric analysis (TGA) was employed to determine the amount of graphene in the LVO NPs-GNs (2 g−1 is obtained (Powder X-ray diffraction (XRD) experiments were carried out to reveal the crystallographic phases of the final product, with the result shown in  NPs-GNs . It is iobtained , ESI†. S−1 observed on LVO NCs-GNs at 0.1 A g−1 based on the mass of the active material LVO, which is much higher than that of LVO NCs (212 mA h g−1). This is considered to be because the ultrathin graphene nanosheets act as conducting routes between the LVO NPs, resulting in significantly reduced contact resistance. Remarkably, the reversible capacity of LVO NPs-GNs is still stable at 237 mA h g−1 even after 200 cycles, while the reversible capacities of LVO NPs gradually reduce to 138 mA h g−1  measurements . Furthermore, the interconnected graphene network structure provides a conductive network for electronic transport from LVO NPs within the whole electrode and thus decreases resistance.More exciting results come from the rate performance of LVO NPs-GNs in the urements  were car−1. After 200 cycles, it is clear that the SG-LVO-GNs composites have a lower capacity than that of the LVO NPs-GNs composites. That is because the large aggregated nanoparticles and restacked graphene sheets are produced in solution via a sol-gel method, which leads to lower active sites for lithium storage 49−1, a capacity of 237 mAh g−1 was maintained after 200 cycles. Even at much higher current density of 6 A g−1, a reversible capacity of 55 mAh g−1 was obtained. All of these results demonstrate that the as-prepared LVO NPs-GNs composite encompasses three key advantages of small particle size, uniform dispersion, and strong synergistic coupling effects. Importantly, these results would shed light on the great potential application of cathode materials as high capacity electrode with high rate capability for next generation LIBs. Very significantly, this work opens the door to the rational design and controllable synthesis of useful graphene-based materials for advanced energy storage.In summary, we describe a versatile interfacial reaction strategy, which is based on the idea of space confinement, for the synthesis of LVO NPs-GNs (~10 nm) composites in a W/O emulsion system. It is demonstrated that as the cathode material of LIBs, LVO NPs-GNs composite with the combination of small particle size, uniform dispersion and strong coupling with the graphene sheets render long cycling stability and high rate capability. At a current density of 0.1 A g3 and 46 mL of concentrated H2SO4 were mixed together in an ice bath for 4 h. Then 6.0 g of KMnO4 was added slowly into the solution. Afterwards, the ice bath was removed and the suspension was stirred for another 3 days. Then the suspension was further treated with 200 mL of warm water (~60 °C) and 10 mL of H2O2 (30%). The mixture was centrifuged at 4000 rpm and washed with diluted HCl and water to neutral. Finally, a homogeneous GO aqueous dispersion (1 mg mL−1) was obtained for further use.GO was prepared from graphite flakes by a modified Hummers method52−1) was slowly poured and intensely stirred for 20 min at room temperature resulting in the formation of a golden water-in-oil emulsion. Then 1.8 mmol of NH4VO3 and 2 mmol of H2C2O4 or 1 mmol of LiOH•H2O was added to this golden water-in-oil emulsion while stirring. After 10 min of vigorous agitation, equivalent volumes of two separate microemulsion solutions containing NH4VO3 and H2C2O4 or LiOH•H2O were mixed rapidly. The suspension of the microemulsion were transferred into stainless steel autoclaves and heated at 200 °C for 16 h, followed by cooling to room temperature naturally. After cooled to ambient temperature, the black participates was obtained by centrifugation, and then washed for several times with distilled water. After drying in the vacuum oven at 70 °C overnight, as-synthesized LiV3O8-graphene was annealed at 400 °C for 2 h in an nitrogen flow in order to remove the residual water molecules and functional groups in the rGO, and to improve the crystallinity of LiV3O8 in the obtained composites, which would further improve its electrochemical performance. For comparison, Pure LiV3O8 nanoparticles were also prepared by the similar procedure without any GNs.In a typical experimental procedure, 5.6 g of Cetyltrimethyl Ammonium Bromide (CTAB) was dissolved in a mixture of 10 ml of n-pentanol and 60 ml of n-hexane. Then, 10 ml of GO aqueous dispersion (1 mg mL−1) was slowly poured and intensely stirred for 20 min at room temperature resulting in the formation of a golden transparent solution. Then 1.8 mmol of NH4VO3 and 2 mmol of H2C2O4 or 1 mmol of LiOH•H2O was added to this golden transparent solution while stirring. After 10 min of vigorous agitation, equivalent volumes of two separate solutions containing NH4VO3 and H2C2O4 or LiOH•H2O were mixed rapidly. The suspension of the solution were transferred into stainless steel autoclaves and heated at 200 °C for 16 h, followed by cooling to room temperature naturally. After cooled to ambient temperature, the black participates was obtained by centrifugation, and then washed for several times with distilled water. After drying in the vacuum oven at 70 °C overnight, as-synthesized LiV3O8-graphene was annealed at 400 °C for 2 h in an nitrogen flow in order to remove the residual water molecules and functional groups in the rGO, and to improve the crystallinity of LiV3O8 in the obtained composites, which would further improve its electrochemical performance.In a typical sol-gel experimental procedure, 10 ml of GO aqueous dispersion  and high resolution transmission electron microscopy  with an accelerating voltage of 200 KV. TG analysis was carried out with a TG/DTA6200 instrument. The specific surface area was measured by the Brunauer-Emmett-Teller (BET) method using ASAP2020. Additionally, Raman spectra were recorded at room temperature by employing an InVia Raman spectrometer using 633 nm red laser with 10% intensity to determine the extent of graphitic disorder.The resulting sample was characterized by means of X-ray diffraction  with monochromated Cu K radiation at a scanning rate of 2° min6 dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) and diethyl carbonate (DEC) at a volumetric ratio of 1:1:1. The discharge-charge tests were conducted at various rates within a voltage window from 1.5 V to 4.0 V (vs. Li+/Li) on the Battery Testing System (BTS) battery testing system . Electrical impedance spectroscopy (EIS) experiments were carried out on a Parstat 2273 advanced electrochemical systems in the frequency range mainly from 100 kHz to 10 mHz with the a.c. signal amplitude of 5 mV.The LVO NPs-GNs active material powder (~240 mg) was mixed with Super P carbon black and polyvinyldifluoride , with weight ratio of 80:10:10, in N-Methylpyrrolidone (NMP) solvent to produce an electrode slurry. The mass of active materials was calculated at ca. 3.2 mg and integrated into two-electrode CR2025-type coin cells for electrochemical measurements, with LVO NPs-GNs electrode as cathode, metallic lithium foil as anode, porous polypropylene film as separator; electrolyte was 1.0 M LiPFHow to cite this article: Mo, R. et al. Ultradispersed Nanoarchitecture of LiV3O8 Nanoparticle/Reduced Graphene Oxide with High-Capacity and Long-Life Lithium-Ion Battery Cathodes. Sci. Rep. 6, 19843; doi: 10.1038/srep19843 (2016).


In this paper, we report highly conductive, highly flexible, light weight and low cost printed graphene for wireless wearable communications applications. As a proof of concept, printed graphene enabled transmission lines and antennas on paper substrates were designed, fabricated and characterized. To explore its potentials in wearable communications applications, mechanically flexible transmission lines and antennas under various bended cases were experimentally studied. The measurement results demonstrate that the printed graphene can be used for RF signal transmitting, radiating and receiving, which represents some of the essential functionalities of RF signal processing in wireless wearable communications systems. Furthermore, the printed graphene can be processed at low temperature so that it is compatible with heat-sensitive flexible materials like papers and textiles. This work brings a step closer to the prospect to implement graphene enabled low cost and environmentally friendly wireless wearable communications systems in the near future. Wireless wearable communications is a field of increasing research interest due to the numerous potentials offered in areas such as healthcare and fitness monitoring145911However, graphene, the allotrope of carbon nanotube, is a very promising material for wireless wearable communications applications owing to its high conductivity and unique properties5202224However, even though profound progress has been made in graphene active devices, the pace of developing graphene passive RF components has far lagged behind. This is because, in spite of graphene’s high conductivity, both exfoliated and CVD  graphene sheets have very high surface resistance, hindering their applications in RF passive components27293031294 S/m, which is almost double of 2.5 × 104 S/m from previously reported RGO (reduced graphene oxide) with binder and 10 times higher than that from binder-free method29We have developed binder-free technique which is not only compatible with heat-sensitive substrates like papers and textiles, but also offers high conductivity and mechanical flexibilityThe RF passive components in this paper are made of printed graphene. Here we briefly introduce the preparation of printed graphene, and the details are included in the Method sectionThe conductivity and surface resistance of the printed graphene under various compression ratios (the compression ratio is defined as the ratio of the thickness decrement of compressed sample over un-compressed sample thickness) are measured, as shown in TLs are basic structures designated to carry signals and are essential for RF circuits, or indeed any electronic cirucitsThe performance of a TL is mainly determined by material and geometrical parameters such as material losses, substrate material dielectric constant, line gaps, signal line thickness and etc. The insert in The scattering parameters of these lines are measured using Agilent E5071B VNA See  and propα and β are attenuation constant and phase constant, respectively. To eliminate the effect of impedance mismatch on analyzing conductor loss, absorption attenuation, which is defined as the ratio of power entered into the input port of the network over the output power of the network, is calculated bywhere The attenuation is unitized to per Moreover, the superior flexibility of the printed graphene enabled TLs is experimentally verified with the lines of Antenna is used to send and receive RF signals in communications systems. For wearable communications systems, both mechanical flexibility and effective radiation are demanded. For the first time, effective radiation of printed graphene enabled flexible and wearable antenna is experimentally demonstrated in communication frequency bands, such as mobile cellular and WiFi spectrums. 11 at 1.97 GHz is −18.7 dB, and another peak is at 3.26 GHz with −19.2 dB, revealing good impedance matching. The reflection coefficient is under −8 dB from 1.73 GHz to 3.77 GHz, which covers the bands for Wi-Fi, Bluetooth, WLAN  and mobile cellular communications. The maximum gain is 0.2 dBi at 1.92 GHz and above −1 dBi from 1.82 GHz to 3.72 GHz, demonstrating an effective radiation from the printed graphene antenna to the free space. With comparison of reflection coefficients corresponding to different bending cases, it can be seen that the reflection coefficients are not sensitive to the bending and do not vary much. The impedance matching points are almost unchanged. However, the antenna gain changes, especially at higher frequency region. This is because the antenna gain is determined by current distribution on the antenna. When the antenna is bended, the current distribution will be altered, leading to variation on antenna gain performances. Despite that gain at higher frequency band around 3.26 GHz degrades visibly with increasing bending, the gain at lower band around 1.9 GHz to 2.2 GHz has much less variations. This frequency band is where wireless wearable communications systems operate. The experimental data here demonstrate that even when the printed graphene antenna is bended, the radiation at this this frequency band can still be effective.The reflection coefficients of the antenna under these four different bending cases were measured using VNA (Agilent E5071B), and the gain was obtained using three-antenna methodThe corresponded radiation patterns under cases (a)–(d) at 1.97 GHz in elevation plane were also measured using antenna measurement system . The data were recorded for every 10 degree rotation and shown in With the aforementioned verification for the flexibility and efficient radiation of the printed graphene enabled antenna, here we go a step further to prove its potentials in wireless wearable communications systems by presenting a real life scenario shown in 10We have presented highly conductive and flexible printed graphene TLs and antennas using graphene nanoflakes aiming for wireless wearable communications applications. The feasibility of using printed graphene to transmit/receive RF signals through wires and wirelessly has been demonstrated experimentally. The superior flexibility of the printed graphene enabled TLs and antennas has been fully verified with measurements under different bending and twisting cases. An on-body signal transmission on mannequin has been also presented by using printed graphene antennas conformed to the model’s arms for radiating and receiving RF signals wirelessly. It is clearly evident that the sound mechanical flexibility and effective radiation of the printed graphene enabled antennas have successfully facilitated the on-body wireless communications. This work has unambiguously proved that printed graphene can bring transformative change to the formation of RF passive components such as TLs and antennas for wearable applications. Furthermore, the fabrication process is simple and low cost and thus suitable for commercial mass production. Combined with other profound advantages in lightweight, mechanical flexibility and environmental friendliness, printed graphene can be ideal for low cost consumable wearable electronics.Graphene nanoflakes were dispersed in N-Methyl-2-pyrrolidone (NMP) solvent to form a uniform 10 wt% graphene ink, i.e. Grat-Ink 102E. Less than 1 wt % of non-ionic polymer-type surfactants was contained in the ink. The presence of the surfactants improve the dispersion of graphene flakes and viscosity helping in deposition of a uniform film. The Grat-Ink 102E, prepared as described above, was used to print the samples in this study. Conventional paper was used as the substrate, and the patterns of the samples were printed by 150 mesh stainless-steel screen via a manual laboratory screen-printing table. They were dried at 100 °C for 10 minutes. Further a rolling compression procedure was followed using compression roller  to obtain highly dense graphene laminates. The different compression ratio and thickness of samples are controlled by adjusting the space between two rollers. High reproducibility can be guaranteed when roller distance is fixed during operation. The sheet resistance of the graphene laminate pattern was measured by the 4-point probe . The thicknesses of un-compressed and compressed graphene patterns were measured with digital thickness gauge . A total of 10 measurements at different spots were carried out to obtain the average value of each sample.How to cite this article: Huang, X. et al. Highly Flexible and Conductive Printed Graphene for Wireless Wearable Communications Applications. Sci. Rep.5, 18298; doi: 10.1038/srep18298 (2015).


Direct deposition of graphene layers on the flexible glass fiber surface to form the three-dimensional (3D) core-shell structures is offered using a two-heating reactor chemical vapor deposition system. The two-heating reactor is utilized to offer sufficient, well-proportioned floating C atoms and provide a facile way for low-temperature deposition. Graphene layers, which are controlled by changing the growth time, can be grown on the surface of wire-type glass fiber with the diameter from 30 nm to 120 um. The core-shell graphene/glass fiber deposition mechanism is proposed, suggesting that the 3D graphene films can be deposited on any proper wire-type substrates. These results open a facile way for direct and high-efficiency deposition of the transfer-free graphene layers on the low-temperature dielectric wire-type substrates.81.05.U-; 81.07.-b; 81.15.Gh Graphene has been reported by numerous papers on the growth[2 g-1)[Graphene as typical spe growth-6, propee growth,8, and ae growth-11. In me growth, catalyse growth, batterye growth, and wate growth, a smalle growth-25. Diffe growth,15, carbe growth, graphene growth,16,17,23e growth,25, havee growth, hydrothe growth, laser-be growth, and CVDe growth approache growth. The rese growth. The pere growth. Three-d[2 g-1), is also[2 g-1),24,25. H2 strip of copper foils serving on the catalyst for the thermal dissociation of CH4 was located in higher constant-temperature zone , and the glass fiber membrane substrates  were spaced in the lower constant-temperature zone (600°C). Next, the horizontal quartz tube was pumped to 1.0 × 10-6 Torr and heated in the meanwhile. When the temperature reached 300°C, the Cu foil surrounding the tube was annealed in the flow of H2 and Ar (100 sccm/500 sccm) to remove the copper oxide. After another 30 min of annealing at 1,000°C, CH4 (50 sccm) and H2 (50 sccm) were introduced for 10 to 120 min of growth. Finally, the furnace was cooled down to the ambient temperature rapidly by simply opening the furnace.As shown in Figure Following growth, the morphology of the sample was characterized with scanning electron microscope  and transmission electron microscope . Raman spectra were obtained with a HORIBA HR800 Raman microscopy system  (laser wavelength 473 nm and laser spot size about 0.5 mm). The resistance of the sample was measured by depositing the silver electrode on the surface.-1. For the Raman spectrum of the sample grown for 10 min, The I2D/IG intensity ratio is approximately 1.1, and the full width at half maximum (FWHM) of 2D band is approximately 45 cm-1, which represents one to two layers of graphene film[I2D/IG intensity ratio is approximately 0.5, and the full width at half maximum (FWHM) of 2D band is approximately 55 cm-1, which represents three to five layers of graphene film[Figure ene film. For theene film. Compareene film. In partIt is possible to investigate the state of the graphene by transferring it to a small holey copper grid using TEM. The HR-TEM image  growth is necessary due to the lower melting point of the glass fiber, which can be obtained by the revised CVD system with the two-heating reactor. The mechanism of synthesis of core-shell graphene/glass fiber structures by using such revised CVD system has been discussed here. The higher constant-temperature zone offers enough power for the dissociation of methane with the assist of copper catalyst, and the lower constant-temperature zone makes that the decomposed carbon atoms deposit readily on the substrate. Meanwhile, the distinct form of the temperature variation effectively controls the regions that the evaporated Cu atoms and the decomposed carbon atoms deposit. The gently declined temperature zone can make the evaporated Cu atoms deposit on the region close to the higher constant-temperature zone. Higher-2 wafer and wire-type fiber substrates, while the grown graphene layers are different, especially after a longer time growth. The plant SiO2 wafer substrate and single-mode fiber  are also used here to deposit graphene film for 120 min in the same CVD process. Figure -1 are also observed in both of the Raman spectra  related to a graphene layer structure is also hardly observed. The I2D/IG intensity ratio is only 0.2, and the full width at half maximum (FWHM) of 2D band is up to approximately 70 cm-1. These results represent that there are many graphene layers and many defects are formed on the wire-type glass fibers.It should be stressed that the graphene film can be grown on the plant SiO2 substrate are predominantly monolayer, due to the growth process is self-limited. As is well known, SiO2 has higher surface energy than after it is covered by graphene. Namely, the cohesion energy between SiO2 and graphene is higher than that of graphene-to-graphene. Therefore, after being covered by a layer of graphene, the carbon species become hard to nucleate on the graphene-covered area due to the relatively weak cohesion energy, refusing to form the second layer[2 wires. The metal elements existed in the SiO2 wires are caused by the formation of the glass membranes. All of the overlaps and defects can be used as the catalyst sites to further grow the graphene layers. From Figure In fact, graphene growth on the plant SiOnd layer. But, on2, SMF, and glass fiber membrane substrate. The excellent electrical properties further demonstrate that high-quality graphene layers can be prepared using such two-heating reactor CVD system in the relatively low temperature. The lower sheet resistance of the glass fiber membrane samples is caused by the more layers of the graphene films.We also measured the sheet resistance (Rs) of the prepared graphene film obtained at room temperature. The calculated average value of the Rs is approximately 700, 300, and 180 Ω/sq for the plant SiOWe have demonstrated the facile low-temperature growth of 3D graphene/glass fiber wire-type structures using a two-heating reactor. The higher constant-temperature zone offers enough power for the dissociation of methane with the assist of copper catalyst, and the lower constant-temperature zone makes that the decomposed carbon atoms deposit readily on the substrate. Graphene layers can be grown on the different diameter wire-type glass fiber surface to form graphene/glass fiber wire-type structures. The morphology and electrical properties of such structures can be controlled by changing the growth time. These results suggest that the 3D graphene films can be deposited on any proper wire-type substrates.The authors declare that they have no competing interests.CY and BM are the corresponding authors and designed the experiments and sample preparations and drafted the manuscript. YX, CZ, ZS, CC, XL, and SJ took part in the sample preparation and characterizations and discussed the results. All authors have read and approved the final manuscript.2Se3, and MoS2. XL works in Lishan College at Shandong Normal University; her research focus is solar materials. SJ and CC are professors in the College of Physics and Electronics at Shandong Normal University. They are M.S. Supervisor. Their main interests include nanomaterials, mode-locked lasers, and laser plasma.BM is a professor in the college of Physics and Electronics at Shandong Normal University, China. He is a Ph.D. supervisor. His main research interests include nanomaterials and laser plasma. CY has graduated from SungKyunKwan University (SKKU), Korea. Currently, he works at Shandong Normal University. His research subject is nanomaterials and their applications. YY, CZ, and ZS are currently doing their Ph.D. at Shandong Normal University. Their research subjects are related to 2D nanomaterials such as graphene, Bi


Background: The Loess Plateau, an ecologically vulnerable region, has long been suffering from serious soil erosion. Revegetation has been implemented to control soil erosion and improve ecosystems in the Loess Plateau region through a series of ecological recovery programs. However, the increasing atmospheric CO2 as a result of human intervention is affecting the climate by global warming, resulting in the greater frequency and intensity of extreme weather events, such as storms that may weaken the effectiveness of revegetation and cause severe soil erosion. Most research to date has evaluated the effectiveness of revegetation on soil properties and soil erosion of different land use or vegetation types. Here, we study the effect of revegetation on soil organic carbon (SOC) storage and erosion-induced carbon loss related to different plant communities, particularly under extreme rainstorm events. Materials and methods: The erosion-pin method was used to quantify soil erosion, and soil samples were taken at soil depths of 0–5 cm, 5–10 cm and 10–20 cm to determine the SOC content for 13 typical hillside revegetation communities in the year of 2013, which had the highest rainfall with broad range, long duration and high intensity since 1945, in the Yanhe watershed. Results and discussion: The SOC concentrations of all plant communities increased with soil depth when compared with slope cropland, and significant increases (p < 0.05) were observed for most shrub and forest communities, particularly for natural ones. Taking the natural secondary forest community as reference , the relative soil loss and SOC loss of the other 12 plant communities in 2013 ranged from 1.5 to 9.4 and 0.30 to 1.73, respectively. Natural shrub and forest communities showed greater resistance to rainstorm erosion than grassland communities. The natural grassland communities with lower SOC content produced lower SOC loss even with higher soil loss, natural secondary forest communities produced higher SOC loss, primarily because of their higher SOC content, and the artificial R. pseudoacacia community with greater soil loss produced higher SOC loss. Conclusions: These results indicate that natural revegetation is more effective in enhancing SOC storage and reducing soil erosion than artificial vegetative recovery on hillsides. However, natural secondary forest communities, with higher SOC content and storage capacity, may also contribute to larger SOC loss under extreme rainstorms. Soil, the largest pool of terrestrial organic carbon in the biosphere and approximately 3.3 times the size of the atmospheric pool and 4.5 times the size of the biotic pool ,2, playsThe Chinese Loess Plateau has long experienced serious soil erosion, and severe soil and water loss has led to widespread land degradation . Land usConversion of land use to agriculture has many potential implications for the mobilization and export of SOC . Floodini.e., trees for soil and water conservation, such as Robinia pseudoacacia, Pinus tabuliformis, Caragana intermedia, and Hippophae rhamnoides) and “economic forests”  [Artemisia scoparia, Lespedeza davurica, Artemisia gmelinii, Bothriochloa ischaemun, Sophora viciifolia, and Quercus liaotungensis, respectively [Revegetation probably enhances the carbon storage capacity of terrestrial ecosystems on the Loess Plateau ,28. The ulgaris) . Howeverulgaris) ,32,33,34ulgaris) ,36. In tectively ,38. Althectively ,40, it iectively . Owing tectively , correspectively ,44 or thectively ,46,47. HThus, the objectives of this study were to examine the effects of revegetation on soil organic carbon storage and carbon losses caused by soil erosion on hillsides in response to extreme rainstorm events in the hill and gully area of the Loess Plateau by analyzing: (1) changes in soil organic carbon content and capacity for soil carbon storage; and (2) soil erosion and erosion-induced carbon loss of different plant communities. The results of this study could provide references for strategies towards the optimization of vegetation restoration and climate change mitigation in the Loess Plateau region.2 is the primary tributary in the middle reaches of the Yellow River and belongs to the hill-gully region of the Loess Plateau. The climate is semi-arid, with mean annual precipitation of 500 mm (420–540 mm), and mean air temperature of 9.5 °C (8.80 °C to 10.2 °C). The seasonal distribution of precipitation is uneven, characterized by intensive rainfall from July to September that accounts for more than 60% of the annual rainfall. Soils are predominantly loess and have a texture of 64%–73% silt and 17%–20% clay; the loose soils are vulnerable to dispersion and transport [The study area was located in the Yanhe watershed at N 36°23′–37°17′ and E 108°45′–110°28′ . The watransport ,49. Quercus liaotungensis, Pinus tabuliformis, Platycladus orientalis, and Acer buergerianum. The dominant shrub species include Syringa julianae, Sophora viciifolia, Periploca sepium, and Ostryopsis davidiana. And the dominant herb species include Artemisia scoparia, Stipa grandis, Stipa bungeana, Artemisia gmelinii, Artemisia giralaii, Thymus mandshuricus, Bothriochloa ischaemum, Lespedeza davurica, and Carex lanceolata. The primary introduced tree species include Robinia pseudoacacia, Populus simonii, Hippophae rhamnoides, Caragana intermedia, and Salix matsudana. The economic forests are dominated by Malus pumila, Prunus davidiana, and Armeniaca sibirica [.The natural vegetation is composed of grassland, shrub and secondary forest. The dominant tree species include sibirica .Artemisia scoparia (A), Stipa bungeana + Lespedeza davurica (SL), Artemisia gmelinii + Stipa bungeana (AS) and Artemisia gmelinii + Artemisia giralaii+Bothriochloa ischaemum(AAB); two natural shrubland communities of Sophora viciifolia − Artemisia gmelinii + Stipa bungeana (SAS) and Syringa julianae − Carex lanceolata (SC); two natural forestland communities of Quercus liaotungensis − Syringa julianae − Carex lanceolata (QSC) and Acer buergerianum − Syringa julianae − Carex lanceolata (ASC), two artificial shrubland communities of Hippophae rhamnoides − Artemisia gmelinii + Stipa bungeana (HAS) and Caragana intermedia − Artemisia gmelinii + Stipa bungeana (CAS); and three artificial forest communities of Armeniaca sibirica − Artemisia gmelinii + Stipa bungeana (AAS), 6–8 years Robinia pseudoacacia − Artemisia gmelinii + Stipa bungeana (RAS1) and 15 years Robinia pseudoacacia − Artemisia gmelinii + Stipa bungeana (RAS2). Each community had three replicate sites distributed in different sub-watersheds, and three replicates of slope croplands  were used as the reference . Soil bulk density of each plot (3 replicates) was measured collecting soil with a bulk sampler (100 cm3) near the soil sampling points, and comparing the original mass of each soil core with the mass after oven-drying at 105 °C for 24 h. At each site, soil samples were collected with a soil auger  from nine points in an S-shaped pattern that paralleled the slope at depths of 0–5 cm, 5–10 cm and 10–20 cm. The soil samples from the nine points in each depth were mixed, respectively. Live plant materials (roots and shoots) and pebbles from each sample were separated in the laboratory and discarded. All samples were air-dried, crushed, and passed through a 0.15 mm sieve prior to the SOC analysis. SOC was determined by using the oil bath-KjX is the average soil erosion of each site, iD is the average depth (mm) of the nine nails in each plot, iB is the average soil bulk density (g·cm−3) of each plot, 103 is the unit conversion factor, S is the soil erosion (t·km−2·yr−1) of each plant community, SL is the soil organic carbon loss (t·km−2·yr−1) of each plant community, and jP is the average soil surface (0–5 cm) organic carbon percent content (%) of each site; i is the plot number of each site and m is the total number of plots, j is the site number of each plant community and n is the total number of sites.As the topsoil was disturbed and transported once water erosion had taken place, the organic carbon percentage content (%) of 0–5 cm soil layer was used as the base value to calculate soil organic carbon loss. The soil erosion and soil organic carbon loss in different plant communities were calculated using the following equations:Q. liaotungensis − S. julianae − C. lanceolata (QSC), with the lowest soil erosion and the highest soil organic carbon, was used as a reference to calculate relative soil loss and soil organic carbon loss of the other communities. The relative soil loss and soil organic carbon loss in different plant communities were calculated using the following equations:SR and SLR is the relative soil loss and relative soil organic carbon loss, respectively, kS and kSL is the soil erosion and soil organic carbon loss in different plant communities, k represents the 13 plant communities, QSCS and QSCSL is the soil erosion and soil organic carbon loss of the natural forestland community Q. liaotungensis − S. julianae − C. lanceolata (QSC), respectively.As the absolute values were obtained in a year experiencing extraordinary storm events, relative soil loss and soil organic carbon loss values were considered to be more meaningful. Therefore, the natural forestland community p < 0.05. Statistics were run using SPSS 16.0 . Figures were drawn using Sigmaplot 12.0 .A two-way analysis of variance (ANOVA) was used to examine the effects of plant community and soil depth on soil organic carbon content. A one-way ANOVA was used to identify the effects of plant community on relative soil loss and relative soil organic carbon loss. If significant effects were detected with the ANOVA, differences between individual means were tested using the Tukey Honestly Significant Difference (HSD) test at p < 0.05) at all soil depths. The SOC content in each soil layer of the natural secondary forest communities was significantly higher (p < 0.05) than in other natural plant communities. In addition, the SOC content of the AS community was significantly higher (p < 0.05) at each soil depth than in other natural grassland communities, and there was no significant difference between the other natural grassland communities. The SOC content of the natural secondary forest and shrub communities was significantly higher (p < 0.05) than the SOC content of artificial forest and shrub communities, respectively. In addition, the SOC content of each soil layer was not significantly different between artificial forest communities (except for the RAS1) or between artificial shrub communities. The two-way ANOVA indicated that plant community and soil depth had significant effects on SOC content . Compare−1 at 0–5 cm, from 3.89 to 26.71 g·kg−1 at 5–10 cm, and from 2.71 to 18.44 g·kg−1 at 10–20 cm (p < 0.05), but this change was not significant for the grassland communities. SOC content was significantly higher (p < 0.05) in the 0–5 cm soil layer than in the deeper soil layers of the forest community (except for RAS1) and shrub communities (except for the HAS). The SOC content of the different plant communities ranged from 4.86 to 52.89 g·kg10–20 cm . As soilIn July 2013, the Yanhe watershed experienced consecutive heavy rainfalls with broad range, long duration and high intensity. At each meteorological station , the tot−2·yr−1 to 5145 t·km−2·yr−1. The QSC community had the lowest soil loss and was used as a reference to calculate the relative soil loss of the other plant communities. The relative soil loss within the four natural grassland communities ranged from 3.1 to 4.1, and the A community had the lowest resistance to erosion. There was no significant difference in relative soil loss between the two natural shrub communities, which showed a higher resistance to erosion than the grassland communities. Relative soil loss of the secondary forest communities was 1 and 1.5 and showed the greatest efficacy for reducing erosion. In the two artificial shrub communities, relative soil loss was 3 and 3.9. Relative soil loss of the artificial forest communities ranged from 3.4 to 9.4, and the 6–8 years R. pseudoacacia community showed the lowest resistance to erosion among the 13 plant communities  and the AAS community (0.66). No significant difference was found between the two natural forest communities (1.05 and 1). The 15 years R. pseudoacacia community had the highest relative SOC loss between the 13 plant communities  content of all the vegetation types were higher than slope cropland , artificial shrubs (Prunus armniaca) and immature forest plantations (Robinia pseudoacacia). In our study, compared with slope cropland, the SOC content for R. pseudoacacia land was not significantly higher after six to eight years of revegetation, but a significant increase was observed at the soil surface (0–5 cm) after 15 years  also showed increased tendency . Similaret al. , who sho15 years . Lu et a , large areas of slope cropland were converted to trees, shrubs, or grasses within the Loess Plateau region ,58. Planet al.  found thet al. [H. rhamnoides, with a mean canopy cover of 92% and a litter depth 30 mm, is a powerful agent of erosion control during extreme hydrological events . However, H. rhamnoides did not achieve a similar effectiveness in controlling soil erosion in our study, which can be accounted for by the significantly lower canopy cover and litter depth . Natural secondary forest communities, especially the QSC, were most effective at protecting the soil from erosion, which can be unequivocally attributed to the dense canopy structure and the higher litter cover , especially in the 0–5 cm soil layer, and natural vegetative recovery was a more effective pathway for increasing SOC concentration and enhancing SOC storage than artificial vegetative recovery in the Chinese loess hill and gully region. R. pseudoacacia communities, with higher soil loss, produced greater SOC loss; and natural secondary forest communities, with higher carbon-concentrated soils and SOC storage capacity, may produce more SOC loss from water erosion under extreme rainstorm events.Soil erosion and erosion-induced carbon loss is tightly linked with vegetation types under extreme rainstorm events. Grassland communities, with a higher soil loss and a lower SOC content, had less SOC loss; shrub communities were intermediate in SOC content and loss; artificial


Finding new ways to control and slow down the group velocity of light in media remains a major challenge in the field of optics. For the design of plasmonic slow light structures, graphene represents an attractive alternative to metals due to its strong field confinement, comparably low ohmic loss and versatile tunability. Here we propose a novel nanostructure consisting of a monolayer graphene on a silicon based graded grating structure. An external gate voltage is applied to graphene and silicon, which are separated by a spacer layer of silica. Theoretical and numerical results demonstrate that the structure exhibits an ultra-high slowdown factor above 450 for the propagation of surface plasmon polaritons (SPPs) excited in graphene, which also enables the spatially resolved trapping of light. Slowdown and trapping occur in the mid-infrared wavelength region within a bandwidth of ~2.1 μm and on a length scale less than 1/6 of the operating wavelength. The slowdown factor can be precisely tuned simply by adjusting the external gate voltage, offering a dynamic pathway for the release of trapped SPPs at room temperature. The presented results will enable the development of highly tunable optoelectronic devices such as plasmonic switches and buffers. Here, the slowdown factor or group index relative to free space is defined as gc/v47789101112131415161819202122et al. first observed a slowdown of a SPP mode in a metallic Bragg grating by a factor of 2et al. proposed a graded grating structure to reduce the speed of light and realize a rainbow trapping effect on a metal surface19Optical signals in a medium of refractive index et al. found that graphene with spatially modulated conductivity patterns can be used as a one-atom-thick platform for transformation opticset al. showed that graphene sheet arrays are capable of steering light efficiently through the SPP coupling between individual monolayers2631Graphene, a two-dimensional monolayer of carbon atoms arranged in a honeycomb lattice, exhibits exceptional electronic, mechanical and optical properties242627282930313233343536373839404142Here, we propose a novel structure composed of a monolayer graphene and a silicon based graded grating structure. Graphene and silicon are separated by a silica spacer layer and the surface conductivity of graphene can be tuned via an external gate voltage. We theoretically and numerically demonstrate that the SPP mode in graphene shows an exceptional slowdown factor above 450 with a broad bandwidth of ~2.1 μm in the mid-infrared optical region. Furthermore, the length of graphene structure is about 1/6 of the operating wavelength. Such a small size possesses a huge potential for the realization of on-chip optoelectronic components. The slowdown factor as well as the rainbow trapping performance of the system can be readily controlled via the external gate voltage, rendering the release of trapped waves feasible at room temperature.h . A previous report showed that μ = 230000 cm2V−1s−1 could be obtained experimentally in high-quality suspended graphene2 substrate could reach 40000 cm2V−1s−1 at room temperatureμ = 20000 cm2V−1s−1 is chosen in our studyvf is set as 106 m/ssn) shows a linear dependence on the external gate voltage described by the following equation47In graphene, dε is the relative permittivity of SiO2 layer. Accordingly, sn can be set by the external voltage bV and the thickness h of SiO2 spacer, thereby controlling the chemical potential and surface conductivity of graphene. The dispersion relation of SPP modes in graphene can be derived from Maxwell's equations48In this equation, k0 = 2π/λ is the free-space wave vector of light and λ is the operating wavelength in vacuum. In the mid-infrared region, the dielectric permittivities of SiO2 and air are assumed to be dε = 3.9 and cε = 1.0, respectivelyeffn of the SPP mode, which is extremely sensitive to h and bV. Generally, the effective refractive index decreases with increasing bV due to the enlarged electric field. Thus, a larger h gives rise to a larger effective refractive index because the electric field on the graphene is smaller with a fixed voltage. In the mid-infrared region, the surface conductivity of graphene can be simplified into the Drude-like form27effn) is proportional to the square root of h, while inversely proportional to the square root of bV. The analysis is also verified by the calculation results  nearby the graphene.Here, ults see . It shouible see . Thus, t2. The Si substrate has a groove grating with period p, width w and depth d. The thickness of SiO2 spacer (the distance between the graphene and Si substrate) is t. Here, the groove depth d is constant. In general, a Bragg grating is a periodic modulation of the refractive index of the propagation medium, which is designed to selectively reflect a specific wavelength of light and transmit the others. One common way to achieve this is by stacking two materials with different refractive indiceseffn as described in the previous section.According to the Bragg scattering condition, the wavelength at which SPP modes in graphene are reflected by the grating can be derived fromeffn,1 and effn,2 represent the effective refractive indices of the SPP mode in the graphene with the two different areas above the silicon grating: effn,1,where the separation between graphene and Si is low and effn,2, where it is high  with increasing grating groove depth d. bV. Here, the blue-shift is caused by the change of Re(effn), which decreases with increasing the applied voltage bV. From k0 increases with the decrease of Re(effn).Here high see . m equalgv of light propagating in a mediumd. The group velocity is obtained from the slope of the tangent of a dispersion curve at a given point c/gv) of the graphene Bragg structure as a function of frequency (or wavelength). It demonstrates that a light signal in the graphene layer propagates at velocities more than 450 times slower than the speed of light as its frequency approaches the cutoff frequency. The slowdown factor is limited by ohmic losses in graphene and can be further improved by changing the physical factors such as carrier mobilities in graphene . To broaden the spectral region within which light signal can be slowed down efficiently, a graded grating structure  is introduced as illustrated in d is chosen to gradually increase from 100 nm to 400 nm along the x-axis, while pitch (p = 40 nm), width (w = 20 nm) and SiO2 thickness (t = 100 nm) remain constant. In order for the light trapping effect to occur, the grade gradient must satisfy the adiabaticity condition, which can in our case be expressed as δ = ∂k−1/∂x ≪ 1δ < 0.013 at the wavelength of 10 μm  distribution in the x-y plane of the structure for incident wavelengths of 8.0, 8.5 and 9.0 μm. The wavelengths are chosen to be located between the previously calculated cutoff frequencies for the minimum and maximum groove depths in the structure of d = 100 and 400 nm. x-axis, which is in excellent agreement with the results shown in λ = 7.65 to λ = 9.73 μm) feasible. The bandwidth corresponding to ~8.5 THz is improved by a factor of 4 when comparing with the results in Ref. gv can potentially be slowed down ever further and eventually approach zero.bV. Moreover, a stepwise increase of gate voltage will move the location at which a given wave is trapped continuously along the direction of propagation, as illustrated in the inset of bV = 85 V) is plotted in the inset of Another desired feature of a light tapping structure is the ability to release trapped waves in a controlled manner. It has been demonstrated that trapped waves in metal-based plasmonic waveguides can be released by introducing thermo-optic materialsIn this report, a novel structure consisting of a graphene monolayer and a graded silicon grating, which is separated from the graphene by a silica spacer layer, has been proposed. It has been demonstrated that the graphene-based plasmonic structure is capable of slowing down the group velocity of mid-infrared light propagating in graphene by a factor of more than 450. Numerical simulations as well as theoretical calculations reveal that both the grating groove depth and the applied gate voltage can be employed to efficiently tune the effective refractive index of the graphene monolayer. This allows for an exceptional tunability of the system's slowdown, light trapping and light release characteristics. By using a graded grating, incident light of a given wavelength can be trapped at a specific position in the graphene structure. Thus, optical input signals with different wavelengths can be separated spatially and trapped at specific positions in the graphene monolayer. The operating spectral bandwidth of this effect is ~2.1 μm in our structure and the trapping occurs on a length scale of one micrometer only, which is less than 1/6 of the wavelength of the propagating light. In particular, increasing the applied gate voltage allows for a controlled and systematic release of the trapped light at room temperature.The unique optical features of the graphene-based plasmonic structure combined with its simple tunability may pave the way towards the realization of nanoscale optoelectronic devices, in particular on-chip optical buffers and switches for signal processing and communications.The proposed graphene based structures are simulated using the finite-element method (FEM) software package COMSOL Multiphysics. In simulations, the graphene monolayer is represented by an ultrathin layer with a thickness of Δ = 1 nm2727It should be noted that Δ is not the actual thickness of a graphene monolayer (~0.33 nm). It is found that deviations between results obtained for Δ = 1 nm and Δ = 0.33 nm could be negligible if the simulation mesh is chosen to be sufficiently fine1920212338To theoretically calculate the dispersion relation of the graphene-based grating structure, we employ the following characteristic equationK is the Bloch wave number of SPPs in the direction along x axis. φ1 = k0neff,1(p-w) and φ2 = k0neff,2w represent the plasmonic phases of the graphene zones with SiO2 thickness of t (non-groove parts) and t + d (groove parts), respectively.Here, H.L. conceived the idea, carried out the numerical simulation and wrote the manuscript text. C.Z., Z.Q.M., X.M.L., H.M.M., R.P. and M.G. discussed the design of the proposed structure and simulation results, as well as improved the manuscript presentation. All authors discussed the results and substantially contributed to the manuscript.Supplementary Information


An optical device configuration allowing efficient electrical tuning of surface plasmon wavelength and absorption in a suspended/conformal graphene film is reported. An underlying 2-dimensional array of inverted rectangular pyramids greatly enhances optical coupling to the graphene film. In contrast to devices utilising 1D grating or Kretchman prism coupling configurations, both s and p polarization can excite plasmons due to symmetry of the grating structure. Additionally, the excited high frequency plasmon mode has a wavelength independent of incident photon angle allowing multidirectional coupling. By combining analytical methods with Rigorous Coupled-Wave Analysis, absorption of plasmons is mapped over near infrared spectral range as a function of chemical potential. Strong control over both plasmon wavelength and strength is provided by an ionic gel gate configuration. 0.04eV change in chemical potential increases plasmon energy by 0.05 eV shifting plasmon wavelength towards the visible, and providing enhancement in plasmon absorption. Most importantly, plasmon excitation can be dynamically switched off by lowering the chemical potential and moving from the intra-band to the inter-band transition region. Ability to electrically tune plasmon properties can be utilized in applications such as on-chip light modulation, photonic logic gates, optical interconnect and sensing applications. Graphene is a flat monolayer of carbon atoms tightly packed in a two-dimensional honeycomb lattice. Although graphene was only recently discovered it has attracted a lot of attention as it combines remarkable electronic, photonic and mechanical properties1234578Several methods have been implemented in order to couple and dynamically control plasmons in graphene. 1D trench based silicon diffraction gratings have been used as a wave vector/phase matching component between incident photons and plasmons in graphene. This provides control over the plasmon frequency by altering the grating lattice constant or by applying a voltage which alters the chemical potential in graphene10111214151616171921Obtaining strong coupling and highly tunable plasmons in graphene up to near infrared and visible frequencies is a difficult but highly anticipated task. In this work an inverted pyramid array diffraction grating with an ionic gel25Theoretical calculations as well as Rigorous coupled-wave-analysis simulations were undertaken demonstrating excitation of a plasmon mode, with excellent control of plasmon energy up to near infrared spectral range, using realistic chemical potential values for graphene. A plasmon energy shift from 0.65 eV to 0.84 eV when changing the chemical potential of graphene from 0.45 eV to 0.6 eV was achieved.We find that the structure supports a high frequency odd vector parity mode originating from the multi-interface nature of the device. This supports higher plasmon frequencies than typical single interface modes. Optimization of geometrical parameters such as pyramid size and pitch length were undertaken in order to achieve high coupling efficiency and demonstrate the scalable nature of the device. Unlike graphene micro and nanostructures, that can only support bound localized plasmon excitations12131415161710In practice n-doping of the graphene layer in combination with careful choice of the electrochemical window of ionic liquids used in the ionic gel can provide chemical potentials above 0.6 eV. Thus operation of the device can be extended for larger plasmon energies allowing plasmon excitations in the visible region of the spectrum.z orbitals of the neighboring carbon atoms overlap, forming bonding and antibonding states and thus the π-bands of graphene5* states form the conduction band5Carbon atoms have a total of six electrons out of which only four valence electrons can participate in bonds. The remaining two core electrons are strongly bound to the nucleus. In graphene carbon atoms are arranged in a honeycomb lattice formed by the spThe position of the chemical potential can easily be shifted above or below the Dirac point,  by applying a voltage. The carrier concentration in Graphene in relation with the applied voltage can be calculated as follows27Vg is the applied voltage, ε0 and εr the permittivity of vacuum and the relative permittivity of the substrate respectively, eq the electron charge, and d the substrate thickness. Having obtained the carrier concentration of the system the Chemical potential can be calculated aswhere vf Fermi velocity. To observe the change in optical behavior of graphene, conductivity is calculated as a function of wavelength taking into account the intraband and interband transitions. Chemical potential is obtained by use of the Kubo formulawhere ћ is the reduced Planck constant and, T the temperature, t the hopping parameter, and ω the angular frequency. By including a cubic term in the density of states this equation goes beyond the Dirac-cone approximation thus providing highly accurate results for high photon energies. Even though the response of the permittivity is essentially determined by valence and conduction electrons, the highly polarized environment originating from core electrons shouldn’t be ignored. The dielectric function including the contribution of the core electrons (background permittivity) can be expressed:wheredg graphene’s thickness (taken as 0.34 nm).where real) and 2.b (imaginary) parts at a temperature T of 300 K and a hoping parameter t of 2.7 eV for photon energies between 0.4 eV and 3 eV and chemical potential It should be mentioned that for wavelengths shorter than 410 nm (3.02 eV) an exciton-dominated peak with a maximum at 270 nm (4.6 eV) begins to appear35imaginary permittivity is positive, corresponding to energy loss for photons propagating through the material. This loss is due to absorption of photons by valence electrons participating in vertical interband transitions. In the same spectral region real permittivity has a stable value of 5.5 due to the polarization originating from the core electrons as seen in real and imaginary permittivity at the limit where photon energy equals twice the chemical potential in graphene  between the interfaces is smaller than the decay length The electrostatically controlled plasmon wave vector dispersion in graphene can be obtained by calculating the relation between the plasmon wave-vector and frequency. In multilayer systems of alternating dielectric/conducting materials each individual interface with a conducting layer can support Transverse Magnetic (TM) modes of bound surface plasmon polaritons37spersion . Taking where y of air . Since dx(z) component of electric field is odd, Hy(z) component of magnetic field and Ez(z) component of electric field are even functions) and x(z) is even, Hy(z) and Ez(z) are odd functions)sp) being greater than that of incident photons (ћk0) for the same frequency. Because of the mismatch in wave-vector, surface plasmons cannot normally be generated and thus phase matching is required. In this device, phase change is achieved by the introduction of a 2-dimensional grating below the graphene in the form of an inverted pyramid array. A simple one-dimensional groove approximation  features in the graphene dispersion and grating phase match conditions arising from the simple analytical analysis  is a highly efficient semi-analytical method for simulating electromagnetic behaviour of periodic structures. Electromagnetic fields and device geometries are represented by a sum of harmonic functions in Fourier space, and fields are solved in the form of a transmission line problem. RCWA simulations are particularly useful for graphene devices because (in contrast to FDTD or FEM methods) they don’t require solution of Maxwell’s equations over dense grids. Instead, structure is divided into uniform layers in the z direction and electromagnetic modes calculated by applying a layer by layer analytical solution which goes far beyond the simplified 3 layer system described in the previous section.In this section, relationship between geometrical parameters associated with the underlying inverted pyramid array diffraction grating  transfer process. Graphene is safely modelled as a 0.34 nm thick layer  with permittivity given by An absorption peak is observed away from the interband transition region and at the location of the phase match frequency appearing as a sharp (white) line. As graphene chemical potential increases, the real part of permittivity becomes increasingly negative due to higher quantity of free carriers. Thus a blue-shift in plasmon excitation frequency is observed (dispersion line moves to larger energy), thereby confirming electrically tuneable plasmon absorption.Looking more closely at the superimposed lines for the analytical model, for the single interface mode (cyan line) it predicts plasmon excitations at lower frequencies compared to RCWA method, whereas they are in excellent agreement to RCWA solutions for odd vector parity mode (black line). This provides proof that the excited mode is indeed a high frequency odd mode, and that the analytical model is actually very accurate. The higher plasmon frequencies supported by this mode when compared to plasmon excitations in single interface systems makes it ideal for scaling plasmons in graphene towards shorter wavelengths. In both cases strong modulation of plasmon excitation energy can be clearly observed with 0.04 eV shift in chemical potential resulting in ~0.05 eV shift in plasmon energy. Intensity of the absorption peak heavily depends on optical loss in graphene, mainly characterized by the imaginary part of permittivity, with higher losses corresponding to broader and lower peaksThe underlying 2D grating geometry can be scaled to shift the coupled graphene Plasmon frequency to match a broad range of incoming wavelengths and incidence angles, and also improve coupling efficiency. Plasmon absorption strength depends heavily on diffraction efficiency of the underlying grating structure used for phase matching. Improved diffraction efficiency increases coupling between incident light and graphene plasmons, resulting in higher intensity plasmon absorption peaks.Diffraction efficiency is related to density and size of diffractive structures. Optimization of size and spacing between inverted pyramids results in significantly improved diffraction efficiency. Effect of pyramid width (w) is investigated in frequency) is found to be unaffected by pyramid size.Plasmon absorption becomes stronger with increasing pyramid width, until the pyramid becomes approximately ¾ the size of the pitch where it begins decreasing again. Investigating this further, Diffracted photon k-vector is related to grating pitch (α) and so provides control of phase match frequency between incident photons and graphene plasmons. This is investigated in The analytical calculations are found to be highly accurate agreeing with RCWA simulations within 0.001 eV (1 nm).Virtually no shift in excitation energy is observed as a function of incidence angle  for a 10Phase matching can only occur for surface plasmon polaritons propagating perpendicular to the diffraction features when incident photons are polarized in the same direction10Finally it is interesting to see what happens when the aspect ratio of the system changes and how this affects plasmon excitations for different incident photon polarizations. Increasing the width (w) of only one side of the pyramid (moving from square to rectangular structures) breaks the symmetry, thus an increase of coupling efficiency for the polarization satisfying excitations perpendicular to the direction of the extended feature is expected. At the same time a decrease of efficiency is expected for the other polarization. This can be observed in 2 V−1 s−1 has been demonstrated (by employing current induced heating in order to reduce impurities), these high mobility values are limited over a small range of carrier concentrations2 V−1 s−1 at low temperatures and above 50.000 cm2 V−1 s−1 at room temperature) but once again for larger carrier concentrations the scattering loss increases2 V−1 s−1 and 1200 cm2 V−1 s−1 for unsuspended graphene layers172644It has been reported that dissipative losses in graphene in the TerahertzEven though this study is a purely theoretical approach, it is important to investigate how the device performs when including experimentally obtained mobility values in the calculations. In this case simplified equations for the conductivity of graphene are used instead of 46g is demonstrated in where the mobility is included through the phenomenological scattering rate By including the permittivity values for different mobility rates when modeling the graphene layer for the RCWA simulations the effect of dissipative loss can be observed in the absorption spectra as seen in In conclusion the reported optical device configuration shows strong electrical modulation of surface plasmon energy and absorption intensity. The underlying 2-dimensional array of inverted pyramids is highly efficient for coupling photons to the graphene film supporting excitation of plasmons equally for both s and p polarizations due to the structure symmetry. By optimizing the diffraction efficiency of the underlying structure significant increase in plasmon absorption intensity was observed. The device provides highly efficient dynamic modulation of the plasmon energy operating over a very large spectral range and up to the near infrared for currently easily achievable graphene chemical potentials. Assuming higher chemical potentials operation of the device can be extended to the visible spectrum as is. Furthermore, plasmon excitation can be effectively shut down by lowering the chemical potential providing dynamic means of photonic switching which can be exploited for high density optical interconnects. Plasmon absorption was also found to be highly unaffected by angle of incidence thus providing the possibility of exciting plasmons on the monolayer with the use of high numerical aperture lenses. Finally an analytical model assuming a multilayer setup was presented with excellent agreement to the RCWA simulation results for the high frequency odd plasmon mode providing an easy way to estimate the operation and design of new devices. Over-all the device can be utilized in a large number of possible applications including sensors, photonic logic gates, optical interconnects and modulators.How to cite this article: Matthaiakakis, N. et al. Strong modulation of plasmons in Graphene with the use of an Inverted pyramid array diffraction grating. Sci. Rep. 6, 27550; doi: 10.1038/srep27550 (2016).


We report ZnO/glass surface acoustic wave (SAW) humidity sensors with high sensitivity and fast response using graphene oxide sensing layer. The frequency shift of the sensors is exponentially correlated to the humidity change, induced mainly by mass loading effect rather than the complex impedance change of the sensing layer. The SAW sensors show high sensitivity at a broad humidity range from 0.5%RH to 85%RH with < 1 sec rise time. The simple design and excellent stability of our GO-based SAW humidity sensors, complemented with full humidity range measurement, highlights their potential in a wide range of applications. However, the ever-fast progressing science and technology require humidity sensors with better sensitivity, wider sensing range, faster response, shorter recovery time, and lower cost than what is now commercially available914etc in humidity sensors has resulted in many exciting progresses over the recent years. However, the development of novel sensitive materials and high performance humidity sensors, especially for applications requiring fast, low humidity level detection deserve more investigation and research.Measurement and control of environment humidity are of great importance in industrial processes, agricultural productions, and research experiments12256Functionalized graphene exhibits unique properties in chemical and biological sensing161718194etc27et alet al reported a SAW humidity sensor based on electrospun polyaniline/poly nanofibers sensitive layer with a sensitivity of ~75 kHz/%RH from 20 to 90%RHet al investigated SAW humidity sensors with silver nanoparticles as the sensing layer and obtained a sensitivity of over 10.6 kHz/%RHet al demonstrated humidity sensing characteristics of SAW sensors with atomizing GO sensitive layer with a sensitivity of 1.54 kHz/%RHet al and Ciplys et al investigated the mechanisms of SAW sensors with a graphene layer, and pointed out that the mass loading and viscoelastic effects are responsible for the increased attenuation observed19Surface acoustic wave (SAW) devices are one of the building blocks for electronicsWe prepared GO nanoflakes from natural graphite crystals using methods reported elsewhereGO dispersions allow deposition on target substrates by various methods such as drop-, spin-, spray-, and dip-coating23−1 and 1350 cm−1 which are known as the G and D peaks, respectively. The G peak corresponds to the E2g phonon at the Brillouin zone center. In pristine graphene−1. The presence of double-bonds (C = C) in our GO sample causes the blue-shift of the G band−1. The D peak originates from the breathing modes of six-atom rings and requires a defect for its activation. For the case of GO, this primarily comes from lattice defective states . Also, for the case of defected graphene samples like GO, G peak broadening is commonly observed as a result of the activation of q≠0 phonons−1. The high ID/IG ratio (~1.1) indicates large defect density in our GO sample. Considering FWHM(G) and ID/IG in our sample, we use I(D)/I(G) = C′(λ)La2 to find the cluster size, La, with C′ = 0.55 nm−2a ~ 1.4 nm. 2, O-C-O and O-C = O bonds, respectively. These oxygen-related chemical bonds increase the hydrophilicity of the GO layers, thus enhancing the humidity sensitivity of the SAW devicesThe typical Raman spectrum of the GO layers is shown in −1 is attributed to the -OH groups in stretching vibrations. This peak implies the good hydrophilicity of the GO samples used for our humidity sensing. Other absorption peaks at 1725 cm−1 originates from the C-O stretching vibrations of carbonyl and carboxylic groups, at 1627 cm−1 from the C-H, at 1398 cm−1 from the C-OH, at 1240 cm−1 from the C-O-C and at 1112 cm−1 of C-O stretching. These are all consistent with the results of the XPS spectrum. The presence of such carboxyl and hydroxyl functional groups in GO enhances the water adsorption ability of the sensing layer for humidity sensing.λ = 2d sin(θ)) of about 9.0 Å, which is much larger than that of bulk graphite crystal XRD pattern of the GO layers used in our experiments is shown in 2 gas to pass through for sensing. The relative humidity in the box was controlled by changing the flow ratio of dry N2 to wet N2 into the box, while keeping the total flow rate at 500 sccm. All the experiments were conducted at 25 ± 2°C.λ = 12 and 20 μm and resonant frequencies at ~225 MHz and ~140 MHz, respectively, were fabricated. They were coated with various GO layers for the humidity sensing experiments. SAW sensors with wavelengths of rf~140 MHz in Group A, sample D8 with a GO thickness of 200–300 nm over the whole surface exhibits the most significant frequency shift, i.e. the highest sensitivity, followed by the sensors with thinner or smaller area GO layers. Similarly, for the devices with a frequency of rf~225 MHz, D10 with a thicker GO layer has a larger frequency shift than that of D9 with a thinner GO layer.Moisture can be easily absorbed by the GO layer as it is a hydrophilic material 41434442319Δf, induced by a loaded mass, Δm, can be expressed asrf is the resonant frequency, μ and ρ are the shear modulus and the density of the substrate, respectively, A is the sensing area. sΔρ = Δm/A) change of the adsorbed water on the surface at various humidity for sensors D5-D10, indicating that the surface mass density increases non-linearly with the linear increase in humidity. Since the mass increase is associated with the number of water molecules, it actually reflects the nonlinear increase of water molecules adsorbed when the humidity increases. The sensor with thicker GO layer has higher capability to adsorb more water molecules, hence larger frequency shift. Note that we normalize the surface mass per unit area to eliminate the GO coverage difference from sample to sample. The increased frequency shift, hence the sensitivity, is attributed to the improved hydrophilicity and surface area of the active GO layers used. Assuming the hydrophilicity for ZnO and GO is similar, the increased surface mass density can be considered as a result of the increased sensing area, that can be calculated with respect to that of sample D1 with clean surface  as an example. They can be described by the following relation, 0f is the initial resonant frequency, 0RH is the reference relative humidity, a and b are two coefficient constants. The relationship has excellent linearity (0.9763<R2<0.9774) for both the sensors. The sensitivity of a humidity sensor is defined asΔf and ΔRH are the frequency shift and humidity change, respectively. From Eq.(3), the humidity sensitivity of all the sensors can be calculated with the results summarized in rf~225 MHz are 70–90% higher than those of sensors D6-D9 with similar GO layers but different resonant frequency, rf~140, showing that the resonant frequency has a significant effect on sensitivity of the SAW sensors. The sensitivity of the sensors increases as the resonant frequency increases.The frequency responses to humidity are approximately exponential as shown in Δf and insertion loss vs. RH when the humidity is changed from 10%RH to 85%RH and back to the initial value, showing little hysteresis to the humidity change. The rf shifts down, while the insertion loss increases with humidity. Both the frequency and insertion loss show fast response when the humidity is changed in a stepwise fashion. This indicates that the residual moisture in GO layer is very limited, and is not detrimental to the accurate measurement of humidity, even when fast response is necessary.As the sensor with a GO thickness of 100–130 nm has high sensitivity and fast response, it has been investigated in detail. rf~140 and 225 MHz) are far away from the ionic and dipole relaxation frequency of water molecules. Therefore, the impedance (conductivity) change induced by water molecules at SAW resonant frequencies is expected to be negligible. A detailed discussion about the surface conductivity window is presented in In general, adsorption of moisture decreases the surface complex impedance. This, in turn, may change both the acoustic velocity and attenuation of a SAW device49shσ ~ 0.2 Ω−1), it will screen off any minor surface conductivity change of the GO layer induced by adsorbed water. Therefore, the structure of D12 can eliminate the effect caused by the surface conductivity variation, and a smaller frequency shift is expected for D12 than that of D5 if there is a water-induced conductivity change in the narrow window. To further determine whether the resonant frequency shift is caused by the conductivity change or not, we designed an experiment with samples D5 and D12  were further investigated  of GO may produce protons, which may induce additional mass and change the surface conductivity. However, the change in mass on the surface is very small owing to the chemical reaction, which has little mass exchange involved, and will not change the resonant frequency. The generation of free proton carriers may partially contribute to the total change of the surface conductivity of the sensors with GO layer, which has been proven to be not the major factor to affect the resonant frequency change as discussed above. Therefore we can conclude that the possible interaction of free carrier protons via reaction of GO with water would not affect the sensing results obtained in this work.The viscoelastic effect is another possible cause responsible for the frequency shift upon moisture absorption, and especially important for SAW humidity sensors with a polymer coating. It is difficult to separate its effect from the mass loading effect19In summary, ZnO on glass SAW humidity sensors with GO sensitive layers have been fabricated and characterized. The sensitivity of the SAW sensors is positively correlated with GO layer thickness, resonant frequency, and the covered surface area by the GO sensitive layer. The frequency shift of the sensors is exponentially sensitive to the humidity change, and is caused by mass loading effect. The sensors with an extended coverage of a drop-casting GO layer over IDTs area have the best performance, followed by those with a GO layer in between the IDTs and those with spin-coated GO layers. The SAW sensors show very fast response to humidity change with a rise time of less than 1 sec, and the total fall time of less than 19 sec. They also show good stability at various humidity levels for up to 60 days without much deterioration. Our results demonstrate SAW devices with GO sensing layer are suitable for applications in various fields such as health and environment humidity monitoring at room temperature.2 with 100 and 50 sccm flow rates were employed for the deposition with the substrate temperature and the deposition pressure at 200°C and 2 Pa, respectively. The bias voltage at target was 75 V and the deposition power was 175 W. The thickness of ZnO is ~3.0 ± 0.06 μm for all the devices used in this study. After deposition, the samples were annealed at 400°C for 10 min in N2 atmosphere  to reduce the stress and defects in the films. The samples were then characterized by X-ray diffraction , atomic force microscopy , and scanning electron microscopy  as previously reportedZnO piezoelectric films were deposited on the glass substrate by direct-current (DC) reactive magnetron sputtering. The optimized deposition conditions have been reported previouslyλ = 12 and 20 μm were fabricated to investigate the effect of resonant frequency on the sensing performance. The corresponding resonant frequencies, rf, are approximately 225 and 140 MHz, respectively. All the SAW devices have 50 pairs of IDT fingers and 10 pairs of reflecting gratings. The transmission spectrum (S21) and insertion loss of the sensors were investigated at various relative humidity (RH) using a network analyzer , which was controlled by a LabVIEW-based software through general purpose interface bus (GPIB).The SAW devices were fabricated on 500 μm thick Corning 2318 glass substrates with ZnO as the piezoelectric layer60Graphene oxide layers were characterized by Raman spectrocopy , X-ray photoelectron spectroscopy , X-ray diffraction , and Fourier transform infrared spectroscopy . The thickness and morphology of the GO layers were characterized by profilometer  and scanning electron microscopy .2 gas with various humidity levels to pass through and two SMA (SubMiniature version A) interfaces for transmission measurements. The relative humidity in the box was controlled by changing the flow ratio of dry N2 to wet N2 into the box, while keeping the total flow rate at 500 sccm. A commercial hygrothermograph (TASI-621 TASI, based on SHT71GO material was prepared and deposited on the surface of the SAW devices more than a month before sensing experiments. The SAW sensors were placed in a hermetic box with two through-holes for NW.X., M.H. deposited ZnO and Al thin films, fabricated SAW devices; Z.X. provided the GO samples; W.X., N.M. conducted the characterization of the GO materials. W.X., X.H., W.W. and J.C. set up the humidity sensing experiment and assisted the sensing experiments. W.X. and T.S. measured all the sensors. Y.X., T.H. and J.K.L. supervised the project, analyzed the results and modified and revised the paper. All authors contributed to the discussions.Supplementary Information


Retroelement activity is a common source of polymorphisms in human genome. The mechanism whereby retroelements contribute to the intraindividual genetic heterogeneity by inserting into the DNA of somatic cells is gaining increasing attention. Brain tissues are suspected to accumulate genetic heterogeneity as a result of the retroelements somatic activity. This study aims to expand our understanding of the role retroelements play in generating somatic mosaicism of neural tissues. Whole-genome Alu and L1 profiling of genomic DNA extracted from the cerebellum, frontal cortex, subventricular zone, dentate gyrus, and the myocardium revealed hundreds of somatic insertions in each of the analyzed tissues. Interestingly, the highest concentration of such insertions was detected in the dentate gyrus—the hotspot of adult neurogenesis. Insertions of retroelements and their activity could produce genetically diverse neuronal subsets, which can be involved in hippocampal-dependent learning and memory. Approximately 40% of the human genome is comprised of multiple copies of retroelements (REs) due to their winning streak in the course of mammalian evolution . The majIt has been long considered that the majority of retrotranspositions occur in the germ line, while the mobility of REs in somatic cells is strictly suppressed. Mammalian cells possess multiple mechanisms of inhibiting REs expression, including siRNA , miRNA , piRNA-iHere we applied a high-throughput approach to directly compare the number of autonomous (L1) and non-autonomous (Alu) retroelement somatic insertions in various human adult brain regions and a control non-nervous tissue. Whole-genome Alu and L1 profiling was performed for four brain regions including the dentate gyrus, the only region of the adult human brain that was shown to retain significant neurogenic capacity.in vitro and in vivo in the mouse dentate gyrus [Previously, activation of L1 retrotranspositions was associated with a switch from neural stem cells to fast proliferating neural progenitor cells te gyrus , 28. Thete gyrus . In the te gyrus , 31, whete gyrus –35. To aFor library preparation, we modified the suppression PCR-based method of retrieving REs terminal and flanking sequences from genomic DNA , 37. BriA total of 10,709,681 and 61,213,133 high-quality reads were obtained for L1 and Alu libraries, respectively. The detailed information on the number of reads and somatic insertions detected in each library is shown in A total of 7,497 potentially somatic L1 and 8,990 potentially somatic Alu insertions were identified in the tissue libraries . All theA total of 3,798 somatic L1 and 4,314 somatic Alu elements from all libraries integrated into genes (overwhelmingly into introns). Another portion of somatic insertions (436 L1 and 393 Alu) was detected within 5,000 bp upstream of the gene transcription start sites . In ordeInterestingly, across all samples analyzed, the distribution of somatic L1 or Alu insertions was very similar, namely, the percentages of somatic L1 or Alu that integrated into the genes or 5 kb region upstream genes were 50–51% and 5.5–6.5% for L1 or 47–49% and 3.5–5% for Alu, respectively . The samFinally, we analyzed the orientation of somatic retroelement insertions relative to genes (for those retroelements that integrated into introns or 5 kb regions upstream genes). Strikingly, intronic L1 elements preferentially integrated in the opposite orientation relative to the gene  −40.96 ±Nested PCR and Sanger sequencing of the PCR products were carried out to validate the potentially somatic insertions. We selected 34 L1 and 26 Alu elements integration events for validation . We confIn this study we for the first time showed an increased number of L1 somatic retrotranspositions in the dentate gyrus of the human brain in comparison to other brain regions and the myocardium by directly sequencing and mapping the somatic insertions. Several recent studies proposed that activation of L1 retroelements coincides with neuronal differentiation , 23, 28.Notably, we did not find any increase in the retrotranspositions in another putative neurogenic zone of the adult mammalian brain, the SVZ. However, several recent studies indicated that in humans, unlike rodents, the neurogenesis in the adult SVZ is negligible , 35. RobInterestingly, we showed that the number of somatic L1 retrotranspositions in promoters and genes is higher than expected for all brain samples and the myocardium. This observation is different from the data obtained by Ewing and Kazazian  where auThe orientation of genic L1 insertions was observed to be biased towards counter-orientated state in all brain regions and myocardium. This can be caused by a higher negative effect of co-oriented insertions on gene expression (e.g. knock-down of gene expression) and is similar to the results obtained by Ewing and Kazazian . Howevercis-preference to the self RNA [Similar to the somatic L1 insertions, the Alu insertions demonstrated the most persistent expansion in the dentate gyrus. However, the rates of Alu propagation in the rest of the samples was not as equal as for the L1. The percentage of somatic Alu elements was variable and significantly different between the regions analyzed. This can probably be explained by the differences between the mechanisms of Alu and L1 suppression , 39 or bself RNA .Interestingly, the number of somatic Alu integration events in genes and promoters was similar to the expected values for all regions analyzed, but the DG. Furthermore, in the DG while Alu integrated preferably in the genes, they avoided integrating in the promoter regions, which is opposite to L1. Moreover, DG was the only brain region in which the orientation bias of the somatic Alu insertions was observed. Altogether these facts suggest that cells of the DG carrying new Alu insertions are subject to selection.The data on both L1 and Alu somatic insertions obtained in the current work indicate an increased retrotranspositional activity in the DG. Since our results are based on the analysis of a single donor we cannot exclude the possibility that the observed pattern of the somatic insertion distribution in brain tissues is unique and can vary in other members of the population. However, our results match the data obtained by qPCR  indicatiWe have not observed any insertions which were represented by many sequencing reads on the one hand and could be considered somatic on the other. This indicates that the retroelement hops in the genome occur mainly in adult tissues or at the stage of late development, but not during embryogenesis. This corresponds to the results of Baillie and colleagues  who haveOur results are consistent with the studies that were performed in mice. Although L1 can retrotranspose in many regions of the mouse brain , an injeA three room standard was applied for sample preparation: all procedures with genomic DNA were performed in room 1; PCR preparation was performed in room 2; electrophoresis and other post-PCR activities were performed in room 3.Primers for validating potential somatic insertions lied out of the sequences which comprised the resulting Illumina libraries in order to avoid the amplification of the contaminating molecules from these libraries.Tissue samples were taken within 12 hours after death from a 72 year old male individual. Tissue samples were frozen in liquid nitrogen immediately after sectioning and then stored at -80°C. The study was approved by the local ethics committee of the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences and conducted in accordance with the Declaration of Helsinki. As no consent could be obtained from the donor, the written consent was provided by the next of the kin. Genomic DNA was extracted from five frozen tissue samples of a single individual: cerebellum, frontal cortex, subventricular zone, dentate gyrus and myocardium, using the standard phenol-chloroform extraction method.The library construction protocol included the step of genomic DNA digestion by restriction enzymes , adapter ligation and two steps of suppression PCR selectively amplifying the insertion sites of the most active RE subfamilies (L1Hs and AluYa5). Sequences of the oligonucleotides used for library preparation are shown in Data analysis included the use of standard tools: Bowtie2 , 47 and The coordinates of the potential somatic insertions were intersected with the coordinates of the known genes and genes promoter regions  present in hg19 by the Galaxy tool “Join”. Statistical analysis was done using R software  includinThe analysis of Alu and L1 distributions in different brain areas and of the genomic distribution of the somatic L1 and Alu insertions was performed using an overdispersion test. The distribution of Alu and L1 in the dentate gyrus was compared with the distribution in all other samples combined using the Poisson test. Binomial tests were applied for the analysis of somatic L1 and Alu orientation relative to nearby genes. Monte Carlo simulations of random retroelement distributions throughout the genome were performed to analyze the randomness of the Alu and L1 distributions in promoters and genes.Nested PCR was performed for the validation of the selected somatic retroelement insertions. PCR products were Sanger sequenced. Primer structures and sequences are given in Nested PCR was performed to amplify the RE insertion flanking sequences from gDNA. Primer structures are given in S1 Materials and MethodsFor more details see The European Nucleotide Archive accession number for the Illumina sequences reported in this paper is PRJEB4787.S1 Table(XLSX)Click here for additional data file.S2 Table(PDF)Click here for additional data file.S1 Materials and Methods(PDF)Click here for additional data file.