This paper presents a cold field emission electron source which overcomes these problems based upon using a graphene-coated nickel point cathode. Preliminary experiments demonstrate that it provides stable emission for relatively large tip diameters (micron sizes), can operate in high vacuum conditions (>10−8 torr) and has an ultralow work function value of 1.10 ± 0.07 eV. It has an estimated reduced brightness value of 1.46 × 109 A m−2 sr−1 V−1 for cathode tip-radius of 170 nm and the measured energy spread ranges from 0.246 eV to 0.420 eV for a tip radii range of 260 nm to 500 nm, which is comparable to state-of-the-art conventional cold field emission sources.There have been several long-standing problems of cold field emission sources for electron microscopy and lithography that have prevented their widespread use, such as their inherent ultrahigh vacuum condition requirement (<10 Traditional cold field emission electron sources rely on single crystal tungsten sharpened wires. Here, the authors use graphene-coated nickel point cathodes to devise alternative cold field emission electron sources for electron microscopy and lithography applications. The most common type of cold field emission electron source in high-resolution microscopy usually utilizes a single crystal (310)-oriented tungsten sharpened wire as the cathode, whose tip radius is in the 100–200 nm range with a work function (ϕ) of 4.4 eV5. Typically, electron emission from the cathode occurs when the field strength at the cathode tip exceeds values around 4 V nm−1, allowing electrons to escape from the cathode surface by quantum tunneling5.Within the wide variety of electron sources used for electron microscopy and electron beam lithography, cold field emission electron sources have the highest brightness, coherence and lowest energy spread, making them the best choice for high-resolution applications−9 torr for W(310)) and, secondly, their inherent current instabilities, both in their long-term and short-term emission5. As a result, the stable and reliable Schottky electron beam source, which involves heating the cathode to 1800 K, is the most widely used type of electron source for high-resolution electron microscopy applications, despite it having significantly lower brightness, coherence and higher energy spreads than cold field emission sources7. Another important limitation of conventional cold field emission electron sources is that their emission current decays significantly  within the first hour of usage, subsequently requiring cathode flashing (Joule heating at high temperatures) at regular intervals, as short as a few hours, to reach the original emission current levels5.Despite their desirable electron optics properties, cold field electron emission sources suffer from some well-known practical difficulties that have prevented their widespread use. Two such long-standing technological challenges include, firstly, their requirement of ultrahigh vacuum (UHV) conditions ), but also have relatively large supporting wire dimensions (in the millimeter range), providing mechanical and thermal stability for the field emission. The multiple micro-fabricated emitters involving graphene sheets or graphene coating where graphene field emission has been demonstrated so far requires much more development before it can be applied to the subject of electron beam microscopy and lithography.One material, reported to have good field emission properties, but not yet used in cold field emission sources for electron microscopy/lithography applications, is graphene. Graphene, a single layer of carbon atoms arranged in hexagonal lattices, is well known for having a wide range of promising applications owing to its excellent thermal, mechanical and electrical properties20, or a graphene ring structure21. In the case of the loosely hanging ultrathin and freestanding graphene flake, it cannot be used for practical applications, since the graphene flake can easily be damaged or detached from the supporting tungsten probe by back bombardment of high-energy positive ions. In the case of the graphene ring cathode, it requires the use of a non-conventional electron beam column, one which forms a ring beam focus at the specimen plane, instead of the normal single-point focus.So far, the only single-tip emitters involving graphene consist either of overlaying an ultrathin (~1 nm) graphene flake on to a blunted tungsten probe−8 torr) with high current density. Stable electron emission has been experimentally obtained from a cold field emission gun with a single-tip cathode diameter in the micron range and in HV conditions. Successful cold field emission from single-tip emitters has up to now only been possible in UHV conditions with sub-micron tip radii, typically in the 0.1 to 0.2 μm range. The experiments reported here were carried out on a few-layer graphene-coated Ni wire cathode design, and demonstrate it to have an ultralow work function (1.10 ± 0.07 eV), requiring around an order of magnitude lower applied electric field strengths (~0.5 V nm−1) than comparable conventional single-tip cathodes. This significantly lower electric field strength requirement makes it possible to have field emission from larger diameter tips (in the micron range), and also reduces the kinetic energies of back-bombarding positive ions. This leads to better current stability and less damage to the cathode tip, and also makes it feasible to operate the gun at less stringent vacuum conditions. Based upon experimentally measured angular intensity results, the Graphene-Ni single-tip cathode is predicted to have a higher reduced brightness than comparable conventional cold field emission electron sources, and there is no obvious need for regular thermal flashing of the cathode. These advantages come from its ultralow work function and relatively low applied electric field strength at the tip apex. The single-tip Graphene-Ni wire cathode source as presented here appears to have overcome many of the practical difficulties which have so far hindered the widespread use of cold field emission sources for electron/microscopy applications.Here we report a few-layer graphene-coated nickel (Graphene-Ni) wire cathode in the sub-micron to micron size that can operate in high vacuum (HV) conditions  images of the graphene-coated Ni tips (of four different tip radii) as depicted in Fig. 25.A two-step process Fig.  was used−1, a G peak at about 1586 cm−1 and a 2D peak at about 2705 cm−1. The position and shape of the G peak confirms the formation of sp2 phase carbon and provides further evidence of the presence of graphene26. In addition to the relatively high G peak, the D peak which shows the presence of sp3 carbon atoms or defects is close to the background level, indicating insignificant defects in the as-grown graphene layers and the film exhibits high graphitic crystallinity26. The intensity ratio between 2D and G (IG/I2D) peak provides a good measure of the number of graphene layers, and this ratio was around 1.77, a value indicative of a few-layer graphene structure27.To confirm that the Ni cathode wire is covered with graphene after the CVD process, energy-dispersive X-ray spectroscopy (EDS) was employed to examine the chemical composition of the grown film. Figure 28). Different regions of the graphene flake were examined and the results consistently indicated the high crystallinity of the deposited graphene film  and high-resolution transmission electron microscopy (HRTEM) were used to further investigate the crystallinity, lattice structure and the thickness of the graphene flake. The SAED pattern Fig.  of the g−3 sr. The test setup was subsequently placed in a HV (4 × 10−8 torr) chamber for field emission tests. A negative voltage Vc was applied to the cathode (while the rest of the setup was grounded) and the current leaving the anode plate, referred to here as total current (It), and the current reaching the Faraday Cup, referred to here as the sample current (Is), were recorded. The measured (It − Vc) (red) and (Is −  Vc) (blue) emission characteristics for a cathode of tip radius of 400 nm are plotted in Fig. 29. The F-N formula is given as:A has the dimension of area [m2], ϕ is the work function in [eV] and F is the local electric field on the cathode tip, which is given as β being the field enhancement factor, d the anode to cathode tip spacing. The total current (It) reaches a maximum value of 4.2 µA, at which point (Is) was recorded to be 136 nA, corresponding to a maximum normalized angular current density −1 kV−1, where 6, respectively.An experimental cold field emission electron gun setup  before (orange) and after (violet) it is coated with graphene. Work function estimates were extracted from the slope of the graph in the F-N plot, the cathode to anode distance (d), and field enhancement factor (β), using Supplementary Eq. d was measured accurately in a SEM, and SEM imaging also provided an estimate of the tip radius, which was approximated to be spherical in shape. The Lorentz-2EM boundary element software30 was then used to numerically solve for the potential field distribution around the tip, and derive a simulated value for the field enhancement factor β . The work function estimates from the F-N plots using this method were calculated to be 5.80 eV for the bare Ni tip and 1.03 eV for graphene coating Ni tip. The 5.80 eV value for the bare Ni tip agrees within 6% of the one reported previously for bulk Ni by other researchers23, confirming that the work function estimates derived from the present experiment are relatively accurate. Further confirmation of the accuracy comes from calculating the work function for the graphene-coated Ni tip by taking the ratio of the two F-N plots shown in Fig. d and β. The work function value for the graphene-coated Ni tip using this second method was calculated to be 1.1 eV, giving better than 7% agreement with the value (1.03 eV) derived directly from the F-N plot using d and β. The cathode surface area Sp which contributes to the current collected by the Faraday Cup, was also estimated using simple direct ray tracing simulations  an increase in the graphene density of states, caused by the enhanced cathode tip electric field, on the order of 0.5–1.5 V nm−1, raising the Fermi level32. The combination of these two effects is most likely responsible for the dramatic reduction of work function value, as measured here, a value of 1.1 eV which, to the best of our knowledge, is the lowest reported value for single-tip pointed cathodes.One of the stand out features of the Graphene-Ni point cathodes reported here is their ultralow work function values. This significant finding was extracted from the experimental results shown in Fig. Br are required, and it can be estimated from the following expression33:e is the electron charge, I′ is the angular current density, mα is the angular magnification, rtip is the tip radius and<Et> is the mean tangential energy. For cold field emission,33, where ħ is the reduced Planck constant and m is the electron mass. Direct ray tracing of electron trajectory paths leaving the cathode surface using the Lorentz-2EM software were carried out to estimate mα and F and when used together with the measured angular current density I, gun brightness Br estimates were obtained 34 and graphene-coated point cathodes having tip dimensions that roughly fall in the middle region. The estimated Br value of 2.51 × 109 A m−2 sr−1 V−1 of a graphene-coated cathode of tip radius 170 nm is very close to the highest reported Br value of 3.98 × 109 A m−2 sr−1 V−1 for a conventional tungsten cold field W(310) emitter with a tip radius of 160 nm5, and is higher than the value of 9.86 × 108 A m−2 sr−1 V−1 for a W(111) emitter with a tip radius of 120 nm29. It is worth noting that Br values from even larger size tips are still relatively high and comparable to the Br value obtained from the state-of-art tungsten field emitters. A summary of the typical operating parameters for the graphene-coated point cathode is listed in Supplementary Table Br due primarily to the large value of I′ and the substantially small value of <Et> as a result of the low local electric field strength F required to produce electron emission. A high brightness electron beam is affected by statistical Coulomb interactions . The results predict that the brightness will only be lowered by Coulomb interaction effect significantly for the smaller Graphene-Ni cathode tip radius (reduction by around 30% for the 170 nm tip radius), and is not expected to significantly lower the brightness estimates for the larger Graphene-Ni cathode tip radii , as reported in this paper, are therefore expected to have an order of magnitude lower RMS noise ratio values as compared to conventional tungsten cold field emitters. Figure Is) of ~0.168 nA, ~1.86 nA and ~8.52 nA, which corresponds to angular current densities of ~0.056 µA sr−1, ~0.62 µA sr−1 and ~2.84 µA sr−1 respectively. Stepwise changes in emission currents were observed and such fluctuations may be attributed to events such as adsorption, desorption or flip-flop of adsorbate molecules at the tip of the emitter38. The short-term RMS noise ratios were calculated to be in the range of 5–10%, relatively low for the HV conditions in which they were taken, confirming the better performance expected by theoretical considerations (for larger tip sizes). To further verify the structural robustness of the graphene-coated point cathodes, It every 8 h for 3 days as shown in Fig. 5. In the case of the graphene-coated cathode, there was no obvious need for flashing of the cathode tip. The RMS noise ratios were found to be between 20 and 30% in each 8 h period throughout the 3-day test duration. Repeated field emission tests of the graphene-coated point cathode were carried out in a HV chamber, confirming that the graphene-coated point cathode has highly repeatable field emission characteristics  noise ratio , and is comparable to that obtained from carbon nanotubes emitters40  and Schottky emitters41  for the same frequency range.The frequency characteristics of the electron emission process was investigated by plotting the normalized spectral density A preliminary estimate of the energy spread was carried out predicting that the graphene-coated Ni point cathode exhibits comparable energy spread to the conventional W310) cold field emitter  T.F. electron emitter, respectively.Figure 5 and Schottky emitter6. The error bar is calculated by error propagation due to the uncertainty in the tip radius (±30 nm) and the instability in the emission current (±5%). The overall energy spread values are lower than or comparable with state-of-the-art conventional cold field emission sources. This is due to a lower work function ϕ . The feasibility of using such large size tips and relatively poor vacuum conditions comes from their experimentally measured ultralow work function value of 1.1 eV. The estimated reduced brightness of these new type of cold field emission sources, as well as their measured energy spread, are comparable to conventional single crystal tungsten cathode cold field emission sources. These results establish the promising prospect of using them as high brightness high-resolution electron sources for electron microscopy and lithography applications, similar in performance to conventional single crystal tungsten cathode cold field emission sources, while at the same time having better emission stability and less stringent vacuum requirements. Electron gun structures that can accommodate the Graphene-Ni electron point source need to be developed in which the source is accurately aligned with optical axis and accelerated directly after emission to avoid Coulomb interactions; this will be the subject for future studies.21. The sharp Ni tip serves as a template and catalyst for the growth of graphene. In this work, the deposition of a few-layer graphene is achieved by using the CVD method with solid carbon source PMMA (poly(methyl methacrylate)) as feedstock, since this method avoids the use of high temperatures which may change the morphology of the sharpened tip. Supplementary Fig. 2O3 boat loaded with solid PMMA was placed at the inlet side of the quartz tube, just outside of the heating zone. The Ni tip was then either heated to 900 °C for tip diameters greater than 400 nm or heated up to 800–850 °C for tip diameters less than 400 nm, maintaining a 500 sccm Ar/H2 (95%/5%) flow. The solid PMMA source was then heated to 150 °C for 8 min after the furnace reaches the set temperature. After this, the furnace was simply opened for the precipitation/formation of few-layer graphene on the Ni tip.A typical electrochemical etching process was used for preparing a sharp Ni tip having a radius of a few hundred nanometersThe microscopic morphologies of the cathode were investigated by using a scanning electron microscope equipped with EDS (FEI Nova 230). The crystallinity and thickness of the graphene were examined by Raman spectroscopy (WITecCRM200 with 532 nm laser (2.33 eV excitation)) and HRTEM .−8 torr. A schematic of the experimental electron gun setup that was used to analyze the performance of the cathode is shown in Supplementary Fig. d was measured accurately in a SEM) away from a grounded hole anode plate having a radius of 0.5 mm, and aligned to a hole aperture (probe hole radius = 0.5 mm) that was placed in front of a Faraday Cup for beam current measurements. The solid angle of collection defined by the aperture was ~3 × 10−3 sr. A cylindrical sector energy analyzer (Focus Electronics CSA 200) was installed to measure the electron energy distribution. The energy analyzer was operated at constant pass energy of 10 eV and the energy scan was conducted by sweeping the retarding potential between the analyzer and the entrance focusing lens. A W(100) T.F. electron gun was employed to calibrate the electron analyzer before capturing the data.Field emission properties of the graphene-coated point cathode were obtained in a vacuum chamber at a pressure of ~4 × 10The data that support the findings of this study are available from the corresponding authors upon request.Supplementary Information(PDF 1169 kb)


Podisus nigrispinus. Neurotoxic and growth inhibitor insecticides were used to compare the lethal and sublethal effects from neem oil on this predator. Six concentrations of neem oil were topically applied onto nymphs and adults of this predator. The mortality rates of third, fourth, and fifth instar nymphs increased with increasing neem oil concentrations, suggesting low toxicity to P. nigrispinus nymphs. Mortality of adults was low, but with sublethal effects of neem products on this predator. The developmental rate of P. nigrispinus decreased with increasing neem oil concentrations. Longevity of fourth instar nymphs varied from 3.74 to 3.05 d, fifth instar from 5.94 to 4.07 d and adult from 16.5 and 15.7 d with 0.5 and 50% neem doses. Podisus nigrispinus presented malformations and increase with neem oil concentrations. The main malformations occur in wings, scutellum and legs of this predator. The neem oil at high and sub lethal doses cause mortality, inhibits growth and survival and results in anomalies on wings and legs of the non-traget predator P. nigrispinus indicating that its use associated with biological control should be carefully evaluated.This research investigated the effects of neem oil on mortality, survival and malformations of the non-target stink bug predator,  Botanical insecticides have eco-toxicological advantages compared to traditional synthetic insecticides, because they can have favorable eco-toxicological properties , which make them suitable insecticides for organic agriculture1224513Azadirachta indica A. Juss  have insecticide effect against pests as reported for Coleoptera79111214The neem oil, Azadirachtin is the main compound of the neem oil with insecticidal activity and can be found in fruits and leaves1617The neem oil is a feeding inhibitor, delaying development and growth, reducing fecundity and fertility, changing behavior and causing anomalies in eggs, larvae and adults of insects or mites71920Azadirachtin has higher toxicity by ingestion than by contact, which allows it to be used somewhat selectively against phytophagous pests22Podisus nigrispinus Dallas (Heteroptera: Pentatomidae) is a common zoophytophagous insect that is used in the biological control of agriculture and forest pests in the America252627P. nigrispinus in biological control has been reported for larvae of the defoliators Alabama argillacea Hübner, Anticarsia gemmatalis Hübner, Spodoptera exigua Hübner, and Trichoplusia ni Hübner (Lepidoptera: Noctuidae)28293031Eucalyptus plantations273334P. nigrispinus and pesticides such as chlorantraniliprole, deltamethrin, imidacloprid, methamidophos, spinosad and thiamethoxam has been successfully demonstrated36The stink bug predator, Despite the potential benefits of neem oil, this product is mainly sprayed directly onto plant leaves1236P. nigrispinus.The objective of this study was to evaluate the toxic effects of topical applications of different concentrations of neem oil on the survival and development of the non-target predator −1 of neem oil, pyriproxifen, and imidacloprid. The two different lethal concentrations levels (LC50 and LC90) . The LC50 and LC90 values indicated that pyriproxifen  and imidacloprid  were the most toxic compounds to the P. nigrispinus nymphs followed by neem oil . The lethal concentrations (LC50-90) value of the pyriproxifen , neem oil , and imidacloprid  showed the toxicicity of these compounds to the P. nigrispinus adults. Mortality was always <1% in the control.The highest mortalities of this predator were obtained with 50 and 100 μL mLnd LC90)  of each P. nigrispinus  with the concentrations of 0.5, 1, 20, 25, 33 and 50%, respectively   , in the concentrations of 0.5, 1, 20, 25, 33 and 50%, respectively  . The mor < 0.05) . Mortaliectively . MortaliP. nigrispinus varied at different concentrations for fourth  and fifth  instars and adults  compared to the control  and fifth  instar nymphs and adults . In general, survival rates declined at 20, 25, 33 and 50% neem oil concentrations.Neem oil concentrations had a strong effect on the survival of nymph to adult h instar . This suP. nigrispinus presented malformations  with its number increasing proportionally with the neem concentrations (0.5 > 1 > 20 > 25 > 33 > 50%) (Nymphs and adults 3 > 50%) . MalformP. nigrispinus adults with higher severity as the neem concentrations increased. The main malformations were the hemelytra size reduction  mimic as the neem oil and pyriproxyfen, which also leads to adult malformation and reproductive impairment of individuals emerged41The toxicity profiles for the neem oil compared to two insecticides as positive control on the stink bug predator, P. nigrispinus. Our results showed that neem oil at different concentrations  affected the nymphs and adults P. nigrispinus. Survival was higher in adults (91.4%) than in fourth (72.3%) and fifth (76.4%) instar nymphs, indicating that P nigrispinus was more susceptible in the immature stages. Previous studies on its prey, Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae), show 18.5% larval survival at 25% concentration of neem oil and displayed abnormalities after the last larval moultHere, the term selectivity refers to the toxicological selectivity of neem oil on non-target organism as P. nigrispinus nymphs may be a sublethal effects of the neem oil on this predator. Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) larvae died before the pupa stage after application of 0.5 ppm azadirachtin, probably due to feeding inhibitionMacrolophus caliginosus Wagner (Hemiptera: Miridae) showed similar chronic toxicity in all instars with different neem oilsMyzus persicae Sulzer (Hemiptera: Aphididae) and had sublethal effects on the predatory ladybird beetle Eriopis connexa Germar (Coleoptera: Coccinellidae)The concentrations of neem oil caused mortality on the third, fourth, and fifth instar nymphs. On the other hand, neem as a botanical pesticide has many excellent attributes including its broad-spectrum in insect growth regulatory effects, systemic action in some plants, minimal effects on natural enemies and pollinators, rapid degradation in the environment, and no toxicity to vertebrates245P. nigrispinus nymphs after exposure to 33 and 50% neem oil suggests susceptibility of this predator to neem compounds. Increase duration of the nymph stage may affect reproductive fitness, because females with shorter lifespan lay higher numbers of eggsThe longevity of fourth and fifth instar P. nigrispinus nymphs after treatment with concentrations of neem oil, suggests a degree of tolerance. Concentrations of neem oil between 0.1 and 10% cause mortality in various hemipteran pests and predators such as Bemisia argentifolii Bellows & Perring (Aphididae)Clavigralla scutellaris Westwood (Coreidae)Macrolophus caliginosus Wagner (Miridae)Myzus persicae Sulzer (Aphididae)Nezara viridula Linnaeus (Pentatomidae)Nilaparvata lugens Stal (Delphacidae)Picromerus bidens Linnaeus (Pentatomidae)P. nigrispinus if used in concentrations lower than 25%.The survival <25% of fourth and fifth instar Calliphora vicina Robineau-Desvoidy , Manduca sexta Linnaeus (Lepidoptera: Sphingidae), and Oncopeltus fasciatus Dallas (Hemiptera: Lygaeidae), show that JH biosynthesis and catabolism were affected by azadirachtin improving the insect growth regulatory effects505153P. nigrispinus adults exposed to neem oil in the third instar were similar to those found in the coccinellids Chilochorus bipustulatus and Phroscymnus anchoragoM. caliginosusNezara viridula Linnaeus (Hemiptera: Pentatomidae) exposed to commercial neem oils have malformations in the antennae, ocelli, tarsi, odoriferous glands, scutellum, genitalia and mouth parts115657Several malformations, possibly related to defective molting, were observed from 1 to 50% of neem oil concentrations. Azadirachtin was established as an insect growth regulator with a novel mode of action. The basis for its mode of action was known to involve the neurosecretory–neuroendocrine pathway and perhaps other sites including cell cycleP. nigrispinus nymphs, especially at concentrations <25%. However, sublethal effects, such as increased mortality rates of fourth and fifth instars, longer instar duration and body malformations indicate that the use of neem oil associated with biological control using the predator P. nigrispinus should be previously evaluated for the use in IPM.Ideally, phytochemical insecticides should be toxic to pests with low or no impact on predators. In this study, topical applications of neem oil showed low acute toxicity for P. nigrispinus were obtained from mass rearing of the Laboratório de Controle Biológico do Instituto de Biologia Aplicada à Agropecuária . They were maintained at 25 ± 2 °C at 75 ± 5% relative humidity and 12-h photophase. The insects were kept in wooden cages (30 × 30 × 30 cm) coated with nylon and glass, and received ad libitum Tenebrio molitor (L.) pupae (Coleoptera: Tenebrionidae), Eucalyptus grandis (W. Hill ex. Maiden) leaves and waterNymphs and adults −1) and others neem oil isomers concentrations for tropical regions. Ecocert Brazil is accredited by the Ministry of Agriculture, Livestock and Supply of Brazil and by international organizations according to ISO Guide 34 Vegetable Bioneem is an organic Brazilian product composed of oil obtained from cold extraction of neem seeds, without the addition of solvents or pesticides, and certified by Ecocert Brazil as a natural insecticide with repellent properties. This product was developed with azadirachtin , 700 g L−1. These insecticides were diluted in 1 L water to produce a stock solution by adjusting 100 g L−1 per insecticide and to obtain the required concentrations. Insecticide efficacy was determined by calculating the lethal concentrations (LC50 and LC90) values under laboratory conditions for each formulation. Six concentrations of vegetable bioneem, pyriproxifen, imidacloprid besides the control (distilled water) were adjusted in 1 mL stock solution (treatments and distilled water): 1.56, 3.12, 6.25, 12.5, 25, and 50%. For each treatment, aliquots were taken from the stock solution and mixed with distilled water in 5 mL glass vials. Different concentrations of the treatments were applied in 1 μL of topical solution in the body of each individual of P. nigrispinus. Fifty third instar nymphs and fifty adults were used per concentration and were placed individually in glass vials (2 × 10 cm) with a cotton lid and maintained in the dark. The number of dead insects in each vial was counted after neem and insecticides exposure at intervals of 6 h over 6 days.Neem oil with 1800 to 2200 ppm of azadirachtin  was compared with two different insecticides used as positive control in this study. The following commercial insecticides were tested at their maximum label rates: pyriproxifen , 100 g LP. nigrispinus scutellum in order to ensure the absorption of the pesticide. Fifty-two individuals of third, fourth, fifth instar nymphs and adults  of P. nigrispinus were used per concentration and individually placed in plastic containers (15 × 10 cm) with a perforated lid, fed on T. molitor pupae, E. grandis leaves, and water under laboratory conditions. First and second instar nymphs were not tested because they are too small to the volume of insecticide applied. The number of dead insects per concentration was daily counted after neem oil exposure until adult emergence.Six concentrations of neem oil besides the control (liquid glycerin), were adjusted in 10 μL stock solution (neem oil and liquid glycerin): 0.5, 1, 20, 25, 33 and 50% aliquots were taken from the stock solution and mixed with liquid glycerine in 5 mL glass vials. Different neem oil concentrations were topically applied in 1 μL solution onto insect scutellum with an analytical 10 μL syringe. The glycerin was chosen due to applied solution adherence in the P. nigrispinus nymphs and adults was daily registered. To monitor nymph and adult development, 1,200 third-instar nymphs were placed individually in Petri dishes (90 × 15 mm) with moistened cotton ball and fed on T. molitor pupae. Nymphs were maintained at 25 ± 2 °C at 75 ± 5% RH and 12-h photophase until, fourth and fifth instars and adult emergence. Survival and duration of fourth and fifth instar nymphs, and adults, after emergence, were recorded. Longevity and survival were determined from third instar nymph with the six neem oil concentrations.The development of P. nigrispinus adults were photographed.The number of malformed nymphs and adults was quantified per concentration after topical application of the neem oil on third instar nymphs. Severe morphological abnormalities of the 50 and LC90, and their confidence limits were determined by logistic regression based on the concentration probit-mortalityThe LCHow to cite this article: Mourão, S. A. et al. Toxic effects of the neem oil (Azadirachta indica) formulation on the stink bug predator, Podisus nigrispinus (Heteroptera: Pentatomidae). Sci. Rep.6, 30261; doi: 10.1038/srep30261 (2016).


To provide proof-of-concept, these 3D printed electrode architectures are characterised both electrochemically and physicochemically and are advantageously applied as freestanding anodes within Li-ion batteries and as solid-state supercapacitors. These freestanding anodes neglect the requirement for a current collector, thus offering a simplistic and cheaper alternative to traditional Li-ion based setups. Additionally, the ability of these devices’ to electrochemically produce hydrogen via the hydrogen evolution reaction (HER) as an alternative to currently utilised platinum based electrodes (with in electrolysers) is also performed. The 3DE demonstrates an unexpectedly high catalytic activity towards the HER (−0.46 V vs. SCE) upon the 1000th cycle, such potential is the closest observed to the desired value of platinum at (−0.25 V vs. SCE). We subsequently suggest that 3D printing of graphene-based conductive filaments allows for the simple fabrication of energy storage devices with bespoke and conceptual designs to be realised.3D printing technology provides a unique platform for rapid prototyping of numerous applications due to its ability to produce low cost 3D printed platforms. Herein, a graphene-based polylactic acid filament (graphene/PLA) has been 3D printed to fabricate a range of 3D disc electrode (3DE) configurations using a conventional RepRap fused deposition moulding (FDM) 3D printer, which requires no further modification/ Over the recent decade there has been an acceleration of interest in the fabrication and application of advanced 2D nanomaterials, such as; graphene13via the utilisation of 3D printing. 3D printing has the ability to provide a beneficial platform for the creation of low cost 3D components for an array of applicationset al.4Ti5O12 (LTO) and LiFePO4 (LFP), using a direct-ink writing protocol with corresponding specific capacity values of 131 and 160 mAh g−1 respectively. Fu et al.et al.fully graphitic-based ‘ink’ has also been recently considered by Zhu et al.via a direct-ink writing protocol containing graphene oxide and graphene nanoplatelets for application as a supercapacitor. This 3D printed aerogel is reported to exhibit a capacitance of 4.79 F g−1 at a current density of 0.4 A g−1 within an aqueous solution of 3 M KOH, deduced utilising the weight of the full device.Currently, there has been a natural progression towards the design and fabrication of complex structures in-situ curing and layering of the ‘ink’ is far from ideal for the creation of freestanding 3D printed electrochemical systemset al.wt.) have been reported by Wei et al.et al.et al.via a conventional 3D printing fabrication method.These direct-writing protocols are useful, however in the majority of scenarios the via the hydrogen evolution reaction (HER), as an alternative to commonly utilised platinum based electrodes currently utilised within electrolysers is demonstrated.This paper reports, for the first time, the utilisation of 3D printable electrochemical energy storage architectures using a graphene-based PLA filament (graphene/PLA) fabricated/printed using a conventional RepRap FDM 3D printer shown in –C explorvia an array of characterisation techniques.In order to benchmark this new electrochemical platform, the physicochemical properties of the graphene/PLA and the printed 3DE are first considered via thermogravimetric analysis (TGA). First, the thermal properties of the graphene/PLA filament are compared with an industry standard PLA Next, the surface uniformities of the graphene/PLA filament and the 3DE were examined utilising scanning electron microscopy (SEM). quasi-layer graphene, with characteristic graphitic D, G and 2D peaks at 1250, 1500 and 2700 cm−1 respectively. Additional comparative analysis of the industry standard PLA and the graphene/PLA have also been undertaken and are presented within −1 are determined for graphene/PLA and the printed 3DE respectively, which are much higher values than that of monolayer or quasi-layer graphene, where values correspond to 28 cm−1  −1  i.e. 100–1000 cm−1, it is evident that there is an inclusion of peaks that are characteristic of titania (TiO2) at 145, 190, 400, 650 cm−1 similar to TiO2 samples recently analysed by Leong et al.2 belongs to either an anatase or brookite arrangement (probably mixed phase). It is important to note that the additional peak present at 890 cm−1 is due to the amorphous silica (i.e. glass slide) used for analysis.Raman analysis was performed  upon the1, C2 and C3 are typical of the chemical composition of PLA, however it has been reported by Vergne et al.1 peak indicates an increase within the presence of non-oxygenated carbon bonds (i.e. C-C), presumably from the incorporation of graphene into the structure. Evaluation of the deconvoluted XPS analysis is represented within X-ray photospectroscopy (XPS) analysis of the printed 3DE was next compared in terms of its atomic carbon and oxygen content, depicted in III) chloride was next undertaken and benchmarked against literature. The utilisation of this probe has been chosen due to its outer-sphere redox mechanism that is insensitive to the C/O ratio groups and is affected only by the electronic structure of the 3DE (i.e. edge plane like-sites/defects)22quasi-reversible system over the chosen scan rates (5–500 mV s−1), as the peak-to-peak separation is over that of 59 mV. Further analysis of this data was carried out in the form of a plot of log10Ipvs. log10ν for the graphene/PLA and printed 3DE, exhibiting gradients of 0.44 and 0.42 respectively, where such values are expected for the case of a semi-infinite diffusion model, with no presence from thin-layer effectsk0obs, were deduced using both electrode platforms (as described in the Methods section). The k0obs values for were found to correspond to 1.00 × 10−3 cm s−1 and 4.58 × 10−4 cm s−1 for the graphene/PLA filament and the 3DE indicating a smaller amount of edge plane sites when compared with that of other traditional graphitic-based electrodes, with the graphene/PLA exhibiting faster electron kinetics than that of the 3DE. The observed k0obs for graphitic-based electrodes has regularly been shown within the literature to be contributed from two planes of the graphitic material; firstly the edge plane sites and secondly the basal plane sites. However, it is well reported that the edge plane sites are vastly superior in terms of electron transfer (ca. 0.4 cm s−1) than their basal plane counterparts (ca. 10−9 cm s−1). Therefore, it is commonly understood that the k0obs = k0edge(θedge), where θedge,is the amount of edge sites present on the electrode surface as reported by Hallam et al. and Davies et al.24et al.via TGA previously). Next, Electrochemical characterisation of the fabricated 3DEs and graphene/PLA filament using the redox probe hexaammineruthenium (4 (Fe2+aq) was also considered232+aq), which is also existent within the blank solution of HClO4  sulfate in 0.2 M HClOvs. SCE)vs. SCE), however upon repetition of this procedure the 3DE demonstrates signs of severe adsorption/fouling of the electrode surface. Clearly, there is an increase in the peak potential from ~+0.5 V (vs. SCE)  to ~+0.8 V (vs. SCE) (utilising this printed 3DE) that can be associated to the reduced amount of edge plane sites available, which is in agreement with the results exhibited utilising the outer-sphere redox probe hexammineruthenium (III) chloride. Analytes that are renowned for their surface catalysed (C/O groups) were next analysed, namely, ascorbic acid and dopamine hydrochloride. The sole analysis of the printed 3DE was next considered using a selection of analytes that are affected from a mixture of electronic properties and the surface orientated groups upon the electrodes. First, we analyse NADH within a pH 7.4 PBS. Banks and Compton6 in 1:1 (v/v) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) was used as the electrolyte. Notably, graphene/PLA anodes were 3D printed with the same geometries as a CR-2016 coin cell (i.e. a diameter of 17.75 mm with a thickness of 1 mm) using a conventional RepRap 3D printer (as described within the Methods section). The utilisation of these 3D printed discs as a potential anode material within a lithium-ion coin cell were next considered. It is important to note that these freestanding anodes do not require a current collector and can simply slot into any coin cell configuration, as shown in vs. Li/Li+) using an Arbin battery cycler . st, 50th and 100th cycle, with relatively low discharge specific capacities of 40, 33 and 16 mAh g−1 respectively, however it is clear that there is a large irreversible capacity loss with the values corresponding to 5 mAh g−1. This sizeable deviation could be attributed to the high specific surface area of the 3DE and the formation of the solid electrolyte interface (SEI). Nevertheless, it is apparent that over time there is an improvement within the overall reversibility of the system. Additionally, upon the 1st discharge/charge cycle the voltage presented is relatively large compared to that of other graphitic anode materials, with values of ~+2.25 V (vs. Li/Li+), which dissipates over time to the voltage region expected from a graphite based material, indicating that there could be metallic impurities residing upon the electrode surface. The cycling capability of the 3DE was next explored and is shown in + ions being unable to be extracted from the cavities within the 3DE. Upon cycle numbers 3–120, the rechargeable specific capacity improves, and a columbic efficiency of ~85% is achieved on the final scan, with an irreversible capacity reaching a maximum of 40 mAh g−1 , if we consider the full weight of the printed 3DE the maximum specific capacity can only reach 3.69 mAh g−1. This is relatively low compared to other graphite-based anode materials, however it should be noted that the weight of the active material within this freestanding graphene/PLA anode is much larger than that of the typically deposited nanomaterials. For example, within the field an ‘ink’ composite is fabricated utilising a small amount of active material that is then mixed with binders and additives, which is then deposited in a uniform fashion upon a copper foil. The rate capabilities  as a separator. 1 M solution of LiPFbilities  of the 3Despite the low amount of conductive material within the composite, the overall performance of this 3D printed system within this proof-of-concept shows promising experimental data. The columbic efficiency and overall reversibility of the system could also indicate that there are some possible parasitic reactions occurring within the composite.2SO4 (as mentioned in the Methods section), leaving a completely freestanding solid-state structure utilising 3DEs, depicted in the inset of 2SO4 acting as a solid-state electrolytic layer, over a range of −2.0 V to 2.0 V, at a scan rate of 25 mVs−1 and is depicted in via galvanostatic charge/discharge cycling over 200 cycles, and is described in terms of specific capacitance of the weight of the entire device, et al.A 3D printed solid-state supercapacitor, 3D-SC, is developed to evaluate the potential of this 3D printable graphene filament utilising two 3D printed discs and sandwiching a solid electrolyte between the two, creating a fully freestanding supercapacitor. The solid electrolyte is prepared by mixing 6 g polyvinyl acetate (PVA) with 10 mL of 1.0 M HCS) values of the 3D-SCs. Current literature utilises an array of methods in the calculation of CS, however the differences observed for each method are not reported. Thus, in this work a diverse range of methods were utilised to calculate the CS values and CObs is the observed capacitance (F) of the entire device. Furthermore, mDevice is the mass (g) of the entire device, both electrodes and the mass of the solid electrolyte layer. Also mWE is the mass of the working electrode only and Actm is the mass of the active material in the working electrode i.e. graphene, assumed to be 8% of the total working electrode:Attention was next turned towards obtaining the specific capacitance , it is clear that the values, although not competitive with advanced nanomaterials, demonstrate the capabilities and potential for the fabrication of low cost, non-toxic 3D supercapacitative architectures.+ + 2e− → H2). Platinum-based materials are commonly utilised for the HER, as this pure metal exhibits an extremely low binding energy of the H+ ions, which in turn allows for a low onset potential to occurth scan of the 3DE, BDDE, EPPGE, GCE and platinum in 0.5 M H2SO4 as is common within the literaturevs. SCE) to that of EPPGE and BDDE and at −0.78 V (vs. SCE) and −0.76 V (vs. SCE) whilst being superior to GCE at −1.05 V (vs. SCE). The current density achieved by the 3DE is negligible in comparison to all the other electrodes examined. Note that the HER onset is the potential at which the observed current initially begins to deviate from the background current. Whilst the 3DE proved to be relatively ineffectual as an electrocatalyst towards the HER it was essential to assess its electrochemical stability. This is a practical consideration for real world applications of 3DE as electrode materials where concerns over longevity and durability are paramount. It is evident that upon inspection of th scan the HER onset is −0.70 V (vs. SCE) whilst the 1000th scan the HER onset potential is −0.46 V (vs. SCE), which is the least electronegative all of the other carbon-based electrodes examined herein. The comparatively low overpotential for HER onset observed for the 1000th scan of the 3DE is the closest observed to the desired value of platinum at −0.25 V (vs. SCE) thusly making it the most beneficial electrode towards the HER of all the carbon-based electrodes examined. It can therefore be theorised that the electrochemical reaction mechanism occurring has altered to account for this.Research into 2D nanomaterials such as graphene have received enormous interest from a plethora of scientific disciplines into the exploration and exploitation of its unique properties; we next apply this 3D printed graphene structure towards the creation of hydrogen within an electrolyservia Tafel analysis. Tafel analysis was performed on the faradic regions of the LSV’s. Tafel slope values of ca. 167, 150 and 60 mV/dec−1 were determined for the 1st, 10th and 1000th 3DE scans. Interpretation of these values suggest that over the course of 1000 LSV scans the rate limiting step of the HER reaction mechanism on the 3DE changed from the “adsorption Volmer” step to most likely the “discharge Heyrosky step”, the observed change being indicative of the 3DE gaining an improved electrocatalytic prospectus. We postulate that when the 3DE is exposed to the acidic electrolyte, hydrolysation of the PLA chain occurs thus allowing a greater number of areas of reactive material to be revealed, which in this case we suspect is due to titanium-derived contaminants possibly created within the manufacturing stage of the graphene/PLA filament. Such hypothesis is compounded by the detection of titanium-based compounds revealed within both Raman and EDS analyses. Last, we have analysed the 3DE after its exposure to the acidic medium via XPS  platform has been analysed towards its ability to create hydrogen via the hydrogen evolution reaction, in which these 3DEs exceed expectations and exhibit an extremely competitive onset potential compared to that of a platinum electrode. We believe that this platform (or similar) is the basis of next generation futuristic 3D printed energy architectures due to the following advantages:freestanding electrochemical platform.3D printing provides the fabrication of a There is no need for a metallic current collector upon the Li-ion anode utilised, therefore offering a simplistic and low cost fabrication protocol for anode materials.ex-situ post-curing/modification.The thermoplastic 3D printing of the filament can also improve the electrochemical behaviour with an increase of oxygenated species upon the surface of the 3D printed electrode platform.For the first time, proof-of-concept has been demonstrated utilising a printable 3D graphene-based PLA filament that has been 3D printed into useful electrochemical geometries. These systems are characterised both physicochemically and electrochemically, then are applied as only 8% graphene and 92% thermoplastic (PLA), and yet, still works as a battery anode/supercapacitor material! It should be noted that future work will examine a range of percentages and bespoke architectural structures.In terms of this 3DE being used as a Li-ion anode and a solid-state supercapacitor the authors understand that the output is not highly competitive with current literature, however one must consider that in reality this anode/supercapacitor is comprised of All chemicals used were obtained from Sigma-Aldrich at an analytical grade and were used without any further purification. All solutions were prepared with deionised water of resistivity not less than 18.2 MΩ cm. Voltammetric measurements were carried out using an Autolab PGSTAT100  potentiostat.via Solidworks, to create a circular disc electrode with a range of diameters with a thickness of 1.0 mm  , with a f 1.0 mm . The potf 1.0 mm , a satur2O < 0.5 ppm, O2 < 0.5 ppm) using the metallic lithium counter/reference electrode, a polypropylene separator (Celgard 2400), an electrolyte of 1 M LiPF6 in ethylene carbonate and dimethyl carbonate  and a 3D printed graphene/PLA anode (with a diameter of 17.75 mm and a thickness of 1 mm). Charge–discharge measurements were carried out galvanostatically over a voltage range of 0.01–3.00 V using the Arbin battery test system (BT2000). A solid-state 3D printed supercapacitor (3D-SC) was developed utilising two 3D printed discs (as mentioned previously) and sandwiching a solid electrolyte between the two. The solid electrolyte is prepared by mixing 6 g polyvinyl acetate with 10 mL of 1.0 M H2SO4. The solution is heated to roughly 80 °C and mixed vigorously until a consistent gel is formed. A small sheet of polyester is wrapped around one disk providing a mould for the electrolyte gel, which is poured into the mould, with a 2 mm thick uniform coverage, the opposite electrode is forced into the mould before the solution solidifies. The resulting structure is left to cool for 24 hours, before the mould is removed, leaving a freestanding completely solid-state structure utilising 3DEs, the dimensions of which are illustrated in the inset of 2SO4 solution used to explore the hydrogen evolution reaction (HER) was vigorously degassed prior to electrochemical measurements with high purity, oxygen free nitrogen.CR2016-type coin cells were assembled inside a mBraun glovebox  images and surface element analysis were obtained with a JEOL JSM-5600LV model equipped with an energy-dispersive X-ray (EDX) microanalysis package. Raman Spectroscopy was performed using a Renishaw InVia spectrometer with a confocal microscope (×50 objective) spectrometer with an argon laser (514.3 nm excitation) at a very low laser power level (0.8 mW) to avoid any heating effects. Thermogravimetric analysis (TGA) was conducted utilising a PerkinElmer TGA 4000. The PLA samples were subject to a gradual temperature increase of 10 °C per minute, over a range between 25–800 °C, under a flow of nitrogen (40 ml/min). The X-ray photoelectron spectroscopy (XPS) data was acquired using a bespoke ultra-high vacuum system fitted with a Specs GmbH Focus 500 monochromated Al Kα X-ray source, Specs GmbH Phoibos 150 mm mean radius hemispherical analyser with 9-channeltron detection, and a Specs GmbH FG20 charge neutralising electron gun. Survey spectra were acquired over the binding energy range 1100–0 eV using a pass energy of 50 eV and high-resolution scans were made over the C 1 s and O 1 s lines using a pass energy of 20 eV. Under these conditions the full width at half maximum of the Ag 3dk0obs, were determined utilising the Nicholson method through the use of the following equation: ψ = k0obs[πDnνF/(RT)]−1/2 where ψ is the kinetic parameter, D is the diffusion coefficient, n is the number of electrons involved in the process, F is the Faraday constant, R is the universal gas constant and T is the temperatureψ, is tabulated as a function of ΔEP (peak-to-peak separation) at a set temperature (298 K) for a one-step, one electron process with a transfer coefficient, α, equal to 0.5. The function of ψ (ΔEP), which fits Nicholson’s data, for practical usage (rather than producing a working curve) is given by: ψ = (−0.6288 + 0.0021X)/(1 − 0.017X) where X = ΔEP is used to determine ψ as a function of ΔEP from the experimentally recorded voltammetry; from this, a plot of ψ against [πDnνF/(RT)]−1/2 allows the k0obs to be readily determined−6 cm2 s−1 for hexaammineruthenium (III) chlorideAeff, given that for a co-planar macro electrode in the electrochemically quasi-reversible case, the Randles–Ševčík equation (at 298 K): IpQuasi = 2.65 × 105n3/2D1/2v1/2[C]Aeff, where the notation is the same as above and [C] is the concentration of electroactive substance, the geometrical surface of the area (AGeo) was calculated from the contact area of the graphene/PLA and printed 3DE immersed within the 1 mM hexaammineruthenium (III) chloride/0.1 M KCl solution. The real area percentage  was carried out utilising the following equation: AReal (%) = Aeff/AGeo × 100.The values of the heterogeneous electron transfer rate constant, How to cite this article: Foster, C. W. et al. 3D Printed Graphene Based Energy Storage Devices. Sci. Rep.7, 42233; doi: 10.1038/srep42233 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Renal medullary carcinoma is one of the rarest malignancies arising from the kidney. Despite various aggressive therapeutic regimens, mortality remains significantly high (95%) with a median overall survival of 5 months. Furthermore, the scarcity of this malignancy renders randomized clinical trials impossible. We examined the expression of programmed death ligand 1 (PD-L1) in two new renal medullary carcinoma cases, investigated their responses to the PD-L1 inhibitor nivolumab and explored the predictive role of the rate of PD-L1 expression in such response.Two African-American patients  with sickle cell trait who presented to our center with hematuria and flank pain were diagnosed with metastatic renal medullary carcinoma. PD-L1 was expressed at rate of 25% and 60% in patient 1 and 2 respectively. Following nephrectomy, they were started on nivolumab. Patient 1 initially responded to the treatment with regression of metastatic lesions. However, following this early response, patient 1 who has been receiving nivolumab for more than 15 months, was noted to have a disease progression. Patient 2 had disease progression after 3 months of nivolumab therapy.Although PD-L1 is expressed in these patients with renal medullary carcinoma, response to nivolumab was only observed in patient 1 whose tumor has the lowest rate of PD-L1 expression. This may suggest that in RMC, response to PD-L1 inhibition therapy may not correlate with the rate of PD-L1 expression. First described in 1995 by Davis et al., renal medullary carcinoma (RMC) is a rare and aggressive malignancy almost exclusively observed in individuals with sickle cell trait (SCT) and sickle cell disease (SCD) , 3. It mRecent advances in cancer immunology have demonstrated the crucial role of the immune system in cancer progression, resulting in the identification of multiple therapeutic targets and the development of novel immunotherapy drugs . NivolumHerein, we report the expression of PD-L1 in two RMC patients, their responses to PD-L1 inhibition with nivolumab and the predictive role of the level of PD-L1 expression in such response.The patient is a 24 year-old African-American female with SCT who presented with a one month history of gross hematuria and intermittent right flank pain in December 2014. Computed tomography (CT) imaging revealed a well-defined solid mass with a central necrosis within the upper pole of the right kidney measuring 6.0 cm × 3.9 cm × 5.0 cm and two pulmonary nodules (3 and 2 mm in size) in the left lower lobe concerning for metastatic disease. Thus in January 2015, right radical nephrectomy was performed. Histological and Immunohistochemical (IHC) analysis revealed RMC. Further genetic study revealed SMARCB1 mutation as previously reported in RMC . Follow The patient is 57 year-old African-American male with SCT who presented with hematuria and right flank pain. Subsequent CT scan revealed a mass on the upper pole of the right kidney. He underwent in July 2016 a right nephrectomy which revealed a tumor size of 7.4 cm × 4.8 cm × 4.8 cm and RMC histology. As seen in patient 1, PD-L1 was expressed on 60% of this patient’s tumor Fig. . A PET sDespite very aggressive treatments, RMC still has a very high mortality rate. Treatments include nephrectomy and chemotherapy . PatientBeckermann et al. recently reported a complete response to nivolumab in a patient with RMC whose tumor also expressed PD-L1 . In suchWe reported the expression of PD-L1 in two patients with RMC and their responses to nivolumab. The choice of this therapy was based on the expression of the PD-L1 and on the relatively safe toxicity profile of nivolumab. Although in these patients PD-L1 was expressed, response to nivolumab was only observed in the patient with the lower expression level of PD-L1. This suggests that in RMC, PD-L1 expression may not be the sole predictive marker for response to PD-L1 inhibition therapy. As suggested by Hugo et al. in melanoma, additional genomic and non-genomic makers may be involved in RMC response to PD-L1 inhibition . Further


Graphene is the first 2-dimensional material and possesses a plethora of original properties. Graphene and its derivatives have exhibited a great potential in a number of fields, both medical and nonmedical. The aim of this review is to set the theoretical basis for further research in developing graphene-based endovascular materials. An extensive search was performed in medical and bioengineering literature. Published data on other carbon materials, as well as limited data from medical use of graphene, are promising. Graphene is a promising future material for developing novel endovascular materials. Certain issues as biocompatibility, biotoxicity, and biostability should be explored further. Material specifications and techniques are critical for the evolution of endovascular surgery.2-bonded carbon atoms in a sheet-like arrangement. Its unique structural, chemical, thermal, and other properties [Graphene is a two-dimensional carbon allotrope comprised of spoperties –3 have boperties –15. Grapoperties . Its derThe use of GO as a delivery substrate of water-insoluble cancer medication was first reported in 2008. The properties of graphene and its derivatives have demonstrated immense biomedical applicability , 17–23. In vitro studies by Paul and Sharma in 2011 reported that graphene, when in contact with blood, does not absorb activated C3 (C3a), indicative of complement activation not taking place [ng place . In a si in vivo, supporting the biocompatibility of graphene [The ratio of adsorbed serum fibrinogen to albumin (FAR) indicates both the biocompatibility of materials in contact with blood and the degree of platelet activation and clot formation in a proportionate manner . Graphengraphene , 27.Fibrin, the first step towards thrombus formation, forms when electrons transfer from fibrinogen molecules to a biomaterial. At room temperature, graphene sheets do not demonstrate significant electron transfer; therefore, graphene does not trigger conversion of fibrin to fibrinogen and the consequent thrombosis. This ability of graphene to not induce clot formation could be expanded by drug-eluting graphene scaffolds. The lower thrombogenicity of graphene could potentially decrease stent occlusion.π-electrons, promoting π–π bonds with other molecules [Graphene is rendered a suitable drug-delivery substrate due to the presence of reactive functional groups and localised olecules , 29. Weaolecules . Other solecules , 32.Lee et al. reported that the conjugate of graphene and unfractionated heparin resulted in enhanced anti-Xa activity approximately 30-fold higher than a solitary GO coating . in vitro as a substrate for integrating antithrombotic enzymic systems [Xue et al. used graphene coating systems .Chemical vapor deposition during graphene development increases caspase-3 activation, the lactate dehydrogenase release, and the generation of reactive oxygen species in neural pheochromocytoma-derived PC12 cells .μg/mL in contrast to r-GO sheets that become toxic in higher concentrations (>100 μg/mL) [μg/mL after 1 hour [Wang et al. reported that GO demonstrated a cytotoxic effect on human fibroblast cells in blood concentrations exceeding 50 mg/L . Hu et a0 μg/mL) . These rr 1 hour . On the  in vitro cytotoxicity to various cell lines, even at concentrations reaching 100 mg/L [On the contrary, GO covered in a biocompatible coating showed low100 mg/L , 40. in vivo cytotoxicity of graphene have reported significant GO accumulation in lungs of rats and mice after intravenous GO injection. Pulmonary toxicity was dose-dependent and obvious at GO doses ≥10 mg/kg [Animal studies on10 mg/kg , 41. Oth10 mg/kg .Radiolabeled intravenously administered polyethylene glycol covered GO (GO-PEG) in an animal model accumulates mainly in the reticuloendothelial system and lung . Radiolaμg/mL causes <11% cell destruction and <7% DNA fragmentation and therefore it should be considered a safe dose [ in vivo dose of 1 mg graphene per kilogram of the animal model's body weight results in the same cytotoxic effect as 10 μg/mL dose in vitro, possibly due to the in vivo hard corona and dilution [μg) or graphene concentrations higher than 100 μg/mL demonstrate strong cytotoxic effects resulting in >72% cell death and >29% DNA fragmentation.A study of GO-PEG nanoribbons in cancer cell imaging and photothermal therapy concluded that the threshold of 1 afe dose . A simildilution . High-doThe biocompatibility of graphene is questioned by Monaco and Giugliano, due to the limited number of studies on different graphene derivatives . The proCytotoxicity of graphene sheets on reproduction and gestation of mammals of both genders has been reported by Akhavan et al. . This to in vitro toxicity upon smooth muscle cells and aortic endothelium [Podila et al. demonstrated the vascular biocompatibility in an animal model by finding insignificantothelium , 27. Aliothelium , 48. E. coli and S. aureus exposed to graphene derivatives sustained substantial viability loss. This was more prominent when exposed to r-GO, as sharper edges of the r-GO particles compared to other derivatives cause increased cytotoxicity. S. aureus and other Gram-positive bacteria were affected more severely, probably as the contact with the material surface induced membrane damage and efflux of cytoplasma [ E. coli cells in contact with GO and r-GO showed significant loss of viability, but GO surfaces demonstrated better results. Once more, the toxicity mechanism is considered to be bacterial membrane damage caused by material edges; the different results might be explained by the GO production method. Vacuum filtration results in material particles lying entirely flat with only a small number of material edges oriented perpendicularly.Two studies report a substantial loss in bacterial cell viability in contact with either GO or r-GO surfaces orientated such that a great number of exposed material edges exist . E. colitoplasma , 51. In toplasma  reported E. coli growth rates 3-fold higher with preferential attachment to areas with dense allocation of GO particles [In complete contrast, a study has suggested that there is no cytotoxic effect to bacteria in contact with GO and reportedarticles . Vacuum  E. coli [ E. coli, C. metallidurans, B. subtilis, and R. opacus was reported to be higher than the activity of unmodified GO surfaces, especially against Gram-positive bacteria. Despite the observed antibacterial activity of GO-polyvinyl-N-carbazole, there was insignificant cytotoxicity towards eukaryotic cells.The antibacterial properties of GO or r-GO films in combination with a variety of other known antibacterial substances have also been studied. Lactoferrin and chitosan on a GO or r-Go composite film showed significant cytotoxicity against E. coli . Other s E. coli , 55. The E. coli [Antibacterial activity and stimulation of human cell growth on other GO-polymer composites have been studied and a composite of GO and poly-L-lysine (GO-PLL) showed potent cytotoxic effect on E. coli . DiazoniKrishnamoorthy et al. found that r-GO minimum inhibitory concentration (MIC) was lower for Gram-negative bacteria antibacterial activity by using r-GO sheets, probably due to the thinner peptidoglycan layer of these organisms .Only one publication reports on how the particle size of GO and r-GO affects antibacterial activity and that larger GO sheets had a more potent antibacterial activity, probably as larger GO sheets have a greater ability to effectively wrap and isolate bacterial cells preventing further proliferation . These f E. coli cells were able to reduce GO particles' oxygen containing functional groups as much as 60% in 48 hours, leading to an antibacterial effect [Under acidic conditions, E. coli growth by 99.9%. The interaction of GO-Ag with E. coli and P. aeruginosa has been studied, with the authors reporting that bacteriostatic activity is directly proportionate to the concentration of the Ag particles [Adding silver particles (Ag) to GO surface increases antibacterial activity . Composiarticles . P. aeruginosa [ P. aeruginosa viability decreased in a dose- and time-dependent manner on contact with GO or r-GO. Dose-dependent antibacterial activity is caused by the production of ROS, leading to cell death.Gurunathan et al. studied the antibacterial activity of GO and r-GO onruginosa . P. aeruThe interest of bioengineers and surgeons in carbon allotropes has been growing and has been the focus of intensive research in many fields , 64–71. Since its production in 2004, graphene has been the tip of the bioengineering spear towards newer and more novel biomaterials. Graphene's unique properties give bioengineering specialists the opportunity to develop new or improve existing materials. In order for a material to be safely deployed and analysed in humans, several characteristics should be investigated: prolonged wear and friction resistance, thrombogenicity, biotoxicity, biocompatibility, interactions with surrounding tissues, and so forth.The unique structural features of GO give GO excellent biocompatibility, stability, solubility, and drug-bearing capability. Cellular uptake of GO-PEG loaded with chemical drugs has also given promising results . OligolaGraphene is the lightest, strongest, and thinnest carbon allotrope and these unique characteristics make graphene a future candidate for construction of stent and endograft scaffolding, but research is necessary to show the number of layers and the allotrope to be used. Several studies exist on how diamond-like carbon (DLC) is already being employed as a stent coating –94. ThesAs stent material corrosion is already reported, the wear withstanding properties of endomaterials require specific testing –97. Six Apart from being a building material of stent scaffolds, monolayer graphene may have a future potential as graft material. Graphene sheets are impermeable membranes, to both liquids and gases , and cou in vitro cytotoxicity of carbon coatings in different cell lines [ hard corona, interacts with the biological surroundings of the nanoobject and it can significantly affect the potential cytotoxicity of graphene [Biotoxicity and biocompatibility of graphene and its derivatives are two subjects that have been the focus of many studies , 41. Somll lines –36, 41. ll lines , 27, 47.ll lines , 40. Thill lines . This lagraphene . Identicgraphene .Two drawbacks regarding all these studies are that they fail to show a specific threshold of systemic toxicity depending on the dose of released carbon particles and almost all studies are conducted on carbon coatings other than graphene. E. coli and S. aureus. To this moment, no consensus has been reached regarding the antibacterial activity of graphene or graphene-derivative surfaces, but available data suggests that cytotoxicity against bacterial cells varies to some extent on the orientation of the surface particles, a result of the production method used [Deployed stent grafts, especially in endovascular AAA repair, could become infected, resulting in complications and high postoperative morbidity and mortality . There hhod used , 55, 102Carbon-coated stents release no metal ions into the bloodstream preventing the allergenic or toxic effects of copper, steel, or nitinol stents. Allergic reactions to nickel released from nitinol stents could be significant as toxic effect of Ni ions is already reported in the literature .From all the above, it is obvious that graphene-coated or graphene-built scaffolds have certain advantages over existing bare metal, cobalt-chrome, or nitinol made scaffolds. Without releasing metal ions and by presenting lower thrombogenicity, graphene scaffolds could lead to improved long-term patency and less allergic reactions compared to today's endovascular scaffolds. Metal corrosion, which is evident in other scaffolds after long-term contact with the bloodstream, does not affect graphene scaffolds. The potential of graphene to embed and release molecules could further improve patency by releasing antiplatelet or anticoagulation agents and increase safety by preventing bacterial colonization and preventing in-stent stenosis by releasing cytostatic molecules in well-controlled doses. Particularly, the latter characteristic has only been demonstrated in graphene, while the already used materials  do not present with this characteristic.Some obstacles need to be overcome before deployment of graphene-made materials in humans. Initial data on biostability and biocompatibility are promising, but findings on biotoxicity are ambiguous. Numerous clinical, safety, and regulatory trials are also necessary. However, research to date suggests that graphene and its derivatives could change the face of endovascular surgery.


We propose a novel method to achieve tunable plasmon focusing in graphene/photonic-crystal hybrid structure exhibiting all-angle negative refraction at terahertz frequencies. A two-dimensional photonic crystal composed of a square lattice of dielectric rods is constructed on the substrate of a graphene sheet to provide the hyperbolic dispersion relations of the graphene plasmon, giving rise to the all-angle plasmonic negative refraction. Plasmon lensing induced from the negative refraction is observed. We show that the ultracompact graphene-based system can produce sub-diffraction-limited images with the resolution significant smaller than the wavelength of the incident terahertz wave. Moreover, by adjusting the Fermi energy of the graphene, the imaging performance of the proposed system can remain almost invariant for different frequencies. Our results may find applications in diverse fields such as subwavelength spatial light manipulation, biological imaging, and so forth. As the rapid development of information processing in the past few decades, miniaturization and integration have become the prevailing trend of electronic-photonic system used for digital communication. Suffered from the diffraction limit, traditional photonic devices are bulky and cannot be integrated with the electronic components on the same chip. Surface plasmon-based photonics offer a solution to this dilemma. Surface plasmons (SPs) are electromagnetic wave which propagates along the metal/dielectric interface and can be guided by metallic nanostructures beyond the diffraction limit1471012Graphene, a two-dimensional material where carbon atoms are arranged in a honeycomb lattice, has attracted significant attention due to its linear dispersion and zero electron density of states at the Dirac point141823In this paper, we show that all-angle negative refraction of plasmons can be achieved in graphene/photonic-crystal hybrid structure. We demonstrate that plasmon focusing based on the negative refraction can be used to attain subdiffraction-resolution imaging at THz frequencies. Our results show that the resolution of the image is significant smaller than the wavelength of the graphene plasmon. Furthermore, the focusing performance of the proposed structure can be maintained for different frequencies by changing the Fermi energy of the graphene.a and pillar radius r. The surface normal of the PC is along ΓM [(11) direction]. Ion-gel is sandwiched between TPX and ITO/SiO2 substrate. Gold patch on the graphene sheet is used as an electrode and ITO is used as the other electrode. In the following simulations, graphene sheet is treated as an ultrathin layer with thickness 0.5 nm, the radius of Si pillars is set as r = 0.3a, where a = 2 μm. Metal micro-particle, illuminated by an incident beam, can work as an optical antenna which can convert the incident light into a localized near-field. When such an antenna is placed on graphene, the high-momentum near-field components match the wave vector of the graphene plasmon, thus exciting graphene plasmonsT = 300 K), the graphene optical conductivity obeys a Drude dispersion model35Before the investigation of the properties of the propagating graphene plasmons, we need to evaluate the effective index of the graphene plasmons. The complex surface conductivity of graphene can be deduced from Kubo formula−13 s, which corresponds to the measurement under the DC mobility μ = 10000 cm2/(V·s)36εr1 and εr2, the dispersion relation of plasmon in graphene can be written as37In the following simulations, the relaxation time is set as τ = 6.4 × 10neff = kspp/k0.The effective index of the graphene plasmon can be obtained from Ef = 0.8 eV, we calculated the plasmonic band structures using the plane wave expansion methodω = 0.0468 × 2πc/a. M. In these cases, group velocity determined by ∇kω(k) points toward MΓM direction as illustrated in Next, we investigate the band structures of the graphene plasmon in the considered system. The eigenfunction of the graphene/PC hybrid structure was derived (see Methods). For the considered system at the Fermi energy ΓM direction, if the equifrequency contour is convex, the incident plasmon wave will couple to a Bloch mode that propagates into the graphene-PC region on the negative side of the boundary normal direction. As shown in k · ∇kkω ≥ 0, it means that the group velocity is not opposite to the phase velocity along the ΓM direction. Therefore, the negative refraction of the plasmon wave in the considered graphene-based system does not involve a negative effective index.When the propagating plasmon is incident from the graphene-TPX region to the graphene-PC region, the wave-vector component parallel to the interface is conserved so that the boundary condition is satisfiedc/a to 0.0468 × 2πc/a, i.e., from 6.96 to 7.02 THz. Compared to the previous design of AANR using PC structureSuch a negative refraction phenomenon can be used to realize plasmonic imaging with subwavelength resolution. To achieve better imaging performance, it requires that the graphene plasmon wave at any incident angle experiences negative refraction when entering the graphene-PC region. To achieve this phenomenon, the graphene-PC contour should be convex and larger than the graphene-TPX contour. In this case, the incident wave at any incident angle, from −90° to 90°, can be refracted with negative refraction angle in the graphene-PC region, which is named the all-angle negative refraction (AANR). From the calculation results, we find that AANR can occur in the first band. When the Fermi energy is set as 0.8 eV, the AANR frequency range is from 0.0464 × 2πa from the left-hand surface of the PC. Ez field in the considered system with Ef = 0.9 eV. Here the frequency is 0.0494 × c/a = 7.41 THz, which lies within the AANR frequency range. It is seen that the plasmon wave is focused on the right-hand side of the graphene-PC region. The central position of the image of the dipole is at a distance 1.20a from the right-hand surface of the PC. Similar plasmon imaging behavior can be achieved at different frequencies by choosing a suitable Fermi energy of graphene.To demonstrate how the AANR of the graphene plasmon can be used for THz imaging, we have performed finite-difference time-domain (FDTD) simulations with perfectly matched layer boundary conditions on the graphene-based hybrid system. The simulations were conducted via FDTD SOLUTIONS, a commercial 3D FDTD-method Maxwell solver. As shown in Ef = 0.6 eV and f = 6.03 THz, Ef = 0.7 eV and f = 6.51 THz, Ef = 0.8 eV and f = 6.975 THz, Ef = 0.9 eV and f = 7.41 THz, respectively. It can be seen from To evaluate the imaging quality, 0 to 0.187λ0 (λ0 is the wavelength of terahertz wave in vacuum) as the Fermi energy increases from 0.6 eV to 0.9 eV, which means that tunable imaging has been achieved at THz frequency range. Our simulations show that such a system can resolve two point sources, oscillating in phase, with a distance of For the comparison of the imaging resolution at different Fermi energy, we plot the FWHM of the point images versus the Fermi energy in In summary, we reported a novel design of graphene/PC hybrid structure to achieve tunable plasmon lensing. We showed that a 2D PC patterned on the substrate of a graphene sheet can realize all-angle negative refraction of the graphene plasmon in the first energy band, which results from the hyperbolic dispersion relations of the graphene/PC structure. We also showed that such a negative refraction of graphene plasmon can be electrically tuned by adjusting the Fermi energy of graphene, making adjustable wide-range negative refraction possible. In the presence of the tunable negative refraction effect, subdiffraction imaging was attained and the imaging performance can be maintained for different frequencies by changing the Fermi energy of the graphene. Our results suggest an effective mechanism for controlling the propagation of graphene plasmon and may find applications in ultra-compact subwavelength spatial light modulators.r and ε1 respectively, the Si cylinders are arranged in a square with a lattice constant of a, the dielectric constant of TPX is ε2. The graphene-Si region and the graphene-TPX region have different values of effective index for the in-plane plasmons.Consider a graphene sheet is deposited on a 2D PC, which is composed of a 2D array of Si cylinders surrounded by TPX background. Assume that the radius and the dielectric constant of Si cylinders is neff = kspp/k0 = ksppc/ω, where the wave vector of the graphene plasmon kspp can be described by In the THz frequency range, the optical conductivity of graphene obeys the Drude dispersion model  is the dielectric constant of Si or TPX. Since the energy of the plasmon is strongly confined at the graphene sheet, we only consider the Ez componentswhere kspp can be expressed by valid Helmholtz equationFor the propagating plasmon (TM mode), εspp(r) is the effective dielectric constant for the graphene-Si or graphene-TPX region. By expanding Ez(r) and εspp(r) in reciprocal space, the eigenfunction of our system can be derived aswhere ψ(G) and Ez(G) are the Fourier expansion coefficient of εspp(r) and Ez(r). ψ(G) can be expressed as,where the Combining To facilitate the calculation, we define three matrices A, B, and C:Combining β = ω2/c2. By changing the form of the where By using Scheme for fabricating our proposed device is shown in On the other hand, a monolayer graphene is fabricated on Cu substrate using chemical vapour deposition (CVD) methodHow to cite this article: Zhong, S. et al. Tunable plasmon lensing in graphene-based structure exhibiting negative refraction. Sci. Rep.7, 41788; doi: 10.1038/srep41788 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Moreover, we combine GHPM with metal-insulator-metal (MIM) structure to propose another symmetrical GHPM with a modulation depth of 0.6 dB·μm−1. Our modulators which utilize the light-matter interaction tuned by electro-doped graphene are of great potential for many applications in nanophotonics.Electro-optical modulators which work at the near-infrared range are significant for a variety of applications such as communication and sensing. However, currently available approaches result in rather bulky devices which suffer from low integration and can hardly operate at low power consumption levels. Graphene, an emerging advanced material, has been widely utilized due to its tunability by gating which allows one to realize active optical devices. Plasmonic waveguides, one of the most promising candidates for subwavelength optical confinement, provide a way to manipulate light on scales much smaller than the wavelength. In this paper, we combine the advantages of graphene and plasmonic waveguides and propose a tunable graphene-based hybrid plasmonic modulator (GHPM). Considering several parameters of the GHPM, the modulation depth can reach approximately 0.3 dB·μm High-integration density of optical devices and miniaturization of device size remain major challenges in micro and nanotechnology. Due to the existence of the diffraction limit, traditional optical devices are difficult to operate in micro-nano size. Plasmons, the collective oscillations of valence electrons in conducting materials, possess a number of appealing properties for photonic technologies, the most salient of which are (1) their small spatial extension compared with the light wavelength; (2) their strong interaction with light; (3) the huge optical enhancements produced by the strong interaction. Compared to other waveguides, plasmonic waveguides can break the diffraction limit and provide subwavelength optical confinement by storing optical energy in electron oscillations within dissipative metallic regions8. Therefore, plasmonic waveguides have been regarded as one of the most promising candidates for manipulating light on nanoscale.The need for fast, compact and low-energy consumption electro-optical modulators has motivated research into optical structures capable of guiding light with deep subwavelength confinement10. (2) High speed operation. With a carrier mobility as high as 200,000 cm2/(Vs) at room temperature  in our simulation), graphene-based electronics may have the potential to operate at ultrafast condition (over hundreds of GHz)11. The Fermi energy and hence the optical absorption can be rapidly modulated via band-filling effect13. (3) Strong light-graphene interaction. A monolayer graphene can possess a much higher optical absorption of ~2.3%, which is much higher than that of compound semiconductors at the same thickness14. What’s more, the strong plasmonic response of graphene also makes it a promising material to manufacture highly integrated devices. For graphene plamsonics, there are two classes: propagating (waveguide) and localized (nanostructure) graphene plasmons. And for coupling of graphene plasmons, there are also two classes: near-field (directly) and far-field (phase) coupling. Recently, some novel processes based on phase-coupling scheme of localized graphene plasmon resonances have been proposed to realize ultra-high contrast optical modulations16. (4) Compatibility with CMOS processing. During the past decade, graphene-based optoelectronics integrated with CMOS processing have been already demonstrated that makes it attractive in numerous applications such as graphene optical modulators17, detectors and sensings19. Based on these advantages, graphene-based modulators will be competitive with ultrafast modulation speed and low operation voltage across a broad optical bandwidth. Although there are many kinds of graphene-based modulators has been demonstrated20, it is still largely unexplored to combine the graphene with plasmonic waveguides.Graphene, a single layer of carbon atoms in a hexagonal lattice, holds an attractive potential to realize fast and compact optoelectronic devices. For applications in optical modulators, graphene has several unique characteristics. (1) Broad optical bandwidth. Graphene has a constant absorption from visible to infrared wavelengths which covers the optical fiber communication bandwidth−1 can be obtained at the wavelength of 1550 nm. What’s more, combining with the metal-insulator-metal (MIM) structure, the modulation depth can reach 0.6 dB·μm−1. These results open a viable route toward electro-optical modulation within technologically important frequency range.In this paper, we propose a tunable graphene-based hybrid plasmonic modulator (GHPM) combining the advantages of graphene and plasmonic waveguides. By realistic simulation, a significant modulation depth of ~0.3 dB·μm24 to simulate the plasmons dispersion.Before describing the structure of our device, it is essential to explore the optical response of monolayer graphene firstly. Whether our device is modulated by the exciting graphene plasmons or interband absorption, the result is demonstrated as follows. The graphene plasmons dispersion is shown in Fig. EF, the property of graphene performs as the interband absorption due to the strong quantum quenching via coupling to interband absorption. And in our research , ћω is always larger than 2EF so that the property of graphene shows as interband absorption instead of plasmon modes excitation. Incidentally, interband absorption modulates the propagating modes by affecting the graphene conductivity derived by Kubo formula (details see Methods) and further changing the refractive index as shown in Fig. Figure EF ≈ 0.4 eV. Due to the effect of optical Pauli blocking here, the optical absorption of graphene is close to zero. This effect is based on the change of graphene optical conductivity induced by the shift of the Fermi energy produced by electrical doping (details see Methods). To completely block optical absorption in graphene at the wavelength of 1550 nm, we need to shift the Fermi energy from pristine values of EF = 0 to EF = 0.4 eV.As shown in Fig. m and diameter d separated from a silicon slab of permittivity εd and thickness hd by a nanoscale dielectric gap of permittivity εs and thickness h. And a monolayer graphene is inserted between the silicon slab and the silica substrate. The dielectric material surrounding the silver nanowire is the same material used as the substrate. In our simulation, the electrodes are far enough on the guide mode so that those effects can be neglected. In order to clearly display the structure of our device, we neglect the cladding surrounded the metal nanowire in Fig. In this paper, we propose a plasmonic modulator tuned by a monolayer graphene. This device is compatible with the conventional integrated circuits process. Figure d = 12.25 and εs = 2.25 at 1550 nm29. The refractive index of Ag is 0.14526 + i11.35926. At first, the cylinder diameter, gap thickness and silicon slab thickness are set at 200, 4 and 50 nm, respectively. The conductivity of graphene is derived above. In the following study, we study the GHPM firstly, in which the modulation is realized by shifting the Fermi energy by electrical doping from 0 eV to 0.4 eV at the wavelength of 1550 nm. Then, we adjust the cylinder diameter d, the dielectric gap width h and the silicon slab width hd to control the modulation depth.In the simulations, we choose the working wavelength at 1550 nm. Figure −1 27), the modulation depth of our modulator can reach approximately as high as 0.3 dB·μm−1 at low gating voltages where the cylinder diameter, gap thickness and silicon slab thickness are set at 200, 4 and 50 nm, respectively. Meanwhile the insertion loss is approximately 0.02 dB·μm−1 which can be neglected. To further research the relationship between modulation depth and the structure parameters, we calculate the modulation depth by varying the cylinder diameter d, the dielectric gap thickness h and the silicon slab thickness hd. Relevant results are shown in Fig. Here we mainly analyze the modulation depth of this proposed modulator. Compared to the previous hybrid modulators  waveguides29. Although IMI waveguides suffer lower propagation loss, the MIM waveguides provide tighter modes confinement near the graphene layer due to the SPPs modes coupling. As the modes distribution shown in Fig. −1 which is higher than that of GHPM where the cylinder diameter, gap thickness and silicon slab thickness are set at 200, 4 and 50 nm, respectively. Meanwhile the insertion loss is 0.05 dB·μm−1 which is much smaller than the value of modulation depth.Actually, there are many proposed plasmonic waveguides utilizing the insulator-metal-insulator (IMI) structure to achieve long range propagation−1 is achieved for a broad band of wavelengths, from 1350 nm to 1600 nm. Another significant parameter shown in Fig. As shown in Fig. As shown in Fig. −1. What’s more, the modulation depth of the SGHPM is achieved a higher value (~0.6 dB·μm−1) than that of the GHPM. Our hybrid modulators have a great potential in graphene-based nanoscale optical devices.In this paper, we have proposed a tunable graphene-based hybrid plasmonic modulator (GHPM) combining the advantages of graphene and plasmonic waveguides. The modulated optical signals are obtained by electrically tuning of the graphene’s refractive index and the subwavelength confinement is achieved via plasmonic waveguides. The numerical simulations at the wavelength of 1550 nm have shown that the GHPM with relatively low loss and nanoscale light confinement can gain an attractive modulation depth of nearly 0.3 dB·μm30. At temperature T = 296 K, the conductivity σ of graphene is given bytotal is the conductivity of monolayer graphene which consists of intraband conductivity σintra and interband conductivity σinter and ћ is the reduced Plank’s constant. σ0 = 60.8 μS, λ = 1550 nm, relaxation time τ1 = 1.2 ps for interband conductivity and τ2 = 10 fs for intraband conductivity are constants, so that the conductivity of graphene is calculated as a function of Fermi level EF. The permittivity of monolayer graphene is derived byIn our research, as relative discussion proposed in the text, the optical response of graphene is described by the conductivity which is modeled utilizing Kubo formula31, as shown in Figs EF is the Fermi level at gate voltage Vg, vf is the Fermi velocity ~106 m/s, and α = ε0εd/(e × hd) is the capacitor constant. In the case of hd = 20 nm, when the gate voltage is swept from 0 to ~8 V, EF changes from 0 to ~0.4 eV to achieve modulation. Thus the proposed modulators can be electrical tuned through electric field effect.In our proposed modulators, the carrier concentration in monolayer graphene is dynamically controlled by employing a top-gate voltageThe mode properties are investigated by means of the finite-element method (FEM) with the scattering bound condition.Mp is given byER is the extinction ratio and L is the active region length. The ER is calculated byPmax and Pmin is the maximum and minimum electromagnetic power, respectively. The Pmax and Pmin are given bykmax and kmin is the maximum and minimum imaginary part of the effective mode refractive index, respectively.The modulation depth Aeff/A0), where A0 is the diffraction-limited mode area and defined as λ2/4, and the effective mode area Aeff is defined as the ratio of the total mode energy and the peak energy density which is given byWm and W(r) are the electromagnetic energy and energy density, respectively .The normalized effective mode area is defined by (f3dB) is calculated byR (~600 Ω) and C (~0.2 pF) are the total resistance and total capacitance of modulators, respectively. After considering the contact resistance and quantum capacitance of monolayer graphene33, the modulation speed of the proposed modulators is ~1.3 GHz. And the energy consumption of our modulators are calculated byVpp ≈ 8 V is the peak-to-peak voltage here. 1/4 comes from the fact that in an NRZ signaling scheme, and for a random bit sequence, one complete charge/discharge cycle occurs on average once every four bits32. Thus the energy consumption of our modulators is at the level of 1 pJ/bit.Here we briefly evaluate the modulation speed and the energy consumption of our proposed modulators. Since the two modulators have the same basic structure, their modulation speed and power consumption are approximately equal. The modulation speed which can be described by 3 dB bandwidth (