Samples with diverse urea/GO mass ratios were treated at 800 °C in inert atmosphere to generate graphene with diverse microstructural characteristics and levels of nitrogen doping. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the microstructural features of the products. The effects of doping on the samples structure and surface area were studied by X-ray diffraction (XRD), Raman Spectroscopy, and Brunauer Emmet Teller (BET). The GO and urea decomposition-reduction process as well as nitrogen-doped graphene stability were studied by thermogravimetric analysis (TGA) coupled with mass spectroscopy (MS) analysis of the evolved gases. Results show that the proposed method offers a high level of control over the amount of nitrogen inserted in the graphene and may be used alternatively to control its surface area. To demonstrate the practical relevance of these findings, as-produced samples were used as electrodes in supercapacitor and battery devices and compared with conventional, thermally exfoliated graphene.Graphene sheets doped with nitrogen were produced by the reduction-expansion (RES) method utilizing graphite oxide (GO) and urea as precursor materials. The simultaneous graphene generation and nitrogen insertion reactions are based on the fact that urea decomposes upon heating to release reducing gases. The volatile byproducts perform two primary functions: (i) promoting the reduction of the GO and (ii) providing the nitrogen to be inserted  Graphene, the two dimensional material consisting of an atom thick layer of carbon in a spangement , and itsangement ,4. GO caangement ,6. Once angement , plasma angement , sonicatangement ,9, electangement  and use angement ,13,14,15While graphene produced from GO has been reported as a material with a promising electrochemical performance when used for the manufacture of supercapacitor and lithium ion battery electrodes, its practical energy storage capacity is still well below the theoretical values ,17. TherThe intial work, published in 2010 , was folThe microstructural characteristics of the nitrogen-doped graphene samples were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM)  and compThe first evidence of nitrogen insertion in the doped samples was encountered in the spectroscopic data generated. The energy dispersive X-ray spectroscopy (EDS) spectra  of sampld002 peak toward higher angles  as the urea/GO ratio in the precursor increases. This suggest that the presence of urea not only affects the exfoliation process, but that the amount of urea may be used to control the level of exfoliation and thus the interlayer spacing in graphene samples. As shown previously, the decomposition of urea generates additional volatile species that aid the reduction of the GO (more complete reduction), but also results in an overall less effective expansion process [To obtain further insight into potential structural changes in the graphene with increasing urea content, we analyzed all samples using X-ray diffraction (XRD). The obtained XRD patterns a reveal  process . Consequ process  or to th process . However process ,34,36,372-carbons, as well as the resulting second order and combination modes. The most notable spectral change is the increase in the D band-to-G band intensity ratio (ID/IG) with increasing urea content. Although, according to XRD data  than most urea/GO-derived samples, even without any nitrogen inclusions. This discrepancy results from differences in the exfoliation mechanism as previously discussed [ID/IG therefore provides a fast and convenient tool to estimate the concentration of nitrogen atoms in doped-graphene samples. For a more detailed description of the Raman spectra of urea/GO-derived graphene samples, the reader is referred to work by Mowry et al. [XRD data , both iniscussed . Given ty et al. . While Raman measurements provided indirect evidence for a direct relationship between urea content and level of N-doping, we conducted thermogravimetric analysis (TGA) coupled with mass spectroscopy (MS) to directly evaluate the N-content of the samples. TGA was also conducted in order to identify the differences in thermal stability of the diverse samples. The burn off temperatures of the specimens were studied under an oxygen-containing atmosphere and the mass spectral signal of the byproducts generated as the carbon structure burns off. 2 (hence similar onset temperatures for oxidation), the burn off rate is higher for samples containing less urea. These samples are more exfoliated, and thus more porous, as compared to graphene with higher stacking order. At temperatures around 500 °C, mass transport becomes the rate-limiting reaction step in carbon nanomaterial oxidation, leading to reduced oxidation rate in low porosity materials. In addition, the lower concentration of two dimensional defects (due to nitrogen repair of lattice defects during exfoliation with urea in a nitrogen atmosphere) also contributes to the higher thermal stability with increasing urea content. The TGA-MS results are thus in good agreement with XRD and Raman data, providing further evidence for the increment in structural order with increasing urea content. While all samples consist of graphitic sp2 as main byproduct for pure graphene and CO2 and NO for doped graphene under the atmosphere and conditions used. As concentrations of nitrogen in the precursor increase, the temperature at which maximum NO and CO2 leave the structure/off gas increases  surface area measurements for samples with diverse doping levels show an exponential decay as the amount of urea used in the precursor increase (correlated to the nitrogen doping level). Such change is also evident when weighing the same amount of the different powders: As the amount on nitrogen introduced increase, the level of exfoliation decreases. See 2  demonstrated superior capacitive characteristics to the un-doped graphene proving that the doping has a positive benefit to the electrical properties of the material. The 0.33 sample performed nearly identically to the bare thermally exfoliated graphene. The 0.2 and 0.16 samples demonstrated worse electrical characteristics than others, further emphasizing the presence of an optimal peak doping concentration in the vicinity of 0.25.Nitrogen-doped graphene has also been reported to provide superior electrochemical performance and cycle stability in Li-ion batteries, as compared to pristine graphene ,45. The reversible/Cirreversible capacity ratio. Under this consideration, N-doped graphene would be the more favorable anode material (0.52 vs. 1.49); (3) Given the lower surface area values of N-doped graphene (<10 m2/g), we can conclude that the addition of urea is an effective way to control the extent of GO exfoliation, allowing for the optimization of Creversible/Cirreversible in graphene materials. As expected, the thermally exfoliated graphene is subject to a high irreversible capacity loss (>1600 mAh/g), exhibiting a reversible specific capacity of ~860 mAh/g at the end of the 1st cycle. However, in contrast to previous studies ,45, the 2 units, there seems to be an optimal value (sample with 0.25), demonstrating that despite the reduction in surface area, there must be an addition in charge mobility that improves sample performance.The resulting capacitance of the un-doped graphene prepared by thermal exfoliation in units of F/g was remarkably higher when compared with doped samples. Specific capacitance has been strongly correlated to the surface area of the graphene or doped graphene employed in the electrode material. Such phenomenon could be explained when relating the capacitance to the number of charges interacting at the electric double layer: the higher the surface area, the larger the sites where charges in the interface could be created. However, once the capacitance values get normalized by surface area, using F/mreversible/Cirreversible ratio in lithium ion batteries. High control over surface area and interlayer spacing may also provide opportunities for other advanced battery technologies, such as sodium ion batteries, where conventional graphitic materials are unsuitable. Electrochemical testing demonstrated that addition of urea offers a unique pathway to optimize the critical CWhile an in-depth discussion of the electrochemical performance of urea/GO-derived graphene is outside the scope of this study and will be published elsewhere, the presented data demonstrates the unique characteristics of urea/GO-derived graphene and the opportunities in energy storage applications. GO was produced from synthetic graphite powder  following a variation of the Hummer’s method . A mixtuin situ via the thermal reduction of graphite oxide in the presence of urea under inert atmosphere (reduction expansion synthesis). A sample in which no urea was employed, along mixtures with urea/GO ratios of 0.16, 0.2, 0.25, 0.33, 0.4, 0.6, 0.8, and 1 were used as precursors. The urea/GO mixtures were ground by hand in a mortar, placed in an alumina boat, and introduced into a quartz tube provided with airtight end adapters for atmosphere control. The quartz tube was flushed with nitrogen and inserted for 10 min into a Lindberg tubular furnace preheated to 800 °C. Previous studies demonstrated that the urea completely decomposes by 600 °C, however, by heating to 800 °C the mixtures seem to achieve a greater degree of expansion and oxygen groups loss, producing a higher quality product [Doped graphene was produced  product . The resScanning and transmission electron microscopy were employed to study the microstructure of the samples. A Zeiss Neon 40  operating between 2–20 kV was employed for SEM studies. A JEOL 2010F FASTEM  field emission gun STEM/TEM equipped with Gatan image filtering (GIF)  system was used to acquire the TEM and EELS data. Energy dispersive X-ray spectroscopy was performed utilizing the TEM. −1. The Cu X rays generated had a λ of 1.5418 Å. The diffraction data was analyzed using Xpert Highscore Software  using the ICDD PDF2  database.Powder samples were analyzed by X-ray diffraction using a Philips PW1830 X-ray diffractometer  operating in a continuous scan mode from a 2θ of 5° to 70°. Two second steps were utilized with a step size of 0.020° at a speed of 0.01° sRaman spectroscopy studies were carried out using an inVia confocal raman microspectrometer  with 514-nm laser excitation under ambient conditions. Spectra were recorded using a total accumulation time of 20 s. Nitrogen isotherms were used to determine total surface area and micropore volume distribution employing Brunauer Emmet Teller (BET) and Horvath-Kawazoe (HK) methodologies, respectively. A Quantachrome Nova 4200e surface area and pore size analyzer  using 9 mm large bulb long cell was employed for this analysis. Samples were degassed following an increasing temperature profile, starting at 100 °C for 30 min, followed by 300 °C for 150 min.Thermogravimetric and evolved gas mass spectral analyses were performed to identify the various off gassing temperatures and constituents of heated samples. A Netzsch STA 449 F3 Jupiter connected to a MS403C Aëolos mass spectrometer  was used. The temperature programmed oxidation of the doped samples generated in the furnace was conducted in an atmosphere that contained 80% inert gas and 20% oxygen (simulated air) with the intent of promoting the burn off of both the un-doped graphene and the doped samples.N-Methyl-2-pyrrolidone (NMP) and polyvinylidene fluoride (PVDF) . For supercapacitor testing, the resultant slurry was spread onto 25 μm thick roughened nickel foil to a height of 350 μm using a film applicator, placed into a Barnstead Lab-Line L-C oven  at 100 °C for 1 h and then punched into 15 mm disks using a MTI Corporation precision disc cutter. The completed electrodes were assembled in pairs between two acrylic non-conductive polymeric blocks, separated by a celgrad membrane  soaked in electrolyte KOH solution. For battery electrode preparation, slurries were cast on a copper foil using a blade-applicator. The dried electrodes (thickness ~0.2 mm) were cut to 12 mm-diameter disks, transferred to an Ar-filled glovebox, and assembled in CR2032 coin cells in half-cell configuration . Electrochemical testing was conducted in an electrolyte containing 1M LiPF6 in EC:DMC:DEC (1:1:1). Capacitor and battery electrodes were fabricated using a mixture of the as-produced graphene or doped graphene, acetylene black, Battery and capacitor testing was conducted using a Maccor Model 4200M tester . Capacitance was evaluated by applying three different current sources for a set number of cycles and measuring the resultant voltage trends. The currents and number of cycles utilized were 150, 350, and 500 μA for 50, 50, and 20 cycles, respectively. Battery testing was conducted using a charge/discharge rate current of C/10. We were able to successfully dope graphene with nitrogen functional groups with a high level of control over the degree of doping utilizing the reduction expansion synthesis (RES) method. SEM and TEM analysis revealed that the graphene produced resulted in thin sheets of disordered graphene, as is typical for samples made by reduction of graphite oxide. EELS analysis provided unequivocal evidence that nitrogen was embedded in the structure of graphene. Similarly, EDS shows nitrogen peaks in the doped samples further demonstrating the effectiveness of RES in doping the graphene. The BET surface area measurements for samples with diverse doping levels show an exponential decay as the amount of urea used in the precursor increase. These values can be controlled by modifying the amount of urea in the precursor samples.d” of the (002) planes as the concentration of nitrogen increased. The Raman intensity ratio between D and G band, ID/IG, increases with increasing urea content while the G band position remains nearly unchanged. These results confirmed the trends observed by BET analysis and indicated that there is a pronounced surface area loss as the amount of doping increases. XRD analysis of various levels of doped graphene revealed peak shifts indicating lower interplanar spacing “All doped samples demonstrated to have high thermal stability up to 550 °C when studied by TGA and mass spectral analysis performed under temperature programmed oxidation conditions. The MS data corroborated that the amount of urea in the precursor samples can be directly linked to the amount of nitrogen species lost during temperature programmed oxidation/burn off of the samples, thus providing a path to control the amount of nitrogen species included in the structure and the surface area of the products.Indeed, the introduction of nitrogen impurities by RES method in graphene produced from GO had a large effect in the graphene structure and improved the performance of electrodes based on such nitrogen doped graphene. Doping graphene with nitrogen clearly represents a step ahead in the development of electrode materials for new energy storage devices and the method presented herein provides a route to introduce a controlled amount of nitrogen and imprint a specific surface area in the products.


Photoresponse studies reveal that photoresponsivity in one-layer MoS2 is surprisingly higher than that in seven-layer MoS2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS2/graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS2 device.Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS Vertical integration of two-dimensional materials can open unprecedented possibilities towards design of efficient optoelectronic devices. Here, the authors investigate the photoresponse properties of a graphene/MoS2/graphene heterostructure, revealing promising quantum efficiency performances. However, Shockly–Read–Hall recombination and Langevin recombination in the WSe2/MoS2p–n junction could compromise the carrier extraction performanceThe two-dimensional 2D) layered materials such as graphene and semiconducting transition-metal dichalcogenides (TMDs) can exhibit peculiar electronic properties depending on their exact composition, thickness and geometry1D layered34678910111271572/graphene vdWHs by creating a device with two distinct regions containing one-layer (1L) and seven-layer (7L)-MoS2 to exclude extrinsic device factors. Significantly, we discover a surprisingly higher photoresponsivity and internal quantum efficiency (IQE) by going from ML MoS2 device to a monolayer device. The discretized electrostatic potential barriers were introduced to interpret the photocarrier tunneLling and extracting in ultrathin vdWHs.Here we report a layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructure device on Si/SiO2 substrate. A focused laser was used to generate electron-hole pairs in the MoS2 layer, which can be separated by the asymmetric potential between the top graphene (GrT)/MoS2 and the bottom graphene (GrB)/MoS2 junction to produce photocurrent . The GrT layer is located directly on the MoS2 flake  to overlap with MoS2 flake and the GrB.The photocurrent generation in our devices was mapped by scanning photocurrent microscopy, where a focused laser beam was raster-scanned over the sample, while the photocurrent was being measured (Ids–Vds) data obtained in the dark  through ultrathin tunnelling barrier of 1L-MoS2ocurrent . Figure measured . The spaAeff, ϕB, q, m, m, d and h are effective contact area, barrier height, electron charge, free electron mass, effective electron mass, barrier width (MoS2 thickness) and Plank's constant, respectivelywhere −1) of the device. The photoresponsivity of 1L-MoS2 increases with decreasing the laser power could be attributed partly to absorption saturation in MoS2 and partly to the screening of a built-in electric field by the excited electrons in the conduction band of MoS2 (ref. 2 increases with increasing the laser wavelength and a maximum photoresponsivity of 68 mA W−1 in 1L-MoS2 vdWHs was achieved at the wavelength of 633 nm and the laser power of 100 nW (2/graphene vdWHs device (∼30 mA W−1 without plasmonic enhancement)72) and previous reports (5∼30 nm MoS2), which will be further discussed by comparison of external quantum efficiency (EQE) and IQE between 1L-MoS2 and 7L-MoS2 vdWHs in Based on the photocurrent response and input laser power, we can determine the photoresponsivity  and the GrT layer is located directly above the MoS2 flake (inside the solid line), to overlap with MoS2 flake and the GrB. The number of layers of MoS2 was then confirmed by Raman spectra measurements 152 (band gap ∼1.3 eV)To further unambiguously illustrate the difference between monolayer and ML MoSe device . The 8 μurements  and atom2 region exhibited much more pronounced photocurrent than the 7L-MoS2 region (Ids–Vds) data obtained in the dark . This is a rather surprising and counter-intuitive discovery, considering that the 7L-MoS2 should have significantly higher optical absorption than 1L-MoS2 , the second factor  dominates in our device.The enhanced photoresponsivity of 1L-MoSc) is thus given (in 2D) byIn general, the spectral dependence of the photocarrier generation rate can be estimated from first principles, using the Fermi golden rule. The probability of transition from a valence band state (υ) to a conduction band state . It is also noted that the IQE in 1L-MoS2 region steadily increases when the photon energy is reduced to approach the bandgap of 1L-MoS2 (1.82 eV (ref. 2 (1.82 eV). It is noteworthy that in this region k2 is nearly independent on the thickness. According to the theoretical calculations, 1L-MoS2 has a much larger density of states near the band edges, at the valence band top due to the heavier hole masses, and near the conduction band edge, due to the presence of the 2D van-Hove singularities . The hilarities , increas2 is driven by diffusion and drift process, which is dictated by different band bending at GrT and GrB MoS2 interface (originated from the difference of GrT and GrB doping densities)72 having a continuous band bending  and GrT (2.7) are determined by the standard approximation of ɛGrB=(ɛ21L-MoS+ɛ2SiO)/2=4.2 and ɛGrT=(ɛ21L-MoS+ɛair)/2=2.7, respectively22ɛ21L-MoS=4.5  can be determined by the difference of electron tunnelling probabilities between bottom and top junction barriers, which is normalized by the sum of tunnelling probability to top (TT) and bottom junction barrier (TB) (I)=(TT–TB)/(TT+TB)). The potential barrier was sliced to thin square barriers with width of 0.01 nm and then the tunnelling probability was calculated through overall square barriers  strongly relies on the excitation photon energy  is not altered appreciably in response to the energy of excited electrons (or absorbed photon energy), because effective barrier height (U–E) of the bottom and top junction changes by the similar magnitude  because of the decrease of effective barrier height (U–E), whereas the tunnelling probability to the TT remains almost at 1 regardless of the electron energy. Consequently, the photocarrier extraction rate (I) decreases in proportion to electron excitation energy  decreases in proportion to the electron excitation energy  were calculated in terms of the electrostatic potentials.The electrostatic potentials were calculated in terms of the number of MoS2 layers . The reg2) is shorter than that of indirect gap (7L-MoS2), which should be taken into account in recombination process during carrier drift. We have measured the carrier lifetime in direct gap (1L-MoS2) and indirect gap (7L-MoS2) based on transmission change in pump–probe measurement (δnx) by initial excited carriers (δ0) for 1L-MoS2  and ML-MoS2  along with carrier drift distance  rate into graphene layer, much shorter than carrier lifetime in 1L-MoS2 (60 ps), resulting in highly efficient transfer of photo-excited carriers in MoS2 into graphene before recombination. Therefore, we multiplied photocarrier extraction rate (I) in 1L-MoS2 by 100% of normalized excited carrier density. I) reaches around 65% when the number of MoS2 layers is reduced from 7L-MoS2 to 1L-MoS2 and the photon energy approaches the bandgap (1.82 eV). The calculated I are in good agreements with measured IQE of 1L-MoS2  and open circuit voltage (Voc) by an external gate voltage  of the GrB due to the relatively strong electrostatic screening by ML-MoS2  is approximately twice of that in single layer (MoS2), the IQE in our device is about twice higher. The lower IQE in in graphene/1L-WSe2/1L-MoS2/graphene p–n heterojunctions may be partially attributed to Shockly–Read–Hall recombination and Langevin recombination, which is not present in graphene/1L-MoS2/graphene devices.In summary, we have reported an unusually efficient photocarrier generation from monolayer MoS2/graphene device, the graphene was grown with a chemical vapour deposition process272 (300 nm SiO2) substrate, and patterned into 8 × 30 μm strips as the bottom electrode using a photolithography and oxygen plasma etching process. The MoS2 flakes were then transferred onto the graphene strips through a dry transfer approachT electrode was transferred and patterned on the MoS2 flake and GrB. Directly overlapping graphene area was patterned and etched away, to avoid short circuit between the GrT and GrB. The metal electrode, for probe contact or wire bonding purposes, was patterned on the bottom and GrT electrodes by e-beam lithography followed by e-beam deposition of Ti/Au (50/50 nm).For the fabrication of the vertical heterostructures of graphene/MoS2 heterostructures were excited with a cw solid-state laser at a wavelength of 405 and 532 nm. A low laser power of ∼100 μW was used to avoid heating and PL saturation. The PL of MoS2 samples were calibrated by using rhodamine 6G molecules as the standard. Raman spectroscopy  was used to characterize the MoS2 and graphene with a wavelength of 514 nm (2.41 eV) and a Rayleigh line rejection filter. As Raman scattering efficiency has usually little layer thickness dependence, the PL spectra normalized by Raman intensity reflects directly the luminescence efficiencyElectrical transport measurements were conducted with a probe station and a computer-controlled analogue-to-digital converter at room temperature. The scanning photocurrent measurements were conducted with the same electrical measurement system under a SP2 MP Film confocal microscope coupled with Ar/ArKr laser  and HeNe laser . All optical measurements were carried out under ambient conditions at room temperature by using an inverted microscope coupled to a grating spectrometer with a charge-coupled device camera. The optical beams were focused on the sample with a spot diameter of ∼1 μm. MoSet al.The DFT calculations were performed using the Quantum ESPRESSO codea) used was optimized for the primitive unit cell. The supercell length along the direction perpendicular to the plane c is taken to be twice the lattice parameter, except for preliminary bandstructure calculations performed using a smaller c, which are identified in the text. The Brillouin zone was sampled using a 2 × 2 × 1 Monkhorst–Pack gridThe monolayer was modelled using a supercell consisting of 4 × 4 unit cells of the monolayer material, comprising a total number of 48 atoms. The lattice parameter  and the delay between the two pulses is controlled by a mechanical delay stage (Newport M-IMS300PP).The femtosecond laser source is based on a 250 kHz Ti:sapphire regenerative amplifier (Coherent RegA 9050), which provides a 1.55 eV photon energy, 50 fs pulse width and 6 μJ per laser pulse. The Reg A output pulse is separated into two pulses by a ratio of 7:3. The 70 % laser pulse is used to generate 3.1 eV pump–photon energy by second harmonic generation in a 1 mm-thick beta barium borate crystal. The other 30% laser beam is focused in an ultra-clean sapphire disk to generate a white-light super-continuum, which serves as a probe pulse. Both the pump and the probe pulses are focused on the 1L-MoSThe data that support the findings of this study are available from the corresponding author upon request.How to cite this article: Yu, W. J. et al. Unusually efficient photocurrent extraction in monolayer van der Waals heterostructure by tunnelling through discretized barriers. Nat. Commun.7, 13278 doi: 10.1038/ncomms13278 (2016).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Supplementary Figures 1-9, Supplementary Notes 1-6 and Supplementary References


Even higher efficiency is expected for tritium separation. With no fundamental obstacles for scaling up, the technology's simplicity, efficiency and green credentials call for consideration by the nuclear and related industries.Thousands of tons of isotopic mixtures are processed annually for heavy-water production and tritium decontamination. The existing technologies remain extremely energy intensive and require large capital investments. New approaches are needed to reduce the industry's footprint. Recently, micrometre-size crystals of graphene are shown to act as efficient sieves for hydrogen isotopes pumped through graphene electrochemically. Here we report a fully-scalable approach, using graphene obtained by chemical vapour deposition, which allows a proton-deuteron separation factor of around 8, despite cracks and imperfections. The energy consumption is projected to be orders of magnitude smaller with respect to existing technologies. A membrane based on 30 m Thousands of tons of water are processed every year for hydrogen isotope separation, using extremely costly technology. Here the authors demonstrate a fully-scalable graphene electrochemical pump, which promises to dramatically reduce the energy and capital costs. The production remains expensive for two reasons. First, the low natural abundance of deuterium (0.015%) implies that huge amounts of water should be processed 2221Separating hydrogen isotopes is a task of vast proportions. Over a thousand tons of heavy water DO are prorium 0.01% impliesIt has recently been shown that perfect monolayers of graphene and hexagonal boron-nitride (hBN)—impermeable to thermal atoms and molecules8101213The current report explores the feasibility of graphene-based electrochemical pumps for industrial-scale separation of hydrogen isotopes. We suggest that this can be achieved by roll-to-roll−1. We limited the size of the tested membranes to 1 square inch. This was chosen for convenience only. The discussed fabrication can be extended to produce graphene-on-Nafion membranes of virtually any size, following recent advances in growth and transfer of large-area CVD graphene1517The graphene membranes studied in this work were fabricated as illustrated in 1015172O–H2 and D2O–D2 with a chosen atomic fraction of protium; this fraction remained fixed during a given measurement and could be changed as required. The opposite side of the membrane faced a vacuum chamber connected to a mass spectrometer. This setup represents an electrochemical pump102, D2 and protium deuteride (HD)—which are detected by the mass spectrometer for each of the fixed protium fractions in the feedThe permeability of protons and deuterons across the graphene-on-Nafion membranes was studied using mass spectrometry2, D2 and HD) for different atomic fractions of protium in the feed. The data for the permeated gases can be converted directly into protium atomic fractions (see ‘Mass spectrometry measurements' in Methods). The latter are plotted in 21There are two key characteristics to monitor in these measurements: isotope selectivity and hydrogen throughput. Let us discuss the selectivity first. α≈10, where Hfeed and Hpermeate are the protium atomic fractions in the feed and permeate, respectively. This relation is plotted in α≈10 (dashed red curve). α≈8 (the best fit is shown by the solid black curve). At first glance, this may seem surprising because holes in graphene provide a much easier permeation path1011with a large separation factor A) which for potential applications needs to be as high as possible. Φ as a function of the electric current I through our devices. The dependence is accurately described by Faraday's law of electrolysis Φ=I/2FA, where F is Faraday's constant and the factor of 2 accounts for two atoms in each H2 molecule. This means that we reached 100% Faradaic efficiency for converting electron current into hydrogen flux such that one hydrogen molecule was generated in the permeate chamber for every two electrons pushed through the electrical circuit, in agreement with previous experiments using micrometre-size 2D monocrystals10The second key characteristic of electrochemical pumping is its throughput  or, equivalently, ∼40 tons of heavy water per annum. The latter number is comparable with a typical annual output of existing heavy-water production plantsWe typically applied biases th V see  inset. Tα∼10 for ideal graphene at room temperatureα∼8 is still high enough to minimize the amount of feed that needs to be processed. Using the Rayleigh equationP required is given by P=IV. Therefore, with an operational voltage of ∼0.5 V, the power density (p=P/A) per unit of gas flux is given by p/Φ=2FV∼26 Wh mol−1 (which depends only on the applied voltage), in agreement with the data in E ∼20 GJ per kg of 20% enriched heavy water.For the known throughput and separation factor, it is straightforward to estimate the energy needed to enrich hydrogen with the natural deuterium concentration of 0.015% up to 20% required for primary heavy-water production2E,α). The most utilized technologies today are the Girdler-Sulfide (GS) and monothermal-NH3/H2 processesα∼1.3 and 6, respectively, and both require E∼30 GJ kg−1. Our electrochemical pumping exhibits =, outperforming all the other technologies. Moreover, the above estimate for E was rather conservative, so we believe that the energy costs can be reduced by at least an order of magnitude by a number of design changes. For example, the operating temperature can be increased to 60 °C, which would result in an exponential increase in graphene's proton conductivity; by a factor of 10 as proven in previous experiments10E . Next, the opposite side of the Cu substrate (covered with CVD graphene on both sides) was plasma etched to remove graphene from that side. Then, the CVD graphene (still on Cu substrate) was placed on the carbon-cloth/Nafion stack and the whole assembly was hot pressed in a laminator . The Cu substrate was then etched in ammonium persulfate solution and the device was left in DI water to remove residues of the etchant. At this point the transfer of CVD graphene onto the Nafion substrate was complete. Finally, to facilitate proton permeation (see main text), the graphene side of the carbon-cloth/Nafion/graphene stack was decorated with Pd nanoparticles deposited by e-beam evaporation  and covered by hand with another piece of carbon cloth .A Nafion membrane  was hot pressed on a carbon-cloth substrate  is related to the H2 and D2 molar fractions  in the permeate chamber via the law of mass action: [HD]2/{[H2][D2]}=K(T) where K(T) is a constant. Therefore, using a control sample (no graphene), we calibrated the HD response using this law.Devices for mass spectrometry were placed in a custom built fuel cell set up that could be connected to our mass spectrometer. This set up was placed in between the feed and permeate chambers. In these experiments we monitored the molar fraction of the gases in the permeate chamber for a fixed deuterium atomic fraction in the feed. The feed chamber was then evacuated and the vapour–gas mixtures of Hgraphene . To caliAll relevant data are available from the authors.How to cite this article: Lozada-Hidalgo, M. et al. Scalable and efficient separation of hydrogen isotopes using graphene-based electrochemical pumping. Nat. Commun.8, 15215 doi: 10.1038/ncomms15215 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Supplementary Figures, Supplementary Notes and Supplementary References


Plasmonic structured illumination microscopy (PSIM) is one of the promising wide filed optical imaging methods, which takes advantage of the surface plasmons to break the optical diffraction limit and thus to achieve a super-resolution optical image. To further improve the imaging resolution of PSIM, we propose in this work a so called graphene nanocavity on meta-surface structure (GNMS) to excite graphene surface plasmons with a deep sub-wavelength at mid-infrared waveband. It is found that surface plasmonic interference pattern with a period of around 52 nm can be achieved in graphene nanocavity formed on structured meta-surface for a 7 μm wavelength incident light. Moreover, the periodic plasmonic interference pattern can be tuned by simply changing the nanostructures fabricated on meta-surface for different application purposes. At last, the proposed GNMS structure is applied for super-resolution imaging in PSIM and it is found that an imaging resolution of 26 nm can be achieved, which is nearly 100 folds higher than that can be achieved by conventional epi-fluorescence microscopy. In comparison with visible waveband, mid-infrared is more gently and safe to biological cells and thus this work opens the new possibility for optical super-resolution imaging at mid-infrared waveband for biological research field. Various methods were developed to improve the optical imaging resolutions1357Graphene, as a two-dimensional (2D) material formed by carbon atoms in honeycomb arrangement14151719In this work, we propose a so called graphene nanocavity on meta-surface (GNMS) structure model by intelligently integrating graphene nanocavity with meta-surface for super-resolution imaging in PSIM method. The dispersion relationship of the model is firstly discussed and then followed by simulating the structure by employing FDTD method. It is found that the plasmonic interference pattern generated on graphene has a period of 52 nm for a 7 μm incident light wavelength. There have been PSIM techniques based on surface plasmons excited on the surface of thin silver, and the imaging resolution improvement with 3 to 4 folds in comparison with conventional epi-fluorescence at visible waveband have been reported112124According to Maxwell’s electromagnetic theory, the H and E field in each layer of GNMS can be expressed.In Layer 1,In Layer 2 and 3,In Layer 4,i = 1–4 stands for the wavenumber along x direction in each layer. ω is the angular frequency, εi is the relative permittivity of the materials in layer i, and k0is the free-space wave vector. Under the assumption that surface current exists on graphene, one can obtain a series of relationships by matching the boundary conditions at each interface.Here, x = d1, since the boundary condition is At interface By combining x = d2) can be derived by considering boundary conditions of Similarly, the relationships between layer 2 and 3 (x = 0) and the boundary conditions are Because there is no surface current exists at the interface between layer 3 and 4 τ can be calculated by nc, μdc and vF stands for electron concentration, carrier mobility and the Fermi velocity respectively. If we define When vF = 106 m/s and carrier mobility is μdc = 10000 cm2V−1s−1.In this paper, the carrier mobility Fermi velocity is set as For comparison, the dispersion curve of single-graphene structure  method was employed to simulate the GNMS structure (See Methods Section). To explain the function of the grating in meta-surface on the graphene plasmonic interference pattern, parameters of the silver grating including duty cycle, material and period are discussed respectively. 2O3, the peak intensity is quite weaker. We attribute this reason to the possible contribution localized surface plasmonic enhancement effect of metal and semiconductor materials.In order to show the effect of the grating material on graphene plasmons, grating structure with different materials was studied and the results are shown in γ will be set as 0 approximately for accuracy when the grating duty cycle is small.Furthermore, the effect of the period of metal grating on graphene plasmons was also discussed for the same duty cycle of 0.1 and the results are shown in d and the height of silver grating d2. d2 through the dispersion To tune the graphene plasmons in nanocavity, the influence of the structural parameters on the graphene plasmonic interference field is systematically studied. The structural parameters that can be changed include the thickness of water film ΔMoreover, it is found that the period of graphene plasmonic interference pattern can also be tuned by changing the chemical potential of graphene. λemission/(2NA+2NAeffective), where λemission is the wavelength of incident light and NAeffective represents NAeffective, the higher resolution limit the PSIM can be achieved. Since the period of the plasmonic pattern is 52 nm, the resolution limit can be achieved is 25 nm for PSIM. The proposed GNMS structure can be applied for super-resolution imaging at mid-infrared waveband. If DNA or protein is put in the nanocavity, the formed plasmonic pattern can be used to illuminate the biological sample as a structured illumination light for PSIM method. 11As a summary, we have proposed a so called GNMS model for PSIM method to improve the optical imaging resolution. The GNMS model takes advantage of merits of both graphene and meta-structure. As proved by both analytical and numerical simulations, deep compression of the period of plasmonic interference pattern can be achieved in graphene nanocavity at mid-infrared waveband. Moreover, the proposed GNMS model can be applied for optical imaging resolution when applied in PSIM method. The rigorous numerical simulation results show that the imaging resolution has been enhanced for more than 100 folds by GNMS in comparison with traditional optical imaging method. More importantly, as the infrared light is safer than visible light for biological samples, the proposed GNMS method should be more preferred for biological research when applied in optical imaging.th mesh accuracy which is the highest is used. The mesh type is set as auto-uniform which means that the minimum grid is the 34th of the minimum wavelength. The periodical boundary condition is set along both y and z axes and PML boundary condition is used in x direction. In addition, in the region of water film and silver grating, a finer grid of 0.5 × 5 × 0.5 nm3 is used to ensure the sufficient precision near graphene regions.The proposed GNMS is simulated by using Finite Difference Time Domain (FDTD) software supported by Lumerical Solutions Inc. In the simulation, temperature is set as 300 K, the model of graphene is represented by a 2D-rectangle to reduce the simulation time and ensure the precision of the simulation. The scattering rate and chemical potential of graphene are set according to the design, and the conductivity scaling of graphene keeps 1. Furthermore, in the simulation the 8In the numerical experiment of super-resolution imaging, a 10 nm quantum dot is used as the object. The PSF in far field was calculated by the first order Bessel functionsJ1 is the first-order Bessel function, NA is the numerical aperture of oil objective, λe represents the reflection wavelength of the quantum dot and is the radius of quantum dot, thus in the far field, the image of the quantum dot can be obtained. For GNMS based PSIM method, O(r) is set as 1 at where the dot is illuminated. Furthermore, at least three different phase, i.e. 0, 120°, −120°, of the illumination pattern should be recorded to realize the image reconstruction. This can be achieved by changing the angle of the incident light or by employing the vortex beams with different topological charges.Where How to cite this article: Yang, J. et al. Super-Resolution Imaging at Mid-Infrared Waveband in Graphene-nanocavity formed on meta-surface. Sci. Rep.6, 37898; doi: 10.1038/srep37898 (2016).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


The programmed death receptor 1 (PD-1) protein is a cell-surface receptor on certain lymphocytes that, with its ligand programmed death ligand 1 (PD-L1), helps to down-regulate immune responses. Many cancer types express PD-L1 and evade immune recognition via the PD-1/PD-L1 interaction. Precision therapies targeting the PD-1/PD-L1 pathway have the potential to improve response and thereby offer a novel treatment avenue to some patients with cancer. However, this new therapeutic approach requires reliable methods for identifying patients whose cancers are particularly likely to respond. Therefore, we conducted a systematic literature review assessing evidence on test validation and scoring algorithms for PD-L1 immunohistochemistry (IHC) tests that might be used to select potentially responsive patients with bladder/urothelial cell, lung, gastric, or ovarian cancers for immunotherapy treatment.To identify evidence on commercially available PD-L1 IHC assays, we systematically searched MEDLINE and Embase for relevant studies published between January 2010 and September 2016 and appraised abstracts from recent oncology conferences (January 2013 to November 2016). Publications that met the predefined inclusion criteria were extracted and key trends summarized.In total, 26 eligible primary studies were identified, all of which reported on the test validation metrics associated with PD-L1 IHC tests in lung cancer, most using immunohistochemistry testing. There was significant heterogeneity among the available tests for PD-L1. Specifically, no definitive cutoff for PD-L1 positivity was identifiable, with more than one threshold being reported for most antibodies. Studies also differed as to whether they evaluated tumor cells only or tumor cells and tumor-infiltrating immune cells. However, all of the tests developed and validated to support a therapeutic drug in the context of phase 2–3 clinical trials reported more than 90% inter-reader concordance. In contrast, other PD-L1 antibodies identified in the literature reported poorer concordance.Published validation metric data for PD-L1 tests are mainly focused on immunohistochemistry tests from studies in lung cancer. The variability in test cutoffs and standards for PD-L1 testing suggests that there is presently no standardized approach. This current variability may have implications for the uptake of precision treatments. Checkpoint inhibitor therapy is a recent development in the field of cancer immunotherapy and precision medicine, and involves targeting immune pathways that enhance the body’s ability to recognize and destroy tumor cells (TCs). One key mediator in such pathways is the programmed death receptor 1 (PD-1) protein, a cell-surface receptor on certain lymphocytes. The interaction between PD-1 and its ligand, programmed death ligand 1 (PD-L1), plays a crucial regulatory role in the human immune system by inhibiting the body’s immune response to foreign antigens. However, many cancer cell types express PD-L1 and thereby activate PD-1/PD-L1 signaling, thus enabling these tumors to evade immune recognition. Precision therapies that focus on the PD-1/PD-L1 pathway can offer a novel treatment avenue to some patients with cancer. Five PD-1/PD-L1 immunotherapies  have now been approved by the United States (US) Food and Drug Administration (FDA) and/or European Medicines Agency (EMA) for a variety of indications following the publication of clinical trials demonstrating their efficacy improving therapeutic response.Although research into the effectiveness of these types of immunotherapy is rapidly evolving, there remains some uncertainty regarding the extent to which measuring levels of PD-L1 expression in individuals’ tumor tissue helps to identify patients who are most likely to respond to treatment. For example, in Hodgkin’s lymphoma, most tumors have been reported to express PD-L1, so assessing expression in patients can contribute only minimally to clinical decision-making about suitability for treatment ) to ensure the search was comprehensive.Systematic searches were conducted in MEDLINE® (via PubMed) and Embase® European Society for Medical Oncology (ESMO)Society for Immunotherapy of Cancer (SITC)International Cancer Immunotherapy ConferenceAmerican Association of Cancer Research (AACR)International Association for the Study of Lung Cancer (IASLC)Supplementary searches were undertaken to capture ‘grey’ literature—data from sources not indexed in the electronic databases. To capture such evidence, proceedings from the three most recent meetings of the following six subject-specific conferences were searched:Study selection was based on criteria that were defined a priori and are summarized in Table Data abstraction of the included studies was performed using a predefined data abstraction template designed in Microsoft Excel®. For each included study, data were captured by a single investigator, with validation of the accuracy and completeness of this abstraction being performed by a second reviewer. Any discrepancies were resolved in a discussion with a third investigator. Specific key information was abstracted from included studies on the following: patient population, type of test, test developer, test platform, test-scoring algorithms, test thresholds/cutoffs, and test-validation metrics. Due to the variety of study designs considered in this review, it was not possible to undertake a risk-of-bias assessment using a single standardized tool. Heterogeneity in the studies also meant that a quantitative meta-analysis of their data was not appropriate; therefore, the evidence abstracted from included studies was qualitatively synthesized and key trends were summarized.The indexed database searches yielded 950 records. After removing publications duplicated between databases, 589 abstracts remained and were screened, of which 57 met the criteria for detailed review of their associated full-text publications. Of these 57 publications subjected to full-text screening, 12 were eligible for inclusion in the SLR, as they reported on PD-L1 test validation metrics for commercially available tests. An additional eight studies were identified from the supplementary search and 10 conference abstracts also met the eligibility criteria. Therefore, a total of 30 references (collectively representing 26 unique study populations and four linked publications) were included in the review. The study screening and selection process is illustrated in Fig. All 26 included studies reported on test validation metrics associated with PD-L1 tests in lung cancer. One of the studies also reported data relating to bladder/urothelial cell cancer . No evidPD-L1 IHC 22C3 pharmDx by Dako (referred to hereafter by the antibody 22C3): 3 studies –6PD-L1 IHC 28–8 pharmDx by Dako (referred to hereafter by the antibody 28–8): 7 studies –12VENTANA PD-L1 SP263) Rabbit Monoclonal Primary Antibody by Roche (referred to hereafter by the antibody SP263): 6 studies 3 Rabbit , 13–15VENTANA PD-L1 (SP142) Assay by Roche (referred to hereafter by the antibody SP142): 9 studies –20PD-L1 (E1L3N®) XP® Rabbit mAb #13684 by Cell Signaling Technology [CST] (a reagent provider): 9 studies , 20–254059 by ProSci, Inc.: 1 study h5H1 by Advanced Cell Diagnostics: 1 study 9A11 (developer not reported): 1 study Across the 26 included studies, eight antibodies for detecting PD-L1 expression in patients with lung cancer were identified, as follows:In all cases, PD-L1 expression was evaluated using an immunohistochemistry (IHC) platform. One of the studies specified that diaminobenzidine tetrahydrochloride was used as the reagent to produce the “brown staining” for the IHC process . Three sThree studies looked at the IHC-SP142 (Roche), developed alongside atezolizumab , 16, 17Two studies looked at IHC-SP263 (Roche), developed alongside durvalumab , 28Two studies looked at IHC-22C3 (Dako), developed alongside pembrolizumab , 5One study looked at IHC-28-8 (Dako), developed alongside nivolumab The antibodies manufactured by Dako and Roche had all been originally developed and validated to support a therapeutic drug in the context of a clinical trial. These antibodies were evaluated in eight studies as follows:The thresholds and scoring systems used to determine PD-L1 positivity varied between the antibodies and across studies. Eleven studies , 23, 28 A further 11 studies , 24–27 uA second study  that incThere was variation among the studies with regard to the cell type tested, specifically, whether PD-L1 expression was measured on TCs and/or tumor-infiltrating ICs. Nine studies tested TCs only , 26, 27,Most studies (18/26) focused on a single antibody and reported validation metrics that were specific to the one test under investigation, without comparing its performance with that of another antibody or testing approach. The results of these studies by outcome are summarized below and in Table Two studies reported on the extent of agreement in test results when different types of samples  were tested, and these found some conflicting results. One study looked at the use of the SP142 test (Roche) in biopsy and surgical-resection samples. It reported an overall discordance rate of 48%  and a κ score of 0.218, indicating poor agreement between the test outputs from the different sample types .Seven studies reported data relating to the comparative performance of two or more tests, and their key findings are summarized in Table Three of the head-to-head comparison studies , 13, 15 One study reported on inter-observer concordance based upon a six-step scoring system which integrated the criteria employed by the four different clinical trial tests  and found moderate agreement using this harmonized approach (κ = 0.47 to 0.49) [One study reported on the test-validation performance of a PD-L1 test in bladder/urothelial cell cancer for the antibody SP142 (Roche) and found it had acceptable inter-reader concordance between pathologists (> 90%) when measuring PD-L1 expression in both IC and TC in bladder/urothelial cell cancer .The results of this SLR demonstrate that there are varied cutoff and scoring algorithm approaches among the commercially available PD-L1 antibody tests in lung cancer. There is, for example, no commonly accepted standard or threshold for determining positivity for each of the antibodies based on the proportion of PD-L1–positive cells. Further differences between scoring algorithms relate to the way in which staining patterns are interpreted; some studies have investigated the use of proportional scoring , 23, 28 In general, our review found that the concordance between tests developed in a clinical trial setting to accompany a therapeutic product was deemed acceptable, with inter-reader concordance exceeding 90% . This fiOur findings are in line with other reviews in this topic area , which have also reported on the variations in cutoffs used for different antibodies to determine PD-L1 positivity –32. In pOne limitation of our review is that of the existing commercially marketed tests considered, most were IHC tests, with only three studies reporting on QIF , 20 and The heterogeneity in the findings of this review has important implications for clinical practice. Notably, the lack of standard thresholds for responder identification and concordance between a subset of tests indicates the existence of (1) potential risks for efficient treatment selection and use of precision therapies; (2) confusion about whether it is important to request a particular PD-L1 test; and (3) potential adverse effects on patient management decisions . However, it is also important to note that no study from our search results reported evidence for these possibilities. Ambiguity around test thresholds, decision algorithms, and interchangeability of PD-1/PD-L1 testing could also present uncertainty for those payers who view accurate prediction of the subpopulation of treatment responders as being a key value of precision therapy approaches. Where there is variability in the interpretation or selection of particular tests, there is the potential for physician confusion, interpretation dilemmas, and payer uncertainty.There are illustrative examples of such difficulties from previous attempts to introduce biomarker testing to the selection of precision therapy and patient management. In the case of IHC and molecular testing for epidermal growth factor receptors, for instance, the substantial variability in test cutoffs or thresholds and the potential for variable interpretation of early-generation tests have been well documented. Following early introduction of tests for this marker and initial launch of EGFR-targeted agents, some health technology assessment and payer organizations  and there is limited information on the extent, if any, to which the tests might be interchangeable. Developing strategies to address this variability in available IHC tests and publishing data that clarify the value of non–IHC-based approaches, such as FISH and next-generation tests that incorporate PD-L1, will be important to address as the availability of precision treatments focused on these biomarkers continues to increase.


Graphene has been widely used in the active material, conductive agent, binder or current collector for supercapacitors, due to its large specific surface area, high conductivity, and electron mobility. However, works simultaneously employing graphene as conductive agent and current collector were rarely reported. Here, we report improved activated carbon (AC) electrodes (AC@G@NiF/G) simultaneously combining chemical vapor deposition (CVD) graphene-modified nickel foams (NiF/Gs) current collectors and high quality few-layer graphene conductive additive instead of carbon black (CB). The synergistic effect of NiF/Gs and graphene additive makes the performances of AC@G@NiF/G electrodes superior to those of electrodes with CB or with nickel foam current collectors. The performances of AC@G@NiF/G electrodes show that for the few-layer graphene addition exists an optimum value around 5 wt %, rather than a larger addition of graphene, works out better. A symmetric supercapacitor assembled by AC@G@NiF/G electrodes exhibits excellent cycling stability. We attribute improved performances to graphene-enhanced conductivity of electrode materials and NiF/Gs with 3D graphene conductive network and lower oxidation, largely improving the electrical contact between active materials and current collectors. With the increasing requirement of energy storage devices in the modern technology society, supercapacitors have drawn great attention due to the higher power density, quicker charge and discharge rate, and longer cycle life compared with traditional lithium-ion batteries ,2,3,4. A2, Co3O4, NiXMn1-XO et al.) with high capacitance and their composites are the most famous active materials being studied now [At present, the relatively low energy density is still a key bottleneck of supercapacitors. The formula al range ,9,10,11.died now ,15,16,17died now ,19. Howedied now ,21,22,23Current collector, as an essential part of a supercapacitor, plays an important role in collecting current and supporting electrode materials. The conductivity and adhesion with active materials of a current collector can directly influence the specific capacitance ,25,26,27Moreover, conductive additives also are of great importance in an operational electrode. The most common conductive additive is carbon black (CB) . The addHere, activated carbon (AC) electrodes were prepared with CVD graphene-modified nickel foams (NiF/Gs) as current collectors and high quality few-layer graphene as conductive additive (AC@G@NiF/G). On one hand, few-layer graphene as conductive additive directly improves the conductivity of the electrodes. On the other hand, CVD graphene on NiFs not only increases the conductivity and stability of the current collector, but also as a buffer layer to strengthen the adhesion to active material, providing a highly effective electrical contact for fast charge transfer from AC active material to current collectors with the underlying 3D graphene network . Due to 2) was obtained from HGP technology CO., LTD . The aqueous membrane (NKK-MPF 30AC-100), Polyvinylidene Fluoride  and carbon black  were purchased on Taobao (https://item.taobao.com/item.htm?spm=a230r.1.14.16.73d46067nVvMYK&id=530857358840&ns=1&abbucket=3#detail).The activated carbon (AC) powder (Kuraray YF-50) was received from Kuraray international trade CO., LTD. . The graphene powder  was brought from SZgraphene nanotechnology Company . The Potassium hydroxide  and N-Methyl pyrrolidone  were brought from Sinopharm Chemical Reagent Company . The nickel foam , and then annealed at 1000 °C for 10 min under the gas flow of Ar (200 sccm) and H2 (300 sccm), in order to remove the oxide layers on NiFs. Methane (CH4) was then injected into the quartz as carbon source to growth graphene under ambient pressure with gas flow of Ar (400 sccm), H2 (200 sccm) and CH4 (100 sccm) at 1000 °C. After 10 min, the quartz was fast cooled to room temperature under the gas flow of Ar (200 sccm) and H2 (300 sccm). After growth of graphene, the color of NiF/Gs changed from shallow to deep.NiFs were placed in the middle of a quartz tube furnace, and then the furnace should be vacuumized and filled with Ar twice to eliminate the residual air in the furnace. Before growth NiFs were heated to 1000 °C in 30 min under the gas flow of Ar (200 sccm) and HCertain amount of AC, graphene, CB and PVDF were mixed in NMP by a high-shear dispersion homogenizer  at 1800 rpm/min for 4 h to obtain uniformly dispersed slurries. And then, these slurries were dip coated on NiF/G or NiF current collectors and dried at 130 °C in vacuum for 24 h to prepare AC electrodes. The current collectors were made into two specifications (square with 1 cm × 1 cm and circular piece with diameter 13 mm). The square electrodes were used to take electrochemical measurements with a standard three-electrode method. The circular electrodes were used to fabricate symmetrical supercapacitors. Two electrodes with similar mass of electrode materials were assembled into a button capacitor with the membrane , electrolyte (6 M KOH) and button cell module (CR 2025).The morphology of NiF/G current collector, raw material powders and AC electrodes was observed using scanning electron microscope . The Raman spectra were carried out by a Raman spectrometer . The X-ray photoelectron spectroscopy (XPS) spectra were measured by an X-ray photoelectron spectroscopy . The transmission electron microscopy  was used to characterize the morphology and layer number of high quality few-layer graphene. The specific surface areas were tested by a specific surface area analyzer (BET)  LTD., Shanghai, China). The surface resistance of electrode materials was measured by a surface resistance meter . The test of resistivity and resistance of current collectors were carried on by a multifunction digital four-probe tester . All the electrochemical measurements of electrodes and supercapacitors were performed by an electrochemical workstation  in 6 M KOH aqueous solution as the electrolyte, using a standard three-electrode method and two-electrode method, respectively.AC@G@NiF/G electrodes with different graphene conductive additive amounts of 3–10 wt % were prepared using NiF/Gs as current collectors and few-layer graphene sheets as conductive additive a. The ACThe AC@G@NiF/G electrodes show the higher specific capacitances, energy densities and rate capabilities, which can hardly occur without the use of NiF/G current collectors. Graphene can be obviously observed on the surface of NiF after CVD growth, which remarkably increases the roughness of the current collector . And eleIn order to illuminate the contribution of the NiF/G current collectors, AC electrodes on common NiF current collectors with graphene conductive additive of 5 wt % (AC@G@NiF-5) were made as comparison to AC@G@NiF/G-5 electrodes. Cyclic voltammetry (CV) curves at scan rates of 10–500 mV/s and galvanostatic charge-discharge (GCD) curves at current densities of 0.1–1 A/g within a voltage range of −1–0 V of the AC@G@NiF-5 electrode are shown in This superior rate capability can be attributed to the significantly lowered ESR, which may be derived from the enhanced electrical contact between active materials and current collectors by CVD growth graphene, as evidenced by the electrochemical impedance spectroscopy (EIS) analysis a. The mu2O3 at 531.93 eV, and Ni(OH)2 at 531.07 eV in the O1s spectrum of NiF .The roles of NiF/G current collectors are considered as three aspects. Firstly, graphene of high specific surface area depositing directly on NiF as a carbon buffer layer between AC material and NiF, strengthens the adhesion of active material on current collector, and then improves the contact at interface. It is consistent with m of NiF a. Peaks from air a–c. Aftex months b,c, denoAll these three points about the graphene buffer layer have a high conductivity 3D network and chemical stability which guarantees the superior electrochemical performance of the AC@G@NiF/G-5 electrode, such as higher specific capacitance, energy density, better rate capability, cycling stability, and lower resistance.The electrochemical properties of AC@G@NiF/G electrodes with graphene conductive additive varying from 3 wt % to 10 wt % are demonstrated in Few-layer graphene nanosheets were used as conductive additive instead of traditional CB to prepare the AC@G@NiF/G composite electrodes, which plays an important role in performance enhancement of electrodes. As a contrast, AC electrodes on NiF/G current collectors with CB as conductive additive (AC@CB@NiF/G electrodes) were made by the same method as AC@G@NiF/G electrodes. The CV curves at the scan rate of 50 mV/s and corresponding specific capacitances as functions on scan rates of AC@CB@NiF/G electrodes with different CB additive amount of 3–10 wt % are demonstrated in Two AC@G@NiF/G-5 electrodes with the same mass of the active material were assembled to a symmetric supercapacitor (SSC) with the electrolyte being a 6 M KOH aqueous solution. The CV curves Raman 10–500 mV/s shown in In summary, we demonstrated a kind of performance-enhanced electrodes of supercapacitors involved in NiF/G current collectors and graphene as the conductive additive. Firstly, the NiF/G current collectors guarantee the conductivity and stability of the current collectors and strengthen the adhesion with active materials, which provide a much more effective electrical contact for fast charge transfer from active materials to current collectors. Secondly, the addition of graphene as the conductive additive directly improves the conductivity of the electrode. Both the NiF/G current collectors and the highly conductive graphene additive make the performances of as-prepared AC@G@NiF/G electrodes superior to those of AC@CB@NiF/G and AC@G@NiF electrodes. Just at low addition of graphene conductive additive of 5 wt %, the AC@G@NiF/G-5 electrodes show best electrochemical properties, specific capacitance 123.6 F/g and energy density 17.2 Wh/kg at the current density of 1 A/g. The SSA assembled by AC@G@NiF/G-5 electrodes also shows excellent cycling stability with almost no decrease of specific capacitance after 10,000 cycles. The results are expected with reference value for researchers for fundamental research and industrial application of graphene-modified supercapacitors or even batteries.


The new three-dimensional structure that the graphene connected with SWCNTs  can solve graphene and CNTs′ problems. A comprehensive study of the mechanical and electrical performance of the junctions was performed by first-principles theory. There were eight types of junctions that were constituted by armchair and zigzag graphene and , , , and  CNTs. First, the junction strength was investigated. Generally, the binding energy of armchair G-CNTs was stronger than that of zigzag G-CNTs, and it was the biggest in the armchair G-CNTs . Likewise, the electrical performance of armchair G-CNTs was better than that of zigzag G-CNTs. Charge density distribution of G-CNTs  was the most homogeneous. Next, the impact factors of the electronic properties of armchair G-CNTs were investigated. We suggest that the band gap is increased with the length of CNTs, and its value should be dependent on the combined effect of both the graphene’s width and the CNTs’ length. Last, the relationship between voltage and current (U/I) were studied. The U/I curve of armchair G-CNTs  possessed a good linearity and symmetry. These discoveries will contribute to the design and production of G-CNT-based devices. The novel three-dimensional structure that graphene connected with carbon CNTs (G-CNTs) is currently receiving much attention. Like graphene and CNTs, the G-CNTs has excellent mechanical and electrical properties. Furthermore, it can solve the problems of the agglomeration of graphene and the intertwining of CNTs. Thus, G-CNTs have been used in many applications such as transparent conductors , superca2/CNTs nanocomposites  in uniform electron gas.The calculations of the junctions of G-CNTs were performed by DFT, a kind of quantum mechanics researching for the electronic structure of the multi-electron system. It has been widely used in the study of physical and chemical properties, including nanomaterials of graphene and carbon nanotubes ,49. DFT (i)Expanding the Kohn-Sham total energy expression of DFT to 2nd order in terms of electron and magnetization density fluctuations;(ii)Representing the Hamiltonian elements in a minimal basis of pseudo-atomic orbitals; (iii)Expressing the charge density in terms of Mulliken charges; (iv)Expand the magnetization density in terms of non-overlapping spherically symmetric functions; (v)Replacing the remaining terms with a short range repulsive energy. The reader interested in it can read Frauenheim’s study .The calculations of the relationship of band gap with the length of CNTs and the side length of graphene and the curve of U/I were performed by DFTB. In DFTB theory, the total energy of it can be described as Equation (5). After five transformations, the expression can be converted to Equation (6):−6 eV, and the MAX force was 0.03 eV/Å.In this calculation, the ultrasoft pseudo potential was used to describe the interaction between electrons and ions. The cutoff energy was 340 eV, and the Brillouin zone was sampled using a 9 × 9 × 1 Monkhorst-Pack  k-point In this paper, different kinds of G-CNTs were investigated to find a stable structure with excellent performance via DFT and DFTB. Generally, the binding energy of A-G-CNTs was stronger than that of Z-G-CNTs. Moreover, arm-60 had the biggest binding energy, while zig-40 had the smallest one. At the same time, the charge density distribution of arm-60 was the most homogeneous. Compared with the band gap between A-G-CNTs and Z-G-CNTs, it was found that the electrical performance of A-G-CNTs was better than that of Z-G-CNTs. Additionally, the band gap was increased with the length of CNTs, and its value should be dependent on the combined effect of both graphene’s width and CNTs’ length. Finally, the U/I curve of arm-60 had a good linearity, and it possessed good symmetry. In addition, arm-60 has the biggest electric current under the same voltage. These discoveries provide a strong support for better application of G-CNTs, such as sensors, transparent conductors, supercapacitors, and batteries.


Participants underwent a minimum of 2 sessions in 1 week or maximum of 10 sessions in 5 weeks’ time. Tinnitus loudness was measured in pre-post design using a 10-point numeric rating scale. There was a significant reduction in tinnitus loudness after tDCS of DLPFC. There was no significant difference between the intensity and duration of stimulation. As the number of sessions increased, there was a higher reduction in the tinnitus loudness; however, this effect plateaued after 6 sessions.Neuromodulation is defined as the process of augmenting neuroplasticity via invasive or non-invasive methods. Tinnitus is the perception of sound in the absence of its external source. The objective of this study was to optimize the parameters of transcranial direct current stimulation (tDCS) of dorsolateral prefrontal cortex (DLPFC) for tinnitus suppression. The following factors were optimized in the dose-response design ( Several non-invasive neuromodulation techniques—such as transcranial magnetic stimulation (TMS), neurofeedback, transcranial direct current stimulation (tDCS), and transcutaneous electrical nerve stimulation (TENS)—have been used as tools for researching various health conditions2. Research on using neuromodulation to treat these conditions is in its infancy, but early studies have shown great promise. The primary goal of neuromodulation is to augment neuroplasticity, so that the brain can be primed to respond better to management. It is hypothesized to work via modulating neuronal excitability and/or synaptic strength, disturbing the neural networks underlying the pathology3. The primary focus of the present study is tDCS. TDCS has been used widely for various neuropsychiatric conditions such as anxiety, depressive disorders, schizophrenia, obsessive-compulsive disorder, chronic pain, and Parkinson’s disease4. However, we still lack a complete understanding of the mechanism underlying tDCS5 and how to optimize it for specific conditions.Neuromodulation is defined as the process of augmenting neuroplasticity by using invasive or non-invasive methods2; and stimulation duration = 20–30 minutes per session9. TDCS is a well-tolerated and comfortable technique. The most common side effects are mild tingling and light itching sensations under the electrodes, during the stimulation11. Depending upon the polarity of the stimulation, tDCS can increase or decrease cortical excitability in the stimulated brain region. Anodal stimulation elicits an excitatory effect due to neuronal depolarization; cathodal stimulation conversely elicits and inhibitory effect due to neuronal hyperpolarization12.TDCS has been applied to more than 3,000 individuals without any significant adverse effects using the following protocol: current intensity = 1–2 mA; electrode size = 25–35 cm13. Nearly linear effects of stimulation intensity (0.2–2.0 mA) and duration (1–13 min) were found14. Since these early studies, a tendency in tDCS research is to increase duration and intensity of stimulation with the anticipation of greater outcome effects15. However, the number of studies looking at the duration and intensity are limited. Furthermore, most studies do not account for the number of sessions needed to induce a therapeutic effect in patients. Each of these parameters is potentially relevant for clinical outcomes.Initial studies have demonstrated the duration and strength of the tDCS after-effects are dependent upon the intensity and duration of stimulation16, and is commonly described as ringing, buzzing, cricket-like, hissing, whistling, and/or humming17. Tinnitus is a highly prevalent condition18 and adversely affects the overall quality of life of sufferers19. Tinnitus perception is the result of change in neuronal activity21. The first published evidence of tinnitus suppression by tDCS came in 200622. Since then, there have been several studies confirming the transient suppressive effect of tDCS on tinnitus23. TDCS has been used as a research tool for transient tinnitus suppression for at least a decade23. However, to convert tDCS from a research tool to a clinical tool, more research is needed in the direction of converting the transient impact into a lasting one23. Garin et al.24 were the first to document lasting after-effects of tDCS, but these long-term effects could not be replicated. Garin suggested a need for optimization of tDCS parameters for long-term tinnitus relief.Take, for instance, the application of tDCS to tinnitus. Tinnitus is an auditory phantom sensation experienced when no external sound is present27. Shekhawat et al.26, for example, conducted a dose-response study and found that tDCS of left temporoparietal area (LTA) with a 2-mA current intensity and a 20-minute duration is the most effective setting for transient tinnitus suppression. In another study, Shekhawat et al.25 found both LTA and dorsolateral prefrontal cortex (DLPFC) to be effective stimulation sites for transient tinnitus suppression. This study also conducted a human head modeling experiment demonstrating the distribution of electric field during non-invasive brain stimulation as shown in Fig. 23 supporting the stimulation of LTA for tinnitus loudness suppression and DLPFC stimulation for tinnitus annoyance suppression. DLPFC not only contains auditory memory cells but has also been associated with auditory attention, early inhibitory modulation of input to primary auditory cortex, and a facilitatory effect on auditory memory storage32. DLPFC is actively involved in modulating tinnitus loudness and annoyance33. The optimization trial by Shekhawat et al.26 looked specifically at LTA as the site of stimulation; there is no evidence about DLPFC optimization as the site of stimulation. We therefore decided to stimulate DLPFC for the present study.Optimizing the settings of tDCS is necessary to maximize the impact of tDCS on tinnitus suppression. There has been some early research in the area of optimizing tDCS stimulation parameters  for tinnitus suppressionThere is no literature addressing the frequency of tDCS sessions needed for optimal tinnitus suppression. Thus, there are several open questions: how many sessions of tDCS are needed for optimal results? What should the washout period be between the tDCS sessions? What would be the outcome of head-to-head comparisons of multiple sessions of tDCS? The current trial was therefore designed with the aim to optimize tDCS of DLPFC by investigating the impact of current intensity (1.5 mA or 2 mA), duration (20 minutes or 30 minutes), and number of sessions  on tinnitus suppression.Participants were recruited through the Tinnitus Research Initiative (TRI), Antwerp, Belgium. Data were collected in the context of a clinical treatment and are retrospectively analyzed here. Participants provided written informed consent in accordance with Declaration of Helsinki that their data could be used for research purposes. The study was approved by the ethical committee of University of Antwerp, Belgium and was carried out in accordance with the approved guidelines. Participants were eligible for inclusion if they were 18 years or older with chronic tinnitus for a minimum of 6 months. Participants were excluded if they had any contraindications to undergo tDCS such as: metal implants in the head or body, epilepsy, heart condition, pregnancy, psychotropic medications as screened by a neurologist.One hundred eleven participants  with average tinnitus duration of 5.9 years completed this trial. Demographic details of participants included in this study are documented in Table et al.26. There were five variables in the ‘sessions’ used . These variables were selected based on the scoping review conducted by Shekhawat et al.23. Participants underwent a minimum of 2 sessions over the course of a week and maximum of 10 sessions over 5 weeks’ time. The participants were randomly assigned. Based on the registration of participants for this trial, they were randomly allocated to undergo one of the five stimulation session options .This was a dose-response study aiming to optimize the number of tDCS sessions needed to suppress tinnitus perception. Participants underwent tDCS of DLPFC with two current intensities (1.5 mA or 2 mA) and two durations (20 minutes or 30 minutes) based on the trial conducted by Shekhawat et al.23. Tinnitus loudness was assessed before and after the end tDCS sessions.Tinnitus loudness was evaluated using a 10-point numeric rating scale, where 1 to 10 represented a spectrum of tinnitus from ‘very quiet’ (1) to ‘as loud as imaginable’ (10) based on the scoping review conducted by Shekhawat http://www.eldith.de). Rubber electrodes with a surface area of 35 cm2 were encased in electrode sponges soaked in NaCl solution (0.85%) based on Dundas et al.34. The cathode was placed over the left DLPFC (F3) and the anode over the right DLPFC (F4) as determined by the international 10/20 Electroencephalogram System. Sham stimulation was not used in this study as the focus was to optimize the number of sessions required to suppress tinnitus perception in a dose-response manner.TDCS was performed using a specially developed, battery-driven, constant current stimulator with a maximum output of 10 mA  and between-subjects sessions , current intensity (1.5 or 2 mA), and stimulation duration (20 or 30 minutes). We additionally conducted a univariate ANOVA with the percentage of change on the tinnitus loudness rating scale as the dependent variable and sessions, intensity, and duration as independent variables. Furthermore, an independent t-test was used to compare the effect of the number of sessions on the percentage of change on the tinnitus loudness rating scale. We conducted another independent t-test to compare the effect of stimulation intensity and stimulation duration for the 6 sessions only. At the request of one reviewer, we also added a generalized linear model including sessions, current intensity, and stimulation duration as independent variables and percent change on the tinnitus loudness rating scale as dependent variable.We applied a one-way ANOVA with sessions, current intensity, and stimulation duration as independent variables and responder rate  as the dependent variable. We further ran an independent t-test to compare the effect of stimulation duration for responder rate for each number of sessions separately. We also added a generalized linear model with sessions, current intensity, and stimulation duration as independent variables and responder rate  as the dependent variable.F = 95.29, p < 0.001) showing a significant reduction in tinnitus loudness after tDCS treatment  in comparison to before treatment . This effect was moderated by the number of sessions  = 8.36, p < 0.005). However, no interaction effect was obtained for either the intensity of stimulation  = 0.14, p = 0.71) or the duration  = 0.19, p < 0.66). Figure F = 5.59, p = 0.02) but not for either the intensity  = 0.62, p = 0.43) or the duration  = 1.81, p = 0.18). Table t = 3.69, p = 0.001) and between 4 vs. 8 sessions . No significant effect was obtained between 6 vs. 8  or 8 vs. 10 sessions . A comparison between 2 vs. 4 sessions  revealed no significant effects. However, comparisons between 2 vs. 6  and between 2 vs. 10  sessions each revealed significant effects. In addition, comparisons between 4 vs. 6 sessions  and between 4 vs. 10 sessions  yielded significant differences. However, these two effects do not survive Bonferroni correction for multiple comparisons. No significant difference was obtained between 6 vs. 10 sessions .A repeated-measures ANOVA yielded a significant effect for pre- vs. post-stimulation tinnitus loudness numeric rating scale  or duration   and stimulation duration 20 or 30 min.) for 6 sessions; however, our analysis revealed no significant effects for intensity (0 min. fo2(6) = 16.63, p = 0.011) showing that the number of sessions has an effect  = 11.91, p = 0.018) on the percent change on the tinnitus loudness rating scale. However, intensity  = 0.014, p = 0.91) and duration  = 0.08, p = 0.77) do not generate an effect. A closer look at the parameter estimates shows that both 2  = 6.06, p = 0.014) and 4  = 4.96, p = 0.026) sessions significantly differ from the other sessions. 6  = 0.31, p = 0.86) and 8  = 0.24, p = 0.63) sessions also differ from 10 sessions.To verify the effect of the number of sessions on tinnitus suppression, we also applied a generalized linear model including sessions, current intensity, and stimulation duration as independent variables and percent change on the tinnitus loudness rating scale as the dependent variable. This analysis revealed an overall effect  = 2.66, p = 0.038). Specifically, our results demonstrate that more people respond to 6 sessions of 20 minutes than to 6 sessions of 30 minutes   and 10  sessions, but these do not survive correction for multiple corrections. No interaction was obtained for 4 and 8 sessions. No significant effects were obtained for the main effect of sessions, intensity, and duration or for the interaction effects of session × intensity, intensity × duration, and sessions × intensity × duration.A one-way ANOVA with session, duration, and intensity as independent variables and responder rate  as the dependent variable revealed an effect for interaction between sessions x duration  = 41.12, p < 0.001) of omnibus test. We also found an interaction between sessions × duration  = 24.61, p = 0.003). A pairwise comparison shows a significant difference between 6 sessions of 20 minutes and 6 sessions of 30 minutes (p = 0.036).To verify the effect of sessions on tinnitus suppression we also applied a generalized linear model including sessions, current intensity, and stimulation duration as independent variables and responder rate  as the dependent variable. This revealed a significant effect  = 2.08, p = 0.089), indicating a trend that more people respond to 6 sessions of 20 minutes than to 6 sessions of 30 minutes   and 10  sessions, while no duration-related differences were obtained for 4 or for 8 sessions. The effect for 2 and 8 sessions do not remain after correction of multiple corrections. No effect was obtained for the main effect of sessions, intensity, and duration or for the interaction effects of session × intensity, intensity × duration, and sessions × intensity × duration.A similar analysis was conducted for responder rate (one-point drop) on the numeric rating scale demonstrating a marginally significant effect for sessions x duration  = 49.45, p < 0.001) of omnibus test. We find an interaction between sessions x duration  = 28.17, p = 0.001) A pairwise comparison shows a significant differences between 6 sessions of 20 minutes and to 6 sessions of 30 minutes (p = 0.036).To verify the effect of sessions on we also apply a generalized linear model including sessions, current intensity, and stimulation duration as independent variables and responder rate (one-point drop) as the dependent variable. This revealed a significant effect likelihood ratio  and durations (20 min and 30 min) of stimulation that we tested. Based on this study, the optimized setting for repeated tDCS of DLPFC to reduce tinnitus loudness would be: intensity = 1.5 mA; duration = 20 minutes; sessions = 6 sessions over 3 weeks’ time, with a washout period of 3–4 days between each session.39. Most of these studies did not report any positive impact. Note, however, that these studies all used a similar protocol of five tDCS sessions on five consecutive days. It is possible that using five sessions on five consecutive days without longer intermittent periods cancels out the tinnitus suppressive effect observed after a single session of tDCS. Other studies suggest that applying repeated sessions produces cumulative changes in therapeutic applications40. Our data are consistent with this latter idea, showing that repeated stimulation results in cumulative changes in cerebral function, but that this effect was not linear. Six sessions clearly achieved a greater effect than 2 or 4 sessions but results did not improve with additional sessions. These findings will inform future clinical trials especially for tinnitus management where multiple stimulation sessions will be used.Few attempts have been made to study the impact of multiple sessions of tDCS on tinnitus suppression26. However, that study only focused on LTA as the site of stimulation and did not attempt to optimize the number of sessions. TDCS of LTA with a current intensity of 2 mA and 20 minutes duration was the most effective setting in that study for transient tinnitus suppression. However, in the present study we explored DLPFC as the site of stimulation and specifically the optimum number of sessions for tinnitus suppression. The results of the present study recommend 20 minutes duration as optimum for DLPFC stimulation, with an intensity of 1.5 mA. This fits with previous research that did not show significant changes in higher vs. lower intensities resulting in identical excitability after-effects and short-latency intracortical inhibition41. This is also supported Bastani and Jaberzadeh, who reported a uniform effect of 0.3 and 2.0 mA on cortical excitability42. Initial studies showed an effect of tDCS dependent upon duration (from 1 to 13 min)14. Our study shows no difference in the amount of reduction for 20 vs. 30 minutes of stimulation, suggesting a non-linear saturation point where 30 minutes does not generate a greater effect than 20 minutes. Looking at the responder rate, 30 minutes of stimulation actually seems to induce a lower responding rate than 20 minutes. This fits with previous findings that suggest that stimulation duration of anodal tDCS increased the percentage of responders13. It is however not clear why 20 minutes works better than 30 minutes. However, previous trials looking at the optimization of neuromodulation were focused on HD-tDCS and compared both LTA and DLPFC as the site of stimulation25. The winning setting for tinnitus suppression in that trial was: 2 mA current intensity, 20 min duration, and both locations were effective in modulating tinnitus loudness and annoyance. A possible reason for this could be explained by the difference in research design and number of extra sessions participants underwent in the present trial (2–10 sessions), which was limited to only 2 sessions in the HD-tDCS trial.Previous research already conducted a dose-response study to optimize the current intensity  and duration (10 and 20 min.) for tinnitus suppressionet al.43 conducted a double blind, sham controlled trial investigating the self-administered domiciliary tDCS treatment for tinnitus. Forty three participants with chronic tinnitus underwent tDCS of LTA and DLPFC for 10 sessions on 10 consecutive days. TDCS was not shown to be effective in tinnitus suppression, however. The washout period in this trial was <1 day, similar to other trials39 which did not find a positive impact of tDCS on tinnitus. This is further evidence that back-to-back sessions on consecutive days is not effective for tinnitus suppression and masks the impact of individual sessions. Contrary to the above studies, there were three trials that resulted in significant transient reduction in tinnitus44 and long term suppression of tinnitus24 using different washout periods. Faber et al.9 and Frank et al.44 conducted tDCS on alternative days (6 sessions in 2 weeks) after each session of anodal, cathodal and sham tDCS; Garin et al.24 used a two-week washout period. In the present study, we used a washout period of 3–4 days between each session of tDCS. We recommend >1 day washout period between tDCS sessions to sustain the impact on tinnitus suppression. Conducting the sessions on consecutive days does not facilitate the plastic changes that lead to tinnitus suppression.Hyvärinen 45 with the winning settings of the present study. It would also be interesting to incorporate a positive control such as a DLPFC-related task as a confirmation of target engagement. Multi-session tDCS (6 sessions) with a 3–4 day washout period exploring different sites of stimulation would also be valuable.The design of this trial was a dose-response paradigm, aiming to optimize multiple sessions of tDCS. We therefore did not use sham controlled sessions. For future research, we recommend double blind, sham controlled trialsFinally, we recommend investigating the long-term impact of multiple session tDCS on tinnitus loudness and annoyance. It would be valuable to explore multi-session tDCS (6 sessions) by alternating the stimulation between LTA and DLPFC . This could facilitate the stimulation of neuroanatomical structures between the LTA and DLPFC, resulting in stronger priming of the brain for tinnitus modulation. This could also be an effective method to overcome the technical limitations of simultaneously stimulating LTA and DLPFC.This study was the first attempt to optimize the settings of tDCS for DLPFC stimulation to modulate tinnitus, especially to optimize the number of sessions needed for tinnitus suppression. TDCS of DLPFC resulted in a significant reduction of tinnitus loudness. The optimal setting for repeated tDCS stimulation of DLPFC to reduce tinnitus loudness, as reported by our study, would be: intensity = 1.5 mA; duration = 20 minutes; sessions = 6 sessions over 3 weeks’ time with a washout period of 3–4 days. The present study revealed a non-linear cumulative change in cerebral function as a result of multisession tDCS. We recommend further research using randomized control design, investigating multiple stimulation of two different sites (LTA and DLPFC), and exploring the long term impact of tDCS on tinnitus loudness and annoyance. Furthermore, more biochemical, molecular, and behavioral evidence is needed to support our study’s conclusions.