Sucha controlled hydrogenation of high-quality and high-specific-areasamples converts the original conductive graphene into a wide gapsemiconductor, with the valence band maximum (VBM) ∼ 3.5 eVbelow the Fermi level, as monitored by photoemission spectromicroscopyand confirmed by theoretical predictions. In fact, the calculatedband structure unequivocally identifies the achievement of a stable,double-sided fully hydrogenated configuration, with gap opening andno trace of π states, in excellent agreement with the experimentalresults.Conversion of free-standinggraphene into pure graphane—whereeach C atom is sp In graphane, the conjugationof graphene π electrons is thus disrupted, leading to an insulatingbehavior with band gap predicted to depend on the H chemisorptionconfiguration.2Maximum storage ofhydrogen in carbon-based materials is ideallyachieved in graphene by forming the so-called graphane, where eachcarbon atom in the honeycomb lattice is bound to hydrogen with alternatelyup and down sp14 with non-negligible contamination and defects. The maximum H uptakedepends on both the morphology of graphene specimens  and the hydrogenation methods. Several attemptsto incorporate a high percentage of hydrogen have been carried outin the last decades, exploiting a variety of strategies on differentsamples. Hot10 andcold14 plasma deposition and molecular H2 high-temperature cracking9 were applied to exfoliatedgraphene layers,10 to chemical-vapor-deposition(CVD) grown flakes,16 or even to metal–supported samples,17 reaching at most a partial hydrogenation of monolayergraphene, with an upper limit of H uptake Θ ∼ 36 at.%,14 while an almost stoichiometric bulkgraphane has been obtained from halogenated reduced wrinkled and layeredgraphenes.18 The limit of hydrogenationin single-layer graphene can be due to several concurrent drawbacks,such as oxygen contamination, the influence of the substrate, andthe presence of defects/edges in graphene flakes (either pre-existingor induced by the hydrogenation itself).Experimentally, however,only a low H storage capacity has beenreached so far (∼36 at. %) on single-layer graphene20—can present great advantages to achieve a high uptake ofhydrogen in graphene. The free-standing, curved structure at the submicrometerscale, with intrinsically smooth rippling, can foster hydrogen chemisorption,favored by the increased electron affinity of hydrogen and the energybarrier decrease in the convex regions21 induced by the pull out of the C atom toward the H proton.23A crucial challengeto fully exploit graphene for hydrogen storageis to employ defect-free graphene specimens with very high specificsurface area, where hydrogen can adsorb strongly enough on the surfaceas to form a thermodynamically stable arrangement, achieving an idealgraphane pattern. Nanoporous graphene (NPG)—constituted bya compact, bicontinuous interconnected 3D arrangement of high-qualitygraphene veils, composed of one to a few weakly interacting layers2/g)26 and very low density of defects, together with insitu, highly controlled hydrogenation by H2 cracking inthe ultrahigh vacuum (UHV) condition. In this way, we can controlthe absence of contamination of the sample during the H exposure andrealize a thermodynamically stable prototype of semiconducting graphane.A spectromicroscopy photoemission study, combined with state-of-the-arttheoretical predictions, demonstrates an unprecedentedly high H uptakein NPG, accompanied by a spectral electronic density of states aspredicted for ideal graphane, achieving for the first time an almostcomplete saturation in fully free-standing graphene of the availableC sites with hydrogen.We here exploit high-quality NPG samples, with high specificarea(1000 m2/g)26 arranged in a compact 3D structure; see 2) unveils the porous structure (pore size inthe submicrometer to few micrometer range) constituted by a foldedtubular graphene sheet with continuous almost flat areas and interconnectedchannels, with some wrinkles and without frayed edges.26 A detailed analysis of the NPG microscopic structure at the atomicscale, reported elsewhere,19 revealed moirésuperstructures due to suspended graphene layers with misoriented(turbostratic) stacking in some regions. Within this macroscopic 3Dgraphene architecture, the microscopic structure preserves all the2D graphene hallmarks.192), analogous to those employed for other suspended 2D systemssuch as hexagonal boron nitride bubbles,27 and after verifying that no detrimental effects were induced bythe laser beam on the NPG sample. The Raman spectrum presents a lowintensity of the defect-activated “D” Raman peak ifcompared to the “G” peak, associatedwith the doubly degenerate (iTO and LO) phonon modes at the Brillouinzone center. More importantly, the Raman spectrum shows a high intensityof the “2D” peak, a double-resonant second order modeactivated by in plane breathing of the hexagonal rings.28 The 2D/G Raman band intensity ratio was mappedover a mesoscopic area /[I(sp2) + I(sp3)].Hydrogen uptake can beidentified by the distortion of the pristineC–C sp3 being bound, has never been achieved experimentallybefore in fully free-standing low-defect graphene. In fact, only partiallyhydrogenated graphene was observed until now—either on transferredmonolayer flakes37 or on substrate-supported graphene8—with maximum uptake Θ ∼ 36%14 and with a high level of contamination and defects. Thepresent successful procedure can be ascribed both to the morphologyof the self-suspended, free-standing and bicontinuous NPG host andto the ultraclean and highly controlled, fully-UHV hydrogenation procedure.This extraordinary and unprecedented hydrogen uptake,which isin line with a chemisorption model for graphane with almost each Csp3 hybridization, due to the C–H bonding, to theopening of a semiconducting gap in graphane. Photoemission spectromicroscopyof both core levels and the valence band can combine local informationon the hybridization state (core levels), with the evolution of thespectral density close to the Fermi level  at the samespatial scale. We measured a spatially resolved photoemission mappingof a partially hydrogenated NPG sample (Θ ≈ 50%), asto be able to identify regions with different degrees of hydrogenation,correlating valence band with core level spectral shapes. 2 core-level component normalizedto the whole sp2 + sp3 signal, as deduced bythe fitting analysis (see Supporting Information) over the whole hydrogenated NPG specimen. This intensity variesin the map depending on the local hydrogenation state, as shown inthe exemplifying spectra of 2 hybridization isstill dominant [cross in panel (a)] correspond to the C 1s spectrumdisplayed in panel (b), while zones with higher values of sp3 component [star in panel (a)] correspond to the C 1s spectrum inpanel (c). The 10 × 10 μm2 blow up in 2 bond dominates, the spectraldensity of states presents a definite 2p-π peak at a bindingenergy of about 3 eV [see shaded area in panel (e)], which is thesignature of the graphene band structure, while in the regions wherethe sp3 component emerges, the spectral density drasticallychanges and the 2p-π peak is almost quenched. It is worth notingthat the density of states close to the Fermi level EF is strongly reduced for all the pixels where the sp3 component dominates.A crucial point is to correlate the appearance of the distortedsp%) the quenching of the density of states below EF suggests a definite transition to a semiconductingstate,as clearly observed in EF. Theascertainment of a definite correlation between the emergence of C–Hsp3 bonding and the position of the VBM unambiguously ascribesthe gap opening to the distortion of the bond to sp3, althoughthe assignment of the hydrogen adsorption sites cannot be unambiguouslyidentified from the photoemission experiment.At H saturation coverage (Θ ∼ 90Supporting Information). We hereafter report the results for three representative(the most stable ones) structures, that is (38); 2-side H-Gr, i.e.,graphane;2 and 2-side hydrogenated bilayer graphene(H-bGr). Quasi-particle corrections within the G0W0 approximation39 are included to overcome the DFT limitation in the descriptionof the electronic properties and ease the comparison with experiments(see Table S1 in Supporting Information). The single-sided hydrogenationleads to the appearance of an indirect gap of 5.6 eV. For the double-sidedhydrogenation, we predict a direct gap of 4.7 eV for the H-bGr and6.1 eV for H-Gr, the largest of the series, in line with previouscalculations.2 For a more direct comparisonwith experiments, in 40 Irrespective of the exact position of the VBMonset, the single-sided H-Gr system noticeably presents a structuredDoS at the VBM, originating from the 2p-π orbitals of the unsaturatedside, that is totally absent in the experimentally achieved saturatedphase of 41 without any 2p-π contribution, in excellent agreement withthe experimental data. Most of the spectral weight is indeed arisingfrom the sp3 hybrid orbitals, lying in the energy regionbelow −6 eV. This compares well in terms of energies and overallshape with the experimental spectrum . The experimental curve is, however, mostly featureless, probablydue to the specific spectral amplitudes in this energy range,42 not accounted for in our calculations. Overall,we can conclude that the calculated band structure and quasi-particleDoS unequivocally allow us to establish the achievement of double-sidedhydrogenated single- and bilayer graphene configurations.To corroborate and better understand the correlation between degreeof H chemisorption and emergence of a wide-gap semiconducting phase,we simulated by means of density functional theory (DFT) calculationsthe spectral density for different hydrogenated graphene phases, includingsingle-sided and double-sided hydrogenated single- and bilayer graphene,with different registry and hydrogenation configurations .Ni–10 mbar), and prior to the acquisitionthe NPG samples were degassed at 600°C for several hours to removecontaminants from air exposure. The sample was kept cooled at theliquid nitrogen temperature to avoid radiation damage.19 Valence band data with 21.22 eV photon energyon the saturated H-NPG sample was taken at the Lotus laboratory, Rome,by using an analogous UHV setup.The spectromicroscopyphotoemission experiments were performed at the ANTARES beamline ofthe SOLEIL synchrotron radiation facility. The nano-X-ray photoelectronspectroscopy (XPS) microscope is equipped with two Fresnel zone platesfor beam focusing, whereas higher diffraction orders were eliminated,thanks to an order selection aperture. The sample was placed on aprecision positioning stage located at the common focus point of thehemispherical analyzer and the Fresnel zone plates. This setup wasused for the collection of both point-mode spectra and imaging-modespectra. In the imaging mode, the photoemitted electron intensityfrom the desired energy range is collected over the sample to forma 2D image resolved at the submicrometer range. Core-level and valenceband spectra were taken with 350 and 100 eV photon energy, respectively.The spatial resolution was in the submicrometer range (near 600–700nm). The analyzer pass energy was set to 100 eV (200 eV) for the spatiallyunresolved (resolved) mode. All measurements were made under ultrahighvacuum (104 lasers (DPSSseries by Lasos) emitting at 532 nm. The Raman signal was spectrallydispersed by a 750 mm focal length ACTON SP750 monochromator equippedwith a 300 groove/mm grating and detected by a back-illuminated N2-cooled Si CCD camera (model 100BRX by Princeton Instruments).The laser light was filtered out by a very sharp long-pass Razor edgefilter (Semrock). The micro-Raman (μ-Raman) spectral resolutionwas 2.4 cm–1. A long working distance 100×objective with NA = 0.75 was employed to excite and collect the light,in a backscattering configuration. The laser spot size determinedexperimentally is characterized by a Gaussian shape with σ =0.28 μm. Moderate laser powers  were employed, afterchecking that the spectrum was analogous to that acquired with muchlower power (a factor of ∼70).For Raman measurements, the excitationlaser was provided by single frequency Nd:YVO48 The Perdew–Burke–Ernzerhof (PBE) generalized gradientapproximation for the exchange-correlation functional was used,49 together with Optimized Norm-Conserving Vanderbilt(ONCV) pseudopotentials.50 The quasiparticleband structure for the DFT optimized geometries was computed withinthe GW approximation to the electron self-energy,as implemented in the yambo code.54 Calculations were performed by employing an automated yambo-AiiDAbased workflow.57The ground-state properties ofH-passivate graphene were investigated from first-principles by usinga plane-wave pseudopotential implementation of the density functionaltheory (DFT), as available in the Quantum ESPRESSO package.


The photoelectrons were extracted through the graphene protection layer in a reflection mode, and we achieved QE of ~ 0.17% at ~ 3.4 eV, 1/e lifetime of 188 h with average current of 8.6 nA under continuous illumination, and no decrease of QE at the pressure of as high as ~ 1 × 10–3 Pa. In comparison, the QE decreased drastically at 10–6 Pa for bare, non-protected CsK2Sb photocathodes and their 1/e lifetime under continuous illumination was ~ 48 h. We attributed the improvements to the gas impermeability and photoelectron transparency of graphene.Protection of free-electron sources has been technically challenging due to lack of materials that transmit electrons while preventing corrosive gas molecules. Two-dimensional materials uniquely possess both of required properties. Here, we report three orders of magnitude increase in active pressure and factor of two enhancement in the lifetime of high quantum efficiency (QE) bialkali photocathodes (cesium potassium antimonide (CsK In recent years, however, there has been growing interest in their use as high-brightness photocathodes for advanced accelerators and electron microscopes. The next-generation accelerators require high-brightness electron bunches in short pulses that cannot be achieved with thermionic or field emission electron sources. Cesium potassium antimonide (CsK2Sb) is one of the best performing photocathodes available with a good balance between QE and the operation pressure15.The QE can exceed 10% at 532 nm and operation pressure is at 10–8 pascals (Pa). Metal photocathodes are the most robust type known, but the QE is generally in 10–3–10–4% with an exception of cleaned magnesium (Mg) that can reach as high as 0.3% at ~ 250 nm16 and cannot be driven by a high-power green laser. Cesiation of surfaces such as gallium arsenide (GaAs) and metals is an alternative, however, extreme ultrahigh vacuum of ~ 10–9 Pa is necessary to maintain the QE17. The promise of CsK2Sb as an electron source for accelerators is supported by the demonstration of record-high beam currents of 60 mA in a DC injector with 30 h 1/e lifetime5.Bialkali antimonides have been established as high quantum efficiency (QE) semiconductor photocathodes since their discovery in the 1950s. Historically, they have been widely utilized as photosensitive materials in radiation detectors and camera tube technologies–8 Pa and short operation lifetime. Increasing the operation pressure and extending the lifetime of bialkali antimonide photocathodes will reduce the number of replacements needed and the time lost for tedious photocathode replacement procedures (including a weeks-long baking of the system). Furthermore, the increased operation pressure will broaden the types of accelerators that bialkali antimonide photocathodes can operate in. There had been previous attempts to protect free-electron sources. Around year 2000, there were a collection of studies to coat bialkali photocathodes with 10–20 nm of more robust materials such as sodium iodide (NaI), cesium iodide (CsI) and cesium bromide (CsBr)21. While they succeeded in increasing the operation pressure, the thickness of the coating was similar to the thin photocathode thickness itself thus the concept was rather hetero-structuring than coating. With an advancement of two-dimensional (2D) material research over the past decade or so23, it is timely to apply the coating concept again with 2D materials. The 2D materials uniquely possess critical material properties for the purpose; namely, electron/photon transmissivity and gas impermeability. Graphene for example, transmits electrons due to its atomic thinness while being impermeable to gases due to its packed hexagonal atomic structure. Its optical transparency for monolayer is as high as 97.5% in a visible range24. The geometric pore size of graphene is 0.64 Å, which make it impermeable to even helium (He) atoms29. In addition, graphene is chemically inert and electrically/mechanically stable, which are all advantageous as a protection coating layer.The remaining technical challenges for implementing these photocathodes in accelerators are their low operation pressure of 102Sb photocathodes between graphene and a thin metal film to evaluate the feasibility of using graphene as a protective layer for bialkali antimonides. Specifically, we deposited photocathodes on a free-standing bilayer of graphene and sealed them with a 15–35 nm thick Ni films. Photoelectrons were then extracted through the graphene protection layer in a reflection mode, and the photocathode lifetime under continuous light irradiation was investigated at 10–8 Pa. Lifetime of photocathodes without protection was also measured to provide a comparison. We followed the lifetime measurements with active pressure measurements, which measured the QE as a function of pressure to gain insight into whether the graphene protection can increase the operation pressure of CsK2Sb photocathodes or not.In this study, we sandwiched CsK2Sb photocathodes to evaluate the feasibility of graphene protection layer in improving their active pressure and the lifetime. Our strategy to achieve this was to deposit thin metal films onto CsK2Sb photocathodes via thermal deposition from the opposite side of graphene protection layer. We had already established a protocol to fabricate CsK2Sb photocathodes on graphene protection layer34 thus the remaining task was to select an appropriate sealing metal for our purpose. It is well known that substrate material has severe effects on the QE of deposited ~ 20 nm think CsK2Sb photocathodes8, therefore it was crucial for us to identify a metal with minimal degradation. We tested copper (Cu), gold (Au) and Ni as metal substrates. Our QE testing method was to deposit CsK2Sb photocathodes onto commercially available metal foils rather than depositing thin metal films onto CsK2Sb photocathodes. We assumed that this testing method will provide us with necessary information regarding material compatibility between the metals of interest and CsK2Sb. The same CsK2Sb deposition conditions as that for graphene protection layer was used for consistency (see Method section for details). Cu was chosen for its high thermal conductivity, which could meet the needs to operate photocathodes in cryogenic temperatures such as that for cavity structures. Au was chosen for its chemical inertness, which could prevent photocathodes from interacting with corrosive gases such as oxygen and moisture. Ni was chosen for its potential material compatibility with CsK2Sb based on our prior studies34. We did not test molybdenum (Mo) despite its known material compatibility with CsK2Sb because of a concern on its high evaporation temperature. There is a report that the QE of CsK2Sb photocathodes start to degrade at temperatures higher than 60 oC11 thus we only tested metals with lower evaporation temperatures this time.Overall concept of this study was to create sealed CsK2Sb photocathode deposited on Cu, Au, Ni, and stainless steel (SUS) foil substrates at 10–8 Pa, where SUS was a reference. It was evident that QE was lower for every metal that we tested in comparison with SUS (12.8% at ~ 3 eV), however, Ni showed a minimal decrease compared to Cu and Au. Specifically, Ni showed the QE of ~ 12.5%  whereas the QE for Cu and Au substrates were as low as 6.5%  and 6.4% , respectively. Prior study of alkali photocathode deposition on Cu substrate reports alloying between Sb and Cu as a possible cause of the QE decrease. They performed in-situ synchrotron X-ray diffraction (XRD) and identified peaks associated with Sb-Cu alloy35. It is possible this is the cause of our observation on the QE decrease for Cu and Au substrates. The least decrease of QE observed for Ni substrate might indicate that the alloying between CsK2Sb is minimal among Cu, Au and Ni. This can be explained by electron affinity of Cu, Au and Ni, which Au has almost twice the value of Cu and the value for Ni is lowest among the three metals. Most direct technique to investigate the alloying between CsK2Sb and metal substrates of our interest is to perform XRD. However, this is not trivial as CsK2Sb quickly oxidizes upon its exposure to pressure above 10–6 Pa during the sample transfers. As an alternative, we coated monolayer graphene on Cu and Au substrates and deposited CsK2Sb on top of them to see if there is any improvement in the QE. We hypothesized that if we can reduce the QE decrease via graphene coating, then alloying is playing a role in the QE decrease as graphene is reported to perform well as a diffusion barrier for metals37. Figure –8 Pa. We observed a clear increase in the QE for CsK2Sb photocathodes deposited on graphene-coated Cu and Au substrates in contrast to non-coated counterparts in the dark environment . Moreover, graphene-coating prevented a QE decrease of CsK2Sb photocathodes even when the substrates were used multiple times. The QE decreased drastically when bare, non-coated Cu and Au substrates were used as substrates for multiple times after thermally cleaning off the photocathode films at 500–600 °C in vacuum for 1 h  and molybdenum (Mo) substrates31. In our previous study, synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) revealed that there was residual photocathode material on Si and Mo substrates even after the thermal cleaning, indicating that there was strong bonding/alloying between the photocathode and the substrates. In sharp contrast, we observed no residue after the cleaning for the graphene-coated substrates, which suggested that the strong bonding/alloying was no longer there. Therefore, the graphene-coating on Cu and Au is most likely acting as a diffusion barrier as expected. Our cross-section scanning electron microscopy (SEM) images on cesium antimonide (Cs3Sb) photocathodes deposited on graphene-coated and bare, non-coated Au substrates support the argument (taken after exposure to air). The Cs3Sb-Au boundary was sharp for a graphene-coated case  calculations also supported our hypothesis that graphene coating can prevent alloying between the photocathode elements and metal substrates. We calculated the binding energies between Cs, K and Sb atoms on Cu, graphene-coated Cu and graphene substrates as summarized in Table 2Sb photocathodes deposited on transmission electron microscopy (TEM)-grid-supported graphene. The QE was measured in a reflection mode from the CsK2Sb side, as illustrated by the inset, and measured at the pressure of 10–8 Pa. Successful CsK2Sb deposition on graphene is evident from a typical QE response that quickly increases around 2 eV and signature hump around ~ 2.5 eV. Moreover, the peak QE of ~ 13.6% at ~ 3.4 eV is consistent with our previous studies34.Figure 2Sb photocathodes through bilayer graphene protection layer prior to Ni seal was ~ 0.92% at ~ 3.4 eV, which is consistent with our recent study30. Our QE of CsK2Sb photocathodes through bilayer graphene protection layer takes TEM-grid transparency into account (see Method section for details). The QE dropped to ~ 0.17% at ~ 3.4 eV after Ni seal, most likely due to the chemisorption and the temperature increase during the Ni deposition . 15 nm thickness was selected based on the knowledge that metals need ~ 15 nm thickness to form uniform and continuous films, which is required for this study to exhibit sufficient seal. Metal films below 15 nm are reported to form islands unless unique treatments are performed on substrate surfaces to control the wettability of metals.The QE of CsK2Sb photocathodes. The first test was a lifetime under continuous illumination. The sealed photocathodes were irradiated continuously with a green laser (532 nm) and the QE was measured in a reflection mode through bilayer graphene protection layer under a pressure of 10–8 Pa. 1/e lifetime  of 188 h with average current of 8.6 nA was extracted from an exponential curve fitting  as the origin of degradation. Another known source of QE degradation is ion back bombardments40 although the effect may be much smaller compared to more susceptible surfaces such as that of cesiated GaAs. The collection voltage of 300 V can ionize H2 and H2 is known to permeate through graphene slightly more than other gases such as oxygen and moisture. Thus, it is possible that H2+ ion back bombardments are the source of QE decrease in our case. We plan to check this in a separate study by inducing controlled gases, including hydrogen, into the deposition chamber and monitoring the QE degradation.The origin of QE decay for bare, non-protected CsK30 and there is room for improvement toward the theoretical value of ~50% for monolayer. There are reports that have achieved up to ~ 60% electron transmission through monolayer graphene42, thus we plan to work on optimizing our material synthesis and device fabrication procedures to ensure the highest possible graphene quality in our next set of study. Ensuring the highest QE from CsK2Sb photocathodes is another factor that can be improved upon. The highest reported peak QE of CsK2Sb photocathodes can reach > 25% in contrast to the ~ 14% we observed in this study. Protected photocathodes with QE in the ~ 1% range and lifetime in the ~ 2-week range are expected after the above-mentioned issues of leakage, ion back bombardments, graphene material quality, and the QE of CsK2Sb photocathodes are solved.The challenge—aside from addressing the leakage/ion back bombardment issue—is to achieve high QE. We need the QE in the ~ 1% range for green to meet the demands for high-brightness advanced accelerators because of the commercially available laser power (~ 10 W). One way to address this challenge is to improve the quality of our graphene protection layer. The electron transmission efficiency through our current bilayer graphene is ~ 5%2Sb photocathodes can withstand their QE at average current of 2.4 nA. Similar to the lifetime under continuous illumination case, we irradiated the protected photocathodes with a green laser and measured the QE in a reflection mode through bilayer graphene protection layer. The pressure was gradually increased to atmospheric pressure by inducing air into the vacuum chamber. We observed no decrease of the QE up to ~ 1 × 10–3 Pa, which is three orders of magnitude increase in the active pressure of CsK2Sb photocathode . Furthermore, the active pressure of ~ 1 × 10–3 Pa for the graphene protected CsK2Sb photocathodes was one order of magnitude higher than that of Cu photocathode (~ 1 × 10–4 Pa)  Fig. b, a type2Sb, that can be excited by a green laser yet active in one order of magnitude higher pressure than metal photocathodes . Although the current level in this study is lower than those used in accelerator facility operations, the qualitative implication of our results on the future operation of photocathode components in accelerators can be large. Specifically, we may be able to reduce the replacement time of photocathodes from weeks to a few days. We may no longer need to remove all non-heatable parts for the baking to achieve ultrahigh vacuum pressures of 10–8 Pa. The increase of operation pressure will also broaden the types of accelerators bialkali antimonide photocathodes can operate in because of the reduced baking requirement.The significance of our achievement is that we succeeded in demonstration of a novel photocathode type using 2D material, graphene protected CsK2Sb with oxygen and moisture. We confirmed by SEM that TEM-grid-supported graphene substrates do not rupture upon their exposure to air when CsK2Sb was thermally removed at 500–600 °C prior to venting the deposition chamber  when exposed to air. This is most likely due to rapid chemical reactions/oxidation of CsK2Sb photocathodes and to improve their active pressure and lifetime under continuous illumination. We achieved an increase of three orders of magnitude in the active pressure and a factor of two enhancements in the lifetime of the protected photocathodes. Specifically, QE of ~ 0.17% at ~ 3.4 eV, 1/e lifetime of 188 h with average current of 8.6 nA under continuous illumination, and no decrease of QE at the pressure of as high as ~ 1 × 10–3 Pa were achieved. In comparison, the QE decreased drastically at 10–6 Pa for bare, non-protected CsK2Sb photocathodes and their 1/e lifetime under continuous illumination was ~ 48 h. Moreover, the active pressure of ~ 1 × 10–3 Pa achieved for our protected CsK2Sb photocathodes was one order magnitude higher than that of a bare, non-protected Cu photocathode, a type of photocathodes that is known to be the most robust. We attribute the active pressure and lifetime improvements to the gas impermeability and photoelectron transparency of graphene. Our results pave a pathway toward meeting the ~ 2-week turnaround time for feasible operation of accelerators using high-brightness bialkali photocathodes.To conclude, we investigated the efficacy of graphene-Ni thin film sandwich structure to seal CsK2Sb photocathode was then deposited onto the cleaned foil substrates. Briefly, the photocathodes were fabricated by sequential thermal evaporation of potassium (K), cesium (Cs), and antimonide (Sb) sources in a vacuum chamber with a base pressure of 1.0 × 10−8 Pa. Antimonide was deposited first for ~ 10 nm, followed by ~ 60 nm worth of potassium, and, finally, ~ 120 nm worth of cesium. The exact thicknesses of potassium and cesium were determined by the saturated QE values monitored during the growth using a 532 nm green laser. Detailed experimental setup for CsK2Sb photocathode deposition is described in Reference8. For cross-section SEM imaging, Cu and Au films with ~ 100 nm thickness was deposited onto Si single crystal substrate with 100 nm oxide layer via electron-gun (e-gun) evaporation.Commercially available Cu, Au, Ni and SUS foils were used as purchased (Alfa Aesar and Goodfellow). Those foil substrates were thermally cleaned in ultrahigh vacuum at 500–600 °C for an hour prior to the deposition. CsK43 on Cu substrates were purchased from Graphenea and transferred onto TEM mesh grids using an established polymer-supported method that involves distilled water exposure44. Bilayer graphene, instead of the monolayer, was used to minimize mechanical voids generated during the transfer process. Polymer support was removed using acetone. The graphene on TEM grids were thermally cleaned in ultrahigh vacuum at 500–600 °C for an hour to remove residue from polymer support during transfers. CsK2Sb photocathode was then deposited onto the graphene using the same condition as that for sealing metal selection. CsK2Sb photocathodes on TEM-grid-supported graphene were lastly sealed by 15–35 nm Ni thin films deposited via thermal evaporation. The deposition rate of Ni thin films was ~ 0.06 Å/s. The evaporation area of Ni thin film was 6 mm diameter circle thus large enough to cover the entire 3 mm diameter TEM-grid with CsK2Sb photocathode on graphene and seal it at the edge.Free-standing graphene was first prepared on commercially available TEM metal mesh grids with a 3 mm diameter. Graphene consisting of mainly monolayer regions with some multiple layer regions was synthesized via chemical vapor deposition (CVD)2, and the photocathodes were biased at −100 to −200 V to ensure the effective collection of photoelectrons. The laser power was adjusted to 0.6 mW, and the typical photo-current level was several µA for spectral response  and several nA for lifetime measurements. The QE spectral response for CsK2Sb photocathodes on TEM-grid-supported graphene was initially measured from the photocathode and the graphene sides separately. The QE from the graphene side was measured through bilayer graphene protection layer and it was measured before and after Ni thin film seal. In all QE that is measured from graphene side, the TEM-grid transparency of 40% is considered . The lifetimes of Ni sealed photocathodes were measured from the graphene side, under continuous illumination. A 532 nm green laser was used for all lifetime and operation pressure measurements. The lifetime measurements were performed at 10−8 Pa. The pressure was intentionally increased to atmospheric pressure by inducing air for the active pressure measurements.Reflection mode QE values were measured in vacuum using lasers in the visible wavelengths. The laser spot size was 0.5 mm45 as implemented in the Vienna ab initio Simulation Package (VASP)46. The generalized gradient approximation (GGA) of the Perdew–Burke–Ernzerhof (PBE)47 functional was used to represent the exchange–correlation interaction. The metal substrates were represented with slab models with a vacuum gap in the direction normal to the surface to eliminate the interactions between the replicas due to the periodic boundary conditions. The binding energies of adatoms are defined as Calculations were performed with the use of density functional theory (DFT) and the projector augmented-wave (PAW) method


Owing to the strong interface coupling, the graphene layer feels an effective confinement potential well imposed by two‐dimensional (2D) Mo2C crystal. Employing cross junction device geometry, a series of resonance‐like magnetoresistance peaks are observed at low temperatures. The temperature and gate voltage dependences of the observed resonance peaks give evidence for geometric resonance of electron cyclotron orbits with the formed potential well. Moreover, it is found that both the amplitude of resonance peaks and conductance fluctuation exhibit different temperature‐dependent behaviors below the superconducting transition temperature of 2D Mo2C, indicating the correlation of quantum fluctuations and superconductivity. This study offers a promising route toward integrating graphene with 2D superconducting materials, and establishes a new way to investigate the interplay of massless Dirac fermion and superconductivity based on graphene/2D superconductor vertical heterostructures.The realization of high‐quality heterostructures or hybrids of graphene and superconductor is crucial for exploring various novel quantum phenomena and devices engineering. Here, the electronic transport on directly grown high‐quality graphene/Mo 2C vertical heterostructures provide an ideal platform for exploring the interplay of massless Dirac fermion and superconductivity. This low‐temperature transport reveals the geometric resonance by the interaction of the carriers with the boundaries of the potential well formed at the graphene/Mo2C interface, and the potential well can be effectively modified through superconducting proximity effect in heterostructures.Directly grown graphene/Mo For these hybrid superconducting devices, a highly transparent superconductor‐graphene junction is critically important. Thus improving the quality of junction device and creating a clean and strong coupled interface is an essential part to investigate the fundamental quantum phenomena. Experimentally, previous studies on graphene/superconductor devices were usually prepared by the evaporation of superconducting materials over graphene. However, it is inevitable to create defects and contaminants at contact interface, and even it is difficult to induce superconductivity coupling with graphene by proximity effect. In addition, with the rise of van der Waals heterostructure, another technique of transferring and stacking 2D materials makes a compelling route to explore the proximity effect in hybrid graphene–superconductor devices. Whereas this transfer method depends on advanced techniques to produce sharp and clean interfaces, the devices also undergo weak interfacial interaction and interface contaminants leading to largely degrade device performance.In recent years, intense attention has been devoted to the study of graphene and other 2D crystals, which not only lead to the emergence of exotic electronic states, but also serve as atomically thin building blocks for the development of novel devices with new functionalities and promising applications.2, 3 By creating atomically thin graphene p‐n junction, various peculiar charge scattering characteristics for massless Dirac fermions, such as Klein tunnelling, Veselago lensing, and Berry phase switch, have been demonstrated experimentally. In previous experimental studies, different nanofabricated approaches are used for tackling the resonant scattering potential in graphene, such as etching antidots, substrate engineering, 1D electron guide, ballistic cavities, and depositing periodic gates. However, above nanopatterning procedures inevitably induce extra damage and reduce sample mobility by disorder. Additionally, due to the depletion at boundaries, a well‐defined scattering potential is hard to be realized resulting in a significant distortion of the electron cyclotron orbits. So far, these studies of transport in graphene subjected to scattering potentials have been limited to the nanofabrication techniques. The proximity effect induced scattering potential in superconductor/graphene heterostructure junction interface has not been explored.On the other hand, understanding the scattering processes in 2D materials and heterostructures is fundamentally and technologically important.14 By 2C, TaC, and WC. In α‐Mo2C crystals with excellent thermal and chemical stability, the 2D superconductivity has been demonstrated. For 2D heterostructures, we also have developed a two‐step CVD approach to fabricate high‐quality graphene/Mo2C vertical heterostructures with the double layers of Cu/Mo foils as growth substrates. Employing this approach, a high‐quality graphene/2D superconductor vertical heterostructure with uniform well‐aligned lattice orientation and strong interface coupling has been obtained. Compared with the van der Waals heterostructures by conventional transfer and stacking method, this directly grown 2D superconductor/graphene heterostructure has a clean and uniform interface, offering an interesting platform to explore the effect of interface scattering on the transport phenomena.Recently, we have developed a chemical vapor position (CVD) method to synthesize a series of high‐quality ultrathin transition metal carbides (TMCs) crystals, including Mo, and WC.27 In 2C vertical heterostructure devices. By fabricating graphene cross junction with heterostructure located in the central region, we are able to induce an electrostatic potential well to probe charger scattering in graphene. The magnetoresistance curves show a series of resonance‐like peaks at low fields. The temperature and gate voltage‐dependent magnetoresistance behavior are in quantitative agreement with geometric resonance scenario in which the cyclotron radius of incident electron is compatible with effective central scattering boundary. Moreover, the amplitude of magnetoresistance resonance peaks below the superconducting transition temperature Tc of Mo2C exhibit a different temperature dependence from the normal state, indicating that the presence of proximity‐induced superconducting gap can effectively modify the confinement strength of the potential well in heterostructure. Our results show that the vertical graphene/Mo2C heterostructure exhibit a clean and strong coupling interface for the study of the interplay between Dirac‐like quasiparticles and superconductivity.In this study, we investigate the low‐temperature transport properties of directly grown graphene/Mo22.12C heterostructure and device fabrication process is schematically depicted in Figure 2C vertical heterostructures has very high quality due to the unchanged reaction atmosphere and there is strongly coupled interface between graphene and 2D Mo2C crystal. Besides, the high crystalline quality of 2D Mo2C can be confirmed by HAADF‐STEM characterization; there is no visible defect or disorder in a large of ≈25 × 25 nm2 region  was performed to identify the sharp and uniform interface for our graphene/Mo2C heterostructures, as shown in Figure Ambient‐pressure CVD growth of graphene/Mo2C crystal as a scattering potential well on the charge transport properties of graphene, we fabricated a four‐terminal graphene cross junction with Mo2C in the central, as illustrated schematically in Figure 2C crystals. A typical measurement configuration for the cross junction device is manifested in Figure 2C/graphene devices by using conventional transfer method for comparison. The device fabrication process is schematically depicted in Figure In order to study the effect of Mo2.2Figure 2C with length scale of 1.8 μm is located in the center region of cross junction. The inset of Figure 2C crystal. Figure 2C heterostructure cross junction resistance as a function of backgate voltage obtained at zero magnetic field. The device exhibits p‐type transfer characteristics with the Dirac point located at around Vbg ≈5 V. The inset of Figure T = 1.9 K under high magnetic fields. The observation of quantum Hall plateaus also confirms that our direct growth method of graphene/Mo2C heterostructures have high quality. By applying the gate voltage, we can easily change the carrier density of graphene, which is an advantage for changing the Fermi wavelength of electron in graphene that can help to study the effects related to typical length scale of our device.R(B) of graphene/Mo2C heterostructure devices for various temperatures in the magnetic field range from ‐1 to 1 T. In order to characterize the transport through the pristine and heterostructured graphene in the cross‐junction region for comparison, we also fabricated a multi‐terminal Hall bar devices, as illustrated in the inset of Figure  By contrast, the heterostructure device in the presence of central Mo2C crystal displays a broad resistance bump structure, showing an increase of resistance below ±0.25 T. Another feature of the heterostructure device is the appearance of pronounced magnetoresistance oscillations at low fields. Figure T= 2 K, a series of resonance‐like magnetoresistance peaks can be clearly identified, superimposed on the magnetoresistance traces. These resistance peaks that appear at the specific magnetic fields are reproducible and stable, located symmetrically with respect to the zero field  and Mo2C (≈4.75 eV), charge transfer from graphene causes hole doping with the Fermi level displaced below the Dirac point, which is consistent with the observed p‐type transport characteristics. As a consequence, an electrostatic scattering potential well can be formed in the central heterostructure region. Similar potential barrier has been reported in other graphene heterostructures. The bottom panel of Figure  As a perpendicular magnetic field is applied, injected electrons move along the cyclotron orbits entering into the potential well imposed by the heterostructure, leading to additional charge carriers scattering at the boundaries. When the magnetic field is swept to meet resonance condition, the cyclotron orbits of electrons form a stable closed orbit which is confined within the potential well, giving rise to the magnetoresistance peak at certain magnetic fields. Similar commensurability magnetoresistance oscillations have been also observed in 2D electron gas subjected to a periodically modulated potential. According to the description of classical electron cyclotron motion radiuskF=2πns is Fermi wave vector, ℏ is Planck's constant, ns is the carrier density of the graphene. Thus, the resonance condition can be achieved by varying the magnetic field or carrier density.Considering graphene/Moachieved.31 Con2C heterostructure based junction devices, we carried out the gate voltage‐dependent magnetoresistance measurements. Figure Dirac ≈5 V). Thus, with increasing gate voltage in the hole side, the carrier density is tuned to decrease. When the gate voltage is increased approaching the Dirac point, it can be found that the resonance peaks gradually move to lower magnetic fields, as indicated by the dashed lines. Such evolution is expected from Equation (R(B) of stacked Mo2C/graphene devices using transfer method taken at different temperatures and gate voltages, respectively. In contrast to the magnetoresistance behavior of our grown directly Mo2C/graphene heterostructure devices, no resistance bump structure and oscillations were observed in stacked devices. The gate voltage evolution of magnetoresistance is also not regular. No noticeable feature of resonant scattering was observed. These comparative results further support that the presence of clean and strong coupling interface in our directly grown Mo2C/graphene heterostructures can effectively modify the potential well, being responsible for the observed geometric resonance.To further investigate geometric resonance in graphene/MoEquation  since th2.4n∝Vg. Therefore, we can quantitatively evaluate the B* by performing a square root dependence of the gate voltage. For clarity, the gate voltage at the Dirac point has been shifted to zero. Figure B* of order 3, 4, 6, 7 magnetoresistance resonance peak as a function of ΔVg1/2. The dashed lines show the results of linear fitting. It can be clearly seen that the values of B* scale with Vg1/2, which is consistent with the picture of geometric resonance in a hard‐wall potential well of 2D graphene/Mo2C heterostructure cross junction.We next carry a quantitative analysis of magnetoresistance resonance peaks. For monolayer graphene, the carrier density near the Dirac point is induced by gate voltage with linear dependence 2C is 1.8 µm and the area is close to 2.5 µm2, here approximately considered as an equilateral triangle model. For the third‐order resonant peak, the characteristic magnetic field B* is 0.11 T. According to the Equation 1/2/eBa, and kBTa(B) = ℏωckFa/4π2. The fitting results are shown as gray dashed lines in Figure Tc ≈ 4 K of 2D Mo2C, highlighted by the blue region in Figure Tc suggests a connection with superconductivity which is developed in Mo2C. For our graphene/Mo2C heterostructures, superconductivity would expect to be induced in graphene through strong couple interface. As a result, a proximity‐induced superconducting gap could be formed in the interface region, which has been identified in hybrid graphene‐superconductor structures by using scanning tunnelling microscopy. Comparing with the situation in the normal state, the presence of proximity superconductivity gap may modify the confinement strength of the potential well underneath the Mo2C in the junction region. Therefore, the different temperature dependence of the magnitude of resonance peaks provides the evidence for superconducting modification effect.Finally, we turn our attention to the effect of superconductivity on the magnetotransport properties of graphene/Mo. Figure 40 ∼ T−α with α ≈ 0.5, which is related to the dephasing mechanism of Coulomb interaction between charge carriers. As the temperature is further lowered, the growth of amplitude deviates from the ∼ T−0.5 dependence. The characteristic temperature (≈ 4–5 K) is comparable with the Tc value of Mo2C crystals, suggesting that the fluctuations are strongly influenced by the induced superconductivity in heterostructure. Previous experimental and theoretical studies in mesoscopic normal metal/superconductor systems have found that the proximity effect would modulate the conductance fluctuations, which have been attributed to the presence of the Andreev reflection at the interface. However, the magnitude of the fluctuations and its relation to superconductivity and mesoscopic structures remain a controversy. Our graphene/Mo2C heterostructure with clean and strong coupling interface may provide an ideal platform for studying the relationship between conductance fluctuations and proximity effect in graphene.We further take the analysis of overall conductance fluctuations averaged over magnetic fields, which can provide additional information on charge carrier scattering and dephasing mechanisms. In order to quantify the conductance fluctuations, we subtract the slowly varying background conductance. Figure 42 For32C vertical heterostructure. We observe a series of resonance‐like magnetoresistance peaks at low temperature. The evolution of the magnetotransport features with temperature and gate voltage can be explained in terms of geometric resonance by the interaction of the carriers with the boundaries of the potential well formed at the graphene/Mo2C interface. Further analysis of the amplitude of magnetoresistance resonance peaks and magnetoconductance fluctuations reveals the different temperature‐dependent behavior between the normal and superconducting state, indicating that the confinement strength of the potential well can be effectively modified through superconducting proximity effect in heterostructure. Our findings open the door to exploration of directly grown graphene/2D superconductor vertical heterostructures as the ideal platform for investigating the interplay of massless Dirac fermion and superconductivity.In conclusion, we have realized high‐quality hybrid graphene‐superconductor devices with clean and strong coupling interface based on directly grown graphene/2D superconducting Mo42C heterostructure followed these steps. A Cu foil was cut into pieces and placed on the top of Mo foil which had the same size of the Cu foil. Then, they were placed in a quartz tube as the growth substrate of graphene/Mo2C heterostructure. First, using methane  as the carbon precursor and under H2(200 sccm)/Ar(500 sccm) as the carrier gas, we set growth temperature of 1070 ° C in a horizontal tube furnace. After 30 min, the graphene has been formed. The Cu/Mo substrate was heated to 1090 ° C to grow 2D Mo2C. At the present temperature, Cu foil started to melt and covered the entire Mo substrate. The methane through graphene further reacted with Mo to form α‐Mo2C, which was underneath the graphene on the liquid Cu/Mo substrate. Finally, setting flow rate of methane made the samples cool down to room temperature.Ambient‐pressure CVD growth of graphene/Mo2C heterostructure on Cu/Mo substrate was confirmed by Raman spectroscopy with a 632.8 nm laser (Jobin Yvon LabRAM HR800). The cross‐sectional HRTEM image of graphene/Mo2C heterostructure was taken by TEM with a voltage of 300 kV (FEI Titan3 G2 60‐300), and cross‐sectional sample was processed by Focused Ion Beam with Ga source (Zeiss Orion NanoFab).Graphene/Mo2C heterostructures were transferred onto SiO2/Si substrates by means of conventional poly(methyl methacrylate)‐mediated method. After the transfer process, the graphene/Mo2C heterostructures crystals were selected and located by optical microscopy. Titanium/gold(5/90 nm) electrodes were patterned on each arm of the cross junction by means of standard electron beam lithography followed by electron beam evaporation of the metals. The electrical transport measurements were performed in a physical property measurement system (Quantum Design DynaCool) from room temperature to 1.8 K. Here, the standard four‐terminal resistance was measured using the low‐frequency lock‐in technique with an excitation current of 1–5 µA at a frequency of 17.77 Hz. The magnetic field was applied perpendicular to the plane of the sample.The graphene/Mod method.26 AftThe intensities of Raman data in Figure The authors declare no conflict of interest.Supporting InformationClick here for additional data file.


Objective: To investigate whether a higher number of transcranial direct current stimulation (tDCS) sessions results in a greater improvement in upper limb function in chronic post-stroke patients. Materials and methods: A randomized, sham-controlled, double-blind clinical trial was conducted in 57 chronic post-stroke patients (≥ 3 months after their injuries). The patients were allocated to receive sessions of tDCS combined with physiotherapy and divided into three groups . The Fugl-Meyer Assessment of Upper Extremity (FMA-UE) was used to assess the sensorimotor impairment of the patients’ upper limbs before (baseline) and after five and ten sessions. The percentage of patients who achieved a clinically significant improvement (> five points on the FMA-UE) was also analyzed. Results: The FMA-UE score increased after five and ten sessions in both the anodal and cathodal tDCS groups, respectively, compared to the baseline. However, in the sham group, the FMA-UE score increased only after ten sessions. When compared to the sham group, the mean difference from the baseline after five sessions was higher in the anodal tDCS group. The percentage of individuals who achieved greater clinical improvement was higher in the stimulation groups than in the sham group and after ten sessions when compared to five sessions. Conclusions: Our results suggest that five tDCS sessions are sufficient to augment the effect of standard physiotherapy on upper limb function recovery in chronic post-stroke patients, and ten sessions resulted in greater gains. Stroke is one of the leading causes of physical disability among adults worldwide , with apTranscranial direct current stimulation (tDCS) is a potential tool for increasing and accelerating cerebral cortex reorganization and facilitating motor learning by modulating cortical excitability . After aIncreasing evidence points to tDCS as an adjunctive treatment in post-stroke motor rehabilitation ,19. DespSeveral factors can influence the achievement of the best motor response with tDCS post-stroke, and questions still remain regarding the ideal dose of the number of sessions . Indeed,To the best of our knowledge, no randomized clinical trial has investigated whether higher doses of tDCS produce greater clinical improvement in upper limb motor function. The dose of a non-pharmaceutical intervention is unclear, and inconsistent terminology can incorporate multiple dose dimensions, such as frequency, intensity, duration, and intervention length . Here, tThis double-blind, randomized, sham-controlled clinical trial was performed between November 2017 and January 2019 at the Laboratory of Applied Neuroscience (LANA), Universidade Federal de Pernambuco, Brazil.www.clinicaltrials.gov (NCT03446378).All participants signed an informed consent form after being informed of the study objectives and procedures, which was performed in accordance with the Declaration of Helsinki. This study was approved by the local research ethics committee and was registered at Participants were recruited from a pre-existing list at the research laboratory via telephone. Patients of both sexes were included according to the following criteria: (i) diagnosis of hemorrhagic or ischemic stroke, confirmed by magnetic resonance imaging/computed tomography; (ii) ≥3 months after ictus; (iii) presence of sensorimotor sequelae in the upper limb; and (iv) age between 18 and 75 years. The exclusion criteria were as follows: (i) other neuromusculoskeletal injuries; (ii) cognitive deficits assessed by the Mini Mental State Examination (MMSE) ≤18 points ; (iii) cwww.randomization.com. This was stored on paper and kept in an opaque sealed envelope to keep the allocation confidential. Patients were randomized into three groups: (i) cathodal tDCS, (ii) anodal tDCS, and (iii) sham tDCS. The outcome evaluators were blinded to tDCS. A non-involved researcher was assigned to apply the tDCS. As such, this study was double-blinded.Randomization of patients who met the eligibility criteria was performed by an external researcher who was not part of any research process through the website Initially, patients were evaluated using the Fugl-Meyer Assessment of Upper Extremity (FMA-UE) at pretreatment (baseline) and after 5 and 10 sessions. The Global Perception of Change Scale was also applied after starting treatment of five and ten sessions. The intervention protocol consisted of ten sessions of tDCS combined with physiotherapy for two consecutive weeks (5 days a week) .During the tDCS intervention , two electrodes (5 × 7 cm) soaked in saline solution were applied to the scalp of the patients, applying a low-amplitude direct current (2 mA). The location of the primary motor cortex (M1) of the non-lesioned and lesioned hemispheres was based on the international 10/20 positioning system electroencephalogram. For the anodal tDCS group, the electrode was placed in the motor area ipsilateral to the lesioned hemisphere at points C3 or C4 (according to the 10/20 reference system), and the cathode was positioned over the contralateral supraorbital area. In the cathodal tDCS group, the cathode was positioned over the C3 or C4 motor area of the non-lesioned hemisphere, and the anode over the supraorbital area ipsilateral to the lesion. The sham tDCS group was subjected to the same procedure as the anodal tDCS group. The stimulation protocol lasted 20 min with a ramp up and down of 10 s, except for the sham tDCS group, which lasted 30 s to achieve a good level of blinding . After eAll patients, regardless of the stimulation group, underwent physiotherapy sessions. Each session consisted of kinesiotherapy for the rehabilitation of sensorimotor impairment of the upper limb, lasting 45 min. The kinesiotherapy protocol highlights 12 points following the neuroplasticity principles of Kleim and Jones . These tThe outcome of the present study was related to impairment of upper limb motor function through the Fugl-Meyer Assessment of Upper Extremity (FMA-UE). The FMA-UE includes the motor domain and coordination/velocity. There is a total of 33 items, each of which contains an ordinal scale of three levels: (0) cannot be performed, (1) partially performed, and (2) performed completely, with a total score from 0 (complete hemiplegia) to 66 points  for the upper limb ,43. The The normal distribution of data was analyzed using the Kolmogorov–Smirnov normality test. First, comparisons among the groups  at baseline were performed according to the demographic and clinical characteristics of the samples. The chi-square test was used for categorical variables, and the Kruskal–Wallis and one-way ANOVA tests were used for categorical variables.time (before and after 5 and 10 sessions) and among the factor groups . Mauchly’s sphericity test was used to evaluate the validity of the sphericity assumption, and when necessary, was corrected using the Greenhouse–Geisser test. The paired t-test was used to compare the baseline and post-intervention assessments (baseline to after five sessions and baseline to after 10 sessions) in each group.For the FMA-UE, repeated measurements for ANOVA 3 × 3 were calculated using the within-subject factor In addition, the number of patients who reached the minimal clinically important difference (mCID) of the FMA-UE was calculated at the end of 5 and 10 sessions. The assessment of patients’ mCID was considered as the minimum difference of five points obtained through FMA-UE for clinical improvement , which wp < 0.05).All statistical analyses were performed using the statistical software IBM SPSS , version 23.0, UFPE, Recife, Brazil for Windows, with a significance level of 95%  but not for groups  and interactions . Compared to the baseline, the FMA-UE score increased after five and ten sessions in the anodal and cathodal tDCS groups. However, in the sham group, the FMA-UE score increased after only ten sessions  between the anodal and sham groups after five sessions.p > 0,05; chi-square test). However, the percentage of people who achieved greatly improved and very much improved categorizations of FMA-UE was greater in the tDCS group than in the sham group after five and ten sessions  with ten sessions (the most common number of sessions among the studies) on upper limb function post-stroke recovery. Based on our findings, five tDCS sessions were sufficient to augment the effect size of physiotherapy on upper limb function recovery in chronic post-stroke patients. Previous research has demonstrated that both five and ten tDCS sessions can improve upper limb recovery.In our study, mCID was achieved in all groups after five and ten sessions, but for a greater number of participants in the stimulation groups  than in the sham group. These findings are consistent with a previous report that compared the mCID of three groups  combined with a physiotherapy technique after 12 sessions, at a frequency of three times a week . Taken tIt is important to mention that a meta-analysis  suggesteThe results of the present clinical trial showed that conventional therapy associated with anodal stimulation provided an improvement in upper limb function. These findings are in line with previous publications ,31,35, sAlthough there was homogeneity in the motor impairment level among our groups, a difference in patient stratification, regardless of the level of structural reserve, is likely to be the main limitation of our study. This could have influenced our result regarding the superiority of the anodal over the cathodal protocol. Nevertheless, in future studies, it may be interesting to compare the dose–response of both tDCS protocols in studies that choose stimulation protocols based on a neurophysiological evaluation of the level of the patient’s structural reserve. Another interesting direction for future work would be to compare the effect size of multiple tDCS sessions with clinical assessments in other domains of the International Classification of Functioning, Disability, and Health (ICF) , such asA further limitation of this study is that the sample size was not calculated; therefore, as this is related to the power analysis, the data should be interpreted with caution. Finally, a further limitation of the study is the lack of a cut-off for FMA in patients with different motor impairment levels.In summary, our preliminary evidence indicates that conventional therapy plus tDCS typically produces an earlier and greater effect than physical therapy alone, especially in anodal tDCS. Moreover, this clinical improvement is even faster and more effective with a minimum of five sessions, and as the number of sessions increases, clinical gains in upper limb function potentiate greatly.


The surface morphology, roughness, wettability, and degradation of coated and uncoated samples were analyzed by scanning electron microscopy, interferometry, and contact angle. The results showed that the specimens coated with NbGO (cp Ti-NbGO) showed the highest surface roughness (Ra = 0.64 μm) and were hydrophobic. The contact (θ) angle between water and the surface of uncoated specimens (cp Ti), coated with GO (cp Ti-GO), coated with a mixture with GO and Nb2O5) (cp Ti-NbGO), and coated with Nb2O5 were 50.74°, 44.35°, 55.86°, and 100.35°, respectively. The electrochemical corrosion tests showed that coating with graphene oxide increased the corrosion resistance and coating with Nb2O5 decreased the corrosion resistance. The negative effect of the effect of Nb2O5 coating in corrosion resistance compensated for the release of Nb2O5, which helps osseointegration, increasing cell viability, and proliferation of osteoblasts. The NbGO coating may be a good way to combine the bactericidal effect of graphene oxide with the osseointegration effect of Nb2O5.Graphene and niobium oxide are used in biomaterial coatings. In this work, commercially pure titanium (cp Ti) was coated with graphene oxide (GO), niobium pentoxide (Nb Titanium and its alloys are widely used as biomaterials. Its main feature is osseointegration since the titanium oxide film on the surface enhances the adhesion of proteins and bone cells. The wrought titanium 6-aluminum4-vanadium ELI alloy (Ti-6Al-4V ASTM F136), alpha plus beta titanium alloy forgings (ASTM F620), and wrought titanium 6-aluminum7-niobium alloy (ASTM F1295) have adequate mechanical properties for use as a biomaterial, but they release toxic ions (Al and V), decreasing its biological activity. Another problem observed is that among the different causes of failures of orthopedic prostheses and dental implants, the adhesion of biofilms and chronic inflammatory processes deserves to be highlighted. In the case of implants, biofilm adhesion can also facilitate peri-implantitis. Despite the various procedures adopted to minimize this problem, implant scraping and the use of antibiotics are the most efficient. Even so, the inflammatory process can be recurrent, leading to implant loss. For this reason, surface treatment and chemical modifications of titanium alloys for implant biomaterials application are important.Escherichia coli and Streptococcus iniae. In high concentrations, GO inhibits the action of Gram-negative bacteria [Graphene oxide (GO) has a bactericidal effect and does not inhibit cell growth. The antibacterial activity of GO is based on the production of hydroxyl radicals, which attack the cell membranes of bacteria, causing their death. During the process, reactive oxygen species are generated, which lead to oxidative stress, exceeding the antioxidant defense capacity of the bacteria and causing damage to their lipids, proteins, and DNA. The morphology of GO is formed by nanosheets with sharpened edges that break the bacterial membrane, causing the intracellular matrix to drain into the medium . GO inhibacteria .2O5) is the most stable thermodynamically [2O5 enhances cellular viability and proliferation after 21 days. The cells present good adhesion and are homogeneously distributed on the surface. Previous results showed that the lactate dehydrogenase activity was similar to the titanium surface with and without Nb2O5 coating, indicating a similar number of cells.Among niobium oxides, niobium pentoxide  were used in the present work. The material was supplied by Conexão Sistema e Prótese . The samples were acid-etched with a mixture of sulfuric acid, hydrochloric acid, and distilled water and washed in an ultrasonic bath with distilled water before all testing.2O5 and a mixture of GO and deposition and Nb2O5 followed similar routes. The deposition of graphene oxide was carried out by electrodeposition in an aqueous solution . The graThe surface morphology of three samples from each group was investigated by scanning electron microscopy  before and after coating.The sample wettability was measured by the contact angle method. Contact angle measurements were performed with deionized water, using the sessile drop technique. The equipment used was the FTA 100 goniometer .Literature results showed that osseointegration is the main parameter for the success of dental implants, which means a protein and bone cell attachment on the implant surface . This atTwo electrochemical analyses were carried out to evaluate the adhesion of the coating on sample surfaces and to analyze the influence on corrosion resistance. The first electrochemical testing was the evolution of the open circuit potential (OCP), which was monitored for 3600 seconds. The second performed testing was potentiodynamic polarization to obtain the polarization curves. For potentiodynamic polarization, a sweep rate of 0.001 V/s and potentials of −0.500 V to 1 V were used. The electrolyte was a physiological solution containing 0.9% of NaCl at room temperature. The equipment used was an AUTOLAB potentiostat/galvanostat . The cell used for the analyses consists of a calomel reference electrode, a platinum counter electrode, and the sample disc as the working electrode.The statistical analyses were performed by an ANOVA variance calculation followed by Tukey's test. For statistical analysis, PRISM GRAPH 9  software was used.2O5 particles. Figures 2O5 particles and translucent graphene sheets.Figures Roughness and wettability are important parameters to evaluate the success of dental implants. Hydrophobic surfaces decrease the primary interactions with cells in an aqueous environment. It is usually reported that biomaterial surfaces with moderate hydrophilicity improve cell growth and material biocompatibility .Graphene oxide, obtained by the oxidation of graphite flakes, has hydrophilic characteristics, good dispersion, and compatibility with various polymeric matrices , 13 TitaThe analysis of the simultaneous influence of surface wettability, roughness, and chemical composition on osseointegration is complex. Surface treatments modify the wettability of implants, making them hydrophilic or hydrophobic. Some proteins interact with hydrophilic surfaces, and others interact with hydrophobic ones. Smooth surfaces are suitable for interaction with fibroblasts, and rougher surfaces are suitable for interaction with osteoblasts. As for the wettability, it is possible to estimate the relationship between the surface energy and the contact angle. There is an inversely proportional relationship between the two properties, regardless of whether the samples have micrometer (Ti G4) or submicrometer (Ti Hard) grain size .Cell adhesion and scattering occur on surfaces with moderate wettability and contact angles between 50° and 80°. The fixation and proliferation of osteoblasts increase as the surface wettability increases , 17. TheClassifying surfaces as hydrophilic or hydrophobic is not enough to determine a good relationship between the material surface properties and cellular adhesion and to analyze the possibility of implant osseointegration . The infμm. Samples coated with niobium pentoxide had Ra 0.44 ± 0.03 μm. The samples coated with graphene oxide had Ra = 0.47 ± 0.04 μm. Statistical analysis showed no statistically significant difference among three of the four groups studied. The cp Ti-NBGO group had the highest average roughness (Ra = 0.64 ± 0.47 μm), which represents a statistically significant difference from the other groups.The Ra parameter is most used in the literature to characterize the surface roughness of dental materials and applies to most manufacturing processes. Among the disadvantages of using the Ra value, we highlight the fact that this parameter only quantifies the average roughness. It makes no distinction between peaks and valleys and does not define the shape of the irregularities. For this reason, in the present work, the roughness measurements were complemented by the RMS and Rz parameters. The RMS value corresponds to the square root of the mean of the squares of the ordinates, that is, the root means square deviation. The Rz parameter corresponds to the arithmetic mean of five values of the distances between peaks and valleys. These parameters were quantified to analyze the influence of coatings on surface roughness, which act directly on the cell's adsorption of micrometric surface characteristics .The cell interaction with the implant surface is influenced by topography at macroscopic levels and roughness at the microscopic level. Increasing the surface area of the implant increases the number of possible sites for cell attachment, facilitates tissue growth, and increases mechanical stability. However, this is not a general rule. The level of roughness must be controlled because the cells need anchorage points on the implant surface to initiate proliferation and ensure mechanical stability. When the surface has a roughness much smaller than the cells' sizes, there may be an absence of adhesion sites. On the other hand, if the implant has a larger quantity of small peaks or valleys, the surfaces may be smooth and the cells, likewise, cannot be fixed .μm have better osseointegration and mechanical stability than smooth or rougher surfaces. Implants with surface roughness between 0.8 and 1.5 μm and with nanoroughness have the best success rates [Dental implant surfaces with Ra between 0.8 and 2.0 ss rates . Possiblss rates  Some celss rates . On a smss rates .μm and a removal torque of 62.08 N·cm. Implants with Ra = 1.51 μm are removed with a torque of 66.56 N·cm. The implant with greater Ra (1.0 μm) needs a torque of 76.45 N·cm to be removed. These results show that osteoblasts have a better affinity for surfaces with medium roughness (Ra = 1.0 μm) [In vivo tests with rabbits showed that machined implants without surface treatment have Ra = 0.32 ± 0.03  1.0 μm) .Considering that RMS is the standard deviation of Ra, it can be said that the values of Ra and RMS are complementary. The deposition of graphene on metal surfaces forms a protective barrier that increases the corrosion resistance  and the 2O5 may be associated with the lower stability of niobium oxide than titanium oxide, which is confirmed by the Ellingham diagram [2O5 release is the desired effect since it may help osseointegration, increase in cell viability, and the proliferation of osteoblasts [This decrease in corrosion resistance after the deposition of Nb diagram . Howevereoblasts .2O5. This behavior may be associated with lower niobium oxide stability than titanium oxide. However, this Nb2O5 release is the desired effect since it may help osseointegration, increase in cell viability, and osteoblast proliferation [Based on the Ellingham diagram , it is pferation .2) than without coating cp Ti (51.61 ± 4.49 mJ/m2), cp Ti-NB (40.80 ± 13.47 mJ/m2), and cp Ti-NBGO (46.10 ± 6.38 mJ/m2). These surface energy values are adequate for protein and cell adhesion.Wettability measurements showed that the Ti samples coated with graphene oxide (cp Ti-GO) had lower surface energy (12.94 ± 9.33 mJ/mμm, niobia coated samples had Ra = 0.44 ± 0.03 μm, graphene oxide coated samples had Ra = 0.47 ± 0.04 μm, and samples coated with both niobia and graphene oxide had Ra = 0.64 ± 0.47. Statistical analysis of the roughness parameters showed no statistically significant difference among samples from the first three groups and a significant difference with the last group.Roughness measurements showed that uncoated samples had Ra = 0.52 ± 0.06 2O5 coating decreases corrosion resistance, and the coating with both materials may be beneficial since the release of Nb2O5 helps in osseointegration, increasing cell viability, and proliferation of osteoblastsThe anodic potentiodynamic polarization curves show that the graphene oxide coating increases corrosion resistance, the NbBased on experimental results, it is possible to conclude that


Graphene and its derivatives have lately been the subject of increased attention for different environmental applications of membrane technology such as water treatment and air filtration, exploiting their antimicrobial and antiviral activity. They are interesting candidates as membrane materials for their outstanding mechanical and chemical stability and for their thin two-dimensional (2D) nanostructure with potential pore engineering for advanced separation. All these applications have evolved and diversified from discovery to today, and now graphene and graphene derivatives also offer fascinating opportunities for the fight against infective diseases such as COVID-19 thanks to their antimicrobial and antiviral properties. This paper presents an overview of graphene-based 2D materials, their preparation and use as membrane material for applications in water treatment and in respiratory protection devices. The COVID-19 pandemic was the defining global health crisis of our time—a novel infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) . This tyInfectious diseases caused by viruses threaten the health of both humans and animals, but often, viral diseases can be alleviated or even eradicated by vaccination . In the Graphene (G) is a carbon sheet one atom thick and made up of condensed six membered rings. It is a two-dimensional allotrope of carbon, separated from graphite for the first time in 2004 by A. Geim and K. Novoselov who were awarded the 2010 Nobel Prize in physics for this discovery . Single-Graphene-based materials are widely applied in green energy such as fuel cell, solar cell, lithium-ion batteries (LIBs), supercapacitor, dye-sensitized solar cells (DSSC), photocatalysis and photo-electrochemical cells for hydrogen evolution via water splitting . ReducedGraphene oxide and its derivatives, such as others nanoscale materials, have been widely explored for their antimicrobial properties due to their high surface-to-volume ratios and unique chemical and physical properties ,25. On tThis review, after an initial overview on application of graphene-based membrane for water purification, focuses on the antibacterial and antiviral activity of graphene-based materials and the possibility of using graphene-based membrane for reusable and recyclable masks.Graphite is a 3D material that is organized and built up by millions of graphene layers. Graphene (G), being one-atom thick layer of extended sp2 carbons, represents the limit of the thinnest possible 2D conductive surface, exhibiting very fast electron mobility and high charge carrier density . Until nOther derivatives of graphite are graphene oxide (GO), reduced graphene oxide (rGO), N-doped G (NG), graphene quantum dots (GQDs) etc. . One of 4 is used for graphite oxidation in the presence of H2SO4, NaNO3, and H2O2. The second is the Brodie method that is performed by adding potassium chlorate to slurry of graphite in fuming nitric acid ..65]. The membranes present a composite structure with 2D layered GO supported on macroporus PAI C,D. The Moreover, new PVDF-GO mixed matrix membranes were also developed using DMSO as non-hazardous solvent, in place of traditional substances of very high concern (SVHC), in a combined vapour- and liquid-induced phase separation process in which water in vapour or liquid form works as a non-solvent for the polymer inducing its precipitation. The protocol developed did not include any chemical additive generally used as pore former  in phase separation process for the production of porous membranes . The preContamination of water with bacteria, protozoans and viruses is a serious problem because water acts as a carrier for infectious pathogens that spread harmful diseases . The literature available regarding the separation of viruses from the water mostly denotes the use of polymeric membranes depending on their pore size . In factQu et al. reported that COVID-19 can survive in stool samples for 4 days and that this virus has been positively detected in stool samples of infected patients . In otheMembranes for water purification and water desalination are being used more and more to address global challenges of pollution and scarcity of water . Highly E. coli and creates strong interactions between itself and lipid molecules in bacteria [Some authors reported that the antibacterial ability of graphene can be increased when doped with metal nanoparticles , becausebacteria . Escherichia coli  and Staphylococcus aureus  [E. coli using recycled graphene oxide–iron oxide–silver nanocomposites [Magnetic graphene-based nanocomposites are used as an antibacterial agent for water purification ,86. Bothositive) . These cositive) . The larmposites . Other sThe growing antibacterial resistance spectrum of bacterial infections required the development of novel and efficient antibacterial agents. Biocidal nanomaterial is usually used in the science field to improve medical devices’ wastewater treatment, food packaging, synthetic textiles and dentistry . The increased attraction towards graphene and graphene derivatives such as graphene oxide and reduced graphene oxide is determined by the bactericidal activity of G on several Gram-negative and -positive bacteria . G is onEscherichia coli investigating its antimicrobial mechanism [Escherichia coli than against Staphylococcus aureus because of the absence of any additional outer membrane in the case of S. aureus. E. coli was more damaged by the GO coatings than S. aureus, probably for the oxidative stress from GO [Sometimes authors reported different behavior of graphene derivatives in terms of antibacterial effect. Liu et al. compared the antibacterial activity of graphite (G), graphite oxide (GtO), graphene oxide (GO), and reduced graphene oxide (rGO) toward a bacterial model such as echanism . The autechanism . Other sechanism . De Fariechanism . These oechanism . Many auechanism ,99. The echanism . For exa from GO . Investigating the interactions of GO with Gram-positive and Gram-negative bacteria, often the antimicrobial effects of GO are concentration and time dependent. The main structural difference between these two types of bacteria is that Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane, while Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane. E. coli strain and human HeLa cells. The typical bacterium Escherichia coli and HeLa cell were used to evaluate the antibacterial activity and cytotoxicity of the ZnO/GO composites, respectively. The antibacterial activity of the ZnO/GO composites is dependent on the content of zinc in the composites. It is mainly due to the synergistic effect of ZnO and GO: the possibility of bacteria contact to zinc was increased as ZnO NPs and released zinc ions from ZnO NPs were enriched on the GO sheets. The intimate contact of the E. coli cells and ZnO NPs on the GO sheets enhanced the permeability of the bacterial membrane and the local free zinc concentration around bacteria. The cell viability loss induced by the composites is dose-related. GO exhibited no viability loss, even at relatively high concentrations (50 μg mL−1), indicating the low toxicity of GO to HeLa cells. Similarly, even when the concentration of ZnO/GO-1 (prepared with mass ratio of ZnO/GO was 3:1) reaches 20 μg mL−1, the cell viability is still over 90%. However, a concentration of ZnO NPs (240 μM) decreased the cell viability to 30%. These results illustrate that the ZnO/GO composites cause much lower cytotoxicity than an equivalent amount of ZnO NPs alone. In another study [E. coli after 12 h. This antibacterial activity was probably caused by the synergy of the physical interactions of graphene with bacterial membranes and the antibacterial properties of ZnO that have the aptitude to photo catalytically generate H2O2 and to penetrate cells and disrupt the bacterial membrane. Furthermore, graphene oxide can be easily modified with silver NPs, obtaining the advantages of the physical properties of GO and the strong antibacterial activity of Ag NPs [P. aeruginosa. De Faria et al. [P. aeruginosa over the concentration range investigated. While the GO–Ag nanocomposite showed an antibacterial activity with a minimum inhibitory concentration ranging from 2.5 to 5.0 μg/mL. Moreover, the results showed a 100% inhibition rate of the adhered P. aeruginosa cells on stainless steel surfaces after exposure to the GO–Ag nanocomposite for one hour. This interesting result showed the possibility of using GO–Ag nanocomposites as antibacterial coatings material to avoid the growth of biofilms in food packaging and medical devices.Wang et al.  studied er study , ZnO/graf Ag NPs . Some rea et al.  reportedLukowiak et al.  reportedThe interaction of G-based nanomaterials with bacterial cells depends on their sheet size, surface area, roughness, hydrophilicity, dispersibility and functionalization . The sepThe interaction of bacteria with GO follows a different mechanism when it is in suspension form or immobilized on a coated surface . The phyThe biocidal strength order of Gr-based nanomaterials dispersions is reported as follows: G hybrid NPs, GO and G B; while Despite virus vaccination being the most widely used method for alleviating or eradicating some diseases, attenuated vaccines are not available for all viral infections . The risIn recent years, graphene oxide derivatives were studied to inhibit some viruses such as herpes simplex virus type-1 (HSV-1) competing with the heparan sulfate in binding HSV-1 . One of the major viral pathogens of the lower respiratory tract of infants is the respiratory syncytial virus (RSV). Yang et al.  demonstrVery few studies have reported on the inhibition of the entry and replication of enveloped DNA virus (herpesvirus) and RNA virus (coronavirus) in their target cells by using graphene-based material . Ye et aYe et al. analyzed the impact of GO charge by observing the antiviral activity of GO conjugated with cationic polymer PDDA or nonionic PVP . The resChen et al.  investigA significant advantage of GO-Ag nanocomposites over free Ag NPs is the increasing biocompatibility of the material and the toxicological effects of reducing associated with metallic nanoparticles due to their immobilization on GO. GO-Ag nanocomposites have a specific surface area, are not corrosive and are highly dispersible in water. An important use of GO sheets is as a supporting and stabilizing agent in preventing the agglomeration of the Ag NPs that showed a spherical-like morphology and an average size of 7.5 nm, which is suitable for antiviral activity ,113,118.The study of graphene-based membrane with antiviral activity is still at a nascent stage. Akhavan et al., fabricated Graphene−tungsten oxide composite thin films with sheetlike surface morphology that were applied in photoinactivation of viruses under visible light irradiation . The virGraphene possesses excellent light-to-heat conversion ability owing to its superior thermal conductivity. Deokar et al. designed a graphene-based photothermal antiviral agent that captures and destroys viruses . They syThe main transmission mode of virus such as COVID-19 is through short-range aerosols and droplets . Micron-For this reason, the use of disposable surgical masks or respirator are common for patients, doctors, and even the people in high-risk areas. The United States Centers for Disease Control and Prevention (CDC) recommends the usage of N95 filtering facepiece respirators (FFR) as personal protective equipment for healthcare professionals . The CDCThe N95 FFR is composed of multiple layers of polypropylene with a meltblown layer that is 100−1000 μm in thickness with polypropylene microfibers’ diameters in the range of ∼1−10 μm . These fThe use of disposable surgical masks is common for patients, doctors, and for all people in highly risky areas . As explIn general, the mechanisms of disinfection or sterilization of bacteria and viruses include protein denaturation , DNA/RNA disruption , and cellular disruption , but these methods can modify the masks’ filtration efficiency . Liao et2 laser scribing  filter-based 3D-printed facial protective equipment [Huang et al. identified the bacteria viability on common face masks and found that the majority of bacteria (90%) remain alive after 8 h . The autquipment . The autquipment . Indeed,quipment . For thiquipment  who carrSeveral efforts have been made by the research communities around the globe to contain and reduce the impact of COVID-19. However, the rapid spread of COVID-19 virus was not easily to reduce, and it remains very important to prevent airborne transmission with a respirator filter obtained by using innovative or existing technologies. Very interesting materials that can be used for this purpose are graphene and graphene oxide. This review, after an initial overview on application of graphene-based membrane for water purification, focuses on the antibacterial and antiviral activity of graphene-based materials and the possibility of using graphene-based membrane for reusable and recyclable masks in order to help researchers to find in graphene materials help to fight dangerous viruses and bacteria.The increased attraction towards Graphene and graphene derivatives such as graphene oxide and reduced graphene oxide is determined by the bactericidal activity of G on several Gram-negative and -positive bacteria. G is one of the most recently developed biocidal nanomaterials for its robustness, mechanical strength, great surface area and resistance to degradation, due to its superior surface-to-volume ratio. The attachment and adherence of G to biological cells is due to their active segments, edges, and surfaces. The interaction of G-based nanomaterials with bacterial cells depends on their sheet size, surface area, roughness, hydrophilicity, dispersibility and functionalization.Very recently the possibility was reported to make reusable masks coated on graphene that can be sterilized under sunlight irradiation where the surface temperature can quickly increase to over 80 °C. Other authors produced a prototype for a customizable/multi-used protective respirator mask in which CuO and GO nanoparticles should inactivate viral particles.The study of graphene-based membrane with antiviral activity is still at a nascent stage that needs further work. Indeed, despite the great interest in the use of graphene to modify the mask filters due to its potential use as antibacterial and virucidal properties, additional research efforts should be direct also to the use of new methodologies to complement the actual standard tests and ensure the security of the filters modified with nanomaterials.


The activity of brain-derived neurotrophic factor (BDF) in the central nervous system has been well-studied, but its physiological role in other organs has not been clearly defined. This review summarizes the current findings on the functionality of BDNF in various peripheral tissues and discusses several unresolved questions in the field.Brain-derived neurotrophic factor (BDNF) is an important growth factor in the central nervous system. In addition to its well-known activities in promoting neuronal survival, neuron differentiation, and synaptic plasticity, neuronal BDNF also regulates energy homeostasis by modulating the hypothalamus’s hormonal signals. In the past decades, several peripheral tissues, including liver, skeletal muscle, and white adipose tissue, were demonstrated as the active sources of BDNF synthesis in response to different metabolic challenges. Nevertheless, the functions of BDNF in these tissues remain obscure. With the use of tissue-specific Bdnf knockout animals and the availability of non-peptidyl BDNF mimetic, increasing evidence has reported that peripheral tissues-derived BDNF might play a significant role in maintaining systemic metabolism, possibly through the regulation of mitochondrial dynamics in the various tissues. This article reviews the autocrine/paracrine/endocrine functions of BDNF in non-neuronal tissues and discusses the unresolved questions about BDNF’s function. In . In 1].  disease . The neu disease ,7,8.Bdnf and Ntrk2 (the TrkB gene) knockout mice revealed that mBDNF participates in the regulation of body weight through controlling food intake i) release [2+]i is crucial in their cellular function, such as cardiomyocytes and the pancreatic β-cells, deleting TrkB.T1 abolished the action of BDNF, which impedes heart contraction and insulin secretion [TrkB.T1 gene results in a greater Ca2+ flux between the cytoplasm and sarcoplasmic reticulum to increase contractility [TrkB.FL and TrkB.T1 as well as their functional interaction in various tissues might represent an additional regulatory mechanism for BDNF response in peripheral tissues. Hence, it would be necessary to consider the role of TrkB.T1 in studying the BDNF’s function in the future.It is also important to determine the dominant receptor of BDNF to exert its metabolic functions in different tissues. The dogma that BDNF only relies on TrkB.FL to initiate the biological activities has been changed since the discovery that TrkB.T1 could transduce intracellular signals by provoking intracellular calcium ([Ca release . This fi release ,136. Howecretion ,137. Becactility . The difLast but not least, peripheral tissues-produced mBDNF might act on the CNS to modulate cognitive functions. When considering together that mBDNF is a well-recognized myokine whose expression is increased after exercise, muscle-derived mBDNF is secreted into the circulation . Althoug


Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide ,2. The eThe practice-changing phase III IMbrave150 trial compared the combination of the PD-L1 inhibitor atezolizumab plus bevacizumab versus sorafenib monotherapy in treatment-naïve patients with advanced HCC ; of noteThe role of another immune-based combination including two ICIs, the PD-L1 inhibitor durvalumab and the anti-CTLA-4 antibody tremelimumab, has been explored in the HIMALAYA trial  21,22,2,222,23. From this point of view, this Special Issue welcomes papers exploring the current state of the art and future perspectives in the immunotherapy of HCC. The Special Issue will aim to assess key open questions in HCC immunotherapy, including preclinical studies, novel immunotherapies and immune-based combinations, biomarkers of response, experimental therapies, real-world experience with immune checkpoint inhibitors, and several other topics.