Magnetic domain structure and spin-dependent reflectivity measurements on cobalt thin films intercalated at the graphene/Ir(111) interface are investigated using spin-polarised low-energy electron microscopy. We find that graphene-covered cobalt films have surprising magnetic properties. Vectorial imaging of magnetic domains reveals an unusually gradual thickness-dependent spin reorientation transition, in which magnetisation rotates from out-of-the-film plane to the in-plane direction by less than 10° per cobalt monolayer. During this transition, cobalt films have a meandering spin texture, characterised by a complex, three-dimensional, wavy magnetisation pattern. In addition, spectroscopy measurements suggest that the electronic band structure of the unoccupied states is essentially spin-independent already a few electron-Volts above the vacuum level. These properties strikingly differ from those of pristine cobalt films and could open new prospects in surface magnetism. Just a decade after being isolated, graphene has attracted considerable attention in the scientific community. Studies on this material allowed the discovery of rich and fascinating phenomena12371317181920With its weak spin-orbit coupling and hyperfine interaction, graphene also offers new opportunities in nanomagnetism2526272829353637pz and Co 3d orbitals60 molecules are deposited on top of a Co thin film43If magnetism can be induced in graphene when contacted to a ferromagnet17181920Using spin-polarised low-energy electron microscopy and spectroscopy, we investigate in this work the in-plane to out-of-plane spin reorientation transition (SRT) that occurs upon Co intercalation between graphene and Ir(111), with a special focus on the determination of the surface magnetic anisotropy. The most striking result of our study is the observation of an unusually gradual thickness-dependent SRT: the canting angle the magnetisation vector makes with the surface normal is found to change by less than 10 degrees per additional Co monolayer, meaning that about 10 Co atomic layers are required to drag magnetisation into the surface plane. Analysis of this reorientation transition allows estimation of the second and fourth-order surface anisotropy terms, which both differ substantially from the values determined in pristine cobalt films. In particular, the second-order term is found to be unusually large, confirming that graphene favors perpendicular magnetic anisotropy. Besides, measurement of all three Cartesian components of the magnetisation vector during the SRT reveals that in-plane and out-of-plane magnetic domain patterns are characterised by different length scales that evolve differently when the cobalt thickness is increased. While in-plane domains show no change throughout the spin reorientation transition, meandering out-of-plane domains with well-defined, slowly decaying periodicity are observed when the cobalt film gets thicker. A complex three-dimensional spin texture is deduced from sets of magnetic images in graphene-covered cobalt films, in sharp contrast with what is found in pristine surfaces. Finally, spin-dependent reflectivity measurements suggest that spin-scattering asymmetry is suppressed when the energy of the incoming electrons becomes larger than a certain threshold value, regardless the thickness of the cobalt film.in situ, in the spin-polarised low-energy electron microscope (SPLEEM) available at the National Centre for Electron Microscopy of the Lawrence Berkeley National Lab. In a SPLEEM, an electron beam is directed at the sample in normal incidence and electrons that are backscattered from the surface are used for imaging. Because the energy of the incoming electrons is low, typically a few eV above the Fermi level of the material under investigation, the technique is surface sensitive and a few atomic layers are usually probed. The electron beam being spin-polarised, the technique is also sensitive to the surface magnetisation. The main strength of the technique is the capability to orient in any space direction the spin polarisation of the incident electron beam, thus allowing to probe unknown magnetic configurations. Moreover, since the energy of the spin-polarised electron beam can be tuned continuously, reflectivity measurements can provide useful information on the spin-split band structure of unoccupied electronic states4647All measurements were done −11 mbar range). An Ir(111) single crystal was used as a substrate and its surface was cleaned in a preparation chamber attached to the microscope, following a procedure based on repeated cycles of Ar+ ion sputtering and high temperature (1200 °C) flashes under oxygen (10−8 mbar). A last temperature flash (1200 °C) was done in the microscope chamber to remove the oxide layer. Graphene was grown by chemical vapor deposition, following a well-established procedure−8 mbar, typically for several tens of minutes), while keeping the substrate at about 600 °C, leads to the formation of a single layer of graphene, covering >99% of the Ir(111) surface, thanks to the self-limited mechanism involved in the ethylene decomposition4043404043504043515253The samples studied in this work were fabricated and imaged under ultra-high vacuum conditions /(I+ + I−), where I± is the reflected intensity for a spin polarisation ±P0, is a function of the incident energy. In most cases, the spin asymmetry changes in sign and amplitude depending on details of the unoccupied band structure of the material. Examples of energy-dependence of SPLEEM contrast can be found in previous literature55When a low-energy, spin-polarised electron beam is directed at a metal surface, part of the incident electrons enters the crystal and part of the incident intensity is backscattered. If the metal is ferromagnetic, the backscattered intensity depends on the relative orientation of the incoming spin polarisation and the direction of the local magnetisation within the material. This mechanism leads to a magnetic contrast in SPLEEM, which is used to image magnetic domain patterns. For common ferromagnetic metals, such as Fe, Co and Ni, the spin asymmetry When the same surface is graphene-terminated, the spin asymmetry is drastically modified. In particular, it shows a peculiar feature: while the spin asymmetry first increases as the incident energy becomes larger than the surface work function, it quickly decreases to become negligible above 5 eV, and up to at least 20 eV . Within this energy window, the graphene-covered Co surface seems non magnetic. Although the Co surface is of course ferromagnetic, above a certain threshold energy, the incident spin-polarised electrons do not suffer substantial spin-dependent elastic or inelastic collisions.This suppression of the spin asymmetry above a few electron-Volts is thickness-independent. Indeed, comparing the spin asymmetry of 3 and 9 ML-thick Co film intercalated between graphene and Ir does not show clear differences see . Our expIn the following, we study the spin reorientation transition (SRT) that occurs when the amount of intercalated cobalt is increased, and we compare it to the SRT observed in pristine cobalt. For thin-enough films, magnetisation is out-of-plane, while it is in-plane for thicker films. To investigate how magnetisation rotates, we image magnetic domain patterns for different cobalt thicknesses in the three Cartesian coordinates. From the set of SPLEEM images, we deduce the local direction of the magnetisation vector as a function of Co thickness. SPLEEM measurements for Co films intercalated between graphene and Ir(111) are reported in θ and φ, as illustrated in the inset of M thus continuously rotates from θ = 0° to θ = 90°. In the canted phase, the θ values can be extracted from 59The magnetisation vector can be represented in terms of the two spherical angles The SRT of our Co films can be described by the anisotropy flow model, in which the influence of both the surface and the interface on the magnetisation is accounted for by their respective phenomenological anisotropy constantsnd-order and the shape magnetic anisotropies, and K4 is the 4th-order term of the magnetocrystalline anisotropy. Minimising E with respect to θ gives three possible equilibrium states: θ = 0°, θ = 90° and θ dependence of the Co film thickness t, we express K2 and K4 by the phenomenological ansatzwhere Ks2 and Ks4 are the sum of two terms associated with the Co/Ir(111) and graphene/Co interfaces. In this expression, Kb2 and Kb4 stand for the bulk anisotropy values. Hence, the SRT is delimited by two critical thicknesses:Note that the interface anisotropy constants tc1 < tc2, then the θ dependence of the Co thickness reads:If tc2 − tc1 and where Δ = Ms = 1.44 × 106 A/m, Kb2 = 5.0 × 105 J/m3 and Kb4 = 1.25 × 105 J/m3)Ks2 and Ks4. For bare Co, we find Ks2 = 0.64 mJ/m2 and Ks4 = −0.03 mJ/m2, which are comparable to the values found for Co films on Au(111) or Pd(111)58Ks2 = 2.20 mJ/m2 and Ks4 = 0.16 mJ/m2. Considering that nd-order anisotropy term, the 4th-order term (Ks4) is found to be positive, while it is usually negative in the case of bare Co film in contact with Ir(111), Au(111), Pd(111) or Pt(111)58Ks4 determines the upper thickness limit tc2 of the SRT, its positive value in graphene-covered Co is associated to this exceptionally large thickness range.Fitting our data with We note that in-plane and out-of-plane magnetic domains show distinct patterns: while in-plane domains are large with complex symmetry see , out-of-θ averaged over a set of SPLEEM images. In the following, we measure θ, pixel by pixel, to get a local estimate of the canting angle and to determine how it evolves within a given field of view. 6667In the previous section, we determined the canting angle A is the exchange stiffness constant. The limit case of uniform (non-twisted) magnetisation corresponds to ρ ≈ 0 or tan (ρ)/ρ ≈ 1. For the graphene/Co interface, ρ ≈ 0.28 giving tan ρ/ρ ≈ 1.03 M can be assumed to be uniform across the Co film.We could wonder whether the magnetisation is uniform within the film thickness or if it also curls in the direction perpendicular to the surface. In fact, spin-twisted configuration may arise in some systems in which the spins at the outermost atomic layer feel a strong anisotropy and remain aligned along the surface normal, while those in the middle of the film are tilted towards the film plane to minimise the magnetostatic energy6969in situ grown graphene/Co/Ir(111) heterostructures. Compared to bare Co/Ir(111) films, we found that the graphene capping layer drastically affects the spin texture and the spin-dependent band structure of the intercalated Co film. Similarly to what has been reported recently when PcCo molecules are deposited on a ferromagnetic surfaceUsing the capabilities of SPLEEM microscopy to probe the band structure of unoccupied electronic states and to resolve spin configurations in all space directions, we investigated the magnetic properties of How to cite this article: Vu, A. D. et al. Unconventional magnetisation texture in graphene/cobalt hybrids. Sci. Rep.6, 24783; doi: 10.1038/srep24783 (2016).


We therefore propose that surface detachment of membrane invaginations results from an ability of CADs to interfere with PIP2 interactions with cytoskeletal or BAR domain proteins. This establishes a detubulating action of a large class of pharmaceutical compounds.Several cell types develop extensive plasma membrane invaginations to serve a specific physiological function. For example, the megakaryocyte demarcation membrane system (DMS) provides a membrane reserve for platelet production and muscle transverse (T) tubules facilitate excitation:contraction coupling. Using impermeant fluorescent indicators, capacitance measurements and electron microscopy, we show that multiple cationic amphiphilic drugs (CADs) cause complete separation of the DMS from the surface membrane in rat megakaryocytes. This includes the calmodulin inhibitor W-7, the phospholipase-C inhibitor U73122, and anti-psychotic phenothiazines. CADs also caused loss of T tubules in rat cardiac ventricular myocytes and the open canalicular system of human platelets. Anionic amphiphiles, U73343  and a range of kinase inhibitors were without effect on the DMS. CADs are known to accumulate in the inner leaflet of the cell membrane where they bind to anionic lipids, especially PIP It is not surprising therefore that altered T tubule structure is emerging as a likely contributory factor to heart failure in several disease models1011Adaptation of cellular membrane morphology allows specialized cells to perform dedicated functions. For example, photoreceptors develop surface membrane invaginations or internal membrane disks to increase the surface area for expression of opsins and other proteins, thereby increasing sensitivity to light1245612 circulating platelets, which have a limited lifespan of 5–9 days192122Another important surface invagination system is the demarcation membrane system (DMS) of megakaryocytes, large polyloid marrow cells responsible for producing blood platelets13141516Despite their importance, the control and stability of plasma membrane invagination systems is poorly understood. Previous measurements of the megakaryocyte DMS have mainly relied on EM studies which are time-consuming, difficult to quantify and require measurements in fixed tissues192+ signalling, most of which had no effect on the percentage dye entering the megakaryocyte DMS  within the surface-connected tubules of this membrane invagination system see . When ex15cyte DMS . Howevercyte DMS . This efcyte DMS . W-7 waste DMS 26. Moreovete DMS 26. Taken t2 after 150 μM W-7 , likely reflects a small amount of surface membrane blebbing or micovilli14In untreated megakaryocytes, the impermeant, reversible membrane indicator FM 1–43 stained the DMS extensively through the extranuclear volume, as shown previously for the irreversible styryl lipophilic dye di-8-ANEPPS252+ (ionomycin or BAPTA)  . TogetheH-pyrrole-2,5-dione) (33β)-3-Methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-2,5-pyrrolidinedione) (2) turnoverAnother inhibitor within our screen that prevented extracellular HPTS access to the DMS tubules is the phospholipase-C (PLC) inhibitor, U73122 (1-amino]hexyl]-15-dione) . A prope5-dione) . In contdione) 33. FurtherWe were also interested in whether reagents that collapse the DMS exert similar effects on specialised membrane invagination systems in other cell types. Although cardiac myocyte T tubules have a similar or slightly larger diameter than the DMS815212 is a major target for CAD binding in the membrane392, and PIP3, however these are less abundant compared to PIP2 under resting conditions2 plays widespread roles in recruiting proteins to the membrane via electrostatic docking interactions and pleckstrin homology (PH) domains, including scaffolding molecules that link the plasma membrane to the cytoskeleton402 through polycationic regions and have diverse roles in cellular architecture and function through their ability to curve membranes40422 in DMS formation2 is the submembranous cytoskeletal protein spectrin, which can bind through its PH domain and is also important for DMS formation2 which interferes with the ability of this phosphoinositide to interact directly or indirectly with the cytoskeleton in manner that is regulated by BAR domain proteins. This can explain the W-7-induced movement of the peripheral plasma membrane away from the underlying DMS, along with DMS collapse P2. Future studies using megakaryocytes derived in vitro will also need to ensure that the properties of the DMS within cultured cells match those of the native tissue. In our initial studies of standard megakaryocyte culture systems, membrane capacitance measurements indicated considerably lower levels of DMS in cultured megakaryocytes compared to similar size or even smaller cells obtained directly from the marrow .Cationic amphiphilic drugs (CADs) represent one of the largest classes of pharmaceutical compounds, which are used as anti-depressants, anti-malarial, anti-bacterial, anti-arrhythmic and cholesterol-lowering reagentscollapse . Collapss U73122 . Further2 in DMS formation, the importance of this lipid in T tubule formation is unclear. However, in myotonic dystrophy, altered skeletal muscle T tubule formation results from expression of a mispliced variant of Bin1 that loses its ability to bind to phosphoinositides2 shows a periodicity that coincides with T tubule location2 depletion leads to loss of T tubules2 contributes to the function of this scaffolding protein in the heart, including tubule morphology and optimal positioning of voltage-gated Ca2+ channels near ryanodine receptors4552In contrast to the direct suggestion of a role for PIP2 by such drugs may also interfere with other cellular roles dependent upon this phosphoinositide such as endocytosis, exocytosis and regulation of ion channels and transporters406364662122Phenothiazines such as trifluoperazine and chlorpromazine are used as anti-psychotics on the basis of their action at D2 receptors303155565761In conclusion, this study provides evidence for a key role of negatively charged lipids in the stability of specialised membrane invagination systems such as muscle T tubules and megakaryocyte demarcation membranes. The ability of cationic amphiphiles to detach T tubules and the DMS from the cell surface provides a useful tool for the study of these surface invagination systems, however it should also be considered in the design of CADs as therapeutic treatments.U73343 and U73122 were from Tocris Bioscience . Staurosporine was from Enzo Life Sciences . KT 5720 was from Santa Cruz Biotechnology . Jasplakinolide and LIM kinase inhibitor 1 LIMKi3 were from Calbiochem . FM 1-43 was from Invitrogen . Glutaraldehyde, 25% EM Grade was from Agar Scientific . All other reagents, including HPTS were from Sigma-Aldrich .egakaryocytes and ventricular myocytes were isolated from adult male Wistar rats (300-400 g) following euthanasia in accordance with the UK Animals Scientific Procedures Act. Cells were used within 12 hours of dispersal from the native tissue. Femoral and tibial marrow cells were extracted as described in detail elsewhere2, 1 mM CaCl2, 10 mM HEPES, 10 mM glucose, pH 7.35 with NaOH. Ventricular myocytes were prepared using retrograde perfusion via a Langendorff cannula as described in detail elsewhere2+-free Tyrode’s solution  and rapidly cannulated via the aorta. After perfusion for 6 minutes with 0CaTS, the perfusate was switched to 0CaTS with an enzyme mix  and then exchanged for 2 mM Ca2+ Tyrode’s solution (2CaTS) on identification of rod-shaped cardiomyocytes. The heart was then cut down, and cardiomyocytes isolated from the tissue in a shaking water bath. Cells were resuspended in fresh 2CaTS, filtered to remove undigested tissue and resuspended in fresh 2CaTS. For confocal recordings, myocytes were immersed into NPS with 1 mM EGTA that had an estimated free Ca2+ of 50 nM  to avoid spontaneous contractions, prior to addition of FM 1–43 (8 μM). Washed human platelets were prepared using a previously established method that minimizes spontaneous activationg for 5 minutes to obtain platelet-rich plasma (PRP) which was treated with apyrase (0.32 U/ml) and aspirin (100 μM) to reduce spontaneous activation by released nucleotides and thromboxaneA2, respectively. Washed platelet suspensions were prepared by centrifugation of PRP at 350 g for 20 minutes and resuspension in nominally Ca2+-free NPS containing 0.32 U/ml apyrase but without aspirin. Human erythroleukaemia (HEL) cells were sourced and cultured as described elsewhereMhttp://imagej.nih.gov/ij/, 1997–2012). In order to avoid uptake of fluorescent indicators by endocytosis, all experiments were conducted at room temperature and measurements made within 5 min of exposure to the fluorophore. For wash experiments, the reagents were removed by multiple exchange of the extracellular medium and indicators added after 2 or 120 minutes. HPTS was excited at 488 nm and emission collected at 500–600 nm. FM 1–43 (8 μM) was excited at 488 nm and emission collected at 550–650 nm.Confocal fluorescence imaging was conducted on an Olympus IX81 inverted microscope equipped with a FluoView1000 laser scanning module . All experiments used a 60x oil immersion lens  and a confocal slice thickness of 1.25 μm. Confocal images were visualized and analysed using ImageJ software .We used standard confocal fluorescence imaging to measure entry of an extracellular impermeant fluorescence indicator  into tubules of the DMS as a means of quanitifying this plasma membrane invagination system. This approach represents an extension of previous work with 2-photon fluorescence microscopy2, 1 mM MgCl2, pH 7.35 with HCl), washed 3 times and postfixed for 90 minutes in 1% aqueous osmium tetroxide with 1.5% potassium ferricyanide. After further washing, the samples were stained for 60 minutes in 1% aqueous uranyl acetate, washed, pelleted, and embedded in 3% agar gel. Once set, the agar pellets were cut into 1 mm cubes, serially dehydrated by ethanol, and then transferred through a series of pure ethanol mixed with an increasing concentration of Spurr’s modified resin . After several exchanges in pure resin, the samples were polymerised for 16 hours at 60 °C. Sections of approximately 90 nm thickness were cut using a Reichert Ultracut E ultramicrotome , collected onto copper mesh grids and counterstained for 2 min in Reynold’s Lead citrate. Sections were viewed on a JEM-1400 TEM (JEOL UK) with an accelerating voltage of 80 kV and images captured using a Megaview III digital camera with iTEM software . The OCS was quantified as the percentage cytoplasmic area occupied by all vacuolar regions within an individual platelet.After treatment with reagent or vehicle control, suspensions of marrow cells or human platelets were fixed for 60 minutes in 1.25% glutaraldehyde in 0.1 M sodium cacodylate  under the control of Clampex v6.0 electrophysiological software (Molecular Devices). Currents were low-pass filtered (5 kHz) and acquired at a rate of 50 kHz. Capacitative current transients were recorded in response to 60 ms duration −10 mV voltage steps from a holding potential of −80 mV and membrane capacitance calculated from the integral of the current as described in detail elsewhereP > 0.05; ns), or significant at P < 0.05 (*), P < 0.01 (**), P < 0.001 (***) and P < 0.0001 (****).Data were presented as the mean ± SEM and significance was determined using one way ANOVA with Bonferroni post-testing, with the exception of changes in platelet OCS area which was assessed using Student’s unpaired T test with Welch’s correction (GraphPad Prism 6). The level of significance is indicated as not significant .


Graphene and its bilayer structure are the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and photonics. Their realistic applications in emerging nanoelectronics usually call for thermal transport manipulation in a controllable and precise manner. In this paper we systematically studied the effect of interlayer covalent bonding, in particular different interlay bonding arrangement, on the thermal conductivity of bilayer graphene using equilibrium molecular dynamics simulations. It is revealed that, the thermal conductivity of randomly bonded bilayer graphene decreases monotonically with the increase of interlayer bonding density, however, for the regularly bonded bilayer graphene structure the thermal conductivity possesses unexpectedly non-monotonic dependence on the interlayer bonding density. The results suggest that the thermal conductivity of bilayer graphene depends not only on the interlayer bonding density, but also on the detailed topological configuration of the interlayer bonding. The underlying mechanism for this abnormal phenomenon is identified by means of phonon spectral energy density, participation ratio and mode weight factor analysis. The large tunability of thermal conductivity of bilayer graphene through rational interlayer bonding arrangement paves the way to achieve other desired properties for potential nanoelectronics applications involving graphene layers. Graphene, the first two-dimensional atomic crystal available to us, has attracted great attentions due to its supreme mechanical4ab initio total energy calculations have identified that the interlayer sp3 bonds in graphite can be formed by femtosecond-laser excitation3 bonds can lead to monotonic reduction of the thermal conductivity of bilayer graphene as a function of interlayer sp3 bond concentration. However, in fact, interlayer bonding  simulations, we investigated the effect of interlayer sp3 bonded bilayer graphene structures, we first investigated the size effect on the thermal conductivity of regularly bonded bilayer graphene with interlayer sp3 bonding density of 6.25%, as shown in 3 bonded bilayer graphene structures we studied. Note that the thermal conductivities are different for armchair and zigzag directions, which should be due to the difference of the detailed topological arrangement of the interfacial bonding in armchair and zigzag directions. The thermal conductivity of the regularly bonded bilayer graphene with interlayer sp3 bonding density of 6.25% converges for simulation box size of ~5 nm and 10 nm for armchair and zigzag direction, respectively. This is comparable with the convergence size of 10 nm for single layer graphene from our separate simulation run. Note that the results shown in To get a converged size for calculating the thermal conductivity of the interlayer sp3 bonding, the thermal conductivity of randomly bonded bilayer graphene decreases monotonically. However, the thermal conductivity of regularly bonded bilayer graphene changes non-monotonically. Especially, there are two obvious peaks at the interlayer bonding densities of 6.25% and 12.5%. The results suggest that the thermal conductivity of sp3 bonded bilayer graphene depends on not only the bonding density, but also the detailed topological arrangement of the interfacial bonding. The thermal conductivity of sp3 bonded bilayer graphene falls in a broad range between several tens and a few hundred W/mK, indicating that the interlayer bonding is an effective way to manipulate the thermal transport properties of bilayer graphene, which could be very beneficial for varieties of potential applications.The thermal conductivity of bilayer graphene as a function of interlayer bonding density is presented in Researchers have shown that covalent bonds will influence the thermal conductivity disregard whether there is a second layerIn order to explore the mechanisms for the non-monotonic thermal conductivity results of the regularly bonded bilayer graphene and the generally higher thermal conductivity as compared with the randomly bonded structure, we investigated the phonon mode dependent thermal conductivity of bilayer graphene by performing spectral energy density (SED) analysis. First, the phonon normal modes are obtained by16where the eigenvector and the phonon lifetime is obtained by fitting the Lorentzian function2021ν is the phonon branch, κα denotes the thermal conductivity in α direction, cph is phonon volumetric specific heat calculated by kB is the Boltzmann constant, V is the system volume, υg,α is α-component of the phonon group velocity, τ is the phonon lifetime. Note that the above phonon SED method has been successfully used by us to perform the phonon mode analysis for a wide variety of nanostructures, e.g., two-dimensional silicenewhere The frequency dependent phonon lifetimes of bilayer graphene (interlayer bonding density of 6.25%) with randomly and regularly bonded structures are compared in 3 bonded bilayer graphene (not shown for brevity) show the obviously different feature between the randomly and regularly bonded bilayer graphene. To identify the phonon frequency dependent relative contributions of the overall thermal conductivity, we also calculated the accumulated thermal conductivity percentage as a function of frequency for both the randomly and regularly bonded bilayer graphene, as shown in 2627283 bonds would lead to dramatic reduction in phonon MFP. Combining Using the above definition for thermal conductivity, we obtained four results of the thermal conductivity of bilayer graphene with interlayer bonding density of 6.25%: We show in Furthermore, the comparison of the frequency dependent phonon lifetime and square of phonon group velocity of regularly bonded bilayer graphene between interlayer bonding density of 6.25% and 15% is shown in pλ, defined for each mode λ as3031323334Furthermore, we analyzed the phonon mode localization by calculating the participation ratio i sums over all the atoms studied, α is a Cartesian direction and sums over x, y, and z, εiα,λ is the vibrational eigenvector component corresponding to the λth normal mode, and N is the total number of atoms. The participation ratio describes the fraction of atoms participating in a particular phonon mode and, hence, it varies between O(1) for delocalized states to O(1/N) for localized states. 3 bonded bilayer graphene between random and regular bonding configuration with the same interlayer bonding density of 6.25%. It can be seen that when the phonon frequency is lower than 2.5 THz, the participation ratio for the randomly and regularly bonded bilayer graphene are nearly the same, while for the higher frequency, the regularly bonded bilayer graphene has a significantly larger participation ratio than the randomly bonded structure throughout the whole frequency range, suggesting that the high frequency phonon modes dominate the enhancement of the thermal conductivity of regularly bonded bilayer graphene compared to the randomly bonded bilayer graphene. This is consistent with results of 3233where j (atoms) and is alternatively restricted to the sp2 bonded C atoms and the sp3 bonded C atoms. Consequently the sum of the mode weight factors in the whole bilayer graphene structure should be equal to unity, i.e.,2 bonded C atoms and vice versa. 3 bonded bilayer graphene between random and regular bonding configuration with the same interlayer bonding density of 6.25%. Unlike the phonon participation ratio, there is no obvious difference for the mode weight factors of sp2 and sp3 bonded C atoms, suggesting that the phonon mode weight factor may only depend on the interlayer bonding density, not on the detailed interfacial topological arrangements.where the prime denotes that sum over 3 bonded C atoms is larger than that of 6.25% interlayer bonding density. The above mode weight factor results combining with that of To analyze the mechanisms for the non-monotonic interlayer bonding density dependent thermal conductivity of the regularly bonded bilayer graphene, we further calculated the phonon participation ratio and mode weight factor for the regularly bonded bilayer graphene with different bonding density. The comparison of the phonon participation ratio between bonding density of 5%, 6.25%, 8.75%, 12.5% and 15% is shown in 3 bonding density on the thermal conductivity of bilayer graphene, especially the results of the randomly and regularly bonded bilayer graphene structures were compared in detail. The thermal conductivity of randomly bonded bilayer graphene decreases monotonically with the increase of interlayer bonding density, which follows the same trend as that obtained in literature. However, for the regularly bonded bilayer graphene structure, we observed the unexpectedly non-monotonic interlayer bonding density dependence of thermal conductivity. The phonon spectral energy density, participation ratio and mode weight factor analysis were performed to explore the underlying mechanism for this counter-intuitive phenomenon. We found that the lifetimes of low-frequency (<5 THz) phonons for randomly and regularly bonded bilayer graphene are nearly the same, which is consistent with the general knowledge that the low-frequency phonons are not sensitive to the detailed interfacial bonding configuration, considering that the characteristic size of the covalent bonding is on the order of only a few angstroms, which is much shorter than the typical wavelength of the low frequency phonons. In contrast, for medium-frequency (5–30 THz) and high-frequency (30–50 THz) phonons the lifetimes in the regularly bonded bilayer graphene are greatly larger than that of randomly bonded structure, especially for the medium-frequency phonon modes which have a rather large contribution to the higher thermal conductivity of the regularly bonded bilayer graphene than the randomly bonded structure. By evaluating the relative importance of the contributions of phonon lifetime and square of phonon group velocity, we conclude that, compared with random bonding, the much higher thermal conductivity of the regularly bonded bilayer graphene is mainly due to the large enhancement in the group velocity of the phonon modes in the medium-frequency range (5–30 THz). In addition, we observe that the thermal conductivity of bilayer graphene depends on not only the interlayer bonding density, but also the detailed topological arrangement of the interlayer sp3 bonds. We find that, comparing the regularly bonded bilayer graphene between different bonding densities, the change of phonon lifetime, instead of the change of group velocity, is the main reason for the non-monotonic thermal conductivity dependence. We also characterize the phonon mode localization by calculating the participation ratio and provide evidence that the participation ratio at different bonding density resembles the non-monotonic dependent thermal conductivity. Again this can be correlated with their atomic structure, where the regular bonding density of 6.25% and 12.5% has more homogeneous sp3 bonding than that of other bonding densities, which should be responsible for their different phonon band structure. We believe that our analysis provides a comprehensive understanding of the underlying mechanism and the abnormal phenomenon identified in this study can also be extended to other similar bilayer and multilayer structures, that is, the thermal transport properties of bilayer and multilayer structures can be effectively modulated by tuning the detailed arrangement of the interlayer bonding. Other physical properties like electronic and optical properties may also be tuned in the same way and thus such interfacial bonding engineering could offer a robust approach to target desired properties for potential electronic, thermoelectric, photovoltaic, and opto-electronic applications.To summarize, equilibrium molecular dynamics simulations were performed to investigate the effect of interlayer spn × n supercells with each unit cell constructed by a bilayer honeycomb lattice and composed of 320 carbon atoms, where n is ranging from 1 to 6 in our simulations. The structures of a unit cell of bilayer graphene with different interlayer sp3 bonding are shown in 3 bonding. To form the sp3 bonded bilayer graphene structures shown in NPT (constant pressure and temperature) ensemble for 100000 steps. Thirdly, the fix on the bonded atoms is removed and the entire system is relaxed with NPT ensemble for additional 1000000 steps. Finally, the stable bilayer graphene with inter-layer bonding is achieved. For each model system we have carefully checked the topography and bonding density of the interlayer bonding before and after structure relaxation, and also before and after the later on EMD simulation of calculating thermal conductivity. For all cases we confirm that there is no change for the topological configurations of the interlayer bonds and the interlayer bonding density due to temperature fluctuations. To investigate the effect of the topological configuration of the interlayer bonding on the thermal transport in bilayer graphene, here we constructed both the randomly and regularly distributed bonding structures. In our simulations, we only considered the interlayer bonding density lower than 15% but the thermal conductivity of nanostructures is very sensitive to the component of the structuresOur model system of bilayer graphene sheets consist of x and y directions (in-plane), and a free boundary condition is used in z direction (out-of-plane). In the first stage of the MD simulations, we relaxed the system at constant atmospheric pressure and room temperature (300 K) for 0.1 ns, using the Nosé-Hoover thermostat and barostat45NPT relaxation, we continued to relax the system with NVT (constant volume and temperature) ensemble for 0.1 ns using the Nosé−Hoover thermostat and NVE (constant volume without thermostat) ensemble for additional 0.1 ns.The adaptive intermolecular reactive empirical bond order (AIREBO) potentialFollowing equilibration, the thermal conductivity of bilayer graphene was estimated by the Green-Kubo method47V is volume, kB is the Boltzmann constant, T is temperature, where Ei is the total energy  of atom i, i, i defined as44where withα and β denote the x, y or z direction. The three terms in the definition of Sαβ define the contribution from two-body, three-body and four-body interaction, respectively. The thickness of bilayer graphene was chosen as 0.68 nm in calculating the system volume, which is equal to two times of the van der Waals diameter of the C atomwhere We used a unit cell of bilayer graphene structure with 2.13 nm × 1.97 nm (320 atoms) as the input for the phonon normal mode calculation. And limited by the large unit cell, we only used a 4 × 4 supercell (5120 atoms) for the phonon spectral energy density analysis. To achieve enough frequency range for bilayer graphene, we sampled the atomic velocities with a time interval of 9 fs, and the max phonon frequency we can achieve is about 55.56 THz which is a little larger than the max frequency of bilayer graphene. It is worth pointing out that, strictly speaking, there is no periodicity for the randomly distributed bonding structure and the wavevector-related phonon information cannot be obtained for the phonon spectral energy density calculations, here we just distributed the atoms irregularly in the unit cell to achieve the randomly bonded bilayer graphene structure.How to cite this article: Zhang, X. et al. Robustly Engineering Thermal Conductivity of Bilayer Graphene by Interlayer Bonding. Sci. Rep.6, 22011; doi: 10.1038/srep22011 (2016).


In this paper, COOH+/graphene was prepared by modified Hummers' method and implanted by COOH+ ions. The structure and surface chemical and physical properties of COOH+/graphene were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurement. Systematic evaluation of anticoagulation, including in vitro platelet adhesion assays and hemolytic assays, proved that COOH+/graphene has significant anticoagulation. In addition, at the dose of 5 × 1017 ions/cm2, COOH+/graphene responded best on platelet adhesion, aggregation, and platelet activation.Graphene may have attractive properties for some biomedical applications, but its potential adverse biological effects, in particular, possible modulation when it comes in contact with blood, require further investigation. Little is known about the influence of exposure to COOH Graphene, the thinnest two-dimensional 2D) allotrope of carbon, is a novel nanomaterial with a single sheet of carbon atoms packed in a perfect honeycomb structure ,2. It isD allotro+ ions were implanted into graphene, instead of MWCNTs, to achieve a better anticoagulant material. Except toxicological and ecological risks, anticoagulation is a prerequisite for the use of graphene in biological or medical applications. It is necessary to evaluate the anticoagulant risks of graphene [Enhancement of the surface properties of medical implants for improved integration into their biological environment is a major focus of current biomaterial research . Ion impgraphene . Rabbit + implantation-MWCNTs when compared with pristine MWCNTs [+ implantation introduced functional carboxyl groups into the surfaces of materials. The existence of hydroxy and other oxygen-containing functions was thought to be able to induce the hydrophilicity of MWCNTs [+ implantation could also enable it to exhibit attractive anticoagulation [+/graphene shows better anticoagulation than pristine graphene for platelets and red blood cells. In addition, the content of carboxyl group in COOH+/graphene affected its anticoagulation. Compared with our earlier works, the ion implantation in this study is in great dose and high purity. The findings presented in this study also throw light into that COOH+/graphene may serve as an excellent candidate material for potential biomedical applications in various areas.Some previous investigation demonstrated that the anticoagulation of MWCNTs was greatly influenced by surface functional groups. In our previous work, we focused on cell and blood compatibility of MWCNTs by different functional groups -20. The e MWCNTs ,16. The f MWCNTs ,21. To ggulation . In the +/graphene were as follows: in the first step, graphene was ultrasonically dispersed in an organic solvent called 1-methyl-2-pyrrolidinone (NMP) for several hours to make it dissolved evenly. The concentration of graphene was 0.5 mg/cm2. Then, the graphene solution was sprayed by airbrush with Ar flow on the heated (100°C) SiO2 wafers which were used as support materials for graphene. Next, baking was done for 3 h (250°C) under argon protection to remove the organic solvent completely [+ ions were implanted on graphene using a Kaufman-100 implanter . The COOH+ was generated from methanoic acid, which would be ionized by heating in water bath and bombardment of accelerated electrons in ion source [2 [−2 Pa. The different doses of COOH+/graphene  were obtained by adjusting the irradiation time.The graphene powders were produced according to modified Hummers' method -26. Detampletely ,27. Finan source ,11,13. Tn source . The beaource [2 ,29, and +/graphene was analyzed with sessile drop method. Deionized water was dropped onto the sample surface, and images were recorded using the CAM KSV021733 optical contact-angle inclinometer . The process lasted for ten times, and the results came from the average of these data. Scanning electron microscope (SEM) imaging was performed using a field-emission scanning electron microscope . X-ray photoelectron spectroscopic (XPS) measurements were performed on a Kratos Axis Ultra Al  X-ray photoelectron spectrometer .The surface hydrophilicity of graphene and COOHPlatelet-rich plasma (PRP) was prepared by centrifuging the fresh blood with anticoagulant at 1,200 rpm for about 15 min. The fresh blood was withdrawn from a healthy rat. Additionally, PRP was put immediately into 24-well culture plate which all the samples were placed in them. The 24-well culture plates were placed immediately in the incubator at 37°C for 30 min. The samples were then fixed in glutaraldehyde, dried with critical point drying, and plated for examination of SEM.+/graphene in vitro, we measured the absorption of free hemoglobin (Hb) at 545 nm in the plasma. The samples were immersed in the physiological salt water and placed in the water bath at 37°C for 30 min. The diluted blood  was successively added into the solution of all groups. After incubation at 37°C for 60 min, the blended liquid was centrifuged at 1,000 rpm for 5 min. The supernatants were transferred into the cuvettes, and the optical density (OD) values were measured at 545 nm with a spectrophotometer. Hemolysis ratio was calculated by the formula in Figure A, B, and C are the average absorbance of samples, negative controls, and positive controls, respectively [In order to investigate the hemolysis of pristine graphene and COOH+/graphene. The transparent nature of the folded crystalline layers is clearly shown in this figure. Graphene and COOH+/graphene exhibit typical wrinkled structure, indicating the high surface/volume ratio and two-dimensional structure of graphene. And COOH+/graphene show more wrinkles with the COOH+ dose increasing. The most remarkable effect of carboxyl ion implantation also can be seen in the contact angle measurements as shown in Figure 17 ions/cm2 leaves a contact angle of 20° ± 2°. COOH+/graphene with 5 × 1017 ions/cm2 leaves a contact angle of 4° ± 2°. COOH+/graphene with 1 × 1018 ions/cm2 leaves a contact angle of 16° ± 2°. But the droplet on pristine graphene's surface remains highly spherical with the angle of 70° ± 2°, which implies that the pristine graphene is more hydrophobic than COOH+/graphene. As we know, graphene as well as other carbon nanostructures are naturally hydrophobic, so surface wettability is highly improved by COOH+ ion implantation. And the materials' surfaces are rich in oxygen after carboxyl ion implantation. Surface hydrophilia may have an effect on anticoagulation property because the initial phase of connection affects the contacts between blood and materials through various forces and adsorbing sundry proteins [+/graphene is an oxygen-containing graphene derivative with partial breakage of sp2-sp2 bonds into sp3-sp3 bonds for inserting some pendent groups . These functional groups facilitate the interaction between the host solution and implanted samples. It gives us much inspiration to realize that COOH+ ion implantation may bring great advantages for biomaterials to improve their anticoagulation properties [Figure proteins . COOH+/goperties .Figure 2+/graphene are presented in Figure +/graphene are different as displayed in the figure. COOH+/graphene shows distinguished COOH+ signal. The oxygen-related functional groups such as hydroxyl (C-O), carbonyl (C = O), and hydroxy (C-OH) were present in COOH+/graphene, as O content increases from 6.97 atm.% for pristine graphene  to 10.In vitro platelet adhesion testing is carried out to study the quantity, morphology, aggregation, and pseudopodium of the adherent platelets [+/graphene are shown in Figure +/graphene with 1 × 1017 ions/cm2 > COOH+/graphene with 1 × 1018 ions/cm2 > COOH+/graphene with 5 × 1017 ions/cm2. It is clear that the number of platelets on the COOH+/graphene is lower than that on the pristine graphene, and the number of adhered platelets decreases by COOH+ ion implantation in graphene, which performs preferable anti-adhesive capacity for COOH+/graphene. The value of COOH+/graphene with 5 × 1017 ions/cm2 is even lower than that of COOH+/graphene with 1 × 1018 ions/cm2. Comprehensively considering the results of both platelet adhesion and water contact angle assays, the platelet numbers adhering to the surface reduce obviously as surface wettability increases. The enhanced wettability of both functionalized graphene results in the reduction of platelet adhesion, which may lead to the improvement in anticoagulation. Figure +/graphene, as shown in Figure +/graphene has much better anticoagulation than pristine graphene. Nevertheless, COOH+/graphene show slightly thrombogenicity at a fluence of 1 × 1018 ions/cm2. Thrombogenicity occurring on the material surface in contact with blood is a complicated process. The surface free energy has an important effect on the process, particularly for some hydrophilic polymers that show less platelet activation. Compared with pristine graphene, COOH+/graphene with 1 × 1017 ions/cm2, 1 × 1018 ions/cm2, and 5 × 1017 ions/cm2 shows the lowest platelet aggregation and activation, although some platelets exhibit the slight activation  cann than 5% . The des than 5% . Slight  than 5% . And aft+ ion implantation while microstructural aspects, microstructure, and valence bond were systematically investigated. The interaction of red blood cells and platelets with pristine graphene and COOH+/graphene were investigated and compared detailedly. Three kinds of COOH+/graphene were shown to exhibit lower platelet adhesion, aggregation, and platelet activation than pristine graphene under the same conditions, especially for the COOH+/graphene with 5 × 1017 ions/cm2. No significant toxicity effects could be found on COOH+/graphene. The COOH+/graphene showed an observable improvement in anticoagulation as the COOH+ ion was implanted. This study demonstrated superior anticoagulation of COOH+/graphene with 5 × 1017 ions/cm2 as promising and effective biomedical material for biomaterial industry.We have shown here that functionalized graphene was successfully acquired by COOH


Moreover, the sensor is capable of detecting MB over broad concentration ranges from 1 nM to 100 μM. Therefore, AgNPs/GF is a highly promising SERS substrate for detection of chemical substances with ultra-low concentrations.In this work, a novel platform for surface-enhanced Raman spectroscopy (SERS)-based chemical sensors utilizing three-dimensional microporous graphene foam (GF) decorated with silver nanoparticles (AgNPs) is developed and applied for methylene blue (MB) detection. The results demonstrate that silver nanoparticles significantly enhance cascaded amplification of SERS effect on multilayer graphene foam (GF). The enhancement factor of AgNPs/GF sensor is found to be four orders of magnitude larger than that of AgNPs/Si substrate. In addition, the sensitivity of the sensor could be tuned by controlling the size of silver nanoparticles. The highest SERS enhancement factor of ∼5 × 10 The LSP wavelength compression ratio (λ/λsp whereλsp = LSP wavelength) due to 2D confinement of LSP on graphene surface could be in the range of 40 ~ 70The rise of graphene has opened up many promising applications in various fields due to intriguing relativistic properties of graphene such as massless fermion dispersion, high electron mobility, high conductivity, etc. Recently, there are numerous articles claiming that SERS on graphene could be greatly enhanced in comparison with other substrates. Wang 2 detection at very low concentration67Graphene is also a promising material for chemical sensing due to its excellent physical, chemical and electrical properties including large effective surface area, high electron transfer capability and good chemical stability. For example, electrochemical sensors based on microporous three-dimensional 3D) graphene foam (GF) has demonstrated excellent chemical sensing performances with high sensitivity, low detection limit and good stabilityD graphenAccording to Kneipp9ε0 and ε are vacuum and metallic-nanomaterial dielectric constants, respectively, d is the distance from analyte to silver nanoparticle surface, r is the radius of the metallic nanoparticle, E0 are outgoing (enhanced) and incoming electric field intensity, respectively.where PG, the electric field on graphene (EG) will be given byThe EM enhancement will be analyzed using the LSP model on graphene surface where plasmonically metallic sphere is placed onto the graphene surface as depicted in ω = induced dipole frequency and c = light velocity. Assuming that the graphene response latency is negligible, εG = the dielectric constant of graphene. Putting PG into (2), it can be shown thatwhere where λ0 = the wavelength of incident light, εr = the dielectric constant of medium, α = fine constant and EF = Fermi energy of graphene. The enhancement factor (EF) depends strongly on the dimensionless ratio, whereTherefore, the enhancement factor of ∼100 could be achieved on flat graphene.There are two most common types of chemical sensors: electronic and optical. Optical chemical sensors have recently earned much attention due to short detection time, high selectivity, wide dynamic range and non-contact measurement capability. Among various optical sensing platforms, SERS is becoming increasingly popular due to its extremely-high sensitivity with the detection limit as low as a single molecule and high specificity at ultra-low analyte concentrations. Recently, many chemical sensors using a flat graphene sheet as a SERS substrate have been reported16H18N3SCl) detection. In addition, SERS performances are optimized by varying the Ag nanoparticle size via the control of sputtering time.Nevertheless, the performances of flat graphene platform should be further improved by employing 3D graphene structure2) that appears like a thin black sponge. A portion of graphene foam examined by field-emission scanning electron microscopy (FE-SEM) is illustrated in To obtain the most effective surface enhanced Raman scattering, the SERS substrate should be excited at its LSPR peak. The typical LSPR peak of AgNPs-GF measured by UV-Vis absorption spectroscopy is demonstrated in −1 are enhanced substantially as the sputtering time increases from 20 to 30 seconds. In contrast, MB peaks, background signal and noise peaks are greatly diminished when the sputtering time increases further to 40 s. Thus, the optimal sputtering time of AgNPs on GF for the highest MB signal is 30 s. However, the magnitudes of background signal and noise peaks from contaminations also increase considerably compared with the signal peaks. The impurity peaks are also amplified due possibly to the multiple-cascaded amplification process in graphene foam structure and very broad LSPR peak of AgNPs/GF hybrid. Thus, there will be a trade-off between sensitivity and specificity of the SERS sensor based on the AgNPs/GF structure. A practical solution to this problem is to apply a suitable noise filtering system, which can effectively eliminate the majority of noise peaks.−1 can be clearly observed in the SERS spectra for 100 μM and 1 μM MB concentrations while SERS spectra for 1 nM and 1 pM MB concentrations shows only four  and one (446 cm−1) MB Raman peaks, respectively. In addition, SERS intensity at a given MB peak increases monotonically as the MB concentration increases from 1 pM to 100 μM. The detection limit for MB is taken to be 1 nm as it is the lowest concentration that four MB peaks can still be observed. The results demonstrate the possibility of using GF platform for detection of trace-level molecules or low concentration of biochemical analytes.Silver-decorated graphene foam with the average particle size of 50 nm (30 s sputtering time) was used as SERS substrate to detect MB with varying concentration from 1 pM to 100 μM as demonstrated by SERS spectra in 4.From overall results, graphene foam decorated with silver nanoparticles has shown high SERS enhancement factor and excellent MB detection sensitivity. In addition, the Ag sputtering time of 30 s, which produces the average Ag particle size of 50 nm, yields optimal sensitivity for MB detection with a low detection limit of 1 nM. With a short sputtering time (10 s), there is very low density of small Ag nanoparticles. The large distance between small AgNPs will exhibit low local field enhancement and hence low SERS sensitivity. The increase of sputtering time from 10 to 30 s will result in the larger particle size and higher particle density, leading to enhancement of local electric field and LSP. However, AgNPs will become too dense and approaches a thin-film structure as the sputtering time becomes longer than 30 s, resulting in lower surface enhancement capability. In addition, the large particle size will cause non-radiative multimode excitation of LSPIn the multiple cascaded amplification process as schematically depicted in According to multiple cascaded amplification scheme, the electromagnetic enhancement factor (EF) can be expressed asAssuming thatThus,Am(νl)2 = SERS enhancement factor of silver, typically 104–105, Am(ν) = SERS electromagnetic gain of a noble metal (m), ν = light frequency, νl and νs are incident and scattering light frequencies, respectively, and Ag(ν)2 = SERS enhancement factor of graphene4.where 0, which is given byIn the absence of graphene, EF is defined as EFDividing 4 which is in the same order of magnitude as the estimated value from the experiment of 5 × 104. However, the other amplification mechanism, the collective excitation model, will also be considered since the first scheme still exhibits considerable discrepancy.Therefore, the theoretical ratio of enhancement factor for AgNPs substrates with and without GF is 10The collective excitation model as depicted in DefineandIG) and graphene foam (IGF) can be computed asThus, the amplification gains of graphene  could be estimated as 1 mm/0.1 mm ~ 10 layers. Thus, the enhancement factor of AgNps/GF substrate based on collective excitation scheme could be ~102 or 100, which is much lower than the enhancement factor from the experimental data of ~5 × 104. Therefore, the multiple cascaded amplification process, which yields a high enhancement factor of 104, is the more likely mechanism for the explanation of large SERS enhancement of AgNPs/GF substrate.For the AgNPs/GF substrate in this work, GF thickness is 1 mm and inter-layer distance between graphene layers is roughly 0.1 mm. Therefore, the average number of graphene layers  and hydrogen (H2) was used as the carbon precursor and reducing gas carrier for graphene synthesis. C2H2/ H2 (3/24) mixture were flowed through Ni foam located at the center of a horizontal tube furnace under a vacuum pressure of 0.2 Torr at 700 °C for 3 minutes and then cool down rapidly at a rate of more than 10 °C per minutes under hydrogen flow at a pressure of 1 Torr. Carbon atoms from C2H2 were dissolved on Ni surface and then segregated as graphene layer on Ni scaffold during cooling process. The resulting grahene coated Ni foam was etched in 3 M HCl solution at 60 °C for 30 minutes in order to remove the Ni scaffold. The GF was then decorated with silver nanoparticles (AgNPs) using DC magnetron sputtering with varying sputtering time from 10 to 40 s. The sputtering was conducted in argon at a vacuum pressure of 3 × 10−3 mbar with a DC current of 0.2 A.Graphene was grown on commercial Ni foams, which were simultaneously utilized as catalyst and scaffold, by chemical vapor deposition (CVD). Acetylene . The surface morphology of Ag-decorated graphene foam was examined using field emission scanning electron microscopy . The optical absorption spectrum of AgNPs-GF was measured by UV-Vis absorption spectrometer .SERS measurement was conducted using a portable Raman spectrometer (Enwave Optronics Field-type EZRaman-M) with the laser wavelength of 785 nm (red) and reflection detection at zero degree. Before MB detection, Raman spectrum of SERS substrate was measured in order to determine the baseline signal. Afterwards, MB solution was dropped onto a SERS substrate and then exposed to the laser in order to take Raman spectrum. Firstly, SERS measurement was carried out at a fixed MB concentration of 1 μm on AgNPs/GF substrates prepared with different Ag sputtering times (10–40 s) in order to determine the optimal Ag deposition time. Next, the SERS measurements were repeatedly performed on each substrate with varying MB concentration from 1 pM to 100 μM to obtain calibration curve and sensitivity. Lastly, SERS experiments were done on different SERS substrates including AgNPs/GF, AgNPs/Si, Si, and graphene at a fixed MB concentration of 1 μM in order to compare the performances of AgNPs/GF substrates and determine the enhancement factor derived from GF structure. It should be noted that the graphene substrate used for the comparison was a planar CVD graphene layer grown on a copper foil.How to cite this article: Srichan, C. et al. Highly-Sensitive Surface-Enhanced Raman Spectroscopy (SERS)-based Chemical Sensor using 3D Graphene Foam Decorated with Silver Nanoparticles as SERS substrate. Sci. Rep.6, 23733; doi: 10.1038/srep23733 (2016).


However, these edge states are highly susceptible to edge roughness and interaction with a supporting substrate, complicating the study of their intrinsic electronic and magnetic structure. Here, we focus on atomically precise graphene nanoribbons whose two short zigzag edges host exactly one localized electron each. Using the tip of a scanning tunnelling microscope, the graphene nanoribbons are transferred from the metallic growth substrate onto insulating islands of NaCl in order to decouple their electronic structure from the metal. The absence of charge transfer and hybridization with the substrate is confirmed by scanning tunnelling spectroscopy, which reveals a pair of occupied/unoccupied edge states. Their large energy splitting of 1.9 eV is in accordance with  The zigzag edges of graphene host edge-localized electronic states with aligned electron spins, but these states strongly interact with metallic substrates. Here, the authors measure the electronic structure of graphene nanoribbons after transferring them to an insulating support. Recent advances in the fabrication of precise graphene nanostructures open the door to tailoring their electronic properties to the needs of specific applications. In the case of graphene nanoribbons (GNRs) with armchair edges, a bottom-up approach has been shown to deliver control over width and edge termination down to the atomic level236789151617181918ab initio many-body perturbation theory calculations, which we use to systematically distinguish between edge states localized at the zigzag edges and the energetically and spatially distinct states associated with the armchair edges in the GNRs under study.Here, we focus on the electronic properties of the atomically precise zigzag edges formed at the termini of bottom-up fabricated armchair graphene nanoribbons (AGNRs). To decouple their electronic structure from the metal substrate, on which they are grown, we transfer the AGNRs onto NaCl islands by a scanning tunnelling microscopy (STM)-based multistep manipulation routine. Using scanning tunnelling spectroscopy (STS), we find that electronic decoupling of the edge states establishes a large energy splitting between occupied and unoccupied edge states. This is in accordance with m=7, which are synthesized with atomic-scale precision on a Au(111) single crystal surface using a recently established bottom-up methodn) GNRs, where n specifies their length along the armchair direction in units of carbon zigzag lines. Finite  GNRs host two qualitatively different sets of electronic π-states. One set derives from the Bloch states of the bulk GNR, which are delocalized along the GNR. The short zigzag edges at the termini of the GNRs give rise to another set of states that are localized near the termini6n) GNRs on Au(111) indicated only one, possibly degenerate, edge state near the Fermi level, which may be explained by hole-doping of the GNRWe focus on short AGNRs of width n on a Au11 singleafter the synthesis. Here, we use atomically thin insulating NaCl films that are deposited directly onto the metal surface. In contrast to bulk insulators, these films still allow the electronic properties of adsorbates to be investigated by STM/STS, while considerably reducing their interaction with the metal substraten) GNRs to the Au(111) growth substrate, which enables lateral manipulation and controlled pick-up of individual GNRs by the STM tipI/dV) spectrum exhibits two peaks centred at −0.5 and 1.3 V, as shown in As the synthesis relies on the catalytic activity of the metal surface, the transfer onto an insulating substrate needs to occur GW approximation. The framework provides accurate fundamental gaps, both for bulk insulatorsBeing a theory of the electronic ground state, Kohn–Sham DFT is not designed to describe the charged excitations that take place in STS, which involve the addition/removal of electrons to/from the sample. Although the orbitals of the non-interacting Kohn–Sham system are often found to be accurate approximations of the corresponding quasiparticle wave functionsab initioGW calculations for finite  GNRs, which can be viewed as open-shell molecules with one, singly occupied state localized at each terminus. Their fundamental gap is given by the energy splitting ΔZZ between the occupied and empty edge-localized states. A significant Kohn–Sham gap opens only in the spin-unrestricted formalism, where breaking of spin symmetry gives rise to staggered sublattice potentialsn⩾12. Starting from the PBE orbitals and orbital energies, we compute quasiparticle corrections in the G0W0 approximation. The fundamental gap ΔZZ is found to converge rapidly as a function of length, yielding a value of n⩾12  GNR and the edge states of extended zigzag edges). Direct comparison to experiment would require the inclusion of dynamical screening not only by the electrons of the GNR itself, but also by those of the NaCl monolayer and the underlying Au substrate, which is expected to lead to significant reduction of the fundamental gapZZ=1.9 eV is fully compatible with a fundamental gap of 2.8 eV, reduced by screening from substrate electrons.Here we perform r finite , n GNRs,ZZ is essentially independent of the separation between the zigzag edges, in accordance with the G0W0 predictions (cf. n) GNRs, the additional quantum confinement at the short zigzag edges selects one particular wavelength along the zigzag edge and the corresponding edge state is energetically isolated from the delocalized states of  GNRs.To investigate finite size effects, ribbons of different lengths have been moved onto NaCl islands and inspected. 17ions cf. . Similarions cf. . In the n) GNRs. Their width of 7=3 × 2+1 carbon dimer rows identifies  GNRs as members of the 3m+1-family of AGNRs, which have the largest band gapsI/dV spectra taken at the centre of a  GNR, featuring two sharp peaks at –1.2 and 2.3 V. These peaks indicate the onsets of the highest occupied and the lowest unoccupied bulk states, respectively, yielding a bulk band gap of ΔAC=3.5 eV. In contrast to the energy splitting ΔZZ of the localized edge states, we find that the bulk band gap ΔAC decreases continuously from 3.5 eV for the shortest  GNR to 2.9 eV for the longest  GNR under study, as shown in n) GNRs on Au(111)GW approximation predict a band gap of 3.7±0.1 eV for freestanding  GNRs2AC=2.9 eV is still below this value, it is significantly larger than the 2.4 eV measured for the  GNR on Au(111)We now turn to the delocalized bulk electronic states of decoupled 7, , n GNRs.gest 7, 4 GNR undeme, respectively (me is the free electron mass). We note that the bands appear with different intensity in STS because of the finite tip-sample distance and refer interested readers to the corresponding study on Au(111) for detailsG0W0 approximation. Although the band gap is found to open from 1.6 to 3.6 eV -GNR has been determined via Fourier transformed (FT) STS-GNR has n) graphene nanoribbons from Au(111) to an insulating monolayer of NaCl without introducing any defects. The delocalized electronic states of  GNRs are separated energetically from the states localized at the zigzag termini, making it possible to investigate the effect of electronic decoupling on both classes of states separately. Using STS, the band gap between delocalized states is found to increase from 2.4 to 2.9 eV upon electronic decoupling, whereas no significant modification of the effective masses is observed. Furthermore, we find an energetic splitting of the states localized at the zigzag termini that has long been predicted for freestanding zigzag edges, but is missing completely in  GNRs on Au(111). Both its substantial size of ΔZZ=1.9 eV and its independence on edge separation down to 3 nm are in agreement with ab initio many-body perturbation theory calculations of the GNRs' intrinsic electronic structure, indicating that decoupling by a single layer of NaCl indeed allows to study the intrinsic properties of graphene zigzag edges. We therefore expect that the experimental strategy established here will particularly benefit the eagerly awaited exploration of the low-energy spin physics at graphene zigzag edges using spin-sensitive methods.We have demonstrated the transfer of atomically precise  using an Omicron low-temperature STM. The Au(111) substrate was cleaned by standard argon sputtering and annealing cycles. The GNRs were grown on Au(111) following the recipe by Cai et al.I/dV spectra were recorded using the lock-in technique with Urms=20 mV.Sample preparation and STM measurements were performed in an ultrahigh vacuum system .Supplementary Figures 1-5, Supplementary Table 1, Supplementary Notes 1-3 and Supplementary References


Earlier studies have demonstrated that emotional stimulation modulates attentional processing during goal-directed behavior and related activity of a brain network including the inferior frontal gyrus (IFG) and the caudate nucleus. However, it is not clear how emotional interference modulates behavior and brain physiology during variation in attentional control, a relevant question for everyday life situations in which both emotional stimuli and cognitive load vary. The aim of this study was to investigate the impact of negative emotions on behavior and activity in IFG and caudate nucleus during increasing levels of attentional control. Twenty two healthy subjects underwent event-related functional magnetic resonance imaging while performing a task in which neutral or fearful facial expressions were displayed before stimuli eliciting increasing levels of attentional control processing. Results indicated slower reaction time (RT) and greater right IFG activity when fearful compared with neutral facial expressions preceded the low level of attentional control. On the other hand, fearful facial expressions preceding the intermediate level of attentional control elicited faster behavioral responses and greater activity in the right and left sides of the caudate. Finally, correlation analysis indicated a relationship between behavioral correlates of attentional control after emotional interference and right IFG activity. All together, these results suggest that the impact of negative emotions on attentional processing is differentially elicited at the behavioral and physiological levels as a function of cognitive load. In everyday living, we perceive a complex visual environment and fully analyze many items and events at one time. Attentional control allows the flexible allocation of attentional resources to relevant stimuli while suppressing stimuli that are less relevant. This cognitive process provides a top-down bias for analysis and representation of relevant information in the face of concurrent and non-relevant information  task, which requires increasing levels of attentional control processing associated with a physiological linear increase in prefrontal activity . Inclusion criteria were absence of any psychiatric disorder, as evaluated using the Structural Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders IV, of any significant neurological or medical condition revealed by clinical and magnetic resonance imaging evaluation, of history of head trauma with loss of consciousness, and of pharmacological treatment that could influence cerebral metabolism or blood flow, or drug abuse in the past year. The Wechsler Intelligence Scale—Revised was used to evaluate the intelligent quotient (IQ) . Socio-economic status : All three sizes of arrows were congruent in direction with each other. The cue was the word BIG.Intermediate level of attentional control (INT): The big arrow was incongruent in direction to the small and the medium arrows; the cue was the word SMALL.High level of attentional control (HIGH): The medium sized-arrows were incongruent in direction to the big and the small arrows; the cue was the word SMALL.Subjects performed a task Figure  that wasEmotional interference was obtained using unfamiliar faces with either fearful or neutral facial expressions derived from a validated set of facial pictures  displayed above each attentional stimulus to press a button corresponding to the direction of the large or small arrows (either right or left). They were instructed to respond to the attentional stimuli with the thumb of their right hand using a button box , and to press the response button as fast and accurately as possible. Furthermore, they were asked to move their thumb to a small plastic knob placed between the buttons after each response. All subjects were trained on attentional stimuli of the task prior to the fMRI session to stabilize performance. More specifically, just before fMRI scanning, subjects were instructed on task rules and performed the task outside the fMRI environment until the average behavioral performance did not grossly vary across trials in terms of behavioral accuracy . No instructions related to emotional stimuli were administered.A total of 192 attentional stimuli was preceded by the respective 192 stimuli providing emotional interference, which were 96 fearful and 96 neutral facial expressions. There were 64 stimuli for each level of attentional control. Thirty two stimuli of each attentional level were preceded by facial stimuli with fearful expression, and 32 by facial stimuli with neutral expression. This design resulted in 6 conditions: fearful-low attentional control; fearful-intermediate attentional control; fearful-high attentional control; neutral-low attentional control; neutral-intermediate attentional control; neutral-high attentional control. The order of the stimuli was randomly distributed across the session  while subjects performed the emotional variable attentional control (EVAC) task. The first 4 scans were discarded to allow for signal saturation. post hoc analysis to correct for multiple comparisons. Because of our priori hypothesis, post hoc analysis of the interaction between the level of attentional control and emotional interference was performed for each level of attentional control between fearful and neutral faces.Analysis of variance (ANOVA) was used to compare behavioral data (% correct responses and RT of correct responses). We included only subjects who had an average accuracy above 50% (forced choice between two options). Bonferroni correction was used fort statistic was then used to produce a statistical image for BOLD responses relative to brain processing of stimuli associated with correct responses for each condition. A random effects ANOVA was used at the group level to investigate the main effect of emotional interference, of attentional control stimuli, and their interaction. For all analyses on activity during the EVAC task, we focused our attention on the orbital and triangular parts of IFG and on the caudate nucleus because of their central role in the regulation of cognitive and emotional processes as well as in their integration. Thus, we used a statistical threshold of p < 0.05, k ≥ 5, Family Wise Error (FWE)-corrected for multiple comparisons within brain regions of interest , as defined by the WFU pickatlas software, version 1.04 .Analysis was completed using the event-related module within Statistical Parametric Mapping 5 (SPM5).post hoc analysis was performed on parameter estimates extracted from clusters crossing the statistical threshold of p < 0.05 (FWE corrected) within the predefined ROIs using MarsBar.To further investigate directionality of the interaction between emotional interference and attentional load, F = 31.25; p < 0.000001; average number and % of correct responses: HIGH 26.55, 82.9%; INT 29.52, 92.3%; LOW 31.32, 97.9%), no effect of emotional interference  = 0.98; p = 0.3), and no interaction between level of attentional control and emotional interference  = 1.37; p = 0.2). Post hoc analysis of the main effect of increasing level of attentional control showed a significant difference across all three levels .ANOVA on accuracy data indicated a main effect of increasing level of attentional control  = 103.25; p < 0.000001), no effect of emotional interference  = 0.07; p = 0.7), and an interaction between level of attentional control and emotional interference  = 14.23; p < 0.00002) . Post hoc analysis of the interaction between the level of attentional control and emotional interference indicated a statistically significant difference between RTs at the lower level of attentional control when preceded by presentation of fearful facial expressions . An effect of emotional interference was also present at the intermediate level of attentional control, but in the opposite direction . At the higher level of attentional control, a statistical trend in the same direction of the lower level was found .Furthermore, analysis of RTs revealed a main effect of increasing level of attentional control   .Consistent with previous studies  Figure . Similar Figures . A statip > 0.2). However, there was a significant negative correlation between parameter estimates in right IFG and RTs at the low level of attentional control after neutral facial expressions were shown  . Finally, no significant brain activity-RT correlations were found at the intermediate and high levels of attentional control (p > 0.15).No significant correlations were found between behavioral accuracy data and brain activity in clusters showing an emotional interference by attentional load interaction  Figure . No signOur results indicated differential effects of emotional interference on behavior and activity in prefronto-striatal brain areas during attentional control as a function of cognitive load. In particular, stimuli eliciting the lower level of attentional control were associated with slower RTs as well as greater activity in the right side of the IFG when anticipated by fearful, relative to neutral, facial expressions. However, the interaction between emotional stimuli and the intermediate level of attentional control was associated with the opposite behavioral pattern but with a similar effect on brain activity, this time taking place in both sides of the caudate. Finally, no statistically significant behavioral or imaging effects of emotional interference were found at the higher level of attentional control. Together, these findings suggest that negative emotions modulate goal-directed behavior and related brain activity when low and intermediate levels of attentional control are required, but they do not impact attentional processing when high levels of attentional control are required. More generally, these results suggest that negative emotions may modulate cognitive efficiency during attentional control processing.At the lower level of attentional control, the presentation of fearful, relative to neutral, faces before attentional stimuli was associated with longer RTs. Slower performances of attentional processes by negative emotions has been previously reported  induced by fearful facial expressions modulates detection of other environmental cues. Similar results have been reported recently (Phelps et al., A limitation of this study may be the number of trials used at the high level of attentional control, which could explain the statistical trend we found in behavioral and imaging data between fearful and neutral interference. According to a previous study, 25 trials are sufficient to provide stable activation maps (Murphy and Garavan, In conclusion, this study suggests that emotionally irrelevant stimuli during attentional control processing modulate behavior and brain activity in right IFG and both sides of the caudate as a function of cognitive load. These findings add knowledge to some aspects of the complex functional architecture underlying the integration of emotion and attention in the human brain and could have potential clinical implications. Impairment of emotional and cognitive functions have long been regarded as characterizing several major psychiatric disorders such as schizophrenia, bipolar disorder, depression, and anxiety disorders (Bertolino et al., Dr. Bertolino is a full time employee of Hoffman-La Roche, Ltd. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Cardiac sarcoidosis is a major cause of death in patients with systemic sarcoidosis. Cardiac manifestations are seen in 2.3% of the patients. Atrioventricular (AV) block is one of the common manifestations of cardiac sarcoidosis. Other presentations of cardiac involvement include congestive heart failure, ventricular arrhythmias, and sudden cardiac death. The presence of AV block in young patients should raise the suspicion of sarcoidosis. AV block may be the only manifestation and patients may not have clinical evidence of pulmonary involvement. Here we describe a young male presented with exercise induced AV block rapidly progressing to complete heart block with recurrent syncope needing urgent pacemaker implantation. Factors that suggested an infiltrative process included his young age, rapidly progressive conduction abnormalities in the ECG in the absence of coronary disease, and previous history of cutaneous sarcoidosis. Sarcoidosis is a multisystem disease of unknown aetiology characterized by the formation of noncaseating granulomas in many tissues. The granulomas mostly affect the lungs and lymph nodes . Cardiac47-year-old male presented to the cardiology out-patient department (OPD) with shortness of breath and chest discomfort on exertion since one week. Chest discomfort was related to exertion and relieved by rest. He has hypertension and hypertriglyceridemia controlled well on oral Amlodipine and Fenofibrate since one year. He does not smoke, drink alcohol, or use any recreational drugs. The patient gives past history of cutaneous sarcoidosis which was diagnosed by biopsy of the lesion one year back. He was evaluated for systemic sarcoidosis and was found to have hilar lymph nodes by computed axial tomography of chest and was advised for a follow-up CT after 6 months. The follow-up CT scan showed improvement and the patient was asymptomatic. Corticosteroids were not started at that time as the patient was concerned about the side effects of steroids on longterm. Hence he was advised for regular follow up. Three months after this evaluation, he presented to our OPD with the present symptoms. Physical examination did not show cutaneous lesions, his pulse was regular at 62 beats per minute and the blood pressure was normal. Cardiovascular examination revealed normal S1 and S2 with no gallop, murmurs, or rub.At the time of presentation his electrocardiography (ECG) revealed sinus rhythm with a rate of 62 per minute with prolonged PR interval and right bundle branch block (RBBB) . CardiacHe has undergone urgent temporary pacemaker implantation. This was followed by permanent pacemaker implantation with Victory XL DDDR pacemaker . He made an uneventful recovery. He remained asymptomatic afterwards. A workup for the autoimmune profile was normal, serum calcium was 8.6 mg/dL, and the serum angiotensin converting enzyme level was elevated. Pacemaker interrogation showed he is fully dependent on pacemaker at 2 weeks after discharge. He remained symptom-free following the procedure. He was evaluated by an internist and a dermatologist after the surgical wound was healed. Based on the clinical presentation and available reports he was started on immunosuppressive therapy with steroids. Presently his ECG shows sinus rhythm with RBBB and pacemaker on demand mode. He is doing well one year after the procedure.Cardiac sarcoidosis is a major cause of death in patients with systemic sarcoidosis. Clinically evident sarcoidosis involving the heart affects 2.3% of patients . Common Cardiac involvement can occur at any point during the course of sarcoidosis. Asymptomatic heart involvement is more common in systemic sarcoidosis. When symptomatic, cardiac involvement can present as CHF, AV block, cardiac arrhythmias, and SCD. The clinical presentation of cardiac sarcoidosis reflects the changes in myocardium caused by granulomatous deposition leading to inflammation and subsequently scar. These become the source of ventricular arrhythmias and conduction block.In a prospective study of 32 patients aged less than 60 years presenting with CHB, 34% had previously undiagnosed cardiac sarcoidosis. This group had higher adverse cardiac events compared with patients without sarcoidosis [The prognosis of symptomatic cardiac sarcoidosis is not clear, but 5-year mortality rates exceed 50% . IncidenReaching a correct diagnosis early in the course of the disease is difficult unless sarcoidosis is also present in other organs. Early administration of immunosuppressant therapy (high dose steroids) may stop or reverse cardiac damage . Our patAn accurate and early diagnosis is essential to enable prompt treatment of arrhythmias. The recovery of his rhythm back to sinus after the institution of steroid also justifies the presumptive diagnosis of cardiac sarcoidosis in this patient. Early institution of steroid therapy is advised in patient with systemic sarcoidosis to prevent fatal cardiac complication even if they are asymptomatic.


A facile production of highly porous graphene foam by using flame treatment of graphene oxide (GO) is proposed. Highly porous architectures with randomly distributed micro-crack and micro-slit were produced due to the high temperature induced ruinous reduction and rapid expansion of GO. Synchronously, abundant oxygen-containing groups (OCGs) on GO sheets could be effectively removed after flame treatment, which renders significantly increased conductivity to the resultant flame reduced GO (FR-GO). The synergistic effect of micro/nanostructuring and the OCGs removal makes FR-GO a promising candidate for electrode materials. Compared with chemically reduced GO (CR-GO), FR-GO delivers much higher specific capacity. It gives us some hints that flame treatment of graphene-based material is a smart strategy for cost-effective production of anode materials for commercial application. Recently, it is also found that optical approach for preparation of porous graphene is also very powerfulet al., achieved a reduced free-standing GO paper as high-rate capable anodes for LIBsAs a new family member of carbon materials, graphene, which is a single layer of two-dimensional (2D) honeycomb-structured carbon lattice, is promising to achieve outstanding electrochemical performance16In this work, we design and fabricate highly porous graphene foam from exfoliated GO paper by using candle flame treatment. The ultra-high temperature of the outer flame was found to be capable of removing the oxygen-containing groups (OCGs) on GO sheets, which not only leads to the formation of highly porous structures but also dramatically improves the conductivity of the flame reduced graphene oxide (FR-GO). The hierarchically porous architecture effectively improves the surface area, which enlarges the contact area between the electrode and the electrolyte. Therefore, the mass transfer has been significantly promoted. It needs to point out that our approach is simple, low-cost, chemical-free and environmental benign for the preparation of porous graphene anodes towards high energy density rechargeable commercial energy storage devices. We also propose that the conductive and porous graphene foam can be widely used in curvilinear electronics, catalytic, biofuel and biomimetic systems.+Notably, the OCGs on the surface of GO sheets would influence the interaction between lithium ions and grapheneTo evaluate the surface wettability change before and after the flame treatments, static water contact angle (CA) of the two samples was measured. As shown in 2, would destroy the GO sheets and generate more defects. Additionally, the emission of carbon species also leads to significant expansion along the lateral direction. It could be clearly observed from the edge of the open pore that the FR-GO sheets curl up, which significantly increases the interlayer spacing. To get further insight into the porous structure along the lateral direction, we further examine the profile structure of the FR-GO sample by SEM. As shown in Taking advantage of the high temperature of the outer flame, the GO paper has been reduced in a drastic manner. As soon as the GO approaches the outer flame, the intense thermal effect would trigger the rapid removal of OCGs, leading to the formation of a highly porous structure due to the drastic expansion. 0 region and in the range of 0.4–1.0, respectively, indicating the presence of mesopores of different pore sizes. Pore size distribution (inset of 2/g) and large pore volumes (1.4 cm3/g). These results show that the FR-GO sample is highly porous, revealing great potential as anode materials for LIBs. For comparison, the GO sample shows a relative low BET surface area of 31 m2/g , Raman spectra, TG curve and X-ray photoelectron spectroscopy (XPS) have been implemented to characterize the FR-GO sample. M images .−1 and 1600 cm−1, which correspond to D and G band, respectively. After flame treatment, the peak intensity changed slightly. The G band is attributed to an E2g mode of graphite associated with the vibration of sp2 bonded carbon atoms, whereas the D band peak is related to the oscillations of carbon atoms with dangling bonds in plane terminations of disordered graphite. After the flame treatment, the intensity ratio of D band and G band, ID/IG, slightly decreased from 1.27 for pristine GO to 0.89 for FR-GO. The removal of oxygen defects would render a much higher content of sp2 carbon, represented by a significantly increased G band peak. The decrease of ID/IG ratio indicates that the flame reduction of GO could effectively remove the oxygen defects and partially reconstruct the sp2 network of graphene.It is well known that Raman spectroscopy has been widely used for characterizing carbon materials. As shown in To further evaluate the residual OCGs on FR-GO sample, thermogravimetric (TG) heating curves of GO and FR-GO have been measured in nitrogen . The weiIn order to analyse the reduction degree of FR-GO sample, we measured the XPS of pristine GO and the resultant FR-GO, respectively. As shown in st, 2nd, 3rd, 50th, 100th, 150th and 200th cycle at 0.33C. In the first cycle, a long voltage region below 0.5 V (vs. Li/Li+) is observed, which is mainly due to the lithium-ions intercalation into the graphene layers33+ on functional groups and its consumption of large amount of Li+ due to the formation of the SEI layer in the first cycle. It was suggested that the CE can be increased dramatically by doping graphene oxide into sucrose to reduce its specific surface area or further enlarge the interlayer lattice distance of FR-GO36The electrochemical performance of FR-GO and chemical reduction graphene oxide (CR-GO) is shown in 2/g) of FR-GO may greatly reduce the transport lengths of Li+, by which Li+ could be electrochemically adsorbed on both sides of graphene sheets383935The excellent performance of the as-synthesized FR-GO could be assigned to the following reasons. First, the highly porous architecture –dimethyl carbonate (DMC)–diethyl carbonate (DEC)  was utilized as the electrolyte and Li foil was used as the counter electrode.Electrochemical measurements of the FR-GO were evaluated with LIR2032 Coin-type half-cells assembled in an argon filled glove box (MB200MOD). The working electrodes were fabricated by a mixture of 10 wt% acetylene black, 70 wt% active materials, and 20 wt% polyvinylidene difluoride (PVDF) binder with N-methyl-2-pyrrolidone (NMP) solution. Following that, the resultant slurry was uniformly coated on a copper foil with a plastic blade, of which it was put in a vacuum oven at 100 °C overnight. A Celgard 2400 microporous polypropylene membrane was applied as the separator, 1.0 mol L-1 from room temperature to 800 °C, Ar has been used as inert gas.The static water contact angle (CA) measurements were made using the Contact Angle System OCA 20  at ambient temperature. The CAs were measured by the sessile-drop method with a water droplet of 5 μL. SEM images were obtained by using a field-emission scanning electron microscope . X-ray photoelectron spectroscopy (XPS) was performed using an ESCALAB 250spectrometer. Powder X-ray diffraction (XRD) patterns were collected on a Rigaku D/MAX 2550 diffractometer with Cu Kα radiation (λ = 1.5418 Å). Raman spectrometer equipped with a liquid-nitrogen-cooled argon ion laser at 514.5 nm (Spectra-Physics Stabilite 2017) as the excitation source; the laser power used was about 10 mW at the samples with an average spot size of 1 μm in diameter. Thermogravimetric (TG) curves were carried out on a NETZSCH STA 449C with a heating rate of 20 °C minHow to cite this article: Jiang, H.-B. et al. Flame treatment of graphene oxides: cost-effective production of nanoporous graphene electrode for Lithium-ion batteries. Sci. Rep.5, 17522; doi: 10.1038/srep17522 (2015).


The ECG on admission shows ectopic atrial tachycardia with multilevel block: variable Mobitz type II exit block to the atrium and Wenckebach phenomena in the atrioventricular node . Chest computed tomography scan also showed mediastinal adenopathy (not shown). This combination of findings narrowed the differential diagnosis to atrial infiltration due to sarcoidosis or lymphoma/tumours. Biopsies collected during minimal thoracotomy established the diagnosis of sarcoidosis (not shown).In cardiac sarcoidosis, conduction disturbances are related to granulomatous infiltration of the conduction system . Their eThis case underlines that when conduction disturbances are seen in younger patients, a search for cardiac structural abnormalities is warranted and sarcoidosis should be suspected .