In addition, the growth temperature was substantially reduced to as low as 100 °C, which is the lowest temperature reported to date for pristine graphene produced by CVD. Our modified CVD method is expected to allow the direct growth of graphene in device manufacturing processes for practical applications while keeping underlying devices intact.There is significant interest in synthesizing large-area graphene films at low temperatures by chemical vapor deposition (CVD) for nanoelectronic and flexible device applications. However, to date, low-temperature CVD methods have suffered from lower surface coverage because micro-sized graphene flakes are produced. Here, we demonstrate a modified CVD technique for the production of large-area, continuous monolayer graphene films from benzene on Cu at 100–300 °C at ambient pressure. In this method, we extended the graphene growth step in the absence of residual oxidizing species by introducing pumping and purging cycles prior to growth. This led to continuous monolayer graphene films with full surface coverage and excellent quality, which were comparable to those achieved with high-temperature CVD; for example, the surface coverage, transmittance, and carrier mobilities of the graphene grown at 300 °C were 100%, 97.6%, and 1,900–2,500 cm It is therefore indispensable to synthesize graphene at reduced growth temperatures, permitting large-area fabrication with relatively low cost. Several groups have demonstrated that a drastic reduction in growth temperature can be achieved by using plasma-enhanced CVD (PECVD), where plasma generates reactive species1719201719Graphene, a two-dimensional monolayer of Additionally, the typical graphene growth routes are mostly performed in low-pressure conditions in order to achieve a high degree of graphene crystallinity. Although the vacuum CVD process has been widely used for graphene growth, atmospheric pressure CVD (APCVD) growth of graphene of appreciable quality is desirable in order to lower the manufacturing cost and increase throughput. Moreover, severe evaporation of metal catalysts in low-pressure conditions, which may lead to deterioration of the graphene quality, can be significantly suppressed by increasing the working pressure. However, oxygen and water molecules in ambient air should be avoided to obtain high-quality graphene. In this study, we developed a modified APCVD route to synthesize graphene on Cu foils, which is called the “oxygen-free APCVD” process. In this method, we extended the graphene growth step in the absence of residual oxidizing species that may influence the formation of amorphous and oxidized carbon layers. Using this method with benzene as a carbon feedstock, large-area, continuous graphene sheets with excellent quality were synthesized on Cu foils at 300 °C. The growth temperature was substantially reduced to as low as 100 °C, which is the lowest temperature reported to date for pristine graphene produced by CVD.2/Si substrate. The OM and SEM images show the same contrast over the entire film area, in contrast to the film grown by APCVD. This reveals the formation of a continuous graphene film. Moreover, the Raman measurement indicates a monolayer graphene with a low defect density , which indicates the formation of a uniform, continuous graphene film with the monolayer coverage of >99% by merging adjacent graphene domains . For the growth time of 30 sec, the defective graphene flakes were synthesized on a Cu foil . As the ecreased , reveali domains . For lon domains .−1  of the device were 1,900 and 2,500 cm2 V−1 s−1, respectively204-derived monolayer graphene at ~1,000 °C by LPCVD1120The quality of our graphene film grown by oxygen-free APCVD was further tested by electrical transport measurements in a field-effect transistor (FET) configuration, which was fabricated on a 300 nm-thick SiOet al. that oxygen influences graphene nucleation and reduces the nucleation densityThe graphene growth from aromatic benzene molecules involves the following steps: (1) benzene molecules are introduced into the furnace by bubbling liquid benzene with argon and hydrogen as the carrier gases at ambient pressure; (2) the carbon sources then undergo adsorption on Cu surfaces and catalytic dehydrogenation at low temperatures to form highly reactive hexahydric ring species, leading to the formation of graphene nuclei; (3) continual growth of graphene takes place when hexahydric ring-containing molecules are incorporated into the edges of graphene nuclei that are chemically active . In prev19212426272 V−1 s−1. Even when the growth temperature was substantially lowered to 100 °C, graphene films were synthesized, but with reduced surface coverage. This demonstration is a significant step toward the direct growth of graphene in device manufacturing processes for practical applications such as CMOS back-end interconnects and flexible devices.We developed a modified CVD route, called the oxygen-free APCVD process, to synthesize large-area, continuous monolayer graphene films from benzene on Cu at as low as 300 °C at ambient pressure. The oxygen-free APCVD process introduces a step consisting of pumping and purging cycles prior to graphene growth, which leads to the absence of oxidizing impurities during growth and thus to the formation of uniform and continuous monolayer graphene films of improved quality. The graphene grown at 300 °C had properties comparable to those of 1,000 °C-grown graphene, with surface coverage of 100%, optical transmittance of 97.6%, and field-effect mobilities of 1,900–2,500 cm−4 Torr and then purged with argon. This process was repeated five times to flush the air contained in the quartz tube . After a mixture of hydrogen and argon  was supplied into the quartz tube, the pump was switched off, and the quartz tube was kept at ambient pressure. To increase the Cu grain size and ensure the removal of native oxide and a smooth Cu surface, the Cu foil was annealed at 1,000 °C for 30 min under a hydrogen and argon atmosphere and was subsequently rapidly cooled down to the desired growth temperature (25–300 °C). Once the desired temperature was reached, the flow rate of hydrogen gas was changed to 20 sccm without flowing argon (purging gas) while the carbon source was introduced by bubbling liquid benzene  at room temperature. The carbon source was supplied to the quartz tube with 5 sccm of argon flow (carrier gas) for 5 min, producing a monolayer graphene. The graphene growth was completed by stopping the supply of benzene, and the furnace was subsequently cooled to room temperature while hydrogen and argon  continued flowing without supplying benzene. For comparison, graphene was synthesized at 300 °C by APCVD  without the introduction of the pumping and purging step. To transfer the graphene onto a heavily p-doped Si substrate with a thermally grown 300 nm-thick SiO2 layer or a glass substrate, poly(methyl methacrylate)  was spin-coated on the graphene/Cu, which was baked at 60 °C for 5 min to remove the solvent from the polymer14Cu foil  was used as a catalytic substrate to grow graphene. The Cu foil was first cleaned with 18% HCl, deionized water, acetone, and isopropyl alcohol and subsequently dried with nitrogen. Then, it was loaded into the hot center of a quartz tube. Prior to graphene growth, the quartz tube was pumped down to ~10p-doped Si substrate with a thermally grown 300 nm-thick SiO2 layer, which were used as the bottom gate and gate dielectric, respectively. After transferring the graphene sheet onto the substrate, source and drain electrodes were deposited using photolithography, followed by electron-beam evaporation of Ti/Au. Then, a second photolithography and an oxygen plasma treatment were performed to pattern the graphene channel. Typical channel width and length were 8 and 40 μm, respectively.Graphene FETs were fabricated using standard photolithography techniques. The substrate was a heavily The surface morphology of graphene was visualized by optical microscopy  and field-emission scanning electron microscopy . Raman spectroscopy  with a laser excitation wavelength of 532 nm was used to characterize the thickness, quality, and uniformity of the graphene films. Optical transmittance was measured using an UV-vis-nIR spectrometer  to examine the thickness and uniformity of the graphene transferred onto a glass substrate. The electrical properties of the graphene were studied in vacuum at room temperature using a semiconductor parameter analyzer  and a four-point probe measurement system .How to cite this article: Jang, J. et al. Low-temperature-grown continuous graphene films from benzene by chemical vapor deposition at ambient pressure. Sci. Rep.5, 17955; doi: 10.1038/srep17955 (2015).


The paper presents the results of investigations on resistance structures based on graphite oxide (GRO) and graphene oxide (rGO). The subject matter of the investigations was thaw the sensitivity of the tested structures was affected by hydrogen, nitrogen dioxide and carbon dioxide. The experiments were performed at a temperature range from 30 °C to 150 °C in two carrier gases: nitrogen and synthetic air. The measurements were also aimed at characterization of the graphite oxide and graphene oxide. In our measurements we used (among others) techniques such as: Atomic Force Microscopy (AFM); Scanning Electron Microscopy (SEM); Raman Spectroscopy (RS); Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Microscopy (XPS). The data resulting from the characterizations of graphite oxide and graphene oxide have made it possible to interpret the obtained results from the point of view of physicochemical changes occurring in these structures. This is2  and WO3 2 [3  can serv2 [3 . It is t2 [3 ,8 or for2 [3 . The app2 [3 ,11.The techniques applied for the preparation of graphite oxide  and its In this paper, the authors present the results of experiments aimed at investigating the responses of resistance structures based on graphite oxide and graphene oxide exposed to different atmospheres. We also present the results of characterization of the layers comprising, among others, an analysis of the composition and topography of the surfaces. The aim of our investigations was to understand the physicochemical phenomena occurring during contact of the sensor structures with the given gaseous atmospheres.x group pollute the natural environment, leading to the formation of smog and affecting the lungs [Our investigations were focused on the detection of three dangerous gases: nitrogen dioxide, hydrogen and carbon dioxide. Gases from the NOhe lungs . Hydrogehe lungs . Carbon he lungs . Both hyhe lungs ,17 and ta-58 nm, Lc-30 nm, d002-0.336 nm and Cdaf-99.5%), supplied by Graphit Kropfmühl AG  was ground and sieved to a particle size <20 µm and oxidized according to the methodology described in Commercial natural graphite powder  was used as an acid. KMnO4 and NaNO3 were slowly added to keep the temperature in the 10–15 °C range. After their addition, the reaction temperature was maintained between 10 and 20 °C. After each reaction, 120 mL of milli-Q water and 50 mL of 3% H2O2 were slowly added. The mixture was stirred for 30 min and then centrifuged, the supernatant being decanted off. The graphite oxide was washed with milli-Q water and centrifuged repeatedly until a neutral pH was achieved. Graphite oxide was finally dried overnight under vacuum at 50 °C and stored in the presence of P2O5 as desiccant. Graphene oxide was obtained from graphite oxide by thermal treatment at 900 °C in a vertical furnace, under a nitrogen flow of 50 mL/min. The residence time at the final temperature was 5 min. Concentrated H2sp bonded carbon network. We used a combination of several measurement methods to reveal the structural evolution from pristine graphite to graphite oxide and next to graphene oxide . The further sections discuss the results obtained using these methods.Both graphite oxide (GRO) and graphene oxide (rGO) possess unique properties that differ from those of pristine graphite because of the structural changes arising due to the introduction of oxygen functionalities into the −5 mbar). The microscope magnification was ×1000 and ×5000. Additionally, the investigations by means of scanning electron microscopy were extended by applying an energy dispersive spectrometer X-ray (EDX) detector. This detector allows for qualitative and quantitative analysis of the sample composition. The measurements were examined by using a Nova NanoSEM 450 microscope  operating under low vacuum (0.3 mbar) at an accelerating voltage of 10–15 kV and using a large-field secondary electron detector.The topography of the surface of graphite oxide and graphene oxide was investigated by means of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). For measurements using Scanning Electron Microscopy, an INSPECT S50  instrument was used. The measurement parameters were: HV = 5 kV, bias = 0, spot = 3.0 and HV = 2 kV, bias = 1400 V, spot = 3.5 for graphite oxide and graphene oxide, respectively. In order to illustrate both materials, an Everhart-Thornley Detector (ETD) was used. The measurements were made under high vacuum conditions  using the intermittent contact mode. The images were obtained at a resonance frequency equal to 136.281 kHz, both for graphite oxide and graphene oxide. The HA_NC tip was used in those measurements. Moreover, the Raman Spectroscopy (RS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD) and X-ray Photoelectron Microscopy (XPS) were also applied for the characterization of the layers. The Raman spectra were obtained from the N_TEGRA Spectra platform (NT-MDT). In the measurements, the wavelength was equal to 532 nm. The spectra were recorded with a resolution of 2.89 cm−1.FT-IR measurements were made with a Tensor 27 spectrometer . Absorbance spectra of discs with a KBr/sample ratio of 500:1 were collected at a resolution of 4 cmXRD measurements were taken with an X’Pert PRO PW 3040/60 by PANalytical B.V.  diffractometer. Samples of ground graphite, graphite oxide and thermally reduced graphene oxide were deposited onto glass and analyzed by using Co Ka1 radiation with a voltage of 40 kV and a current of 30 mA.3sp hybridization (285.4 eV), hydroxyl and epoxy groups (286.5 eV), carbonyl or quinone groups (287.6 eV), carboxyl groups (288.9 eV) and a satellite peak corresponding to the π–π* transition in the aromatic systems (290.4 eV). The O1s excitation was resolved into two peaks corresponding to C=O groups such as ketone and carbonyl (531.7 eV), hydroxyl and epoxy functionalities (533.4 eV) and a carboxyl group (535.3 eV). Curve fittings were performed using an iterative least squares algorithm (CasaXPS software) with a Gaussian-Lorentzian (70/30) peak shape and Shirley background removal. The resulting spectra represent the binding energies of pyridinic (398.5 ± 0.2 eV), amine (399.4 ± 0.2 eV), hydroxypyridinic (400.5 ± 0.2 eV), quaternary-N (401.2 ± 0.2 eV) and N-oxide (402.9 ± 0.2 eV) groups.The elements present in graphite oxide and graphene oxide as well as their chemical state were identified by XPS analysis. X-ray Photoelectron Microscopy was carried out using a PHI 5000 VersaProbe—Scanning ESCA Microprobe™  and a monochrome Al Kα source (1486.6 eV). The charging of the sample was corrected applying the C1s peak at 284.5 eV as an internal standard. Curve fitting of the spectra was performed using a Gaussian-Lorentzian peak shape after conducting a Shirley background correction. The high-resolution C1s signal was deconvoluted into five individual peaks ascribed to graphitic carbon (284.5 eV), carbon atoms with The elementary composition of graphite oxide and graphene oxide  was determined directly using a Vario Macro Cube automatic elementary analyser .The properties of graphite oxide and graphene oxide as a function of temperature were investigated by the following techniques: Thermogravimetric (TG), Differential Thermogravimetric (DTG) and Differential Scanning Calorimetry (DSC). TG, DTG and DSC curves were obtained using a TG-STA209LUXX unit . The samples were tested in the range from 40 to 1000 °C with a heating rate of 10 K/min and a flow of argon kept at 25 mL/min.The resistance of sensor samples as a function of temperature was tested in a measuring system designed and realized by the staff of the Department of Optoelectronics of the Silesian University of Technology . This system allows presetting and control of the temperature of samples. The measurements were made within the range of temperature from 30 °C to 150 °C. The same system made it possible to measure the resistance at various degrees of temperature in various gaseous atmospheres. It can preset and control the composition of the gaseous atmosphere over the samples (the gas flow: 100 mL/min and 500 mL/min in the undertaken experiments). The measurements were taken in the atmospheres of nitrogen and synthetic air, which were used as carrier gases, as well as in the atmosphere of hydrogen, nitrogen dioxide and carbon dioxide at various concentrations in the carrier gases.The tested sensor structures  differedTo obtain a 1.2% (wt.%) solution the appropriate amounts of graphite oxide and graphene oxide (sensitive layers) were mixed with ethanol  and then transferred to an ultrasonic bath . After 24 h ultrasonication a homogeneous dispersion was obtained, which was deposited on the basic structures. After that the basic structures were placed in an vacuum dryer  and dried at 22 °C under nitrogen atmosphere for 24 h. Next, the dried structures were annealed with temperature ramp 2 °C/min to the final temperature of 100 °C at which were maintained for additional 3 h. Afterwards the temperature was increased up to 150 °C using the same ramping program and kept for 2 h under reduced pressure (20 mbar) to removal of any residual ethanol from the prepared structures. The whole annealing process were conducted in an inert atmosphere of nitrogen to avoid oxidation of the samples.2. The application of the sensitive layer on such large surfaces caused that the obtained results were repetitive for different groups of sensors  of the surface of graphene oxide is presented in The results of tests carried out when applying Atomic Force Microscopy confirm the difference in the development of these structures. The topography  of 0.3363 nm. The intensity of this peak sharply decreases for GRO, and a new 001 peak appears at 2Θ = 13.18°. The d001 interlayer distance calculated for this sample is 0.7795 nm, which is in agreement with its high degree of oxidation [002 amounts to 0.3393 nm.The crystalline structure of synthesized graphite oxide and graphene oxide, as well as that of the parent graphite, were analysed by XRD. As shown in xidation ,24. The 2sp and 3sp hybridization accompanied by some shoulders at higher binding energies due to the presence of oxygen linkages [2sp hybridization. The C1s spectrum consists of a peak at 285.4, 286.2, 287.0, 287.9, 288.9, and 290.4 eV assigned to C–C, C–O, C=O, O–C–O, O=C–OH and π–π* transition in aromatic systems [The oxygen speciation was studied by means of XPS measurements. linkages ,26. The linkages . The speThe O1s core-level spectra for GRO, shown in i.e., the widest) occurs in the range of 3320–3430 cm−1 and is attributed to the C–OH stretching vibrations of a hydroxyl group [−1 and is attributed to the C=C skeletal vibration of non-oxidized graphite [−1 and is attributed to the alkoxy C–O stretching vibration [The FT-IR spectra of the samples of graphite and graphene oxides are presented in yl group ,32,33,34graphite ,33,34. Aibration ,32,34.−1 and is attributed to the C=O stretching vibrations of a carbonyl group (at the edges of planes of the graphite layer) [−1 are characteristic for asymmetric and symmetric stretching vibrations of the C-H bond in CH2 and CH3 groups [i.e., the widest) peak is located at approximately 1220 cm−1 and is attributed to the stretching vibration of the epoxy group C–O–C [−1 and is attributed to the C=C skeletal vibration of the graphene planes [−1, is attributed to C–OH stretching vibrations of a hydroxyl group [−1) is attributed to the stretching vibration of the carbonyl group C=O [The next peak with the lowest intensity is located at approximately 1730 cme layer) ,32,34,353 groups ,34. The up C–O–C ,32,34,36e planes ,33,34,36−1 (D) and 1550–1600 cm−1 (G) [The Raman spectra of graphite oxide and graphene oxide are shown in cm−1 (G) . The ratThe presence of additional elements in the analyzed structures was also confirmed by application of other methods of measurements, for example Scanning Electron Microscopy with the EDX detector. EDX maps are shown in Nevertheless, the analyses are in quite good agreement, but the EDX and EA data confirm the presence of sulphur in the samples. On the basis of the maps, it may be concluded that the samples are very uniform over the entire volume.The properties of graphite oxide and graphene oxide change together with the temperature, affecting directly the properties of sensor structures based on the mentioned materials. Therefore, measurements were accomplished using the TG/DTG, and DSC techniques and also measuring the resistance at various degrees of temperature.Analysing the data from Sensor structures are also characterized by various resistance values. In the course of the oxidation process, the incorporated oxygen overcomes the van der Waals bonds and as a result, the interplanar distances increase. The reduction of graphene oxide eliminates a considerable amount of oxygen and changes the impedance characteristic of the material. A reduction in the amount of groups containing oxygen increases the electronic conduction, resulting in a decrease of resistance.It ought to be mentioned that the resistance of graphite oxide changes in a different way with the rise of temperature than the resistance of graphene oxide. The conductivity of a structure containing graphite oxide increases with the rise of temperature (within the range from 50 °C to 150 °C), both in nitrogen and in synthetic air. The character of these changes is linear. In the case of nitrogen, the rate of changes amounts to 37.7 mΩ/°C, whereas for synthetic air it amounts to 38.6 mΩ/°C. In the structure with graphene oxide, the resistance grows with the increasing temperature. For nitrogen, the rate of changes amounts to 7.8 mΩ/°C while for synthetic air it is equal 8.1 mΩ/°C. The results are presented in The different conductivity characteristics are probably due to the changes occurring in the atomic bonds of materials. The connection of oxygen to graphite (during the formation of graphite oxide) is at the expense of double bonds in the graphite. The effect of this is the degradation of the π set and the change in the mechanism of conductivity of the current in the obtained graphite oxide (from electron to semiconductive). A further reduction results in a partial regeneration of the structure of the π bonds by removing the oxygen from the structure and a return to electron conductivity which is decreasing with an increase in the temperature in the obtained reduced graphene oxide.Subsequent experiments were devoted to investigations concerning the sensor properties of the structures with graphite oxide and graphene oxide in varying gaseous atmospheres. As the first test, the resistance was recorded during an alternate dosing of hydrogen with a concentration of 4% in synthetic air. These investigations were executed at various temperatures within the 30 °C to 150 °C range. The resistance of the graphite oxide structure did not change in spite of changes in the composition of the surrounding atmosphere . Such a character of the changes may be explained by the formation of dangling bonds in the reduction process. Favorable spots for the adsorption of the gases are created in the structure contributing to electric response changes; hydrogen adsorbing onto the structure transfers electrons and as a consequence the resistance of the structure is increasing . This faThe difference between the resistance during the dosing of nitrogen or synthetic air and the resistance during the dosing of hydrogen (4% in a carrier gas) increases . It is cThe sensor structure with graphene oxide was characterized by changes of the resistance during the dosing of nitrogen oxide. In such a case, both during alterdosing nitrogen oxide with various concentrations in the nitrogen, and nitrogen oxide in synthetic air, the resistance of the structure dropped in the case of dosing nitrogen dioxide. The structure with graphite oxide did not change its resistance in spite of changes of dosing gases. Exemplary characteristics are presented in In contact with the structure, nitrogen dioxide behaves like a donor of electrons, reducing the resistance of the structure ,21,41. T2 and the carrier gas: nitrogen and synthetic air.During the experiments, neither the structure with graphite oxide nor the structure with graphene oxide changed their resistance due to their contact with carbon dioxide in a distinct way. Insignificant changes of resistance were recorded , but mosThe paper deals with a technique for obtaining graphite oxide by applying Hummer’s method and the technique of getting (on this graphite oxide) reduced graphene oxide. The paper presents the results of investigations concerning the chemical and physical properties of the obtained materials.viz. XPS, EDX and AE methods, which confirmed a considerable reduction in the amount of oxygen in the graphene oxide. Changes caused by the reduction were also confirmed by Raman’s Spectrometry and the methods TG/DTG as well as DSC.The investigations performed by means of the SEM and AFM techniques have proved that the surfaces of graphite oxide were evidently more developed than the surfaces of reduced graphene oxide. The thermal reduction involved a separation of numerous functional groups from graphite oxide, resulting in a change of the chemical composition of the obtained material. These changes were confirmed by three methods of measurements, independent of each other, 2 in atmospheres of synthetic air . The investigations have proved that a resistance structure with a layer of reduced graphene oxide can react to NO2 already at a concentration of ppb in an atmosphere of carrier gas. This provides options for its practical use in sensing of nitrogen dioxide obtained by means of the method suggested in this paper.Investigations on the sensitivity of the electric properties of the resistance structures based on graphite oxide and reduced graphene oxide to chosen gases were also performed. Generally, it may be assumed that the possibility of using graphite oxide for gas sensors is rather limited. It seems that there are considerable perspectives for applying reduced graphene oxide for detecting NO


PD-L1 expression was significantly associated with poorer five-year-EFS . Further studies in osteosarcoma are needed to determine if targeting the PD-L1:PD-1 axis improves survival.Osteosarcoma patient survival has remained stagnant for 30 years. Novel therapeutic approaches are needed to improve outcomes. We examined the expression of Programmed Death Ligand 1 (PD-L1) and defined the tumor immune microenvironment to assess the prognostic utility in osteosarcoma. PD-L1 expression in osteosarcoma was examined in two patient cohorts using immunohistochemistry (IHC)  and expression was validated using quantitative real time PCR (n = 21) and western blotting (n = 9). IHC was used to determine the presence of tumor infiltrating lymphocytes and antigen-presenting cells (APCs) in the tumor. Expression of PD-L1 was correlated with immune cell infiltration and event-free-survival (EFS). The 25% of primary osteosarcoma tumors that express PD-L1 were more likely to contain cells that express PD-1 than PD-L1 negative tumors . Expression of PD-L1 was significantly associated with the presence of T cells, dendritic cells, and natural killer cells. Although all immune cell types examined were present in osteosarcoma samples, only infiltration by dendritic cells (28.3%  Osteosarcoma is the most common primary malignant bone tumor in children and young adults1246789In recent years, numerous studies have sought to define the interplay between the immune system and tumor, with the potential to target this interaction for therapeutic intervention. In many malignancies, both innate and adaptive immune cells play a role in the tumor microenvironment, with communication between natural killer (NK) cells, antigen presenting cells (APCs) such as macrophages and dendritic cells (DC), and lymphocytes allowing for effective tumor control1213Immune cells are initially attracted to tumor cells by the presence of tumor specific antigens. Cancers with higher mutational loads present greater numbers of tumor specific neoantigens and are frequently associated with robust immune infiltration111617191822Tumors escape immunosurveillance by expressing immune checkpoints, such as programmed death ligand-1 (PD-L1)24272930323334Previous studies have begun to examine the role of PD-L1 in osteosarcoma. Utilizing quantitative real-time PCR (qRT-PCR), PD-L1 mRNA expression was associated with lymphocyte infiltration22PD-L1 expression was quantified in osteosarcoma patient and standard cell lines by qRT-PCR. Three quarters of patient derived cell lines, all the osteosarcoma standard cell lines , and two thirds of tumor specimens demonstrated expression of PD-L1 mRNA greater than the negative MCF7 control cell line; however, only a small subset expressed PD-L1 at the same level as the positive control, breast cancer cell line MDA-MB-231. Specifically, three of the sixteen cell lines , 19% , and fouPD-L1 protein expression was validated with western blotting: 3 of 10 patient samples (30.0%) and 4 of 10 osteosarcoma patient derived cell lines (40%) demonstrated detectable levels of PD-L1 protein . mRNA anPD-L1 protein expression was subsequently examined using IHC  on an osThe presence of six groups of tumor infiltrating immune cells was examined by IHC in whole slides . PresencPD-L1 positive tumors were associated with infiltration by multiple immune cells types as compared to PD-L1 negative tumors, which demonstrated infiltration by fewer immune cells types. Tumors expressing PD-L1 were significantly more likely to demonstrate infiltration by all immune cell types compared with PD-L1 negative tumors . Tumors expressing PD-L1 compared to those that were PD-L1 negative were more likely to demonstrate infiltration by CD3+ T-cells , CD56+ NK cells , CD68+ macrophages , and CD1a+ DCs . In addition, immune cells were significantly more likely to express PD-1 in PD-L1 positive tumors compared with PD-L1 negative tumors  .IHC indicated that PD-L1 expression and immune cell infiltration is heterogeneous within the whole slide samples examined. Two osteosarcoma tumor maps, containing slides from multiple areas of tumor, were examined in order to assess the consistency of PD-L1 expression and tumor infiltrating immune cells across whole tumors. Four slides were selected from the map for patient A, containing tissue from four locations across the tumor mass . Six sliPatient A’s tumor was PD-L1 negative across all sections examined  and pativs. 69.4%, p = 0.01). In contrast, although the TMA cohort showed a trend for poorer survival with PD-L1 expression , this result did not achieve statistical significance  and CD68+ macrophages   . Infiltr= 0.032) .In this study we demonstrated that PD-L1 was expressed in up to 25% of osteosarcoma samples, as determined by IHC using whole slide tumor sections. It is noteworthy that only 6.8% of osteosarcoma tumors, examined using a TMA containing 1 mm cores, were PD-L1 positive. It seems likely that this discrepancy between whole slides and the TMA is a result of the heterogeneity of PD-L1 expression in osteosarcoma—although PD-L1 positive cells were robustly stained, they made up a small fraction of cells examined on whole slide tumor sections. It is also possible that creation of the TMA, which is created to maximize areas of viable tumors, may bias against areas that are PD-L1 positive. These results suggest that IHC using a 1mm TMA may underestimate the number of PD-L1 positive osteosarcoma tumors.ΔCT method, found that the 84.2% of primary osteosarcoma tumors express detectable PD-L1 mRNAA previous study, using a 2Our results validated pervious PD-L1 mRNA expression reported in osteosarcoma323334In this study, we have shown that PD-L1 expression in primary tumors may be a prognostic marker for poorer survival. In addition to identifying PD-L1 as a potential prognostic marker that may be present in up to 25% of osteosarcoma cases, we demonstrated that PD-L1 positive osteosarcoma tumors have higher numbers of TILs and APCs than their PD-L1 negative counterparts. Although infiltration by TILs is significantly higher in PD-L1 positive tumors and their presence trends with worsened survival, there is no significant association between TILs and patient survival. On the other hand, presence of either of the APCs examined, was significantly associated with worsened survival.in vitroTumor associated macrophages (TAMs) are present in multiple solid tumors, including breast, gastric, and ovarian cancers394041Although previous studies may suggest that the opposite may be the case, we found that the presence of CD68+ TAMs in primary tissue may be significantly associated with worse survival in osteosarcoma. In previous studies, by capturing both monocytes and mature (M1 and M2) macrophages with CD14 staining, the role of mature macrophages may have been confounded. In our current study CD68 staining captures both pro-inflammatory M1 and pro-tumor M2 macrophages. In order to clarify the role of macrophages in osteosarcoma, future studies should correlate the presence of CD68+/CD80+ M1 and CD68+/CD163+ M2 macrophages to osteosarcoma survival.It is also possible that osteoclasts, a subset of CD68+ bone specific macrophages, may impact osteosarcoma patient survival. Presence of osteoclasts in osteosarcomas have been linked to conflicting outcomes in past studiesPresence of a second APC, CD1a+ DCs, is also associated with poor survival in osteosarcoma. With the recent advent of DC vaccines as a cancer treatment, multiple groups have shown that DC vaccines have varying levels of effectiveness in animal models of osteosarcoma51525357A major limitation of this study is the small number of samples available in this single institution analysis of the tumor immune microenvironment in osteosarcoma. Our sample size was further limited by the lack of associated clinical data for a subset of tumors. Although the non-significant correlative outcome results in the TMA may be explained by the limited sample assessed in each core, and the limited sample number, these represent two different patient cohorts and we cannot rule out the possibility that the prognostic correlation is purely a random occurrence in a small patient population. Further studies are necessary to validate that these results can be recapitulated in a larger multi-institutional cohort.In conclusion, we have shown that tumor infiltration by either CD68+ TAMs or CD1a+ DCs may be associated with poorer survival in osteosarcoma. Furthermore, PD-L1 is expressed in a subset of primary osteosarcoma samples at the time of biopsy, and it may be prognostic for increased mortality. PD-L1 expression is associated with TILs and APCs, including PD-1 positive immune cells. Due to its expression in a significant number of osteosarcoma tumors and an abundant presence of immune cells, the PD-L1:PD-1 axis may be a promising target for immunotherapy in osteosarcoma, particularly given osteosarcoma known genetic complexity. Further evaluation of PD-L1 protein expression is warranted in a larger cohort of patients with osteosarcoma. Currently a phase II study of pembrolizumab (anti-PD-1 antibody) in patients with advanced sarcomas, including osteosarcomas, is ongoing, the results of which may be informative.2 humidified atmosphere at 37 °C.Both osteosarcoma standard cells lines  and isolated cells were cultured in Eagle minimum essential medium supplemented with 20% fetal bovine serum (FBS) and antibiotics. PD-L1 negative MCF7 breast cancer cells, PD-L1 positive MDA-MB-231breast cancer cells, and PD-L1 negative 3T3 cells were cultured in Dulbecco’s modified Eagle’s medium supplemented with 10% FBS. Primary osteosarcoma cultures were generated using standard collagenase disaggregation of surgical specimens from seven osteosarcoma patients, as has been described previously2 were constructed using tumors collected from a second cohort of patients . The tumors were collected in accordance with an IRB approved research protocol with patient/guardian informed consent as described previously−ΔΔCT method. MCF7 and MDA-MB-231 cell lines were used as a negative and positive control for PD-L1 mRNA expression, respectively. Due to lack of detectable amplification of PD-L1 in the negative control, the CT value for MCF7 was set to 40 for calculations.RNA was extracted from flash frozen osteosarcoma tumor samples from 15 patients using Trizol reagent (Invitrogen) and converted to cDNA using Superscript II transcriptase (Life Technologies). qPCR was performed using commercially available TaqMan primers for PD-L1 . Relative gene expression was normalized to an internal control, GAPDH, and calculated using the 2Tumors, collected from osteosarcoma patients were used to construct a TMA, as has been described previously60Multiple slides were selected from tumor maps that were previously generated for clinical purposes using osteosarcoma specimens obtained with parental consent from two patients enrolled in an IRB-approved bio-banking protocol at Montefiore Medical Center. Samples were analyzed from multiple locations within the tumor mass and surrounding tissue at the time of definitive surgery following neoadjuvant chemotherapy. A set of slides was generated for each patient and this was related to the specimen map, which provided each slide’s location within the tumor.Immune staining was optimized for proper antigen retrieval and antibody concentrations using immune tissue for positive controls and brain tissue for negative controls. Osteosarcoma tumor slides were baked at 60 °C for one hour and antigen retrieval was performed using either tri-citrate buffer, pH 6.0 or tris-EDTA buffer pH 8.0 at 100 °C for 20 minutes. Slides were de-paraffinized using xylene, rehydrated along an ethanol gradient, and blocked using dual endogenous enzyme-blocking reagent (Dako) and a subsequent normal goat serum block (Santa Cruz). Slides were incubated overnight at 4 °C in primary antibody followed by a one hour room-temperature incubation with secondary antibody. Antibody concentrations and information can be found in Slides were scanned and graded by three independent reviewers without previous knowledge of patient outcomes or demographics. Slides were graded with a quartile score based on the percentage of positive staining cells present in the core/slide . If scores between the three graders were discordant the average, rounded to the nearest whole integer, was used. A tumor with a score of 1 or higher, representing ≥1% staining, was considered positive for PD-L1 expression or immune cell infiltration. Images of IHC staining were obtained at 20× magnification using the Pannoramic Scanner and captured using Pannoramic Viewer (3DHISTECH Ltd).Patient demographic data from each cohort was reported as frequencies for categorical variables and means with standard deviations for continuous variables. The association between the expression of PD-L1 and the presence of immune cells was assessed using Fisher’s exact test or chi square analysis. Kaplan Meier curves were generated assessing the association between EFS and PD-L1 expression or immune cell infiltration, and the Log-rank (Mantel-Cox) test was utilized (GraphPad Prism software). Survival curves were generated using expression thresholds of negative, defined as no staining (grade 0) and positive defined as at least 1% staining .How to cite this article: Koirala, P. et al. Immune infiltration and PD-L1 expression in the tumor microenvironment are prognostic in osteosarcoma. Sci. Rep.6, 30093; doi: 10.1038/srep30093 (2016).


Electrostatic interaction between the most electronegative element fluorine (F) and hydrogen (H) is one of the strong interactions in hydrogen bonding, and here we report the selective binding of ammonia/ammonium with F in fluorographene (FG) resulting to a change in the impedance of the system. Very low limit of detection value of ~0.44 pM with linearity over wide range of concentrations (1 pM–0.1 μM) is achieved using the FG based impedance sensor, andthisscreen printed FG sensor works in both ionized (ammonium) and un-ionized ammonia sensing platforms. The interaction energies of FG and NH3/NH4+ are evaluated using density functional theory calculations and the interactions are mapped. Here FGs with two different amounts of fluorinecontents −~5 atomic% (C39H16F2) and ~24 atomic% (C39H16F12) - are theoretically and experimentally studied for selective, high sensitive and ultra-low level detection of ammonia. Fast responding, high sensitive, large area patternable FG based sensor platform demonstrated here can open new avenues for the development of point-of-care devices and clinical sensors.Single molecule detection using graphene can be brought by tuning the interactions  Helicobacter pyloribacterial stomach infection. The amount of exhaled air available will be minimal and hence high sensitive ammonia breathe sensors are highly demanding, but lacking at present. Apart from ammonia gas sensors, analysis of ammonia (ionized/un-ionized) level in blood is also of interest in medicine. Blood ammonia monitoring has of interests in sports medicines (0.1 to 10 ppm) and pediatrics (>100 μmol/L) too34Several articles have been reported in the past discussing the development of various gas sensors, and ammonia is one of the gases taken seriously due to its natural and industrial origin1234Presently various sensing platforms are existing for ammonia: metal oxide based sensors6791114via doping and defects. Further, robustness and availabilities of different detections mechanisms of the graphene based devices (electronic transducers (field effect transistor), electrochemical  sensors etc.) attract the development of graphene based sensors1617Graphene based biosensors are receiving tremendous scientific attention due to the engineering possibilities of graphene by bringing specificity and sensitivity in the device et al. have reported Density Functional Theory (DFT) calculations based graphene oxide (GO) – ammonia interactionset al. reported a reduced GO (RGO) based conductometric ammonia sensor with the LOD of 200ppm and also mentioned its some extend of selectivity towards ammoniaTang 0.25)x)252627Relatively high thermal stability of fluorographene (300–400 °C)via residual groups. FG based screen printed electrode is developed and its efficacy in ammonia sensing using impedance spectroscopy is demonstrated. Large area patternability of chemically derived FG is shown using a soft-lithography process, indicating the possibilities of FG based different sensor geometries.In the present study, we report the interactions of FG and ammonia (unionized and ionized (ammonium)) using DFT calculations. The interactions between graphene and ammonia are also explored to compare the strength of FG-ammonia interactions. The FGs in the present study are derived from fluorinated graphene oxide  and the role of residual functional groups in the interactions is not studied. Later, using Fourier Transform-Infrared (FT-IR) studies, we found that the interaction between fluorine and ammonia is prominent than other hydrogen bonding interactions via sp3 hybridization. FG is an atomically layered material as it is evident from the electron microscope images given in the supporting information, 4+). The DFT studies reveal that FG is having strong interactions with ammonia compared to graphene  due to the strong hydrogen bonding between C-F in FG and N-H in ammonia. The optimized structures of complexes are shown in 4+  is higher than the G-NH4+, the difference is less than that in the case of ammonia. This might be due to the enhanced electrostatic interaction between positively charged of ammonium ion and graphene (π electrons).FG has a carbon honeycomb lattice like in graphene with covalent fluorine (F) attached to carbon 4+) and graphene/FG were calculated from HOMO and LUMO energies of the corresponding complexes. The calculated energy gaps are shown in 3/NH4+ and FG is less than that of NH3/NH4+ and graphene. This can be due to the strong interactions of NH3 or NH4+ with FG, making the energy differences between HOMO and LUMO smaller. Further, the electrostatic potential maps of the interactions are shown in 3/NH4+ has strong electrostatic interaction with negatively charged 2p orbital of fluorine on FG, leading to a hydrogen bonding (electrostatic) interaction. The interaction maps show considerable orbital overlapping of NH3 and NH4+ with FG, while little interaction between NH3 and graphene is observed as it is reported by other researchers4+ shows a better interaction with graphene due to its positive charge.The optimized structures and electrostatic interactions between ammonia/ionized ammonia (NH19 Nuclear Magnetic Resonance (NMR) spectrum, as shown in the supporting information, −1 in theoretical FG is due to the =CH stretching of the end terminated hydrogen while in the case of FG experimental spectrum it is due to the –OH stretching from residual functional groups. In −1is clear in both theoretical and experimental spectra. The FG has been exposed to ammonia gas (pressure ~1 psi) for different exposure times, and the corresponding FT-IR spectra are shown in The theoretical prediction of interaction between FG and ammonia is experimentally validated using FT-IR and micro Raman spectroscopy. Chemically derived (explained in the method section) FG powder (low resolution transmission electron microscope (TEM) image and high angle annular dark field TEM images are shown in 25−1, respectively. The G band of graphene originates from the vibration of in-plane sp2 carbon. The D band is attributed to the defects in graphene. There are no considerable changes in the positions and intensity ratios of D and G bands before and after the exposure of ammonia indicating that the graphene structure is not disturbed after the ammonia exposure The micro-Raman spectra of graphene and FG before and after exposing to ammonia are shown in via the electrostatic hydrogen bonding is utilized for the development of an ammonia sensor, as explained in the following section. Electrochemical impedance spectroscopy (EIS) was used to study the binding of ammonia on FG modified screen printed electrodes  increases with increase in ammonium ion concentration. The increase in Rct is attributed to the binding of ammonium to the FG via hydrogen bonding. In order to confirm that the observed change in impedance is due to surface modification of SPE and not due to superimposed effects, ratio of charge transfer resistance for the desired concentration (Rct(Ci)) and charge transfer resistance of the blank FG electrode (Rct(Co)) is plotted against the logarithm of ammonia concentration (ct(Ci)/Rct(Co) = 1.723 + 0.055 log CNH3. This shows that the sensor works in a linear concentration of ammonia in the range of 1 pM to 0.1 μM with a correlation coefficient of 0.998. Sensitivity of the sensor can be deduced from slope of this curve, resulting to a value of ~0.055 M−1. The limit of detection (LOD) of the sensor has been calculated according to Long and Wineforder methodIt is evident from the ntration . Figure where S.D. is the standard deviation of the blank, a is the linear coefficient, and b is the angular coefficient (sensitivity). The calculated LOD is found to be ~0.44pM.ct (ΔRct) values and the logarithm of ammonia concentrationsreveals a linear detection range for ammonia concentrations in the range of 1 pM to 0.1 μM with 4.4 × 10−13M (0.44 pM) limit of detection. The linear relationship could be characterized using the linear equation: ΔRct (kΩ) = 3.832 + 0.293 log CNH3 (kΩ). This FG modified SPE exhibits a sensitivity of 0.293 kΩ M−1 with a correlation coefficient of 0.997 and standard deviation of 0.018 kΩ  and 5 mM[Fe(CN)6]3− (ferricyanide). The experimental set up is shown in supporting information Further, EIS measurements are also conducted by direct purging of ammonia in to the phosphate buffer solution (PBS)  containing the mixture of 5 mM4− and 5 mM[Fe(CN)6]3 over the frequency range 105–0.01 Hz with 5 mV as the alternating current amplitude. Using the redox probe (5 mM [Fe(CN)6]3−/4−), change in charge transfer resistance (Rct) at electrode/electrolyte interface has been investigated in electrochemicalimpedance.Electrochemical impedance studies (EIS) were conducted using a Biologic potentiostat, model SP-300. Low-cost, screen-printed electrodes  spectrometer. The micro-Raman spectra of GO and FGO samples were studied using LabRamXploRA Raman spectroscope (excitement wavelength 632 nm).http://pubs.acs.org.TEM images of FG, XPS and NMR data of FG, schematics of screen printed electrode and ammonia sensing set up are provided in the supporting file. Theoretically evaluated bond lengths observed in free graphene and FG is also provided in the supporting file. SEM image and Raman mapping of large area printed FG microelectrodes is provided. Direct ammonia sensing data is also provided. Ammonia sensing results  with high fluorine containing graphene is also provided. This material is available free of charge via the Internet at How to cite this article: Tadi, K. K. et al. Fluorographene based Ultrasensitive Ammonia Sensor. Sci. Rep.6, 25221; doi: 10.1038/srep25221 (2016).


Go = 2e2/h (=12.91 kΩ−1), and in some devices partially quantized including a series of with (n/7) × Go, steps are observed. Such an organic memory device exhibits reliable memory operation with an on/off ratio of more than 10. We attribute the quantized conductance to the existence of a 1-D electron waveguide along the conductive path. The partial quantized conductance results likely from imperfect transmission coefficient due to impedance mismatch of the first waveguide modes.Quantized conductance is observed at zero magnetic field and room temperature in metal-insulator-metal structures with graphene submicron-sized nanoplatelets embedded in a 3-hexylthiophene (P3HT) polymer layer. In devices with medium concentration of graphene platelets, integer multiples of  Go = 2e2/h  in a suspended graphene nanoconstriction at cryogenic temperature of 4.2 K. The observed quantized conductance was attributed to the graphene zigzag or armchair edges that provide effective boundary conditions for the quantum mechanical wave functions. In 1998, Frank et al. [Go conductance per nanotube. Calculations by Sanvito et al. [Graphene  has attrk et al. , 11 obseo et al. , 14 are o et al. –17 in tao et al.  showing Here, we present experimental observation of integer and partially quantized conductance at room temperature in metal-insulator-metal (MIM) structures consisting of graphene nanoplatelet (GNP) ribbons suspended in a 3-hexylthiophene polymer (P3HT) layer interposed between metal copper and gold electrodes.2-bonded carbon atoms densely packed in a honeycomb crystal lattice. The number of stacked layers is typically between 5 and 30. The lateral dimension of the flakes ranges between 100 nm and a few micrometers. The graphene platelet ribbons are substantially flat, but when made thin by exfoliation, they can be curved, curled, or buckled indicating a single flake or a stack of a few carbon sheets [Our graphene-based MIM devices have been fabricated on a thermally oxidized silicon wafer using standard semiconductor processes. The thermally oxidized silicon wafer was first cleaned using acetone and subsequently rinsed in isopropanol and deionized water. The wafer was then patterned photolithographically and deposited with a bottom gold (Au) electrode using electron-beam physical vapor deposition (EBPVD). GNP powder provided by PPG Industries  was firsn sheets , 22. Ultn sheets –22. The n sheets –26. We nFour types of samples have been manufactured with regard to GNP content in the polymer: (i) no GNP, (ii) 0.05 mg/ml, (iii) 0.1 mg/ml, and (iv) 0.2 mg/ml of GNP concentration.Go or repeatable fractions of Go, respectively, as function of applied voltage. Figure υ = 0.225 V/s (V(t) = υ × t) along the positive x-axis from 0 to 2 V. The current is observed to increase gradually and ohmically in the low-voltage region, and then abruptly increase at three voltages, specifically at 0.75, 1.2, and 1.87 V to 10, 162, and 409 μA, respectively. The initially high-resistance state (HRS) of about Roff = 100 kΩ is reduced during the voltage sweep to a final low-resistance state (LRS) of Ron = 5 kΩ. Figure Go. Conductance increases with voltage discretely, and instead of displaying flat plateaus as in quantum Hall effects, it displays sloped rises whose slopes decrease with the subsequent two steps. To characterize this behavior in terms of energy consumed, we have calculated the energy consumed between individual discrete jumps. For the first slope we obtain, assuming a linear voltage ramp rate υ:From these four types of devices, only devices with 0.1 mg/ml show integer and partial quantized conductance as shown in Figs. V1 = V(t1) = 0.72 V, V2 = V(t2) = 1.22 V, and υ = 0.225 V/s) we obtain Estep(1) = 1.03 × 1015 eV. As this number is many orders of magnitude higher than kT, thermal effects can be ruled out for being responsible for the sloped conductance. Assuming that somewhere in the device a one-dimensional filament is being formed, one could attribute the slope to progressive thickening of the conductive filament constituting a waveguide. Another possible explanation is that the transmission coefficient of the electron waveguide is a function of the applied voltage. When the transmission coefficient is close to unity, it causes an integer quantized conductance jump. In Fig. Go instead of nGo as in Fig. V = 1.3 V to V = 1.45 V, it can be seen that the conductance changes abruptly from 1Go to 2Go and above V = 1.5 V rises from 2Go to 3Go. In addition, from V = 0.0 V to V = 1.3 V, a sequence of smaller conductance steps within the 0Go to 1Go interval is also observed, indicating that the partial quantized conductance coexists with integer quantized conductance. The best fit to the partial quantized conductance within the 0Go to 1Go interval can be obtained by assuming a fraction vGo with v = 1/7, 2/7, 3/7, 4/7, 5/7, and 6/7, although 3/7 is slightly off the experimental value. The resolution of the partial conductance steps between 1Go and 2Go is always much less pronounced and appears to follow the same multiples of 1/7. Steps with 8/7, 9/7, 11/7, and 13/7 can be clearly identified. In the third conductance step, from 2Go to 3Go, only a rudimentary partial quantized conductance can be discerned. The behavior shown in Fig. Icc is imposed during the set operation. Such a case is shown in Fig. Icc = 0.1 mA. It can be seen that the hysteresis is now pronounced and readily detectable as a difference in logic state “0” for off-state and “1” for on-state. The conductance observed during the set transition of 1.4 V has been extracted and is plotted in Fig. Using the data from Fig. Icc), which is commonly used in resistive random access memory devices less the device be damaged. Icc is the maximum current that is allowed to flow through the device. In resistive random access memory, devices under the Icc limitation quantized conductance is also observed when a fresh device is subjected to negative bias. In Fig. Vreset = −0.7 V can be observed.As we consider Au/P3HT/Cu cells for potential memory applications, we have performed the set operation under imposition of the so-called compliance current  than the ionization energy for Au (9.23 eV).” As shown in Fig. + ions migrate across the polymer and reach a GNP platelet where they are reduced to Cu atoms. Under a positive bias applied to the Cu electrode, Cu+ ions may be injected into the polymer and form a conductive filament between the Cu electrode and graphene platelets whose other end makes a contact with the Au electrode. As a result of this, the Cu+ ions could aggregate more densely in the polymer than along the graphene surfaces and form tiny nanofilaments connecting the graphene layers to each other or to the electrodes. One observes that when a negative bias is applied to the Cu electrode, a strong enough field is able to ionize the neutralized Cu atoms of the nanofilaments and rupture them, disconnecting them from the graphene nanoplatelets.Following the explanation adopted for Cu and Au nanofilaments and quantum point contacts in mesoscopic physics , 31, we  devices , 33. TheGo), for wider constrictions, second and higher modes are transmitted. Each mode contributes a unit Go to the conductance if the transmission coefficient of the mode through the constriction is unity (perfect transmission without backscattering) [2). At a GNP concentration of 0.1 mg/ml, we find a 50 % chance that one graphene nanoribbon will span the entire dielectric distance. At a GNP concentration of 0.05 mg/ml, not a single case of bridging has been observed. On the other hand, at concentration of 0.2 mg/ml, the very high measured conductance value points to multiple graphene nanoribbons in parallel bridging the two metal electrodes. While the highly conductive devices with GNP concentration of 0.2 mg/ml do not display quantized conductance effects, they are a good material candidate for stretchable transparent electrodes [The 1-D conducting bridge forms a constriction of width of the order of the Fermi wavelength of the electron. For a width approximately half of the Fermi wavelength, one transverse mode will contribute to conductance (1ttering) , 31. Yetectrodes . On the The non-unity transmission coefficients are caused by the sensitivity to the electrostatic environment. Likewise, in memristive devices, in contrast to conventional resistors and capacitors, the resistor and capacitor  are voltIn summary, we have observed integer and partial quantized conductance occurring in graphene nanoplatelets doped organic polymer films at room temperature. The quantized conductance is likely a result of the formation of a 1-D waveguide with a voltage-tunable transmission coefficient. The device shows a distinct I-V hysteresis and lends itself for memory applications


Halomonas spp. CAM2 by introducing single layer graphene coatings. The use of this nanomaterial has been poorly explored for antifouling application.Biofouling, the colonization of artificial and natural surfaces by unwanted microorganisms, has an important economic impact on a wide range of industries. Low cost antifouling strategies are typically based on biocides which exhibit a negative environmental impact, affecting surrounding organisms related and not related to biofouling. Considering that the critical processes resulting in biofouling occur in the nanoscale/microscale dimensions, in this work we present a bionanotechnological approach to reduce adhesion of biofilm-producing bacteria Our study revealed that graphene coatings modify material surface energy and electrostatic interaction between material and bacteria. Such nanoscale surface modification determine an important reduction over resulting bacterial adhesion and reduces the expression levels of genes related to adhesion when bacteria are in contact with graphene-coated material.Halomonas spp. CAM2. Hydrophobic-hydrophilic interaction and repulsive electrostatic force dominate the interactions between Halomonas spp. CAM2 and material surface in saline media, impacting the final adhesion process. In addition no bactericide effect of graphene coatings was observed. The effect over biofilm formation is localized right at coated surface, in contrast to other antifouling techniques currently used, such as biocides.Our results demonstrate that graphene coatings reduce considerably adhesion and expression levels of adhesion genes of biofilm-producing bacteria  Marine fouling is the accumulation of micro and macroorganisms on underwater surfaces, which provide a favorable mechanism to survive in the environment. The economic impact of fouling on shipping vessels, oceanographic sensors, power plants and aquaculture systems, among others, has been estimated to be in the range of 50 billion euros per year –3. In paCurrent techniques to prevent (antifouling) and fight fouling (fouling-release) include physical  and chemical methods . Although the choice of the right strategy will depend on the cost and application possibilities, antifouling coatings are probably the most cost-effective method for boats and other surfaces. They are typically based on the controlled release of organic solvents into the environment to kill the colonizing microorganism. However this approach offers a non-localized solution, affecting surrounding organisms related and not related to fouling. As a consequence, the use of certain biocides has been restricted by some countries and in Europe a large amount of data has been gathered as part of the Biocidal Products Directive  .The critical processes at the biointerface resulting in biofouling occur in the nanoscale/microscale dimensions: it follows therefore that surface properties which could control biofouling need to be on the same length scales . Search Graphene is a one-atom thick carbon sheet that has emerged as a new carbon compound with multiple applications in a wide range of industrial processes and products. While graphene is a promising candidate in electronic applications, its use for biological applications, such as antifouling, has been poorly explored. There are many reports of bacterial interaction with graphene oxide (GO), formed by micro- or nano-sized flakes of functionalized graphene in powder, solution or coating –18, whicHalomonas spp. CAM2, which is used as a model marine bacterium.In this report we present a physico-chemical and biological approach to reduce fouling formation in its initial growth stage as biofilm, by introducing graphene coatings that reduce bacterial adhesion to coated surfaces. Nanoscale behavior is discussed in the particular case of biofilm-producing 2 samples was carried out to evaluate their composition, microstructure, topography with atomic resolution, graphitic quality and contamination.Micro and nanoscale characterization of as-grown graphene on Cu and graphene transferred onto SiO2 process is described in materials and methods section.Scanning electron micrographs of single layer graphene (SLG) grown on Cu showed some contrast at micrometer scale that could be identified as graphene domains Fig. b. Atomic2 samples prior to bacteria contact was screened by SEM, optical microscopy and STM. Wrinkles in CVD graphene grown on Cu are formed by differential thermal expansion, as the metal contracts more than the graphene during post-growth cooling  = 2−ΔΔCt.Relative quantification of each target gene  encoding for adhesin in each experimental sample, and control versus reference gene rDNA16S) was performed in according with Livak Eq. 6S was pe


TrkB is a high affinity receptor for the brain derived neurotrophic factor (BDNF) and its phosphorylation stimulates activation of several intracellular signalling pathways linked to cellular growth, differentiation and maintenance. Identification of various activators and inhibitors of the TrkB receptor and greater understanding their binding mechanisms is critical to elucidate the biochemical and pharmacological pathways and analyse various protein crystallization studies. The data presented here is related to the research article entitled “Brain Derived neurotrophic factor is involved in the regulation of glycogen synthase kinase 3β (GSK3β) signalling”  Specifications TableValue of the data•Three dimensional molecular model of the cyclic peptide cyclotraxin B was generated for the first time to determine its interactions with the TrkB receptor.•Future studies to determine pharmacological, biochemical or interaction studies of TrkB receptor or related molecules will be facilitated by the interaction and binding parameters reported here.•Binding interactions of CTXB with TrkB will determine its potential usage in pharmacological studies and development of new derivatives and ligands.1The data shown here elucidates molecular modeling of cyclic peptide cyclotraxin B which is a TrkB inhibitor. Active site of the extracellular D5 domain of the TrkB receptor which is primarily involved in this interaction was also modelled. Finally the cyclic peptide inhibitor was also identified and docking carried out with the extracellular D5 domain of TrkB. The interacting amino acid residues that are involved in docking are identified and various interaction parameters provided in detail using a combination of molecular modeling and molecular docking computational tools.22.1via MOPAC  method Cyclotraxin B (CTXB) is a cyclic peptide chain of 10 amino acid linked by a disulphide bridge 2.2The primary structure of TrkB receptor and its various domains were examined 2.3in silico assessment of the potential binding of selected CTXB residues to different regions on the TrkB D5 surfaces. This binding interactions were assessed in terms of probability of CTXB participating residues binding to the TrkB D5 receptor surface and theoretical scores determined using the PepSite2 server The protein motif was subjected to PepSite2 is a computational tool that scans the surface of a given protein for patches or grooves that are likely to influence binding of individual amino acid residues or peptides up to ten amino acids and provides a score that reflects the propensity of the peptide to bind to that region. The PepSite score is expressed in relative units and the higher scores reflects superior binding. We applied PepSite in a sliding window of 10 residues to assess the binding of the TrkB-D5 domain and CTXB peptide sequence (CNPMGYTKEG). The scores of the CTXB binding to different regions of TrkB D5 domain are presented  [1].2.4The protein-peptide docking was performed with the PatchDock software available in the public domain


In-situ homogeneous dispersion of noble metals in three-dimensional graphene sheets is a key tactic for producing macroscopic architecture, which is desirable for practical applications, such as electromagnetic interference shielding and catalyst. We report a one-step greener approach for developing porous architecture of 3D-graphene/noble metal (Pt and Ag) nanocomposite monoliths. The resulting graphene/noble metal nanocomposites exhibit a combination of ultralow density, excellent elasticity, and good electrical conductivity. Moreover, in order to illuminate the advantages of the 3D-graphene/noble metal nanocomposites, their electromagnetic interference (EMI) shielding and electrocatalytic performance are further investigated. The as-synthesized 3D-graphene/noble metal nanocomposites exhibit excellent EMI shielding effectiveness when compared to bare graphene; the effectiveness has an average of 28 dB in the 8.2–12.4 GHz X-band range. In the electro-oxidation of methanol, the 3D-graphene/Pt nanocomposite also exhibits significantly enhanced electrocatalytic performance and stability than compared to reduced graphene oxide/Pt and commercial Pt/C. Graphene, a two-dimensional structured carbon material, has captured the attention of the scientific community considerably due to its exceptionally high mechanical strength, ultrahigh specific surface area, and unique conductivity11454510115451671321et al. have reported ultra-light 3D-graphene–based cellular monoliths using a cost-efficient freeze-casting process with ultra-low density, superelasticity, good electrical conductivity, and high-energy absorption efficiencyRecently, three dimensional (3D) graphene assemblies have been used as 2425262728In the present work, we develop a greener, efficient, and low cost one-step approach to large-scale production of 3D-graphene/noble metal (Pt or Ag) nanocomposites by freeze-casting of partly RGO and metal salt solutions. The as-obtained 3D graphene/noble metal (Pt or Ag) nanocomposites were characterized by various spectroscopy studies and correlated with microscopic and surface area analysis. The structure, electrical conductivity, and mechanical properties of as-synthesized 3D-graphene/noble metal (Pt and Ag) nanocomposites were also investigated. The resulting 3D-graphene/noble metal (Pt and Ag) nanocomposites show a combination of ultralow density, excellent elasticity, and good electrical conductivity. Further, the enhanced conductive 3D-graphene/noble metal (Pt and Ag) nanocomposites were extended to EMI studies, in which enhanced conductivity is a necessary criterian. It is interesting that the 3D-graphene/noble metal (Pt and Ag) nanocomposites showed enhanced shielding effectiveness when compared to bare 3D-graphene. In addition, 3D-graphene/Pt nanocomposite is used in electrocatalytic activity study of methanol electro-oxidation. Here, the large and accessible pores of variable sizes helps for quick transportation of reactants to electro-active sites is provided by the 3D-graphene network; in addition, the high electrical conductivity of catalysts are maintained overall. As a result, in the electro-oxidation of methanol, 3D-graphene/Pt nanocomposites show excellent electrocatalytic properties such as a high electrocatalytic performance, abnormal poison tolerance, and dependable stability, which are of a higher grade compared to those of Pt/reduced graphene oxide nanocomposites and commercial Pt/C.2PtCl6.6H2O), and Silver nitrate (AgNO3) were purchased from Sigma-Aldrich. All other chemicals employed were of analytical grade, purchased from Merck Specialties Private Limited, India. Commercial Pt/C  was obtained from Sigma-Aldrich. All the chemicals employed were used as-received without any further purification.Natural graphite powder of a particle size of 45 μm (99.99% purity), Hexachloroplatinate (H2PtCl6.6H2O = 4.5 mg/AgNO3 = 2.5 mg) separately in a cylindrical glass vial of a capacity of 4 ml. To this, ascorbic acid (15 mg) was added and kept in a heating oven at 100 °C for 30 min to get partly reduced GO dispersion and a reduction of metal ions. Each vial was then frozen for 0.5 h in a dry ice bath. After being thawed (at room temperature), the vial was put into a heating oven at 100 °C for 4 h, to further reduce GO to obtain a gel. The gel was then successively subjected to dialysis (to remove dissolved species), freezing drying, and was then dried for 24 h at 50 °C. A detailed schematic representation of the synthesis procedure is presented in the GO aqueous dispersions was prepared by using a reported literature process30λ = 1.541 Å); a Magna-IR spectrometer-50 (Nicolet) was used to record FTIR spectra by a standard KBr pellet method. Raman scattering was performed by a RAM HR 800 Micro laser Raman system with a 519 nm Ar+ laser. The chemical states and surface compositions of the as-synthesized samples were analyzed using XPS . The morphology of the samples was examined by HRTEM using the Phillips-CM 200 electron microscope. The composition of the as-prepared samples was analyzed by an ICP-AES . The specific surface area, pore volume and size distribution of as-synthesized samples were analyzed by Micromeritics instrument ASAP 2020, and the specific surface areas were determined by the multipoint Brunauer−Emmet−Teller (BET) method. The samples were degassed at 60 °C for 4 h, before the analysis. Cylindrical-shaped (~10 mm in height and ~12 mm in dia.) samples were prepared for electrical conductivity measurements and compressive tests. A broadband dielectric spectrometer (Novocontrol) with an Alpha-A frequency analyzer were used to study the AC conductivity of the as-synthesized samples in the frequency range of 1 Hz to 10 MHz. Conductivity measurements were carried out by putting the samples in between the gold-plated copper electrodes. The compressive tests were executed in an Instron  that utilized a load cell (10 N) and had a strain rate of 100% per minute. EMI shielding properties were measured by using PNA Network Analyzer N5222A (Agilent) in the X-band. Catalyst ink was prepared by dispersing 5 mg of each catalyst in a mixed solution of 5 mL of Millipore water, 1 mL of iso-propanol, and 10 μL of Nafion® solution under sonication for 20 min. The 20 μL of the catalyst ink (well dispersed) was drop-casted on the glassy-carbon electrode (0.07 cm2), named as the modified glassy-carbon electrode. Potentiostat/Galvanostat Autolab-302N with GPES 4.9 software was used for the electrochemical measurements. Electrochemical measurements were conducted in a three-electrode system. A platinum wire and a saturated calomel electrode (SCE) were used as counter electrode and reference electrode, respectively. A modified glassy-carbon electrode (3 mm diameter) was used as a working electrode. All the measurements were executed at room temperature. The volumetric solution was purged with high purity nitrogen gas for 5–15 min before an electrochemical scan. All the electrochemical potentials are reported against the reversible hydrogen electrode (RHE) in the manuscript.The structural examination of as-synthesized specimens were performed by using a Powder XRD diffractometer (Philips PW 3040/60) with Cu Kα radiation  nanocomposites by using a low cost wet shaping technique, which generally called freeze casting. In this process, phase separation took place between the solid particles and forming ice, and the rejected particles mounted up between the developing ice templates3228303334353637et al. groupGO and metal salt solution in presence of ascorbic acid produced 3D porous assemblies in freeze-casting process. To understand the mechanism, a control experiment was conducted by using a reported processXRD was used to explicate the phases and structural parameters of the as-synthesized GO and 3D-graphene/noble metal (Pt and Ag) nanocomposites samples; the results are shown in −1, and shifted to 1577, 1579 and 1580 cm−1 for the bare 3D-graphene, 3D-graphene/Pt and 3D-graphene/Ag respectively, which is close to the value of pristine graphene  is correlated with the change in the average size of the sp2 domains. The ID/IG ratios for GO, bare 3D-graphene, 3D-garphene/Pt and 3D-graphene/Ag nanocomposites are calculated to be 0.82, 1.1, 1.11 and 1.13 respectively. The increase in ID/IG ratios of bare 3D-graphene, 3D-garphene/Pt and 3D-graphene/Ag nanocomposites than GO indicated that the decrease in the average size of the sp2 domains. Even, the created new sp2 domains of reduced GO are smaller in size than the ones which is present in GO before reductionRaman spectroscopy is extensively used to observe the electronic and structural properties in carbonaceous materials. graphene . The shi−1 (O-H stretching), 1730 cm−1 (C=O stretching vibration of the COOH groups), 1405 cm−1 (O-H deformation vibration of tertiary C-OH), 1222 cm−1 (C-O stretching vibration of phenolic C-OH), and 1045 cm−1 (C-O stretching vibrations of epoxy groups). The band at 1612 cm−1 is related to the bending vibration of the adsorbed water molecules or skeletal vibrations of unoxidized C-C bonding−1 respectively. The shifting of the stretching vibration peaks towards lower wave number with increase in mass of the noble metals suggested the chemical interaction of metal ions with the graphene sheets. Also, O-H bending vibration peaks of adsorbed water molecules was become more prominent in 3D-graphene/noble metal nanocomposites and shifted to lower wave number with increasing the mass of noble metals. The O-H bending vibration peaks of H2O are observed at 1612, 1568 and 1572 cm−1 for GO, 3D-graphene/Pt and 3D-graphene/Ag monoliths respectively. The significant shifting of wave number towards lower side in 3D-graphene/noble metal nanocomposite might be due to the chelation of water molecules with the noble metals.The FTIR spectras of the as-prepared 3D-graphene–based noble metal (Pt and Ag) nanocomposites along with GO are shown in 2 carbon peak (284.5 eV), the intensities of the various oxygenic functional groups and the intensity of the sp3 carbon peak (285.1 eV) were effectively reduced in the case of the 3D-graphene/Pt nanocomposite. It was further confirmed that GO was successfully reduced to graphene in the 3D-graphene/Pt nanocomposite through the freeze-casting method. 5/2 and 4f7/2). The most intense doublet Pt 4f peaks at 71.1 eV (4f7/2) and 74.6 eV (4f5/2 ) are assigned to metallic Pt0, whereas the second doublet Pt 4f peaks at 72.1 and 77.51 eV are assigned to PtII. The appearance of PtII could arise from the partial oxidation of Pt0 on the graphene surface. Moreover, from 2 carbon of graphene via oxygen (Pt-O-C)5/2 and Ag 3d3/2 respectively, and suggested that the presence of metallic Ag0The surface chemistry of the GO, 3D-graphene/Pt and 3D-graphene/Ag nanocomposites was investigated by XPS analysis. The surface morphologies of the 3D-graphene/noble metal nanocomposites were examined by FEG-SEM. 6 Hz due to the incorporation of noble metal (Pt and Ag) particles in the 3D-graphene nanosheets. The real part of AC conductivity was derived by complex conductivity using the relation:where dc is the frequency-independent conductivity or dc conductivity (at ω=0), and A is the temperature-dependent constant. The addition of noble metal particles in 3D-graphene shows a prominent increase in conductivity, indicating frequency-independent behavior. The AC conductivity (σ′ (ω)) is almost constant over the frequency in 3D-graphene/Ag and 3D-graphene/Pt nanocomposites, which is ascribed to the dc conductivity, in which the electrode polarization is negligible. A similar type of behavior was observed in carbon nanotube-based composites earlierwhere ω is the angular frequency, exponent s is the function of frequency and is limited to 0.7 to 0.9. σThe dispersion of noble metal (Pt and Ag) particles on the 3D building blocks of nanosheets increases the conductivity to 0.032 S/cm in 3D-graphene/Ag and 0.01 S/cm in 3D-graphene/Pt nanocomposites. The electrical conductivity of 3D-graphene/noble metal nanocomposites (Ag and Pt) was significant to the compressed graphene nanosheets and graphite oxide reported earlier43The compression test of 3D-graphene/noble metal (Pt and Ag) nanocomposite at 50% strain was investigated to identify the stress-strain behavior under cyclic loading. The 3D-graphene/noble metal (Pt and Ag) nanocomposite was compressed to up to 50% strain under pressure; it recovered its original shape immediately after the pressure was released . The com50In support of conductive studies, the electromagnetic interference shielding properties of 3D-graphene and 3D-graphene/noble metal nanocomposites were studied in the X-band (8.2–12.4 GHz) by measuring shielding parameters using a vector network analyzer . The shi53PI corresponds to input power, and PT corresponds to Transmit powers.where where The shielding properties of 3D-graphene/noble metal nanocomposites were compared with the host 3D-graphene. The total SE in the composites is mostly dominated by the absorption phenomenon. It is interesting that the 3D-graphene/Ag nanocomposite showed better shielding properties than 3D-graphene/Pt and 3D-graphene. The SE of 28 dB for the 3D-graphene/Ag nanocomposite put forward a shielding power of ~99.6% in an average film thickness of 0.8 mm. Additionally, 3D-graphene/Pt showed an enhanced SE of 24 dB compared 3D-graphene (~18 dB). The total SE by the absorption phenomenon is mainly due to the interaction of electric dipoles with the electromagnetic field of radiation and the functional groups of functionalized 3D-graphene attained by the addition of noble metal  particles. Thus, the incorporation of fillers in the 3D-graphene plays an important role for improving the structure and electrical conductivity, which also revealed by our earlier studySE in terms of permittivity (ε), conductivity (σ′) and permeability (μ′) is expressed as:There by suggesting that the proportionate increase in conductivity in the 3D-graphene/Ag nanocomposite leads to substantial enhancement in the shielding effectiveness. Similar results have been reported earlier, in which carbon foam was embedded with Ni particles to improve the shielding properties2SO4. The CVs are scanned from −0.2 to 1.0 V with a scan rate of 50 mV s−1 in the 0.5 M solution of H2SO4 (N2-saturated). It has been observed that there are three potential regions on CVs of the commercial Pt/C (20 wt%), the RGO/Pt nanocomposite and the 3D-graphene/Pt nanocomposite. The first potential region from −0.2 to 0.05 V presents adsorption/desorption of hydrogen. The 2nd potential region from 0.1 to 0.3 V indicates the double layer capacitance region. The 3rd potential region from 0.4 to 0.9 shows the metal oxidation/reduction region. The 3D-graphene/Pt nanocomposite shows higher double–layer capacitance when compared to commercial Pt/C and the RGO/Pt nanocomposite. This is because of the larger surface area of the 3D-graphene as compared to the RGO and carbon black. The larger surface area of 3D-graphene is confirmed by the Brunauer-Emmett-Teller (BET) surface area analysis, which indicates that the specific surface area of the carbon black, RGO and 3D graphene are 94, 122 and 155 m2/g  and 36% more than that of the RGO/Pt nanocomposite (15.2 m2/g). The higher ESCA of Pt in the 3D-graphene/Pt nanocomposite may be due to the homogenous distribution of the Pt nanoparticles on the 3D-graphene (as indicated in TEM) and the distinct structure of 3D-graphene .In order to explore the potential application of 3D-graphene/noble metal nanocomposites as an electrocatalysts further, we have selected the 3D-graphene/Pt nanocomposite to study its catalytic activity in methanol oxidation. 155 m2/g , respectf) to the backward-scan peak current (Ib) that is, If/Ib value59f/Ib value for Pt/C, RGO/Pt, and 3D-graphene/Pt are 0.85, 1.06, and 1.3 respectively, signifying that the 3D-graphene/Pt nanocomposite has higher efficiency in the methanol oxidation in the forward direction.The electrochemical activities of the commercial Pt/C (20 wt%), RGO/Pt nanocomposite and the 3D-graphene/Pt nanocomposite were compared by CV for the oxidation of methanol, and the subsequent results are presented in the 56573OH and 0.5 H2SO4 for 2000 s. The initial current decay in all cases is due to the development of double layer capacitance. Subsequently, the current decays slowly, which can be attributed to the adsorption of a small amount of carbon monoxide (COads) species on the surface of the catalyst during electro-oxidation of methanol42− species on the surface of the catalysts, which inhibits the reaction active sites of the catalystsThe long-term catalytic activities of the Pt/C, RGO/Pt nanocomposite and the 3D-graphene/Pt nanocomposite were examined by a steady-state chronoamperometry measurement. In this study, we have demonstrated a general and clean method to fabricate 3D-graphene/noble metal (Pt and Ag) nanocomposites built from partially reduced graphene oxide and metal precursors using a facile and cost-effective freeze-casting method. The as-synthesized 3D-graphene/noble metal (Pt and Ag) nanocomposites consisted of a highly interconnected porous structure and exhibited enhanced mechanical properties and conductivity due to the incorporation noble nanoparticles (Pt and Ag) in the 3D-graphene building block. Their electrocatalytic performance and electromagnetic interference (EMI) shielding effect has been further investigated. The as-synthesized 3D-graphene/noble metal (Pt and Ag) nanocomposites exhibit an excellent EMI shielding effectiveness when compared with bare 3D-graphene, and can be used for electromagnetic radiation or as a radar-absorbing material in civil and military applications. Electrocatalytic activity of the 3D-graphene/Pt nanocomposite in methanol oxidation has been demonstrated, which shows high electrocatalytic activity, reliable stability and abnormally high poison tolerance compared to the RGO/Pt nanocomposite and Pt/C. The resulting 3D-graphene/noble metal (Pt and Ag) nanocomposites with highly interconnected micro and macro porous structures, and good electrical, mechanical and catalytic activities hold considerable promise of a new pathway for application in photocatalysis, pressure sensors, actuators, and electrode materials.How to cite this article: Sahoo, P. K. et al. Ice-templated synthesis of multifunctional three dimensional graphene/noble metal nanocomposites and their mechanical, electrical, catalytic, and electromagnetic shielding properties. Sci. Rep.5, 17726; doi: 10.1038/srep17726 (2015).


During the growth process, defects such as vacancies are unavoidably present at the interface between graphene and h-BN. In the present work, typical vacancy defects, which were located at the interface between graphene and h-BN, were studied by density functional theory. The interface structure, mechanical and electronic properties, and failure behavior of the hybrid graphene/h-BN sheet were investigated and compared. The results showed that the formation energy of the defective graphene/h-BN interface basically increased with increasing inflection angles. However, Young’s modulus for all graphene/h-BN systems studied decreased with the increase in inflection angles. The intrinsic strength of the hybrid graphene/h-BN sheets was affected not only by the inflection angles, but also by the type of interface connection and the type of defects. The energy band structure of the hybrid interface could be tuned by applying mechanical strain to the systems. These results demonstrated that vacancies introduced significant effects on the mechanical and electronic properties of the hybrid graphene/h-BN sheet.Hybrid graphene/ Discontinues, such as vacancies, fault lines and cracks, are unavoidably present near and along the graphene/h-BN interface to reduce elastic strain energy. As we know, the atoms in the defect are not in perfect crystalline arrangement. The mechanical properties of this hybrid material may be further affected and may give rise to large impact on the performance of devices based on such material. Vacancies are one of the most popular point defects on two-dimensional (2D) material surface. Similar to graphene and some other graphene-like materials2728h-BN interface should serve as fracture nucleation center under high tension load. Their mechanical properties are more complicated due to the existence of two different types of atomic lattices. It is therefore worthwhile to study the possible relationship between the mechanical properties of graphene/h-BN and the defect parameters. However, recent experimental and theoretical studies focused on the patterns, electronic and thermoelectric properties of the graphene/h-BN interface303132h-BN interface.More recently, using scanning tunneling microscopy (STM), Loh and co-workers clearly observed discontinues and dislocations along the interface of a graphene/h-BN sheet. In particular, the perfect interface and interfaces with typical vacancy defects located along the interface were studied by density functional theory (DFT). The interface structure, defect formation energy, mechanical properties, changes of the energy band during tensile process, and failure behavior of the hybrid graphene/h-BN interface with and without defects were studied and compared.The present work aims to investigate the potential effect of the interface on the mechanical properties and failure behavior of the hybrid graphene/h-BN sheet was investigated using DFT method. Generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) function was chosen to describe the graphene/h-BN interfaceh-BN surface to minimize the influence between adjacent layers. In addition, the distance between adjacent interfaces was set as more than 20 Å to minimize the influence between them. Å 10 × 10 × 1 k-point mesh was set up during the geometry equilibrium with all the atomic structure parameters fully relaxed. All calculations were realized using the DMol3 module (Accelrys Inc.).The mechanical properties and failure behavior of the interface of hybrid graphene/h-BN domains could form an interface with either a zigzag linking edge or an armchair linking edge. In the present work, both the zigzag edge interface (G-BN-zz) and armchair edge interface (G-BN-am) between graphene and h-BN domains were considered  zigzag shape, its adjacent interface edge possesses a carbon-nitrogen (C-N) configuration.As reported by previous experimental observationsFor either the zigzag interface or the armchair interface, six typical vacancy defects located at the interface were selected as probes to analyze the effects of vacancies on the mechanical properties and failure behavior of the interfaces. Due to the combinations of single atom vacancies (SV) or double atom vacancies (DV), the interface may turn into different line defects. The nomenclature and structure of the defect models are shown in h-BN sheets with defects usually exhibit a slight warping. To reflect the structural changes of graphene/h-BN interface due to the vacancy defects, inflection angle was defined  angles, C-C bonds and B-N bonds were observed on the hybrid graphene/h-BN interface without defects (for both the zigzag and armchair edge interface).As shown in  defined  and collh-BN surface.For the C-B zigzag interface with vacancies, the maximum elongation (3.8%) of C-B bond relative to the system without defects occurred at the vacancy of the zz-SV(CB)-B system; while for the C-N zigzag interface with vacancies, the maximum change (2.8%) of C-N bond was found at the interface of zz-SV(CN)-N system. When comparing the system with defects and an armchair interface without defects, the changes of C-B and C-N bonds were up to 13.3% and 2.9%, respectively. The maximum elongation of the C-B bond appeared at the interface of the am-SV-B system; while that of the C-N bond was found at the interface of the am-SV-C(B) system. Due to the dangling bond around the vacancies, several atoms (N or B) around the vacancies exhibited a slight elevation (0.35 Å to 0.58 Å) from the graphene/h-BN interface. It can be expressed as45Formation energy was introduced to describe the thermodynamic stability of the vacancies on the hybrid graphene/Etotal and EG−BN are the energies of the hybrid graphene/h-BN sheet with and without vacancies, respectively. μC, μB and μN denote the increased (n > 0) or decreased (n < 0) chemical potential of carbon, boron and nitrogen atoms, respectively. L is the periodic length along the interface line. Formation energies of all the graphene/h-BN systems are shown in h-BN interfaces with defects ranged from 6.3 eV to 14.4 eV, which were comparable to that of the defect on pristine graphene and h-BN sheet4where h-BN interface basically increased with increasing inflection angles. Actually, graphene/h-BN interfaces with SV defects exhibited relatively lower formation energies  of that for graphene (h-BN), while that of the armchair edge interface reduced to 72.0% (86.2%) of that for graphene (h-BN)  see . Thus, th-BN systems basically decreased with increasing inflection angle. The relatively flat interface, such as BN-G-am (744 GPa) and am-SV-C(B) (700 GPa) systems, has the highest Young’s modulus amongst all systems. When the inflection angle of the interface reaches more than 20°, Young’s modulus of the systems significantly decreases to less than 70% of that of the graphene/h-BN interface without defects. The fitted line in As shown in τ0 = 761 GPa is the approximate highest Young’s modulus of the graphene/h-BN interface without defects. Obviously, the warpage of graphene/h-BN interface significantly decreases the Young’s modulus of this hybrid material. As we know, a curved surface is usually easier to be deformed than a completely flat surface, as the initial deformation for a curved surface was the spreading of the surface rather than the elongation of the chemical bonds. Thus, the higher the inflection angle, the easier the deformation to occur at the graphene/h-BN interface.where h-BN interface with and without defects show obvious brittle fracture characteristic  and nearly equal to that of the prinstine h-BN . The graphene/h-BN armchair interface possessed an intrinsic strength of 95 GPa, which was 13% higher than that of the zigzag interface.The morphology of stress-strain curves for both the graphene/stic see , i.e., rh-BN) sheet with grain boundaries on the surface showed an obvious linear relationship with the inflection angles of the surface, i.e., the intrinsic strength basically showed linear decrease with the increase of the inflection angles. As shown in h-BN sheet, although the increase of the inflection angles affect the intrinsic strength of the defective systems to a certain extent, no clear linear relationship was found between the intrinsic strength and the inflection angles. The warpage of the graphene/h-BN sheet might decrease the strength of the surface as a larger inflection angle effectively causes a 2D surface to become more bulk, which is close to its 3D structures. Nevertheless, apart from the strength decrease, other factors may also affect the strength of the system.As reported in previous works4After a careful analysis of the results, it was found that for the models with defects and a zigzag edge interface, the intrinsic strength showed close relationship with the type of the interface (C-B edge or C-N edge) where the vacancies were located at. Vacancies which were located at the C-B edge introduced more detrimental effect on the intrinsic strength of the systems than that located at the C-N edge shown in . As the h-BN interface without defects and much lower than that of the pristine graphene or h-BN.The critical failure strain corresponding to the intrinsic strength ranged from 12% to 8% for the defective models with a zigzag edge interface and 14% to 9% for the defective models with an armchair edge interface, respectively. These values were comparable with the critical failure strain of the graphene/h-BN sheet. So, the relationship between the intrinsic strength, the critical failure strain and the linear density of the vacancies along the interface was studied. With limited computing resource, just one type of vacancy defect was selected on each interface edge, i.e., single carbon vacancy on the zigzag (C-B) edge interface and single nitrogen vacancy on the armchair edge interface. As shown in h-BN interface.For the following discussion, we define the defect degree of vacancies as the linear density of the vacancies along the interface. It is desirable to reflect the influence of the defect degree of the interface on the strength of the graphene/On the other hand, the relationship between the inflection angles and the defect density based on the analysis of these two defect types were discussed. The inflection angles were summarized in h-BN interface due to the tensile load, the configuration of the interfaces with different strains were observed. The fracture process for several typical interfaces with defects was collected in h-BN sheets occurred at or near the interface, which indicated that the interface had weak mechanical strength of such material. For a zigzag interface without defects, the fracture appeared on the C-B interface rather than the C-N interface, as a C-N bond possessed shorter bond length and higher interaction energy than a C-B bond. When the vacancies were located at the C-B interface, still the C-B interface fractured with the elongation of C-B bonds under tensile load  the defect-free graphene/h-BN systems with the zigzag edge interface; (ii) the defect-free graphene/h-BN systems with armchair edge interface; (iii) the zz-SV(CB)-C system with a carbon vacancy defect at the graphene/h-BN (C-B) interferce; (iv) the am-SV-N system with a nitrogen vacancy defect at the graphene/h-BN interface. For each model, the electronic band structure of the system in the absence of mechanical strain and that with mechanical strain closed to its critical failure strain, were calculated and analyzed.Pioneer researches have demonstrated that mechanical straining can alter the band gaps of graphene nano-ribbons significantly3637The energy band figures were collected in the h-BN sheet, which were located at the interface between graphene and h-BN domains, were studied by DFT method. The interface structure, mechanical properties, changes of the energy band during tensile process, and failure behavior of the hybrid graphene/h-BN sheet were investigated and compared. The results showed that the formation energy of the defective graphene/h-BN interface basically increased with increasing inflection angle. While Young’s modulus for all of the graphene/h-BN systems decreased with increasing inflection angle. The intrinsic strength of the hybrid graphene/h-BN sheets was affected not only by the inflection angles but also by the type of the interface connection and the type of the defects. The electronic properties of the hybrid interface might be affected significantly by the mechanical strain. The information obtained in this work would provide fundamental information for the application of the hybrid graphene/h-BN materials in nano-devices.In summary, twelve important typical vacancy defects of the hybrid graphene/How to cite this article: Ding, N. et al. Mechanical properties and failure behaviors of the interface of hybrid graphene/hexagonal boron nitride sheets. Sci. Rep.6, 31499; doi: 10.1038/srep31499 (2016).