We investigate the networked nature of the Japanese credit market. Our investigation is performed with tools of network science. In our investigation we perform community detection with an algorithm which is identifying communities composed of both banks and firms. We show that the communities obtained by directly working on the bipartite network carry information about the networked nature of the Japanese credit market. Our analysis is performed for each calendar year during the time period from 1980 to 2011. To investigate the time evolution of the networked structure of the credit market we introduce a new statistical method to track the time evolution of detected communities. We then characterize the time evolution of communities by detecting for each time evolving set of communities the over-expression of attributes of firms and banks. Specifically, we consider as attributes the economic sector and the geographical location of firms and the type of banks. In our 32-year-long analysis we detect a persistence of the over-expression of attributes of communities of banks and firms together with a slow dynamic of changes from some specific attributes to new ones. Our empirical observations show that the credit market in Japan is a networked market where the type of banks, geographical location of firms and banks, and economic sector of the firm play a role in shaping the credit relationships between banks and firms. One key economic questions in the description of markets is whether a market is characterized by an underlying networked structure . In factIn our approach we consider the Japanese credit market as a bipartite network of banks and firms. Bipartite networks are quite common in complex systems. Classic examples are networks of actors and movies, board members and companies, authors and scientific papers, etc. The customary investigation of bipartite networks is done by performing a one-mode projection for one or both of the two sets of vertices . This apComplex systems can be monitored over long periods of time. The analysis and modeling of these systems in terms of networks can be done by considering the network connections observed for the whole time period and/or by analyzing the network at successive time intervals as, for example, daily, weekly, monthly or yearly time intervals. Here we investigate the bipartite network of credit relationships yearly from 1980 to 2011 by obtaining 32 distinct credit networks. For each year we obtain the credit network and its community structure by using Barber’s BRIM (bipartite recursively induced modules) algorithm [To investigate the time evolution of the communities detected for different years, and, more generally, the time evolution of the underlying networked structure, we need a method that tracks the dynamics of the different communities over time. This method is needed because we are interested into the dynamics of the communities and due to an unavoidable level of uncertainty related to the statistical nature of the community detection process. In this paper, we propose a method which is able to track the time evolution of communities obtained at successive periods of time. The method is more general than just using transition probabilities and it is based on a statistical test which is robust with respect to the heterogeneity of the size of communities and therefore works for communities of different sizes. Our statistical validation procedure of the time evolution of communities allow us to track efficiently the evolution of the communities over time.The dynamics of the networked structure of the system is investigated by characterizing the communities obtained for different years in terms of the over-expression of attributes of banks and firms concerning (i) the regional location of firms, (ii) economic sectors of firms, and (iii) the types of banks. The statistical validation of the over-expressed attributes is done by using the method presented in . This meThe paper is organized as follows. In Subsection “Dataset” of Material and Methods we briefly discuss our dataset. Subsection “Community detection in bipartite networks” discusses community detection in the bipartite network of the Japanese credit market. Subsection of Results entitled “Time evolution of communities” introduces a method used to track the time evolution of communities detected in networks and obtained for successive time periods. Subsection “Over-expression of attributes” presents the empirical results obtained in the characterization of the over-expression of attributes of banks and firms in each community over the years and in Section “Discussion” we draw our conclusions.Our dataset is based on a survey of firms quoted in the Japanese stock exchange markets  and in Japanese over-the-counter (OTC) markets. The data were compiled from the firms’ financial statements and survey by Nikkei Media Marketing, Inc. in Tokyo, and are commercially available . The surThe number of banks of the database changes year by year by selecting the partition associated with the highest modularity among the 20 performed runs. It was 225 in 1980, remained approximately constant until 2001 and then decreased to 166 in 2011. The number of firms was first increasing from the value of 1414 in 1980 to the value of 3034 in 2006 and then decreasing to the value of 2706 in 2011. The number of firms increased from 1802 in 1995 to 2602 in 1996 in the presence of the first inclusion of the OTC firms in the database. During the same years the number of banks increased from 219 to 226. The density of links in the bipartite network defined as number of observed links over number of potential links was on average decreasing from the value of 0.0867 in 1980 to the value of 0.0398 in 2011. The variation of the density of links was not too large during the first inclusion of the OTC firm. In fact the density of links decreased from 0.0721 to 0.0601 from 1995 to 1996. In the supporting information we provide a summary statistics for the banks and firms of our database. Specifically, for each year we provide the occurrence of the different type of attributes characterizing banks and firms see  Tables. The Japanese credit market has been previously analyzed by considering one-mode projected networks , an eigeConcerning financial institutions, commercial banks are long-term, city, regional (primary and secondary), trust banks, insurance banks and government-related financial institutions including credit associations but excluding the Bank of Japan. We remark that failed banks are included until the year of failure, and that merger and acquisition of banks are processed consistently to identify surviving banks. For quoted firms, those who are active in each investigated calendar year are all included even if they failed later during the considered years.i and firm j when a credit relation (short and/or long) is present between i and j. Links are described by a binary variable (just indicating the presence or absence or a credit relationship), i.e., in the present investigation the bipartite network is an unweighted network.In our bipartite network a link is present between bank Community detection in large and dense bipartite networks has been considered in the past years by several authors , 9–12 anThe algorithm of Barber  is the oIn our analysis we have repeated the application of BRIM community detection algorithm a number of times for each year we investigate. Specifically, for each investigated year in each run we apply the algorithm 100 times and we perform 20 independent runs.To quantitatively evaluate the differences which are present among the partitions obtained in the 20 independent runs performed for each calendar year, we evaluate the adjusted Rand index (ARI)  among alTo provide an indication of the differences observed among the partitions obtained in independent runs, in t + 1 in which one detects an over-expressed amount of elements of a given community of year t. The community detection procedure has a certain degree of stochasticity and degeneracy with respect to small differences of the fitness measure and therefore the membership of an element into a given community might also just be due to chance. We therefore need a method detecting over-expression of the same composition in communities of two successive years that is based on a carefully devised statistical procedure which is robust to the size heterogeneity of the different communities.The communities detected by using the BRIM algorithm and discussed in the previous section are obtained year by year. It is therefore of interest to properly put communities detected on a given year in relation with communities detected in the following year. A time evolution of the communities can be detected by considering what are the communities of year t there are Nt communities i = 1, ⋯, Nt and in period t + 1 there are Nt+1 other communities j = 1, ⋯, Nt+1. For all the t we search amongst all Nt+1 communities of period t + 1 which communities t. Specifically, let us call Nt,t+1 the number of distinct vertices in the two consecutive periods t and t + 1. The probability that p-valuep-value threshold pt, the above methodology gives us a way to select the communities in year t + 1 that are linked to a given community in year t in a statistically robust way.We propose the following method. Suppose that in period p-value threshold must be corrected to take into account that we are performing a multiple hypothesis test comparison. Indeed, for each pair of consecutive periods we perform the test Nt ⋅ Nt+1 times against the null hypothesis of random distribution of elements among two partitions of communities of consecutive periods. Moreover we perform these tests for all pairs of consecutive years in our dataset, i.e., from 1980 to 2011. The most restrictive multiple hypothesis test correction is the Bonferroni correction, which prescribes that the modified p-value threshold pB is:pt = 0.01.To avoid the presence of false positive, the To better understand the key aspects of our method it is worth comparing the results of the statistical validation procedure with a simple indicator as the transition probability. Let us define the transition probability for community In t evolves into the largest community of year t + 1 for all the investigated years. In addition to this primary channel of community evolution we also detect that in some years other smaller communities merge part of them into the largest one . For the sake of clarity, among the communities merging into the largest community, only communities at one year distance from the largest community of each year are shown in the figure. In the following section we will investigate the over-expression of the attributes characterizing the elements of the largest community observed in each calendar year.In t with communities at year t + 1 but, differently than in t + 1 and communities at year t different from the one already shown in the figure. The additional incoming validated connections from other communities of the previous year are not shown to make the figure readable. As in In t to communities at step t + 1. In One way to visualize time evolving communities is the one using so-called alluvial diagrams . These dThe color pattern of The identification of bank-firm communities and the statistical validation of their time evolution provides the basis for detecting and understanding the networked structure of the credit system and its time evolution. A further step is to look for information characterizing the obtained communities and their time evolution. In other words it is important to characterize the communities in terms of attributes over-expressed by the elements belonging to the same communities with respect to an appropriate random null hypothesis. The method used here was introduce in . It shouRt where 0.01 is the univariate threshold and Rt = (NS + NP + NB) ⋅ Nt is the total number of tests done in the statistical validation of communities of the year t. More specifically, NS is the number of distinct economic sectors, NP is the number of distinct Japanese prefectures, NB is the number of types of banks, and Nt is the number of communities detected at year t. In this way, we minimize the number of false positive but unavoidably increase the number of false negative.The metadata available for the characterization of firms and banks allows us to identify the economic sector and the prefecture of the main office of firms and the type of bank. The summary statistics for each year and for each attribute is provided in the supporting information  Tables. The over-expressed prefectures are the prefectures of Kanagawa (14) and Tokyo (13), i.e. two prefectures of the so-called greater Tokyo area. The Table also shows the over-expression of the main economic sectors of the firms belonging to the community. The over-expressed economic sectors are Electric and electronic equipment (EEE) for the time period 1980–1993, and Services (S) and Wholesale trade (WT) for the time period 1996–2011.In summary the credit relationships preferentially detected in the largest community change type of over-expressed economic sector during the years 1995–1996. On the other hand, the over-expression of bank type and geographical location remains essentially the same before and after 1996.To rule out the possibility that the changes observed in the over-expression of economic sectors are due to the 1996 inclusion of the OTC firms we have repeated the community detection and the over-expression characterization by considering the listed firms and the OTC firms separately. Information about the number and attributes of listed and OTC firms is given in the supporting information  Tables.The results of the separate analyses are presented in In The second branch starts in 1980 and ends approximately in 2005 . The choice of a one-to-one correspondence between banks’ partitions and firms’ partitions also simplify our analysis of joint over-expression of attributes of banks and firms. With this approach we have been able to show the existence of layers of the credit market involving an over-expression of groups of firms characterized by specific (i) economic sectors, (ii) regional locations (prefectures), and (iii) specific types of banks. These empirical observations show that the credit market in Japan is a networked market.The robustness of our results is shown by the ability of our approach in detecting both the long term stability and the slow dynamics of the detected communities. The time evolving communities have been tracked from each year to the next one by using a newly introduced statistical method able to track the time evolution of communities detected in successive periods of time also in the presence of size heterogeneity of the communities. It is worth noting that our method presently used to track time evolution of communities can also be easily adapted to link communities detected in a multiplex network.S1 Table(XLSX)Click here for additional data file.S2 Table(XLSX)Click here for additional data file.S3 Table(XLSX)Click here for additional data file.S4 Table(XLSX)Click here for additional data file.S5 Table(XLSX)Click here for additional data file.S6 Table(XLSX)Click here for additional data file.S7 Table(XLSX)Click here for additional data file.S8 Table(XLSX)Click here for additional data file.S9 Table(XLSX)Click here for additional data file.S10 Table(TXT)Click here for additional data file.S11 Table(TXT)Click here for additional data file.S12 Table(TXT)Click here for additional data file.S13 Table(TXT)Click here for additional data file.S14 Table(TXT)Click here for additional data file.S15 Table(TXT)Click here for additional data file.


Boiling heat transfer (BHT) is a particularly efficient heat transport method because of the latent heat associated with the process. However, the efficiency of BHT decreases significantly with increasing wall temperature when the critical heat flux (CHF) is reached. Graphene has received much recent research attention for applications in thermal engineering due to its large thermal conductivity. In this study, graphene films of various thicknesses were deposited on a heated surface, and enhancements of BHT and CHF were investigated via pool-boiling experiments. In contrast to the well-known surface effects, including improved wettability and liquid spreading due to micron- and nanometer-scale structures, nanometer-scale folded edges of graphene films provided a clue of BHT improvement and only the thermal conductivity of the graphene layer could explain the dependence of the CHF on the thickness. The large thermal conductivity of the graphene films inhibited the formation of hot spots, thereby increasing the CHF. Finally, the provided empirical model could be suitable for prediction of CHF. Following the demonstration by Geim and Novoselov23810et al.−1m−1 (at room temperature). Although the thermal conductivity of these graphene films is significantly smaller than has been reported for single graphene flakes, it remains larger than that of many other substrates, and hence graphene remains attractive for heat transfer applications. However, despite the favorable heat transport properties, little information about applications of graphene on thermal system is available. The characteristics of a heated surface, including the surface wettability1314161821Since graphene typically exists in the form of ultra-thin microscale flakes, much effort has been invested to synthesize large-area films that retain the properties of graphene. Jang Here, we report that thin graphene films on a heated surface may result in more efficient dissipation of heat in the lateral direction, which inhibits the formation of dry/hot spots during boiling, leading to an increase and CHF. The role of graphene films on the heated surface was investigated using infrared high-speed visualization of the boiling process. We found that the graphene layer led to an increase in the CHF via lateral heat transport, which inhibited the formation of hot/dry spots. Pool-boiling experiments were carried out in the Pohang University of Science and Technology (POSTECH) pool-boiling experimental facility, which is illustrated in the schematic diagram shown in colloidV is the volume of the RGO flakes, A is the area of the film, δ is the thickness of the film, graphiteρ is the density of the graphite, and colloidρ is the density of the RGO colloid. The filtered graphene film was transferred to the surface of the silicon heater  high-speed visualization  for 2 minutes during each step of the experiment. At large heat fluxes, the power supply was shut down when a sudden increase in the wall temperature was observed, which corresponded to the CHF.Prior to each experiment, deionized (DI) water was boiled for 1 hour using a cartridge heater to degas the water. Two wires were soldered to each electrode to apply a voltage and measure the temperature using the correlation shown in All images of the infrared high-speed visualization were trimmed and processed using Matlab and Image J. Raw image data appeared too dark, and so nucleation could not be observed. Therefore, the brightness and contrast were adjusted for each experimental case; this adjustment did not result in a change in the recorded temperature. One- and two-dimensional data arrays of the temperature distribution were extracted for the selected domain to analyze the temperature distribution and the changes with time thereof. The overall temperature distribution, one-dimensional temperature profiles, and temperature plots were obtained from the extracted data.H.S.A. designed the experiments and all procedures, and was the main author of the paper. J.M.K. carried out the experiments, provided the figure artwork, performed the data analysis, and contributed some written material to the manuscript. T.J. K. assisted with the analysis of the graphene film. S.C.P., J.M.K. and D.I.Y. also carried out experiments, fabricated experimental apparatus, and acquired and interpreted the SEM and TEM data. Y.P. carried out the visualization experiments using the infrared camera and fabricated some of the experimental apparatus. K.W.H. analyzed the AFM data. H.J.J. assisted with the analysis of the surface characteristics and boiling performance. H.S.P. assisted in the analysis of the IR visualization. H.K. and M.H.K. equally directed the project. All authors discussed the results and contributed to the paper.Supplementary informationVideo clip of IR high-speed camera in real time


At the scan rate of 5 mV s−1, the specific capacitance of the polypyrrole-CNT-graphene (PCG) electrode film was 453 F g−1 with ultrahigh energy and power density of 62.96 W h kg−1 and 566.66 W kg−1 respectively, as shown in the Ragone plot. A nanofibrous membrane was electrospun and effectively used as a separator in the supercapacitor. Four supercapacitors were assembled in series to demonstrate the device performance by lighting a 2.2 V LED.Supercapacitors also known as electrochemical capacitors, that store energy via either Faradaic or non-Faradaic processes, have recently grown popularity mainly because they complement, and can even replace, conventional energy storage systems in variety of applications. Supercapacitor performance can be improved significantly by developing new nanocomposite electrodes which utilizes both the energy storage processes simultaneously. Here we report, fabrication of the freestanding hybrid electrodes, by incorporating graphene and carbon nanotubes (CNT) in pyrrole monomer via its  Given the current energy crisis and depletion of finite sources, high performance energy storage systems (ESSs), capable of storing energy from both renewable and non-renewable sources, are essential to meet the increasing energy demand. Electrochemical capacitors39Performance of the electrode can be further improved, without compromising the structural integrity and the operating life of supercapacitors, by fabricating hybrid nanocomposites11121315161719202223242526273132Although nanocomposite electrodes exhibit high specific capacitance, they are limited by their low energy/power densities and high discharge rate. One way to improve the performance of these films lies in the fabrication technique. Several methods have been proposed to fabricate hybrid thin films such as layer-by-layer (LBL) electrostatic self-assembly and spin-coating homogeneously mixed solutions on a substrate3435in-situ polymerization of PPy. Supercapacitor performance depends also on electrochemical window provided by different types of electrolytes, such as aqueous, organic, solvent free ionic liquids or solid state gel electrolytes. It is important to compare the performance of nanocomposite electrodes in various electrolytes. In this study, we analyzed the nanocomposite in three different aqueous electrolytes, namely, ascorbic acid (Vitamin C), sodium sulfate, and sulfuric acid. The highest specific capacitance was observed in the electrode containing graphene and CNT in presence of sulfuric acid electrolyte. Furthermore, while fabricating the supercapacitor device, a novel nanostructured electrospun fiber membrane, made from polycaprolactone (PCL), was used as a separator. Lastly, the performance of this electrode based supercapacitor was measured using a 2.2 V light emitting diode (LED), revealing a slow discharge rate when compared to conventional commercial capacitor. After charging it for 30 s, the LED sustained a light for 3 minutes using a stack of 4 devices in series. The hybrid nanocomposite electrode polypyrrole-CNT-graphene (PCG) will be termed as PCG-n, where n is the % concentration of the graphene and CNT combined in PPy, henceforth.In this study, we report a hybridized electrode utilizing EDLC materials such as graphene and CNT within polypyrrole, a pseudocapacitive material, forming a stable and high performance freestanding electrode. This was achieved by electropolymerization of the monomer Py in the presence of graphene and CNT, yielding a nanocomposite polypyrrole electrode. Several nanocomposite electrodes were prepared with increasing concentration of graphene and CNT, such as 0.01 wt%, 0.05 wt % and 0.1 wt% in the A hybrid PPy-graphene-CNT freestanding electrode was fabricated using potentiostatic electrochemical polymerization, as shown in As evident from the SEM images , the cono, which is a characteristic peak of amorphous PPy, and arises mainly due to the scattering from PPy chains at the interplanar spacing. In the case of the PCG 0.01 nanocomposite a sharp peak is observed at approximately 2θ = 25.75o suggesting the incorporation of graphene and CNT in PPy matrix, improving the crystallinity of the structure. Using Bragg’s law, the distance between crystals can be calculated and it is found that the average d_spacing of PPy is 3.024 Å and that of PCG is 3.456 Å. The characteristic peak of the PCG nanocomposite has shifted due to the intercalation of the graphene and CNT in the PPy matrix, resulting in an increase in d_spacing.The effect of crystal formation with and without the presence of graphene and CNT can be observed with the XRD patterns. Cyclic voltammetry (CV) tests were performed to identify the charge storage mechanism of the control PPy and hybrid PCG electrodes in three different electrolytes, namely sulfuric acid (SA), sodium sulfate (SS) and ascorbic acid (AA). As shown in −1 at 5 mV s−1, in comparison to PPy electrodes in SS and AA electrolytes. Along with the highest specific capacitance, the SA electrolyte also exhibited a low decrease in the specific capacitance with a corresponding increase in the scan rate as shown in −1 the specific capacitance saturated to ~100 F g−1 even with a corresponding increase in the scan rate. Furthermore, −1 with the PCG 0.1 electrode at scan rate of 5 mV/s.Based on the CV tests, the specific capacitance was calculated with respect to various scan rates as shown in A supercapacitor device was fabricated as shown in To further demonstrate the performance of the supercapacitor device, a circuit was implemented to charge and discharge the supercapacitor to an external load, in this case a 2.2 V light emitting diode (LED) was used. In order to light up the LED, a stack of 4 supercapacitor devices were assembled in series and they were enclosed tightly within a CR-2032 button cell holder. The circuit was implemented as shown in in-situ synthesis of polypyrrole-CNT-graphene nanocomposite resulting in a controlled layered structure with high porosity. The resulting electrode has high ion accessibility, due to the fact that no organic binders were used to fabricate the thin film, which would otherwise reduce the ionic access to the active materials in the supercapacitor electrodes. This fabrication technique is also useful to develop micro-supercapacitors and biosensors because of its ability to precisely deposit the conductive nanocomposite material on the existing circuits.The novelty of the electrode fabrication technique lies in the ease of the −1 and a power density of 566.66 W kg−1 at the scan rate of 5 mV/s. For the PCG 0.1, an ultrahigh energy density was obtained in the range of 9.62 W h kg−1–62.96 W h kg−1 and a power density in the range of 1416.66 W kg−1–8665 W kg−1 at various scan rates. These electrodes exhibit high power density from EDLC materials and simultaneously exhibit high energy density from the pseudocapacitive type of materials which could results in many high power applications. The power density  and the energy density  of the electrode material was calculated by using the following expressionsThe electrochemical performance of the nanocomposite electrode was improved by increasing the concentration of graphene and CNT when incorporated in PPy as shown in the Ragone plot in Here, V is the initial voltage during discharge; m is the mass of electrodesv is the scan rate (Vs−1)Here The use of electrospun nanofibers as a separating membrane has also improved the performance of the supercapacitor device. Owing to small fiber diameter (~600 nm) and high surface area, the fibrous nanostructures act not only as an efficient permeable membrane across the hybrid electrodes but also as an electrolytic reservoir, which helps to slow the overall discharge in device. The supercapacitors can be integrated into many applications such as microelectrode arrays38402SO4 as supporting electrolyte in 25 mL of DH2O for 1 h. To make PCG nanocomposite with concentrations 0.01% w/v (PCG0.01), 0.05% w/v (PCG0.05) and 0.1% w/v (PCG0.1), an equal amount of graphene and CNT  were dispersed in 25 ml Py solution. This solution was stirred magnetically for 1 h, followed by sonication for 2 h to ensure that graphene and CNT were dispersed thoroughly. PPy and PCG films were synthesized potentiostatically at the scan rate of 20 mV s−1 and 10 mV s−1 respectively. The potential window for both samples was from [800–900 mV] and they were scanned for 100 cycles to obtain free standing films.The polypyrrole (PPy) film was prepared using pyrrole (Py)  monomer solution. The Py solution was prepared by stirring 0.87 ml of Py along with 0.355 g of NaThe performance of electrodes was studied in the presence of different electrolytes such as ascorbic acid (AA), sodium sulfate (SS) and sulfuric acid (SA). AA electrolyte was prepared using 10 mM Ascorbic Acid in 50 mM Phosphate Buffer Saline (PBS). 0.5 M of SS electrolyte was prepared by adding weighted amount of sodium sulfate salt to deionized water and stirring until a clear solution was achieved. As SS is a neutral salt, its pH is near 7. Lastly, sulfuric acid, which was the strongest electrolyte used, had a pH close to 0 in a 1 M solution.The nanocomposite electrodes were characterized electrochemically  using cyclic voltammetry. A three-electrode setup, consisting of a Pt counter electrode, an Ag/AgCl reference electrode and a PPy or PCG-n as working electrode was used for the electrochemical analysis. The capacitance values were calculated from the cyclic voltammogram using the following equationC is the specific capacitance (F g−1), m is the mass of the active electrode material (g), [V = V+−V−] is the potential difference and v is the scan rate (m V s−1). The total charge transferred during the cycle can be calculated by integrating the area under the curve of CV. The potential difference for each electrolyte was, VAA [−300 mV–800 mV], VSS , and VSA [−200–800 mV]. The electrodes were weighed before and after the deposition on graphite electrode in order to calculate the mass of the active nanocomposite material. A 3 mm cylindrical graphite rod was used for all experiments and it was covered using an insulating tape on its surface leaving only the base uncovered for deposition. This ensured that same surface area was maintained during each experiment.Where o–80o using CuKα radiation (λ = 1.5406 Å) operated at 40 kV and 40 mA. Using Bragg’s law, the distance between crystals were calculated as followsThe structural morphology of the nanocomposite films were characterized using scanning electron microscope . X-ray diffraction study was performed using Bruker Advanced diffractometer. The XRD patterns were recorded in the 2θ range of 10How to cite this article: Aphale, A. et al. Hybrid Electrodes by In-Situ Integration of Graphene and Carbon-Nanotubes in Polypyrrole for Supercapacitors. Sci. Rep. 5, 14445; doi: 10.1038/srep14445 (2015).


Highly confined surface plasmons on graphene attract substantial interest as potential information carriers for highly integrated photonic data processing circuits. However, plasmon losses remain the main obstacle for implementation of such devices. In near-field microscopic experiments performed at the wavelength of 10 μm we show that a substantial reduction of plasmon damping can be achieved by placing a nanometric polymer nano-dots spacer between the graphene layer and the supporting silicon oxide slab making graphene quasi-suspended. We argue that reduction of plasmon losses is attributed to weaker coupling with substrate phonons in the quasi-suspended graphene. Oph ≈ 0.2 eV) and sufficiently high doping level (ħω < ħωinter)16171819211213212526Mid-infrared graphene plasmons (GPs) have attracted tremendous interest in recent years owing to an unprecedented spatial confinement and tunability by electrostatic gating1234567810111214GPs damping due to the coupling with the substrate optical phonons can be reduced by shifting an excitation wavelength out of the corresponding phonon line, as has been demonstrated2228292 and SiCAdditionally, as it follows from theoretical analysis313233In this work we experimentally study the effect of quasi-suspended graphene on mid-infrared GPs. The monolayer graphene is placed above a chemically engineered nanostructured spacer (NS) on the substrate, that leads to a “quasi-free-standing”-like graphene38401 = 10 μm or λ2 = 11.2 μm correspondingly. A p-polarized beam is focused on the tip. This generates, in each point during the scanning, cylindrical GPs travelling in all directions out of the tip along the graphene flake. Launched GPs are reflected back from the graphene edges, collected by the tip and scattered out in the far-field. Pseudo-heterodyne interferometric detection of the scattered light allows us to record the amplitude of tip-scattered field, Es, as well as topography in each point of the scan (see Methods section for more details).To experimentally image GPs, we use scanning plasmon interferometry technique2411 = 10 μm due to the strong coupling between GPs and SiO2 optical phonons222 wafer, taken at λ1 = 10 μm and λ2 = 11.2 μm. Corresponding cross-sections of Es along yellow dotted lines are plotted in 2 = 11.2 μm, GPs appear as half GP-wavelength spaced fringes, at λ1 = 10 μm plasmon field is significantly damped and nearly invisible due to the strong interaction with substrate phonons. In this paper, we use the ratio R between the first maximum of the electric field (close to graphene edge) and the field magnitude in the inner part of the flake, (Es)pl/(Es)bg, to represent the damping rate of GPs. Moderately damped GPs at λ2 = 11.2 μm (out of SiO2 phonon line) is characterized by R ≈ 1.5, while for λ1 = 10 μm, the ratio R ≈ 1. Thus, different damping values are characterized by different R. In the following study we will experimentally analyze a possible enhancement of the parameter R for the case of excitation at λ1, by inserting a spacing layer between graphene and the SiO2 substrate.We investigate on samples which initially (when no spacer is applied) possess strongly damped GPs. Experimentally this is realized at an excitation wavelength λ2 spacer we apply the following fabrication processes: (1) thermally oxidized Si-SiO2 wafer is covered with a photoresist by spin-coating, followed by softbaking (2) the photoresist is partially cross-linked by dry-etching, (3) the sample is sonicated in a stripper and rinsed with 2-propanol (see Methods section for more details). This leads to the formation of few-nm thick nano-dots layer of novolac-based polymer2 roughness and the damping-related factor R in the graphene  than it actually presents in the sample. It is well-known that AFM records the tip trajectory as it goes along the surface, rather than the true topography of the sample during measurements4445Graphene is then mechanically exfoliated on top of the fabricated spacer. A typical atomic-force microscope (AFM) image and the height profile of a graphene flake above NS are shown in 2 without any continuous base-layer of polymer beneath. Zoomed-in AFM topography inside the cyan dotted square in 2 surface is formed by randomly placed nano-dots with an average height of 1.2 nm, a typical size of 20 – 40 nm and a typical spacing of 10 – 100 nm.Additional scratching and AFM measurements of NS close to the flake location, as well as presented further optical s-SNOM data, show that nano-dots have been grown directly on SiO2 (at λ1 = 10 μm). The image corresponds to the bottom part of the tapered ribbon displayed in 2 substrate  with randomly distributed black spots which represent the near-field signal of polymer dots. Therefore, we conclude that the roughness in topography observed within NS beneath the flake does not lead to considerable reflections/scattering of GPs field. This agrees with previously reported observationsgp/2) of propagating GPs reflected from the dot. Additionally, as it can be seen from 1 = 10 μm. Additional, study of the same graphene flake at λ2 = 11.2 μm, where SiO2 phonon damping effects can be excluded ; the refraction index of the polymer n = 1.45. The GP is launched in the graphene from the left-hand side. The evolution with the distance of the absolute value of vertical component of plasmonic electric field is plotted in the graph in 2, that represents a significant suppression of damping and agrees with the experiment. Our model describes only the effect of spacing and partial suspension of graphene sheet from SiO2, while the value of the mobility is fixed.Finally, the physics of mid-infrared plasmon damping and propagation in graphene on NS-SiOIn summary, we demonstrate that lifting exfoliated graphene from the silicon dioxide surface with an ultra-thin nanostructured polymer spacer, helps with the control of mid-infrared plasmon damping and propagation. Polymer nano-dots result in spacing and partial suspension of graphene that is beneficial for remote phonons screening. Owing to the ultra-small thickness of the spacer, the nanoscale roughness does not lead to strong chaotic reflections of GPs at the polymer nano-dots, that is one of requirements for unperturbed performance of possible devices fabricated in graphene on top of NS. Numerical simulations of plasmons propagation in graphene placed above silicon dioxide covered with polymer nano-dots show an increase of the propagation length and a suppression of damping that is in agreement with the experiment. This work contributes to understanding of mid-infrared GPs damping mechanism, and gives insight into the fundamental problems of interaction of the plasmons with deeply subwavelength nanostructures.2 wafer (285 nm oxide thickness) was covered with AZ 5214E photoresist by spin-coating at 4000 rpm for 30 s. The thickness of the resulting photoresist film is about 1.6 μm. (2) The wafer was then softbaked for 100 s at 105 °C. (3) The resulting sample was dry-etched for 4.5 min in the Plasma-Therm 790 series RIE . The dry-etching process leads to a higher degree of cross-linking, within the novolac-based polymer component of the photoresist due to a possible overheating/UV exposure from the plasma. The dry-etching does not remove the photoresist film completely with the chosen etching time. (4) Then the sample was sonicated in NI555 stripper for 5 min at room temperature, and finally, it was rinsed thoroughly with 2-propanol and dried with nitrogen.To fabricate the NS, we use the polymer which is, essentially, self-organized as a highly nanostructured film during the process of ultrathin (nanometric) films fabrication. The following process was performed. (1) Virgin thermally oxidized Si-SiO2 laser. Background-free near-field imaging is given by the demodulation of recorded optical signal at higher harmonics of the tapping frequency . We note that, as commonly known, near-field optical images recorded with the QCL laser (λ1 = 10 μm) typically show lower signal to noise ratio compare to the CO2 laser (λ2 = 11.2 μm). With reference to Neaspec GmbH, this difference in performance is mainly attributed to intrinsic laser specific aspects in the sense how the mid-infrared lasing is realized in the two lasers.Our setup is based on a commercial s-SNOM (Neaspec GmbH) performing measurements with a Pt-coated Si tip at the tapping frequency Ω of about 250 kHz and the tapping amplitude of about 60 nm. We use Daylight Solutions tuneable QCL laser and temperature-tuneable Access Laser CONumerical simulations are based on the finite-difference time domain method presented in the reference1 = 10 μm we can define the first field maxima close to the graphene edge and the field magnitude in the inner part of the flake, while due to strong damping, it is not possible to clearly define multiple maximums of GPs field over the flake. Therefore we implemented another damping-related factor, (Es)pl/(Es)bg, which compares the near-field magnitude in the first maximum and the inner part of the flake where a plasmon, reflected from the edge, has been already completely damped. As it was verified above, on the example of strong and weak damping, this factor can be used for qualitative comparison of GPs damping strength.A.M.D. proposed the idea of the paper, performed samples fabrication and near-filed measurements, analysed data and prepared the main manuscript text. J.T. performed numerical simulations. J.T. and X.C.Y. contributed to samples fabrication. Q.J.W. and N.I.Z. supervised the project and contributed to the manuscript text. All authors discussed the results and commented on the manuscript.How to cite this article: Dubrovkin, A. M. et al. The reduction of surface plasmon losses in quasi-suspended graphene. Sci. Rep.5, 09837; doi: 10.1038/srep09837 (2015).Supplementary Figure S1-S5


A possible approach to achieve quasi-freestanding graphene on a substrate for technological purpose is the intercalation of alkali metal atoms. Cs intercalation between graphene and Ni(111) therefore is investigated using density functional theory, incorporating van der Waals corrections. It is known that direct contact between graphene and Ni(111) perturbs the Dirac states. We find that Cs intercalation restores the linear dispersion characteristic of Dirac fermions, which agrees with experiments, but the Dirac cone is shifted to lower energy, i.e., the graphene sheet is n-doped. Cs intercalation therefore decouples the graphene sheet from the substrate except for a charge transfer. On the other hand, the spin polarization of Ni(111) does not extend through the intercalated atoms to the graphene sheet, for which we find virtually spin-degeneracy. Graphene is gaining attention for its unique two-dimensional structure and special electronic properties, which are interesting for many applications14π bands22Intercalation of noble metal atoms can restore the original band structure to give rise to quasi-freestanding graphene+1 state, so that it does not participate in chemical bonding but acts purely as spacer.In the following, we consider the structural, electronic, and magnetic properties of graphene on Ni(111), using density functional theory, and analyze the changes when intercalating the system with different concentrations of Cs atoms. By the large atomic radius of Cs a very efficient decoupling of graphene from the substrate can be expected. Cs is an alkali metal with one electron in its outer shell and thus strongly favors a CsThe 1 × 1 unit cell of the graphene on Ni(111) consists of 4 Ni layers and 1 C layer on top. To determine the favorable lateral shift between the two materials, we study four structural configurations: (i) Hollow, where each atom of the topmost Ni layer is in the center of a C honeycomb. (ii) Face centered cubic (fcc), where three of the C honeycomb atoms are located on top of atoms of the topmost Ni layer and the center of the C honeycomb is located on top of an atom of the second Ni layer. (iii) Hexagonal close packed (hcp), which is similar to the fcc case but with the center of the C honeycomb located on top of an atom of the third Ni layer. (iv) Bridge, where the center of the C honeycomb is located between two atoms of the topmost Ni layer. ENi is the total energy per atom in bulk Ni and EC is the total energy per C atom in graphene. The fact that the bridge configuration is only 10 meV higher in energy than the fcc configuration implies that it is accessible as well. Even the hcp configuration might be accessible with low probability. Indeed, these configurations experimentally can coexist25where dC/Ni, see dC/Ni. We obtain finite though small magnetic moments of −0.02 and 0.03 μB on the two C atoms due to Ni-C hybridization, in agreement with the results reported in ref. The C-C bond length in the fcc configuration is 1.44 Å, whereas it is 1.42 Å in pristine graphene. This small tensile strain corresponds to the mentioned small lattice mismatch. The obtained perpendicular distance between graphene and the Ni(111) surface, μB comes from the Ni atoms, where atoms in the first layer show magnetic moments of 0.67 μB and atoms in the other layers show 0.68 μB.We next consider a 2 × 2 supercell with graphene artificially placed in a distance of 6 Å from the Ni(111) substrate, see μB, which is close to the bulk Ni value of 0.67 μB, to values of 0.49 μB for the atom directly below Cs and 0.59 μB for the other atoms in the same layer.We find that intercalation of Cs enlarges the distance between the graphene sheet and the Ni(111) substrate to 6.0 Å post relaxation (3.1 Å from graphene to Cs and 2.9 Å from Cs to Ni). The in-plane Cs-Cs distance is 5.0 Å. We note that the graphene sheet shows no significant structural modification, see We next consider larger supercells, see As another ferromagnetic substrate we have also considered Co(0001) to check whether our results for Ni(111) are of general validity. The band structure of the 2 × 2 supercell, see We have investigated the effect of Cs intercalation on the structural, electronic, and magnetic properties of graphene on Ni(111) and Co(0001). An fcc configuration is found to be energetically favorable in agreement with previous experimental and theoretical results, and therefore is chosen for studying the intercalation. Different supercell sizes have been considered to examine the effect of the Cs concentration. In agreement with experimental results, the Cs intercalation restores the Dirac cone, since it decouples graphene from the substrate, resulting in n-doped quasi-freestanding graphene. Both for the Ni(111) and Co(0001) substrates the graphene sheet exhibits no trace of spin polarization.Density functional theory is employed using the Vienna Ab-initio Simulation PackageHow to cite this article: Alattas, M. and Schwingenschlögl, U. Quasi-freestanding graphene on Ni(111) by Cs intercalation. Sci. Rep.6, 26753; doi: 10.1038/srep26753 (2016).


Consequently, the external laser beam can control the propagation of the graphene SPP between the ON and OFF status. This all-optical modulation effect is still obvious when the spot size of the external laser is reduced to 400 nm while the modulation depth is as high as 114.7 dB/μm.We report a theoretical study showing that by utilizing the illumination of an external laser, the Surface Plasmon Polaritons (SPP) signals on the graphene sheet can be modulated in the sub-micron scale. The SPP wave can propagate along the graphene in the middle infrared range when the graphene is properly doped. Graphene's carrier density can be modified by a visible laser when the graphene sheet is exfoliated on the hydrophilic SiO The development of information technology requires the highly integrated signal processing circuits. Gradually, the evolution of signal processing systems was mainly separated into two directions, the electronic one and the optical one. The all-electronic processing technique is quite mature in now days and the feature size of the most advanced devices has been reduced to 14 nm according to Intel, which means the all-electronic signal processing circuits can be ultra-compactAs the carrier of the optical signals, the waveguide plays an important role in optical circuits. Silicon optical waveguides can be used as modulators to reach the speed as 100 GHz, but the thickness of the waveguide is as large as hundreds of nanometers456792111213142/Si substrate and the initial status of the graphene is p-doped2 layer is as thick as 290 nm. The SPP wave can propagate along such a graphene waveguide since its permittivity is suitable, which is demonstrated as Here we theoretically propose an all-optical modulation method for the SPP wave within the size of hundreds of nanometers. This modulator is based on the surface plasmonic wave, which is supported by the doped graphene sheet. The excitation of the graphene SPP has been discussed in lots of papers9102/Si substrate, is lower than the Dirac point as sn ≈ 4 × 1012 cm−2 according to Ref. cμ ≈ 0.217 eV. By bringing in an external visible laser illuminating on the graphene and gradually increasing the laser's power, the graphene is changed from the p-doped status to the light p-doped status, and finally to the quasi-neutral status. The wavelength of the external laser is 532 nm and a laser power as large as 0.6 mW can rise the graphene's Fermi energy to the Dirac point, which is shown as cμ = 0.001 eV.Graphene is a special two-dimensional material since its permittivity can be obviously changed when its chemical potential is varied. The chemical potential can be treated as the same value as the Fermi energy for the room temperature1217σ), is positiveσ) < 0. For the purpose of investigating the mode property of the SPP wave on the graphene, it is necessary to utilize the relation between the graphene's conductivity (σ) and the chemical potential (cμ), which is illustrated as the Kubo formulasε) of graphene should be obtained, so that its conductivity (σ) and thickness (Δ) are taken into the calculationWithin a certain range of wavelength, the TM polarized wave can be supported by a doped graphene once if the imaginary part of the graphene's optical conductivity, Im is almost zero in the infrared range when the graphene is in the quasi-neutral status (cμ = 0.001 eV). As ε) becomes larger as the doping level of the graphene becomes higher. So, the doped graphene plays the role as a thin layer of metal and it forms the Insulator-Metal-Insulator (IMI) structure together with the air and the SiO2/Si substrate. In order to give a better support for the SPP mode, the value of −Re(ε) needs to be larger so that the highly doped graphene should be chosen to form the IMI structure. Meanwhile, the loss of the SPP waveguide is another important parameter to be concerned, which is indicated by the imaginary part of the graphene's permittivity, Im(ε). ε) of the quasi-neutral graphene is always larger than that of the doped graphene, which means the propagation distance of the SPP is longer when the graphene is doped in a higher level. Within the range of 0.001 eV ≤ cμ ≤ 0.217 eV, we can draw the conclusion that the graphene SPP waveguide is in the ON status when the graphene's chemical potential is cμ = 0.217 eV while it is in the OFF status when cμ = 0.001 eV.From the analysis above, the graphene's permittivity is dispersive with different wavelengths and different chemical potentials. Since the external laser can change the graphene's carrier density from 4 × 102 layer is 290 nm, which is much larger than the lateral decay length of the graphene SPP so that we only consider about the dispersion of the SiO2 material in the simulation. The data of the silicon dioxide (glass) is obtained from Ref. 2 material is nearly lossless within 1 μm ≤ λ ≤ 7.634 μm, which oppositely indicates the SPP wave propagating along the graphene sheet may suffer from a severe loss when λ is larger than 7.634 μm.The permittivity of the air is always 1 for any range of wavelength. Apart from the dispersive permittvity of the graphene, the dispersive property of the substrate material is also necessary to be taken into consideration. The thickness of the SiOSPPk), which can be influenced by the chemical potential (cμ), the permittivity of the SiO2 substrate (subε) and the wavelength in free space (λ0) according to Ref. 2, which is shown in SPPδ = 1/2Im(SPPk). The propagation distance of the SPP wave is demonstrated in λ0) increased, SPPδ becomes larger until λ0 = 7.634 μm. For λ0 > 7.634 μm, SPPδ drops very quickly because the SPP energy penetrates inside the SiO2 substrate and it is lost severely due to the large Im(ε) of SiO2. The red, blue and green curves in SPPδ is as large as hundreds of nanometers when the graphene is doped. However, when the graphene is illuminated by the external laser and be tuned back to the quasi-neutral status, SPPδ is smaller than 1 nanometer, which is demonstrated as the insert diagram in SPPλ) is much smaller than λ0 since SPPλ = 2π/Re(SPPk). From the results shown in λ0 is hundreds of times larger than SPPλ when the graphene is doped. As the insert of λ0 is more than ten thousands times larger than SPPλ when the external laser makes the graphene be in the quasi-neutral status. Similarly, the lateral penetration depth of the SPP wave (iδ) shows the same trend since iδ = SPPλ/2π, which is demonstrated in One of the key parameter of the graphene's SPP wave is the wave vector  between the ON and OFF status as big as possible. part see . In this2-Ag nano-strcuture even confine the light energy within a feature size of several nanometers to design the sub-diffraction-limited lasers24As far as the diffraction limit is concerned, the spot size of the external laser can be only reduced to about half of its wavelength, which means the illumination length can only be reduced to the sub-micron scale. If the spot size of the laser is as small as several nanometers, the proposed SPP modulator may obtain a smaller feature size. Practically, some experimental data demonstrate that the mode size of the light emission can be reduced and break through the diffraction limit by the hybrid plasmonic structures232425λ0 = 7.634 μm and cμ = 0.217 eV, which indicates the device has to be very short. Being limited by the optical doping level, the chemical potential of graphene can just vary from 0 eV to 0.217 eV. If some other optical doping procedures, which can change the chemical potential in a larger range, are utilized, we may gain a longer propagation distance of the SPP wave. For instance, using the irradiation in the UV wavelength or replacing the SiO2/Si substrate by some other material may gain a better results. Here an assumption is made that the graphene can be optically doped from 0 eV to 0.8 eV. Then, the properties including SPPδ, iδ and λ0/SPPλ are demonstrated in cμ = 0.8 eV, the propagation distance can be increased by more than 10 times to 17000 nm, which will effectively benefit the construction of the optical circuits.Nevertheless, a general and significant problem of the SPP wave also remains in our proposed method: the loss. As the numerical analysis show, the propagation distance of the SPP wave is about 1260 nm for ε) of the graphene is a negative value. The tunability of the permittivity is of great importance in integrated optics but not only graphene possesses such a property. In the future, researchers can try looking for some material with such a tunability, such as some other two-dimensional or the photosensitive substance, to design the all-optical devices.In addition, the reason why we choose graphene to be the waveguide of this all-optical modulator is that the graphene's permittivity can be obviously modified by the external laser and Re(2/Si substrate and utilizing an external laser to illuminate a part of the graphene, a modulation method is proposed for the SPP wave with two specialties including all-optical and small feature size. The illumination length is as short as 400 nm and it obtains an extinction raito as high as 45.9 dB, which means the modualtion depth reaches 114.7 dB/μm. The all-opitcal modulation can be realized in some other silicon structures such as the micro-ring and the fiber but the footprint is in the scale of several microns, which cannot be equal in force with the all-electronic modulation. Based on the all-optical modulation of the surface plasmonic wave, our proposed method decreases the feature size into the sub-micron scale with a quite high modulation depth. Such kind of thoughts can be applied for designing the fundemental devices in the all-optical interconnection systems, which may progress the construction of the large-scale integration optical circuits in the future.In conclusion, by exfoliating the graphene sheet onto a hydrophilic SiOThe simulations are performed in the 2D type with the help of the finite-different time-domain method by using “Lumerical FDTD Solutions”. The effects shown in L.Z.Y. designed the work and wrote the manuscript. C.Y.P. and A.S. provide the optical doping method of the graphene. C.Y.Z. and X.L. discussed about the excitation of the SPP mode on graphene in the simulation. Y.L. and H.Y. performed theoretical analyses and simulations. Y.B.L. and X.Q.J. helped to plot all the figures. J.Y.Y. supervised the project. All authors discussed the results and commented on the manuscript.Supplementary information


Drosophila melanogaster genetic model system.One of the most notable recent advances in electron microscopy (EM) was the development of genetically-encoded EM tags, including the fluorescent flavoprotein Mini-SOG (Mini-Singlet Oxygen Generator). Mini-SOG generates good EM contrast, thus providing a viable alternative to technically-demanding methods such as immuno-electron microcopy (immuno-EM). Based on the Mini-SOG technology, in this paper, we describe the construction, validation and optimization of a series of vectors which allow expression of Mini-SOG in the Drosophila (DMS tag) using PCR-mediated gene assembly. The photo-oxidation reaction triggered by DMS was then tested using these vectors in Drosophila cell lines. DMS tag did not affect the subcellular localization of the proteins we tested. More importantly, we demonstrated the utility of the DMS tag for EM in Drosophila by showing that it can produce robust photo-oxidation reactions in the presence of blue light and the substrate DAB; the resultant electron micrographs contain electron-dense regions corresponding to the protein of interest. The vectors we generated allow protein tagging at both termini, for constitutive and inducible protein expression, as well as the generation of transgenic lines by P-element transformation.We constructed a Mini-SOG tag that has been codon-optimized for expression in Drosophila. The constructed vectors will no doubt be a useful molecular tool for genetic tagging to facilitate high-resolution localization of proteins in Drosophila by electron microscopy.We demonstrated the feasibility of Mini-SOG tagging in The online version of this article (doi:10.1186/s12575-016-0034-1) contains supplementary material, which is available to authorized users. Arabidopsis phototropin 2. Mini-SOG creates EM contrast by generating oxygen singlets when activated by light, which in turn catalyze the conversion of diaminobenzidine (DAB) to a localized osmiophilic polymer [C. elegans cells [Drosophila, and validated and optimized its use in this model organism.The recent development of genetically-encoded tags for electron microscopy such as Mini-SOG  and APEX polymer   was amplified from cDNA prepared from Drosophila embryos. Mitochondrial-targeting sequence corresponding to the N-terminal 31-amino acid mitochondrial import signal of cytochrome c oxidase subunit VIII (CG7181) [Drosophila genome. The DNA sequence of Mini-SOG , with codon frequency threshold set to 20 %. The DMS gene was synthesized by a two-step PCR method [Open reading frame of ne2Av CG599 was amR method  . The reDrosophila cell lines were maintained according to standard protocols. Cells were transfected with 0.1–0.3 ug DNA using Effectene Transfection Reagent (QIAGEN) according to the manufacturer’s protocol. For induction of the metallothionein promoter, 0.2–0.5 mM copper sulphate  was added 24 h post-transfection. Two days following transfection, the cells were harvested for confocal microscopy and photo-oxidation.Cells were incubated with 250 nM of Mitotracker Red (Molecular Probes) in culture medium for 30 min at room temperature, washed once with medium and immediately observed under a microscope.Transfected cells were plated onto gridded 35 mm glass-bottom dishes  for 30 min, and observed under the microscope, either directly or after fixation (as described below). Confocal images were taken using LSM 780 .Photo-oxidation by Mini-SOG was performed essentially as described by Shu et al., 2011 [4) in 0.1 M sodium cacodylate buffer for 30 min, and then washed with pure water three times. The samples were subsequently dehydrated by ethanol series. A 1:1 ethanol:epoxy resin mix was then added to the samples and incubated on a mixer for 30 min. Afterwards, the resin mix was replaced by pure resin and incubated overnight, and an extra change of pure resin was performed. The resin was then allowed to polymerize in a 60 ° C oven for two days. The resin block was trimmed to 0.5 mm cubes, which were further sliced to 50 nm sections using a microtome. These sections were mounted onto copper grids  without any stain and observed by a JEM-1230R microscope (JEOL), at an accelerating voltage of 100 keV, using bright field imaging.Samples were prefixed with 2.5 % glutraldehyde in 0.1 M sodium cacodylate buffer, postfixed with 1 % osmium tetroxide  and inducible . The ubiquitin promoter is derived from the Ubqi-p63E gene (CG11624), which drives high level expression in cell lines and tissues in la flies . We alsola flies . In addiNext we set out to test whether the DMS tags affect protein localization in Clone-8 cells. We generated DMS fusion to histone 2Av (a nuclear marker ), a chimDrosophila cells, using histone2Av fusion. We found that the bleaching of mCherry occurs after around 1 min of reaction, while the photo-oxidation reaction continues to be very robust 4 min after the reaction started, as judged by the continuous increase in the darkness of the osmium deposit in the nucleus (Fig. We subsequently investigated the time dependence of the photo-oxidation reaction by DMS in Next we looked at mCherry-DMS-histone2Av and mito-DMS cells under the electron microscope. It can be clearly seen (Fig. Drosophila tissues. A transgenic line was made by transgenesis using the pUAST-mCherry-DMS-his2Av construct. This line expresses mCherry-DMS-his2Av in the salivary gland and wing discs when crossed to the MS1096 GAL4 driver. Salivary glands from L3 larvae expressing mCherry-DMS-his2Av were dissected, fixed and stained with DAPI. As can be seem from Fig. Drosophila tissue is by DMS tag is robust.Lastly we checked if the DMS tag works in Over-expression sometimes leads to the mis-localization of the tagged protein. Reducing expression levels may be done in several ways. For the MT promoter, reducing the amount of copper added by titration may be enough to reduce expression levels for correct localization. Another way to get around this is to switch existing promoters with a weaker substitute.Expression level:Enough time should be left for a suitable amount of oxidation product to form However, bear in mind that overly extended reactions lead to excessive buildup of free radicals, damaging the internal cellular structure.Reaction time:As with any other exogenous protein tagging method, there is a chance that the DMS tags will affect trafficking and localization of the proteins being investigated. Hence, it is advisable to make both N-terminal and C-terminal tagged fusions, then to choose constructs yielding the most natural expression and trafficking. We created vectors for fusion at both ends for this purpose. Typically, the localization of the endogenous protein could be investigated in a separate immunolabelling control experiment under light microscopy to check for proper localization of the fusion protein before starting the EM experiment.Terminal fusion site:A number of factors should be kept in mind while using of vectors described in this report:Drosophila cells for high resolution EM detection of proteins. These vectors are inducible and can be used for cell culture as well as transgenic preparations. We believe that this vector set will prove to be a useful resource not only to the Drosophila community, but also to anyone interested in using Drosophila as a disease model system in general.In conclusion, we constructed a set of vectors for optimized Mini-SOG mediated photo-oxidation in


The results of the thorough analysis are in agreement with the calculated number of graphene layers from Raman spectra C-peak position values and indicate that the graphene samples studied are few-layered.A model consisting of an equation that includes graphene thickness distribution is used to calculate theoretical 002 X-ray diffraction (XRD) peak intensities. An analysis was performed upon graphene samples produced by two different electrochemical procedures: electrolysis in aqueous electrolyte and electrolysis in molten salts, both using a nonstationary current regime. Herein, the model is enhanced by a partitioning of the corresponding 2θ interval, resulting in significantly improved accuracy of the results. The model curves obtained exhibit excellent fitting to the XRD intensities curves of the studied graphene samples. The employed equation parameters make it possible to calculate the  Graphene, the atom thick material that is the 2D building unit of all carbon allotropes , having jth layer region occupancies and jth layer coverages, for each j ≥ 1, allow for the calculation of the average number of layers of the graphene samples. The calculations are compared to the results obtained by other methods and are in accordance with them.As the characterization protocol that usually follows after graphene production is an important activity, the ultimate aim of this study was to define a reliable model and thus provide a method for determining the number of graphene layers and their distribution by XRD data. To date, XRD data have been used by some authors to determine the distribution of graphene layers or their average number –12. ThisLa for the studied samples, provides a better overall picture with regard to their size and thickness. The nomenclature of the samples presented in this work is the following: graphene samples obtained by electrolysis in molten salts are denominated GMSE1, GMSE3 and GMSE4, and graphene samples produced by electrolysis in aqueous electrolyte are denominated GAE1 and GAE2.Having obtained the number of layers, together with the determined mean crystallite size . It was done using the Laue functions model presented by The XRD pattern of each of the samples was analyzed around the 002 peak, with the attention strictly focused on the line shape. Therefore, the fitting was operated in the range of In The simple model includes graphene thickness distribution and certain parameters, providing calculations of XRD intensities of the theoretical curves:F is a structure factor, N is the maximum number of layers, |f(θ)| is an atomic scattering factor which varies from 6.00 to 6.15 eV/atom with incident radiation ranging from 2 to 433 keV, kaj = (4πdj sin θ)/λ, where dj is the lattice spacing between the jth and the (j − 1)th layer, θ is an angle between the incident ray and the scattering planes, λ is the X-ray wavelength, and βj, having a value between 0 and 1, is the occupancy of jth graphene layer.where Bj = 100βj is the occupancy of the jth layer in percent, and Dj = Bj – Bj+1 is the jth-layer coverage in percent, for each j = 0,1,…,N, assuming β0 = 1 and βN+1 = 0, where N is the total number of layers in the studied sample, regardless of the distribution. Thus, the average number n of graphene layers may be calculated by the following formula:Hence, The simple model  is conves is the parameter that represents the share of each simulating curve, having values between 0 and 1, and M is the number of simulating curves. Through where αs, we propose the partitioning of the 2θ interval [a,b) around the 002 peak. , a1 = a, bs = as+1, s = 1,2,…,s − 1, bM = b and   is few-layered, and the average value for the number of graphene layers is calculated as C-peak. Its position, Pos(C)N, is directly related to the number of graphene layers, N, and it varies with N as given by the following The graphene sample GMSE4 has an asymmetrical experimental 002 XRD peak, as shown in 18 N·m−3 is the interlayer coupling, and μ = 7.6 × 10−27 kg·Å−2 is the graphene mass per unit area.where α = 12.8 × 10j-layer region coverages according to the analysis of the XRD 002 peak with the model in NGL = 3.1 for the dominant structure and NGL = 9.57 for the overall structure. The calculated value of La for the sample GMSE4 was 2.85 nm.The C-peak position at 32.46 cm−1, the number of graphene layers for sample GMSE4 is calculated as N = 2.13. Later within this article this graphene sample is analyzed using the enhanced model and that result is closer to the C-peak position method of calculation.According to the Graphene samples GAE1 and GAE2 produced by electrolysis in aqueous solution from two different raw graphite materials, using nonstationary current regime, are analyzed here. Typical TEM micrographs of the graphene sample GAE1 material are shown in C-peak positions for GAE1 and GAE2, respectively.In The widest blue dotted line in NGL = 2.57 for the dominant graphene structure and NGL = 4.25 for the overall graphene structure. According to the C-peak positions at 33.28 cm−1  and I2 = [27,36) as shown in C-peak.The graphene samples produced by electrolysis in molten salts that are considered and discussed using the enhanced model are sample GMSE3 and GMSE4. Considering GMSE3, the partitioning of the interval [17,36), is done in the following way: jth layer occupancy (Bj) and therefore the coverages of j-layer graphene regions (Dj) in percent for each part of the structure on the whole interval provide the analysis and results shown in The red curve in NGL = 3.13 for the dominant graphene structure and NGL = 8.87 for the overall graphene structure, whereas according to the C-peak position at 39.1 cm−1 and N = 3.3. The calculated value of La for the sample GMSE3 was 2.36 nm.The average value for number of graphene layers according to XRD 002 peak analysis according to I1 = [17,26.75) and I2 = [26.75,36) make the partitioning of the interval [17,36). The coverage of each jth layer of GMSE4 is given in Considering the sample GMSE4 and the enhanced model  as shownNGL = 2.14 for the dominant graphene structure, which is about 80% of the whole graphene sample, and NGL = 8.68 for the overall graphene structure. One could notice that the average graphene layers number calculated using the enhanced model , I2 = [20,23.84), I3 = [23.84,24.84), I4 = [24.84,26.52) and I5 = [26.52,35). The calculations and corresponding curves obtained with the enhanced model  = [16,35) already shown in ed model  are showjth layer occupancy (Bj), and therefore the coverages of j-layer graphene regions (Dj) in percent for each part of the structure over the whole interval are summarized in The black curve in NGL = 2.07 for the dominant graphene structure and NGL = 3.06 for the overall graphene structure.The graphene structure is few-layered, as nearly 95% of the overall structure consist of eight layers or less. The average value for number of graphene layers is calculated as j-layer occupancies and coverages of graphene samples. The enhanced model is suggested to be generally used, because graphene sheets that are subject of research may have highly asymmetrical 002 XRD peaks. Such peaks are inconvenient to be analyzed by the simple model . The study was done at temperatures between 400 and 600 °C in molten salt, and 25 °C in aqueous solution. It should be underlined that, during the electrolysis, the cations reduced at the electrode intercalate at the graphite surface and generate a high mechanical stress that causes exfoliation of the cathode. This phenomenon enables the electrochemical synthesis of graphene to be performed. The electrochemical route also offers the possibility for accurate control of various parameters, such as applied voltage, current density, temperature and morphology of starting material. The morphological structures of the obtained graphene samples were investigated by TEM analysis using a FEI Tecnai G2 Spirit TWIN with a LaB6 cathode. XRD spectra were recorded using a PAN-analytical X’Pert Pro diffractometer (Cu Kα radiation). Raman spectra were recorded using LABRAM ARAMIS-HORIBA JOBIN YVON system with 532 nm wavelength incident laser light, hole 250 μm, slit of 250 μm.


Graphene oxide (GO) is hydrophilic and swells significantly when in contact with water. Here, we investigate the change in thickness of multilayer graphene oxide membranes due to intercalation of water, via humidity-controlled observation in an environmental scanning electron microscope (ESEM). The thickness increases reproducibly with increasing relative humidity. Electron energy loss spectroscopy (EELS) reveals the existence of water ice under cryogenic conditions, even in high vacuum environment. Additionally, we demonstrate that freezing then thawing water trapped in the multilayer graphene oxide membrane leads to the opening up of micron-scale inter-lamellar voids due to the expansion of ice crystals. Graphene oxide (GO) is receiving increasing attention due to its dispersibility in water4In particular, the carboxylic acid groups also contribute to proton conductivity in graphene oxide121314171819graphite oxide has been studied in great detail over a much longer timescale2123242618Despite the wealth of recent papers published on graphene oxide, in-situ atomic force microscopyin-situ observation of a multilayer graphene oxide cross section over a range of relative humidities, using environmental scanning electron microscopy. Evidence for the existence of water ice intercalated in the multilayer GO membrane is provided by electron energy loss spectroscopy (EELS), even under high vacuum conditions.Direct microscopic observation of the interaction between GO and water has not been as extensively studied. The hydration of bilayer graphene oxide has been investigated by Free-standing multilayer GO paper was produced by vacuum filtration from water dispersion, followed by drying. A bespoke microscope stage was manufactured, allowing side-on observation of the sample . Figure in-situ ESEM. The thickness was first measured at a fixed point on the sample, which was used as a reference area at different relative humidity, under fixed focus conditions. The relative humidity was increased stepwise from 30% RH to 95% RH, then decreased following the same data points. This cycle was repeated twice. To ensure saturation between thickness measurements, images were taken 120 seconds after each step; response times of the order 10 to 20 seconds are reported in the literature19The effect of humidity on the membrane was measured by nd order fit (R2 = 0.983). The thickness of the multilayer GO membrane increases from 34.5 μm at 30% RH to to 43.5 μm at 95% RH, corresponding a total increase of around 26%. The thickness of bi-layer GO measured by atomic force microscopy has previously been measured to vary from 0.74 nm at 30% RH, to 0.85 nm at 90%RH; an increase of 14.9%The variation in thickness of the multilayer graphene oxide cross-section with relative humidity is plotted in 25Bound water is relatively immobile and is strongly adsorbed to the adjacent GO by hydrogen bonds, forming a surface monolayer. This may be the only state of water present under “dry” conditions. Confined water is more mobile and is free to move in two dimensions. Bulk water behaves like normal water without constraints and is likely to be present at high relative humidity. The non-linear dependence of the thickness on relative humidity may relate to the differences between these different states of water. Specifically in the case of bound water, the graphene oxide sheets are also expected to be more tightly bound. When bulk-type water is present in the interlayer region the interaction between individual graphene oxide sheets should be much weaker, allowing for more facile intercalation of water molecules under high humidity conditions. Step-wise increases in thickness with relative humidity associated with filling of the interlamellar spaces with discreet monolayers of water were not observed as in some previous studiesInterestingly, although a simple linear dependence of thickness on relative humidity might be expected, the thickness increase is more pronounced at higher relative humidity. This behavior is also seen in other studies on graphite oxide23The effect of cryogenically freezing the multilayer GO was also investigated by ESEM. The relative humidity was maintained at 80%, and the sample stage was rapidly cooled from 1 °C to −20 °C. Following this, the multilayer GO sample was quickly heated to 40 °C. Upon thawing, extensive changes in the morphology were observed . CorrugaThe low-loss region of EELS spectra is a direct measure of the dielectric response to external electromagnetic excitation. This was recorded at high vacuum, on a few-layer region of the multilayer graphene oxide membrane sample first at 28 °C, and then after cooling to −160 °C . The sam363738in-situ SEM and in-situ STEM characterization of multilayer graphene oxide (GO) at different temperatures and relative humidities. The thickness increased gradually with increasing relative humidity, and decreased with decreasing relative humidity. The rate of change in thickness was slower at low relative humidity, suggesting stronger interlayer bonding in drier conditions. Freezing and then thawing the membrane results in strong corrugation of the multilayer graphene oxide membrane as well as the introduction of micron-scale void throughout the cross section. EELS analysis of few-layer graphene oxide under cryogenic conditions revealed that water ice is present even after exposure to high vacuum, suggesting that obtaining completely “dry” graphene oxide is extremely challenging. Intercalation of water inside graphene oxide could be a significant advantage in applications such as fuel cell ionomer membranes, where water uptake even at high temperature is required.In conclusion, we performed Multilayer graphene oxide was prepared by vacuum-filtration of GO dispersion , Oxygen (20%); Flake size: 0.5–5 μm; Thickness: 1 atomic layer - at least 60%; Hummers Method) onto PTFE Millipore filters . The retentate was dried at room temperature for 48 hours and then peeled-off the filter, resulting in a freestanding multilayer grapehen oxide paper-like membrane. The cross section for SEM investigation was prepared by shearing a thin strip GO paper using a tensile strength test machine (SHIMPO FGO-C-TV), resulting in a clean fracture. Simply cutting the membrane with a scalpel generally does not result in a clean cross section, due to extensive slipping of the GO sheets.SEM images were acquired using a dual-beam focused ion beam system , equipped with a cold stage and a humidifier. The acceleration voltage was 20 kV. Samples were mounted on sticky-coated copper tape  which was then attached to a bespoke sample stage, allowing the sample edge to be tilted towards the electron gun in order to be able to observe the cross-section. A schematic image of the set-up is shown in in-situ EELS experiment was performed after 1 hour at room temperature and 1 × 10−5 Pa, then after 1 hour at −160 °C.STEM images were acquired using a Cs-corrected STEM , equipped with a liquid nitrogen cryo-holder (JEOL). The acceleration voltage was limited to 80 kV to avoid knock-on damage of the GO specimen. A spectrometer  attached to the microscope was used for EELS analysis. The energy resolution is 0.5 eV at the full-width half-maximum (FWHM) of the elastic peak. The samples were mounted on double folding grids . The How to cite this article: Daio, T. et al.In-Situ ESEM and EELS Observation of Water Uptake and Ice Formation in Multilayer Graphene Oxide. Sci. Rep.5, 11807; doi: 10.1038/srep11807 (2015).


In this report, by combining particle-swarm optimization method with first-principles calculations, we present a detailed study of structural, electronic, mechanical, and dielectric properties of Al2O3 monolayer. We predict that planar Al2O3 monolayer is globally stable with a direct band gap of 5.99 eV and thermal stability up to 1100 K. The stability of this high-κ oxide monolayer can be enhanced by substrates such as graphene, for which the interfacial interaction is found to be weak. The band offsets between the Al2O3 monolayer and graphene are large enough for electronic applications. Our results not only predict a stable high-κ oxide monolayer, but also improve the understanding of interfacial properties between a high-κ dielectric monolayer and two-dimensional material.The miniaturization of future electronic devices requires the knowledge of interfacial properties between two-dimensional channel materials and high- BN11131416181920sp3 covalent bonds. Furthermore, 2D structures based on binary compounds of the group IV or group III–V elements, have been predicted to be stable by first-principles calculations22232423Two-dimensional 2D) materials present exceptional electronic, optical, mechanical, and thermal properties, as well as a high surface/volume ratio, all of which make them promising for applications ranging from electronics to energy storage. The discovery of graphene, a single layer of carbon atoms arranged in planar honeycomb lattices, has stimulated dramatic research interest on other 2D materials in order to realize novel functionalization and also further miniaturization of electronic devices1D materia345782 have been proposed by first-principles calculations2 with desirable reduced band gap can be formed on a rutile TiO2 (011) surface, for which the corresponding atomic structure has been refined by subsequent theoretical studies3132κ dielectric monolayers have also been found. A Y2O3 monolayer with a hexagonal lattice has been deposited on graphene2, Co3O4, and WO3, have been synthesized by rationally employing lamellar reverse micelles methodκ dielectrics based 2D structures. Al2O3 is an excellent electrical insulator, which has been widely used in current electronic devices. Thus, it is highly desired to explore the stability of its 2D form, and understand the related physical properties. In this study, via density-functional theory (DFT) based first-principles calculations, we predict that planar Al2O3 monolayer with a hexagonal lattice is stable. This oxide monolayer is found to be an insulator with a direct gap of 5.99 eV and a dielectric constant of 2.51. It is further found that the interaction between Al2O3 monolayer and graphene is weak, which leads to band offsets larger than 1 eV.More recently, many efforts have been made to realize oxide based crystalline 2D sheets. For example, a stoichiometric silica 2D sheet with bi-layer tetrahedral configuration has been grown using a Ru (0001) substrate as the support282O3 monolayer with the constrained stoichiometric formula of Al2O3. This method has been used to predict a number of 2D materials successfullyThe particle swarm optimization (PSO) method implemented in the CALYPSO372O3 monolayer, α-Al2O3 bulk, and hybrid structures of Al2O3 monolayer on the substrates of graphene and Al (111) was sampled by Γ centered 18 × 18 × 1, 12 × 12 × 4, 6 × 6 × 1, and 9 × 9 × 1 κ-point meshes, respectively. A vacuum layer with 15 Å thickness has been inserted normal to the Al2O3 surface for all slab structures to minimize the interaction between neighboring image surfaces. In order to get an improved electronic structure, the Heyd-Scuseria-Ernzerhof hybrid functionals (HSE06) were used−6 eV and 0.01 eV/Å, respectively. To explore thermal stability of Al2O3 monolayer, ab initio molecular dynamics (MD) simulations were performed with a time step of 1 fs, canonical ensemble (NVT), and Nosé heat bath on the 5 × 5 × 1 supercell. The dynamic stability was studied by calculating the phonon dispersion using density functional perturbation theory implemented in VASP with a higher electronic convergence criterion of 10−8 eV and analyzed by using the PHONOPY codeα-Al2O3 bulk are in good agreement with previous studies and experimental results48First-principle calculations, using DFT based VASP code40422O3 monolayer predicted by the PSO simulation is shown in h-BN monolayer and graphene. This honeycomb structure is a global minimum in the space of all possible 2D arrangements of Al2O3. Then, the predicted Al2O3 monolayer structure was optimized using first-principle calculations. The equilibrium configuration of Al2O3 monolayer can be obtained from the energy minimum in the equation of state curve in 2O3 monolayer with the optimized lattice constant of 5.84 Å and the Al-O bond length of 1.69 Å α-Al2O3 bulk. The contour plot of ELFs for the Al2O3 monolayer and α-Al2O3 bulk are visualized along the Al-O bond plane, as shown in 2O3 bulk, suggesting dominant ionic bonding character. In contrast, the electron density in the Al2O3 monolayer is slightly more delocalized. This indicates that the ionic bonding is still dominant in the Al2O3 monolayer, but it is weaker than that of α-Al2O3 bulk, consistent with the shorter bond length in the Al2O3 monolayer. The enhanced in-plane covalent bonding character can be seen also from the Bader charge analysis2O3 monolayer, less than To investigate the bonding character of the Al2O3 monolayer, its cohesive energy Ec can be calculated by the following equation:The stability of a material is indicated by the related cohesive energy, and a structure with negative cohesive energy is stable or metastable. For Al2O3 monolayer, and EAl and EO are the energy of isolated single Al and O atom, respectively. The calculated cohesive energy of Al2O3 monolayer is −5.97 eV/atom, which is slightly higher than that of the Al2O3 bulk (−6.56 eV/atom), but it is lower than that of recent experimentally confirmed 2D materials such as silicene (−5.16 eV/atom) and germanene (−4.15 eV/atom)192O3 is promising for an experimental realization.where 2O3 monolayer can also be examined from the calculated phonon spectra. As shown in 2O3 monolayer is dynamically stable and can exist as a free standing 2D structure.The structural stability of the Al2O3 monolayer, ab initio molecular dynamics simulation has been conducted at the temperature of 300 K with a time length of 10 ps. A (5 × 5 × 1) supercell of the Al2O3 monolayer is used to minimize constraints induced by periodic boundary condition. The averaged total energy of the monolayer is nearly constant, and the variation of the Al-O bond length is within 0.1 Å with respect to the average value at 300 K during the simulated time period, as shown in 2O3 monolayer is thermally stable at room temperature. Ab initio MD simulations were also carried out at higher temperatures of 800 and 1100 K, respectively, which show that this monolayer is still stable at the temperature of 1100 K . For the deformed state of Al2O3 monolayer, it is assumed that the contribution of bending to the strain energy density is insignificant, thus the vertical weight of elastic constants is zero. For all the deformed configurations, the positions of all atoms were optimized and the related energies were calculated. In this way, for each type of distortion, we could obtain the strain dependent energy. Then, the in-plane Young’s modulus Ys and Poison’s ratio v were calculated from the following relationship: h-BN monolayer and ZnO monolayer were calculated and summarized in 2O3 monolayer is 47.6 N/m, very close to that of ZnO monolayer (~47 N/m), but much smaller than that of graphene (~342 N/m), BN monolayer (~274 N/m), and Al2O3 bulk (~230 GPa). This clearly shows the relative softness of the Al2O3 monolayer. The softness of the Al2O3 monolayer is also reflected by the flat slope of the acoustic branch at the Γ point in the phonon dispersion2O3 monolayer is susceptible to external influence, with greater tendency to form ripples or out-of-plane deformations, as supported by the above MD simulation results , one of the most promising high-κ dielectrics. Thus, we believe that the band gap of the Al2O3 monolayer is large enough to be used as a dielectric material. From the PDOS and partial charge density . The formation of π bonds is believed favorable to stabilize the 2D planar structure, as shown in other 2D structuresAlsity see , we find2O3 monolayer is shown in εxx and εzz, the total dielectric constant ε can be determined by A dielectric material with high dielectric constant is preferred in order to achieve larger capacitance density. The dielectric constant decreases with the decrease of thickness, and thus it is important to study dielectric properties for a dielectric material with one atomic thickness. The calculated dielectric function of the Al2O3 monolayer is determined by the zero energy limit from the real dielectric function, which is about 1.27. With the inclusion of the ionic vibration contribution (~1.24), the overall dielectric constant is about 2.51. This value is much smaller than that of α-Al2O3 bulk (~10.5) due to the reduced thickness, changed bonding character, and also decreased band gap, but comparable to that of SiO2 bulk (~3.9). It is noted that the calculated dielectric constant of α-Al2O3 bulk is consistent with the experiment value (~9.0). From the imaginary part the dielectric function  graphene supercell matches 2O3 monolayer well. Since the Al2O3 monolayer is relatively soft, it was compressed by about 2.88% and placed on graphene supercell. This small strain on the Al2O3 monolayer yields a 0.18 eV increase in the band gap, but does not alter the electronic properties significantly, as shown in the 2O3 monolayer still favors planar structure, and becomes more stable as its energy is lowered by 0.19 eV per unit cell, compared with free standing Al2O3 monolayer.Experimentally, various substrates have been proposed for growing oxide monolayer such as SiO2O3 monolayer on graphene is shown in 2O3 monolayer, β-Si3N4, and g-C3N3 on graphene, and HfO2 on MoS2 monolayer255455562O3 monolayer planes remain planar. The shortest distance between Al2O3 monolayer and graphene is 3.26 Å, indicating weak interaction between them. The calculated adsorption energy is 13.62 meV/Å2, smaller than that of graphene on Al2O3 (0001) surface2O3 monolayer and graphene.The most stable configuration of the Al2O3 monolayer. From the charge density difference projected on graphene plane  and conduction band offset (CBO), respectively, as shown in 2O3 monolayer. Thus, the real VBO and CBO should be larger than the values in current studies.Due to the weak interaction, the charge inhomogeneity in graphene is insignificant with the presence of the Alne plane , we can 2O3 monolayer, thus it is a potential substrate to grow Al2O3 monolayer, similar to the growth of Y2O3 monolayer on graphene2O3 monolayer, the interface between the Al2O3 monolayer and Al (111) surface has been studied also , forming interfacial Al-O bonds with bond length of 1.9 Å. The strong interaction is also confirmed by the large adsorption energy (2.2 eV per Al2O3 unit) and significant charge transfer (see 2O3 monolayer on Al (111), and it can be expected that the 2D growth of Al2O3 monolayer is difficult on Al (111) substrate by a direct thermal oxidation process. Therefore, inert substrates with weak interaction, same surface symmetry, and small lattice mismatch such as graphene are favored to realize the 2D growth of Al2O3 monolayer via sputtering or other advanced deposition techniques.From the above discussions, we can see that graphene has same surface symmetry, small lattice mismatch, and weak interaction with Alsfer see . This st2O3 monolayer with a direct band gap of 5.99 eV and dielectric constant of 2.51. This Al2O3 monolayer can be further stabilized by the support of graphene. For the interface between Al2O3 monolayer and graphene, we find that the interaction between them is weak and band alignments are much larger than 1 eV. Moreover, the presence of the Al2O3 monolayer does not introduce interface states and electron-hole puddles in graphene. Together with high thermal stability, the Al2O3 monolayer might be a potential dielectric for future electronic applications. Due to similar surface chemistry between graphene and other 2D channel materials such as transposition metal dichalcogenide or phosphene, these results might be applicable to the interface between the Al2O3 monolayer and other 2D materials.In conclusion, based on PSO method and first-principles calculations, we find a stable AlHow to cite this article: Song, T. T. et al. The stability of aluminium oxide monolayer and its interface with two-dimensional materials. Sci. Rep.6, 29221; doi: 10.1038/srep29221 (2016).