By simultaneous control of external electric fields and carrier charging concentrations, we show that the graphene’s Dirac point position inside the MoS2 bandgap is easily modulated with respect to the co-varying Fermi level, while keeping the graphene’s linear band structure around the Dirac point. The easy modulation of graphene bands is not confined to the special cases where the conduction-band-minimum point of MoS2 and the Dirac point of graphene are matched up in reciprocal space, but is generalized to their dislocated cases. This flexibility caused by the strong decoupling between graphene and MoS2 bands enhances the gate-controlled switching performance in MoS2-graphene hybrid stacking-device.Based on the first principles calculation, we investigate the electronic band structures of graphene-MoS For this reason, extensive efforts have been carried out to take advantages from each material and combine them into a single device. Prominent accomplishments in such efforts are the synthesis of stacked graphene-MoS2 junctions2021222425262728293031323334353637382 and graphene are used as a channel and source(S)-drain(D) electrodes, respectively.Molybdenum disulfide MoS12 and gr2 channel are pure metals such as Ti568404142434045464748494251522 is reported as 4.0 eV and the work functions of graphene and Ti are known as 4.5 and 4.3 eV, respectively, MoS2-Ti contact is expected to form a smaller Schottky barrier, leading to a more ohmic behavior. Contrary to this expectation, however, graphene-contacted MoS2 shows higher on-current and lower off-state behaviors, displaying an on/off ratio over ~7.5 × 106 2 and Ti/MoS2 stacking structures, and investigated their electronic band structures by using the first-principles density functional methodF) pinningF and work function under gate-voltages to the strong decoupling between graphene and MoS2 bands in their heterojunction.In FETs, an ohmic contact is usually desired for easy current flows between semiconductor and S/D electrodes. To fulfill this requirement, relevant contact searching is primarily focused on avoiding materials with the rectifying responses to forward and backward biases. Reported S/D electrodes on MoS2 and Ti(S/D)-MoS2 FETs, we have performed self-consistent density functional calculations using the SIESTA code2, we performed the virtual crystal approximation (VCA) by replacing 1.3 × 10−4 atomic % of sulfur atoms with chlorine atoms. This corresponds to 5.0 × 1016 cm−3 electron doping in bulk MoS2 as consistent with experimental observations405960612, we considered two different heterostructures with commensurability conditions: (i) 2 monolayer (6.32 Å) which includes 2.9% lattice contraction of graphene. (ii) 4 × 4 graphene sheet (9.84 Å) was adjusted to 3 × 3 MoS2 monolayer (9.48 Å), resulting in 3.7% lattice contraction of graphene. For the Ti stacking on MoS2, 4-layered Ti lattice (a = 2.95 Å) was placed on 1 × 1 MoS2 monolayer (3.16 Å) which includes 6.7% lattice expansion of Ti.To investigate the gate-voltage tuning effects on the graphene(S/D)-MoSG) always puts into effects of electron charging and electric field variation in a simultaneous way. Once the system reaches a given state of on-current at a specific positive gate-voltage, both direction and strength of current flows are controlled by the drain-voltage (VD). 2 heterojuncion. To describe a weak positive (negative) gate-voltage, we have set the external electric field as E = ± 0.01 V/Å and the electron charging concentration as nc = ± 8.7 × 1012 cm−2. Here the positive and the negative sign represent the positive and the negative VG, respectively. To describe stronger gate-voltages, we have increased the electric field and the electron charging concentration by 10 times.In FETs, gate-voltage  energy (EC) of MoS2 in the graphene/MoS2 system and the Fermi level (EF) of the whole system. As seen in C − EF) in graphene/MoS2 sensitively responds to gate-voltages by decreasing from 0.37 eV (ungated) to 0.03 eV (on-current) in the positive VG, and by increasing from 0.37 eV (ungated) to 0.74 eV (off-state) in the negative VG. Easily reducible Schottky barrier in positive VG means easily diminishable contact resistance333435362, which induces large current flows in drain-voltages. In contrast, a large Schottky barrier in negative VG reduces the unprofitable current leakage in off-states and contributes to the high on/off ratio in itself. The working principles of VD and VG are similar to each other, except that VD additionally controls the chemical potential of graphene with respect to that of MoS2. Thus, the high sensitivity to gate-voltages involves a similar sensitivity to drain-voltages, resulting in a fast slope increase in the ID-VD curve and a corresponding high on/off ratio. Meanwhile, as evaluated in G, the Fermi velocity near the Dirac point decreases from 8.38 × 105 m/s to 8.18 × 105 m/s, and the Dirac point position becomes closer to the CBM energy of MoS2. In contrast, in the negative VG, the Fermi velocity increases from 8.38 × 105 m/s to 8.45 × 105 m/s, and the Dirac point position becomes far away from the CBM energy of MoS2.In graphene/MoSC − ED) is decreased by 0.08 eV from the ungated case (0.37 eV) to the positive VG (0.29 eV), and increased by 0.10 eV from the ungated case (0.37 eV) to the negative VG (0.47 eV). This slightly asymmetric response can be assured by the energy difference between the Fermi level and the Dirac point (EF − ED); increment by 0.25 eV from the ungated case to the positive VG, and decrement by 0.27 eV from the ungated case to the negative VG. As the gate-voltages increase more, the asymmetry increases further. Shown in E = ± 0.1 V/Å and nc = ±8.7 × 1013 cm−2). Intriguingly, G.The energy difference between the CBM and the Dirac point (Ei) We clearly see the absence of graphene-induced gap-states inside the MoS2 bandgap, which would have a flat-band form in k-space and absorb electrons from metals on stacking. This failure in forming the gap-states unlocks the Fermi level pinning and preferably makes the graphene bands flexible. As shown in ii) The linear shape of graphene bands around the Dirac point remains intact and the linearity extends over one electron-volt from the Dirac point with a negligible band mixing between graphene and MoS2. This weak interaction is evidenced from the relatively small binding energy of −0.59 eV and the large equilibrium distance of ~3.23 Å between MoS2 and graphene24F to be located above the CBM to compensate this charge depletion. Even in this extreme electric field, the linearity is retained around the Dirac point, indicating the strong decoupling between graphene and MoS2 bands.The band structures shown in 2 and the Dirac point of graphene coincided at the special k-point K. To extend the validity to more general cases where the CBM point and the Dirac point are mismatched, we consider the supercells of 4 × 4 graphene stacked on 3 × 3 MoS2. In this new stacking, the CBM point is moved to Γ whereas the Dirac point is still located at K as shown in 2 reproduce sensitive and asymmetric responses to gate-voltages. Also, we see that graphene-induced gap-states do not appear, and the linear dispersion around the Dirac point remains intact on stacking and in onward applications of gate-voltages, leading to the strong decoupling between graphene and MoS2 bands. Thus, Thus far, all analyses were performed for the case with the CBM of MoS2, we here analyze the position movement of special k-points from the 1 × 1 hexagonal unit cell to a general hexagonal supercell. am,n = am − bn and bm,n = an + (m + bn), where Before going to Ti stacking on MoSNs,and the geometric condition The location of special k-point K for a general hexagonal supercell is determined by the conditions,2, the band offsets in Ti/MoS2 show very insensitive behaviors to gate-voltages. To see the differences between graphene/MoS2 and Ti/MoS2, we constructed three different Ti/MoS2 stacking configurations  as shown in 2, 2 has a strong band mixing along the Γ-M-K-Γ line in the energy range from −1.0 to 1.0 eV. This strong interaction is expected from a short equilibrium distance ~1.60 Å between Ti and MoS2, which is less than half the distance ~3.23 Å between graphene and MoS2. The binding energy between 2 × 2-Ti and 2 × 2-MoS2 is found to be −8.32 eV, which indicates that Ti and MoS2 stick together 14 times stronger than graphene and MoS2. Comparing G (E = ±0.01 V/Å and nc = ±8.7 × 1012 cm−2). Even when we increase the gate-voltages by 10 times (E = ±0.1 V/Å and nch = ±8.7 × 1013 cm−2), the relative positions of Ti bands are not significantly altered from those in In striking contrast to graphene/MoS2 with those in Ti(S/D)-MoS2. Under gate-voltages, the Dirac point positioning inside the MoS2 bandgap is easily modulated with respect to the co-varying Fermi level, while the linearity of graphene bands remains intact around the Dirac point. Band lineups in graphene/MoS2 explicitly confirms the absence of graphene-induced gap-states, which is thought to prevent the Fermi level pinning and preferably make graphene bands flexible. In contrast to Ti-MoS2, graphene-MoS2 interactions are very weak as evidenced from the small binding energy of −0.59 eV and the large equilibrium distance between graphene and MoS2 ~3.23 Å, which is more than twice the equilibrium distance ~1.60 Å between Ti and MoS2. In effect, the strong decoupling between graphene and MoS2 bands causes a high sensitivity to gate-voltages. We respectively analyzed the fast increasing on-current and the steadily maintained (or lowered) off-current states, which originate from such a sensitive work function tuning of graphene under positive and negative VG; such work function tuning, in sum, leads to the high on/off ratio in graphene/MoS2.In conclusion, by simultaneous control of external electric fields and electron charging concentrations, we have compared the band offsets in graphene (S/D)-MoSHow to cite this article: Baik, S. S. et al. Work Function Tuning in Two-Dimensional MoS2 Field-Effect-Transistors with Graphene and Titanium Source-Drain Contacts. Sci. Rep.7, 45546; doi: 10.1038/srep45546 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Betaproteobacteria and Thaumarchaeota with ecological selection and with seasonal changes in microbial metabolism. We present a conceptual model based on our results in which metabolism increases when oscillating selective pressures oppose temporally stable selective pressures. Our conceptual model is pertinent to both macrobial and microbial systems experiencing multiple selective pressures and presents an avenue for assimilating community assembly processes into predictions of ecosystem-level functioning.Community assembly processes generate shifts in species abundances that influence ecosystem cycling of carbon and nutrients, yet our understanding of assembly remains largely separate from ecosystem-level functioning. Here, we investigate relationships between assembly and changes in microbial metabolism across space and time in hyporheic microbial communities. We pair sampling of two habitat types  through seasonal and sub-hourly hydrologic fluctuation with null modeling and temporally explicit multivariate statistics. We demonstrate that multiple selective pressures—imposed by sediment and porewater physicochemistry—integrate to generate changes in microbial community composition at distinct timescales among habitat types. These changes in composition are reflective of contrasting associations of  The collective effects of community assembly processes  on microbial metabolism of carbon and nutrients in the environment are poorly understood, and they constitute a key knowledge gap in process-based modeling of biogeochemical cycles. Selection and dispersal both have the potential to impact rates of microbial metabolism. For example, selection can enhance metabolism via species sorting mechanisms that optimize the microbiome for a given environment , while dCommunity assembly processes act through space and time to impact community membership, which then impacts microbial metabolism . For insAdditionally, individual taxa are differentially impacted by community assembly processes. Only some taxa contain traits that are under selection in given environmental conditions, and changes in the environment may affect some taxa to a greater extent than others . For exaEnvironmental transition zones present a unique opportunity for examining interactions between microbial metabolism and both long- and short-term assembly processes, as they experience extreme spatiotemporal variation in physicochemical characteristics and microbial community composition across tractable spatial and temporal scales. Here, we leverage inherent variation in hydrology, habitat heterogeneity, and aerobic respiration in a zone of subsurface groundwater-surface water mixing (hereafter termed “hyporheic zone”) to examine the interplay of community assembly processes and microbial metabolism through time. Hyporheic zones are subsurface regions below and adjacent to rivers and streams that experience mixing between surface water and groundwater. The groundwater-surface water mixing within the hyporheic zone can result in blending of complementary resources and, in turn, elevated rates of microbial metabolism relative to other systems .We employ null modeling in conjunction with temporally explicit multivariate statistics to characterize assembly processes driving shifts in microbial communities and microbial metabolism in the Columbia River hyporheic zone. We examine two co-occurring, yet ecologically distinct, habitat types—attached and planktonic communities. Further, we extend the analysis of community assembly processes to individual taxa that likely contribute to observed shifts in microbial metabolism. Our results culminate in a broadly applicable conceptual model coupling changes in selective environments, trait abundance, and ecosystem-level functioning through time.This study was conducted in Hanford Reach of the Columbia River adjacent to the Hanford 300A  in eastern Washington, as described elsewhere , from Ma- as a conservative tracer for groundwater contributions to hyporheic porewater chemistry as employed by We monitored physicochemical conditions for three hydrologically-connected geographic zones  via aqueous sampling (Table S1). The inland environment is characterized by an unconfined aquifer within the Hanford formation and more recent illuvial deposits, and it maintains a distinct hydrologic environment with stable temperatures (∼15°C) and high concentrations of anions and inorganic carbon relative to the river. River water contains high concentrations of organic material and low concentrations of ions with seasonally variable temperatures. The waters from these discrete hydrologic environments experience dynamic mixing in a nearshore hyporheic zone that is regulated by fluctuations in river stage; we focus on ecological dynamics within this zone. To monitor groundwater-surface water mixing across space and time, we utilize Cln = 0-4 at each sampling event, a full breakdown of sample size is listed in Table S2). These samples were collected at three-week intervals from March through November 2014, with the first planktonic samples collected in March and the first attached samples collected after a 6-week incubation period from piezometers installed to 1.2 m depth near the riverbed. Samples collected at each time point were assumed to represent sub-hourly variation in hydrologic conditions, as hydrology fluctuates at sub-hourly rates within a single day in our system , microbial metabolism (aerobic metabolism assayed with Resazurin) per unit active biomass (ATP) defined by Raz:ATP (attached samples only), and 16S rRNA amplicon sequences . Sequences are publically available at doi: 10.6084/m9.figshare.4264148.R software1 to disentangle community assembly processes . The approach uses pairwise phylogenetic distances between communities, calculated using the mean-nearest-taxon-distance (βMNTD) metric (bray), as per bray. RCbray values > 0.95, > -0.95 and < 0.95, or < -0.95 were assumed to indicate dispersal limitation, no dominant assembly process, or homogenizing dispersal, respectively. Significance levels for βNTI and RCbray are based on standard deviations—|βNTI| = 2 denotes two standard deviations from the mean of the null distribution—and alpha values—|RCbray| = 0.95 reflects significance at the 0.05 level. Inferences from both βNTI and RCbray have previously been shown to be robust (We implemented null modeling methodology developed by ) metric , to infe) metric . Pairwise robust .U tests were conducted using the base statistics package in R. Variation in community composition was assessed with PERMANOVA in QIIME  in ‘vegan’ to identify individual species driving community dissimilarity . SIMPER P < 0.05) for subsequent analyses. Organisms were grouped at the class-level to provide sufficient statistical power for analysis. Mantel tests were used to compare the average relative abundance of taxonomic groups identified by SIMPER across samples to associated βNTI and RCbray values . Finally, we compared dissimilarity in species richness between samples within and across attached and planktonic communities to βNTI and further, if -2 < βNTI < 2, to RCbray using Mantel tests to infer community assembly processes generating species turnover between samples.We extracted taxonomic groups of organisms at the class-level containing at least one species identified as having a significant impact on community composition by SIMPER  and decrease in NPOC  associated with a seasonal shift in water stage . Temperature peaked during August and followed a smooth temporal trend . The composition of both attached  and planktonic  communities also changed across our sampling period, but attached and planktonic communities remained taxonomically distinct through time . Main taxa in each environment are presented in Table S3.We observed distinct temporal trends in microbial communities and in groundwater-surface water mixing, characterized by an abrupt increase in ClFigure 1D). Richness was more tightly correlated with temperature  than Cl-  and NPOC . Finally, within both environments, community dissimiliarity increased in concert with differences in species richness .Species richness in both attached and planktonic communities mirrored temperature trends, with the highest number of species observed during the warmest summer months . βNTI was positively correlated with differences in species richness in planktonic samples , with weaker correlations in attached communities  and between attached and planktonic communities .Dissimilarity in microbial communities indicated a possible role for different assembly processes governing species composition among  and across  habitats. We investigated assembly processes across differences in richness to identify processes that impacted species addition to each habitat, and we found that assembly varied between habitats . Conversely, attached communities correlated more tightly with physicochemical attributes over a seasonal timescale .Because selection was a substantial driver of all microbial communities, we further examined the impact of aqueous physicochemistry on communities at both sub-hourly (within sampling date) and seasonal  timescales using stratified and unstratified NMDS analysis. Permutations in stratified NMDS are constrained within the specified grouping , thus controlling for the grouping factor see . Here, wbray. All significant correlations with absolute r values greater than 0.30 are listed in Table S5. Taxa in planktonic communities exhibited no relationships with βNTI (Table S6), but the mean relative abundance of many taxa, including Thaumarchaeota , a class of Acidobacteria , Actinobacteria , and Alphaproteobacteria , displayed correlations with RCbray. The mean relative abundance of Parvarcheota and a class of candidate phyla OP3 (koll11) were positively correlated with βNTI derived from comparisons across attached and planktonic communities . Finally, within attached communities, βNTI was correlated with the mean relative abundance of Thaumarchaeota  and Betaproteobacteria . No correlations were observed between RCbray and taxa within attached communities or across attached-vs.-planktonic communities (Table S6).Similarity percentage analysis revealed species driving differences among attached and planktonic communities during periods of high versus low species richness (Table S5). We extracted phylogenetic classes of organisms containing species identified by SIMPER and examined relationships between their relative abundances and βNTI and RCThaumarchaeota in attached communities and a concomitant decrease in Betaproteobacteria  that corresponded with shifts in hydrology . Oxygenated conditions persisted throughout our sampling period, and Raz:ATP increased seasonally within attached communities, an effect that correlated with day of year  but not temperature, NPOC concentration, or hydrology  P = 0.15). The relative abundance of Thaumarchaeota and Betaproteobacteria in attached communities also correlated positively and negatively, respectively, with Raz:ATP  and exhibited contrasting responses to porewater physicochemical properties (Table S7).We also observed a seasonal increase in the abundance of Our results show pronounced seasonal changes in hydrologic and microbial characteristics within the Columbia River hyporheic zone, as well as variation in the importance of selection and dispersal in structuring attached vs. planktonic communities. These community assembly processes operated at distinct timescales in each habitat and were also associated with changes in the relative abundance of certain taxa. In particular, changes in selection exhibited contrasting relationships with putative heterotrophic and autotrophic taxa in attached communities. Further, changes in community-level microbial metabolism correlated with the abundance of these same taxa in attached communities. Based on our findings, we present a conceptual model applicable within both macrobial and microbial systems that links trait selection, organismal fitness, and ecosystem-level functioning in habitats that are characterized by opposing selective pressures across multiple timescales.Hyporheic microbial community composition shifted in conjunction with seasonal changes in organic carbon concentration, temperature, and groundwater-surface water mixing conditions. These variables each explained some variation in temporal community dissimilarity within attached and planktonic communities, indicating potential influences of selection  and dispersal  over microbial community composition (Table S8). Both selection by the geochemical environment and dispersal from local sediment communities have been demonstrated within the groundwater aquifer in our system ; howeverbray| > 0.95). Because planktonic communities consistently displayed higher βNTI values in comparison to attached communities, often with -2 < βNTI < 2, dispersal processes may play a greater role in structuring planktonic vs. attached communities. In contrast, attached communities always yielded large negative βNTI values suggesting that features of the physical sediment environment may impose stronger selective pressures than aqueous physicochemistry.Our results indicate that homogeneous selection  was the dominant assembly process in attached communities, while planktonic communities were influenced by a combination of homogeneous selection, variable selection , and spatial processes , indicating strong and consistent selective pressures imposed by a relatively stable environment across temporal changes in microbial diversity. Strong consistent selection through time in attached communities suggests that the physical substrate may inherently contain a limited number of ecological niches—potentially related to mineralogy or physical structure—with slow changes in available niche space. In this case, temporal increases in richness were likely due to the addition of taxa that were ecologically similar to existing taxa and occupied similar niche space.Because we observed pronounced seasonal trends in species richness associated with changes in the environment, we used null modeling to assess the extent to which selection versus dispersal influenced community composition across changes in species richness. Homogenous selection prevailed in attached communities as differences in species richness increased . In this case, increases in species richness were likely due to the addition of taxa occupying newly available niche space generated by changes in the selective environment, yielding new taxa that were ecologically dissimilar to existing taxa.In contrast, differences in planktonic species richness were positively correlated with βNTI, with βNTI values supporting a role for more variable selection as differences in richness increased . Both communities experienced a seasonal change in composition; however, variation in planktonic communities correlated with porewater physicochemistry at both the sub-hourly and seasonal timescales . In our system, planktonic organisms may therefore be influenced by short-term fluctuations in groundwater-surface mixing, either through rapid changes in the selective environment or dispersal via hydrologic transport.The timescales at which selection imposes constraints on microbial community composition are poorly understood . Here, wFigure 3B). This short-term stability could be facilitated by a number of potentially complementary mechanisms. For example, attached communities may reside within biofilms, whereby microbial cells are imbedded in a matrix of extracellular polymeric substances. Biofilms are prevalent in aquatic systems and buffer communities against fluctuations in the hydrologic environment , further suggesting that temporal stability in attached communities may be enhanced by high species richness reducing susceptibility to invasion . In particular, positive relationships of Thaumarchaeota  and a class of Acidobacteria  with RCbray and negative relationships of Actinobacteria  and Alphaproteobacteria  with RCbray were among the strongest correlations (Table S6). These positive or negative relationships indicate higher or lower relative abundances, respectively, under higher levels of dispersal limitation. No relationships existed between planktonic taxa abundances and βNTI.In light of rapid hydrologic fluctuations in the porewater environment, relationships between RCbray-abundance relationships in planktonic communities, the trends we observed help elucidate ecological dynamics impacting the abundance of microbial taxa within hyporheic zones. For example, taxa showing positive relationships with RCbray—Acidobacteria and Thaumarchaeota—are widely distributed globally  and a class of the candidate phylum OP3 . Positive correlations between a particular taxon and βNTI across habitat types imply that the taxon increases in abundance as the habitats diverge in selective environments .Additionally, when we examined assembly processes governing differences between attached and planktonic communities, we observed selection for microbial taxa in planktonic communities with unique ecological properties (Table S6). No correlations with RCParvarchaeota and koll11 were almost exclusively found in planktonic communities suggesting that selection in the porewater environment favors these organisms. Although the specific selective pressures regulating the abundance of these organisms are unknown, archaea and members of the PVC superphyla to which OP3 belongs have a cell membrane lacking peptidoglycan that conveys resistance to common antibiotics and have the genetic potential to metabolize C1 compounds such as methane , which occurred during times of low groundwater intrusion . In contrast, members of Thaumarchaeota  increased as homogeneous selection waned during times of high groundwater intrusion . In this scenario positive correlations between a taxon and βNTI indicate that the taxon becomes more abundant as homogeneous selection wanes, and thus, that selection targets traits outside the taxon. In contrast, negative correlations between a taxon and βNTI should indicate that the primary selective pressure is for traits contained within that taxon. Because organisms with wider niche breadths are favored by selection in a greater variety of environmental conditions, positive relationships should be more probable for organisms occupying niches defined by a narrow subset of environmental attributes, whereas negative relationships should be more probable for organisms occupying broader niches. Indeed, Betaproteobacteria and Thaumarchaeota, respectively, contain organisms with diverse and limited metabolic capabilities . The relative abundance of Thaumarchaeota also correlated with physicochemical properties associated with increased groundwater-surface water mixing , suggesting a heightened importance of Thaumarchaeota-mediated nitrification when enhanced groundwater discharge into the hyporheic zone leads to organic carbon limitation  opposes that of a temporally stable environment .Taken together, we hypothesize that selective pressures, both from sediment composition and from porewater physicochemistry, favor diverse heterotrophs within Thaumarchaeota abundance coincident with negative correlations between Raz:ATP and Betaproteobacteria . We therefore infer that seasonally fluctuating selective pressures from the porewater environment impact microbial metabolism via their influences on niche dynamics. We propose that community-level niche diversification generated by a seasonal rise of specialized autotrophs leads to an increase in community metabolic activity despite selection for heterotrophs imposed by the consistent sediment environment.Importantly, changes in community composition in our system are associated with a seasonal increase in microbial metabolism, consistent with work in both micro- and macroecology demonstrating that productivity increases with niche diversification . SpecifiFigure 6). The conceptual model focuses on the combined influences of stable and oscillating selective pressures, which should be prevalent across ecosystems. For example, in terrestrial ecosystems, physical soil properties and soil water content are relatively stable and oscillating, respectively, from the perspective of associated plant communities. Likewise, in subsurface systems (such as presented here), sediment geochemistry is relatively stable over monthly timescales and hydrologic conditions are continuously fluctuating generating dual selective pressures for benthic organisms.Our findings lead to a conceptual model describing relationships between trait selection, organismal fitness, and ecosystem functioning for communities experiencing multiple selective pressures . Because the stable environment applies consistent selective pressures, shifts in the strength of homogeneous selection are driven by changes in the oscillating environment. For instance, given a stable environment represented by the black dot in Figure 6A, the strength of homogeneous selection in Figure 6B is influenced by selection imparted by the oscillating environment, denoted as a gradient from blue to red. In this scenario, increased selection from the oscillating environment causes a decrease in homogeneous selection that results in niche diversification and enhanced microbial metabolism .We specifically hypothesize that selection imposed by a stable feature of the environment can favor organisms possessing traits that oppose traits selected for by the oscillating environment (While future work is needed to validate our conceptual model, our research represents a key step forward in spatiotemporal ecological research by assimilating shifts in community composition, assembly processes, and microbial metabolism. We develop this model by repeatedly sampling attached and planktonic microbial communities within an environmental transition zone over a 9-month time period. Our results indicate a rise in specialist autotrophs associated with increased rates of microbial metabolism when the direction of selection imposed by an oscillating hydrologic environment opposes that of stable selective pressures imposed by sediments. Further, we show that assembly processes operate at different temporal scales in planktonic and attached communities and have taxon-specific effects within each community. Our conceptual model can be applied in a range of ecological contexts beyond microbiology-for example, as a framework for understanding relationships between environmental change and competition under the Stress-Dominance hypothesis in macroecology  and for EG was responsible for analyzing all data and writing with guidance from JS and JF. All other authors contributed substantially to experimental design, data collection, and manuscript revisions.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


The aim of this study was to evaluate how programmed death-ligand-1 (PD-L1) expression is linked to the immunoscore in the context of the tumor microenvironment and to assess the differential prognostic value of PD-L1 expression according to the immunoscore in 153 patients with microsatellite instability-high (MSI-H) advanced gastric cancer (GC).We found that T-PD-L1 (+) and I-PD-L1 (+) were significantly associated with a high immunoscore. The integrated PD-L1 expression of tumor and immune cells was not significantly correlated with the overall survival (OS) of patients. However, a combined survival analysis of PD-L1 expression and immunoscore revealed four distinct subgroups with a statistically significant difference in OS. That is, the PD-L1 (+)/immunoscoreLow group showed the worst and the PD-L1 (+)/immunoscoreHigh group showed the best prognosis. Furthermore, a multivariate analysis revealed that the combined status of PD-L1 expression and immunoscore was an independent and significant prognostic factor for OS in patients with MSI-H GC.The immunoscore was quantified by the number of high-density areas of CD3+ and CD8+ tumor infiltrating lymphocytes both in the tumor regions and compartments , the scores of which range from I0 to I8. By using immunohistochemistry, the expression of PD-L1 was also analyzed in tumor cells (T-PD-L1) and immune cells (I-PD-L1) using four different cut-off values .Our study revealed that PD-L1 expression is associated with the corresponding immunoscore and that the immunoscore can be a relevant marker for the determination of the prognostic role of PD-L1 expression in MSI-H GCs. Gastric cancer (GC) is ranked as the fifth most common malignancy in the world and is the third most common cause of cancer-related death . GC is aProgrammed cell death-ligand 1 (PD-L1) is a 40-kDa type 1 transmembrane protein that is involved in the immunoregulatory system during certain conditions such as autoimmune disease, pregnancy, allograft rejection, and cancer . ActivatMany studies support the concept that TILs have a prognostic value and the “immunoscore” has been demonstrated to be a powerful prognostic indicator. Evidence also indicates that these might be equivalent to the American Joint Committee on Cancer (AJCC)/ Union for International Cancer Control-tumor node metastasis (TNM) staging system in terms of their ability to predict the clinical outcome of patients with malignant tumors –17. PrevIn the current study, we analyzed PD-L1 expression in the context of the tumor microenvironment and assessed 1) how PD-L1 expression is linked to the immunoscore and 2) the differential prognostic value of PD-L1 expression according to the immunoscore.p = 0.059). Although the patients with E-I4 showed the best prognosis, higher scores did not guarantee a better prognosis among patients with E-I0, E-I1, E-I2, and E-I3      or T-IHigh (T-I5 to T-I8) (p = 0.005)   Figure . Regardi) Figure . However) Figure . Althoug) Figure , tumors ) Figure . In mult) Figure , T-I remp = 0.033), less frequent lymphatic invasion (p = 0.002), lower TNM stage (p = 0.030), and a high immunoscore (p = 0.003) compared with T-PD-L1 (−) phenotype (Table p = 0.042), less frequent lymphatic invasion (p = 0.001), less frequent perineural invasion (p = 0.019), less frequent LN metastasis (p = 0.019), lower TNM stage (p = 0.006), and a high immunoscore (p < 0.001) . The frequency of the positive and negative expression of PD-L1 at each cut-off value is shown in Figure  p = 0.00, lower T p = 0.00, lower Tp = 0.639)   . At 5% cut-off value, a similar trend for OS was observed. The expression status of T-PD-L1 and I-PD-L1 could not significantly discriminate the survival outcomes of these patients , although the tendency for a better survival outcome was observed in patients with T-PD-L1 (+) compared to those with T-PD-L1 (−) and in patients with I-PD-L1 (+) compared to those with I-PD-L1 (−) , despite the observation that patients in the T-PD-L1 (+)/I-PD-L1 (+) groups experienced the longest OS compared with the other groups  and T-PD-L1 (−) or between I-PD-L1 (+) and I-PD-L1 (−) . To be m) Figure . However) Figure . In surv) Figure . Notably) Figure  and 3E. s Figure .p = 0.515 for 1% cut-off value; p = 0.242 for 5% cut-off value; p = 0.423 for 10% cut-off value; p = 0.586 for 50% cut-off value)  /T-ILow patients exhibited the worst OS, except for the 10% cut-off value at which PD-L1 (+)/T-IHigh group showed the second best OS. In particular, a distinct difference was noted in the OS between the patients with PD-L1 (+)/T-IHigh and PD-L1 (+)/T-ILow tumors at all cut-off value   /T-ILow tumors   group” while the remainders were classified into the “PD-L1 (−) group”. According to the Kaplan-Meier survival analysis, no significant association was found between PD-L1 expression and OS  Figure  and 4G. ) Figure  and 4H. ) Figure  and 4H. ) Figure , was perp < 0.001), followed by the 5% cut-off value . For I-PD-L1, the level of concordance was similar to that of T-PD-L1, with the highest concordance level at the 1% cut-off value . Representative paired images between these two antibodies are demonstrated in To validate whether E1L3N was appropriate for evaluation of the endogenous PD-L1 expression levels of these tumors, we analyzed the concordance of two different PD-L1 antibodies (E1L3N and 28-8). The frequency of the positive and negative expression of PD-L1 (28-8) at each cut-off value is shown in Figure et al. which demonstrated that the difference in survival was not significant between patients with MSS/MSI-L CRC with high immune-related gene expression and patients with MSI-H CRC [Many recent studies have revealed that the presence of inflammatory cells within the tumor microenvironment is associated with an improved clinical outcome and increased response to chemotherapy and radiotherapy . The corSI-H CRC . They inSI-H CRC , 27.The correlation between PD-L1 expression and microsatellite instability has been demonstrated in several studies. Recently, a phase II clinical trial showed that anti-PD-1/PD-L1 therapy can be beneficial to patients who have advanced stage MSI-H colorectal cancer (CRC) . The corn = 33, 23.1% for 5% cut-off value) as well as in infiltrating immune cells , and a substantial number of tumors showed co-expression of PD-L1 in both tumor cells and immune cells . Although the biological meaning of these differential expression patterns is elusive, they are likely governed by combined innate (intrinsic) and adaptive cellular (extrinsic) factors within the tumor microenvironment [et al. corresponded with our results in that MSI-H GCs exhibited expression of high IFN-γ response genes compared with genetically stable GCs according to a gene set enrichment analysis [et al. [et al.'s group, as their study might have contained MSS/MSI-L GCs in excess of MSI-H GCs. The discrepancy also reflects a fundamental difference in the expression mechanisms of PD-L1 on tumor cells between MSS/MSI-L and MSI-H GCs. In addition, a more significant correlation was noted between I-PD-L1 expression and a high immunoscore. These findings seem plausible considering that CD3+ TILs, CD8+ TILs, and PD-L1-expressing immune cells are inherent components of the adaptive immune system, which are robustly activated in MSI-H GCs.In our study, PD-L1 expression was observed in tumor cells /T-IHigh group showed the best prognosis, at 1%, 5% except for 10% cut-off at which PD-L1 (−)/T-IHigh group showed the best prognosis. Based on previous research, PD-L1 (+)/T-IHigh refers to the group in which the adaptive immune system is primarily activated via the PD-l/PD-L1 signaling pathway, whereas the PD-L1 (+)/T-ILow group is considered to be associated with intrinsic induction of PD-L1 by an oncogenic pathway regardless of IFN-γ expression [High subgroup has the most favorable prognosis, contrary to our expectations, might be because of a compensatory up-regulation of PD-L1 mediated by an ongoing overloaded antitumor immune response, rather than because of tumor immune evasion itself [Low), is most harmful to patients with MSI-H GC. The mechanism by which PD-L1 expression through the intrinsic pathway is associated with the most aggressive behavior has not been clearly elucidated. In addition, the efficiency of anti-PD-1/PD-L1 therapy for patients with tumors driven by the intrinsic pathway is less clear compared to those induced by the adaptive pathway. Although constitutive expression of PD-L1 in tumors is considered as the mechanism that is less likely to be responsive to anti-PD-1/PD-L1 therapy despite their strong and diffuse PD-L1 expression pattern [To date, there has been no standardized scoring system for evaluation of PD-L1 expression in any tumor type, including GCs. A 5% cut-off value was widely accepted because this level was presumed reproducible with no inherent variability in the assay process . Howeverpression . The rean itself , 39. Thi pattern , limited pattern . Using lp value < 0.001) and I-PD-L1 . These results were in line with some previous studies. Schats et al. demonstrated that the 1% cut-off value showed a higher concordance rate than the 5% cut-off value in comparative analysis between E1L3N and SP142 antibodies in malignant melanoma [et al., in their study, demonstrated that E1L3N and 28-8 were highly concordant with each other in triple negative breast cancer and the 1% cut-off value had a higher kappa value than the 5% cut-off value, although the highest kappa value was observed for the 50% cut-off value [At this time, companion (pembrolizumab) or complementary diagnostics (nivolumab and atezolizumab) using different antibodies  coupled with correspondent assay platforms are FDA-approved for selection of patients who are treatable with anti-PD-1/PD-L1 antibodies . Althougmelanoma . Sun et ff value . Based off value . Howeverff value . The intet al. reported that, in patients with stage III malignant melanoma, the most predictive marker of clinical response to PD-1 blockade was the density of CD8+ TILs in the TC and IF and was not PD-1 or PD-L1 expression itself [The correlation between the high density of TILs and a favorable prognosis has been demonstrated in various tissues and tumor types, including colorectal , breast n itself . Considen itself ).In conclusion, our study revealed that the PD-L1 expression is primarily associated with an adaptive immune resistance mechanism and that the immunoscore can be a relevant marker in the determination of the prognostic role of PD-L1 expression in MSI-H GCs.In all, 153 formalin-fixed paraffin-embedded GC tissues were collected from the pathology archives of Seoul National University Hospital, Seoul, Korea. All tumor samples were derived from the patients who underwent radical surgical resection with extended lymph node (LN) dissection at our institution between 2004 and 2009. At our institution, MSI status was routinely evaluated in resected GC specimens by the molecular pathology laboratory. Among 1706 patients, 153 (8.7%) cases of advanced GC with MSI-H were identified. Clinicopathological information, including age, sex, tumor site, tumor differentiation, tumor depth, LN metastasis (LNM), presence of lymphatic, vascular and perineural invasion, TNM stage, Lauren classification, Ming classification, date of surgery, date of last follow-up, and date of recurrence or death, were collected retrospectively from the electronic medical records. We evaluated the OS, which is defined as the date of GC surgery to the date of death or the last clinical follow-up before December 31, 2015. The average OS time, which was 2552 days, ranged from 35 to 4241 days. In this study, death occurred in 46 (30.1%) cases out of all patients with MSI-H advanced GC. Histologic grading and tumor staging were based on the seventh edition of the AJCC Staging Manual. This study was approved by the institutional review board of Seoul National University Hospital.BAT25, BAT26, D2S123, D5S346, and D17S250. We defined tumors as MSI-H when two or more markers showed instability and tumors as MSI-L when one marker showed instability; finally, we defined tumors as MSS when none of the markers was unstable.The methods used for the MSI analysis have been previously described . BrieflyTissue microarrays (TMAs) were constructed as previously described . Tissue CD3, CD8, and two different PD-L1 clones (E1L3N and 28-8) were analyzed by immunohistochemical staining. In brief, the 4-μm thick, formalin-fixed, paraffin-embedded tissue sections were dewaxed in xylene and rehydrated using graded alcohol. Immunohistochemical staining for each marker was conducted using the BenchMark XT immunostainer  under the following conditions: CD3 , CD8 , PD-L1 , and PD-L1 . The immunohistochemical staining protocol for each antibody is summarized in Low  or T-IHigh .All immunostained TMA slides were scanned under high-power magnification (200×) using a scanner system . The Nuclear V9 algorithm of Image-Scope software (Aperio Technology) was used to evaluate the densities of CD3+ or CD8+ lymphocytes as numbers of CD3+ or CD8+ lymphocytes divided by the total area of selected foci (cells per square millimeter) . One corPD-L1 expression was assessed separately in tumor cells (T-PD-L1) and stromal immune cells (I-PD-L1) using the E1L3N clone. The intensity of membranous-to-cytoplasmic staining in tumor cells and stromal immune cells was initially scored on a scale of 0 to 3, as follows: negative (0), weak (1+), moderate (2+), and strong (3+). PD-L1 expression was determined to be positive when moderate (2+) and strong (3+) intensities were observed, and the extent of its expression was evaluated based on the proportion of positively stained tumor and immune cells. PD-L1 expression of tumor and immune cells was assessed by applying four cut-off values - 1%, 5%, 10%, and 50%. And it was defined as positive (PD-L1 (+)) when the number of cells positively stained for PD-L1 surpass that cut-off values. A highest score was recorded if three tissue cores from the same tumor exhibited different PD-L1 expression status. Representative images of PD-L1, CD3, and CD8 immunostaining with matched hematoxylin and eosin-stained samples are shown in Figure n value < 10). A Kaplan-Meier log rank test was performed to compare the OS between the two subgroups. A multivariate survival Cox proportional hazards regression model was used to adjust variables that were statistically significant for the prognosis in the univariate analysis. The concordance between the two different PD-L1 antibodies (E1L3N and 28-8) was evaluated using Kappa-Cohen method. Statistical analysis was performed using IBM SPSS version 20.0 software . All P values were two-sided, and p < 0.05 was considered statistically significant.Categorical variables were compared using Pearson's chi-square test or Fisher's exact test (for cases with an


We present plasmonic devices, consisting of periodic arrays of graphene nanoribbons (GNRs) and a graphene sheet waveguide, to achieve controllable plasmon-induced transparency (PIT) by numerical simulation. We analyze the bright and dark elements of the GNRs and graphene-sheet waveguide structure. Results show that applying the gate voltage can electrically tune the PIT spectrum. Adjusting the coupling distance and widths of GNRs directly results in a shift of transmission dips. In addition, increased angle of incidence causes the transmission to split into multiple PIT peaks. We also demonstrate that PIT devices based on graphene plasmonics may have promising applications as plasmonic sensors in nanophotonics.  The electromagnetically induced transparency (EIT) effect observed in atomic systems produces a sharp and transparent window in a wide range of absorption spectra range. It results from a considerable hindrance between coherent optical transitions ,2,3,4. IGraphene is a monolayer of carbon atoms with a honeycomb-like lattice that is gaining considerable attention because of its excellent electrical and photonic properties, such as strong optical nonlinearity , ultrahiIn this study, the coupling-induced transparency with narrow waveband can be exhibited by a properly designed system based on graphene-contained plasmonic structures by numerical simulation. Compared to previous works, we show the multiple PIT phenomena with our novel asymmetrical graphene nanoribbon structures and integrally analyze the influence factors of the PIT phenomena. First, the bright and dark elements of the GNRs and graphene sheet waveguide structure are analyzed. We observe the PIT phenomenon by presenting the structure devices composed of periodic arrays of GNRs and a graphene sheet. The shift of the transmission notch occurs because of the changes of the coupling distance and the widths of GNRs. The Fermi energy strongly influences the frequencies of plasmons in graphene. In addition, multiple PIT peaks can be obtained by changing the angle of incidence. g is sandwiched by the GNRs and graphene sheet layers.  A transverse-magnetic (TM) polarization  monochromatic plane wave comes normally from the upper surface of the structure. p is the cycle of the unit element; w1 and w2 are the widths of the adjacent GNRs, and d is the distance. The designed device is easy to fabricate. The chemical vapour deposition (CVD) method can be utilized to grow multiple layers of graphene on the silica layer and to manufacture the silicon-based graphene structure waveguide. The momentum relaxation time τ, temperature T, incident wavelength λ, and Fermi energy fE determine the surface conductivity of graphene gσ. It follows the equationIn our simulation, the incident light we employed is at the range of the mid-infrared region. The intraband transition contribution predominates in monolayer graphene . With the is the electron charge and the electron relaxation time is τ = FμE = Fev2, in which Fv = c/300 is the Fermi velocity; FE is the Fermi energy, and μ = 10 m2/(V·S) is the direct current mobility of graphene [t0 = 1 nm is the thickness of the graphene layers. The SPPs modes, ranging from THz to the visible frequencies, could be spread over the graphene layer. The dispersion relation of the SPP modes at subwavelength scale is given by [gk is the in-plane wave vector in graphene, k0 is the wave vector in vacuum. ε1 and ε2 are the dielectric constants of the top and bottom surface materials of the graphene sheet, respectively. The graphene Fermi level can be tuned by adjusting the gate voltage, which can be calculated according to Equation (2).Here, graphene ,34,35. Tgiven by (4)kg=k0w1 and w2. The dark modes are simply graphene sheet layers. The separation between the GNRs and graphene sheet layers is g. To realize the PIT phenomenon, the basic unit of the structure can be formed by combining the bright element with the dark element.To demonstrate the graphene-based PIT phenomenon, we start with nanostructures with different radiation performances, as is shown in p = 1200 nm. To study the PIT phenomenon in graphene nanostructures, we set up a graphene PIT structure, which is constructed by combining the coupled bright element with the dark element as the basic unit. The units array periodically with a period π occurs between the channels of the direct and indirect excitations [Obviously, a PIT-like transparent window can be observed from the transmission spectrum of the graphene PIT structure. The two notches’ wavelengths are at 9.21 and 9.42 μm, and the peak is positioned at 9.36 μm. This phenomenon is essentially analogous to the EIT spectrum in atomic systems. At the PIT peak, almost no reflection can be observed. At the right transmission dip, the reflection is obviously low, revealing a strong absorption. In addition, to make the disturbance between the dark and bright modes visible, we exhibit the |E| distributions at these concerned wavelengths. The dipole mode can be effectively excited at the transparent peak by the incident light of 9.36 μm, while the excitation of the quadruple mode is prevented in the dark element. However, the coupling between the bright and dark modes can indirectly inspire the dark mode. The dark mode will then couple to the bright mode again. It is noticed that a phase difference of itations ,37. TherFE are plotted in FE changes from 0.4 to 0.8 eV. Therefore, the PIT spectrum can be shifted over a rather wide range of wavelengths by tuning the Fermi energy.The optical performances of graphene can be considerably improved by doping or gating as plasmons in graphene are greatly dependent on the Fermi energy. By adjusting the Fermi energy, the electron density in graphene can be changed, resulting in a change in the resonance frequencies of graphene plasmonic nanostructures. As a result, the PIT spectrum of the graphene PIT structure can be dynamically controlled over a wide range of wavelengths. Such tunability can be hard to realize in atomic EIT or other PIT systems. The transmission spectra for structure I at different p = 1200 nm, w1 = 208 nm, g = 350 nm, and FE = 0.6 eV. As the width w2 is increased, dip I keeps red-shifting, whereas the position of dip II remains almost invariant. When w2 = 200 nm, double PIT peaks can be achieved. Dip I is integrated into dip II as w2 increased from 200 to 208 nm. Only one PIT peak can then be observed. When w2 > 208 nm, dip IV is continuously red-shifting and ultimately the only PIT peak disappears. Furthermore, yE consistent with the transmission dips under w2 = 200 nm. The super resonance modes (symmetric and antisymmetric modes) can be found at the transmission dips by the incident light of λ = 8.80, 9.15, and 9.45 μm. At that resonance wavelength, the simultaneous excitement of the two super resonances leads to near-field curtailment in the bright element and enhancement in the dark mode. The two resonant structures are extremely excited and the PIT can be realized when those two resonance modes are at the same wavelength.The transmission spectra of structure I are shown in g values between the graphene sheet and the GNRs are plotted in g shrinks, dip II splits into two notches, and dip III keeps red-shifting while g < 600 nm. yE corresponding to the transmission dips under g = 340 nm. The super resonance modes (symmetric and antisymmetric modes) at λ = 8.80, 9.15, and 9.45 μm related to the transmission dips can also be found. g = 340 nm keeps invariable. With the angle of incidence increasing, dip III splits into two notches, with one blue-shifted and the other red-shifted and triple PIT peaks can be achieved.The transmission spectra of structure I at different gap g. The first and the second layers of GNRs are separated by the gap g2. In one period, the two graphene nanoribbons are on the same symmetry axis. Their widths are defined as w1 and w2, respectively. A TM polarization  monochromatic plane wave comes normally from the upper surface of structure II. The transmission spectra of the structure are shown in p = 600 nm, w1 = 208 nm, and FE = 0.6 eV. As the width w2 increased, we can see a gradual red-shift of dip I. Especially, while w2 = 218 nm, double PIT peaks can be obtained.Furthermore, the second schematic of the structure employed in our design is shown in g2 values are plotted in g2 shrinks. When g2 = 330 nm, double PIT peaks can be observed. While g = 330 nm keeps invariable, the angular-dependent transmission spectra of structure II are plotted in In addition, the transmission spectra of structure II that we calculated at different gap We studied the radiative properties of graphene nanostructures by numerical simulations. Periodic graphene strips can serve as the bright element; a graphene sheet parallel to the periodic graphene strips can serve as the dark element. A graphene PIT structure can be constructed by combining the bright element with the dark element; it shows a PIT spectrum similar to the atomic EIT. Significantly, changing the gate voltage can directly tune the PIT spectrum. The position of the transmission notch greatly depends on the changes of the coupling distance and the widths of GNRs. With the appropriate distance and widths, double PIT peaks can be obtained. In addition, multiple PIT peaks can be achieved by changing the angle of incidence. Our study indicates that the demonstrated PIT devices based on graphene plasmonics may pave a new way for the development of plasmonic sensors in nanophotonics applications.


Intercalation of hydrogen is important for understanding the decoupling of graphene from SiC(0001) substrate. Employing first-principles calculations, we have systematically studied the decoupling of graphene from SiC surface by H atoms intercalation from graphene boundary. It is found the passivation of H atoms on both graphene edge and SiC substrate is the key factor of the decoupling process. Passivation of graphene edge can weaken the interaction between graphene boundary and the substrate, which reduced the energy barrier significantly for H diffusion into the graphene-SiC interface. As more and more H atoms diffuse into the interface and saturate the Si dangling bonds around the boundary, graphene will detach from substrate. Furthermore, the energy barriers in these processes are relatively low, indicating that these processes can occur under the experimental temperature. The exploitation of graphene-based devices crucially depends on the large-scale graphene production. Recently, homogeneous, large area and high quality monolayer graphene was successfully synthesized by epitaxial growth on the wide band gap semiconductor SiC(0001) surface5. This way has been widely regarded as the most promising ways for producing graphene wafers for electronic applications because SiC electronic devices are able to work at high voltages, high temperatures and high switching frequencies6 and are more convenient to integrate into existing device technology8.Graphene has attracted intensive research interest due to the potential applications in nanoelectronics, gas detection, and energy storage10. The covalently bonded between SiC and graphene seriously affects the properties of graphene. No linear dispersion of π bands typical for free standing graphene is observed for this buffer layer4. The influence of the covalent bonding in the interface layer is also one of the primary suspects for the strongly reduced mobility in epitaxial graphene on SiC(0001) as compared to exfoliated graphene flakes, probably due to the introduction of scattering centers into the graphene layer12. Therefore, it is of crucial importance to remove the interface bonding and create quasi-freestanding layers for the practical application of epitaxial graphene on SiC(0001).However, the first carbon layer is connected to the SiC substrate by covalent bonds with the 13, atom intercalation is widely studied to detach the BL from the SiC. Riedl et al.14 firstly demonstrated that the bonds between the BL and the SiC substrate can be eliminated by hydrogen intercalation, and the BL is detached from the SiC substrate and displays the linear π bands as quasi-free-standing graphene monolayer. Similar results were obtained by Virojanadara et al. they exposed graphene-SiC samples to atomic hydrogen fluxes at temperatures higher than 450 °C15. Other experimental groups have also reported decoupling BL by intercalation of other elements such as fluorine16, oxygen19, germanium20, gold21 and so on.Many attempts have been made aiming at the detachment of the BL from the SiC substrate. Except for rapid-cooling technique2 and H diffusion through the BL are very high , and there are also no experimental evidences for hydrogen penetration through graphene25. These results indicate that hydrogen is difficult to directly pass through the graphene to decoupling the BL. Therefore, it is possible that hydrogen intercalation occurs at grain boundaries or defects on the surface27. A. Markevich et al. have modelled diffusion of hydrogen through defective graphene layers using the NEB method27. Their results showed that hydrogen atoms (molecules) diffusion through the hollow defects in graphene layer by overcoming a low energy barrier. It is further found that hydrogen can easily migrate along the graphene-SiC interface, break covalent bonds between the BL and the substrate, and passivate the SiC surface. However, H intercalation from the boundary into the graphene-SiC interface is still poorly understood. In this work, we have systemically investigated the process of H intercalation through the graphene zigzag edge and found that the passivation of H on both graphene edge and SiC surface plays crucial role in the decoupling process.To understand the mechanisms of atoms intercalation into graphene-SiC interface, many theoretical studies have been performed. Based on first-principle calculations, it is found that the energy barrier for H29, as shown in Fig. 33 and theoretical35 studies.To explore the BL decoupling from SiC, a (5 × 5) graphene was placed on the (4 × 4) 6H-SiC (0001) surface with about 1% mismatch. The vacuum separation (>2.0 nm) was used to be to avoid spurious interactions due to the periodic boundary condition. After relaxation, graphene is rippled and covalently bound to the substrate, as shown in Fig. 2 dissociation and H diffusion on SiC have been studied. It is found the hydrogen molecule spontaneously decomposes into two H atoms after adsorbing on the SiC surface. The migration path and energy barrier is shown in Fig. Ebar is the reaction barrier and kB is the Boltzmann constant26 and the pre-exponential factor 1012 S−1 can be viewed as the lower limit of the KT/h, the estimated temperature is about 700 K, which is in reasonable agreement with the experimental value15. Thus the hydrogen atoms can be spread on the SiC surface at the certain temperature.Firstly, HAs shown in Fig. n is the number of H passivation on graphene ribbon edge. For one H atom absorption on the SiC substrate, the absorption energy is obtained by In addition, the absorption energy are calculated to investigate the stability of hydrogen passivation on SiC and graphene edge. For H passivation on graphene edge, as shown in Fig. Diffusion of H atoms into the SiC-graphene interface is the critical step for the decoupling process. To understand this process, we have considered three different diffusion paths for H migration into SiC-graphene interface. Firstly, the graphene edge is bare and H atom directly penetrates into the interface from the right side of Si-C bonds, and the reaction barrier is very high (3.71 eV) with an energy raise of 0.23 eV, as show in the Fig. After H passivation on graphene edge, graphene is still bonded with SiC substrate by two Si-C bonds. To further understand the decoupling of graphene and SiC substrate, we investigate the decoupling by increasing the number of H diffusion into the graphene-SiC interface, as shown in Fig. 36. It is found that the energy barrier is very small (~0.06 eV) and the total energy of final state is 0.85 eV lower than the initial state, thus this process would happen very easily in experiments. From the ELF of the transition state in Fig. 37.Based on the system SiC + 6 H/HG), we have calculated the reaction path and the energy barrier for graphene completely decoupling from SiC substrate, as shown in Fig.  H/HG, we2 molecular decompose into two H atoms on the SiC surface and H atoms diffuse on the substrate. As C atoms on the edge are active, H atoms will saturate on graphene edge, which will weaken the interaction between graphene and the substrate. Finally, graphene will detach from SiC substrate as more and more H atoms saturate the Si dangling bond around the boundary. It is found that the H passivation on both graphene edge and SiC substrate is the key factor to decoupling graphene from the substrate. Furthermore, the energy barriers in these processes are relatively low, indicating that these processes can occur under the experimental temperature.In summary, we have systematically studied the decoupling of graphene from SiC surface by H atoms intercalation from graphene boundary. Our results suggest that the decoupling process can be divided into the following steps. Firstly, H38 with the projector-augmented wave39 (PAW) approach to represent the electron–ion interaction. The exchange and correlation functional was treated by the generalized gradient approximation of Perdew–Burke–Ernzerhof (PBE)40. The energy cutoff of the plane-wave expansion of the basis functions was set to be 400 eV and only Gamma point was used for the Brillouin zone integration. All atomic positions were fully relaxed using the conjugate gradient algorithm until all interatomic forces were smaller than 0.1 eV/nm. The climbing image nudged elastic band (CI-NEB)42 method was employed to determine the transition states and activation barriers.Density functional theory (DFT) calculations were performed using the Vienna Ab Initio Simulation Package (VASP)


P = 0.040) in the miR-197high subgroup but not the miR-197low subgroup. These findings may have clinicopathologic implications for the miR-197/PD-L1 axis and TILs in OSCC.Immune escape of a tumor from tumor-infiltrating lymphocytes (TILs) is induced by PD-L1, which is suppressed by miR-197. We investigated the clinicopathologic implications of the miR-197/PD-L1 axis and its effects on TILs and the clinicopathologic features of oral squamous cell carcinoma (OSCC). We used RT-PCR and immunohistochemistry in 68 OSCC patients to analyze the correlations between tumoral expression of miR-197 and PD-L1 and the degree of tumoral invasion by TILs . PD-L1 levels correlated inversely with miR-197 but correlated positively with TILs. The aggressive features of OSCC, including high stage, angiolymphatic invasion, perineural invasion, and death, were associated with TIL depletion. High T stage (T4) tumors also had low PD-L1 but had high miR-197 expression. In a univariate survival analysis of the full cohort, high miR-197 was associated with poor overall survival, whereas high PD-L1 expression (2+) associated with good overall survival. In a multivariate analysis stratified based on miR-197 (median), high PD-L1 expression (2+) was an independent favorable prognostic factor for overall survival ( Oral cancer accounts for 1% to 5% of human malignancies, and its occurrence has increased for more than a decade . OSCC ocProgrammed cell death ligand-1 (PD-L1) is a cell-surface glycoprotein that induces T cell anergy and apoptosis by activating the PD-1 receptors on T lymphocytes . NormallMicroRNAs (miRNAs) are single-stranded, non-coding short RNAs consisting of 20 to 22 nucleotides that inhibit the translation of genes by disrupting specific messenger RNAs. In recent studies, the expression profiles of miRNAs in OSCC were examined and some miRNAs were found to correlate with tumorigenesis and cancer progression , 10. MiRIn addition to miR-197, PD-L1 is regulated by other microRNAs, including miR-138-5p, miR-513, miR-570, miR-34a, and miR-200, the functions of which have not yet been elucidated in OSCC -18. ConsIn the present study, we contribute to a better understanding of the clinicopathologic implication of the miR-197/PD-L1 axis and TILs in OSCC. We analyzed the expression of miR-197 and PD-L1 and analyzed the number of recruited TILs  and the correlations with various clinicopathologic features and prognosis in OSCC patients.The various clinicopathologic features of OSCC patients are summarized in Table low (<median) and miR-197high (>median) subgroups or between low PD-L1 (0/1+) and high PD-L1 (2+) subgroups (P = 0.049), and PD-1+ TILs were increased in older patients (P = 0.018). The parameters of tumor aggressiveness were associated with depletion of various TILs. Decreased PD-1+, FoxP3+, and CD20+ TILs were associated with higher AJCC stages (3-4) . Specifically, high T stage (T3-T4) was correlated with low numbers of CD3+, CD8+, PD-1+, FoxP3+, and CD20+ TILs , and high N stage (N1-N2) disease had fewer PD-1+ TILs in the primary tumor (P = 0.020). In addition, the tumors with angiolymphatic invasion had fewer CD20+ TILs (P = 0.006), and perineural invasion was associated with fewer PD-1+ and FoxP3+ TILs (P = 0.022 and P = 0.017). CD4+ TIL numbers were lower in patients who died (P = 0.035). When T stage was divided into T1-T3 versus T4, T4 disease had a higher miR-197 level . Because PD-L1 is associated with proliferation and function of TILs, we comparatively analyzed the relations among CD3+, CD4+, CD8+, PD-1+, FoxP3+, CD20+ TILs, and PD-L1 expression , but not with PD-1+ TILs or CD20+ TILs (P > 0.05). When the relation among various TILs was analyzed, frequent positive correlations were observed among CD3+, CD4+, CD8+, FoxP3+, and CD20+ TILs.Based on research that suggests miR-197 indirectly suppresses PD-L1 expression , we analP < 0.001) and angiolymphatic invasion (P = 0.001) were predictors of poor OS in OSCC patients. Similarly, T stage , angiolymphatic invasion (P = 0.001), and N stage (P = 0.007) were associated with poor DFS. High expression of miR-197 was weakly associated with poor OS (P = 0.033), and high PD-L1 expression in tumor cells (2+) predicted better OS , and DFS (P = 0.001 and P = 0.003), but miR-197 or PD-L1 was not associated with OS or DFS.The association between conventional clinicopathologic factors and prognosis in OSCC patients was evaluated Table . Univarihigh subgroup , prognostic factors for OS in univariate analysis, namely, PD-L1, T stage (T3-T4), and angiolymphatic invasion, were incorporated into the multivariate analysis, resulting in PD-L1 and angiolymphatic invasion as independent prognostic factors for OS (P = 0.040 and P = 0.035), whereas angiolymphatic invasion was the only prognostic factor for DFS (P = 0.009). In contrast, multivariate analysis of the miR-197low subgroup  showed that T stage (T3-T4) and angiolymphatic invasion were independently associated with OS (P = 0.005 and P = 0.040), and T stage (T3-T4) was an independent prognostic factor for DFS (P = 0.001), with no prognostic significance of PD-L1 for OS or DFS in the miR-197low subgroup. Therefore, high PD-L1 expression (2+) was a favorable prognostic factor for OS only in the miR-197high subgroup, suggesting that prognostic implication of PD-L1 is influenced by the miR-197 level.Because our results suggested that miR-197 inhibited PD-L1 expression in OSCC, we investigated correlations of PD-L1 with survival according to miR-197 level Table . In the P = 0.040) in the miR-197high subgroup, but not in the miR-197low subgroup.In the tumor microenvironment, the PD-L1/PD-1 axis has become the therapeutic locus in various cancers. In this study, we focused on the clinicopathologic implication of the miR-197/PD-L1 axis and the profiles of recruited TILs in OSCC. We observed the inverse correlation between miR-197 and PD-L1, and the positive correlation between PD-L1 and TILS, suggesting an active network of miR-197/PD-L1/TILs. Aggressive clinicopathologic features were associated with depleted TILs, and high T stage (T4) disease was associated with low PD-L1 but high miR-197 expression. Moreover, high PD-L1 expression (2+) was an independent favorable prognostic factor for overall survival (OS)  produced by TILs, resulting in JAK/STAT activation in tumor cells, and the intrinsic pathway is activated by PI3K/AKT/mTOR signaling , 25. In high and miR-197low subsets, reflecting the mechanism of PD-L1 expression. PD-L1 had prognostic significance only in the miR-197high subset, although it is not yet clear how high expression of miR-197 influences prognostic significance of PD-L1 in addition to expression of PD-L1. It is possible that OSCC with high miR-197 expression at a sufficient level might have an inhibitory effect on the signal from the extrinsic pathway induced by STAT3, while sparing the intrinsic signal. This skewing effect of the PD-L1 pathway with co-activated Akt/mTOR-related downstream signals could influence the biology of OSCC in a complex manner, which remains to be clarified further.We divided our OSCC cohort into miR-197Attempts have been made to identify the relation between PD-L1 expression and the effectiveness of immune-induced host defense against the tumor measured by TILs and prognosis of patients -28. In tIn the present study of OSCC, high miR-197 was associated with higher tumor stage (T4) and poor prognosis, whereas high PD-L1 expression in tumors was associated with good prognosis. Although TILs did not directly correlate with survival of OSCC patients, low numbers of various TILs were associated with aggressive features of tumors, including high stage, angiolymphatic invasion, and perineural invasion. The phase of anti-tumor immune reaction might be different between early tumors and full-blown tumors because of different exposure time and amount of tumor antigens, and the mechanism of associations between miR-197/PD-L1/TILs and stages of disease must be investigated further. Considering that many clinicopathologic factors and outcomes can influence or be influenced by anti-tumor immune reactions , comprehStudies related to the expression of PD-L1 and its prognostic effects in different cancer types show discordant results -40. Varihigh subgroup. Our clinicopathologic analysis of miR-197/PD-L1 and TILs could contribute to understanding of clinical significance of anti-tumor immune reactions in OSCC.This study showed inverse correlation and prognostic effects between miR-197 and PD-L1 expression in OSCC. In addition, we observed that PD-L1 expression on IHC is associated with increased TILs and favorable prognosis in miR-197A total of 68 OSCC patients who underwent curative surgery between 2003 and 2011 at Seoul National University Bundang Hospital were enrolled. We reviewed hematoxylin-eosin (H&E), immunohistochemically stained slides, pathology reports, and medical records to establish the clinicopathologic features of the tumors. TNM staging was determined according to the seventh edition of the American Joint Committee on Cancer guidelines . Tissue -ΔΔCt, where ΔCt = Ct (miR-197) – Ct (U6) and ΔΔCt = ΔCt(tumor) – ΔCt .Total RNA was extracted from 10-μm-thick FFPE tissue sections by use of a RecoverAll Total Nucleic Acid Isolation Kit for FFPE samples , and stored at −80° C until the time of use after measuring the concentration with a NanoDrop 2000 spectrophotometer . To measure the relative expression level of hsa-miR-197 , reverse transcription and real-time polymerase chain reaction were conducted by use of 10 ng of total RNA, Universal PCR Master Mix and a TaqMan microRNA Reverse Transcription kit  with U6 snRNA as an internal reference gene and reactive tonsil tissue as a normal control, as previously described . The relImmunohistochemistry (IHC) staining was applied to TMA sections (4 μm) by use of the Ventana Benchmark XT automated staining system . The following primary antibodies were used: polyclonal rabbit anti-human PD-L1 , monoclonal rabbit anti-human PD-1 , monoclonal rabbit anti-human CD4 , monoclonal mouse anti-human CD8 , mouse monoclonal anti-human FoxP3 , rabbit monoclonal anti-human CD3 , mouse monoclonal anti-human CD20 . Chorionic villi of human placenta were used as positive control, and human skin tissue was used as negative control. In this setting, we adjusted the staining condition for human oral cancer tissues. Immunostaining was interpreted by two pathologists (H.A. and J.H.P.). PD-L1 was stained in cytoplasm or cell membrane of tumor cells or both and graded as 0, 1+ and 2+, according to the intensity of PD-L1.All immunostained slides were blindly evaluated by two experienced pathologists (H.A. and J.H.P.). PD-L1 IHC was defined as membranous or by cytoplasmic positivity and scored as follows: 0 indicates no staining or staining in <10% of the tumor cells, 1+ indicates staining in ≥10% of the tumor cells with weak positivity, and 2+ indicates moderate to strong positivity, which was modified from several previous studies -48. The t-test, Pearson’s correlation test, and Spearman’s rho test were used to examine the relations among expression of miR-197, PD-L1, number of TILs, and clinicopathologic variables. Survival analysis was performed by use of the Cox regression hazard model. For the multivariate survival analysis, clinicopathologic variables with significant P-values (<0.05) in univariate analysis were entered into the multivariate Cox model, and P-values of <0.05 were considered significant. R packages (Version 3.1.2) (http://www.r-project.org) were used in the graphical dot-plot analysis [Statistical analysis was done mainly by SPSS Statistic Version 21.0 software package . Chi-square tests, Student’s analysis -51.


In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on. A number of methods, such as hydrothermal and chemical reduction, electrochemical synthesis, template assisted assembly, and chemical vapor deposition have recently been developed to fabricate highly porous nanomaterials-based cellular monoliths2D macrosc45678910111213141516171819202122232425262728e.g. buckling) of graphene adhered on a biaxially pre-stretched polymer substrate, graphene films can be crumpled with improved hydrophobicity and tunable transparency as well as potential in artificial muscles due to the stretchability3637Recently, utilizing the microstructural topology modulation to optimize the functional properties has been developed in flexible and stretchable electrode systems333435363734Inspired by the ideas of introducing buckled structures to enhance both functional performance and flexibility, here we report a novel strategy for the low-cost, scalable fabrication of a new class of 3D multifunctional polymer-based nanomaterial foams based on a triaxially post-buckling microstructure design. The multifunctional foams are first prepared through self-assembly of individual graphene sheets on a 3D commercial polyurethane (PU) skeleton, and then triaxially compressed to introduce microstructural buckles by a simple top-down processing. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams with NPR as stretchable, flexible smart materials in a variety of applications. More importantly, the buckled structure proposed in this work also offers universal, facile way to design a new class of 3D porous template/nanomaterial monolith, which combine ideal properties for potential applications in 3D flexible electronics, stretchable functional materials. Finally, we also applied such post-buckling strategy into fabrication of polymer-based silver nanowires foams, which showed NPR behavior and demonstrated unusual crack resistance as stretchable conductors.Experimental Section for details)2567101518Experimental Section for details). Note that such triaxial compression treatment in our system is completely different with fracture design reported in Ref. e.g. stretchibility). Our triaxially processed foams  were compressed (~33%) in all 3 orthogonal directions of parent PG foams cuboid. The cross-sectional view of as-prepared foams is investigated by scanning electron microscopy (SEM). As shown in 256710256710−1 and 1350 cm−1). Close examination near the edge of a cracked microfiber further reveals the layered structures of the graphene “skin” 34810111217182224283940414243444546As initially mentioned, the bulk physical properties of this 3D PG foam would be affected by the presence of graphene, as well as by the buckling structural geometry of microfibers. The obtained diverse functionality in such multicomponent foams via incorporation of graphene would definitely be tailored by the buckling structure in our systems. Here we present two examples to confirm such effect of buckled structure. First, when the pure PU foam burned in air condition, the pristine polymer frameworks vanish rapidly, whereas the graphene “skin” coated PG foams still remain as an entire framework with apparent structural shrinkage . Compara810Despite of multifunctional performance, many of applications such as flexible supercapacitors, pressure sensors and elastic conductors require that the 3D monoliths possess excellent mechanical performance during deformation. And unlike the functionalities mainly stemmed from the coated nanomaterials, the overall mechanical properties of this 3D porous template/nanomaterial system would be dominated by the cellular structures. As shown in in situ SEM observation in We further explore the influences of buckled structure and its novel NPR behavior on mechanical properties as they are intriguing from an engineering point of view. For example, on the basis of tensile results in e.g. the improved flexibility and stretchability), the buckled structure we designed in A-PG foams would effectively improve their performance as smart materials.To explore the effects of the buckled structure in our A-PG foams on their functional performance, we further undertook electrical characterizations of our sample in response to mechanical deformation. First, the unique buckled structures of A-PG foams give rise to improved electrical conductivity. As expected, the graphene “skin” that modified onto the polymer skeleton confers conductivity upon the whole surface area of the entire micorfibers network, and the buckled structures further increase the contacts or paths between these conductive network as well as decrease the size of the foams. Indeed, the electrical conductivity of A-PG foams is measured to be 0.001 S/m , three t2151Experimental Section for details). Also similar to our testing results of PG and A-PG foams, it is found that as-obtained A-PA foams exhibit prominent improvements in flexibility and stretchability, compared to PA foams. As shown, the PA foams could catastrophically break under less than 30% tensile strain, whereas the A-PA foams with bucked structures showed remarkable tolerance (more than 100%) to tensile deformation. We also integrated LED lights with our samples as simple demonstrations of stretchable conductors in We further tried to apply our compression-induced buckled structure into the 3D porous template/nanomaterial monolith beyond the PU-graphene foams. Here, we chose Ag nanowires as our functional nanomaterials because of their high conductivity and their increasingly uses in the field of electronic conductors. Melamine (PM) foams (or sponges) were chosen as our polymer templates as they are another commercially available templates with the desirable physical properties and thus widely used in recent reports181920212223242526etc. Considering the similarities between these reports and our results in structural geometry of templates as well as in self-assembling process, we suggest that besides basic self-assembly methods, the simple top-down post-compression treatment might be combined, by which buckled topographic microstructures and negative Poisson’s ratio effect could be achieved. Through such structural design not only the potential performance of individual nanomaterials might be more effectively realized in macroscopic architecture , but also many other bulk mechanical properties can be improved as a result of buckled structures such as toughness, flexibility, stretchablity, damage resistance, which are ideal properties for the use of this next generation of cellular solids in potential applications in 3D flexible electronics, stretchable functional materials and biosystem. Additionally, the bucked structure caused NPR effect further makes the 3D nanomaterial monolith of interests because of the novel behaviors they exhibit under deformation. And we expect that the synergies resulting from functions of nanomaterials and NPR effect will be used widely in future applications such as stretchable capacitors or conductors with high flexibility, shock cushion in body armor, more comfortable  sensor with increased sensitivity and measuring range, easy-to-insert-hard-to-extract stoppers for oil/water separators and so on.Recently, extensive works have employed the strategy of incorporation various types of nanomaterails in conventional porous templates to fabricate 3D nanomaterials-based macroscopic monoliths for various novel applications. In addition to aforementioned PU and PM foams, the porous templates also includes Ni foams2O2 solution , followed by centrifugation and careful washing to clean out remnant salt. Colloidal dispersions of individual GO nanosheets in water (3 mg/mL) were prepared with the aid of an ultrasonic cleaner.GO was prepared from purified natural graphite  following our previous method3 nylon vessel. Commercial available PU foams were cut into 30 × 30 × 90 mm3 cuboids and cleaned by ethanol and deionized water (DIW) with squeezing manually, followed by drying at 80 °C for 5 hours. The PU foams were immersed into the mixture by squeezing in an ultrasonic cleaner and then the vessel was sealed and placed in an 90 °C oven for the reduction of GO sheets. After 12-hour reduction reaction, a gel-like product was taken out from the vessel. After cleaning by adequate ethanol and DIW and drying at 80 °C to obtain the polymer based-graphene (PG) foams. The density of the resulting foams is about 15 mg/mL with 2 wt% graphene. The PG foams with 2–7 wt% graphene could be obtained through changing the concentration of graphene oxide solution from 1 mg/mL to 3 mg/mL. Samples with 2 wt% graphene were used in most of characterization and only electrical-performance-related characterizations employed the samples with 7 wt% graphene.In a typical process, 100 mL graphene oxide solution  was added by 300 μL hydrazine hydrate (80%) and stirred for 2 min at room temperature and then the mixture was poured into a 32 × 32 × 100 mm3) (A Teflon mould with void (inner dimensions 20 × 20 × 60 mm3)  was empl3 nylon vessel. Commercial available melamine (PM) foams were cut into 45 × 20 × 20 mm3 cuboids and cleaned by ethanol and deionized water (DIW) with squeezing manually, followed by drying at 80 °C for 5 hours. The PM foams were immersed into the AgNWs solution by squeezing in an ultrasonic cleaner and then picked out and transferred into a dry oven at 60 °C oven for 12 hours. After 12-hour, a gray foam was taken out from the oven. Then cleaning by adequate ethanol and DIW and drying at 60 °C to obtain the polymer based-AgNWs (PA) foams. A Teflon mould with void (inner dimensions 13 × 13 × 30 mm3) was employed to introduce buckling structure into PM foam. The PM foam was compressed in all three orthogonal directions with 33% strain after stuffing it into the Teflon mould with the aid of tongue depressor and steel plate. After leaving the compressed foam in the oven for 40 min at softening temperature (180 °C) and cooling within moulds (2 hours) to preserve this new configuration, PM foams with negative Poisson’s ratio were prepared (A-PM foams). Then follow the step for preparing PA foams to obtain polymer based-AgNWs (A-PA) foams.The method for the fabrication of PA and A-PA foams was quite similar to that of PG and A-PG foams. 20 mL silver nanowires (AgNWs) solution  was put in an ultrasonic cleaner for 30 min at room temperature and then poured into a 50 × 25 × 25 mmThe microstructure and morphology of the as-prepared foams were characterized by SEM (HITACHI S3400). To give an insight of the microstructure, TEM (FEI Tecnai G2 F20 U-TWIN) observations were conducted directly on as-prepared samples. Raman spectroscope (using the 632.8 nm line of a He-Ne laser) was used to examine the presence of graphene on the microfibers of PG foams. For the electromechanical tests, the top and bottom surfaces of the foams were coated with a uniform layer of silver paste and connected by copper wires. During the compression process, the electrical resistance (Keithley 4200 SCS under a bias of 10 mA) was recorded simultaneously.−1. Cyclic strain controlled loading was used to evaluate the dynamic behavior of the PG and A-PG foams with a ramp rate of 200% min−1. Dynamic compression testing in A dynamic mechanical analyzer  was used to evaluate the mechanical performance of these foams. The dimensions of all tested samples for compression were about 2 cm × 2 cm × 1 cm and 0.2 cm × 0.5 cm × 2 cm for tension. All the samples were applied an initial load of around 0.01 N in order to provide uniform contact. Static compression/tension tests in How to cite this article: Dai, Z. et al. Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson's Ratio. Sci. Rep.6, 32989; doi: 10.1038/srep32989 (2016).