To date, there are no effective therapeutic targeting agents for triple-negative breast cancer (TNBC), and PD-L1 has presented potential as an effective marker of immunotherapeutic agents. The aim of this study was to evaluate the expression of PD-L1 by three different immunohistochemical antibodies in TNBC.Interpretation of all three PD-L1 antibodies showed good concordance among three readers  in both cancer cells and immune cells. Using a tissue microarray (TMA) constructed from 218 cases of TNBC, we performed immunohistochemical staining using three of the most popular commercially used PD-L1 monoclonal antibodies  in cancer cells and immune cells.Using various cut-off values of previous studies , the expression rates in cancer cells were: PD-L1 (E1L3N) , PD-L1 (28-8) , and PD-L1 (SP142) , respectively. At the 5 % cut-off value, the discordance rate among the three antibodies was 6.0–10.6 % and was highest between PD-L1 (SP142) and the other two antibodies. The expression rates in immune cells were PD-L1 (E1L3N) (37.6 %), PD-L1 (28-8) (36.7 %), and PD-L1 (SP142) (19.3 %), and the discordance rate among the three antibodies ranged from 13.8 to 24.8 % and was also highest between PD-L1 (SP142) and the other two antibodies. Among stromal histologic types, higher PD-L1 expression in cancer cells and immune cells was measured in inflammatory-type (p < 0.05). The absence of PD-L1 (28-8) staining in immune cells was associated with shorter disease free survival (DFS) and overall survival (OS)  in univariate analyses, and with shorter OS in multivariate Cox analysis .PD-L1 detection in cancer cells and immune cells varied by antibody clone. The greatest amount of staining occurred with PD-L1 (E1L3N), followed by PD-L1 (28-8) and PD-L1 (SP142). The concordance rate among monoclonal PD-L1 antibodies was higher between PD-L1 (28-8) and PD-L1 (E1L3N). To determine the gold standard antibody and the most appropriate cut-off value, further study of the clinical trial group treated with PD-L1 inhibitor is necessary.The online version of this article (doi:10.1186/s12967-016-0925-6) contains supplementary material, which is available to authorized users. Breast cancer is a heterogeneous disease that has several clinical, histological, and genetic forms. There have been many attempts to categorize this heterogeneous disease, and now molecular classification into five groups  can be accomplished by gene-expression profiling , 2.Among these molecular subtypes, basal-like breast cancer has a more aggressive clinical course than other subtypes and is commonly known as triple-negative breast cancer (TNBC), which is defined clinically as lacking estrogen receptor (ER) and progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). TNBC accounts for 10–17 % of all breast cancers –8. HighlProgrammed death 1 (PD-1) is a check point molecule in immune reactions and can be expressed in various immune cells . PD-L1, Target therapy for PD-L1 in PD-L1-expressing cancers represents a possible treatment for inducing antitumor immune responses. PD-L1-targeted therapy has been investigated in preclinical and clinical trials in many tumors , 26–28 aThe aim of this study was to evaluate the expression of PD-L1 using different immunohistochemical antibodies in TNBC and associated clinical implications.We analyzed 218 patients with TNBC who underwent surgery at Severance Hospital between January 2000 and December 2006. This study was approved by the Institutional Review Board of Severance Hospital. All patients were diagnosed as having invasive ductal carcinoma, not otherwise specified (NOS) by pathologists. We defined TNBC as when IHC for ER, PR, and HER-2 and FISH for HER-2 were all negative.ER and PR immunohistochemistry signal were considered positive when more than 1 % of invasive tumor cells were expressed . HER-2 sdesmoplastic type, with cellular fibroblast/myofibroblast proliferation as the main stromal content; sclerotic type, which has a small cell component and fibrotic collagenous component as its main stromal content; or inflammatory type, with stroma mainly composed of inflammatory cells such as lymphocytes. Tumor staging was based on the 8th American Joint Committee on Cancer (AJCC) criteria. Disease-free survival (DFS) time was measured from the date of the first curative surgery to the date of the first locoregional or systemic relapse, or death without any type of relapse. Overall survival (OS) time was calculated from the date of the first curative operation to the date of the last follow-up or death from any cause. Histologic parameters were evaluated from the H&E-stained slides. Clinical parameters evaluated in each tumor included patient age at initial diagnosis, lymph node status, local recurrence, systemic recurrence, and patient’s survival.Formalin-fixed and paraffin-embedded tissue specimens from 218 cases of primary breast cancer were included. All archival hematoxylin and eosin (H&E)-stained slides for each case were reviewed by one pathologists (Koo JS). The histological grade was accessed using Nottingham grading system . AccordiOn H&E-stained slides of tumors, a representative area was selected and a corresponding spot was marked on the surface of the paraffin block. Using a punch machine, the selected area was punched out and a 3-mm tissue core was placed into a 6 × 5 recipient block. More than two tissue cores were extracted to minimize extraction bias. Each tissue core was assigned with a unique tissue microarray location number that was linked to a database containing other clinicopathologic data.The antibodies and dilution used for IHC are shown in Additional file We evaluated the expression of immunohistochemical markers in cancer cells and peri-tumoral immune cells by light microscopy. Expression in cancer cells was analyzed by various cut-off values  and expression in immune cells was analyzed as follows: negative, no immunostaining; low-positive, stained immune cells ≤30/high power field (HPF); and high-positive, stained immune cells >30/HPF.Interpretation of immunohistochemical staining was performed independently by three researchers . We investigated the proportion of expression (%) in cancer cells according to the above criteria, counted the number of expressed immune cells. Each of three pathologists analyzed the samples and reached a conclusion, which were then analyzed to determine inter-reader concordance. The final results were determined through discussion and multi-view microscopy in the cases that showed discrepancy among the three pathologists.t and Fisher’s exact tests were used for continuous and categorical variables, respectively. The inter-reader concordance rate and concordance rate among PD-L1 antibodies were analyzed using the Kappa-Cohen method. Statistical significance was when p < 0.05. Kaplan–Meier survival curves and log-rank statistics were employed to evaluate time to tumor recurrence and overall survival. Multivariate regression analysis was performed using Cox proportional hazards model.Data were analyzed using SPSS for Windows, Version 12.0 . For determination of statistical significance, Student’s Among the 218 TNBC patients, a desmoplastic type was observed in 138 cases (63.3 %), inflammatory type in 63 cases (28.9 %), and sclerotic type in 17 cases (7.8 %). There was no difference in clinicopathologic factors according to stromal type  showed the highest expression rate in cancer cells  and immune cells (37.6 %) and PD-L1 (SP142) showed the lowest expression rate in cancer cells  and immune cells (19.3 %) for all cut-off values   and PD-L1 (E1L3N) was 6 % (13 cases) and was higher in PD-L1 (28-8)-negative/PD-L1 (E1L3N)-positive (9 cases) than PD-L1 (28-8)-positive/PD-L1 (E1L3N)-negative (4 cases) cells. The discordance rate between PD-L1 (28-8) and PD-L1 (SP142) was 10.6 % (23 cases) and was higher in PD-L1 (28-8)-positive/PD-L1 (SP142)-negative (13 cases) than PD-L1 (28-8)-negative/PD-L1 (SP142)-positive (10 cases) cells. Likewise, discordance was higher in PD-L1 (E1L3N)-positive/PD-L1 (SP142)-negative (15 cases) than PD-L1 (E1L3N)-negative/PD-L1 (SP142)-positive (7 cases) cells  had the highest and PD-L1 (SP 142) had the lowest total positive expression rate. The low-positive rate was higher with PD-L1 (28-8) than PD-L1 (E1L3N); however, the high-positive rate was higher with PD-L1 (E1L3N) than PD-L1 (28-8). In the analysis for expression concordance among the three antibodies in immune cells, the discordance rate between PD-L1 (28-8) and PD-L1 (E1L3N) was 13.8 % (30 cases), with 14 PD-L1 (28-8)-positive/PD-L1 (E1L3N)-negative cases and 16 PD-L1 (28-8)-negative/PD-L1 (E1L3N)-positive cases. The discordance rate between PD-L1 (28-8) and PD-L1 (SP142) was 24.8 % (54 cases), with 46 PD-L1 (28-8)-positive/PD-L1 (SP142)-negative cases and 8 PD-L1 (28-8)-negative/PD-L1 (SP142)-positive cases. Finally, the discordance rate between PD-L1 (E1L3N) and PD-L1 (SP142) was 22.0 % (48 cases), with 44 PD-L1 (E1L3N)-positive/PD-L1 (SP142)-negative cases and 4 PD-L1 (E1L3N)-negative/PD-L1 (SP142)-positive cases  (p < 0.001). For PD-L1 SP142), the concordance rate was higher for positive staining in cancer cells and in negative staining in immune cells  negativity in immune cells was associated with shorter disease-free survival (DFS) and overall survival (OS)   and 64–8PD-L1 showed membranous expression in this study, in agreement with one previous study in TNBC , but theIn this study, the concordance rate between PD-L1 (28-8) and PD-L1 (E1L3N) was high in both cancer cells and immune cells while PD-L1 (SP142) showed low concordance rates with the other two antibodies. Previous studies reported poor concordance  between PD-L1 (E1L3N) and PD-L1 (SP142) in lung cancer , but a hPD-L1 positivity in immune cells (28-8 clone) was an independent prognostic factor in our study, in contrast to previous studies showing good prognosis –53 or poIn breast cancer, tumor infiltrating lymphocytes (TILs) have been linked with good prognosis , as haveClinical trials targeting PD-L1 are underway , 58–60 aThe limitation of this study was the potential difference in results between TMA and the whole cancer tissue section. Breast cancer also shows intracancer heterogeneity, like other types of cancer, and the expression of PD-L1 may cause differences between TMA and the whole cancer tissue section. PD-L1 expression in lung cancer showed a high discordance rate between TMA samples and whole tissue sections . In a prIn conclusion, staining with PD-L1 (clone 28-8), PD-L1 (clone E1L3N), and PD-L1 (clone SP142) monoclonal antibodies in cancer cells and immune cells varied, with the highest staining by PD-L1 (E1L3N) and the lowest by PD-L1 (SP142). The concordance rate among monoclonal PD-L1 antibodies was higher between PD-L1 (28-8) and PD-L1 (E1L3N). PD-L1 positivity in immune cells correlated with a favorable prognosis. To determine the gold standard antibody and the most appropriate cut-off value, further study of the clinical trial group treated with PD-L1 inhibitor is necessary.


The advent of 2D materials integration has enabled novel heterojunctions where carrier transport proceeds thrsough different ultrathin layers. We here demonstrate the potential of such heterojunctions on a graphene/dielectric/semiconductor vertical stack that combines several enabling features for optoelectronic devices. Efficient and stable light emission was achieved through carrier tunneling from the graphene injector into prominent states of a luminescent material. Graphene’s unique properties enable fine control of the band alignment in the heterojunction. This advantage was used to produce vertical tunneling-injection light-emitting transistors (VtiLET) where gating allows adjustment of the light emission intensity independent of applied bias. This device was shown to simultaneously act as a light detecting transistor with a linear and gate tunable sensitivity. The presented development of an electronically controllable multifunctional light emitter, light detector and transistor open up a new route for future optoelectronics. The discovery of graphene and other 2D materials has led to the emergence of a new class of hybrid materials that derive their properties from interfaces between layers of dissimilar materials123567891012131415A wide range of accessible wavelengths, for example, is required for lighting applications as well as wide-bandwidth optical communication. Furthermore, the increasing resolution of displays will necessitate high integration densities of emitters171819Current light emitters have severe limitations that prevent them from supporting these developments. While crystalline semiconductors exhibit composition-dependent emission properties, fabrication challenges arise for each new material combination2324We here demonstrate the potential of metal/insulator/semiconductor heterojunctions between 2D and thin film materials as a composited architecture for efficient and multifunctional optoelectronic devices as shown in 2 layer in the emission process, we first compare the result for both samples of graphene/SiO2/p-GaN and graphene/p-GaN. 2/p-GaN and graphene/p-GaN devices under forward source-drain-bias . The emission peak of graphene/SiO2/p-GaN device around 400 nm can be attributed to the transition from states near the conduction band to acceptor impurity states caused by interstitial Mg atoms near the valence band30312) is characterized by a broad band emission as shown in The fabricated vertical tunneling-injection light emitting transistor on sapphire substrate with the structure shown in SD > 0 V), the bands of p-GaN at the interface near the thin SiO2 are bent upwards and the work function of graphene changes to smaller values  and 5.4 nm blue shift of the p-GaN emission spectrum can be observed .G)G)  is changed from −20 V to 20 V. We observe an on/off ratio of 102 indicating effective suppression of current flow even at large forward biases. Previous reports have shown the high achievable switching speed for graphene-based tunneling transistors which indicates the potential of our approach for high speed emittersThe single layer graphene serves in a two-fold role in our architecture. First, its very small effective electron mass improves the efficiency of tunneling injection2G)G) . To compG). Under positive gate voltage, the device shows higher light emission than that at zero gate voltage. On the other hand, suppressed emission can be observed under negative gate voltage (VG). This behavior shows that our emitter can be operated in a three-terminal configuration as a light emitting transistor. This ability could be exploited in compact light emitters through integration in crossbar matrix arrays for high resolution displays.We now turn to identifying the effect of electrostatic gate control on the light emission process. 2 and p-GaN. This model as shown in the inset of G) is applied. As shown in G) induces hole doping in the graphene that increases its work function and then leads to a larger barrier height The demonstrated light emitting transistor is different from previous LET structures where a gate voltage was used to modulate the carrier transport along a semiconducting channelIn the tunneling-based operating mechanism electrostatic gating introduces a varying density of state in the graphene without affecting the condition of the luminescent material. This advantage is demonstrated when analyzing the bias dependence of the emission spectrum. Commonly, p-GaN exhibits a blue-shift in emission for high bias that is caused by electric field-induced polarizations in the materialThe light emitting transistor structure employed here was found to improve the performance of light emitters. Commercially available LEDs based on multiple GaN/InGaN/GaN quantum wells exhibit a turn on voltage around 2.75 V, which necessitates high operating voltages and increases power consumption. In our device, applying a gate voltage decreases the turn on voltage to 1 V under positive gate voltage and increases it to 12 V for under negative gate voltage. Application of a gate thus increases the efficiency to ~200% compared to ungated conductions. This novel operating mechanism yields unoptimized emission efficiencies of ~50% of commercial multiple quantum well light emitting diodes (MQW-LEDs) , which cIn addition to an enhanced emission, electrostatically controlled tunneling promises faster and more efficient transition between on- and off-states than conventional transistor operation mechanisms7SD > 0 V) and reverse bias (VSD < 0 V) (39D < 0 V) . We obseG) increases, the decrease of the work function of graphene will induce larger band bending of p-GaN. Due to the larger bending the excited electron and holes could be separated much easier and generate a higher photoresponse. The observed linearity in sensitivity with gate voltages improves the accuracy of the sensor compared to traditional photosensors which exhibit an exponential characteristic. The different dependences of photosensitivity on gate voltage (VG) and source-drain bias (VSD) could enable sensors that are adaptable to widely different illumination conditions (through control of VSD) while retaining ultrahigh sensitivity (by modifying VG). Compared with published reports of GaN based photodetectors, the phtoresponse shown here is more than a factor of 10 times higherIn conclusion, we have utilized a heterojunction of 2D materials and ultrathin films in a novel and multifunctional device that serves as light emitter, light detector and transistor. The integration of these unique properties requires less complex fabrication and lend themselves to new applications. It was observed that carrier injection from graphene into a luminescent material created emission from well-defined states and its intensity could be controlled by a gate. The mechanism was found to be based on tunneling through a barrier that could be modified by changing the graphene work function. The application of a gate was shown to enhance the emission efficiency and the performance of the emitter and also enabled multifunctional devices. The presented gate controlled carrier injection mechanism enabled fine control of the device operation, such as tunable detection sensitivity. Finally, the universal applicability of the underlying quantum tunneling mechanism is compatible with a wide range of 2D and quasi-2D materials which enables tailoring of device properties for a bright future for optoelectronics.2 film was deposited on the p-GaN surface as a tunneling barrier via radio frequency (RF) sputtering. Finally, graphene grown by chemical vapor deposition on copper foil was transferred onto the SiO2 with the aid of polymethylmethacrylate (PMMA) following previous reports4244−1 which is the characteristic phonon frequency of the GaN and at 737 cm−1 which was previously found to originate from Mg+2 dopants2 film that protects the graphene and then sputtered 300 nm thick SiO2 film by RF sputtering. To keep the quality of this stacking structure without the damage from one more water transfer of graphene, dry transfer process of graphene onto the thick SiO2 as a transparent top-gate electrode which was followed with previous report−7 Torr and at a constant sample rotation rate. To improve the deposited electrode’s contact resistance, annealing was carried out in a furnace at 400 °C for 20 minutes.A 10 nm thin SiOHow to cite this article: Tan, W.-C. et al. Tunneling-injection in vertical quasi-2D heterojunctions enabled efficient and adjustable optoelectronic conversion. Sci. Rep.6, 31475; doi: 10.1038/srep31475 (2016).


Thermal resistance probed by pulsed photothermal reflectance measurements demonstrated an improved thermal coupling due to functionalization on the graphene–graphene oxide interface. Three functionalization molecules manifest distinct interfacial thermal transport behaviour, corroborating our atomistic calculations in unveiling the role of molecular chain length and functional groups. Molecular dynamics simulations reveal that the functionalization constrains the cross-plane phonon scattering, which in turn enhances in-plane heat conduction of the bonded graphene film by recovering the long flexural phonon lifetime.The high thermal conductivity of graphene and few-layer graphene undergoes severe degradations through contact with the substrate. Here we show experimentally that the thermal management of a micro heater is substantially improved by introducing alternative heat-escaping channels into a graphene-based film bonded to functionalized graphene oxide through amino-silane molecules. Using a resistance temperature probe for  The high thermal conductivity of graphene is considerably reduced when the two-dimensional material is in contact with a substrate. Here, the authors show that thermal management of a micro heater is improved using graphene-based films covalently bonded by amino-silane molecules to graphene oxide. Gao et al.T=13 °C) for a heat flux of 430 W cm−2 after the introduction of a single-layer graphene heat spreader. Moreover, the simulations of graphene heat spreaders were also reported for silicon-on-insulator integrated circuitsR) at the graphene/FLG–substrate interfaceAnisotropic properties of two-dimensional 2D) layered materials make them promising in the application of next-generation electronic devices, among which graphene and few-layer graphene (FLG) have been most intensively studied for thermal management, due to their extraordinarily high in-plane thermal conductivity D layered−1 K−1  of a graphene/FLG–substrate interface is another limiting factor to their thermal performance in devices. Covalent functionalization has been proved to efficiently promote heat transfer between interfaces by introducing additional thermal pathways through the functionalizing molecules18192021222324252627282930313220182526The thermal boundary resistance  bonded to functionalized graphene oxide (FGO) through amino-silane molecules. We probed interface thermal resistance by photothermal reflectance measurements to demonstrate an improved thermal coupling due to functionalization on the graphene–graphene oxide interface and the graphene oxide–silica interface. Molecular dynamics simulations and 2. 3-Amino-propyltriethoxysilane (APTES) has three –Si–O– groups and one –NH2 end, as shown in 2H5 groups of APTES hydrolyse in water and form crosslink bonds with each other. The crosslinked Si–O structure acts as a strong bonding layer between the substrate and GBFs. On the other hand, the –NH2 end of APTES binds onto carboxyl groups on the functionalized graphene film. The FGO layer has a thickness of ∼5 nm. The graphene film was fabricated from chemically reduced GO and can recover relatively high in-plane thermal conductivity after thermal annealing2 substrate. The thermal evaluation device was integrated with micro Pt-based heating resistors as the hotspot and temperature sensorsA GBF bonded to the FGO substrate through silane molecules is shown in I was input into the circuit by applying an outer voltage V in P=V × I. Since the lateral dimension of the hotspot (A=400 × 400 μm2) is much larger than its thickness (260 nm), most of the heat is dissipated through the lateral direction of the hotspot. Hence the heat flux is defined as Q=P/A, and the direction is parallel to the substrate. The calibration relationship between the resistance RT (°C) of the thermal evaluation chip is R(T)=0.21T+112. The temperature measurement uncertainty is ε=±0.5 °C. in situ at the hotspot and compares the thermal performance of the graphene film with and without the functionalization. With a constant heat flux of 1,300±2.3 W cm−2 at the Pt chip, the hotspot temperature decreased from 135±1.2 to 118±1.1 °C (ΔT=17±2.3 °C) with a GBF deposited on non-functionalized GO compared with the case of a bare chip. Such a remarkable temperature decrease is far beyond the measurement uncertainty ΔT>>ε (see T=11±1.9 °C) thanks to the presence of the APTES functionalization. The heat-spreading performance is thus enhanced by ∼57% via the functionalization. We have implemented a finite-element model  GO layer, and the resistance R2 between  GO layer and GBF or SiO2 were measured. The experimental set-up and the procedure of thermal resistance extraction by fitting the photothermal response to the model  method36he model . The nor−1 was used for all three types of molecules. Eph) by atomistic Green's function to characterize the local heat conduction with and without the presence of the molecule (Eph) enables a precise measurement of the atomic-scale molecule-graphene heat transport that the conventional models fail to provide. The phonon transmission functions through different molecules and the associated thermal conductances versus temperature are shown in 11–Si–O3) has the same functional groups as APTES (–N–C3–Si–O3) but has a longer carbon backbone. Such a long chain length has a rather weak impact on the low-frequency phonons due to their very long wavelength but can strongly suppress the phonon transport at high frequencies. On the other hand, when comparing the phonon transmission through the junction of APTES and 3-(Azidopropyl)triethoxysilane (–N−N+N–C3–Si–O3), it is evident to identify a stronger transmission at all frequencies. By comparing the chemical structures in sp2-bonded carbon lattice of graphene to form three-membered heterocycle structures. Given the similar backbone structure, the phonon eigenmodes in the molecule have not been significantly altered, but the transmission is enhanced due to the stronger thermal coupling to the graphene reservoirs. However, the introduction of nitrogen atoms into the sp2 carbon structure can strongly scatter phonons by distorting the structure of the graphene sheet, which leads to a poor thermal performance of the heat spreader.To gain a deeper insight into the impact of molecular structure on the thermal transport along the molecules, we used APTES, 11-Aminoundecyltriethoxysilane and 3-(Azidopropyl)-triethoxysilane as different functional agent on the GO to evaluate their heat-spreading performance on the same thermal test platform. The same concentration of 0.1492, mol kgmolecule . Ξ(Eph) Eph) to characterize the local heat conduction with and without the presence of the APTES molecule. As shown in Eph) for the two adjacent graphene layers without any molecule displays a clear stepwise structure that provides the number of phonon channels. Low-energy phonons (Eph≤10 meV) dominate heat conduction since the adjacent graphene flakes interact only through weak van der Waals (vdW) forces that inhibit the transmission of high-frequency phononsGph, creating more phonon channels through the covalent bond vibrations. This is in line with the transmission calculation of Segal et al.4142Eph=20–100 meV, as was previously observed in an alkane SAM interfaceab initio calculation combined with Green's function  Functional group of the molecule: when the functional agent forms a stronger bond with its substrate than that of the amino-silane molecule, more severe static graphene distortion occurs thus increasing the critical number lc. (iii) Substrate of the graphene film: a highly mismatched substrate yields remarkable surface distortion of the graphene sheets in such a way that two layers of graphene are not sufficient to recover the high basal-plane thermal conductivity.It is clearly seen from y a role : (i) moln and n0 are the phonon occupation numbers out of and at thermal equilibrium. Under the single-mode-relaxation-time approximation, the thermal conductivity is given by Ci and vi are the specific heat per volume unit and the group velocity of the i-th phonon mode. The phonon dispersion of the supported graphene film for ρ=0.081 nm−2 and lG=2, and the extracted relaxation time R for ρ=0.081 nm−2 and lG≥2, as is shown in K is the average vdW coupling constant between the graphene film and its substrate. A previous calculationKZA largely depends on the substrate morphology. The presence of the molecule strongly decreases the film–substrate coupling KZA, thus yielding a longer time We investigate the microscopic origin of the thermal conductivity ion time . The pho0 K ref. . We attrR with the functionalized substrate versus the equivalent APTES molecule number density ρ in κ–ρ relation at low molecular densities). Therefore, the net effect is an increase in the cross-plane thermal resistance between the top graphene films and the lower GO layers compared to the non-functionalization case. In the limit of small number density, we consider the molecules as independent heat conductors connecting the film and the substrate. R agrees well with a reduced model of parallel thermal resistors. Thus, R decreases with the number of molecules. ρ, the interactions among the molecules gain importance and R starts to deviate from the prediction of the parallel-thermal-resistor model, as shown in ρ, the thermal resistance R is lower than that without molecules. However ρ effectively tunes the thermal conductivity of the supported graphene.The cross-plane heat conduction between the top graphene films and the lower FGO layers is governed by the competing effects of (i) the intercalation of the molecules that tends to weaken the interlayer coupling of graphene therefore increasing the cross-plane thermal resistance and (ii) the additional heat channels introduced by the molecules covalently bonding the graphene sheets that tend to facilitate the cross-plane thermal coupling. We investigated the in-plane thermal conductivity et al.et al.The correlation between the in- and cross-plane thermal transport of 2D materials has been recently studied from both theoretical151314−2 can be observed in microprocessors−1 K−1 for Al and Cu, and the low cost. However, for these technologically important metals, the thermal conductivity of a 100-nm-thick film constitutes only ∼20% of the thermal conductivity of the bulk52−1 K−1 , resulting in a large total temperature decrease of 28 °C when operating at 1,300 W cm−2. In comparison, the highest ΔT achieved so far at a similar high heat flux of 1,250 W cm−2 is 19 °C by using a miniaturized thermoelectric coolerT is robust especially at higher heat flux beyond 1,000 W cm−2, as shown in Our work tackles the key technological challenge of efficient thermal management in the industry of the next-generation integrated circuit. The excessive heat from the hotspots accelerates the failure rate and slows down the operating speed of microelectronic devices50K−1 ref. , which i2SO4 ; NaNO3 (2 g); and KMnO4 (12 g) were used to prepare GO dispersion by following Hummers' methodL-ascorbic acid, and polyvinyl alcohol was also added for better suspension. The GBF was prepared via vacuum filtration with polycarbonate filter paper with a pore size of 3 μm. The film thickness was controlled by the filtration volume and the graphene concentration in the suspension. After dissolving the filter paper in pure acetone, a freestanding GBF was obtained. The thickness of the GBF was measured as ∼20 μm. Raman spectroscopy data of the GBF before and after the spin-coating with FGO are shown in (i) Sample synthesis: graphite ; HClassical molecular dynamics simulations were performed using LAMMPSEph) the thermal conductance due to the phonon could be calculated as T refers to the mean temperature of the system, fBE is the Bose–Einstein phonon statistics, and ħ represents the reduced Plancks constant. The thermal conductance due to the electronsTel as fFD is the Fermi–Dirac electron statistics.Thermal conductance How to cite this article: Han, H. et al. Functionalization mediates heat transport in graphene nanoflakes. Nat. Commun. 7:11281 doi: 10.1038/ncomms11281 (2016).Supplementary Figures 1-19, Supplementary Table 1, Supplementary Notes 1-14 and Supplementary References.


With the recent development of commercial-level single-crystal graphene layers, the potential for manufacturing household graphene-based devices has improved, but significant challenges still remain with regards to patterning the graphene into devices. In the case of graphene supported on a substrate, traditional nanofabrication techniques such as e-beam lithography (EBL) are often used in fabricating graphene nanoribbons but the multi-step processes they require can result in contamination of the graphene with resists and solvents. In this letter, we report the utility of scanning helium ion lithography for fabricating functional graphene nanoconductors that are supported directly on a silicon dioxide layer, and we measure the minimum feature size achievable due to limitations imposed by thermal fluctuations and ion scattering during the milling process. Further we demonstrate that ion beams, due to their positive charging nature, may be used to observe and test the conductivity of graphene-based nanoelectronic devices  Moreover, as a direct-fabrication method, He+ milling requires no resists, developer or wash to fabricate features yet can achieve feature sizes comparable to or smaller than EBL. The smaller interaction volume of the helium ion beam with the sample results in reduced proximity effects compared to EBL, and improved sputtering yield in the surface layerScanning helium ion microscopy (SHIM) and ion milling (performed with the same instrument) has emerged as a tool capable of fabricating graphene devices1in situ, thereby allowing for the estimation of the quality of a graphene conductor. Furthermore, SHIM provides unprecedented high contrast images due to its shorter range and superior ion-generated secondary electron (iSE) yieldin situ by varying the size and width of the connecting strip in each device.By varying the length and width of the strip and then imaging the entire structure, we can directly observe how the electrical conductivity changes as a function of pad brightness. As the ion beam impinges on the pad, secondary electrons are ejected from the pad, yielding a significant net positive charge on the pad. Unlike in a scanning electron microscope (SEM) the positively charged ion beam is not capable of compensating for lost secondary electrons. While graphene’s work function can be tuned across the charge neutrality point by an electric field effect+ milled graphene pads (left panel) that have been acquired following the fabrication process. Corresponding SEM images of the exact same devices (right panel) were used to directly compare the effects of imaging with a negatively charged beam. In + do not neutralize at the graphene due to their velocity, but neutralize deeper in the Si wafer. In general, these strips are compensating for lost secondary electrons, and conducting around 1 pA. The transition from bright to dark occurs when the strip is no longer capable of carrying 1 pA. As the width of the strip is increased to 12 nm . Also, this noise (at room temperature) may place a limit on the smallest feature sizes that can be used for graphene circuitry supported by SiO2, which in our case is ~10 nm. This noise does not represent the distribution of electrons within the pad – rather, this noise reflects the instantaneous conductivity of the strip at the moment that pixel is being collected. Of particular interest is the subtle noise in the pad in A second class of graphene devices was explored in order to investigate the impact of the length of the conducting strip. These devices were fabricated to include two smaller regions (i and ii) that have been completely electrically isolated in order create conducting-insulating composites. Similar to in situ conductivity can be observed in micron-size devices . The minimum feature size achievable using SHIM is a product of several factors. There are the typical problems of instrumental drift and electronics stability in the raster scan. The SHIM described here is located in a cleanroom but not a low-noise microscopy suite, and undoubtedly experiences some mechanical noise. Also specific to this technique are the beam shape and ion backscattering which create a larger interaction volume between the beam and substrate than intended. The minimum width of the connecting strips reported here are likely determined by the density of defects along the edges of the strips, which are in turn determined by impingement by ions that escape outside of the illuminated region, either through an imperfect beam profile (tailing) or backscattering. Our experiments indicate that for a very short strip, the minimum width is about 10–12 nm. For longer strips, minimum width increases because the resistivity of strip is in part due to the sum of all defects along the length of the strip. This experiment has an additional limitation because as a focused ion beam technique, the quality of the device is dependent on operator skill in aligning and focusing the instrument.2 sample preparation method does not exclude the possibility of having contaminants from the residual PMMA resist that may be present after the transfer and annealing process (see Methods section). However, for non-CVD graphene, or any 2D material prepared without the need for transfer using a polymer, this approach may entirely exclude unnecessary exposure to solvents and resists.Grain boundaries, which are a common occurrence in CVD-grown graphene can also affect the conductivity of graphene12in situ. The minimum width of the conducting strip attainable with scanning helium ion lithography is limited by the coupled vibrational modes arising from thermal fluctuations within the device. Electrical conductivity through a supported graphene strip is limited by the width of the strip. As a direct-fabrication technique, helium-ion lithography will be a preferred method of patterning graphene-based circuits and devices smaller or comparable in size to EBL, and will eliminate the need for the multistep processes involved in EBL.In summary, we have demonstrated that positively charged ion beams from a SHIM may be used to fabricate devices in supported graphene on an insulator, and then detect conductivity in such devices et al.142 in Ar for 30 mins. Graphene growth was performed by addition of methane with a gradual increase in concentration from 10 to 20, to 40 ppm for 30 mins in each step. After growth, Microchem PMMA 495A4 solution was spin-coated at 2000 rpm on top of graphene on copper foil. Graphene from the back side of copper was etched away by oxygen plasma and copper was dissolved by 1 M FeCl3 in 3% HCl. Graphene/PMMA sandwich floating on water surface was washed by DI water and transferred onto the SiO2 substrate. PMMA was dissolved in acetone with subsequent annealing at 550 °C to remove the PMMA residue.Single layer graphene was synthesized using a method by Vlassiouk +/Ne+ beam at a field of view and pixel spacing that yielded a fluence of ~1 × 1019 ions/cm2 for He+ beam and ~5 × 1017 ions/cm2 for the Ne+ beam. Subsequent high-resolution images were acquired at the same field of view using a 50 μs dwell time.Scanning helium ion microscopy and lithography on single layer graphene was performed using a Zeiss ORION Nanofab He/Ne ion microscope, operating at an accelerating voltage of 30 kV and a beam current of 4.2 pA. All the graphene devices were fabricated using the ion microscope’s built-in patterning software and imported bitmaps. Each milled area was exposed to the HeScanning electron microscopy secondary electron images of the exact same graphene devices were obtained using a Zeiss MERLIN VP SEM equipped with an in-lens detector operating at 3 kV.How to cite this article: Iberi, V. et al. Maskless Lithography and in situ Visualization of Conductivity of Graphene using Helium Ion Microscopy. Sci. Rep.5, 11952; doi: 10.1038/srep11952 (2015).


The timing of turn taking in conversation is extremely rapid given the cognitive demands on speakers to comprehend, plan and execute turns in real time. Findings from psycholinguistics predict that the timing of turn taking is influenced by demands on processing, such as word frequency or syntactic complexity. An alternative view comes from the field of conversation analysis, which predicts that the rules of turn-taking and sequence organization may dictate the variation in gap durations . In this paper, we estimate the role of these two different kinds of factors in determining the speed of turn-taking in conversation. We use the Switchboard corpus of English telephone conversation, already richly annotated for syntactic structure speech act sequences, and segmental alignment. To this we add further information including Floor Transfer Offset (the amount of time between the end of one turn and the beginning of the next), word frequency, concreteness, and surprisal values. We then apply a novel statistical framework (“random forests”) to show that these two dimensions are interwoven together with indexical properties of the speakers as explanatory factors determining the speed of response. We conclude that an explanation of the of the timing of turn taking will require insights from both processing and sequence organization. Imagine a species that squawks at conspecifics. If it only has one message type , messages will have low information value. If there is only one rule of use, namely “one at a time,” communication will exhibit turn-taking, but not much other sequential patterning. Marmoset communication perhaps come close to this  and long turn transitions without talk (“gaps”). The “floor transfer offset” (FTO) provides a way of measuring gaps and overlaps in one single continuous variable .There are some previous studies of the distribution of FTOs. For example, Strömbergsson et al.  find thaHere we list some measures relevant to either production, comprehension, or both, whose importance we can readily check in the data to hand. We consider a number of hypotheses about how these might play a role in response times, measured in FTO.By definition, longer turns can have longer periods of overlap with another turn. Moreover, longer utterances are likely to be more complex than shorter utterances, requiring more processing. However, a longer utterance also gives more time for a listener to begin planning her own turn. Therefore, the predictions for effect of the length of T1 on FTO values are not clear without taking other measures of the content of the turn into account. On the other hand, the prediction for T2 length may be clearer. Planning a long utterance should generally take longer than planning a short one, so the FTO is expected to increase as the length of T2 increases.Psycholinguistic research has shown that word frequency plays a crucial role in ease of processing, both in comprehension and production. In lexical decision experiments for example , frequent words are responded to more rapidly than infrequent words  contrast with words that refer to abstract entities . Concreteness ratings have been shown to correlate with lexical decision times, with concrete words being comprehended faster . Consequently, there may be an asymmetry in the predictions for the syntactic complexity of A's turn and B's turn. While T2 has no way of influencing the relationship between syntactic complexity and when T1 ends (apart from other-initiated repair), there is the option of “buffering” planning at the beginning of T2. Speakers often use turn-preserving placeholders, or hesitation markers, such as “uh” and “um” at the start of their turns to minimize the gap between turns. They may use this extra time to plan their response. This asymmetry in the options for T2 predicts that the syntactic complexity of T2 would only be correlated with the FTO when excluding initial parts of T2 that were simply turn-preserving placeholders.If the timing of turn taking is the primary “ecology” to which language has to adapt . As reported below and in the Supplementary Materials, many of the independent variables in the Switchboard data are correlated.One solution to this problem is to use the method of “random forests” Breiman, . This isFigure 2. This was generated with FTO as the dependent variable and four measures of sequence organization . For clarity, only the first three levels are shown.First, the concept of a decision tree is reviewed. A decision tree is a hierarchy of yes/no-questions that splits data into sub-sets. To illustrate this, consider the tree in n which represents the number of observations in that sub-set. The tree can be read like a solution to a game of “20 questions.” If you are asked to guess the value of an FTO, the decision tree aims to show you the optimal sequence of yes-no questions that will guide your guess. The tree can also be read like a set of rules that describe patterns in the data . For a given turn transition, if T1 is initiating, then we follow the right branch. The next “question” splits the data into T2s with responding actions  and those without. If T2 does include a responding action, we follow the branch to the left, and are asked whether T1 included laughter. If not, then we end up at a terminal category which we might label “adjacency pair,” summarized in a bar chart. This bar chart indicates that the mean FTO is around 200 ms, based on 1130 samples  have a mean FTO of around 300 ms. This fits with work showing that dispreferred responses tend to be delayed . This reflects the trend for males to speak faster than females. For both male and female speakers of T2, slower speech in T1 (higher T1 delta) leads to shorter FTOs. The rightmost leaf represents 314 cases of FTOs between two female speakers where T1 is speaking very slowly (high delta). In this case, the mean FTO is in overlap.The tree in Figure One problem with decision trees is that their structures are not robust. The structure is sensitive to the selection of predictor variables and the particular sample of data  than other turns. Therefore, the tree would split the data into FTOs with high and low frequency T1s. A prediction from the sequence organization account might be that negative responses have higher FTOs, so the tree would split the data into FTOs before positive and negative T2 responses.density function in R set to default parameters) was 169 ms. For comparison, in our Switchboard data, the median for polar questions followed by a response was 199 ms, and , though there was only weak evidence for multicollinearity (maximum variable inflation factor = 3.9). The number of variables also makes the number of possible interactions very high. These two factors make simple linear regression analyses more difficult to interpret, but random forests is a robust to these concerns. Here we report various results relating to the random forests analyses.Many of the predictor variables are correlated with each other . To give an impression of the fit of the model, a single tree was generated . The predicted FTOs correlated with the actual FTOs with r = 0.51, meaning that the model accounts for about 30% of the variation. Another way of assessing the fit is to use the model to predict values for each FTO. When categorizing FTOs into gaps and overlaps, the model correctly categorizes 70% of cases.A random forests model was run with 1000 trees and 3 variables in each tree . This result is difficult to compare with linear models, since random forests work very differently (random forests are based on decision trees which divide data into sub-sets and fit each sub-set separately). Still, the difference between the two suggests that overall trends are weak, but there are more dependable patterns for certain types of transition.Figure t = −0.21, p = 0.83; mean rank for processing measures = 17.8, mean rank for sequence organization measures = 16.1 t = 0.47, p = 0.64).The top five most important variables are whether T1 includes a responding action, T1 duration, T2 duration, T1 speech rate and T1 sex. Measures of processing and sequence organization were not rated differently overall . For duration, speech rate and tree height the importance of the variable for T1 is greater than for T2, suggesting more weight on comprehension and planning. However, the opposite pattern holds for concreteness, frequency, and surprisal measures.There was no large difference in the ranking of measures for T1 compared to measures for T2 . T1s spoken with rates in the fastest quartile lead to FTOs around 100 ms longer than those in the slowest quartile. The speech rate of T2 is ranked as much less important. There is no strong relationship between T2 rate and FTO.r = 0.65, t = 171, p < 0.00001). Notice that here, as with speech rate, the processing factors only have significance in a particular sequential context, demonstrating how the two parameters, sequence organization and processing costs, are interwoven.T1 syntactic tree height is relatively important (ranked 6th most important out of 30), as is the number of clauses for T1 and T2 (ranked 9th and 10th). As the T1 increases in syntactic complexity, the FTO increases. Turns in the simplest quartile lead to FTOs 64 ms shorter than turns in the most complex quartile. There is no strong linear relationship between T2 syntactic complexity and FTO. The relative importance of the number of clauses in T2 may be attributed to the correlation with turn duration . When combined with utterance duration, then, the concreteness of T2 becomes a proxy for distinguishing response tokens (simple to project and plan) from question answers (more difficult to project and plan). Indeed, in a decision tree constructed with only T2 concreteness and T2 duration, T2 concreteness is used in a branch of the tree with short T2 turns and, within these turns, higher concreteness leads to longer average FTOs (positive relationship).r = 0.13), with the correlation being stronger as the length of T1's turn increases . That is the timing of turn transition is more tightly timed when T2 is less concrete .T2 concreteness seems to be more related to the absolute FTO, that is to how close the beginning of T2 is to the end of T1, ignoring whether it's a gap or overlap. There is an overall positive correlation between absolute FTO and T2 concreteness . Whether T2 starts with a responding action, and whether T2 starts with an initiating action are also ranked as relatively important, and since they form the basis of sequence organization they are discussed together here. Figure The most important factor in the whole random forests analysis is whether T1's  dialog act includes a responding action . On average, FTOs are smaller when T1 includes a responding action  is 200.7 ms. This kind of sequence forms the basis of adjacency pairs (see Section 4.1), and agrees very well with results for polar questions from Stivers et al. .The mean FTO is longer when T1 responds and T2 initiates (284.8 ms), a floor transition involving turns which do not form an adjacency pair. For example, in the extract below, B asks a question , and A gives an answer . This is a well-formed adjacency pair. However, if we consider the answer as T1, the next turn T2 is a different question from B. These latter turns are not part of an adjacency pair, but belong to other sequences.Conversation 3254, 0:19   A: Uh, there were a few things different      than the old series, but on the, on      the whole, it was pretty similar.      And, a lot of fun.   B: Lots of little funny spots, huh?T1 A: Oh, yeah, yeah. (Responding)   FTO = + 614 msT2 B: Did they have Thing, and,      (Initiating)   A: Oh, yes, in fact, Thing has a big,      much bigger role than he does in the      series.Another possible case is that in which floor transfers occur between two initiating actions. In such cases, the mean FTO was the longest (298 ms). In our data, these often involve cases of other-initiated repair . The following example is a case of other initiated repair. B asks a question (initiating action), but A does not hear or understand, and initiates a repair sequence on the previous turn. B goes on to rephrase their question, and A resumes the main question-answer sequence:Conversation 3232, 2:13(A and B are discussing scholarships)   B: -- it paid most of my tuition, and,      um, a lot of the book costs and that      kind of thing, so.   A: Wow, that's great.   B: Yeah, I really,T1 A: Was it a Pell grant? / (Initiating)      FTO = +494 msT2 B: I'm sorry, what did you say?      (Initiating)   A: What kind of grant was it?   B: Well, it was called a B E O G,      a Basic Equal Opportunity GrantIn line with our results, Kendrick  finds thFinally, we see that the shortest average FTOs are when both T1 and T2 involve responding actions. In this case, the mean FTO is shorter (157 ms). Many of these sequences involve T1 being a backchannel. Looking closer, we also find that many are part of sequences of assessment. The example below involves a news delivery sequence    A: But, uh, they just go around to      each, uh, door and pick it up.   B: Wow, that's excellent.T1 A: Yeah. (Responding)   FTO = +137 msT2 B: That's good. (Responding)Similarly, in the next example, A responds to B's statement with an assessment in T1, and then B produces a second assessment in T2.Conversation 3526 2:44   B: Yeah it and when it comes on the      manufacturing floor it's about ten      bucksT1 A: I'll be darned (Responding)   FTO = +206T2 B: Yeah (Responding)   A: Huh well   B: Well i watched something on TV a      couple of months ago by uh General      ex uh Surgeon General Kooppost-hoc, we observed that, when T1 is a backchannel, the FTO is around 38 ms lower on average than otherwise. This could occur if backchannels are regularly overlapped because they are not treated as real turns at talk . There is no big difference in means according to whether T2 is a backchannel  and this is reflected in it being ranked as relatively unimportant in the random forests results.T1 including a backchannel is ranked 9th out of 30 in terms of importance. Looking at the effect of this variable Post-hoc tests revealed that FTOs are 55 ms longer on average when T2 includes a negative response . This is in line with a delay for dispreferred responses, but the size of the effect is very small , especially in comparison to the effect of T2 being a responding action vs. not.Whether T2 provides a positive response is ranked in the middle of the distribution of importance. The sex of the speakers is relatively important, with each male in the conversation adding around 70 ms on average to the FTO .The rest of the variables have weaker importance values, but some observations are worth making. Many processing variables are not highly ranked, especially measures of information and surprisal, but also frequency, which goes against the processing predictions.post-hoc t = 5.4, p < 0.00001). FTOs are shortest when there is invited laughter: when there is laugher in both T1 and T2, the average FTO is -142 ms (overlap), as predicted by the literature on laughter in conversation. However, the laugher variables are the lowest rated variable according to the random forests analysis. This could be due to the relatively small number of cases that include laughter (about 4% of cases).FTOs are on average lower for transitions involving laughter . The prediction from processing is that the processing variables would be ranked as more important in this case, since placeholders gives responders time to plan.As discussed in Section 7, the beginnings of some turns may be turn-preserving placeholders, hesitation markers such as “um” and “uh,” that speakers use to “buffer” their response. This could obscure the demands on processing. To explore this, the same model was run, but calculating the FTO as the time from the end of T1 to the first non-turn-preserving placeholder in T2. The full results are available in the Supplementary Materials. The importance estimates in this model were weakly correlated with the main model importance estimates reported in the section above , but may reflect differences in socio-cultural norms or simply individual differences.We began with the observation that communication systems are imaginable, the marmoset system a putative case, in which issues of cognitive load and sequence organization play little role in influencing temporal patterns of behavior. Human communication contrasts on both dimensions, because of the formidable choice of alternatives faced by a speaker and the consequent unpredictability faced by a responder on the one hand, and on the other because sequences of ordered turns map structure onto the sheer fact that T1 is followed by T2.By using a large coded corpus we have been able to track the importance of a set of different measures of each dimension. We conclude that the temporal patterns of dialogue cannot be accounted for by either cognitive or sequence organization factors alone. The two are interwoven with indexical factors in such a way that, for example, the sex of a speaker in a particular initiating sequence type creates an environment where cognitive load plays a particularly strong role in influencing the speed of response. This suggests that an explanation of the timing of turn taking will involve a combination of insights from both cognitive processing and sequential organization.The ways in which factors load only in specific ecological niches make standard regression techniques inapplicable. Here the method employed, random forests, comes into its own, allowing the factor loading to be discerned in specific ecological niche formed by indexical factors, processing factors and sequence factors, as illustrated in the tree in Figure This study has not exhausted the information in the Switchboard corpus. It would be possible to analyze further the different distinctions in dialog actions, such as the distinction between polar questions and content questions . There is also more indexical information such as age and dialect. Speakers were assigned topics of conversation and these may also have stimulated speakers to different degrees, which could affect average FTOs. There are also a range of phonetic information and semantic factors that could be explored. This study thus has distinct limitations. Extending the analysis to other corpora and other languages will however require large amounts of transcribed speech data, matched with processing information such as frequency and surprisal for many languages.All data collected from individuals were from sources where informed consent had been provided.http://tla.mpi.nl/tools/tla-tools/elan/.Source data is available to download online (see the various references in the main text). The analysis software is also available: pympi (Lubbers and Torreira, Extracted and prepared the data: FT; Calculated FTO: FT; analyzed the data: SR, FT; Wrote the manuscript: SR, FT, SL.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.


B along with high in-plane magneto-crystalline anisotropy energy (MAE) of 17 meV. Under the influence of electric field, spin crossover effect accompanied by a change in the MAE is observed. The ascribed change in spin-configuration is caused by the modification of exchange coupling between defect states and a change in the occupation of d-orbitals of the metal complex. Our predictions open a promising way towards controlling the magnetic properties in graphene based spintronic and non-volatile memory devices.Developing nanostructures with tunable magnetic states is crucial for designing novel data storage and quantum information devices. Using density functional theory, we investigate the thermodynamic stability and magnetic properties of tungsten adsorbed tri-vacancy fluorinated (TVF) graphene. We demonstrate a strong structure-property relationship and its response to external stimuli via defect engineering in graphene-based materials. Complex interplay between defect states and the chemisorbed atom results in a large magnetic moment of 7 μ Understanding mechanisms that control magnetism at the nanoscale is crucial for designing novel spintronic and data storage devices. However, understanding these mechanisms remains an open challenge in material science, with a tremendous impact on today’s information technology1234567891012131415sp2 hybridized in honeycomb geometry and exhibit a large surface area. The outer low-energy pz orbitals of C atoms can hybridize with the defect states modulating its electronic and magnetic properties2224252728293031333435Graphene – a single sheet of carbon atoms has unique mechanical, electronic, and optical properties171720d-bands of adatom394143et al. synthesized reduced graphene oxide (RGO) by chemical exfoliation method and obtained fluorinated RGO by annealing RGO with XeF2. The fluorinated graphene is found to be stable and magnetic in the presence of vacancies37In general, MAE is an interplay among spin-orbit coupling (SOC), ligand field and surrounding environment . Thus, one can control the MAE and other magnetic properties by tuning these parameters5in silico identification of promising defects/impurities with desired properties, and thereby investigating structure-property relationship.As defects and doping play an important role in functionalizing graphene484950515253In this work, we investigate the magnetic properties of W atom adsorbed on tri-vacancy fluorinated (TVF) graphene; a schematic picture is shown in 5556Prior to investigate the physicochemical properties of W chemisorbed TVF graphene, we first investigate the thermodynamic stability of TVF graphene. Although nanoporous grapheneF2 molecule and nF is the number of F atoms incorporated. The last term in T) and partial pressure 2, and can be determined via statistical thermodynamics or from thermochemical JANAF TablesIn ab-initio computations for fluorine doped graphene, the phase diagram showing the defect formation energetics as a function of F2 chemical potential (Δμ(F2)) is shown in T-2) for thermodynamically stable TVF graphene with three fluorine atoms lies between −2.45 to −1.85. In the inset of 2) of thermodynamically stable TVF graphene with three F atoms. To ensure the surface thermodynamic stability of the system under real-world synthesis conditions, , the dependence of F2 chemical potential (Δμ(F2)) in the gas phase is translated to the pressure scale at 1100 K.Using 3 molecule in vacuum and a nanoporous of six C vacancies in graphene. Thus, our calculations, as shown in the As depicted in ETVF are the total energies of TVF graphene with and without adsorbed W atom, respectively.where ab-initio MD simulations. In T = 290 K. We find an almost constant energy and a stable ferromagnetic state over the time at T = 290 K, which confirms that the system (W adsorbed TVF graphene) is dynamically stable. We also tested the ferromagnetic stability at room temperature (T = 300 K) for a few hundred steps and found the system to be stable at room temperature and showing FM properties.In order to investigate the total energy and spin moment of the system at a finite temperature, we performed 1, C2, and C3. A stable structure after the relaxation process is achieved as a consequence of the repulsion between F atoms and un-bonded carbon atoms that results in W atom getting bonded with one of the un-bnded carbon atoms and breaking the symmetry of the system. This results in lowering the energy of the system and a Jahn-Teller distortion in the system. The geometrical reconstruction of dangling bonds results in symmetry breaking that results in the total spin magnetic moment of the system to be 7 μB. The physical origin of high spin magnetic moment can be inferred from the high-spin configuration of 5d-series W  adatom on TVF graphene.As shown in d-TM atoms have filled 6s orbitals and partially filled, half filled or completely filled d-orbitals. The electronic configuration of W atom is 5d5↑, 6s1↑. Adsorption of W atom on TVF graphene leads to a rise in the energy of 6s orbitals, which is then minimized through the polarization of 6s orbitals by transferring the charge from 6s to the minority states of 5d-orbitals593). The other two dangling bonds remain unsaturated and induce a finite magnetic moment of 0.70 μB/dangling bond which is same as the magnetic moment of the dangling bonds in absence of the adatom. As W is bonded to one of the dangling bonds by hybridization only, most of the uncompensated charges need to be accommodated on W atom itself, which leads to a large moment of 3.70 μB per W atom. Note that this spin magnetic moment is greater than the magnetic moment of 2.29 μB previously found for W adatom on di-vacancy nitrogenized grapheneThe valence states of 52 couples antiferromagnetically with C1 in the neighboring ring due to change in the occupation of states of both the dangling bonds. This results in decrease in the magnetic moment of the system. Thus the magnetic moment of the hybrid system jumps from a high-spin value to a low-spin value as the electric field changes from 5 to 6 V/nm resulting in a spin crossover effect. As the high- and low-spin states describe the different magnetic states, switching between the two states with an e-field can be used to increase the efficiency and sensitivity of magnetic memory devices.To check the stability of the hybrid system at high electric fields, we calculate its cohesive energy in the absence and presence of e-field. The calculated cohesive energy per atom of W adsorbed TVF graphene at zero and 6V/nm e-fields are 7.66 and 7.67 eV, respectively. These cohesive energies confirm that the defect can withstand high electric fields. The change in spin magnetic moment of W adsorbed TVF graphene as a function of electric field is shown in sp2 orbitals, however a small fraction of this moment also comes from the spin polarized π-orbitals. The electric field shifts the lower edge of the minority states towards the Fermi level, which leads to a decreased magnetic moment contribution by dangling bonds and therefore reduction in the total moment of the system as can be seen in d-orbitals. This further decreases the total spin moment of the system. Thus, through electric field, one can control the alignment of spins on carbon atoms in the defect region. Although the electric field affects the magnetic moment of W, the effect is greater on dangling bonds where the coupling of dangling bonds changes from the ferromagnetic to antiferromagnetic.Quantum mechanically, magnetism of dangling bonds arises primarily from the un-bonded xz(Ex–Ez) = −7.95, ΔEyz(Ey–Ez) = −17.19 and ΔExy(Ex–Ey) = 9.25 meV. This suggests that the easy axis of magnetization lies in the plane of the graphene  and hard axis is perpendicular to the surface lying along the z-axis with an MAE of 17.19 meV. Energy differences between principal magnetization directions are plotted in y–Ez) until the applied e-field reaches 6 V/nm. Beyond the e-field of 6 V/nm, a gradual variation in MAE has been observed as shown in x–Ez = −7.20, Ey–Ez = −12.93 and Ex–Ey = 5.72 meV. Hence, despite the decrease in the energy differences, the easy and hard directions of magnetizations remain unchanged.Despite the large magnetism, the use of any given material in spintronic devices also depends upon its MAE as it decreases the thermal fluctuations in the magnetization of the system. The estimated energy differences for W adsorbed TVF graphene between different magnetization directions are: ΔEd-orbitals and change in the orbital moment can affect the values of MAE5xz (Lx–Lz), ΔLyz (Ly–Lz) and ΔLxy (Lx–Ly), in presence of SOC is plotted in yz (Ly–Lz) is negative beyond an e-field of 5 V/nm and increases gradually indicating an increase in the orbital moment along the z-direction, which would suggest an easy direction of magnetization to be along z-direction. However, since this difference is small (<0.1 μB), it is difficult to predict the direction of easy axis based only upon the difference in orbital momentxy (Lx–Ly) and ΔLxz (Lx–Lz) suggests a switching of MAE at higher electric field. Inclusion of SOC suppresses the magnitude of spin moment, however it has the same trend as the non-SOC case shown in Change in the occupation of To obtain a quantum mechanical picture of the origin of magnetism and MAE, in Lz and Ly (Lx) are the angular moment operators along the principal axes. As, where 〈dzx and dx2–y2 and the coupling between dz2 and dxz through Ly have dominant contribution to y-axis. Although application of electric field increases the coupling between  and  orbtials, we find a decrease in the MAE of the system at higher fields. This decrease is found to be due to the increase in the coupling interaction of  and  orbitals through Lzy- to x-axis is expected to be due to the coupling of dxy with dxz, coupling of dx2–y2 with dyz and the coupling of dz2 with dyz orbitals realized through Lx operator.The DOS in To check the robustness of presented results with respect to the change in exchange correlation potential, we also performed DFT calculations using PBE-sol pseudopotentials. We find that both PBE and PBE-sol yield similar results for structure and magnetism in the absence of SOC at all the fields. Upon inclusion of SOC, the computational cost of calculations increases, therefore we calculated the MAE and orbital moments just at the smaller fields and found that the results change by 2–3 meV, however the overall trend remains the same.In summary, we have investigated the magnetic properties of tungsten adsorbed on nanoporous TVF graphene and have demonstrated the influence of intrinsic defects on the stabilization of the adatom and inhibition of aggregation. Our computational results suggest that the proposed defect is thermo-dynamically and geometrically stable and can be fabricated with existing experimental techniques. Further, we predict that the magnetic properties of the hybrid system can be modified using e-field via the changes in the occupation of W adatom states. As a result of this modulation, we find a switching between high-spin and low-spin states after an e-field of 5 V/nm. Present study also confirms an easy plane anisotropy accompanied by spin crossover in tungsten adsorbed on TVF graphene, which is an important result for non-volatile memory and spintronic devices. Further, we expect to see a change in the direction of magnetization at higher fields or by substituting different adatoms. We believe that our results will stimulate experimental work on these kinds of hybrid systems to develop highly efficient data storage and spintronic devices based on graphene.Ab-Initio Simulation Package (VASP)63−7 eV and a Γ centered k-mesh of size 7 × 7 × 1 is used to sample the Brillouin zone of the systemDensity functional theory calculations are performed using frozen core projector augmented wave method as implemented in Vienna 3Dh symmetry. The other three C atoms in the ring remain non-bonded and are called as dangling bonds. The relaxation breaks the 3Dh symmetry of the system and the W atom shifts towards one of the carbon atoms, as depicted in As demonstrated in the ab-initio molecular dynamic (MD) simulations using Nose-Hoover heat bath schemeTo check the stability of W adsorbed TVF graphene system, we also performed finite temperature How to cite this article: Kumar, P. et al. Tunable magnetism in metal adsorbed fluorinated nanoporous graphene. Sci. Rep.6, 31841; doi: 10.1038/srep31841 (2016).


Graphene monolayers are known to display domains of anisotropic friction with twofold symmetry and anisotropy exceeding 200%. This anisotropy has been thought to originate from periodic nanoscale ripples in the graphene sheet, which enhance puckering around a sliding asperity to a degree determined by the sliding direction. Here we demonstrate that these frictional domains derive not from structural features in the graphene but from self-assembly of environmental adsorbates into a highly regular superlattice of stripes with period 4–6 nm. The stripes and resulting frictional domains appear on monolayer and multilayer graphene on a variety of substrates, as well as on exfoliated flakes of hexagonal boron nitride. We show that the stripe-superlattices can be reproducibly and reversibly manipulated with submicrometre precision using a scanning probe microscope, allowing us to create arbitrary arrangements of frictional domains within a single flake. Our results suggest a revised understanding of the anisotropic friction observed on graphene and bulk graphite in terms of adsorbates. Graphene can exhibit pronounced frictional anisotropy, which was thought to arise because of nanoscale ripples. Here, the authors provide evidence that this effect could instead be a result of adsorbates that self-assemble into a highly regular superlattice of stripes with a period of four to six nanometres. Nanometre-scale surface textures with long-range order often give rise to pronounced frictional anisotropy. These textures sometimes originate from crystal structures: periodic tetrahedral reversals in the antigorite lattice create nanoscale surface corrugations, which generate the anisotropic friction that governs certain seismic processes45From a technological standpoint, nanometre-scale systems with such multistability are appealing platforms for switches or memories. Bistable states in redox centresIn this study, we identify a friction-producing nanotexture that naturally forms on graphene exposed to laboratory air and exploit its multistability to hysteretically switch friction with submicrometre precision. Using high-resolution atomic force microscopy (AFM), we directly image a superlattice of nanoscale stripes on exfoliated graphene and we show that this striped nanotexture produces the anisotropic friction previously observed13141617To image friction, we measure the deflection (diving board motion) and torsion  of a scanned AFM cantilever in light contact with the sample. The deflection signal primarily contains topographic information, while the meaning of the torsion signal depends on scan direction. For lateral scanning  without change in stripe period and with minor change in magnitude of frictional anisotropy  often minimally affects the frictional domains, but scanning at high normal force (30 nN) reproducibly reorients the domains  and highly oriented pyrolitic graphite  and observed no differences in superlattice phenomena between samples produced using different graphite sources or tapes. For hBN exfoliation, we used bulk crystals provided by Kenji Watanabe and Takashi Taniguchi. We also prepared graphene flakes on other substrates  under ambient conditions (40–60% relative humidity) on bstrates , includi−1), to below 100 °C under the same flow of oxygen and argon.We prepared epitaxial graphene heterostructures on oxidized silicon substrates by mechanical exfoliation of hBN followed by graphene growth at 500 °C by a remote plasma-enhanced chemical vapour deposition process described previously−1. We warmed up the samples under various atmospheres including moderate vacuum, helium gas or nitrogen gas; in all of these cases (over ten different samples cycled in the dilution refrigerator or PPMS) we found stripes on every flake or heterostructure  that we checked.We found stripes to appear on our samples after thermal cycling to liquid nitrogen temperatures or below using a variety of methods. Most commonly, and specifically for the sample shown in The epitaxial heterostructure in Q of 400. See All images shown in −1. See −1, whereas for erasing we used scan rates ∼300 μm s−1.For measurements in contact mode, we used silicon probes (MikroMasch HQ:NSC19/Al BS-15) with a nominal tip radius of 8 nm and a typical resonant frequency of 65 kHz. We used a normal force setpoint of 1 nN for all friction and transverse force imaging scans shown, with scan rates ∼10 μm s2.When imaging friction or transverse force, we collected torsion data for both forward-moving and backward-moving scans. To eliminate offsets in the friction and transverse force signals for −11 mbar). Samples were not baked in UHV before experiments. The sample stage was cooled by a copper braid attached to a cold sink held at low temperature by continuous flow of liquid nitrogen; by this method, we achieved a base temperature of 110 K. We used the same sharp probes as for ambient AFM (MikroMasch Hi'Res-C15/Cr-Au). In UHV, the cantilever Q reached 5,000, which significantly restricted scan speed for tapping mode; we therefore used on-resonance frequency-modulation mode, imaging at a typical frequency shift of −30 Hz. For all images, we applied a DC tip-sample bias to nullify the contact potential difference.To study stripe formation with changing temperature , we usedSTM measurements  were cargwyddion.net). All error bars reflect the full width at half maximum of the peaks in the fast Fourier transform; for instance, 12.0±0.5 nm means that the full width at half maximum of the peak maps to 1 nm in real space. The lateral scale of the Park XE-100 was calibrated by measuring the moiré period of graphene/hBN heterostructures grown by van der Waals epitaxy, in which the graphene and hBN lattices are nearly perfectly aligned, and defining this period  to be 13.6 nm. This definition corresponds to the assumption made in ahBN=0.25 nm and agraphene=ahBN/1.018. The lateral scale of the Omicron variable-temperature AFM was calibrated to the lateral scale of the Park XE-100 by measuring the moiré pattern of the same sample in both systems.All values quoted for moiré period and angular orientation are extracted from the fast Fourier transform of the AFM images. AFM images of all heterostructures described in this study are corrected for thermal drift by performing an affine transformation to produce regular moiré hexagons .Supplementary Figures 1-7, Supplementary Notes 1-8 and Supplementary References.Patterning frictional domains on monolayer graphene.


The high ON-state current of 0.8 mA/μm is enabled by a narrow (~0.3 eV) extrinsic band gap, while the smallness of the leakage current is due to an all-electrical doping of the source and drain contacts which suppresses the band tailing and trap-assisted tunneling.In a continuous search for the energy-efficient electronic switches, a great attention is focused on tunnel field-effect transistors (TFETs) demonstrating an abrupt dependence of the source-drain current on the gate voltage. Among all TFETs, those based on one-dimensional (1D) semiconductors exhibit the steepest current switching due to the singular density of states near the band edges, though the current in 1D structures is pretty low. In this paper, we propose a TFET based on 2D graphene bilayer which demonstrates a record steep subthreshold slope enabled by van Hove singularities in the density of states near the edges of conduction and valence bands. Our simulations show the accessibility of 3.5 × 10 Tunnel FETs (TFETs) with interband tunneling are among the principal candidates to meet this demand1d-dimensional TFET channel, the DoS scales with energy E above the band edge as Ed−2)/2/2(10812151920It is intuitive that the abrupt variations of electron and hole densities of states (DoS) near the band edges further enhance the switching efficiency of TFETs2 substrates: the measurements of infrared absorption27583031In this paper, we theoretically demonstrate that graphene bilayer (GBL) represents an ideal platform for the low-voltage tunnel switches due to its peculiar ‘mexican hat’ band structure of GBL formed under transverse electric field22μm is accessible due to the low extrinsic band gap of GBL (~0.3 eV) and large DoS far above the band edges.The advantage of graphene bilayer TFETs over those based on 2d materials with parabolic bands in terms of switching steepness can be illustrated by n- and p-types.Although a number of GBL transistors have been proposed33342 layer playing the role of back gate oxide and substrate for graphene bilayer. Alternatively, the SiO2 layer can be replaced with hexagonal boron nitride (hBN) possessing a small (~1010 cm−2) density of residual charged impuritiesκ dielectric  covers the graphene channel, and the top metal gates are formed above. The side gates near the source and drain contacts induce large densities of holes and electrons, respectively, which also leads to the formation of an abrupt tunnel junction and energy barriers , we choose them to be The fabrication of the device structure in dE in the energy scale, the electrons available for tunneling in graphene bilayer occupy a ring in the momentum space  − fc(E) over the momentum space d2p = 2dp⊥dp||A rigorous expression for the tunnel current density involves an integral of the single-particle velocity gs gv = 4 is the spin-valley degeneracy factor in graphene, pmax(E) is the maximum transverse momentum of electron at a given energy E, pmax(E) = min{pc(E), pv(E)}, where pc(E) and pv(E) are the inverse functions to the electron dispersion in the conduction and valence bands. The limits of integration over energy are the conduction band edge in the channel, Ec, and the valence band edge in the source, Ev. The factor of two before the quasi-classical barrier transparency comes from the presence of two turning points with zero group velocity in the GBL dispersion at which an electron attempts to tunnel.Here, pmin  is the imaginary part of electron momentum evaluated at the midgap, and l is the length of the classically forbidden region (tunneling path length). The latter is given by p⊥ < pmin, and l = 2E(p⊥)/eF for p⊥ > pmin, where F is the electric field at the junction found from the solution of Poisson’s equation, and where Im J(VG)–characteristics of graphene bilayer TFET at different drain bias VD are shown in VG, in agreement with the simple density-of-states arguments and J(VG)-curve slightly increases due to the sensitivity of the tunnel barrier transparency to the junction field. The subthreshold slope at VG = Vth reaches (20 μV/dec)−1 and is limited by the small thermionic current μm and the gate leakage current μm. About 100 mV below the threshold, the ambipolar leakage at the drain tunnel junction becomes pronounced; this can be, however, minimized by placing the drain doping gate at large distance from the control gate.The calculated room-temperature p+ − n+ tunnel diode between source and channel. The emerging negative differential resistance is due to the dependence of the band edges in the channel on the amount of injected carriers: at high electron density, the bands in the channel are lifted upwards, which reduces the source-channel band overlap and switches the tunneling off.The drain characteristics of graphene bilayer TFET shown in VS required to switch the transistor between the ON- and OFF-states. Considering the current at VG = 0 V as the ON-state current (JON = 0.8 mA/μm in VD = 0.15 V), and the leakage current as the OFF-state current (JON/JOFF = 3.5 × 104), we have obtained VS = 150 mV. In a conventional MOSFET, the gate voltage swing VS ≥ 285 mV is required to achieve the same current switching ratio. The average subthreshold slope of our TFET over 4.5 decades of current is 33 (mV/dec)−1. With this characteristic, it outperforms all sub-thermal tunnel switches2/germanium junction with a similar value of the average subthrehold slope was demonstratedμA/μm leaves much to be desired.For low-power applications, the maximization of the highest subthreshold slope is not as important as minimization of the supply voltage I60–figure of merit−1. While the best I60 reported to date equals 6 nA/μm , while in the 2D structures based on III–V materials being narrow-gap in the bulk, the gap value increases significantly due to the quantum confinementThe unique characteristics of GBL TFET surpassing the existing TFETs are enabled by the three factors. First of all, it is the small extrinsic band gap . At 150 mV gate voltage above the threshold, the current density in graphene bilayer exceeds 15 times that in a parabolic-band material. The factor of two is due to the valley degeneracy absent in III-V’s, another factor of two is due to the tunneling at two turning points of the ‘Mexican hat’ dispersion, and the remainder of 3.5 is due to the finiteness of electron momentum at the edge of the ‘Mexican hat’.where The steep switching of the tunnel current by the gate voltage can be masked by the leakage to the gates, band-tail and trap-assisted tunneling192038ρ(E) in the presence of fluctuating potential by integrating the singular ‘bare’ DoS ρ0 over the probabilities of voltage fluctuations37The main reason for the band tailing comes from the fluctuations of electric potential produced by the random charged defects or dopantsV2〉 is the root-mean-square amplitude of the voltage fluctuations proportional to the impurity density ni. The calculated energy dependencies of the ‘smeared’ DoS are shown in ni = 4 × 1013 cm−2, the conduction and valence bands almost merge together, which would result in a poor OFF-state, nothing to say about high switching steepness. A slight peak in the DoS near the band bottom becomes noticeable already at impurity density of 5 × 1012 cm−2 which corresponds to the low-quality graphene on SiO2 substrates. In graphene samples on a high-quality SiO210 cm−2δε ≈ 20 meV. Already for relatively small gate voltages, VG − Vth > δε/e, these corrections are irrelevant and the linearity of the J(VG)–characteristic holds.where 〈κ materials, zirconium oxide (κ ≈ 25) looks as an optimal solution for the GBL TEFT due to the large band offset with respect to graphene (Ub = 2.9 eVmt ≈ 0.3m0ne(h) into the metal gate to be .where J(VG) curve in the proposed FET reaches the maximum of (20 μV/dec)−1, while only 150 mV gate voltage swing is required to change the current density from JON ≈ 1 mA/μm down to JOFF ≈ 2 × 10−5 mA/μm. As a matter of fact, the effects of singular DoS on the interband tunneling are possible just in the TFET structures with an all-electrical doping, where the effects of band tailing and trap-assisted tunneling are minimized.We have proposed and substantiated the operation of a graphene bilayer TFET exploiting the van Hove singularities in the density of states near the band edges. The presence of these singularities leads to the increased steepness of the gate characteristics and to the high ON-state current as well. The subthreshold slope of Such steep switching in the lateral TFETs based on 2d materials is possible if only the van Hove singularities are present both at the top of the valence and the bottom of the conduction band. This property is unique to the graphene bilayer and is absent in other 2d materials , where a ‘Mexican hat’ structure is formed in one of the bands due to the spin-orbit couplingp+ − n+ tunnel junctionsξn and ξp are the electron and hole Fermi energies in the n+ and p+-doped regions (see I(V)-curves. It is worth noting that a widely used phenomenological model of tunneling proposed by EsakiI(V)-curve. In such model, the current reaches its maximum at eV = ξn + ξp and then drops abruptly (I(V) curves are not observed in the experiments, which speaks in favor of our rigorous model of tunneling.At present, it is challenging to quantitatively compare the results our model to the experimental data, which are limited to the characteristics of graphene bilayer Esaki-type The modeling of GBL TFET is based on the self-consistent determination of carrier density and band structure under fixed gate voltagesThe effect of charged impurities present in the substrate on the singular density of states in graphene bilayer is evaluated with Kane’s quasi-classical model of band tailsThe gate leakage current is estimated with a quantum-mechanical model of graphene bilayer tunnel coupled to the continuum of delocalized states in the metal gate. The model is presented in How to cite this article: Alymov, G. et al. Abrupt current switching in graphene bilayer tunnel transistors enabled by van Hove singularities. Sci. Rep.6, 24654; doi: 10.1038/srep24654 (2016).


Drosophila development.Smaug, a protein repressing translation and inducing mRNA decay, directly controls an unexpectedly large number of maternal mRNAs driving early http://genomebiology.com/2014/15/1/R4See related research,  Drosophila protein Smaug. In this issue of Genome Biology, Chen et al. [Regulation of translation and mRNA stability is a key aspect of early metazoan development. One of the best studied factors involved in these processes is the n et al.  report tDuring the first few cell divisions in animal development, the embryo’s genome remains silent. Development relies entirely on maternal RNA, a reservoir of RNA, including mRNA, copied from the mother’s genome during oogenesis and deposited in the developing oocyte, and protein synthesis is regulated exclusively at the levels of mRNA translation, stability and localization. In a process termed maternal-to-zygotic transition (MZT), control of development is then transferred to the zygotic genome. MZT obviously depends upon activation of the zygotic genome, but destruction of a large fraction of maternal RNA is also required. One reason seems to be that re-expression of specific genes from the zygotic genome can be limited to certain cells or regions of the embryo and thus, together with localization or localized destruction of maternal mRNA, contributes to differentiation. MZT ends with the first morphological alterations that depend on zygotic transcription.Drosophila, the first 13 cycles of genome duplication and nuclear division are rapid and synchronous. As these nuclear divisions are not accompanied by cell divisions, a syncytium  results. With the beginning of the much slower 14th division cycle, approximately two and a half hours after fertilization, cell membranes form around the nuclei, which have arranged themselves as a monolayer at the periphery of the embryo. This transition from the syncytial to the cellular blastoderm marks the end of the MZT, while zygotic genome activation begins already around cell cycle 10. The maternal mRNA present before this stage represents about 55% of all protein-coding genes; that is, 6,000 or more transcripts [In the development of nscripts -4. Amongnscripts -4. At lenanos (nos) transcript, which encodes the protein directing the development of the posterior end of the embryo. The majority of the nos message is distributed uniformly throughout the embryo, remains translationally silent, and is degraded during the first 2.5 h of development. A small fraction of nos mRNA, however, which is localized in the germ plasm at the posterior end, escapes repression and destruction, providing the local source of Nanos protein that is essential for posterior patterning. Thus, degradation of maternal mRNA is not just mindless wholesale destruction, but a very finely tuned process that is interwoven with translational control and mRNA localization.One of the best-studied maternal mRNAs degraded through the maternal pathway is the nos mRNA is the protein Smaug, which binds the nos transcript through two Smaug recognition elements (SREs) residing in the 3’ UTR. In contrast to Bilbo Baggins’ eponymous adversary, Drosophila Smaug causes the destruction of the treasure it is sitting on, being responsible for both the translational repression and degradation of nos mRNA. Together with the piRNA machinery [smaug (smg) mutants [nos manifests itself later in development, the early phenotype of smg mutants indicates that there must be other important targets. The only other Smaug-regulated mRNA that has been studied in detail, Hsp83 RNA  [smg mutants.Among the regulators of achinery , Smaug rachinery ,8 and adachinery . Synthes mutants . As a dey Smaug) , is unliet al. [smg and wild-type control embryos and analyzed them by microarrays. The experiments resulted in a high-confidence set of 342 mRNAs that were more strongly polysome-associated in smg mutants, implying their Smaug-dependent repression in the wild-type. Using a statistical analysis, the authors extrapolated that as many as 3,000 transcripts, about one-half of the total number of mRNAs detectable in the early embryo, may be under translational control by Smaug. However, the two well-known Smaug targets, Hsp83 and nos, were not among them. This was not unexpected: Hsp83 RNA is destabilized but not repressed by Smaug, and nos mRNA has been reported (and was confirmed in this study) to be associated with polysomes, even though translation products are not detectable. This is an important caveat, showing that the presence of an mRNA in polysomal fractions does not exclude regulation by Smaug.So how many and what kind of mRNAs are part of Smaug’s treasure? Microarray analyses have shown that at least 20% of all maternal mRNAs are substrates of the maternal degradation pathway . Surpriset al.  examinedet al. identified transcripts of 339 genes that are bound by Smaug. By means of a recently developed computational method, they then scanned the Smaug-bound RNAs and the high-confidence set of 342 translationally repressed RNAs for the presence of potential SREs, stem-loop structures with the loop sequence CNGGN0-4. Both in the bound and in the regulated RNAs, SREs were predicted with a 10-fold higher probability than in non-bound and non-regulated RNAs, respectively. In addition, the selected RNAs contained variant SRE sequences with probabilities matching the binding specificity of Smaug determined in earlier biochemical experiments: high-affinity sites were more enriched than low-affinity sites. These results come as no surprise with regard to the Smaug-bound RNAs; they merely support the reliability of their identification. However, a similar degree of enrichment of the SREs in the translationally repressed RNAs suggests that a large fraction at least of the high-confidence RNAs are direct targets of Smaug. By analyzing data from one of their previous studies [et al. found high degrees of overlap: two-thirds of the Smaug-bound RNAs were also destabilized by the protein, and three-quarters of the binders were also translationally repressed. Similarly, the destabilized and repressed RNAs overlapped to a large extent.How many of the mRNAs regulated by Smaug are direct targets? Using immunoprecipitation of the protein followed by microarray analysis of associated RNA (RIP-chip), Chen et al. concluded that a large fraction of the regulated RNAs are in fact direct targets of Smaug that escaped detection by RIP-chip.What about those RNAs that are destabilized or repressed but were not identified as Smaug ligands? These could be regulated indirectly by Smaug or they could be false-negatives in the RIP-chip experiments. From a significant enrichment of SREs in these classes of RNAs, Chen smg mutants.As the number of Smaug-regulated mRNAs is large, they code for proteins involved in many aspects of biology. Messenger RNAs localized to the posterior pole were prominent among the Smaug targets, as were those encoding proteins involved in the regulation of DNA replication and transcription. More unexpectedly, the list of targets predicts regulatory effects of Smaug on protein folding and proteasome-dependent protein degradation, lipid droplets and even basic energy metabolism. With regard to metabolism, the majority of glycolytic enzymes were identified as potential Smaug targets, and enzyme assays confirmed a modest increase in hexokinase and phosphofructokinase activity in Drosophila embryo seem to be regulated directly by Smaug. Destruction of the protein during cell cycle 14 is presumably necessary to prevent degradation of zygotic transcripts, as many are derived from the same genes as maternal mRNAs. Since Smaug is necessary for zygotic genome activation, including, for example, the synthesis of microRNAs required for the zygotic pathway(s) of maternal mRNA decay, many additional RNAs are controlled indirectly by Smaug. The new data also suggest that Smaug targets are typically both destabilized and translationally repressed. The poly(A) tail is a potent stimulator of translation, so recruitment of the CCR4-NOT deadenylase by Smaug might be sufficient to cause both destabilization and repression. However, in the case of nos, translational repression goes beyond deadenylation [In summary, an unexpectedly large number of mRNAs in the early nylation . The mecMZT: Maternal-to-zygotic transition; RIP-chip: RNA-binding protein immunoprecipitation followed by microarray analysis; SRE: Smaug recognition element.The authors declare that they have no competing interests.


Dear Editor,PD-L1, also known as CD274, plays a vital role in tumor cell related immune escape. It can be expressed on the cell surface of many solid tumors , and tumor associated macrophages (TAM) are recruited by different pathways  and the mutant U5A cells (ifnar2-/-) that lack of type I interferon receptor subunit ifnar2, we found that IFN-α induced PD-L1 in 2fTGH cells, but failed to induce PD-L1 in U5A cells . These data suggested that the induction of PD-L1 by co-culture supernatant may be interferon receptor dependent. To test this hypothesis, anti-IFNAR1 antibody was added to the co-culture medium. We found that the neutralizing antibody reduced splenocyte-induced PD-L1 expression in B16F10 cells  in other normal tissues Supplementary material 2 (PDF 102 kb)Below is the link to the electronic supplementary material.