Fractional quantum Hall effect (FQHE) appeared at 1.7 K after encapsulation by h-BN, yielding ultra-high mobility of ~280,000 cm2 V−1 s−1. Integrated wafer-scale graphene thermal emitters exhibited significant broadband emission in near-infrared (NIR) spectrum. Overall, the proposed methodology is promising for future integration of wafer-scale 2D materials in advanced electronics and optoelectronics.The integration of large-scale two-dimensional (2D) materials onto semiconductor wafers is highly desirable for advanced electronic devices, but challenges such as transfer-related crack, contamination, wrinkle and doping remain. Here, we developed a generic method by gradient surface energy modulation, leading to a reliable adhesion and release of graphene onto target wafers. The as-obtained wafer-scale graphene exhibited a damage-free, clean, and ultra-flat surface with negligible doping, resulting in uniform sheet resistance with only ~6% deviation. The as-transferred graphene on SiO Defect-free integration of 2D materials onto semiconductor wafers is desired to implement heterogeneous electronic devices. Here, the authors report a method to transfer high-quality graphene on target wafers via gradient surface energy modulation, leading to improved structural and electronic properties. Note that, an essential prerequisite is transferring 2D materials from their growth substrates to industrial wafers. Yet, a significant gap still exists in transfer method, which frustrates the recent progress in wafer-scale single-crystal growth of 2D materials10. Conventionally, wet transfer methods commonly use poly(methyl methacrylate) (PMMA) film as a transfer medium to support 2D materials when separated from the growth substrate and scooped from the liquid surface to a target substrate12. For graphene, the wet transfer methods may significantly degrade its properties due to introduced cracks, wrinkles, polymer contaminations, and water doping by water adsorptions on the graphene surface18. These factors act as extra scattering centers to limit carrier mobility and decrease device performance. To overcome these issues, previous attempts have shown that the optimization of PMMA and replacement of PMMA with small molecules or other polymers would facilitate clean graphene transfer27, conformal contact with the target substrate may reduce the formation of cracks and wrinkles31, and the development of dry transfer methods may diminish water doping by preventing the submersion of target substrate in liquids39. However, no method has so far entirely solved these issues, and most approaches are not compatible with high-volume semiconductor technology at the wafer level41.The integration of two-dimensional (2D) materials into current silicon technology may embed high mobility, dangling band-free interface, atomic-scale channel size into practical electronic and optoelectronic devices43. In this case, the higher surface energy of a target substrate, the better it serves as the thin film ‘acceptor’ due to the better wetting and larger adhesion strength at interface44. Thus, the surface energies of transfer medium and target substrates should be engineered to ensure reliable adhesion and release45, critical features for securing the wafer-scale 2D materials integration46. As a result, the gradient surface energy (GSE) modulation approach conduced to the integration of 4-inch single-crystal ultra-flat graphene onto silicon wafers. The transferred graphene wafer maintained its flatness, exhibiting intact and clean surfaces with negligible water doping. Consequently, the resulting wafer-scale graphene illustrated a uniform sheet resistance of only ~6% deviation over a 4-inch area. The as-transferred graphene on SiO2/Si exhibited outstanding electrical performances with smaller Dirac points and much higher carrier mobility  at room temperature when compared to conventional wet transfer (~2000 cm2 V−1 s−1). The quantum Hall effect (QHE) was also observed at room temperature in graphene transferred on SiO2/Si, and fractional quantum Hall effect (FQHE) was recorded at 1.7 K in transferred graphene encapsulated by h-BN with high mobility reaching ~280,000 cm2 V−1 s−1. Furthermore, the integrated thermal emitter arrays fabricated on a 4-inch graphene/silicon wafer showed significant emission with a broad spectrum in NIR region.Here, we designed a multi-functional tri-layer transfer medium with gradient surface energy distribution, according to the thin-film adhesion theory that transfer of thin film from one layer to another layer is mainly dominated by the difference in surface energy of each layerTo minimize the adverse effects of grain boundaries and wrinkles on the charge carrier mobility, single-crystal ultra-flat graphene films were grown on 4-inch Cu111)/sapphire wafers and the details can be found in Methods. A multi-functional tri-layer transfer medium was designed to support the wafer-scale graphene during transfer  and A (the adhesive), respectively; and γAB is the interface energy between phase A and B. The fracture strength σf of the interface is related to λAB by:Km is a function of the mechanical properties. Considering that γAB ≪γA, the fracture strength σf is proportional to the surface energy ratio of the adherend to the adhesive (γB /γA).Most importantly, the surface energy gradually decreased from the destination SiOyer Fig. b, c, who2/Si (γ1) was much larger than that of graphene/borneol (γ2), the complete wetting and reliable adhesion of graphene to the SiO2/Si wafer was facilitated  that is close to PMMA (γ3) ensured the damage-free release of wafer-scale graphene onto SiO2/Si wafer  allowed successful integration of the 4-inch single-crystal graphene onto the SiO 22 Fig. , owing t 22 Fig. . In gene 22 Fig. –14. In t2/Si using the GSE strategy , whose standard deviation was only ~6% over the 4-inch wafer , resulting from the uneven distribution of cracks and contaminations introduced during the transfer21  and 2D band (ω2D) were extracted from the Raman spectra, and the correlation maps were plotted in Fig. ωG = 1582 cm-1, ω2D = 2677 cm-1), corresponding to neither doping nor strain47. The PMMA-transferred graphene films are often deeply p-doped when using wet transfer methods due to water doping at the interface21, leading to changes in the Fermi level of graphene and declined carrier mobility. As shown in Fig. 2/Si wafer experienced deeply p-doping. By comparison, GSE-transferred graphene on SiO2/Si wafer nearly experienced no p-doping and strain, thereby close to the intrinsic graphene  of transferred graphene were gathered in Fig. Γ2D of GSE-transferred graphene (~30 cm-1) was smaller than that of PMMA-transferred graphene (~40 cm-1), indicating GSE-transferred graphene with little random strain fluctuation and potentially high charge carrier mobility49.To examine the doping and strain level of GSE-transferred graphene, the peak positions of G band  was an order of magnitude higher than that of GSE-transferred graphene, showing a relatively low μ of 1930 cm2 V−1 s−1. Accordingly, the average hole mobility of GSE-transferred graphene reached ~6000 cm2 V−1 s−1 . In addition, the mobility of wet-transferred graphene by only using PMMA/borneol as the transfer medium is ~3950 cm2 V−1 s−1, much lower than that of GSE-transferred graphene, which indicate the water-adsorption-induced doping will significantly degrade the electrical properties of graphene  to measure the field-effect carrier mobility of graphene on SiOs−1 Fig. , comparas−1 Fig. , a value2/Si extracted from the Hall effect measurement was 9500 cm2 V−1 s−1 at room temperature. By measuring the Hall resistance (Rxy) and magnetoresistance (Rxx) at different temperatures  and Hall (Rxy) magnetoresistance measurements at 1.7 K with a fixed magnetic field (B = 8.5 T), quantized Hall platform and magnetoresistance zeros were observed at all possible integer fillings of n = 0 and n = 1 Landau Levels (LLs) h/e2 with minimum Rxx at fractional filling factors υ = 2/3 and 4/3 in n = 0 LL, as well as υ = 7/3, 8/3, 10/3, and 11/3 in n = 1 LL were observed, confirming the fractional quantum Hall effect (FQHE) feature. The back gate (Vg) dependent resistant measurements at the different magnetic fields on h-BN-encapsulated transferred graphene Hall-bar device were then performed to resolve the broken Landau level degeneracy and FQHE in the Landau fan diagram  flake was employed to pick up and encapsulate the transferred graphene from SiOate Fig.  to fabriate Fig. . The Halene Fig. . Accordiene Fig. , the extLs) Fig. . Furtherram Fig. . The obs55. As shown in Fig. I through graphene thermal emitter device with narrow constrictions led to enhancements in the Joule heating, as well as localized light emission of graphene at the middle of the constriction56. As shown in Fig. Graphene-based silicon-chip blackbody emitters in the near-infrared region, including telecommunication wavelength hold promise in applications in on-Si-chip, small footprint, and high-speed emitters of highly integrated optoelectronics and silicon photonics2O3 layer was deposited on the graphene before voltage application  camera under vacuum at power density P = 3.0 kW cm−2 , allowing the observation of quantum Hall effect (QHE) at room temperature. Fractional quantum Hall effect (FQHE) also appeared at 1.7 K in the transferred graphene encapsulated by h-BN, with mobility reaching ~280,000 cm2 V−1 s−1. Furthermore, integrated thermal emitter arrays with the 4-inch graphene/silicon wafer illustrated significant emission with a broad spectrum in NIR region. In sum, the proposed methodology can be used as a universal approach for the integration of other intrinsic 2D materials, such as h-BN and 2D MoS2 on the wafer level, paving the way for the development of integrated high-performance electronics and optoelectronics.The transferred graphene enhanced the electrical performance due to the negligible doping level and much fewer scattering centers when compared to conventional PMMA-transferred graphene. The Hall-bar devices fabricated with graphene on SiOFurthermore, our GSE transfer method was successfully reproduced by an independent research group (as shown in the Peer Review file), demonstrating the robust reproducibility of GSE method in the transfer of large-area 2D materials.Ra < 0.2 nm) using a sputtering system (ULVAC QAM-4W). The deposition rate was 0.3 nm s-1 with a power of 300 W at 8 × 10−4 Torr, and a ~500-nm-thick Cu film was obtained on sapphire after 30 min. After that, the Cu/sapphire was then annealed at 1000 °C with 2000 sccm Ar and 10 sccm H2 for 2 h at atmospheric pressure in a homemade annealing furnace to obtain Cu(111) single crystal.The Cu(111) film was deposited on a single-crystal sapphire  and 40 sccm H2 was introduced for graphene growth. Fully covered graphene was obtained after ~2 h, and CH4 gas flow was turned off while the sample cooled to room temperature.The 4-inch Cu(111)/sapphire was heated to 1000 °C with 2000 sccm Ar at atmospheric pressure, then 40 sccm CH59. The heating and annealing processes were carried out under 500 sccm H2 and 100 sccm Ar.Commercially available polycrystalline Cu foils were placed in a homemade annealing furnace equipped with a 6-inch quartz tube. Three heating zones were asynchronously heated up from room temperature to target temperatures  in 40 min and kept for 1 h, which leads to the formation of a temperature gradient through the Cu foils (about 2 °C/cm) and promotes the anomalous Cu grain growth2 for 30 min. Then the growth of graphene was initialed by the introduction of 1 sccm CH4. Fully covered graphene was produced after 1-h growth. Finally, the system was cooled down to room temperature.The rough graphene was grown on Cu(111) foil using a low-pressure CVD system. Firstly, The Cu(111) foil was heated to 1000 °C with 500 sccm Ar, followed by annealing with 500 sccm H4S2O8 . After washing with deionized water to remove residual etchant, the PMMA/Borneol/graphene film was attached to the Si substrates, and the PDMS  was laminated on the surface of PMMA after the graphene was dried using the commercial laminator . The composite film of PDMS/PMMA/Borneol/Graphene was detached from Si substrate in water because the water will intercalate into the interface of graphene and Si substrate due to the hydrophilic surface of SiO2/Si , and the PDMS was exfoliated from the PMMA at 180 °C in 5 min. To further enhance the interaction of graphene and substrate, we baked the graphene at 180 °C for 3 h before removing PMMA and borneol with the vapor of hot acetone , leaving the monolayer graphene on target substrate.A step-by-step protocol is available as a Supplementary Protocol in The detachment of graphene from Cu(111)/sapphire can also be achieved by electrochemical bubbling delamination when PDMS/PMMA/borneol was used as a composite support layer, which reduced the time of transfer of graphene and preserved the Cu(111)/sapphire wafer.4S2O8. After washing with deionized water to remove residual etchant, the PMMA/graphene film was attached to the SiO2/Si substrates at the surface of water. To further enhance the interaction of graphene and SiO2/Si, the PMMA/graphene/SiO2/Si was baked at 180 °C for 3 h before removing PMMA with the vapor of hot acetone, leaving the monolayer graphene on SiO2/Si.First, a layer of PMMA was spin-coated on graphene/Cu(111)/sapphire or graphene/Cu(111) foil at 1000 rpm for 1 min, and baked at 170 °C for 3 min. After that, PMMA/graphene film was detached from growth substrate by etching the Cu film in an aqueous solution of 1 mol/L (NH)Ead, short chain of PMMA (C22H38O8) terminated with -CH3 without introducing additional polarity of the polymer was used in our first-principles calculations. Both borneol and PMMA short chain were placed on the surface of graphene with a ~3.3 A distance, measured from the center plane of molecule to the plane of graphene. The adsorption energy is defined as:To evaluate the adsorption energies of borneol and PMMA on graphene surface a = 24.56 Å, b = 24.56 Å, c = 21.70 Å. The 11 × 11 supercell of graphene was chosen for all the calculations. The PBE with the optB86b-vdW correction functional was used to determine the total energies for each structure, taking into account the Van der Waals interaction between polymer and graphene.All the structures were optimized using the density functional theory (DFT) implemented in VASP. To keep consistency, all the periodic cells are of the same size with 2/Si with marks for alignment. Electron-beam lithography and plasma etching with air (Diener Pico) were employed to pattern graphene into a Hall-bar geometry. After a PMMA mask (PMMA 950 K A4 @ 4000 rpm) was patterned by EBL, Pd/Au (5/40 nm) electrodes were deposited by thermal evaporation , followed by a standard lift-off technique. Limited by the stage size of electron beam lithography, we fabricated 42 graphene Hall-bar devices on 10 slices from the same 4-inch GSE-transferred graphene wafer and 18 graphene Hall-bar devices on 5 slices from another 4-inch PMMA-transferred graphene wafer. The area of each slice is 1 × 1 cm2.Hall-bar devices were fabricated on the graphene/SiOElectrical transport at room temperature was determined using a vacuum-probe station (Lakeshore CRX-VF) with a semiconductor characterization system . Electrical transport at low temperature and magneto-transport data were acquired using a low temperature and strong magnetic electronic measurement system . Device resistance was measured using a lock-in amplifier (Stanford Research 830) with an AC driving current of 0.1–1 μA.2O3 layer was grown by atomic layer deposition method. The Raman spectroscopy of graphene were measured by a confocal microRaman spectroscope  with a solid-state laser at 532 nm. The Raman signals were dispersed by a grating of 1800 lines/mm ensuring a high spectral resolution of ~1.0 cm−1. The spectrometer was calibrated by a quartz tungsten lamb at temperature of 3200 K before measurement. The thermal emission spectra were recorded using a spectrometer and a liquid nitrogen cooled Si CCD with a 50× objective lens. The radiation signal was acquired using an infrared camera. All measurements were carried out at room temperature and in vacuum.The arrays of graphene thermal emitters were fabricated by UV lithography machine, and AlOptical microscopy was conducted on a Nikon Olympus LV100ND. Raman spectra of transferred graphene were collected on a Horiba LabRAM HR Evolution Raman system using a 532 nm laser with a laser spot size 1 μm, and a 100x objective and 600 lines/mm grating were used to collect the Raman signal.The contact angle images of tested liquids on different surfaces were obtained using Biolin THETA optical tensiometer, the volume of the droplet on surface was controlled at about 4 μL.SEM images were obtained on an FEI Quattro S field-emission scanning electron microscope using a 5 kV acceleration voltage. The aberration-corrected STEM images of graphene were performed using a Nion U-HERMS200 microscope at 60 kV.The AFM morphology images were collected on a Brucker Dimension Icon using the ScanAsyst mode.The sheet resistances of transferred graphene on 4-inch wafers were collected by CDE ResMap 178 four-probe resistance tester.Supplementary InformationPeer Review FileSupplementary Movie 1Supplementary Movie 2


Highly flexible, electrically conductive freestanding graphene membranes hold great promise for vibration-based applications. This study focuses on their integration into mainstream semiconductor manufacturing methods. We designed a two-mask lithography process that creates an array of freestanding graphene-based variable capacitors on 100 mm silicon wafers. The first mask forms long trenches terminated by square wells featuring cone-shaped tips at their centers. The second mask fabricates metal traces from each tip to its contact pad along the trench and a second contact pad opposite the square well. A graphene membrane is then suspended over the square well to form a variable capacitor. The same capacitor structures were also built on 5 mm by 5 mm bare dies containing an integrated circuit underneath. We used atomic force microscopy, optical microscopy, and capacitance measurements in time to characterize the samples. Developing technologies related to clean energy, harvesting energy, and the conversion and storage of energy has become a high priority in recent years ,2,3. EneFlexible suspended membranes have enabled a wide range of technologies, from acoustic wave generators and receivers ,9,10,11 For example, single-layer graphene was suspended over a lightweight, flexible, transparent, and conductive bilayer composite of polyetherimide to create an energy-efficient, high-performance nanoelectromechanical transducer . GraphenFreestanding graphene membranes also show promise as a source of vibrational energy for low-power electronics ,32,33,34A graphene-based variable capacitor connected to an energy harvesting circuit is shown as a schematic in The graphene is suspended above a fixed metal electrode to form the variable capacitor. As the graphene membrane vibrates up and down, the distance between graphene and electrode changes, which causes the capacitance to change in time. As the capacitance varies in time for a fixed voltage, electrical charge is forced on and off the graphene membrane. This comes from the equation q(t) = C(t) V, where q is the charge, C is the varying capacitance, and V is the bias voltage. When the charge flows clockwise, it passes through diode D1 and charges capacitor C1. When the charge flows counterclockwise, it moves against the bias voltage V, charges capacitor C2, then passes through diode D2. If the bias voltage source is a rechargeable battery, it will be charged during this half-cycle ,40.Even at a current level of nanoamps, this circuit was found to be 50% efficient when operated at its maximum output power . A recenFor this study, we fabricated an array of freestanding graphene variable capacitors on 100 mm silicon wafers. We used standard silicon fabrication processes, along with other well-established techniques developed by the semiconductor industry ,49,50,51For this study, we used low resistivity (1–10 Ω cm), 500-µm-thick, A buffered oxide etchant (5:1 with hydrofluoric acid)  cut the trench-well-tip structures into the silicon dioxide. Atomic force microscopy (AFM)  and optical microscopy  were used to characterize the etched surface morphology and the top of the wafer. The conductive paths and contact pads were created by depositing a thin Cr layer (5 nm), followed by a thicker Au layer (50–100 nm). AFM and optical microscopy were used to characterize these layers. Graphene, commercially grown on Ni, was used for the large-area graphene membrane transfer (graphene supermarket). A critical point dryer was used to aid in graphene membrane suspension.Mask 1 defines the position and size of the trench, well, and tip features, as shown in The shaded areas of the pattern were etched, while the white areas were protected from the etchant. We designed a square-shaped ring at the right end of the trench, shown in a zoomed-in view at the bottom of The steps for creating the trench, well, and tip feature using lithography are illustrated in 2 layer and baked at 180 °C for 5 min. Then, the lithographic Mask 1 was used during the exposure process to mark the pattern on the wafer. Once exposed, the pattern was developed for 30 s in n-amyl acetate, then 20 s in methyl isobutyl ketone (MIBK) , and finally rinsed with isopropyl alcohol (IPA)  to remove the exposed resist.First, a layer of photoresist AZ 5214  E or e-beam resist polymethyl methacrylate (PMMA) was spin-coated on the SiO2 material isotropically and undercuts the resist to form a tip, as illustrated in The wafer was then placed in a 5:1 buffered oxide etch containing hydrofluoric acid (HF) for 5 min at room temperature. This step etches the exposed SiOTo confirm if the wafer was successfully etched and the resist completely removed, optical microscope images were taken, as shown in Mask 2 defines the position and size of the conductive metal traces and electrical contact pads. The full wafer mask design is shown in The Mask 2 processing steps are illustrated in Optical microscopy and AFM images were used to characterize the wafer after completing the Mask 2 processing steps. An optical photograph of the full wafer is shown in We used commercially available multilayer graphene grown on nickel on a silicon chip . This stage of the process ensures that the graphene membrane covers the well over the tip, that it makes electrical contact with the graphene membrane contact pad, and that it does not make electrical contact with the tip contact pad. The graphene membrane is suspended over the array of tip features and does not contact any of them. The shape of the graphene membrane and its placement location for region B on unit 21 of the wafer is shown schematically as a rectangular green strip in the upper right corner of 3 etchant for 20 min to dissolve the nickel. The tape-PMMA-graphene stack was transferred to DI water to remove the FeCl3 solution. The tape was then removed from the PMMA-graphene stack, and the graphene membrane was placed on the desired region of the wafer. The entire wafer with the PMMA-graphene was then set at an angle for 10 min to dry in position (not shown). The PMMA was later removed by soaking the sample in acetone for 10 min. The sample was then quickly transferred to hexane. The liquid hexane was not allowed to air dry. Instead, the entire system was introduced into a critical point dryer (CPD), which dried the graphene-wafer system and assisted in the suspension of the graphene membrane over the tip features.The large-area graphene membrane transfer process is schematically illustrated in 3. The tape-PMMA-graphene was scooped out of the etchant, placed on our patterned wafer, and then set at an angle to dry. After using hexane and CPD, the graphene membrane was suspended over the tip well structures, as shown in the optical image in The photographs of the various graphene transfer steps are shown in 2 over the TSMC chip at low temperatures to avoid altering the integrated circuit. The TSMC chips were then run through the same three-step process discussed above. After Mask 1, Mask 2, and graphene membrane placement, an optical image of the TSMC chip was taken, as shown in In addition to developing the graphene membrane variable capacitor fabrication process on 100 mm silicon wafers, we also reproduced the process on a bare die containing an integrated circuit built by the Taiwan Semiconductor Manufacturing Corporation (TSMC) . The TSMC chip measures 5 mm by 5 mm and contains a rectifier amplifier circuit for energy harvesting. The top of the TSMC chip has bonding pads around the perimeter, as well as a 3 mm by 3 mm bonding pad in the center. The bonding pads are aluminum and are shown in We used a precision high-resolution capacitance meter (AH 2550A)  to measure the capacitance between the graphene membrane metal contact pad and the tip metal contact pad. A photograph of our setup is shown in The capacitance varied in time for the graphene-membrane variable capacitors that were fabricated on the 100 mm wafers. A typical result is shown in 2 with buffered HF for 5 min at room temperature. The conductive pathways and contact pads were created using the patterned deposition of gold. We performed large-area graphene membrane transfer over the tip regions. We used a critical point dryer to ensure that the graphene membrane was left freestanding over the tip feature. The graphene-tip feature forms a variable capacitor with the graphene membrane as the movable plate. Capacitance and resistance measurements taken from these devices confirmed that the graphene membrane was freestanding over the tip structure and was always moving. In the future, a new TSMC chip will be designed. We imagine it will measure 5 mm by 5 mm, have a central region for graphene that measures 3 mm by 3 mm, and contain 100 graphene variable capacitors. Overlaying the graphene on the chip will automatically connect it to the rectifying circuit below. As the graphene is driven by the ambient environment, the storage capacitors will be charged. A typical low-power application would be a battery replacement for reading a remote sensor and transmitting its value to another location.We described the design and fabrication of an array of graphene-based variable capacitors on both 100 mm silicon wafers and bare dies manufactured by TSMC. We provided a template for building a massive array of membrane devices in parallel with nearly 10,000 individually addressable membrane suspensions on one substrate. Our procedure is easy to follow and requires only two masks to complete. Photolithography or e-beam lithography can be used to pattern the wafers. Trench-well-tip features were created using an undercutting isotropic wet etch of SiO


N = 55) during a face-to-face interaction. We used functional-near infrared spectroscopy hyperscanning to measure dyads' brain activity and microcoded their turn-taking. We also measured infants’ inter-hemispheric connectivity as an index for brain maturity and later vocabulary size and attachment security as developmental outcomes potentially linked to turn-taking. The results showed that more frequent turn-taking was related to interpersonal neural synchrony, but the strength of the relation decreased over the course of the proto-conversation. Importantly, turn-taking was positively associated with infant brain maturity and later vocabulary size, but not with later attachment security. Taken together, these findings shed light on mechanisms facilitating preverbal turn-taking and stress the importance of emerging turn-taking for child brain and language development.Even before infants utter their first words, they engage in highly coordinated vocal exchanges with their caregivers. During these so-called proto-conversations, caregiver–infant dyads use a presumably universal communication structure—turn-taking, which has been linked to favourable developmental outcomes. However, little is known about potential mechanisms involved in early turn-taking. Previous research pointed to interpersonal synchronization of brain activity between adults and preschool-aged children during turn-taking. Here, we assessed caregivers and infants at 4–6 months of age (This article is part of a discussion meeting issue ‘Face2face: advancing the science of social interaction’. Across In early human ontogeny, infants as young as eight weeks of age actively engage in turn-taking in vocal interactions with their caregivers . These e (a)As turn-taking depends on precise temporal coordination, one key candidate underlying mechanism is the mutual entrainment and synchronization of endogenous neural oscillators in the brains of the conversation partners . AccordiImportantly, we know little about when the relation between interpersonal neural synchrony and turn-taking emerges during development. Gaining insights into the functional role of interpersonal neural synchrony is important as it could pave the way for interventions promoting neural synchrony and its related benefits ,24. Furt (b)As infants continue to partake in early proto-conversations, including turn-taking, they become more competent at turn-taking and increasingly initiate turn-taking sequences . We suggEarly turn-taking has been associated with developmental benefits in language processing and acquisition ,29. For Next to infants’ individual development, turn-taking in mother–infant proto-conversations is assumed to be one fundamental feature of interpersonal connectedness ,22 and t. 2 (a)N = 81) were excluded from the neural synchrony analysis due to early termination of the experiment (n = 15), not codable video/audio (n = 5), and bad functional near-infrared spectroscopy (fNIRS) signal quality (n = 6). Subsequent sample sizes were further decreased because parents either did not return the language development questionnaire (n = 27) or did not participate in the home visits to assess attachment (n = 23). Mothers were, on average, 33.35 years old , of European White origin, and highly educated (76% of mothers graduated with a university degree). Participants were recruited from the database of the Department of Developmental Psychology (Wiener Kinderstudien). Most of the registered families were recruited at Vienna General Hospital, and their children were added to the database after their parents gave their written consent. Mothers and infants received a small present for their participation. The local Ethics Committee approved the study (reference no. 00352).Fifty-five mother–infant dyads  were included in the final sample. Infants were all born healthy and full-term (after the 37th gestation week and with a birth weight of more than 2.500 g). Twenty-six additional dyads of the original sample Mothers and infants participated in three conditions: distal joint watching, proximal joint watching and free play. In the joint watching conditions, the infant was seated in a highchair  or in the mother's lap  and watched a calm aquarium video for 90 s. The order of distal and proximal joint watching conditions was counterbalanced. In the free play condition, mother and infant were instructed to freely play face-to-face, as they would at home, but without toys and without singing for five minutes. The free play condition always followed the two watching conditions. Only interpersonal synchrony data from the free play condition are reported here  (i)We used two NIRSport 8-8  devices in the tandem setting and simultaneously recorded concentration changes in oxy-haemoglobin (HbO) and deoxy-haemoglobin (HbR) in mother and infant. The 8 × 2 probe sets were attached to an electroencephalography cap with a 10–20 configuration . The probe sets over the left and right inferior frontal gyrus (IFG) surrounded F7 and F8, whereas the probes on the medial prefrontal area (mPFC) surrounded FP1 and FP2. These regions of interest were based on previous work involving adult–child interactions ,39. In eμMol) in HbO and HbR. HbR analyses are reported in the supplements.fNIRS measurements were processed using MATLAB-based functions derived from Homer 2 . Raw datWe assessed the relation between the fNIRS time series in each caregiver and infant using (Morlet) wavelet transform coherence (WTC) as a function of frequency and time . WTC is Using WTC, we assessed infants' intra-personal inter-hemispheric functional connectivity between homologous channels in the passive distal watching condition (as an age-appropriate resting phase). The frequency band of interest was determined to be 0.063 Hz–0.167 Hz (corresponding to 6–16 s), according to the potential infant HRF function , by visu (ii)κ = 0.98, infant vocalizations: κ = 0.78).To assess vocal turn-taking in the free play condition , tra (iii)The ELFRA-2  is a par (iv)r = 0.75, thus, an averaged AQS score was used in subsequent analyses. These AQS scores ranged between −1.0 and +1.0, with higher scores representing higher attachment security of the observed dyad.We used the Attachment Q-Sort (AQS ) to obse (v)All statistical analyses were calculated in RStudio . We used generalized linear mixed models (GLMM), generalized linear models (GLM), and linear models (LM) to analyse the hypothesized associations between turn-taking, interpersonal neural synchrony, inter-hemispheric functional connectivity, infant's language development and attachment.post-hoc analyses (emmeans) were applied to contrast factors. Multiple comparisons were corrected by using Tukey's honest significant difference. All continuous predictor variables were z-standardized, and distributions of residuals were visually inspected for each model. Models were estimated using maximum likelihood. Model fit was compared using a Chi-square test  of a GLMM with interval (1–5), the number of bidirectional turn-taking, response latencies, and region of interest (ROI: IFG versus lPFC versus mPFC) as fixed factors. We included the interaction between intervals, number of turns, and ROI. ROI was inserted as random slopes and dyads as random intercepts. Random slopes for interval and turn-taking did not lead to model convergence and were thus excluded. To further examine significant main and interaction effects, tio test ).Hypothesis 2: Turn-taking and infants' inter-hemispheric connectivity. We calculated two separate GLM including inter-hemispheric connectivity values as the response variable (assuming a Gaussian distribution and logit link). The first GLM tested infant response latencies, and number of infant-to-mother turns as the main effects. The second GLM tested the effects of mother-to-infant and infant-to-mother overlaps. Further turn-taking variables are considered in analyses reported in the supplements.Hypothesis 3: Infants’ expressive language abilities and turn-taking. Infants' vocabulary at 24 months assessed by the ELFRA questionnaire was entered as the response variable (assuming a Gaussian distribution) of three LM. One included the main effects of dyadic turn-taking . Another one included the main effects of infant turn-taking variables . The third LM included mother turn-taking variables (number of turns and response latency).z-transformed, assuming a Gaussian distribution) of three LM. One included the main effects of dyadic turn-taking . Another one included the main effects of infant turn-taking variables . The third LM included mother turn-taking variables (number of turns and response latency).Hypothesis 4: Infants’ attachment and turn-taking. Infants' attachment security score at 12 months of age assessed by the AQS was entered as the response variable , which yielded 1-ß = 0.856. We, thus, deemed the sample size to be appropriate for this set of analyses.The ery rate ). We alsery rate ) in relaery rate , we assu. 3 (a)N = 55) throughout the free play condition are included in electronic supplementary material, table S1. Number of bidirectional turn-taking and response latencies were highly correlated . Neither frequency of turn-taking nor overlaps from mother to infant or infant to mother were significantly related, p > 0.189.Descriptive statistics for the turn-taking patterns of mother–child dyads ( (b)n = 55) provided a significantly better fit to the data than the null model . The comparison of the full model with the reduced models revealed that the three-way interaction turns*intervals*ROI  and the main effect ROI  were statistically significant. These effects indicate that interpersonal neural synchrony was different between brain regions and that this difference was modulated by the frequency of turn-taking and that their slopes were different over time. Neither the two-way interactions turn-taking*intervals, intervals*ROI, turn-taking*ROI nor the simple effects of turn-taking, intervals and response latencies reached significance (p > 0.139). To understand the three-way interaction, we conducted three separate GLMM to test the interaction between turns and intervals in relation to interpersonal neural synchrony in each ROI. We corrected p-values  for multiple comparisons. The GLMM for the inferior frontal gyrus and lateral prefrontal cortex revealed no significant main effects and interaction effects (p > 0.270). Only the GLMM for the medial prefrontal cortex revealed a significant main effect of turns , a significant main effect of interval , and a significant interaction between turns and intervals . This significant set of effects shows that more frequent turns were related to higher neural synchrony, specifically in the medial prefrontal cortex. Neural synchrony between mother and infant also increased over time. But more specifically, more frequent turns were associated with higher neural synchrony in the medial prefrontal cortex in the first intervals .Firstly, we analysed whether more frequent turn-taking during a proto-conversation was related to mother–infant neural synchrony in frontal regions. The GLMM ( (c)n = 54) output displayed that the frequency of infant-to-mother turns was significantly associated with infants’ inter-hemispheric connectivity , as depicted in p = 0.701). Moreover, infants' and mother's frequency of overlaps were not significantly associated with inter-hemispheric connectivity (p > 0.255). Taken together, more infant-initiated turns in the proto-conversation were associated with higher inter-hemispheric connectivity in infants' brains.Next, we tested infants’ inter-hemispheric connectivity as a neural correlate to infant-initiated (infant-to-mother) turns and infants' (mother-to-infant) response latencies. The first model ( (d)n = 28). The first LM assessed the relation between infants’ vocabulary and dyadic turn-taking patterns and revealed a significant correlation between the number of turns of the dyad and infant vocabulary . More frequent turn-taking was related to infants' larger vocabulary at 24 months (a). Next, we split the dyadic turns into uni-directional turns and ran an additional regression analysis. The result showed that the number of mother-to-infant turn-takings explained more variance in infants’ vocabulary than infant-to-mother turn-taking . The third LM assessed the relation between infants' vocabulary and mother-to-infant overlap frequency and found a significant negative relation . Fewer mother-to-infant overlaps were associated with infants’ larger vocabulary (b). Infants' vocabulary was not significantly related to infant-to-mother overlaps (p = 0.794).We tested the relation between infants' vocabulary at 24 months and dyadic as well as individual turn-taking patterns during the mother–infant interaction at 4–6 months p-corrected > 0.122. In an exploratory analysis, we dichotomized infants’ attachment scores into securely and insecurely attached infants . The te. 4In the present study, we examined turn-taking patterns in mother–infant proto-conversations in relation to interpersonal neural synchrony and developmental outcome measures: infants' inter-hemispheric connectivity, expressive language abilities, and attachment. The more turn-taking mother and infant showed the more they displayed interpersonal neural synchrony during the proto-conversation. The relation was stronger in the initial phase of the interaction and decreased over time. Next, infants’ number of turns was related to higher inter-hemispheric connectivity in infants’ frontal brain regions. In addition, the number of turns in general, but especially infants' turns, was related to a larger vocabulary at 24 months of age. However, mother–infant turn-taking was not related to the infant's attachment security. The results underscore the role of interpersonal neural synchrony in early turn-taking as well as brain maturation and language development as potential outcomes related to coordinated proto-conversation in early caregiver–infant interactions.As predicted, we observed a positive relation between the frequency of turns and neural synchronization between mothers and their infants in a proto-conversation. This association was limited to the medial prefrontal cortex among our regions of interest. Medial prefrontal regions have been implicated in caregiver–infant synchrony, especially in face-to-face exchanges . This isOur hypothesis that neural synchrony might be a shared underlying mechanism for turn-taking across earlier and later human development can therefore neither be fully confirmed nor dismissed. By contrast to the current results, neural synchrony increased over time in mothers and their preschool-aged children in association with more frequent turn-taking in a previous study . There aNext, we examined the relationship between mother–infant turn-taking and infant maturity at the neural level, measured by inter-hemispheric connectivity. Consistent with our hypothesis, we found that more frequent infant-to-mother turn-taking, but not mother-to-infant response latencies, was positively related to brain maturation. These results support previous findings that infants' individual differences in inter-hemispheric connectivity can be identified and related to individual emotional and sensorimotor differences ,28. InteEven though early social interactions are maintained to be a core component of children's language development , few stuNext to supporting the development of infants' language skills, conversational turn-taking is suggested to help build connections between people ,22. PrevOur results highlight the importance of preverbal turn-taking between caregivers and infants in early development. Turn-taking arises together with interpersonal neural synchronization in the medial prefrontal cortex, a potential biomarker of mutual engagement and prediction. Moreover, turn-taking in proto-conversations is related to infants’ brain maturation and language development. Our results also indicate that the range of turn-taking qualities in the present sample might comprise ‘good enough’ communication patterns to facilitate the bond between healthy and (mostly) securely attached infants and their caregivers . TherefoTaken together, our results show that mother–infant turn-taking, similar to later in development , relies


Sporobolus anglicus (previously known as Spartina anglica), a widely distributed saltmarsh plant, is colonized by DMS-degrading microorganisms.Saltmarshes are hotspots of organosulfur compound cycling due to production of dimethylsulfoniopropionate (DMSP) by benthic microorganisms, macroalgae, and saltmarsh vegetation. Degradation of DMSP is a source of dimethylsulfide (DMS), an important precursor for formation of secondary organic aerosol. Microorganisms degrading DMS play a role in controlling the amount of DMS available for emission into the atmosphere. Previous work has implicated sediment microbial populations as a major sink for DMS. Here, we show that 13C-DMS stable isotope probing, microbial community diversity and functional genetic potential in phyllosphere and rhizosphere samples was assessed by high-throughput sequencing of 16S rRNA gene amplicons, cloning and sequencing of methanethiol oxidase genes, and by metagenomic analysis of phyllosphere microbial communities.Dimethylsulfide degradation potential was assessed by gas chromatography and 13C-DMS stable isotope probing and included populations related to Methylophaga and other Piscirickettsiaceae in rhizosphere samples. DMS-degraders in the phyllosphere included Xanthomonadaceae and Halothiobacillaceae. The diversity in sediment samples of the methanethiol oxidase (mtoX) gene, a marker for metabolism of methanethiol during DMS and DMSP degradation, was similar to previously detected saltmarsh mtoX, including those of Methylophaga and Methylococcaeae. Phyllosphere mtoX genes were distinct from sediment mtoX and did not include close relatives of cultivated bacteria. Microbial diversity in the phyllosphere of S. anglicus was distinct compared to those of model plants such as rice, soybean, clover and Arabidopsis and showed a dominance of Gammaproteobacteria rather than Alphaproteobacteria.The DMS degradation potential of microbial communities recovered from phyllosphere and rhizosphere samples was similar. Active DMS-degraders were identified by Sporobolus anglicus suggest that DMS cycling in saltmarshes is more complex than previously recognised and calls for a more detailed assessment of how aboveground activities affect fluxes of DMS.The potential for microbial DMS degradation in the phyllosphere and rhizosphere of  Dimethylsulfide (DMS) is the most abundant biologically formed sulfur compound emitted to the atmosphere and performs a crucial role in the global sulfur cycle . As an i−1 , while trimethylamine monooxygenase has been shown to co-oxidise DMS to DMSO (Thiobacillus thioparus (Hyphomicrobium EG (mtoX) has been identified from the DMS-degrading bacterium Hyphomicrobium sp. VS . Overall diversity in the phyllosphere of S.anglicus was assessed by high-throughput metagenomic sequencing.We assessed DMSP contents of Sporobolus anglicus plants including phyllosphere and rhizosphere were sampled from the Stiffkey saltmarsh (52°57′55.6″N and 0°55′24.0″E) in Norfolk (United Kingdom) in June and October 2012, in February, June, and October 2013 and in August 2014. Between 3 and 6 S. anglicus plants were collected from several subsites within the lower saltmarsh. These subsites were located at a maximum distance of 25 m to each other. Phyllosphere and rhizosphere samples of S. anglicus were used in triplicates. For the above ground parts (phyllosphere), leaf wash, leaf and stem samples were used, whereas below ground parts (rhizosphere) included root samples including endorhizosphere and rhizoplane, and rhizosphere sediment (ectorhizosphere), respectively. Leaf wash samples were prepared according to S. anglicus plant samples, in October 2013, bulk sediment of S. anglicus plants was sampled to characterise the sediment type, particle size, pH, total N, total C, organic matter, and water extractable anions . In August 2014, S. anglicus phyllosphere samples were collected for metagenomics. Plants used for determination of microbial community composition and in incubation studies were generally from areas characterized by a sandy loam sediment  and rhizosphere (roots and sediment) samples were measured as DMS following alkaline hydrolysis as reported and described previously  in samplS. anglicus tissue samples, sediment samples, and stable isotope probing experiments using the FastDNA™ Spin Kit for Soil  following the manufacturer’s instructions. For S. anglicus tissue and sediment samples, 0.5 g of sample was used. Leaf wash samples were collected on 0.22 μm filters as described above. Filters were placed in the lysis tubes and the subsequent steps performed according to the manufacturer’s instructions. DNA for the S. anglicus phyllosphere metagenomes was extracted from triplicate S. anglicus phyllosphere samples according to S. anglicus phyllosphere sample for the extraction of metagenomic DNA.DNA was extracted from all 12C2]-DMS and [13C2]-DMS incubations, and metagenomes. Amplicon samples were sequenced on the Illumina MiSeq platform, metagenomic DNA was sequenced on the HiSeq platform. Library preparation for 16S rRNA amplicon HTS was carried out according to S. anglicus phyllosphere metagenomic sequencing, multiple displacement amplification was carried out using the Illustra GenomiPhi V2 DNA amplification kit  prior to sequencing. Library preparation and paired-end sequencing with a 20 pmol spike-in of PhiX (Illumina) was carried out by the Genomics facility of the School of Life Sciences at the University of Warwick.High-throughput amplicon sequencing was applied for taxonomic classification (16S rRNA gene) of non-enriched phyllosphere and rhizosphere tissue samples, sediment samples, “light” and “heavy” [S. anglicus was carried out according to S. anglicus (leaf wash) was studied in February and June 2013. Leaf wash samples were prepared as described above. All SIP incubations were carried out in triplicates. Approximately 2 g rhizosphere sediment or 1–2 g leaf wash sample was incubated with either [13C2]-DMS or [12C2]-DMS in a 125 ml serum vial sealed with a butyl rubber stopper. Overall, 100 μmol carbon g−1 sample in form of either [13C2]-DMS or [12C2]-DMS was provided over three pulses. Substrate utilization was monitored using gas chromatography as described above. Samples were harvested and processed immediately after DMS was not detectable anymore.DNA-stable isotope probing (DNA-SIP) of DMS-assimilating microorganisms in phyllosphere and rhizosphere of 13C2]-DMS and [12C2]-DMS incubations active DMS-assimilating populations were identified. Fractions were initially analysed by DGGE and subsequently subjected to 16S rRNA amplicon high-throughput sequencing. In addition, individual DGGE bands were cut out and sequenced according to DNA-SIP fractions were used as template for the amplification of bacterial 16S rRNA genes using the primers 341F-GC and 907R . By compmtoX) encoding the methanethiol oxidase was assessed in leaf, root, and rhizosphere sediment samples from June 2012 and in root and rhizosphere sediment samples from October 2012 and February 2013. Functional gene PCRs were performed in a 50 μl reaction volume containing 1 × buffer including MgCl2, 0.8 mM dNTPs (0.2 mM each dNTP), 0.4 μM forward (MtoX41Fmodv2_inos) and reverse (MTOX346Rmod) primer  and BSA  were added to enhance strand separation in GC-rich regions and to help stabilise the enzyme, respectively. PCRs were carried out in a T-100 thermocycler . PCR cycling regime and subsequent cloning of PCR products was carried out according to The presence and diversity of the gene  primer , 2 U TaqRaw fastq reads from 16S rRNA gene amplicon HTS were joined and demultiplexed using QIIME . QualitymtoX sequencing data was carried out using BLASTx , DMSP cleavage , DMS oxidation , methanethiol degradation (mtoX), and genes involved in the downstream metabolism of DMSP, DMS, and methanethiol degradation products, such as genes involved in one carbon metabolism either via the tetrahydrofolate-dependent pathway  or the tetrahydromethanopterin-dependent pathway  and genes involved in sulfur oxidation . E-values are indicated in Metagenomics-Rapid Annotation using Subsystem Technology (MG-RAST) was used for analysis of taxonomic and functional assignment of the metagenomic reads . MG-RASTSporobolus anglicus phyllosphere and rhizosphere samples have been submitted to the Sequence Read Archive (SRA) under the accession number PRJNA670606. Raw read data from the 16S rRNA under dimethylsulfide DNA stable isotope probing have been submitted under the accession number PRJNA670609. Read data of the three Sporobolus anglicus metagenomes have been submitted to the Sequence Read Archive (SRA) under the accession numbers ERX675820, ERX675821, and ERX675822. DNA sequences of methanethiol oxidase genes (mtoX) have been deposited in Genbank under accession numbers MW245658–MW245712.16S rRNA raw read data from S. anglicus tissue samples confirmed that plants sampled for this study had high DMSP concentrations and showed differences in DMSP concentration between plant tissues and sampling sites. The highest DMSP concentrations were detected in S. anglicus leaf, stem, and root tissue samples (−1 fresh weight (FW). DMSP was not detectable or only present at very low concentrations in leaf wash and rhizosphere sediment samples. Variability in the DMSP concentration was observed, not only between different seasons and months, but also between individual plants and their tissues , and particle size distribution , whereas the highest DMSP concentrations in the S. anglicus plants growing in the sandy loam were observed in the stems  in these samples typically took between 4 and 13 days, except for samples from October 2012 where the degradation of the DMS took between 13 and 25 days in leaf wash, root and rhizosphere sediment samples (−1 sediment d−1 (data not shown).The hypothesis that  samples . Degrada samples . The rhiS. anglicus phyllosphere and rhizosphere samples from June and October 2012 and February, June and October 2013. The bacterial community composition of S. anglicus . Also, Deltaproteobacteria showed a high abundance in the rhizosphere  effect size (LEfSe) method  confirmeS. anglicus, multidimensional scaling (MDS) was performed. Plots displaying the 16S rRNA gene-based bacterial community composition at the genus level of all phyllosphere and rhizosphere samples were calculated, showing data points with superimposed codes representing plant part, sample tissue, DMSP content, pH, sampling month, and temperature , Rhodobacteraceae , and Psychrobacter  within the phyllosphere, and Chromatiales (14.04%), Desulfobulbaceae  and Desulfobacteraceae  in the rhizosphere. These analyses corresponded well to the results obtained by the LEfSe analysis.Operational taxonomic units primarily providing the discrimination between the two observed sample clusters  from February and June 2013. DNA was extracted from phyllosphere and rhizosphere SIP incubations with 13C-labelled DMS (and control incubations with 12C-DMS) after degradation of approximately 100 μmol carbon g−1 sample. Initial evaluation of SIP fractions by DGGE analysis of bacterial 16S rRNA amplicons indicated successful labelling (data not shown). Bacterial 16S rRNA amplicon high-throughput sequencing was done for the “heavy” and “light” 12C- and 13C-labelled fractions of each experiment. A total of 6,636,546 quality-filtered, chimera-checked sequences were obtained from 48 samples and assigned to 1,115 distinct OTUs at 97% identity . Taxonomic profiling showed distinct community profiles in “heavy” and “light” DNA fractions of phyllosphere and rhizosphere SIP samples  and other (unassigned) Piscirickettsiacaea (13C-heavy DNA fractions from the phyllosphere were enriched in Gammaproteobacteria [including Methylophaga and other (unassigned) Piscirickettsiacaea] but also highlighted a range of other genera as DMS degraders  oxidizes inorganic sulfur compounds such as thiosulfate, S and sulfides and hydrogen sulfide to sulfate , as well as taxa not previously shown to degrade DMS, but which are shown here as having the potential to contribute to DMS degradation in the phyllosphere of S. anglicus.Thus, SIP identified several candidate DMS-degrading populations including some that were previously linked to DMS cycling (Methylophaga (family Piscirickettsiacaea), Halothiobacillus , or Rhodanobacter (family Rhodanobacteraceae) were not detected in the 16S rRNA gene sequencing data of the same unenriched S. anglicus samples, suggesting that these genera were present at a low abundance. Also, the families Halothiobacillaceae, Rhodanobacteraceae, Xanthomonadaceae, and Alicyclobacillaceae were not detectable in the 16S rRNA gene sequencing data of the same unenriched S. anglicus samples. However, the family Piscirickettsiacaea (family of Methylophaga) could be detected in S. anglicus unenriched samples with relative abundances ranging from 0.1% in some leaf wash samples to 39.2% in root samples and 37.6% in rhizosphere sediment samples (data not shown) highlighting these as potentially abundant DMS degrading bacteria in association with S. anglicus especially below ground.At the genus level, mtoX gene encoding the methanethiol monooxygenase was used as a functional marker gene to detect methanethiol-degrading bacteria  and rhizosphere samples (marked in red and brown) clustered with mtoX clones previously reported from surface sediment of the same saltmarsh  was found in 0.1–0.2% of the metagenomic reads of the S. anglicus phyllosphere.Direct metagenomic analysis based on sequencing of phyllosphere community DNA of three  library . Similarabundant . The micArabidopsis thaliana, clover, soybean, and rice showed major differences in community composition between those plants and S. anglicus likely reflecting the differences in habitat (see A comparison of the taxonomic diversity to phyllosphere metagenomes of itat see .dddP and dddD), DMS oxidation , and methanethiol degradation (Methanethiol oxidase—mtoX), which were all present in the investigated metagenomes  were Gammaproteobacteria and Alphaproteobacteria . The abundance of the gene encoding the DMS monooxygenase (dmoA) was higher in the Sporobolus anglicus phyllosphere metagenomes compared to the DMS dehydrogenase (ddh), suggesting that DMS is more likely to be degraded to methanethiol and used as a carbon and sulfur source via its subsequent degradation to formaldehyde and hydrogen sulfide via the methanethiol oxidase (mtoX) than the oxidation to DMSO via the DMS dehydrogenase , e.g., mch (Methenyl-H4MPT-cyclohydrolase), fhcA (Formyltransferase/−hydrolase), foldD (Methylene-H4F-dehydrogenase/cyclohydrolase), mtdA (Methylene-H4F dehydrogenase), and purU  in C1 and DMS cycling.The phylogenetic affiliation of the organisms encoding these genes was inferred by blast searches of the relevant genes detected in the metagenomic contigs against the NCBI nr database . This shrogenase . DMS is bacteria . AlthougS. anglicus contains DMSP is not a novel finding, it was important in the context of our analyses to assess the environmental and seasonal factors that could affect the DMSP content of S. anglicus sampled in a natural saltmarsh. The DMSP concentrations that we measured were similar to those reported previously (S. anglicus (Sporobolus plants as shown in previous studies with greenhouse or laboratory grown Sporobolus. Here we show that plants sampled from locations with different sediment properties (sand or sandy loam) had different tissue DMSP concentrations. As expected, a higher total N and total C content was shown for the sandy loam in this study  but also between plants suggesting a patchier distribution of these potential DMS degraders seasonally and spatially, which may indicate a lower overall abundance of these bacteria.Active DMS degraders in the rhizosphere were predominantly  strains  or findieriments . InteresmtoX, in unenriched microbial communities demonstrated that MT-degrading microorganisms are closely associated with S. anglicus. Sequences of mtoX clustering closely with Methylophaga are likely to originate from uncultivated Piscirickettsiacaea shown to be involved in DMS degradation by SIP. The finding of an mtoX clade that was only detected in the phyllosphere suggests that some of these Gammaproteobacteria may have a habitat preference, but a better taxonomic placement of these sequences would require more detailed analysis of neighbouring genes in their genomic context or resolving the corresponding genomes as metagenome assembled genomes.The detection of the gene encoding the methanethiol oxidase, S. anglicus-associated microorganisms degrading DMS and related sulfur compounds provided new insights. Although it is challenging to integrate these different datasets seamlessly, the following conclusions can be drawn. Based on SIP, the potential for DMS cycling by Piscirickettsiaceae is clear, but other DMS degraders outside this family were also identified in phyllosphere samples. SIP incubations may favour fast-growing organisms, which potentially outcompete slower growing ones that may be more dominant in situ. Therefore identification by SIP is not necessarily a reflection of their dominance or contribution to the process. This issue could be addressed in future studies under substrate-limiting conditions, ideally using small-scale chemostat experiments.The application of different approaches to characterise Piscirickettsiaceae were present at up to 39% read abundance in some unenriched rhizosphere samples clearly demonstrating that these bacteria can be abundant members of the community. They are thus likely relevant for cycling of DMS (and other C1 compounds) in situ. This was further supported by finding several hits to C1 cycling genes in the metagenomes which were affiliated with Methylophaga and related organisms and mtoX amplicons affiliated with this group. Other candidate DMS degraders may be less abundant in situ, and the lack of genes of sulfur and C1 cycling matching such taxa may be due to a lack of genomes of representative DMS-degrading strains in the sequence databases. This can be illustrated using Methylophaga as an example. DMS metabolism has only been reported for three Methylophaga species and only in genomes of two of these, M. thiooxydans and M. sulfidovorans, have genes involved in DMS metabolism been identified  can be found at: EK and HS conceived the research, analyzed the data, and wrote the manuscript. EK carried out the experimental research. AM supported the data analysis. All authors contributed to the article and approved the submitted version.This study was supported with funding from the Natural Environment Research Council .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.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


X substrate is presented as temperature sensors by semiconductor technology and its electrical properties were measured. The results show that the temperature coefficient of the resistance value is 2.07 × 10−3 in the temperature range of 300–450 K and 2.39 × 10−3 in the temperature range of 450–575 K. From room temperature to high temperature, the “metal” characteristics are presented, and the higher TCR obtained at higher temperature interval is described and analyzed by combining Boltzmann transport equation and thermal expansion theory. These investigations provide further insight into the temperature characteristics of graphene.Graphene membranes act as temperature sensors in nanoelectromechanical devices due to their excellent thermal and high-temperature resistance properties. Experimentally, reports on the sensing performance of graphene mainly focus on the temperature interval under 400 K. To explore the sensing performance of graphene temperature sensors at higher temperature intervals, micro-fabricated single-layer graphene on a SiN Compared with conventional temperature sensors, micro-temperature sensors have attracted research attention because of their miniaturization , intelliaterials ,10. Grapaterials , but theaterials . For thi2/Si substrate, SiN membrane and a suspended architecture [X/Si substrate to explore the temperature characteristics of graphene in a wider temperature range was fabricated in this study.The temperature characteristics of graphene-based sensitive elements such as reduced graphene oxide (rGO) ,14 and gitecture . TherefoIn this article, graphene prepared by chemical vapor deposition (CVD) was developed to a thermal resistance nanoelectromechanical graphene temperature sensor by using standard semiconductor processes such as transferring and sputtering. The temperature characteristics of graphene were tested in the temperature range of 300–575 K, and its temperature characteristics were explained by combining Boltzmann theory and thermal expansion theory. Experimental support for the development of temperature sensors with graphene as a sensitive element in a higher range will be provided in this study. Simultaneously, the previously proposed model was improved from the perspective of thermal expansion of the substrate, and the concept that the tensile strain caused by thermal expansion of the substrate intensifies the “metallic” property of graphene was explained. In the temperature interval studied here, the increase of the positive temperature coefficient (PTC) could be described as the superposition of the dominant scattering mechanism of graphene itself and the tensile strain of the external substrate.X/Si substrate ) pre-deposited with metal electrodes [2 plasma to etch the back graphene of the sample, and 40% FeCl3 was used to etch the Cu substrate supporting the graphene for about 6 h. After that, the PMMA/graphene sample was transferred to the target substrate and heated on a hot plate at 85 °C for 30 min. The PMMA layer was dissolved in acetone (CP) solution at 50 °C for 10 min, and then the target was washed with alcohol (EA) solution and deionized (DI) water. Finally, The graphene was patterned by using lithography and O2 plasma etching. The parameters of O2 plasma etching are as follows: power, 60 W; gas flow, 30 sccm; and etching time 3 min.Graphene was grown on copper substrate by the chemical vapor deposition (CVD) method . A wet tectrodes ,24. The The structure of the graphene temperature sensor is shown in After the graphene temperature sensor device was fabricated, the temperature characteristic of the graphene temperature sensor was tested by using a high-temperature sealed tube and a high-temperature furnace combined with a Wheatstone bridge. 0 was equal to the initial resistance of the sensor at room temperature with a humidity of 45% to 50%. The voltage at both ends of the bridge changed linearly with the change of resistance. The output voltage signal was amplified by an operational amplifier, sampled by a low-pass filter, and finally converted to the corresponding resistance value.To accurately measure the change in resistance during the heating process, the device resistance was measured using a Wheatstone bridge (see illustration). The bridge was equilibrated down at room temperature, where R−1 and 2700 cm−1, respectively, and the intensity ratio of the 2-D peak to the G peak (I2D/IG) is 3.21, which indicates that the transferred graphene is a monolayer film [−1, which indicated that the graphene film was of high quality [To characterize the number of layers and defects of graphene after transferring, samples were subjected to Raman scattering  . As showyer film . No D peThe electrical and thermal conductivity of graphene would be weakened because of the presence of cracks, folds, and organic residues on the graphene surface ,29,30,31tol(T) ≠ ρPH(T) +ρother(T). ρtol(T) represented the temperature characteristic that graphene exhibits as resistance varies with temperature. ρPH(T) represented the temperature characteristic exhibited by phonon scattering, and ρother(T) represented all the scattering mechanisms except phonon scattering. This statement explains the non-linear experimental result in the experiment. The humidity test of the device was carried out, and the results are shown in R0 represents the resistance value at initial temperature T0 and R is the resistance value at temperature T.The temperature coefficient of resistance (TCR) is one of the performance indicators of a temperature sensor. To characterize the performance of the sensor, the TCR can be calculated according to Equation (1). As could be visible in 1 = (5.52425 − 4.2155)/(4.2155·(450 − 300)) = 2.07 × 10−3. The TCR at 450–575 K temperature range can be calculated as follows: TCR2 = (7.13572 − 5.52425)/(5.52425·(575 − 450)) = 2.39 × 10−3.The TCR at 300–450 K temperature can be calculated as follows: TCRX expands with increasing temperature. As a result, the resistance of graphene gradually increases during tensile strain, which indirectly aggravates the “metal” characteristics of graphene, presenting a higher temperature coefficient.After calculation, the TCR of the high-temperature interval is greater than that of the lower-temperature interval. One possible reason is that during the heating process, graphene is subjected to tensile strain from the substrate because SiNA graphene temperature sensor with a temperature range from 300 K to 573 K was fabricated by using standard semiconductor integration technology. Scanning electron microscopy, optical microscopy, Raman analysis revealed that graphene is a single layer of defect-free structure with a clean surface. An electrical performance test using a wheatstone bridge revealed that temperature sensor resistance increased with the increase of temperature, and the reason is that the phonon scattering dominates the presence of the characteristics of “metal” in the temperature range. Simultaneously, the TCR of the high-temperature interval was higher, a possible reason for enhancing this characteristic was explained. In brief, the temperature characteristic of graphene in the range of 300 to 574 K was investigated, and a wide range, good linearity, and high sensitivity graphene temperature sensor has been fabricated, which meets the needs of industrial production and other fields for accurate temperature control at high temperatures.


Overall, this work opens three prominent favorable prospects: exploring the usage of nano-materials prepared by liquid phase exfoliation approach, their effective usage in ion-transport membrane region of MEA and enhancing fuel cell power performance.Graphene, in spite of exceptional physio-chemical properties, still faces great limitations in its use and industrial scale-up as highly selective membranes (enhanced ratio of proton conductivity to fuel cross-over) in liquid alcohol fuel cells (LAFCs), due to complexity and high cost of prevailing production methods. To resolve these issues, a facile, low-cost and eco-friendly approach of liquid phase exfoliation (bath sonication) of graphite to obtain graphene and spray depositing the prepared graphene flakes, above anode catalyst layer (near the membrane in the membrane electrode assembly (MEA)) as barrier layer at different weight percentages relative to the base membrane Nafion 115 was utilized in this work. The 5 wt.% nano-graphene layer raises 1 M methanol/oxygen fuel cell power density by 38% to 91 mW·cm A massive increase in population, day-to-day technological improvements and their related projects, in this era have prompted exponential needs in our energy supply ,2,3. In In spite of LAFC’s advantages, its commercialization is greatly hindered by excess fuel crossover (or permeability) issues degrading power performance at both short and long time-scale operations ,6. Fuel To reduce the impact of this crossover issue so as to improve the power performance of the fuel cell, a barrier layer is applied between the anode electrode and membrane region in their membrane electrode assembly (MEA) ,9. Previ−1·K−1), mechanical stability (Young’s modulus of 1 TPa), electron mobility , surface area (2630 m2·g−1) and optical transparency (97.7%) [From a materials perspective, graphene, the first in the 2D materials family gets enhanced importance due to its exceptional physio-chemical properties: high thermal conductivity (5000 W·m (97.7%) ,14. Espe (97.7%) ,16. This (97.7%)  and Su e (97.7%)  where grFurthermore, Hu et al.  have shoThis concept was utilized in an actual fuel cell system by Holmes et al.  and Yan Xu et al.  used graConsidering the drawbacks of all the previous reports and in an effort to widen the horizons of this research, in this work we have used graphene from liquid phase exfoliation–bath sonication of graphite and utilized them as a barrier layer— showing an effective membrane with high selectivity (proton conductivity to fuel crossover ratio) for performance improvements in various LFACs—methanol, ethanol and propanol, respectively.N-methyl pyrrolidone (NMP), acetone, dimethyl sulphoxide (DMSO), 1,2-dichloro benzene (DCB), acetophenone, water, benzonitrile, 1,4-dioxane) and subjecting to exfoliation by bath sonication [Liquid phase exfoliation involves dispersion of the precursor in a solvent , using spray deposition, which is considered easier compared to the transfer process from furnace to electrode where CVD is used and the mechanical exfoliation method was used ,28,29,30These 2D materials from liquid phase exfoliation methodology were reported to have been utilized in several opto-electronic applications (solar cells and thin film transistors), nano-sensors and nano-composites ,24. To tIn the fuel cell membrane region, it is known that methanol permeability (MP) and proton conductivity are inter-related ,7,8. To The results are evaluated by materials characterization (atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) with elemental mapping and Raman spectroscopy), electrode/membrane characterization—fuel permeability (MP—methanol permeability in case of methanol fuel usage) , water uptake, ion-exchange capacity, proton conductivity, fuel oxidation propensity (FOP)—oxidation current and peak oxidation potential, electrode reaction resistance (ERR), wettability and fuel cell polarization curves  at different fuel concentrations and temperatures.Overall, this work of utilizing a liquid phase exfoliation approach of graphene synthesis, usage as a barrier layer on the anode side of MEA using simple spray deposition and with significant power performance increments obtained, will lead to advantages in multiple fronts: improving the commercial standpoint of LAFCs (efficiency and durability improvements as reported), influx of various liquid exfoliated 2D materials as high selective membranes into the fuel cell field and their further mechanism exploration studies.3)2CO) medium exfoliation, as analyzed thoroughly by previous studies [The above results confirm the exfoliation of multiple carbon layers (40 µm thick) containing graphite onto a few layers of graphene with ~2–4 µm size, as illustrated schematically in the  studies ,15. Thes studies . Further−1, compared to graphite, indicates evaluation of defects and disorders in a sample arising from the exfoliation process [−1) confirms that the material is of few layers [ process ,32. The w layers . These oMore precise information obtained from atomic force microscopy (AFM) and their corresponding surface profiles (marked in grey line) taken for different samples, shows that flake thickness is of 2–5 nm a–d 33,3,35. ThesTo precisely estimate the effect of graphene, this spray was deposited at: 2.5 wt.%, 5 wt.%, 7.5 wt.%, 10 wt.%, 20 wt.% and 25 wt.% values (0 wt.% graphene is noted as standard) on the anode electrode  and evaluated. It can be seen that the average crack separation length changed for the 5 wt.% graphene electrode c, comparChanges in crack separation length are crucial, as previous studies by Hiramitsu et al. , MohseniSince water transport changes also affect the methanol, which has direct influence on power performance ,5,6, it Electrode porosity  by weight loss method offers enhanced simplicity compared to gas-liquid porosimetry methods, and pertains to methanol/water transport in their structure ,39. SimiHence, electrode porosity and contact angle values of different electrodes are determined as explained in the experimental procedure and given in The hydrophobic porosity of electrodes increased with the graphene content, (60% to 73%), higher than that of standard electrode (60%). This is due to high carbon to oxygen (C/O) of 4.5 of the prepared graphene from electron dispersive spectroscopy (EDS) results, compared to platinum (and Nafion ionomer)-containing standard, which are well known for their water-affinity nature. The similar trend is observed in the contact angle measurements due to the above reasons. Studies by Bera et al.  and otheThese changes in hydrophobicity and contact angle values of the electrodes, along with the crack separation (as observed earlier) are expected to play a role in the water/methanol repelling characteristics of the electrode (as previous studied well in literature) and it will be interesting to observe the power performance.Water uptake (WU) and ion-exchange capacities characteristics of a MEA gives an understanding of proton conductivity since protons undergoes Grotthus mechanism movement through functional groups of the membranes ,6,7. HenFrom Membrane characterizations results (methanol permeability (MP), electrochemical mode) and proton conductivity were carried out, as explained in the experimental section and tabulated in It can be seen that MP, electrochemical mode values decrease with the increase in graphene weight percentage, showing that this graphene acted as a barrier layer, preventing fuel permeability thereby preventing undesirable fuel oxidation on the cathode. Meanwhile the proton conductivity has shown a declining trend, indicating that this layer though reduced MP has caused hindrance to proton conductivity. Hence, it can be inferred that the water-repelling nature of the graphene  has resulted in reduced methanol permeation. −1, indicating this layer prevented fuel permeation at the same time minimally affecting proton transfer route.Calculating membrane selectivity for all samples, the 5 wt.% graphene exhibited a high value of 0.77 mS·cm·mA−1) and oxygen (250 mL·min−1) operating parameters, as best standard power performance is obtained in these conditions. To test their effect in fuel cells, standard and graphene-containing membrane electrode assemblies (MEAs) are compared at 60 °C cell temperature, 1 M methanol  has reduced to 110 mA·cm−2, compared to 150 mA·cm−2 for the standard  than 210 mA·cm−2 for the standard —methanol oxidation current of 270 mA·cmstandard b. Also, −1—calculated from x-axis intercept (2) are lower than the standard (1.35 Ω·cm2), (Impedance spectroscopy plot shows that this 5 wt.% graphene barricade layer has reduced proton conductivity from 100 to 85·mS·cmntercept c. Howeve Ω·cm2), c reflectMP results by gravimetric modes as shown in −2 (standard) to 45 mW·cm−2 for 10 wt.% graphene, then to 29 mW·cm−2 for 20 wt.% graphene. This is due to the dominant impact of proton resistance on cell performance  and 75% (22 mW·cm−2 peak power density compared to 12 mW·cm−2 for the standard) performance improvements at 5 and 10 M concentrations, which are far higher than at 1 M concentration power performance results (36% improvement) as shown in polarization curve (voltage and power density profile) in Testing at high methanol concentration is essential, as this can be of great use for comparison to commercial portable sources, henceforth carried out at 5 and 10 M concentrations ,8,9. The−2. Durability testing aids in evaluation of graphene stability for prolonged periods of time henceforth carried out for 20 h at constant current density of 50 mA·cmAfter durability testing, minor reductions in open circuit voltage, peak power density and selectivity values are observed. This is attributed to the dissolution of graphene from the fuel cell electrode due to the high flow rate of incoming fuels. This is evident from top view  and crosIt well-known that graphene prevents ethanol and propanol flow through its channels ,14,15, hOverall, 2D graphene prepared by facile liquid phase exfoliation approach has been utilized as a barrier layer onto the anode side  due to its imparting high selectivity to the membrane region (fuel passage prevention characteristics) and thereby enhanced improvements in performance in methanol/ethanol/propanol systems are obtained. Starting from material characterization results, the high C/O ratio of prepared graphene has aided in enhanced hydrophobicity to the fuel cell electrode, whereas few layer thicknesses resulted in insignificant proton resistance. Combined effect of water/fuel transport on the anode due to changes in electrode crack separation, reduced fuel crossover , enhanced fuel oxidation on anode side and barrier effect have led to high membrane selectivity. This is depicted in the Using this at low weight percentages—5 wt.%, has resulted in 40%, 56% and 75% improvement in 1, 5 and 10 M methanol concentrations in addition to enhancements in ethanol and propanol systems. These beneficial effects are also observed at ethanol and propanol fuel cell systems over a wide temperature range (20 °C to 60 °C). Further increasing the graphene weight percentage (stacking), gives poor performance due to the dominant effect of proton transfer resistance affecting selectivity. In comparison to the previous work reported  the results obtained in this work offer advantages in various prospects: ease in preparation of graphene, utilization methodology, controllability, short- and long-term performance and diverse usage in various LAFCs, which are given in −2, rather than acetone in this work, effect of sonication time, centrifuge speed and duration), studying the effect of flake size, and testing in formic acid, ethanol, hydrogen fuel cells will be of significant interest and be the follow-up of this work.Also efforts like improving the efficiency of exfoliation  are dispersed in pure acetone (Fischer Scientific) and bath sonicated  for 1 h. The exfoliated dispersion is centrifuged at 5000 rpm for 1 h . The supernatant is collected and stored for further testing, whereas thick flakes settled at the bottom are discarded.Graphene from liquid phase exfoliation methodology was prepared according to the procedure by Coleman et al.  as follo−1 Raman shift) studies.Graphene dispersions in acetone were drop-casted (10–20 µL volume) on silicon wafers  and dried 48 h in an oven  at 200 °C, prior to atomic force microscopy (AFM) , scanning electron microscopy (SEM) (with energy dispersive spectroscopy (EDS) surface morphology analysis/elemental mapping by Hitachi S-3400 equipment, Hitachi High-Tech Corporation, Chaoyang District, Beijing, China) and Raman characterizations  with polytetrafluroethylene  in 10 wt.% in iso-propanol . After spray-coating this was placed in an oven (Quincy lab 10 GC model) at 150 °C for 1 h and 70 °C overnight.The MEA was fabricated as described in the procedure ,41 as fo−2 for both anode and cathode was reached. Catalyst ink contains catalyst (60 wt.% platinum on Vulcan XC-72 for cathode and 60 wt.% platinum: ruthenium on anode—from Fuel Cell Store) with 15 wt.% Nafion  in acetone (bath sonicated and stirred to obtain a homogeneous ink).Then catalyst ink is sprayed above the MPL, till a platinum loading of 1.5 mg·cmPolymer electrolyte membrane—Nafion 115  was pre-treated by heating in de-ionized water , 10 wt % hydrogen peroxide  and 1 M sulphuric acid (98% purity from Fischer Scientific and diluted) solutions at 80 °C for an hour, approximately. Then, this is placed between the anode and cathode electrode and fixed in fuel cell test system at 1.5 N·m pressure using Checkline DTW 100f  wrench.−1 of 1 M methanol and 250 mL·min−1 (2 bar) of dry oxygen  by p2) on the anode electrode above the catalyst layer. All other materials and deposition methods used in the MEA preparation, remained the same.In this work, graphene is sprayed at different weight percentages, 2.5 wt.%, 5 wt.%, 7.5 wt.%, 10 wt.%, 20 wt.% and 25 wt.%  is obtained by using DC power supply  by sweeping current from zero to maximum and recording the voltage by multimeter , till the voltage value reaches zero ,41.n-decane (Fischer Scientific) solvent, followed by weighing, where porosity is calculated from the difference in weight of electrodes before and after immersion and then divided by the density of n-decane as described in the procedure [Electrode porosity is obtained by immersing the electrode in pure rocedure ,38.Hydrophilic porosity is obtained by placing the sample in a lab-made set-up, where the electrode is exposed to incoming water vapor as illustrated in the −1) and nitrogen (2 bar—200 mL·min−1) on the cathode, in the fuel cell (anode side as working electrode and cathode as reference/counter electrode) from 0 to 1 V as described in the procedure [This is obtained by running cyclic voltammetry  by passing fuel (methanol or ethanol or propanol depending on experiments) on the anode (10 mL·minrocedure .These are obtained by running impedance spectroscopy (potentiostatic mode) in electrochemical work station CHI 660 model, China, in a working fuel cell at 0.4 V, with the cathode side as working electrode and the anode as a reference/counter electrode, in the frequency range from 25 kHz to 0.02 Hz at an amplitude of 5 mV as described in the procedure ,37. X-ax−1 by passing 10 mL·min−1 of methanol on the anode side and passing 200 mL·min−1 of nitrogen (2 bar pressure) on the cathode side by connecting the working electrode to the cathode and reference/counter electrode to the anode. The value of current plateau at which methanol oxidation becomes constant is noted as ‘MP current density’ and is carried out as described in the procedure from other work [MP  is obtained by running linear sweep voltammetry and scanning from 0 to 1 V at rate of 5 mV·sher work .MP (by gravimetric mode) measurement is carried out in the lab-made set up as given in Electrode wettability (by contact angle) is attained by placing a 20 µL drop of water on a fuel cell electrode and the contact angle was measured between the droplet and the electrode surface after 60 s, using a KRUSS surface analyzer camera ,45,46.MEA) and immersing in water for 24 h (for obtaining wet MEA weight—WetMEA). The difference in weight of the dry and wet sample gives the percentage of water uptake (WU) as given in Equation (2) below. All these measurements are carried out as described in the procedure [MEA—Weight of the wet MEA (grams) and DryMEA—Weight of the dry MEA (grams). WU is attained by drying the MEA at 50 °C for 24 h in an oven  approach of graphite in acetone medium and utilizing them as barrier layer by mounting them next to the membrane on the anode side  in direct liquid alcohol fuel cells (LAFCs) involving methanol, ethanol and propanol systems is proposed. The material characterizations by atomic force microscopy (AFM), Raman spectroscopy and scanning electron microscopy (SEM), show that graphene is of 2–5 nm thickness and 4 µm uniform lateral size.−2. This barrier layer reduces the methanol permeation (MP) from 153 to 112 mA·cm−2, with slight decrease in proton conductivity from 101 to 84 mS·cm−1, which has led to better methanol utilization—overall improving membrane selectivity (proton conductivity to fuel crossover ratio).The cell performance tests exhibit that 5 wt.% graphene barrier layer, at direct methanol fuel cell (DMFC) testing conditions (60 °C and 1 M methanol), increases the maximum power density from for the standard 63 to 91 mW·cmThis methanol barrier effect is more visible at highly concentrated methanol operations, where 36% and 75% improvements in fuel cell performance are observed. Long-term testing for 20 h also confirms this effect by displaying minimal voltage losses.2) and molybdenum di sulphide (MoS2) to be used as barrier layers, overall pushing the commercial circle of direct LAFCs.This newly reported work tends to eliminate limitations by using liquid phase exfoliated graphene as a barrier layer due to its feasibility, environmental friendliness and mass production characteristics—yielding few layer nano-materials, posing competition to expensive and complex—chemical vapor deposition (CVD) and mechanical exfoliation methods, in addition to power performance improvements. This also opens new possibilities for other crystals: hexagonal boron nitride (hBN), tungsten di sulphide (WS


It is widely accepted that solid‐state membranes are indispensable media for the graphene process, particularly transfer procedures. But these membranes inevitably bring contaminations and residues to the transferred graphene and consequently compromise the material quality. This study reports a newly observed free‐standing graphene‐water membrane structure, which replaces the conventional solid‐state supporting media with liquid film to sustain the graphene integrity and continuity. Experimental observation, theoretical model, and molecular dynamics simulations consistently indicate that the high surface tension of pure water and its large contact angle with graphene are essential factors for forming such a membrane structure. More interestingly, water surface tension ensures the flatness of graphene layers and renders high transfer quality on many types of target substrates. This report enriches the understanding of the interactions on reduced dimensional material while rendering an alternative approach for scalable layered material processing with ensured quality for advanced manufacturing. A study of a newly discovered graphene‐water membrane is accomplished. It provides a promising technique for high‐quality graphene process with ultra‐high flatness, and free of defects, leveraging the high surface tension of pure water. These advantages enable high‐performance device fabrication for electronic and biological research. These membranes provide outstanding operational flexibility for the transfer process, but inevitably lead to concerns about mechanical deformation, contaminations, and trapped interfacial residues that impact the performances of graphene‐based devices. On the other hand, graphene process assisted with liquid membranes has rarely been explored or reported before, due to the assumption that liquid surface tension could potentially damage the graphene integrity, or it is impossible to establish free‐standing and stable graphene‐liquid membrane structures.Solid‐state membranes, including polymethyl methacrylate (PMMA),1 para quantum devices, micro‐electromechanical systems, and flexible biosensors.Here, we report a newly observed graphene‐water membrane (GWM) structure, which refreshes our understanding of graphene‐liquid interaction, meanwhile rendering a new material process procedure. We thoroughly investigate the formation mechanism of the as‐observed GWM, particularly the roles of surface tension and contact angle playing, and discover that the GWM enables a new graphene transfer method that directly renders free‐suspended layer or on‐substrate film with improved flatness, thanks to the high water surface tension, which has long been misinterpreted to jeopardize the graphene transfer process. Further, the GWM transfer eliminates residuals induced by conventional solid‐state membranes, inspiring high‐quality and contamination‐free graphene process pathways toward the subsequent development of novel graphene‐based electronics,5 quan2Figure with a leakage rate lower than 10–9 bar cm3 s−1 to minimize defects induced by oxygen during the growth.  Following the growth, we preserve the graphene on one side of the copper foil, while etching the layer deposited on the other side with argon plasma. In this process, instead of protecting the desired surface with polymer coating, we designed a plasma treatment fixture, as demonstrated in Figure −1 ammonium persulfate ((NH4)2S2O8) water solution for copper etching for 3 h, leaving monolayer graphene on the etchant surface. Due to the high surface tension of water (72 mN m−1), the thin copper film and the finally released graphene float freely on the surface and are confined by a polyethylene terephthalate (PET) frame with a 1 × 1 cm2 opening in the center. Subsequently, we exchanged the etchant with deionized (DI) water and rinsed the monolayer graphene several times to remove all ions, including Cu2+ generated during the etching step illustrated in Figure  In contrast, we did not observe any deformations generated through the entire process, suggesting CVD graphene can stand the high surface tension of DI water as long as the graphene quality is carefully preserved. Otherwise, defects developed during growth and physical damage due to improper handling indeed impair the graphene layer, bringing cracks, wrinkles, shrinking, etc., as shown in Figure With the preserved graphene layer facing up, the copper foil is relocated into a specially designed reactor  of monolayer graphene is in the range from 1.05 to 1.1 TPa. Considering a graphene thickness (t) of 0.33 nm, we can calculate the strain (ε) on monolayer graphene induced by the water surface tension (γwater) via the equation:A potential concern of the GWM is whether the large surface tension can tear the graphene layer after it is lifted from the water surface. To determine this, we performed the following analysis. The Young's modulus  1.1 TPa.10 Con10 ConE3D) is provided by the surface tension (γl) of water in the form of D = 2γl. The force per unit width (P) required to peel the graphene can be derived from the energy balance between the work done by the peeling force and the variation of graphene/liquid interfacial energy,θsl denotes the contact angle between graphene and water, and α labels the peeling angle as defined in Figure D ≥ P, i.e., Theoretical prediction resulting from Equation  simulations on the entire peeling process. A graphene film with 4 nm x 10 nm was placed on the surface of the liquid and peeled by applying a mechanical force with the peeling angle of 57.5° at a velocity of 1 nm nsEquation  with wattion , a stable GWM forms when free‐floating graphene is peeled out of the water surface with a frame structure. This observation refreshes our understanding of graphene‐water interaction and exhibits a new hybrid membrane structure that inspires us with a new large‐scale polymer‐free graphene process technique with excellent outcomes.4FigureOne obvious benefit of this GWM is the ensured cleanness of the graphene layer by eliminating the usage of PMMA or other supporting media for processing. Thus, small organic molecules dispersed in the air turn out to be the only contamination source, which can be readily removed by afterward annealing. Indeed, the transition electron microscopy (TEM) image shown in  Figure 2 openings. The inset magnification exhibits the uniform and flawless graphene layer. This one‐step graphene suspension can be attributed to the high graphene quality, and more importantly, the reduced amount of water adhered to the graphene surface when the GMW forms, as indicated by our molecular dynamics simulation that no water adheres to the graphene layer  = 4:1) to remove organic residues thoroughly. Figure  To further confirm the microscopic structure and flatness, we conducted an atomic force microscopy (AFM) study on the graphene transferred with our new method and confirmed a low morphology roughness  of the surface height) of 1.5 nm, as demonstrated in Figure The GWM can also be leveraged for graphene transfer onto many types of substrates. Briefly, we can readily pick up the free‐floating graphene layer from the water surface with the PET retainer, then align and laminate it onto the target substrate, as shown in  target substrates are typically fully merged into the transfer liquid  used in our study. The improvement in graphene flatness drastically enhances its electronic performance. For example, compared with the conventional polymer‐free transfer method shown in Figure One primary reason for this drastic improvement can be attributed to the water film, which bridges the PET frame and graphene layer while stretching and flattening the atomic layer with its surface tension, as explained by Equation . Another22 tarFigure2 frame was patterned on Si substrate  to achieve the graphene growth later at 1000° C by controlling methane (CH4) flowrate at 35 sccm and a mixture of argon and hydrogen (Ar 90%: H2 10%) at 6 sccm.A homebuilt CVD system had been used to grow the monolayer graphene. It is electropolished 0.025 mm copper foil (CU000358 from Goodfellow) is mainly 80% phosphoric acid (H4)2S2O8) (from Sigma‐Aldrich) in 200 ml of DI water to prepare 0.1 M concentration.To etch copper, it is dissolved 4.56 g of ammonium persulfate  is used. All the FET devices were annealed after fabrication at 300° C for one hour under vacuum. Finally, it is shaped to transfer graphene to narrow channels (width = 1 mm) using radiofrequency argon plasma and the strips’ shadow masks.We fabricated shadow masks by following photolithography methods. Later, the electrode shaped mask to deposit Cr 5 nm AuRaman study on suspended and on‐substrated graphene was performed with 785 and 514.4 nm excitations, respectively. AFM scanning of graphene on the Veeco MultiMode AFM system under tapping mode is performed. The measurements of electron mobility on graphene FET devices were done on a homebuilt probe station combined with a source meter unit . SEM was performed on a Zeiss Merlin FE‐SEM system, and the STEM imaging was captured at room temperature using a Nion UltraSTEM U200 microscope operated at 60 kV. Graphene with a width of 4 nm and a length of 10 nm was placed on the surface of the liquid mixture of water and IPA with 42 000 water molecules. The simulation box size for peeling was 9.947 nm × 20.4192 nm × 20.0 nm, and the adaptive intermolecular reactive bond order modeled flexible graphene. The SPC/E and TraPPE‐UA potential models were adopted for water and IPA molecules, respectively. For the nonbonded interactions, the 12–6 pairwise Lennard–Jones potential V (r) = 4ε(σ12/r12 − σ12/r12) and Coulomb interaction qV (r) = iqjq/4πε0r were applied where r is the interatomic distance. At the same time, σ and ε are the equilibrium distance and the interactive well depth of the potential, respectively, iq and jq are the electronic charge counterpart, and ε0 is the permittivity of the vacuum. Specifically, the Lennard–Jones parameters for graphite‐water interaction were σCO = 3.19 Å and εCO = 0.00407 eV. The cut‐off distance was 1 nm in this study. The Lorentz–Berthelot mixing rule was used to determine the inter‐L–J parameters for different components. The particle–particle‐particle–mesh algorithm with a root mean of 0.0001 was used to minimize the error of long‐range Coulombic interactions. All simulations were run in an NVT ensemble with a Nose/Hoover thermostat set at 300 K unless otherwise stated.All graphene layers employed in this study had a size of about 7 mm × 7 mm, and the GWM has a size of 1 cm × 1 cm. The graphene roughness RMS of the three types of transfer was measured from Veeco AFM Nanoscope software. All MD simulations were carried out by the Large‐scale Atomic/Molecular Massively Parallel Simulator package.23 GraThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.