Direct read-out and built-in amplification are accomplished via photogating of a graphene field-effect transistor (GFET) by carriers generated within a deeply depleted low-doped silicon substrate. Analogous to a depleted metal-oxide-semiconducting junction, photo-generated charge collects in the potential well that forms at the semiconductor/insulator interface and induces charges of opposite polarity within the graphene film modifying its conductivity. This device enables simultaneous photo-induced charge integration with continuous “on detector” readout through use of graphene. The resulting devices exhibit responsivities as high as 2,500 A/W  for visible wavelengths and a dynamic range of 30 dB. As both the graphene and device principles are transferrable to arbitrary semiconductor absorbers, D2GIS devices offer a high-performance paradigm for imaging across the electromagnetic spectrum.A sensitive optical detector is presented based on a deeply depleted graphene-insulator-semiconducting (D Achieving sensitivities requisite for practical applications remains elusive however, due to the implicit difficulty of coupling light into an atomically thin layer. In response, nanoantenna enhancement of graphene absorption has been frequently employed5. This paradigm capitalizes upon sub-wavelength structuring of resonant layers atop the device to effectively concentrate the light into the active graphene channel. While these structures enhance photoresponse, light absorption within the graphene layer typically remains less than 50% of the total incident field. Harvesting the photo-induced electron-hole pairs (e–h) is also challenging since the recombination length in graphene is most often only ∼1 μm7. For these reasons, photoconducting graphene detectors typically exhibit sensitivities less than 100 mA/W3. While bolometric operation circumvents the necessity of carrier collection, it still relies on absorption within the graphene layer itself9.Owing to its high-mobility and broadband optical absorption, graphene continues to be pursued for photodetection applications spanning the ultravioletvia photogating. In this scheme, photogenerated charge created within a semiconducting absorber is capacitively coupled to the graphene thereby inducing a charge of opposite polarity within the graphene channel, modifying the graphene’s conductance. Alterations in the channel conductance can be sensed by measuring channel current during application of a constant bias voltage, mimicking a photocurrent. Since the source-drain current (Isd) of the graphene channel is proportional to product of carrier density and mobility (Isd ∝ µnE), graphene’s large ambipolar mobility (~103–105 cm2/Vs)10 acts as a built-in photogain  mechanism enhancing the detector response. For this reason, sensitivities of photogated graphene devices are higher than other architectures reaching values in excess 1,000 A/W14.To circumvent these difficulties, graphene can be utilized—in an alternative paradigm—as an atomically-thin, transparent, charge-sensing layer that detects absorption within a thicker adjacent substrate, rather than serving as the light-absorbing medium itself. Specifically, the large transconductance of graphene field-effect transistors (GFET) can be leveraged 13, pyroelectric materials16, and semiconductors18. Since the graphene in these devices is not responsible for light absorption but only the sensing of charge, absorber choice determines the spectral response. This device concept is thus equally adept at sensing everything from ionizing radiation19 to the infrared20. For this same reason, detector speed, sensitivity, and dynamic range are impacted by the absorber as well. Detector speed, for instance, is dictated not only by the speed of charge coursing through the graphene channel, but also the rate at which photogenerated charge within the absorber gates the channel. Similarly, sensitivity is not only determined by the transconductance of the graphene channel, but also by the generation-recombination dynamics within the absorber. Lastly, dynamic range is limited by the amount of light collected by the absorber rather than graphene’s density of states (DOS). Full utility can only be realized when both the absorber and graphene are ideally employed as a single system. Here—unlike previous reports of photogated graphene devices19 —we show that by operating a graphene-insulator junction with the semiconductor in deep-depletion, a sensitive photocharge integrating detector with continuous localized read-out (from the graphene) and high-sensitivity can be created. These capabilities, in turn, open up the possibility of alternative detecting modalities in which the advantages of signal integration and continuous monitoring can be leveraged.Photogated graphene detectors have been reported using a variety of absorbers including quantum dots2GIS photodetector are presented. Specifically, individual deeply depleted graphene-oxide-semiconductor (D2GOS) photodetectors are realized by transferring graphene atop a low-doped silicon substrate that is coated with a thin oxide. The fabricated devices are analyzed with respect to their photoresponse in the visible. Possessing responsivities exceeding 2,500 A/W, an SNR of ~ 3, and up to 30 dB of dynamic range at room temperature, the device response is explained entirely through a semi-analytical calculation taking into account the basic transfer characteristics of a graphene field-effect transistor combined with depletion and subsequent carrier generation in a low-doped semiconductor.Below, the operating characteristics and principles of a D2GOS detector concept. The device consists of a back-gated graphene-oxide-semiconductor (GOS) junction. Graphene channel conductance is measured using source-drain electrodes with constant bias application. To sense photo-generated charge, the semiconductor absorber is brought into deep depletion by rapid application of a back-gate voltage (Vbg). Figure bg > 0 V. Positive Vbg forces mobile electrons to diffuse into the bulk Si, exposing the space charge within the depletion zone of width W. The surface potential (ψS) at the silicon/oxide (Si/ox) interface goes negative and the electric field within the depletion region separates photo-generated e-h pairs resulting in the collection of holes at the Si/ox interface.Figure 22. This behavior is similar to the integration mechanisms of a classical deeply depleted MOS capacitor with the exception of the top-gate electrode being replaced with a graphene channel that locally senses charge at the Si/ox interface.Since the graphene is capacitively coupled to the underlying Si absorber, the collected holes induce electrons in the graphene channel, modifying the Fermi-level, thus altering the film’s conductivity Fig. . Modific2GOS detectors were fabricated by transferring chemical vapor deposition (CVD) derived graphene onto a lightly doped n-type silicon absorber (Nd ~ 1014 cm−3) capped with 50 nm of HfO2 that was deposited by atomic layer deposition (ALD) (see Methods). The doping level of the Si substrates was verified using secondary ion mass spectrometry (SIMS) and capacitance-voltage (CV) measurements (see Supporting Information). Figure 2GOS detectors with the inset highlighting an individual 200 × 200 µm device. Detectors exhibiting characteristics similar to those reported below were fabricated on several silicon substrates and all results were repeatable across multiple devices indicating the robustness of this design. While the devices characterized here employed silicon absorbers, the methodology is portable to other suitable absorbers making the concept applicable for detector design throughout the visible and infrared. When selecting alternative absorbers, the interplay between several factors must be considered: 1) Fermi level alignment between the graphene and absorber, 2) voltages required to reach graphene charge neutrality and absorber depletion, 3) formation of low-defect absorber/insulator interface, and 4) carrier lifetime.To demonstrate the device described above, Dopt) in an otherwise optically dark environment (see Methods). For these measurements, the current at the drain electrode (Id) was measured during application of 100 mV drain voltage (Vd) while the source electrode was held at ground. Figure d) of a D2GOS detector acquired during two different modes of operation. Figure 2GOS device during application of a back-gate voltage sweep where the Si is first biased into accumulation and then swept into depletion. Figure To characterize the optical response, devices were exposed to 405 nm and 635 nm laser light of varying optical power (PCNP) is at ~ −2 V, indicating that the graphene is n-type possessing a residual carrier concentration of ~1.3 × 1012 cm−2 (see Supporting Information). The resulting Dirac curve is similar to that observed for GFETs atop a degenerately-doped semiconductor substrate except for an interesting difference when Vbg approaches −0.2 V. Specifically, a distinct reduction in transconductance is observed in this region. This behavior is not observed when a degenerately doped semiconductor is used as the substrate. In contrast, under heavy illumination  whereas it is depleted when Vbg > Vfb. CV measurements of Au/HfO2/Si capacitors adjacent to the D2GOS detectors (see Supporting Information) exhibit a flat-band voltage of near −0.2 V. Thus, owing to the similarity in work function between the Au and graphene23, the drastic reduction in GFET transconductance near −0.2 V when unilluminated arises due to the drastic reduction in capacitance commensurate with the flat-band voltage. Simply stated, the GFET is particularly sensitive to the charge environment at the Si/ox interface. Sensing charge at this interface is the basis for light detection and D2GOS detector operation.These transfer curves can be understood by investigating the changes that occur at the low-doped Si/ox interface with gate bias. For a back-gated nMOS capacitor, the system is biased into accumulation when Vd) when the gate biases silicon into accumulation (Vbg < −0.2 V) versus depletion (Vbg > −0.2 V). When biased into accumulation, mobile electrons in the n-type Si collect at the Si/ox interface. The junction behaves like a parallel plate capacitor, where electron charge present at the Si/ox interface depends on Vbg. This charge is approximated by QSi = Cox(Vbg–Vfb), where Cox is the oxide capacitance and QSi is the areal charge density at the Si/ox interface. The voltage induced electron density at the Si/ox interface, in turn, is balanced by an equivalent hole density within the graphene channel. The increased hole density alters the conductance of the graphene channel. In accumulation, recombination rates in the Si increase with the carrier density. As a result, virtually no photoresponse exists when the device operates in accumulation  in graphene and the size of our devices (hundreds of microns), direct photoconduction within the graphene channel is presumed negligible. This claim is supported by the lack of any measureable change in the drain current during accumulation when exposed to different optical powers  shows a typical D2GOS detector photoresponse at a range of incident optical powers when rapidly biased (<1 µs) into deep depletion with a point-to-point sample read-out time of 3 ms (see Methods). In all cases, as charge collects during deep depletion, the graphene’s conductivity increases linearly (increasing Id) due to an increasing electron charge density created by capacitively coupled hole charge in the potential well. For example, drain current increases linearly with incident power. Therefore, the signal is being integrated even as the detector is being continuously read-out. This dual-capability is a differentiating feature of the D2GOS detector. Of note, consecutively collected acquisition loops showed minimal hysteresis (see Supporting Information). Therefore, charge is being integrated at the interface rather than being dictated by traps within the HfO2 dielectric.This ability is quantified explicitly by recording the drain current after sudden application of a positive gate voltage that induces depletion within the Si . Figure d and Id data. Since the D2GOS device possesses a hybrid modality, charge integration with an electrical current readout, an integration time dependent responsivity is a useful metric for quantifying detector performance. While both methods of back-gate biasing give time dependent responsivities that are approximately consistent, we suspect that the slight discrepancy is due to uncertainties associated with estimating voltage sweep timing and the onset of depletion. Due to these uncertainties, the estimated integration times may be slight larger than the reported estimates in Fig. Since collection times for the illuminated device presented in Fig. d at 0 nW is due to dark charge collecting in the potential well at the Si/ox interface. The sources of this accumulated dark charge derive from exposed positive space-charge and holes generated by thermal and surface generation processes. Functionally, dark charge reduces the capability of the detector by both serving as a source of noise while also filling the well thereby reducing dynamic range. To quantify these non-idealities and the detector performance, the signal to noise ratio (SNR) was calculated by (adopted from refs25 and26):Readout is the signal read out noise. To estimate SNR, dark (Id-Dark(t)) and illuminated (Id-Light(t)) data are used. For these estimates Sdt = Id-Light(t)–Id-Dark(t) and Ddt = Id-Dark(t)–Id(0), where Id(0) is the offset drain current prior to application of the Vbg pulse. Readout noise (I/I2) spanning from 10−6 Hz at low frequency to 10−9 at frequencies > 30 Hz. Readout noise at the sampling rate of 333 Hz is inconsequential relative to that arising from dark processes, possessing a magnitude of ~50 nA.Current is transported through the device even when it remains in the dark  and low illumination levels (<5.9 nW). Importantly, SNR increases with longer integration time. However, due to the graphene-enabled readout of the collecting charge, signal can be constantly monitored at speeds determined only by the rate of graphene photogating. Figure Figure tot = 0.8 µC/cm−2, which is near the predicted capacity of ϕmax = CoxVbg = 0.9 µC/cm−2 21. Given our device size of 200 × 200 µm2, this corresponds to a well capacity of ~2 × 109 and ~2.25 × 109 electrons respectively.The dynamic range is determined by the charge storage capacity of the potential well, the time-dependent dark charge filling it, and the readout noise level. Well capacity was measured by monitoring the source-drain current to saturation in the dark after a gate bias of 3 V was rapidly applied (see Supporting Information). Saturation times of 8–9 seconds were observed at room temperature correlating to a well capacity of ϕ2GOS detector is calculated via27d,Sat is the drain current of a saturated well, Id(0) is the drain current just prior to application of the back-gate voltage (t = 0), Id,Dark(t) is the time dependent drain current under dark illumination, and Inoise is the graphene noise current at the sampling time of 3 ms. As shown in Fig. 2GOS detector exhibits a room temperature dynamic range of 10–30 dB depending on integration time. Removal of dark processes—as could be attained under Peltier based cooling—results in an estimated DR of ~60 dB as shown by the dotted line of Fig. 2 interface rather than the graphene as the dark term dominates Eq. Knowing these characteristics, dynamic range (DR) of the D21 with calculation of current transport through a graphene FET influenced by charge at the oxide interface28 (see Supporting Information). The simplistic nature of this model does not capture every detail of the mechanisms governing this device. However, it allows for a comprehensive qualitative understanding of the response while simultaneously reproducing the gross quantitative features present in the data.To further understand the underlying physics of the device, a semi-analytical model was developed to predict device performance and assess future potential. The simulation couples an analytical model of a MOS capacitor biased into accumulation or deep depletion28. Necessary graphene parameters—mobility and residual carrier concentration—were found by fitting device response when the device is optically saturated (see Supporting Information). Photogenerated carriers within the Si are assumed to recombine before gating the graphene when operating in accumulation.When the Si is biased into accumulation, charge induced in the graphene is calculated by treating the junction as an ideal parallel-plate capacitor. Current through the graphene channel is then calculated in the standard mannerWhen biased to deep depletion, the amount of photo-induced, dark and space charge collected in the potential well is calculated iteratively for a given time-step and gate-voltage until self-consistent convergence of space charge width, surface potential, and charge at the Si/ox interface is achieved (see Supporting Information). This charge is then balanced by varying the Fermi-level in the graphene by an amount corresponding to the interface charge density allowing for the photocurrent to be calculated. For all simulations, graphene is assumed to be an equipotential surface due to the low contact resistance (see Supporting Information) and the large magnitude of the back-gate voltage  when compared to the channel bias voltage (100 mV). Charge loss within the gate dielectric  and any effects related to mobile charge within the oxide are ignored (see Supporting Information). Neglecting the potential drops across the contacts is valid owing to the small contact resistance compared to that of the graphene channel itself. With the use of other metals or a substantial increase in graphene mobility, the simplification would likely lose its veracity.d(Vbg) data taken under dark and illuminated conditions compared to that predicted by the simulation as the back-gate is swept. For both cases, the Id(Vbg) is well represented by the simulation in both accumulation and depletion. Transient behavior is also captured as shown by Fig. Figure To first order, the simulation accurately predicts the response for the both the dark and illuminated conditions. There is, however, an offset between the actual and simulated curves. The largest offset is present in early transience for the dark response in Fig. 2GOS-based detector were assessed as the present devices are limited both by the characteristics of the graphene channel and the Si/ox interface. For example, graphene mobility was measured to be 1,200 cm2/Vs despite published upper values for transferred CVD material exceeding 100,000 cm2/Vs10. Similarly, room temperature surface generation/recombination velocities can be reduced by at least 5x with further refinement of the HfO2 deposition technique29. Such improvements will enhance both responsivity and SNR.To this end, the operational limits of D2/Vs  to 10,000 cm2/Vs . Improvement to SNR, by reducing the surface generation velocity from 480 to 10 cm/s, is also considered (see Supporting Information). Increasing mobility enhances the magnitude of the photoresponse  detector. This scalable detector approach circumvents issues associated with absorbing light into atomically thin absorbing layers, as is the case for many graphene-based detectors. These devices, which have not been fully optimized, are capable of low-incident-power optical detection with responsivities exceeding 2700 A/W and dynamic range exceeding 30 dB at room temperature. Importantly, the device simultaneously integrates its signal even as it is continuously read-out opening up the possibility for alternative imaging modalities. This ability to integrate photogenerated signal combined with localized readout makes the D2GOS detector a self-sensing analog of a depleted MOS capacitor, which is the photo-charge collecting backbone of modern charge-coupled device technology. Additionally, the concept demonstrated here opens up the use of non-traditional semiconductors, such as indium arsenide (InAs), indium antimonide (InSb) and mercury cadmium telluride (HgCdTe/MCT), for use in charge integrating applications since the graphene removes the necessity of long-rang lateral charge transport and can be transferred atop virtually any substrate.We have presented the fabrication, characterization, and analysis of a hybrid graphene/depleted-absorber device termed here as a deeply-depleted graphene-semiconductor  at 900 oC for 30 s in a nitrogen atmosphere. Secondary ion mass spectroscopy (SIMS) revealed that the As was present at depths between 500–750 nm from the backside. The backside was then ion milled to remove any native oxide and a 20 nm/200 nm Ti/Au film was e-beam evaporated for the metal contact. The wafer was then rinsed in 1:4 BOE to remove any protective and native oxides and then ~50 nm of HfO2 was deposited by atomic layer deposition (ALD) at 250 oC (TDMAH and H2O sources) onto the front side of the wafer for use as the gate dielectric. Graphene  was then transferred onto the substrate, rinsed in acetone, IPA, and then blown dry with nitrogen gas. The graphene detectors were then patterned by photolithography and etched by a 600 W O2 (gas flows and pressure) plasma in an asher for several minutes. Subsequently, 20 nm/200 nm Ti/Au etch stops were put down on the left and right side edges of the graphene detector using e-beam evaporation whereupon a passivation dielectric was deposited over the complete substrate. In order to ensure good adhesion of the dielectric onto the graphene, 1.5 nm of Al was first deposited by e-beam evaporation and then oxidized, followed by a 50 nm film of HfO2 by ALD. The etch stops were opened by a 65 s Cl2 etch through the HfO2 and the final Ti/Au source and drain contacts were patterned and deposited using e-beam evaporation.Devices were fabricated on 400 µm thick, n-type, low phosphorous doped <111> silicon wafers possessing a resistivity greater than 5000 Ωcm. The backside of the wafer was implanted with 75 As+ ions with an implant energy of 40 keV and an implant dose of 3 × 10d(Vbg) response of the graphene FET for both dark and illuminated conditions, a HP 4155B semiconductor parametric analyzer (SPA) was used. During a typical measurement, one of the SPAs source measurement units (SMU) supplied a small voltage of 100 mV to the device’s drain electrode (Vd), while another SMU was used to hold the source electrode at ground (Vs = 0 V). A third SMU was used to sweep the Vbg  from an initial starting voltage to a final voltage in discrete Vbg steps. LabVIEW was utilized to record the source and drain currents as a function of Vbg. Various voltage step times (SPA integrations times), ranging from 640 µs to 120 ms, were used during Id(Vbg) sweeps to study the transient nature of charge integration in the D2GOS detector. All electronic measurements were made at room temperature in a Signatone probe station located inside an optically dark box that is shielded from EMI. To establish a connection with the back-gate electrode, devices rest on a conductive chuck located on the probe station.To characterize the I2GOS elements a fast acquisition system was used. A Keithley 2400 applied a constant drain voltage and a Keithley 428 fast preamp was employed to measure the current flowing through the graphene channel. A National Instruments USB-6251 applied the back-gate voltage while monitoring the voltage output from the preamp, which is proportional to the input current. The USB-6251 has an analog output voltage slew rate of 20 V/µs, allowing for biasing of the Si into deep-depletion in under 1 µs. The acquisition was controlled using LabVIEW software.To measure the temporal response of D2 radius of 1690 µm. Measured responsivity and SNR presume the entirety of the measured power is absorbed despite the fact that the devices are a factor of 10 smaller. We take this step to account for the possibility of photogenerated holes, created away from the graphene channel, reaching the device and thus gating the graphene17.Photoresponse was characterized using laser sources—635 nm (Thorlabs S1FC635) and 405 nm (Thorlabs S1FC405)—that deliver light to the probe station’s optical microscope. Laser intensity was controlled below the system’s minimum output using neutral density filters. To account for losses by coupling into the probe station’s optics, the intensity of the laser light was measured after the objective lens using a power meter (Thorlabs S130VC) that was positioned on the probe station’s sample chuck. The output optical power at the objective was correlated to the laser controller’s power setting just prior to photo-response measurements. Beam size and shape were quantified using a DataRay Beam ‘R2 profiler. The beam was approximately Gaussian possessing a 1/eSupporting Information


A series of NFMs with various weight percentage of CoCl2 to PA66 were prepared, and their humidity sensitivity based on color changing and quartz crystal microbalance (QCM) were studied. Due to the color change property of cobalt chloride, the as-spun composite NFMs show obviously macroscopic color change from blue to pink as relative humidity (RH) increasing from 12.4 to 97.2%. Moreover, the QCM detection showed a linear dependence on the RH changing and exhibited short response/recovery time (less than 65.4 s/11 s), small hysteresis (less than 11%), good reproducibility, and stability. Owing to the above double sensitive mechanism on RH, the PA66/CoCl2 composite NFM may show great potential applications from meticulous to coarse.Humidity indicators based on composite polyamide 66/cobalt chloride (PA66/CoClThe online version of this article (doi:10.1186/s11671-017-2139-0) contains supplementary material, which is available to authorized users. Relative humidity (RH) sensor is mainly used for monitoring atmospheric humidity environment and shows important applications in warehousing , environIt is now believed that RH sensors based on the electrospun nanofibrous membranes (NFMs) show improved sensor sensitivity due to their large surface area to volume ratio –13, prov2-based optical humidity sensor [While the sensitivity of the above humidity sensors based on electrospun fibers were detected by precise instrument, , 15 it my sensor , 22 haveIn this work, we fabricated PA66/cobalt chloride NFMs by electrospinning and investigated its humidity sensing properties by extensive color change and both fine quartz crystal microbalance (QCM). The results showed that the electrospun PA66/cobalt chloride NFM sensors exhibiting high humidity sensitivity with obviously color change, rapid response/recovery performance, small hysteresis, excellent reproducibility, and good stability.2·6H2O  and PA66 . As a comparison, the concentrations of CoCl2·6H2O in these solutes were 0 (pure PA66), 10, 30, and 50 wt%, respectively. Dissolved these solutes in formic acid at 12 wt% and stirred thoroughly for 6 h at room temperature, then the uniform precursor solutions were obtained.The solutes were CoCl−1 by a syringe pump . The applied voltage was kept at 18 kV, and the distance between the needle and collector was about 15 cm. The ambient humidity was controlled at 50–60% RH, and the temperature was between 20 and 25 °C. Electrospinning for about 30 min, the as-spun composite NFMs could be obtained.The process of fabricating fiber membranes by electrospinning is depicted in Fig. To further investigate the humidity sensitivity of the as-spun NFM, we also selected QCM for precision measurement. The process of fabricating sensing NFMs on the QCM  chip is showed in Fig. 2 solution, in 20 °C), 55.2% RH , 75.5% RH , and 97.2% RH , respectively.The photographs of the colorimetric NFMs were recorded by a digital camera (DSC-TX9C 50i). Absorption spectra were recorded by a UV-vis spectrometer  under absorption mode. The morphologies and structures of the NFMs were characterized by a scanning electron microscopy  and a transmission electron microscope . Fourier transform infrared (FT-IR) spectra were recorded on a Thermo Scientific Nicolet In10 spectrometer. Means for humidity control are saturated salt solution humidity bottles, which have a stable humidity environments of 12.4% RH , 33.6% RH  of the 50 wt% CoCl80 nm of Sensors based on QCM technique has been attracted a lot of interests due to its advantages of high sensitivity and reliability , 23, 24.2 NFMs with different concentrations of CoCl2 under different RH. As can be found that the resonant frequency of the pure PA66 NFM did not show obvious change even at 97.2% RH, revealing that pure PA66 NFM was weakly sensitive to humidity. In contrast, the resonant frequency of the PA66 mixed with cobalt chloride NFMs sensors obviously shifted. The resonant frequencies of all the three sensors were negative growth corresponded to the increasing of humidity. The frequency shifts of the PA66/CoCl2·6H2O (10 wt%) NFM sensor and the PA66/CoCl2·6H2O (30 wt%) NFM sensor are very close and increased slowly below 75.5% RH. After exceeded 75.5% RH, the frequency shifts of the 10 and 30 wt% NFM sensors increased in a steep manner, which maybe due to that the complexes (Co) shielded by the PA66 molecular chain in low-RH regions and liberated in the high hydrated state in the high RH region [2·6H2O further increased, the shielding effect was weakened; consequently, the resonant frequency shift of the 50 wt% NFM sensor was linear negative increase with the increase of RH and its regression coefficient R2 reached 0.9937. Its maximum frequency shift was −6519.5 Hz at 97.2% RH. The results indicating that incorporation of cobalt chloride can increase the humidity sensitive of the QCM-based NFMs sensors and the sensing response increased with increasing concentration of cobalt chloride in the NFMs, and there were more absorption sites [2 which increased the total amount of absorption water molecules. Based on this discovery, the future investigations about coating CoCl2 on PA66 nanofibers using the modified coaxial and triaxial electrospinning processes are worthy of conducting [Figure H region . And at Cl2·6H2O  wt% NFM on sites  on the Nnducting –31.Fig. 2·6H2O NFM humidity sensors were alternately placed into different humidity bottles. The response and recovery characteristic curves for one cycle from three humidity differences: 12.4–55.2% RH, 12.4–75.5% RH, and 12.4–97.2% RH, with the PA66/CoCl2·6H2O  NFMs QCM sensors were shown in Additional file 2·6H2O (50 wt%) NFM sensors’ repeatability was tested in three humidity differences which corresponded to 12.4–55.2% RH, 12.4–75.5% RH, and 12.4–97.2% RH for five cycles showed as a representative  NFM sensors’ humidity hysteresis characteristic. The black line in the figure was measured from low RH to high RH (from 12.4 to 97.2%), i.e., for the adsorption process, and the red line represents desorption process (measured in the opposite direction). The curves between adsorption process and desorption process have good coincidence for the as-spun sensor. The maximum humidity hysteresis was 9.9% (at about 75.5% RH) for PA66/CoCl2·6H2O NFM sensor with concentration of 50 wt% CoCl2·6H2O, indicating a good reliability of these humidity sensors, and the other humidity hysteresis curves of electrospun PA66/CoCl2·6H2O NFM with different CoCl2·6H2O concentration were shown in Additional file Sensor hysteresis is examined to obtain some information about the reliability , 34. Fig2·6H2O NFM may due to their microstructures. Consequently, the SEM and TEM images of the as-spun NFMs samples are examined. As displayed in Fig. 2·6H2O were the form of nonwoven mats with randomly oriented fibers. Figure 2·6H2O (10 wt%) fibers was about 100 to 500 nm. This might due to the increase of the solution conductivity leading to the increase of the solution-jet instability in the electric field [2+) and chloride ions (Cl−) during electrospinning process. Formic acid, a polar monoprotic solvent with high dielectric constant, is capable of attacking the lactam of nylon to produce a series of short chain oligomer/monomer ions (–CONH2+–) [− and Co2+ could further increase the concentration of ions in the electrospinning solution. The increased of ions could initiate the splitting up of subnanofibers from the main fibers and form the spider-net-like structure during electrospinning [2·6H2O (30 wt%) fibers were relatively uniform with a diameter of about 100 nm  NFM. The further increased in the CoCl2·6H2O (50 wt%) concentration led to a fiber-sticking structure which is more clearly showed in the inset of Fig. As mentioned in the background, the high humidity sensitivity of electrospun PA66/CoClic field . In addiCONH2+–) . The Cl−spinning . The PA6 nm Fig. . Figure 2·6H2O (50 wt%) fibers. From Fig. Figure 2·6H2O (50 wt%) NFM in the dry and hydrated states. Comparing the spectra in dry and hydrated states, there are two obvious absorption bands located at 430–900 and 2750–3660 cm−1 in the dehydration curve. The absorption bands at 430–900 cm−1 are attributed to the bending and rocking modes of Co–OH2  and the rocking mode of O–H···Cl (hydrogen bonding with chlorine). The bands at 2750–3660 cm−1 correspond to the stretching mode of Co–OH2 [−1 in the dry state, which cannot found in the hydrated state spectrum as well as the pure PA66 spectrum. It seems that the addition of CoCl2 in PA66 membrane could lead to the formation of coordination bonds between Co ions and PA66 molecular chain (probably the peptide groups), which caused the 1600 cm−1 peak in the dry PA66/CoCl2 NFM; as the NFM adsorbed water molecules, these coordination bonds are gradually destroyed so that this peak disappears in the hydrated NFM [Figure f Co–OH2 , 41. It ated NFM .Fig. 7FTThe humidity sensitive characteristics of the hybrid PA66/cobalt chloride NFMs mainly come from the cobalt chloride. When exposed to dry atmosphere, the cobalt chloride loses its crystalline water, conversely, in a wet environment it absorbs water molecules and turns into hydrated cobalt chloride. In this process, the color of PA66/cobalt chloride NFM changes. Moreover, in the process of dehydration and hygroscopic, the mass of the NFMs also changes, which leads to an according change of resonant frequency. In addition, it is noted that the PA66 has very small contribution to the mass change because the pure PA66 NMF can only cause a small frequency shift when RH changes.2 concentrations on morphology, color, and humidity sensitivity of the NFMs have also been systematically studied. The hybrid membranes exhibit different colors in different humidity conditions, indicating that PA66/cobalt chloride NFMs have promising application in visual hygrometer. Furthermore, PA66/cobalt chloride NFMs deposited on QCM also exhibit interesting humidity sensing properties. Since the nanofibrous structure may increase the sensing area and surface activity, the QCM-based humidity sensor shows high sensitivity, fast response, and recovery time, good reproducibility in moisture-sensitive and longtime stability in a stable humidity environment with a little frequency shift. These results indicate that the PA66/cobalt chloride NFM sensor has potential applications in humidity detection.In summary, hybrid PA66/cobalt chloride humidity sensitive colorimetric nanofibrous membranes have been fabricated successfully by electrospinning. The influences of CoCl


Graphene and its derivatives hold a great promise for widespread applications such as field‐effect transistors, photovoltaic devices, supercapacitors, and sensors due to excellent properties as well as its atomically thin, transparent, and flexible structure. In order to realize the practical applications, graphene needs to be synthesized in a low‐cost, scalable, and controllable manner. Plasma‐enhanced chemical vapor deposition (PECVD) is a low‐temperature, controllable, and catalyst‐free synthesis method suitable for graphene growth and has recently received more attentions. This review summarizes recent advances in the PECVD growth of graphene on different substrates, discusses the growth mechanism and its related applications. Furthermore, the challenges and future development in this field are also discussed. The energetic electrons generated by the plasma boost the ionization, excitation and dissociation of hydrocarbon precursors at relatively low temperature. Thus, low‐temperature growth of graphene can be realized directly on desired substrates by PECVD in the absence of metal catalysts. Therefore, PECVD has attracted more and more attention as a promising method for controllable graphene synthesis. In this review, we summarize recent advances in plasma‐enhanced controllable synthesis of graphene including graphene and VG nanosheets. The growth mechanism and their potential applications such as flexible photovoltaic devices, field‐effect transistors (FETs), sensors, supercapacitors, and charge trapping memory (CTM) are also discussed in detail.2FigureThe experimental setup for PECVD consists of three main parts including the gas, the plasma generator and the vacuum heating chamber, as illustrated in 2, O2 are added as amorphous carbon etchants to produce high‐quality graphene and its derivatives. (iii) Gases such N2, NH3 normally are used to achieve the doping of as‐grown graphene, which can tailor the electrical properties of graphene.Gaseous species are essential for the synthesis of graphene and its derivatives, which can be categorized into three functional groups. (i) The gaseous precursors containing carbon provides carbon radicals for graphene growth via plasma‐enhanced reaction. (ii) Gases such as HDuring the plasma‐enhanced process, the source gas is activated by the energetic electrons generated in the plasma. The ionization, excitation, and dissociation of the source gases all occur in the low‐temperature plasma process. First, the ionization processes proceed via interactions between energetic electrons and gas molecules. Second, high‐energy ions generated in ionization processes subsequently react with source gas molecules. Finally, various radicals form via various dissociation reactions. These radicals are more reactive than ground‐state atoms or molecules, which enable the formation of graphene and its derivatives on catalyzed or noncatalyzed surfaces at low temperature. In order to optimize the synthesis process, the plasma‐enhanced process needs to be understood theoretically and experimentally.V change dramatically, as shown in Figure Simulations of the plasma process have been performed to optimize the growth parameters. A number of plasma models have been developed based on different gas systems.Figure2, CH4 C2H6, C3H8, C2H4, and C2H2) increase linearly with increasing CH4. Radicals  remain almost constant at different CH4/H2 ratios. For the ions, the H2+ and H3+ show a dramatic decrease with the rising of CH4 gas flow while slight increase could be observed for CH5+ and C2H5+ ions, as shown in Figure 2 and related ions (H2+ and H3+) form in the plasma, but other radicals and ions  show no variations with increasing CH4, as shown in Figure 2H5+ ions increase while the other ions  drop drastically, as shown in Figure The densities of ions and radicals are also influenced by the power, gas mixture ratio, gas flow and pressure. In the 1D fluid model of methane/hydrogen system, all species except methane increase slightly at higher plasma power due to more dramatical reactions among electrons, ions and radicals, as shown in 4 and CH4/H2 systems, several models are also used for the Ar/CH4/H2,2H2/H2,2H2/NH3,4/NH3,2H2/NH34 and H2 decrease more dramatically with the plasma power. For nonradical and radical neutrals, higher hydrocarbons (CxHy) are more likely to break into radical fragments due to more intense electron‐neutral reactions in Ar plasma, compared to the CH4 and CH4/H2 systems. In the plasma models containing NH3, additional 22 species, 43 electron‐impact reactions, 48 ion‐neutral reactions and 67 neutral‐neutral reactions should be considered. For the Ar/C2H2/NH3 systems,2H2 and NH3 dissociation reactions. It is speculated that hydrogen related species generated from the NH3 dissociation reactions produce evident etching effects on amorphous carbon structures which is important for the formation of pure CNT structures. Pure and above 30% C2H2 plasma results into amorphous carbon like films and obelisk‐like nanotubes.Besides the CH3, CH, and CH2) and neutrals  are found to change with plasma power. MS is a common method of monitoring species at the substrates, but it is difficult to assess unstable species.xHy neutrals and radicals. The OES provides the information of related ions in plasma processes.The plasma process is also investigated by experiments such as laser‐induced fluorescence spectroscopy (LIFS),2, Ar can serve as amorphous carbon etchant toward high‐quality graphene. Other additional species such as NH3, N2 can dope graphene with heteroatoms and adjusting the electrical properties. All simulative and experimental results above offer information about these species and reactions, which contribute to understanding kinetic growth in the plasma process, which are of great significance to realization of the controllable synthesis of graphene.Plasma‐enhanced process is a complicated process containing various kinds of species and reactions, which play an important roles in the plasma‐enhanced growth process of graphene. For example, the density of carbon related species can influence the morphology of the as‐grown graphene. Additional species such as H3Graphene has been considered as an attractive candidate for future electronic materials due to its excellent electrical properties and atomic thickness. The 2D structure enables graphene to be adapted to current photolithography and integration processes. Among existing synthetic methods, CVD has been considered one of the most promising methods as it can grow high‐quality graphene films at relatively low cost. Large area polycrystalline and millimeter‐sized single crystalline graphene has been synthesized and applied in electronics.3.1Figure Thermal CVD growth of graphene on transition metal substrates usually requires a high temperature (800–1000°C), which is still too high for industrial production. Therefore, low‐temperature synthesis of graphene remains challenging for applications in electronics. PECVD can achieve the low‐temperature growth of high‐quality graphene films on transition metal substrates such as Ni,Figure2 but also sp3 carbon form in the growth process in the absence of hydrogen.The typical dissolution precipitation occurs on transition metal with high carbon solubility such as Ni during the plasma‐enhanced growth process. The substrate temperature, the film thickness and the deposition time make obvious influence on the thickness and the crystalline structure of as‐grown graphene. Peng et al.2/Si substrate by the rapid‐heating plasma CVD (RH‐PCVD).Figure2/Si substrate. At the initial growth stage, hexagonal domains of graphene with size of about 10–20 μm can be observed on the SiO2/Si substrate after etching the Ni layer, as shown Figure 2/Si substrate with high controllability in size and shape. Moreover, the electrical properties of the graphene can be tuned by introducing NH3 plasma during the RH‐CVD growth process. The negative shift in Dirac point can be seen in the transfer curve of N‐doping graphene grown under NH3 plasma, as shown in Figure 3 flow rates result into more negative Dirac point.The dissolution precipitation occurs on not only the surface but also the underneath of transition metals. High‐quality monolayer graphene with a hexagonal domain has been synthesized along the interface between deposited Ni films and SiOFor metal substrate with low carbon solubility, the surface catalyzed dissociation mainly occurs during the graphene growth process. Polycrystalline Cu foil has been used as an excellent substrate for growth of high‐quality monolayer graphene over large area, due to its catalytic nature.x radicals could not be dissociated into C2 by Co catalyzed dissociations, which are necessary for the 2D extension of graphene domains. CHx radicals generated in the plasma can terminate the growth of graphene domains and form new nucleation sites of graphene on Co film, leading to more edge and boundary structures on the Co film. Therefore, the ratio of ID/IG in Raman spectra initially decreases and then increases with the growth process.For metal substrate with high carbon solubility and catalyzed surface, both dissolution precipitation and catalyzed dissociation occur during the growth process. For example, Co is a transition metal with a high carbon solubility of 4.1 at% and catalytic property for the dissociation of hydrocarbon precursors. It has been reported that few‐layer graphene can be successfully grown on polycrystalline Co films at 800 °C by RF‐PECVD.3.22O3, SiO2, and MgO.2 and SiN substrates by thermal CVD.2 V−1 s−1. However, the high growth temperature is not compatible with existing semiconductor technologies.Large‐area graphene with high quality has been grown on transition metal substrates such as Ni or Cu foils by CVD. However, the metal‐catalyzed grown graphene requires posttransfer and catalyst removal for the applications in electronics. Chemical contamination and structural defects  cannot be avoided due to the metal etching process. It is widely believed that direct growth of graphene films on dielectric substrates would promote the widespread application of graphene films in future electronics. The pioneering study has reported synthesis of graphene on dielectric substrates by pre‐depositing sub‐micrometer‐thick Cu films as the buffer layer. The buffer Cu layer is then removed by evaporation in a high temperature low‐pressure atmosphere, but the evaporation of metal films still induces contaminations, wrinkles, and breakage in graphene films.2, atomic layer deposited (ALD) Al2O3, sapphire, quartz, mica, Si and so on at a relatively low temperature ≈550 °C.2 substrates has been studied using atomic force microscope (AFM), as shown in Figure2 substrates with 1.2–1.5 nm thickness, corresponding to 2–3 layers graphene. With the continuous growth, higher density of nanographene islands form and coalesce into a continuous and uniform nanographene films. The as‐grown nanographene films consist of densely packed nanoislands. Raman spectra show characteristic peaks of a graphitic structure with D, G, and 2D peaks and the XPS C 1s spectrum is well fitted with a dominant peak assigned as sp2 carbon, as shown in Figure −1) are obtained using different growth time, indicating that the optical and electrical properties of nanographene films could be adjusted by growth time, as shown in Figure Plasma‐enhanced CVD has attracted much interest as an important method to achieve low‐temperature growth of graphene on dielectrics. Pioneering researches in this field demonstrate nanographene films growth on various substrates such as SiO2/Si substrates, two‐terminal nanographene field‐effect devices could be fabricated by electron‐beam lithography and lift‐off techniques without posttransfer process. The nanographene based devices exhibit an ambipolar field‐effect behavior with the mobility of 15 cm2 V−1 s−1. The mobility is far lower than graphene films grown by thermal CVD due to small crystalline size and numerous edges. Moreover, it should be mentioned that the gate modulation of nanographene based devices is very weak and the on/off ratio is close to 2. Similar nanographene films can be achieved on other substrates such as ALD Al2O3, sapphire, quartz, mica, Si, SiC.With the advantage of direct growth on SiO2 plasma in PECVD.2/Si with the growth temperature as low as 450 °C. Figure2 plasma is introduced to activate edges for the critical crystal growth. Edge growth, edge etching and nucleation are observed during the plasma‐enhanced growth process, as shown in Figure 2 content with the width decreasing from 349 nm to 181 nm, as shown in Figure 2/Si substrates by using graphitic clusters as the grown seeds, as shown in Figure 2 V−1 s−1, similar to the metal‐catalyzed CVD graphene and exfoliated graphene.The plasma‐enhanced CVD enables the growth of nanographene films on arbitrary dielectric substrates. However, applications of nanographene films in electronics are limited to weak gate modulation and low field effect mobility. In order to enhance the electrical properties of the as‐grown graphene, Wei et al. develop the critical crystal growth of graphene by introducing H−1 , which is far lower than the growth rate of metal‐catalyzed CVD. Moreover, the nucleation density of the PECVD can reach ≈107 nuclei cm−1, which is about six orders of magnitude higher than CVD with reduced nucleation density (≈4 nuclei cm−1).Although better electrical properties can be obtained with HCGs grown by critical PECVD, this method still suffers from low growth rate and high nucleation density. For example, the growth rate of the critical crystal growth by PECVD is normally below 10 nm min3.32/Si substrates have been widely used as the common substrate for fabrication of the graphene devices, the electrical transport properties of graphene are largely limited to the surface roughness, impurities, charged surface states and large lattice mismatch of amorphous SiO2. 2D materials have been found to be better substrates due to its electrical properties and ultra‐flat surface. Graphene based devices exhibit high carrier mobility when using h‐BN as the substrateV ≈ 0.7 V nm−1) of h‐BN is comparable to those of SiO2, which enables it an excellent gate dielectric material. The graphene‐based devices on h‐BN substrate show an attracting performance. Graphene/h‐BN hetero‐structures are fabricated via mechanical transfer process. For example, Dean et al. fabricated graphene devices on single crystal h‐BN substrates via poly‐methyl‐methacrylate (PMMA) based transfer techniques.2/Si substrates. Moreover, the h‐BN can behave as an ideal tunnel barrier due to its large band gap (5.2–5.4 eV) and atomically thin structure like graphene. The alternative device fabricated by the h‐BN sandwiched by two graphene electrodes shows high on/off ratio of 106, which provide another effective solution to low on/off ratio in graphene based devices.2 V−1 s−1 and the secondary Dirac cone can be observed due to the moiré pattern.Although SiOFigureDirect growth of graphene on h‐BN by thermal CVD normally suffers from high growth temperature (above 1200 °C) and low growth rate. The PECVD is also used to achieve the low temperature (≈550 °C) epitaxial growth of graphene on h‐BN.4x (x = 1–3), CF4, CHF3, or C2F6), gas composition and proportion,VG nanosheets are 3D internetworks of graphitic sheets arranged vertically on substrates. Because of the spatial alignment effect, VG nanosheets show some unique functional properties such as exposed reactive edges, high surface‐to‐volume ratio and high electrical conductivity. These properties enable VG nanosheets to have a wide range of applications as field emitters, supercapacitors, lithium‐ion batteries, gas sensors and biosensors. PECVD has used as a key synthesis technique for producing VG nanosheets.4.14/H2, CF4/H2, CHF3/H2, and C2F6/H2 as the precursors respectively. The VG nanosheets could grow into not only thin and wavy in CH4/H2 system but also maze‐like morphologies in fluorocarbon/H2 systems. Moreover, the inter‐layer spacing of VG nanosheets increased with using CH4/H2, CF4/H2, CHF3/H2, and C2F6/H2 respectively. Teii et al.2H2/N2/Ar and CH4/N2/Ar as the precursors respectively. It is found that the different morphology of VG nanosheets is due to the difference in the carbon dimer density. Low carbon dimer density of CH4/H2 system contributed to the formation of sp3‐C or amorphous carbon (a‐C) while high carbon dimer density promoted the growth of the pure VG networks. VG nanosheets with more ordered orientation and more uniform sheet height could be obtained in C2H2/H2 system, compared with CH4/H2 precursors.Figure VG nanosheets can grow into a variety of morphologies such as petal‐, turnstile‐, maze‐, and cauliflower‐like with different growth parameters. For example, different kinds of morphologies have been obtained by changing the feedstock gas type.4.2Figure4 diluted in H2 as gas precursors. The density of VG nanosheets is found to be strongly dependent on CH4 concentration and growth temperature. Higher nucleation density and smaller lateral size could be obtained with higher concentration CH4 (10–100%) and growth temperature (630–830 °C), as shown in Figure The density of VG nanosheets can vary depending on plasma power, gas composition, temperature and substrates. Yang et al.4.34/H2 in an ICP system. Their work suggested that hydrogen atoms could act as effective etchant to remove the amorphous carbon. Shang et al.2 and H atoms, which benefit the growth of VG nanosheets. Based on OES measurement in a TM‐MW system, Teii et al.2 formed via direct dissociation reaction in C2H2/H2/Ar gas.All the carbon structures such as amorphous carbon, VG nanosheets, CNTs and diamond carbon can be produced by the PECVD. The effective removal of a‐C has been widely recognized as a crucial and inevitable step to the formation of high‐quality nuclei, and then further vertically grown VG nanosheets.VG nanosheets usually cannot be obtained with pure methane as the precursor because of the absence of the etchant radicals. However, with the use of high‐intensity plasma source, VG nanosheets could be synthesized using pure methane as precursors.55.1In thermal CVD process, the graphene can be grown on the surface of the transition metals by surface catalytic decomposition mechanisms. The metal catalyzed growth of graphene involves surface processes including dissociation of hydrocarbon molecules, formation of C clusters, surface diffusion and extension of graphene nuclei.Figure2/Si, Al2O3, mica, silica and even glass with low growth temperature.Koichiro Saiki et al. have reported the growth of graphene by PECVD on catalytic metal surfaces, and related mechanisms are also discussed in detail.5.2FigureIn the nucleation and coalescence mechanism, nanographene with domain sizes varying from few to tens of nanometers nucleate on the substrates. The nanographene should be enlarged by edge growth rather nucleation in order to obtain high‐quality graphene films. Liu et al. present the competition of etching and growth mechanism in the catalyst‐free growth of the graphene by PECVD.2 plasma is known to etch the graphene from edges.2 plasma treatment, macro‐structural defects are removed and atomically smooth hexagonal configurations form at the edges, as shown in Figure2 plasma treatment according to the previous first‐principles calculations.2 plasma can serve as the active sites for the crystal growth of graphene in the CH4/H2 plasma. After growth, the zigzag configurations transform into armchair configurations, which is in agreement with previous theoretical studies,2 plasma etching and CH4 plasma growth in c‐PECVD is illustrated in Figure Similar competition of etching and edge growth is also reported by Wei et al. in critical crystal growth of graphene.5.32/Si, which can direct the electric field from plasma to the substrate surface.FigureWu et al. first report the successful synthesis of CNWs on sapphire substrate.66.1−1). Till now, graphene films and graphene based composites have been exploited as transparent flexible electrodes in dye‐sensitized solar cells−1).Graphene has potential applications in future photovoltaic devices, due to its high transparency (98%) and extremely low sheet resistance  are networks of graphene sheets and can also be used in carbon‐based solar cells.6.22 V−1 s−1, indicating promising applications in digital logic devices and high frequency devices.2/Si sapp, hire, mica, h‐BN for applications in FETs.2 V−1 s−1. Moreover, nanographene field‐effect devices show weak gate modulation and low on/off ratio. More reasonable synthetic methods are required for graphene films with less boundaries and edges.Graphene is a 2D material with ultrahigh mobility and ambipolar field effect. The room temperature field effect mobility of graphene based transistors have been proved to be as high as 15 000 cm2/Si was observed in the C2H4/H2 plasma.2/Si with the size of about 1 μm. FETs based on HGCs show high mobility in the range of 550–1600 cm2 V−1 s−1, as shown in Figure3/CH4 mixtures by PECVD.3/CH4 plasma.2 V−1 s−1, higher than amorphous nitrogen doped carbon film (10 cm2 V−1 s−1) and comparable to NG (200–450 cm2 V−1 s−1) grown on transition metal. The defect‐free crystalline structure formed the etching and growth process contributes to the outstanding electrical properties of NG films, which shows potential in the future FETs.Catalyst‐free crystal growth of graphene on SiO2/Si substrates. h‐BN is an excellent substrate with atomically smooth surface and small lattice mismatch with graphene. The similar 2D structure and Van der Waals between h‐BN and graphene favor the epitaxy growth in PECVD process. The mobility of graphene films grown on h‐BN by PECVD show the higher mobility of about 5000 cm2 V−1 s−1, compared with graphene grown on SiO2/Si substrates.However, the mobility of HGCs and NG grown by PECVD is still far lower than that of single crystalline graphene.6.3Supercapacitors (electric double‐layer capacitors and pseudocapacitors) have attracted much interest as a new energy storage device because of excellent charge/discharge rates, long cycle life, and high power density.−1 at a scan rate of 10 mV s−1 and negligible capacitance after 1500 cycles at high current density, as shown in Figure2‐VG showed similar electrochemical behaviors as EDLCs. Similar applications of VGs decorated with MnO2 of diverse morphologies and other transition metal oxides have also been reported.Recently, vertical graphene nanosheets (VGNSs) was directly synthesized on Ni foams with natural precursor butter at low temperature.6.4Figure3 by adjusting the growth temperature because higher temperature resulted in higher nucleation sites, leading to a higher gauge factor.Recently, graphene based materials have been widely studied for sensing applications, e.g., in strain sensors,Wearable temperature sensors have been widely used in applications, such as electronic skins, robot sensors and human‐machine interface. CNWs transferred onto PDMS substrates are found to be three orders higher temperature coefficient of resistivity than other graphene materials due to excellent stretch ability of GNWs and large expansion large of PDMS.The carbon nanomaterials normally achieve high sensitivity in the detection of bimolecular due to its extremely sensitive surface. The biosensor has been fabricated by direct growth of VG sheets on the sensor electrode through PECVD.2, H2O, or NH3) on the surface, graphene based devices also show increase or decrease in conductivity. GNWs fabricated on metal electrodes by dc plasma‐enhanced CVD can respond to relatively low concentrations of NO2 and NH3, suggesting a low cost effective method to fabricate large‐scale gas sensors.When absorbing gas molecules , charge storage layer (nanographene), blocking layer (4 nm Al2O3) and gate electrode, as shown in FigureDue to the abundant edges, chemical and thermal stability, low cost, and capability with complementary metal oxide semiconductor (CMOS) devices, nanographene is considerate to be a good candidate as charge trapping material. Zhang et al. have reported nanographene based CTM.4 s. A charge loss of 44% after 10 years' operation is also predicted from data which may be caused by tunneling of neighbor nanographene.The capacitance–voltage (CV) characteristics under different sweep voltages are shown in Figure 7−1. (ii) The growth of single crystalline graphene contributes to higher motilities and more stable electronic properties. Recently, millimeter‐sized single crystalline graphene domains have been achieved on transition metals by conventional CVD, but large domain size of single crystalline graphene has not been synthesized on dielectric substrates by PECVD. (iii) The performance of graphene based devices can be further improved by using more favorable 2D materials. For example, h‐BN is a superior insulting substrate for graphene based device. The graphene grown on h‐BN exhibits higher mobilities with small band gap. Moreover, atomic thin h‐BN also can be used as the tunnel barrier in vertical graphene device. Besides h‐BN, other 2D materials should be explored as the substrates for graphene growth. (iv) VG nanosheets, as a 3D graphene network, have been widely used in various applications, such as photovoltaic devices, supercapacitors and sensors. The controllable synthesis of VG nanosheets with different morphologies and structures benefits the improvement in device performance. In the future, systematic studies are required toward better controllability. In conclusion, PECVD is a more promising method for controllable synthesis of graphene and its derivatives, and should be further explored.In summary, we discuss controllable synthesis of graphene and its derivatives by PECVD and its related applications. Both 2D graphene and VG nanosheets have been synthesized by PECVD on various substrates. Compared with thermal CVD, the growth temperature could be adjusted to be compatible with the level of the Si‐based electronics with the aid of the plasma. More importantly, the successful growth of graphene materials on dielectric, conducting and semiconducting substrates promotes the applications in FETs, sensors, energy conversion and storage devices. However, it remains challenging to realize practical applications of PECVD grown graphene. (i) wafer‐scale synthesis of high‐quality graphene on dielectric substrates would promote its applications in electronics, but PECVD growth rate is too low for industrial‐scale production. For example, the growth rate of critical crystal growth of graphene is below 10 nm min


PD-L1 has recently been shown to be associated with PD-L1 mRNA expression in various malignancies. This study aimed to investigate the association of PD-L1 and PD-L2 methylation with mRNA expression, immune cell infitration, protein expression and human papilloma virus (HPV) infection in head and neck squamous cell carcinoma (HNSCC) patients.DNA methylation of the immune checkpoint gene PD-L1 and PD-L2 correlates inversely with mRNA expression . Methylation of specific CpG-sites of both PD-L1 and PD-L2 were further significantly associated with HPV infection in the TCGA cohort. Immune cell infiltrates correlated significantly with PD-L1 and PD-L2 methylation. In the validation cohort, PD-L1 protein expression was associated with PD-L1 hypomethylation (p = 0.012).DNA methylation of PD-L1 and PD-L2 is associated with transcriptional silencing and HPV infection in HNSCCs. Additional studies are warranted to test PD-L1 and PD-L2 methylation as predictive biomarkers for response to immunotherapies (e.g. pembrolizumab and nivolumab) that target the PD-L1/PD-L2/PD-1 immune checkpoint axis.DNA methylation of PD-L1 and PD-L2 promoter methylation and its mRNA expression were analyzed based on Infinium HumanMethylation450 BeadChip and RNA-Seq  data in a representative HNSCC patient cohort (n = 528) enrolled by The Cancer Genome Atlas (TCGA) Research Network. A validation cohort consisting of 168 HNSCC patients treated at the University Hospital Bonn was analyzed regarding PD-L1 and PD-L2 promoter methylation by means of methylation-specific quantitative real-time PCR. PD-L1 protein expression in the validation cohort was quantified via immunohistochemistry . Head and neck squamous cell carcinoma (HNSCC) is a major health burden with over 60,000 newly diagnosed patients in the U.S. every year . The maj®, Merck & Co., Inc., US) or nivolumab  achieved durable antitumor activity in recurrent and/or metastatic HNSCC. The KEYNOTE-012 and Checkmate 141 trials have revealed overall response rates of 18% and 13.3%, respectively [Treatment with the PD-1 targeting antibodies pembrolizumab  and a small validation cohort from the University Hospital Bonn.Transcription of the gene ng HNSCC . PD-L2 etivation . PD-L1 ativation . PD-L2 htivation . Tumor btivation –21. In Hrognosis . In the PD-L1 promoter methylation within the TCGA cohort, Illumina Infinium HumanMethylation450 BeadChip beads  targeting loci within the promoter regions of the PD-L1 or PD-L2 genes were used  compared to cg07211259  and four out of five PD-L1 . While PD-L2 mRNA expression was significantly higher (p < 0.001) in tumors, PD-L1 mRNA expression showed no difference.For the analysis of d Figure  and 1B. PD-L2 hypomethylation in tumors compared to NATs .The analysis of 161 tumor tissues and 126 NATs from the UKB cohort confirmed PD-L1 and PD-L2 promoter methylation with clinicopathologic variables in both cohorts can be found in The correlations and associations of PD-L1 and PD-L2 showed a significant inverse correlation with the respective PD-L1 and PD-L2 mRNA expression . Clinicopathological correlations and associations of PD-L1 protein expression in the UKB cohort are found in To date, no research exists that firmly establishes a connection between PD-L1 and PD-L2 methylation levels in HPV-positive compared to HPV–negative tumors were found at loci targeted by beads cg19724470 (PD-L1) and cg14440664 (PD-L2)  towards lower methylation in HPV-positive compared to –negative tumors was found for PD-L1 bead cg15837913. PD-L2 mRNA expression was lower in HPV-positive compared to –negative tumors . The PD-L2 qPCR assay targets the binding region of bead cg07211259 which already did not reveal methylation differences between HPV-negative and HPV-positive tumors in the TCGA cohort . However, an association of the PD-L1/PD-L2 methylation and PD-L1/PD-L2 mRNA expression in the TCGA cohort. PD-L2 and PD-L1 mRNA expression was significantly positively correlated with all analyzed immune cell infiltrates (Table + and CD8+) and dendritic cells while the correlation with B cell infiltrates was only weak. Significant inverse correlation between PD-L1 methylation and infiltrates of dendritic and CD8+ T cells  and CD4+ T cells (cg14305799 and cg13474877) were observed. No correlation was found between PD-L1 methylation and infiltration of B cells. In contrast, a strong positive correlation of PD-L2 methylation (bead cg14440664) with B cell infiltrates was observed. While PD-L1 methylation was inversely correlated with T and dendritic cell infiltrates, PD-L2 methylation as determined with the HPV-associated locus targeted by bead cg14440664 showed a strong positive correlation with the infiltration of all immune cells under investigation  were correlated with Recently, the PD-1 checkpoint inhibitors nivolumab and pembrolizumab that block the binding of the PD-1 ligands PD-L1 and PD-L2 have gained regulatory approval for the treatment of recurrent and metastasized HNSCC. There is an evolving body of evidence suggesting that PD-L1 expression on the surface of tumor cells themselves and on tumor infiltrating immune cells may contribute to outcome in HNSCC and other solid tumors under immune checkpoint inhibition. Immunohistochemical assessment of intratumoral PD-L1 protein expression has been used to predict the response to PD-1/PD-L1 immune checkpoint blockage in several solid tumor entitiesfrom early therapeutic attempts on . SubsequA potential pitfall of PD-L1 immunohistochemical tests is based on the fact that expression of PD-L1 may vary greatly in a single pre-treatment tumor specimen, which may indeed be due to a high turnover of membranous PD-L1 protein. It seems crucial to recall that adaptive expression in response to pro-inflammatory factors on the tumor surface may add to heterogeneous PD-L1 protein expression in tumors that lack constitutive activation by innately dysregulated signaling pathways. This may especially hold true for HNSCC, since PD-L1 expression has been shown to involve both constitutive and adaptive mechanisms in HNSCC . While PPD-1 methylation in HNSCC is associated with survival and HPV infection in HNSCC, indicating an epigenetic regulation of the PD-1/PD-L1/PD-L2 immune checkpoint axis in HNSCC [PD-L1 and PD-L2 promoter methylation with the respective mRNA expression, supporting the hypothesis of DNA methylation as an epigenetic silencing mechanism of these immune checkpoint genes in HNSCC. From our point of view, the present study will be of considerable value demonstrating that membranous PD-L1 protein expression may be traced back to differential PD-L1 methylation in HNSCC. In this respect, quantitative methylation analysis seems to be a groundbreaking technical extension potentially offering automated processes to determine immunoresponsiveness in HNSCC. From the oncologist’s point of view, what is needed are biomarkers which can be quickly implemented and robustly determine the individual chance of response.We have shown recently, that in HNSCC . The prePD-L1 qPCR probed 5 CpG sites of which the two CpG-sites included into the bead cg19724470 are only targeted by the qPCR hydrolysis probe and not by the primers. The same limitation applies to the PD-L2 qPCR assay which targets three CpG-sites including the single CpG-sites probed by the respective bead cg07211259. Accordingly, a quantitative approach that allows for methylation analysis at single CpG-site resolution, e.g. quantitative bisulfite sequencing [PD-L2 methylation, a strong positive correlation with immune cell infiltrates, PD-1 expression and HPV-related hypermethylation is found at locus targeted by bead cg14440664. Kadel et al. [PD-L2 locus cg14440664 might originate from immune cells which specifically infiltrate HPV-positive tumors. This would be in line with distinct patterns of HPV-related immune cell infiltrates [Our study suffers from two major limitations. While we were able to show a general inverse correlation between methylation and mRNA expression for all analyzed CpG-sites within the respective gene in the TCGA cohort, the association with HPV infection seems to be much more nuanced and restricted to certain single CpGs. Hence, a more detailed analysis of each single CpG-site is required. This finding also might be an explanation for the discrepant results obtained with the Illumina bead chip and quantitative real-time PCR technologies, which both target different CpG-sites. Bead cg19724470 for example targets two CpG-sites, while the respective iltrates , 27. HowPD-L1 and PD-L2 methylation warrants further evaluation in the context of prospective studies as a biomarker for response prediction to treatments with anti-PD-1/PD-L1 antibodies, i.e. pembrolizumab and nivolumab.Based on our evolving knowledge of the underlying pathways, PD-L1 immunohistochemical testing in the context of therapies with PD-1/PD-L1 antagonists only in part meets the demands on a predictive biomarker. Gene methylation, on the other hand, seems to be a favored candidate for a predictive biomarker in that it can accurately and robustly be determined in various sample types, including minute amounts of formalin-fixed and paraffin-embedded tissues –30. Recehttp://cancergenome.nih.gov/.The results shown here are partly based upon data generated by The Cancer Genome Atlas (TCGA) Research Network: n = 10, no: n = 518), adjuvant postoperative radiation therapy , and adjuvant postoperative pharmacotherapy . The TCGA data set provides data on 36 HPV-driven HNSCC, 243 HNSCC that occurred without HPV infection as well as 50 samples of normal adjacent tissue (NAT). Tumor samples where classified as HPV-positive or -negative by mapping of RNASeq reads [PD-L1 and PD-L2 promoter methylation was assessable for 528 specimens. PD-L1 and PD-L2 mRNA expression data were available from 520 patients.The TCGA patient cohort is comprised of 528 retrospectively enrolled HNSCC patients. Informed consent was acquired from all patients in accordance with the Helsinki Declaration of 1975 by the TCGA Research Network. In addition to surgery, patients received neoadjuvant therapy  was available from 157 samples.168 HNSCC patients who underwent surgical resection at the University Hospital Bonn between 2010 and 2014 were retrospectively enrolled. The study protocol was approved by the ethics committee of the University Hospital Bonn. PD-L1 (m PD-L1) and PD-L2 (m PD-L2) promoter regions HNSCC patient samples was analyzed using seven Illumina Infinium HumanMethylation450 BeadChip beads , which are located in the PD-L1 and PD-L2 promoter region  data of level 2 were downloaded from the TCGA webpage. Background-corrected unmethylated (intensity_U) and methylated (intensity_M) summary intensities as extracted by means of the R package ‘methylumi’ were applied. Methylation of the PD-L1 was performed as described previously [PD-L1 promoter was duplexed with an assay specifically amplifying a CpG-free region within the ACTB gene locus. The target region of this PD-L1 assay overlaps with the target region of the peripheral bead cg19724470 [PD-L2 was assessed using a quantitative methylation-specific real-time PCR assay targeting the locus Chr9:5510477-5510616 (GRCh38.p10) that overlaps with the target region of the central bead cg07211259. PCR composition and cycling program was identical as for PD-L1 assay but with PD-L2-specific oligonucleotides . 20 ng bisulfite-converted template DNA quantified via UV-spectrophotometry was measured in triplicate. Quantitative DNA methylation levels were calculated using the ΔΔCT method adapted for methylation analyses [Bisulfite-converted DNA from the UKB cohort was prepared using the innuCONVERT Bisulfite All-In-One Kit   followineviously . In brie19724470 . mPD-L2 analyses .RNA-Seq Version 2 data  were generated by means of the Illumina HiSeq 2000 RNA Sequencing Version 2 analysis  and obtained from the TCGA Research Network.IHC quantification of PD-L1 protein expression was performed using the PD-L1 antibody clone 22C3  according to the manufacturer’s instructions. PD-L1 expression was regarded as positive in cases with ≥1% positive membranous staining.+ and CD8+ cells, macrophages, and dendritic cells) were obtained from Li et al. [Quantitative data on immune cell infiltrates . Differences between groups were tested using Mann-Whitney U test, Kruskal-Wallis test, Χ2 test, t-test and ANOVA with Bonferroni post hoc analysis. P-values < 0.05 were considered to be statistically significant.The statistical analyses were performed using SPSS, version 23 . Correlations between m


The presence of nanocrystalline structures on graphene matrix in TEM and SEM images of 1@graphene indicate that the cluster (1) has been immobilized. The composite, 1@graphene evolves H2 gas from p-toluene sulfonic acid (TsOH) in a mixture of H2O and CH3CN under ambient conditions with a significant turnover number of 3200. 1@graphene electro-catalyzes H2 evolution at Ep, −1.2 V with remarkable throughput, catalytic efficiency and stability in only H2O or in only CH3CN. The Fe4S4 cluster (1) alone electro-catalyzes hydrogen evolution at Ep, −0.75 V from TsOH in CH3CN. The X-ray crystal structure of the Fe4S4 cluster (1)  shows that it is dianionic with a cumulative oxidation state of +2.5 for the iron centers and short C-S bond distances  indicating the presence of sulfur based radicals.The development of alternate catalysts that utilize non-precious metal based electrode materials such as the first row transition metal complexes is an important goal for economic fuel cell design. In this direction, a new Fe The nanocomposites of hydrogenase mimics with large surface area and versatile electronic behavior are expected to catalyze reduction of protons to hydrogen gas at lower electro-potentials than platinum based electrode materials5. The three known classes of hydrogenases, [NiFe]−, [FeFe]− and FeS−cluster free hydrogenases contain iron at their active site which is coordinated by thiolates, CO, CN− or a light sensitive cofactor 21. Several electro-catalysts for hydrogen evolution have been reported including a series of multinuclear iron sulfur complexes with benzene tetrathiolate bridges, iron carbonyl clusters, cobalt-dithiolene, metallo-porphyrins, low-valent transition metal complexes, diiron dithiolates, multinuclear Fe-S cluster with a Fecubane(μ-SR)Fesubsite linkage, molybdenum-sulfur dimers, cobalt glyoximes, substituted iron glyoximes, carbon nanotube grafted nickel bisdiphosphine complexes, and mononuclear iron(II) polypyridyl complexes29.The presence of the dimetallic iron and heterodimetallic iron-nickel centers at the active sites of the hydrogenases has evoked the researchers to search for a non-platinum catalyst material for proton reduction and Htor Fig. a6–13. E2 evolution at potentials comparable to that of platinum disc electrode32. Recently the research on light driven H2 production has gained momentum. Biomimetic chalcogels incorporating Fe4S4 cubane type clusters linked with (Sn2S12)4− blocks and iron dithiolene complexes have been reported as catalysts for light driven H2 production from water and as solar fuel catalysts34. The Fe4S4 cubane type cluster take part in many biological electron transfer processes which are also coupled with several other enzymatic reactions. The 6H+-6e− reduction of N2 to NH3 by Fe4S4 cubane type cluster alone has been reported by van Tamelen et al.35. Hence, we are interested to find out the efficiency of Fe4S4 cubane type cluster alone as electrochemical hydrogen evolution catalysts. Since the Fe4S4 cubane type clusters are embedded in protein matrix in the biological active site, the stability and catalytic efficiency of the Fe4S4 clusters might be enhanced if they can be embedded or immobilized on a graphene support. Two dimensional nanomaterials of various compositions including graphene have been studied as catalysts in electrochemical reactions such as hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and carbon dioxide reduction36. Recently 2D nanomaterials including functionalized graphene, their hybrids have gained interests in electrochemical energy conversion and storage devices37. Defects existing in the 2D nanomaterials play an important role in tailoring of optical and electric properties. Functionalized graphene obtained by oxidation contains –COOH, –C=O, and –OH functional groups which can be used to immobilize metal ions and organic groups. Several graphene-photocatalyst composites have been developed recently for HER38. Graphene as a matrix would enhance the catalytic performance of the electrocatalysts embedded on it due to its large surface area, excellent conductivity and indefinite durability. Graphene oxide gets folded to close like fisted form and entraps a large molecule such as tetraphenylporphyrin (TPP)39. Several graphene based hybrid electrocatalysts as anodic and cathodic fuel cell electrode materials have been reviewed40. Here in we report a new Fe4S4 cubane type cluster, [PPh4]2[Fe4(μ3–S)4(DMET)4] − and iron(III) dithiolenes have been reported which electro-catalyze Hwith Sn2S24− blockwith Sn2S24− block1) was prepared by the reaction of iron(II) polysulfide, [PPh4]4[Fe2IIS12] with dimethylacetylene dicarboxylate (DMAD) and lithium sulfide (Li2S) in CH3CN under Schlenk conditions. The X-ray structure determination of (1) indicates the presence of dianionic, [Fe4(μ3-S4)(DMET)]2− cluster and [PPh4] cations in 1:2 ratio. The ORTEP view of the anionic part of the cluster (1) is shown in Fig. 4S4 core with four bidentate DMET ligands coordinated to iron. The geometry around each iron atom is square pyramidal formed by three inorganic sulfurs (S2−) and two thiolates of the DMET ligand. The Fe–S bond lengths are similar at all iron centers, (Fe(1) and Fe(2)) and in the range 2.156 Å–2.250 Å. This is in contrast to the longer Fe-S bond distances (2.246 Å–2.383 Å) in the tetra anionic, super reduced cluster, [NBu4]4[Fe3IIIFeII(μ3-S)4(mnt)36−(mnt)1−·]4−· (2) 32. The Fe…Fe separations  are remarkably shorter in the cluster (1) in contrast to those observed in (2)  and four of the C–S bond distances (S(2)–C(2) & S(2A)–C(2A), 1.718 Å and S(6)–C(8) & S(6A)–C(8A), 1.721 Å) are considerably shorter in (1) indicating oxidation of the dithiolene ligands to their monoanionic form containing sulfur based radicals. The lattice packing in the crystals of (1) indicates that the anionic Fe4S4 cluster is fully covered by a group four [PPh4] cations with considerably short S2−(cluster)…H–C(phenyl) (2.91 Å and 3.45 Å) and O(cluster)…H–C(phenyl), (2.43 Å). All of the four S2− in the anionic part are involved in short contacts with C-H of the PPh4 cations. These interactions might provide stability to the cluster skeleton and are reminiscent of the intermolecular interactions observed in native proteins.The cluster ([PPh4]4FeIIS12 wi47. The considerably shorter C−S bond distances in a previously reported [Fe4(μ-S)4(S2C2(CF3)2)4]2− dianion and in cluster (1) indicate that the four monoanionic dithiolates provide only four negative charges to the cluster whereas the four inorganic sulfurs (S2−) provide eight negative charges making up a total of 12 negative charges which are satisfied by the four iron ions and two [AsPh4]/[PPh4] cations49. This confirms that the four iron centers are in a comprehensive oxidation state of +2.5 and the four dithiolene ligands have been oxidized to form monoanionic ligands with four S-based radicals. The appearance of a peak at m/z, 1514 in electro spray ionization mass spectrum 4(DMET)4]}− complex ion in CH3CN. The complex (1) is EPR silent both in the solid state and in CH2Cl2 solution. The diamagnetic nature of the cluster (1) is understood from the room temperature magnetic moment (μeff) of <1 μB. The presence of a band around λ, 823 nm  in the electronic spectrum of (1) in CH2Cl2  is diamagnetic, the S-based radicals are expected to be coupled.The dianionic 1,2-dithiolenes coordinated to metal complexes are known to undergo oxidation resulting in monoanionic ligands with S–based radicals)4(S2C2CF2)4]2− di)4(S2C2CF2)4]2− di1@graphene was prepared by the ultrasonication of Fe4S4 cubane type cluster, (1) and functionalized graphene for 10 h in CH3CN-H2O under an argon atmosphere. It was then evapourated to dryness and the black residue was labelled as 1@graphene. The IR spectral peaks of 1@graphene show significant shifts to lower frequencies compared with the Fe4S4 cluster (1). The doublet at 1718 cm−1 and 1690 cm−1 observed in (1) due to –COO stretching of dithiolenes is shifted to 1616 cm−1 and 1610 cm−1 in 1@graphene and the doublet is also broadened (Supplementary information). This indicates the existence of the H-bonding interactions with –COOH of the f-graphene as shown in Fig. 1@graphene, a broad band is observed at 3324 cm−1 indicating the presence of hydrogen bonded –OH groups. Functionalized graphene and the composite, 1@graphene were further analyzed by scanning electron microscopy (SEM) and results are displayed in Fig. 1@graphene diaplayed a mixture of graphene and the Fe4S4 cubane type cluster (1) as shown in Fig. 4S4 cluster (1) and the composite 1@graphene were dispersed in H2O-CH3CN, deposited onto carbon coated copper grids and analyzed by HR TEM. The results are displayed in Fig. 4S4 cluster recrystallize as nanocrystals. The TEM images of 1@graphene displayed in Fig. 4S4 cluster on the graphene matrix. The Fe4S4 crystals can be immobilized on a functionalized graphene matrix through H-bonding interactions with the –COOH, -OH functional groups which has also been corroborated by IR spectral studies as described above. Because the Fe4S4 cubane type clusters crystallize in the form of nanocubes and microcubes as confirmed by our unpublished results on the cluster, [NBu4]4[Fe3IIIFeII(μ3–S)4(mnt)36−(mnt)1−·]4−· (2) which displays nanocubes on recrystallization from CH3CN on a brass matrix and as nanotriangles on recrystallization from ethanol on a brass matrix. The EDX analysis of these nanocubes and nanotriangles confirmed the presence of carbon, iron, sulphur, phosphorous in the expected ranges as described in our unpublished results.The composite, 4S4 cubane type cluster (1) undergoes three reversible one electron redox processes around E1/2, +0.45 V, +0.11 V and −0.49 V  and two quasi-reversible redox processes around E, −1.01 V and −1.22 V in CH2Cl2  can be assigned to Fe3+/Fe2+ and the one occurring at E1/2, +0.45 V can be assigned to Fe2+/Fe3+ redox process. These assignments of the redox waves of the cluster (1) have been done based on comparison of cyclic voltammetric profiles of various Fe4S4 clusters, iron(II)/iron(III) and nickel(II)complexes of similar dithiolene ligands including classical tetrahedral Fe4S4 clusters of Holm et al.59.The Fe49 V ΔE, 0 mV and 1) electro-catalyzes hydrogen evolution from p-toluene sulfonic acid (TsOH) in CH3CN. On addition of TSOH  to the cluster (1) in CH3CN, the negative current at potential E, −0.72 V was increasing as shown in Fig. p, +0.445 V and Ep, +0.107 V were unaffected by the addition of TsOH. This indicates that the preferential sites of protonation could be the sulfur donors of the radical containing monoanionic dithiolate. The increase in current is due to the reduction of TsOH protons followed by the evolution of hydrogen gas. Controlled potential electrolysis of a mixture of the cluster (1) (0.025 mmol) and TsOH (0.25 mmol) was carried out in CH3CN at Ep, −0.8 V. A net charge of 29 mC passed over a period of 2 minutes. Head space analysis of the electrochemical cell by gas chromatography confirmed the presence of H2 gas. The cluster  consumed 0.25 mmol of TsOH and the TON (turnover number) of (1) in CH3CN is 400. The H2 evolution occurring at Ep, −0.8 V using TsOH is proposed to be promoted by a S-radical based process. The iron bound monoanionic dithiolate type S-donor sites of DMET can be protonated upon addition of TSOH and reduce protons to H2 on application of electric potential. In the process, the monoanionic dithiolate S- donors can in turn get oxidized to a fully oxidized, neutral di-radical ligand. The reduction of protons coupled to the oxidation of monoanionic dithiolate to neutral di-radical ligand is modulated by the iron center. Because similar DMET complexes of several other transition metal ions do not catalyze proton reduction at such a low reduction potential, viz., Ep, 0.72 V.The complex (1@graphene is similar to that of the cluster (1) as shown in Fig. p, −0.41 V, +0.23 V and +0.57 V in CH3CN which are assigned to S-radical based Fe2+/Fe3+ redox processes as described above for the pure cluster in CH2Cl2 (vide supra). The composite, 1@graphene electrocatalyzes TsOH-proton reduction to H2 at Ep, −1.19 V in CH3CN as a solvent. On addition of 0.4g of TsOH (2 mmol in 2 mL CH3CN), overall current of −0.95 mA passed at E, −1.19 V. The increase in current as a function of added TsOH solutions in CH3CN  are shown in Fig. 2 at the same potential, Ep, −1.2 V in water as a solvent with better catalytic efficiency and higher current output. On addition of 0.1 g of TsOH (0.5 mmol in 1 mL H2O), overall current of −3.15 mA passed at E, −1.2 V as shown in Fig. 4S4 cubane cluster, 1) consumed 2 mmol of TsOH with a turnover number of 3200. Formation of bubbles and brisk effervescence were observed upon addition CH3CN (1mL) to the electrochemical cell containing the composite 1@graphene and TsOH in water. This was confirmed to be H2 gas by head space analysis by gas chromatography30. The stability of the Fe4S4 cubane type cluster and its composite, 1@graphene are confirmed in de-aerated water under argon due to the insolubility of (1) in water. The cluster (1) was extracted from the composite after cyclic voltammetric experiments by ultrasonication in CH3CN followed by centrifugation and evapouration to dryness. The elemental analysis of the residue indicated the presence of carbon, hydrogen, nitrogen and sulphur according to the percentage elemental composition of the cluster (1). The composite, 1@graphene isolated from water medium displayed an ESI-MS (−ve) signal at m/z, 1514. The IR spectrum of 1@graphene after catalysis is dominated by peaks due to νNO3  and νS=O (tosic acid) stretching at 1371 cm−1, 1177 cm−1 and 1120 cm−1. But weak signals at 1720 & 1644 cm−1 (-COO of dithiolene) and at 1528 & 1490 cm−1 (-C=C- of dithiolene) coupled with the elemental analytical data indicate that the Fe4S4 cluster is intact. The cluster@graphene is confirmed to be stable in the solid state in water where as it is prone for attack only when it is dissolved in CH3CN or even in a mixture of H2O-CH3CN. This is due to the fact that in CH3CN, the composite functions as an emulsion of graphene in the CH3CN solution of (1) where as in water, it is an emulsion in graphene solution. The composite remains intact with indefinite durability and it is well behaved in pure water. But in a mixture of H2O-CH3CN, both the cluster (1) and graphene get into solution. The composite, 1@graphene shows an enhanced catalytic activity  as compared to the pure Fe4S4 cluster (1) alone . This could be due to in situ reduction of the oxidized Fe4S4 cluster by graphene. As much as the cluster (1) gets oxidized after proton reduction, that much can be reduced on the graphene matrix immediately. The graphene matrix can function similar to an external sacrificial electron donor60. Only graphene in the absence of the Fe4S4 cubane type cluster electrocatalyzes proton reduction at a higher negative potential, ca., −1.7 V as shown in Fig. ca. Ep, −0.41 V itself. Under similar experimental conditions, only TsOH, did not show any response on a GCE in the potential range, E, 0.0 V to −1.8 V (supporting information).The cyclic voltammogram of the composite, 2 gas in water has been achieved by immobilizing the Fe4S4 cubane type cluster, [PPh4]2[Fe4S4(DMET)4] (1) on a functionalized graphene support. A high current output (3200 TON) and an extreme stability of the catalytic material in water was concluded from the cyclic voltammetric and ESI-MS experiments. Only Fe4S4 cluster, (1) electrocatalyzes the same reduction reaction with low catalytic efficiency (400 TON) and concomitant decomposition to dimeric compound, [PPh4]2[FeIII(DMET)2]2. The Fe4S4 cubane type cluster was synthesized in a novel synthetic route and structurally characterized. The cluster (1) is EPR silent and it displays reversible, one electron redox waves around E1/2, +0.107 V and at +0.45 V) which could be assigned to the Fe3+/Fe2+ and Fe2+/Fe3+ redox processes.In summary, an ideal catalytic material for the reduction of TsOH protons to H4]4[FeII2S12] (Electronic Supplementary information) (0.500 g) was added into it. The suspension was stirred for 20 min. followed by the addition of dimethyl acetylene carboxylate (0.5 ml) and freshly purchased lithium sulfide  under argon. The black colored reaction mixture was stirred for 8h at room temperature and then diethylether (100 ml) was added. The reaction flask was closed tightly and allowed to stand at 10 °C for two days under argon. Dark green crystals were formed which were filtered and stored under argon. Dark green single crystals suitable for X-ray diffraction were obtained by layering of diethylether onto acetonitrile solution of the complex under argon. Data for (1): Yield, 0.6 g, C, H, N elemental analysis calculated for [PPh4]2[Fe4S4{S2C2(COOCH3)2}4].2H2O, C, 45.72, H, 3.62; Found, C, 45.53, H, 3.82. ESI-MS (negative) in CH3CN; m/z, 1514 {[PPh4][Fe4III(μ3–S)4(S2C2(COOCH3)2)4]}−; ESI-MS (positive), m/z, 339 [PPh4]+. FT-IR : 3400(br), 2945(m), 1714 (s), 1693 (s), 1433(s), 1238 (s), 1212 (m), 1084 (m), 995(m), 722 (s), 688 (s), 526(s) . UV-visible in CH2Cl2 [λ/nm (ε/M−1cm−1)]: 823 (2200), 582 (4500), 467 (5600). EPR silent, μeff = 0.8 μB at 298K. E ½ = +0.445 V (ΔE = 60 mV), +0.107 V (ΔE = 60 mV) and −0.494 V (ΔE = 60 mV) vs. Ag/AgCl; E, (quasi-reversible), −1.005 V and −1.219 V vs. Ag/AgCl in CH2Cl2-0.2M NBu4ClO4 with GC working electrode.The reaction was done under Schlenk conditions. Acetonitrile (40 ml) was purged with argon gas for 30 min. and iron(II)-polysulfide, 2[Fe4III(μ3–S)4(DMET)24−((DMET)1−∙)2]2−. (CH3CH2)2O. 2H2O. The intensity data for single crystals of (1) was collected at 120 K on a Bruker AXS Smart APEX CCD diffractometer with graphite monochromated MoKα radiation (0.71073 Ǻ). Data reduction and absorption corrections were done using SAINTPLUS program package. The structure was solved by direct and conventional Fourier methods and refined on F2 by full-matrix least-squares technique using SHELXTL program package61. All non-hydrogen atoms were refined anisotropically, H atoms at idealized positions in riding mode. structure data for (1): C76H64Fe4O19P2S12, Mr = 1951.33, Monoclinic, P2/c, a = 13.541(5), b = 13.376(5), c = 24.923(5) (Ǻ), β = 98.859(5)°, Volume = 4460(3) Ǻ3, Z = 4, ρcalcd = 1.453 Mg/m3, μ(MoKα) = 1.018 mm−1, F(000) = 1996, Unique reflections, 22403 at 120 K, Observed reflections, 7840, Parameters, 503, GOF = 1.034, R1 = 0.0632, wR2 = 0.1796. CCDC-871183 of the complex (1) can be downloaded from Cambridge crystallographic data center.The dark green single crystals of the complex (Supplementary Information