Recently, a reproducible and scalable chemical method for fabrication of smooth graphene nanogrids has been reported which addresses the challenges of graphene nanoribbons (GNR). These nanogrids have been found to be capable of attomolar detection of biomolecules in field effect transistor (FET) mode. However, for detection of sub-femtomolar concentrations of target molecule in complex mixtures with reasonable accuracy, it is not sufficient to only explore the steady state sensitivities, but is also necessary to investigate the flicker noise which dominates at frequencies below 100 kHz. This low frequency noise is dependent on the exposure time of the graphene layer in the buffer solution and concentration of charged impurities at the surface. In this paper, the functionalization strategy of graphene nanogrids has been optimized with respect to concentration and incubation time of the cross linker for an enhancement in signal to noise ratio (SNR). It has been interestingly observed that as the sensitivity and noise power change at different rates with the functionalization parameters, SNR does not vary monotonically but is maximum corresponding to a particular parameter. The optimized parameter has improved the SNR by 50% which has enabled a detection of 0.05 fM Hep-B virus molecules with a sensitivity of around 30% and a standard deviation within 3%. Further, the SNR enhancement has resulted in improvement of quantification accuracy by five times and selectivity by two orders of magnitude. Though graphene is intrinsically a zero band gap material, its band gap and carrier concentration can be tailored to a few eV by applying external electric field or by surface adsorption of chemical elements. This feature makes graphene a flexible material for the development of superior electronic devices [Graphene is a planar single sheet of sp devices ,2,3. Suc devices . In this devices .Nanostructures in graphene are in the form of nanoribbons, fabricated by either lithographic patterning of graphene sheets or by chemical processes. The former technique usually yields rough edges with dangling bonds and defects . Such inTo date, most of the studies on graphene noise have been conducted on mechanically exfoliated single layer and bilayer devices ,17,18,19This paper makes the first attempt to enhance the SNR in graphene nanosensors operating in FET mode by controlling the functionalization protocol. For this purpose, graphene nanogrids FET immunosensor has been developed following a similar methodology reported earlier . This had) and 100 nm length (l). Secondly, bilayer graphene has been deposited on nanoporous silicon oxide substrate by electrophoretic deposition (EPD) method. For EPD of graphene, interdigited metal electrodes have been fabricated with high temperature silver paste by screen printing method which has been next cured at 750 °C for 1 min. This has been followed by evaporation of gold metal. The prepared colloidal solution of graphene has been pipetted onto the substrate. Then the electrodes have been connected with two probes of function generator and a sinusoidal voltage (peak to peak 19.5 V) has been applied for 60 s. The graphene deposited substrate has been heated at 75 °C for 2 min. This step increases the adhesion between graphene and the substrate. The aforesaid fabrication results in a nanogrid structure with long and narrow graphene strips alternating with series combination of short and narrow strips on planar regions and within pores.For fabrication of graphene nanogrid structure, firstly nanoporous silicon oxide (NPSO) substrate has been developed by anodic etching of p-type <100> silicon wafers of 10–20 Ω·cm resistivity in a double pond electrochemical bath for 30 min under a constant current source with an electrolyte mixture of hydrofluoric acid (HF) (48 wt%) and dimethyl sulfoxide (DMSO) in the ratio of 1:9 by volume. The structure has been thermally oxidized using a dry-wet-dry sequence in an oxidation furnace for 1 h at 900 °C to obtain pores with 30 nm diameter  the graphene nanogrid structure has been treated with 25%, 10% and 2.5% glutaraldehyde aqueous solutions (procured from Sigma Aldrich) for 2 h, 4 h and 24 h. After treatment, each sample has been rinsed with de-ionized water and for every parameter, optical density (O.D.) measurement has been carried out to estimate the covalent binding of graphene with glutaraldehyde. Then the graphene structure has been incubated with anti Hep-B antibody for 1 h followed by washing with phosphate buffer saline (PBS). This process activates the negatively charged carboxylic groups of graphene and improves the covalent binding of antibodies. After antibody immobilization the nanogrid structure has been incubated with different concentration of Hep-B solution for 10 min. Hep-B solution has been prepared in the range of 50 aM to 10 pM by standard process of serial dilutions . The binGSV) has been applied. The sensing signals of the device have been recorded by monitoring the change in the drain current (DSI) for a given drain-source voltage (DSV) and GSV, when the device has been exposed to different concentrations of Hep-B solution. Further, Hep-C has been used as the non-specific antigen and complex mixtures of Hep-B and Hep-C has been prepared in buffer for testing the selectivity of the sensors. The buffer used for DSI measurement is 20 mM PBS. All the measurements have been carried out on five sets of sensors and the mean and standard deviation have been plotted.Electrical measurements of graphene nanogrid FETs have been performed using a Keithley 6487 instrument  at room temperature. To facilitate electrical measurement, two ends of interdigited electrodes have been used as drain and source. A polydimethylsiloxane (PDMS) container has been glued to the surface in the region between the source and drain to avoid fluctuations due to positioning of the solution droplet. Gate has been realized using a separate platinum electrode which has been inserted into the solution in the PDMS container, through which variable gate to source voltage ) of the transient fluctuations has been computed in MATLAB using Equations (1)–(3):k = 0, 1, …, N/2), t = Sampling interval. Finally according to Parseval’s theorem, Φ(f) has been multiplied by the sampling interval Δt and N to obtain power spectral density function, S(f). Data with equidistant time scale has been recorded and subdivided into sets, containing multiples of 2n data points. For S(f) calculation, spectra consisting of 800 Fast Fourier Transform (FFT) points in frequency have been averaged for 200 s.The fluctuations of Optical density (O.D.) measurements have been performed in a UV-VIS spectrophotometer  to estimate the number of HIgG antibodies attached to the glutaraldehyde treated graphene nanogrid structure. For estimating the binding density of HIgG antibody, HRP conjugated HIgG has been used along with a standard coloring reagent solution. The preparation details of the coloring reagent have been reported elsewhere . The optFor non-destructive examination of number of layers of graphene, Raman spectroscopy has been performed with a laser excitation wavelength of 532 nm and 50× objective using a LabRAM HR Evolution device . The laser power at sample has been maintained below 0.1 mW to avoid laser induced heating and sample damage. The spectrum has been accumulated over 10 s exposure for two sets. The intensity of G band has been used to determine the number of layers of graphene.−1 and a symmetric 2D band at ~2680 cm−1 with an intensity ratio of around 1.4. This confirms the presence of bilayer thickness. The antibody binding has been optimized by tailoring the glutaraldehyde concentration and treatment time for a constant incubation temperature. The concentration of glutaraldehyde solution has been selected as 2.5%, 10% and 25% for three different treatment times . It can be observed from 2 groups of antibodies. The O.D. also tends to saturate after 24 h, probably because the maximum possible binding has already taken place. However, it is observed from The Raman spectrum of RGO shown in DSI has been measured in presence of PBS for different GSV as shown in DSV of 1 V. It has been observed that for negative GSV, the resistance is lower than that for positive GSV which indicates that the graphene layer is p-type. The glutaraldehyde treated RGO surface is negatively charged and the antibody molecules are positively charged. Hep-B virus being negatively charged [DSI increases with increasing concentration of the antigen for negative GSV. Further, due to increase in the carrier concentration, Dirac point shift towards right. For positive GSV, changes in DSI with Hep-B concentration are insignificant which may be attributed to the poor electrophoretic capture on the surface. charged , IDS incDS after Hep-B capture. It is observed from GSV of −30 V. Thus, the variation of sensitivity with different incubation parameters of glutaraldehyde is shown in GSV of −30 V. It is observed from DSI readings is a vital parameter for improving the sensing performance. Moreover, it is observed from The sensitivity has been computed as the maximum fractional change in IS(f)DS/I2) is shown in S(f)DS/I2 increases with incubation time and concentration. Thus, SNR has been estimated as the ratio of sensitivity to DSS/I2 and shown in It has been reported that the low frequency noise in electrical resistance of bilayer graphene is strongly connected to its band structure and carrier density and that the noise increases with increasing carrier density . This haDS-VGSI characteristics in presence of low Hep-B concentration for the optimized and unoptimized sensors. It is observed that the optimized sensor can quantify 0.05 fM antigen within a range of 0.05–0.055 fM which is an error of 10%. On the other hand, the unoptimized sensor detects it within a range of 0.05–0.075 fM which is an error of 50%. The impact of SNR enhancement on selectivity has also been estimated by exposing the optimized and un-optimized sensors to different complex mixtures. From the DSI-GSV characteristics shown in DSI curve for 1 fM Hep-B is significantly reproducible even in the presence of 1 nM Hep-C, whereas in the unoptimized sensor, it shifts significantly if the Hep-C concentration exceeds 10 pM. This indicates that high SNR improves the selectivity by two orders of magnitude. This may be attributed to the increased noise in the unoptimized sensor which probably causes a significant drift in DSI due to non-specific adsorption. Hence the SNR enhancement has led to the realization of a reliable and ultrasensitive graphene nanogrid sensor with a five times and 100 times improvement in quantification accuracy and selectivity respectively.The impact of SNR on the sensitivity characteristics is shown in This paper makes the first attempt to enhance the SNR in graphene nanosensors operating in FET mode by controlling the functionalization protocol. The proposed work is extremely relevant, especially for bilayer graphene nanostructures since the low frequency noise increases with increasing carrier density. The incubation time and the glutaraldehyde concentration have been optimized in graphene nanogrid FET sensor for maximizing the SNR. It has been observed that an incubation time of 4 h with 25% glutaraldehyde concentration results in low level detection of Hep-B virus down to 0.05 fM concentration with an appreciable sensitivity of around 30% and a standard deviation within 3%. Further, the optimized sensor has resulted in improvement of quantification accuracy by five times and selectivity by two orders of magnitude. Hence the proposed methodology for SNR optimization can be extended to different configuration of nanostructured graphene biosensors.


Fairness is a critical component of defensible assessment. Candidates should perform according to ability without influence from background characteristics such as ethnicity or sex. However, performance differs by candidate background in many assessment environments. Many potential causes of such differences exist, and examinations must be routinely analysed to ensure they do not present inappropriate progression barriers for any candidate group. By analysing the individual questions of an examination through techniques such as Differential Item Functioning (DIF), we can test whether a subset of unfair questions explains group-level differences. Such items can then be revised or removed.We used DIF to investigate fairness for 13,694 candidates sitting a major international summative postgraduate examination in internal medicine. We compared (a) ethnically white UK graduates against ethnically non-white UK graduates and (b) male UK graduates against female UK graduates. DIF was used to test 2773 questions across 14 sittings.Across 2773 questions eight (0.29%) showed notable DIF after correcting for multiple comparisons: seven medium effects and one large effect. Blinded analysis of these questions by a panel of clinician assessors identified no plausible explanations for the differences. These questions were removed from the question bank and we present them here to share knowledge of questions with DIF. These questions did not significantly impact the overall performance of the cohort. Group-level differences in performance between the groups we studied in this examination cannot be explained by a subset of unfair questions.DIF helps explore fairness in assessment at the question level. This is especially important in high-stakes assessment where a small number of unfair questions may adversely impact the passing rates of some groups. However, very few questions exhibited notable DIF so differences in passing rates for the groups we studied cannot be explained by unfairness at the question level.The online version of this article (10.1186/s12909-018-1143-0) contains supplementary material, which is available to authorized users. Promoting fairness in assessment is an important priority. Entrance to medical school and progression as a doctor should be determined by ability, not ethnicity or sex . Recognid = 0.42) effects whereby ethnically non-white UK graduates underperformed relative to white UK graduates in assessments at both undergraduate and postgraduate levels. Nor is it merely an assessment issue – questionnaires evaluating the postgraduate working experience find ethnically non-white trainees experience lower levels of satisfaction , a high stakes postgraduate assessment in internal medicine and we compare (a) ethnically white UK graduates against ethnically non-white UK graduates and (b) male UK graduates against female UK graduates. DIF was used to test 2773 questions across 14 sittings, each initially comprising two three hour papers of 100 questions each. We report the results of the DIF analysis alongside a review of questions exhibiting DIF.All analyses were carried out on different diets (forms) of the same high stakes postgraduate examination. The examination is a criterion-referenced written examination comprised of 200 questions, sat in two separate 3 hour papers of 100 questions each, designed to assess core clinical knowledge. Blueprinting, item content and standard setting are all developed and determined by panels of experts with relevant clinical backgrounds.Fourteen sittings were included in this analysis: three each for 2011, 2012, 2013 and 2014, and two for 2015. In total, there were 47,048 candidate entries across the fourteen sittings, which included candidates who had not qualified in the UK. Candidates had been invited to provide information on their protected characteristics, which included sex, whether their primary medical qualification was from the UK or not and whether they were ethnically white or ethnically non-white, as part of the routine application process for the examinations. 6047 candidates failed to provide information on any or all of these questions, and a further 27,307 sittings were excluded due to the candidate not having a UK PMQ. This left 13,694 candidate sittings – all UK graduates – in the present study with graduates who were resitting being included as separate entries for the purpose of the present study. Consequently, some candidates had multiple entries in the analysis, with each entry being a single attempt at the examination, sat during different diets. No candidate had multiple entries for any individual diet. Candidates routinely provided consent for anonymised analysis of examination results, and approval was granted by the MRCP(UK) board for the work to be undertaken.R [difR [lordif package [All analyses were carried out in R . For steR [difR  or for a package . We ran  package . The DIFp < .05 would, with 5546 tests, require p < .05/5546 = 9.01 × 10− 6 for significance after adjusting for multiple testing.For each question we calculated DIF using the logistic regression method  which ca2 [We report the number of questions identified as exhibiting DIF. We further investigated any questions with either a medium or large effect size as measured by Nagelkerke’s R2 . All eig− 6.Table Table Following this analysis, the eight questions were reviewed by an expert panel comprised of ten clinicians of diverse backgrounds  to evaluate the possible causes of DIF. The analysis was blinded. Reviewers were not able to consult with other panel members, and knew only that DIF was present – not the type or magnitude. No reviewer was able to suggest any cogent explanation for the DIF for any item.This paper presents the first evaluation of DIF in the context of a large postgraduate medical examination, the MRCP(UK). In this dataset, which relates to a single high stakes postgraduate knowledge based assessment of single best answer MCQ design, and is comprised of an extremely large sample size of test takers and questions, DIF was detected using simple software and statistical tools. Importantly however the analysis shows most such effects are negligible and only a very small number of questions exhibit DIF of a medium or large effect size. Furthermore, no clear cause of the observed DIF can be derived from analysis of independent blinded panel review.This research shows that methods to evaluate DIF successfully used in other fields can be applied to medical education , 17. DifWe believe that this analytical strategy is simple, advantageous and suggests that DIF evaluation can be one of a range of measures to test fairness. Routine analysis will identify the – apparently rare – cases of notable DIF and so promote fairness at the borderline of pass/fail decisions. Connecting such psychometric analyses with expertise in question writing allows for the development of better training in question-writing, promotes awareness of the possibility of bias in written assessment, and allows for the development of a body of knowledge around questions most likely to produce bias. The notable DIF questions have all been withdrawn from the question bank and publicised amongst question writers, even though the reason for their differential functioning is unclear. As more items are identified in future analyses it may be that common structural or content issues will emerge as explanations.The study had some limitations. Replications on novel datasets are required to evaluate how common DIF effects are in other areas of assessment. As some candidates are prone to resitting, and therefore will have appeared in multiple datasets, exploring whether resitting candidates exhibit DIF compared to non-resitters of similar ability levels would be useful in extending this analysis. Furthermore, evaluation at the undergraduate level would be very helpful given the importance of differential attainment in application to medical school and performance at medical school. While we were able to evaluate possible reasons for question bias, we consulted experts, rather than novices, and work with candidates applying to sit assessment would be a useful comparator to identify why questions might (or might not) be considered biased. Exploring other features of the items – such as length, item type, language complexity and so on – may be a useful avenue of exploration. Furthermore, Identifying and publicising problem questions could be a powerful tool for advancing fairness if other organisations repeated this analysis and pooled the results. Importantly, the causes of DIF were unexplained and whether they are false positives or due to some yet unstudied factor remains open. Relatedly, this method was only one of a family of DIF procedures, and comparing it against other techniques (e.g. Mantel-Haenszel) may yield slightly different results.This research has provided a model for the monitoring and removal of questions with DIF in high stakes assessment. By making such analyses routine, we can promote fairness at the question level and ensure that assessment is based solely on candidate ability. Questions showing DIF were rare, and there was usually little clear relationship of the substantive content of the questions to the DIF found, suggesting that in most cases the DIF was of little meaning in relation to the overall performance of the candidates.Our expert review was blinded to the nature or direction of DIF, but the reviewers knew that DIF was present. A more exacting test, perhaps to be carried out in the future, would be to give examiners a balanced set of questions and say that a third showed DIF evidence of sex differences, a third showed DIF evidence of ethnicity differences, and a third showed no evidence of DIF by sex or ethnicity, and ask them to judge which question was in each type. Our feeling is that examiners probably would be unable to do that task correctly, suggesting that there are few obvious features about these questions which are related to the presence of DIF.Overall it seems highly unlikely that any candidates were disadvantaged by the small effects that were found. The differential attainment of candidates in the various groups does however remain, and remains unexplained, but cannot be attributed to differential item functioning in relation to sex or ethnicity of particular questions in this multiple choice assessment across the range of diets analysed.Additional file 1:High resolution images of the plots contained in the paper. (ZIP 2058 kb)


This paper presents a passive wireless humidity sensor for concrete monitoring. After discussing the transmission of electromagnetic wave in concrete, a novel architecture of wireless humidity sensor, based on Ultra-High Frequency (UHF) Radio Frequency Identification (RFID) technology, is proposed for low-power application. The humidity sensor utilizes the top metal layer to form the interdigitated electrodes, which were then filled with polyimide as the humidity sensing layer. The sensor interface converts the humidity capacitance into a digital signal in the frequency domain. A two-stage rectifier adopts a dynamic bias-voltage generator to boost the effective gate-source voltage of the switches in differential-drive architecture. The clock generator employs a novel structure to reduce the internal voltage swing. The measurement results show that our proposed wireless humidity can achieve a high linearity with a normalized sensitivity of 0.55% %RH at 20 °C. Despite the high losses of concrete, the proposed wireless humidity sensor achieves reliable communication performances in passive mode. The maximum operating distance is 0.52 m when the proposed wireless sensor is embedded into the concrete at the depth of 8 cm. The measured results are highly consistent with the results measured by traditional methods. Structural Health Monitoring (SHM) systems are automated tools, aimed at rapidly identifying the onset of structural damage and at tracking the condition of structures during forced or natural excitation . CurrentThanks to fast and easy installation, wireless sensors are gaining a growing interest. Most of the wireless sensors for SHM are based on Wireless Sensor Networks (WSN), which are battery-powered and permit long-range operating ,9. HowevHumidity is one of the parameters considered as a critical factor in the progress of cement maturity by influencing the stability, the transformation of hydrates, and strength development . The resThere are various kinds of RFID-based humidity sensors. The simplest kind is the chipless RFID temperature sensor, which requires no Integrated Circuits (ICs) and transmits sensor data by changing the radar cross section of the RFID antenna . The chaThis paper presents a novel wireless humidity sensor for SHM. To our knowledge, this is the first work to measure the concrete humidity based on UHF RFID technology. The rest of the paper is organized as follows. Since concrete has distinct electromagnetic properties at different humidity conditions, the total power loss for electromagnetic waves penetrating concrete are analyzed through the 1 MHz to 1 GHz frequency range for various humidity conditions (at depth of 0.2 m), i.e., 0.5%, 2.5%, 5.5%, and 13%. The matlab simulation results are shown in The aim of the proposed RFID sensor is to perform humidity measurement inside the concrete, thus the type of the antenna should be taken into consideration. tP is calculated from the Friis transmission equation [rE is the effective isotropic radiation power of a reader, aG is the tag antenna gain, rη is the RF-to-DC power conversion efficiency of the rectifier, λ is the wavelength of the electromagnetic wave, and d is the communication distance. From Equation (1), the communication distance d can be expressed as:The theoretical practicable operating power of an RFID tag equation :(1)Pt=EtP and higher rη are critical for the design of UHF RFID tag, for rE is limited by regional regulations (4 W is the maximum transmitted power) and aG is roughly determined by the allowable antenna area (1.64 for the λ/2 dipole antenna).Hence, in order to achieve longer communication distance, lower RV for the subsequent circuitry. Once the output of the rectifier reaches the operating voltage, the Power-On-Reset (POR) block generates a reset signal stR for the temperature sensor. The clock generator provides a reference clock CLK for the sensor interface. Because the sensor interface and the clock generator should operate under a stable supply voltage DDV, a regulator block is employed to stabilize the output voltage of the rectifier. This architecture does not include the demodulator and the baseband blocks in the traditional RFID tag, which means that this wireless humidity sensor will operate without any addressing as long as the sensor receives enough energy from the RFID reader [Because concrete is a high-loss material for electromagnetic wave transmission, this paper proposes a novel architecture to lower the overall power dissipation of wireless sensor for longer operating distance. D reader .L is the length of metal electrodes, S is the width of each electrode, and W is the distance between adjacent electrodes. The thickness of the polyimide layer is H, which is generally larger than metal thickness h. For a N finger array sensor, the total sensor capacitance hC can be expressed as [L is the length of metal electrodes, h is the thickness of metal layer, W is the distance between adjacent electrodes, and wetε represents the dielectric constant of the polyimide film with absorbed water. Considering the factors including sensor capacitance, chip area sensitivity, etc., this work chooses N = 40, L = 200 µm, W = 2.5 µm, S = 2.5 µm, h = 1 µm, and H = 2 µm.Inspired by the reported CMOS humidity sensor designs ,28,29,30essed as :(3)Ch=Noscf which is then countered by a 10-bit counter to output the corresponding digital output oB. For a standard ring oscillator, assuming an equal rise and fall time for the different stages respectively, the oscillating frequency of the ring oscillator oscf can be expressed as follows:dt is the delay time of the loop, lI is the current flowing through the inverter, lC is the equivalent load capacitance of the loop, and mV is the swing range of the output voltage which mostly equals the supply voltage DDV. Because lC is mainly determined by the capacitance hC of humidity sensor, oscf is a sensor-controlled frequency and oB is the corresponding digital output of humidity sensor.The capacitive humidity sensor acts as a capacitor when it works with the sensor interface. The traditional interface starts with a capacitance-to-voltage converter, which is then followed by a voltage-to-digital converter ,33. Thisoscf versus temperature on different process corners are shown in oscf achieves good linearity with temperature and the simulated worst case variation across corners is around ±9%.The simulation results of the proposed frequency outP is the average DC output power generated at the output of the rectifier and inP is the average RF power available at the input of the rectifier. From a circuit-level point of view, rη is mainly degraded due to the forward drop of the switch diodes or transistors [N11–22 and PMOS transistors MP11–22 form the differential-drive switch. In order to achieve a flat rη curve, the bias-voltage VN1,2 and VP1,2 are employed to boost the gate-source voltage of NMOS switch and PMOS switch, respectively [SR is added to block the AC component of VN1,2 and VP1,2. In CMOS process, SR could be replaced by a PMOS transistor that operates in the cut-off region to avoid the large silicon area.A popular performance metric of a rectifier is its power conversion efficiency which is defined as:nsistors . Differensistors ,36,37, Fectively . The larU,L) is superimposed on the bias voltages BiasN2 and BiasP2 to provide the shifted voltages GateN2 and GateP2 to the gate of NMOS and PMOS switches, respectively.P0–MP1 and MN0–MN2 compose a start-up block, which is added as a precautionary measure to ensure bias in the desired state. The transistors MP2–MP4 and MN3–MN6 compose a reference generator block to provide a reference voltage REFV of 0.26 V which is compensated by temperature and supply voltage. The transistors MP5–MP10 and MN7–MN9 compose a regulator to generate a stable voltage DDV of 1.0 V for other circuits. DDV − outV characteristic at room temperature of 25 °C. The circuit starts working properly with DDV = 0.47 V. In the supply voltage range from 0.47 V to 2 V, an average reference voltage of 266.5 mV is generated. In this measured DDV range, the output voltage changes at most by 1.8 mV, thus leading to a line sensitivity of 0.441%/V.Due to the large variation of the output voltage of rectifier, a reference circuit with small supply voltage coefficient is necessary to generate a stable reference voltage. The traditional way to generate stable 1.25 V reference voltage is using a bandgap reference circuit . However1–M6 consist of an N stage current-starved inverter, the transistor M7–M9 and M10–M12 consist the current mirrors of inverter. Compared with the conventional structure, the extra transistors MH1, MH2, ML1, and ML2 are employed to reduce the voltage swing [The clock generator always employs ring oscillator architecture based on current-starved inverters. The output voltage of traditional current-starved inverters is close to the supply voltage and ground, which improves the output range while increasing the power consumption. As is shown in ge swing .Microstrip antenna is designed by including a ground plane structure, which has a natural anti-metal advantage compared to the dipole antenna. The length of rectangular microstrip patch antenna length is approximately equal to half of its electrical length, which is not suitable for the miniaturization of tags. As shown in 2 and the diameter of the hole is 0.2 cm.A protection device is necessary before the sensor tag is embedded into concrete, so that the sensor tag is not impaired by hydration heat arising from grouted concrete and not soaked directly in water of concrete. The transmission signal of sensor tag is sent out by electromagnetic wave, hence it is important to pay attention to wireless transmission impedance matching. Based on civil engineering techniques, this study proposes a protective high permeability acrylic package box. In order to keep the sensor in contact with the environment fully, 16 holes were punched on the side and 20 holes were punched at the bottom of the proposed package box. 2 and was equipped with this antenna on FR4 substrate by using flip chip. Then the sensor tag was packaged with the package box for concrete monitoring as shown in rη curve of the proposed rectifier is shown in rη curve. When input power is 13 dBm, the two curves both reach the optimal point 69%. As for the input power range whose rη is above 60%, the proposed rectifier and the conventional rectifier achieve −19 dBm and −7 dBm range, respectively. The measured wetε results in this error. d, the distance of the RFID reader placed above the concrete is H, the incidence angle between the reader and the sensor is θ. The photo of the test site is shown in θ and power transmission is shown in θ is 90°, the power transmission efficiency is 85%. When θ is larger than 75°, the power transmission efficiency is nearly 0%. Hence, in order to achieve the best test results, the incidence angle should be as vertical as possible. When we set θ = 90° and d = 8 cm, we measure the maximum communication distance of RFID reader. A calibrated humidity sensor SHT75 is embedded together with the proposed wireless humidity sensor to monitor the concrete humidity. For each measurement, the reader was instructed to perform 1000 attempts to read the sensor data from the wireless humidity sensor. When the success ratio remains above 80%, the communication distance is considered to be reliable. As shown in We embedded the sensor into the concrete at a depth of 8 cm and then investigated the influence of incidence angle on power transmission. The relationship between the incidence angle This work employs concrete made of normal aggregate  as the sample. The proposed wireless humidity sensor is embedded at a depth of 8 cm inside the concrete sample with the calibrated wired humidity sensor SHT75. The results measured by these two sensors compared with results of the moisture probe are plotted in Humidity monitoring plays an important role in concrete measurement, and thus this work presents a wireless humidity sensor based on UHF RFID technology. Considering the high losses of electromagnetic waves in concrete, a patch antenna is proposed to ensure the sensor tag can work inside of the concrete. The wireless humidity sensor employs a novel architecture and is carefully designed for low power application. The measured results show the proposed sensor tag achieves high humidity linearity with a normalized sensitivity of 0.55% %RH at 20 °C. The maximum operating distance is 0.52 m when the proposed wireless sensor is embedded into the concrete at a depth of 8 cm. The measured results are highly consistent with the results measured by traditional methods. The whole experiment demonstrates that the proposed wireless humidity sensor can provide reliable performance.


Thermal chemical vapour deposition techniques for graphene fabrication, while promising, are thus far limited by resource-consuming and energy-intensive principles. In particular, purified gases and extensive vacuum processing are necessary for creating a highly controlled environment, isolated from ambient air, to enable the growth of graphene films. Here we exploit the ambient-air environment to enable the growth of graphene films, without the need for compressed gases. A renewable natural precursor, soybean oil, is transformed into continuous graphene films, composed of single-to-few layers, in a single step. The enabling parameters for controlled synthesis and tailored properties of the graphene film are discussed, and a mechanism for the ambient-air growth is proposed. Furthermore, the functionality of the graphene is demonstrated through direct utilization as an electrode to realize an effective electrochemical genosensor. Our method is applicable to other types of renewable precursors and may open a new avenue for low-cost synthesis of graphene films. Graphene films are commonly produced by thermal chemical vapour deposition, which is capable of producing high-quality films but still limited by factors such as high cost. Here, the authors report the growth of single-to-few-layer continuous graphene films under ambient-air conditions. Graphene growth occurs by thermal reforming of a natural precursor, soybean oil, in a closed ambient-air environment. Unlike conventional CVD methods or conventional natural precursor methods for growing graphene, the technique does not require any purified gases8The parameters observed to control the quality of graphene include temperature, processing time, precursor, substrate and the ambient-air environment. Nickel acted as a good catalyst for the breakdown of precursor material  into smaller building units that are essential for the synthesis of grapheneTo investigate how the transformation occurred in the process, we have analysed the chemical composition of the annealed soybean oils at different temperatures . During 122 to form water vapour. In particular, water vapour can promote the etching of amorphous carbon deposits on the Ni surfaceAt elevated temperatures, long hydrocarbons in the oil decompose in the presence of OWe have also noticed that a slow cooling can promote excessive carbon segregation from the Ni bulk, which may account for the observed formation of a graphite-like film . AnotherIt is worth mentioning that graphene did not form on other growth substrate materials with significantly lower carbon solubility than Ni, such as the commonly used Cu foil. Moreover, we did not observe graphene formation on graphitic surfaces such as woven carbon cloth . This suThe structural morphology of the graphene film was analysed by transmission electron microscopy TEM; . The disIn addition, selected-area electron diffraction patterns were taken across a typical region of the sample, where a slight rotation between these patterns was observed . The hig2 graphene film grown in the ambient-air process was transferred from the Ni foil substrate to a glass surface, as demonstrated in ID/IG and I2D/IG intensity ratios were taken from four regions R1–R4, as denoted in −1, the graphitic peak (G-band) at ∼1,580 cm−1, and the second-order 2D-band at ∼2,670 cm−1. The D-band is attributed to the finite crystallite size effect and various defects induced in the sp2 carbon materials; the G-band arises from the in-plane vibrational E2g mode of the sp2-hybridized carbon; and the 2D-band is a second-order Raman spectral feature due to the three-dimensional interplanar stacking of hexagonal carbon networksID/IG is 0.15–0.25 and that of I2D/IG is 0.95–1.50, as shown in 2 V−1 s−1 was estimated for the graphene film , sp3 (285.4 eV), nickel carbide (∼282.8 eV) and C–O–C (∼286.5 eV) and O–C=O functional groups . The survey scan of Moreover, this ambient-air process for graphene synthesis was also applicable to Ni foil growth substrates of lower purity. Graphene films of comparable quality were produced with low-purity polycrystalline Ni foils (99%) rather than high-purity foils . Such loThe growth of graphene in an ambient-air environment may initially seem counter-intuitive, as graphene is expected to be destroyed in air at elevated temperatures (above 500 °C). However, we hypothesize that the unique processing conditions promote the controlled synthesis of graphene films in an otherwise destructive environment. Specifically, the thermally dissociated precursor material decomposes in the presence of reactive oxygen species from the ambient-air, leading to the formation of water vapour as a by-product . The watNi foil heat treated in ambient environment without soybean oil, where surface oxidation will be prevalent ;Ni foil heat treated in ambient environment with soybean oil, following procedure as outlined previously for the growth of graphene, where surface oxidation may be prevented .To better understand the growth process and the possible interaction with Ni substrate, we conducted experiments to probe the surface composition of Ni foils following treatments at elevated temperatures. In particular, we investigated the composition of:2, which consequently limited the surface oxidation of Ni at elevated temperatures.Our XPS analyses showed that when the Ni foil was heated in the ambient environment without soybean oil, oxygen was easily identified on the surface (Ni:O ratio of 1:1.83). However, when the Ni foil was heated with soybean oil, the oxygen content was significantly reduced (Ni:O ratio of 2.69:1). These results indicated that the breakdown of soybean oil in the reaction chamber provided a reaction pathway for the consumption of O3, C2H2 and other species, at the ramping stage  was measured to characterize the response of graphene to the surface immobilization of miRNAs. The Rct was observed to increase upon successful immobilization of probe miRNAs on the graphene surface (Rct was observed as the concentration of target miRNAs was increased (Rct by (Rct−R0)/R0, where R0 is the charge-transfer resistance of the reference sample. This increase in ΔRct is attributed to an impeded charge transport at the graphene surface, caused by spatial blocking of the captured target miRNA molecules. In addition, the hybridization between complementary genomic sequences may induce a build-up of negative surface charge, which may repel negatively charged ferricyanide ions and lead to an increase in Rct  technique. The charge-transfer resistance  at physiologically relevant concentrations. This suggests that nonspecific binding at the graphene surface did not interfere with the specific binding events with the target miRNA sequence.The graphene-based sensor also demonstrates selectivity against miRNA sequences that are mismatched by a single RNA base, as shown in  10−14 M . Further 10−14 M . The gra−13 M single-stranded (ss)DNA−13 M ssDNA−12 M  to enable controlled synthesis and tailored properties of the graphene film in the ambient-air process. Further, we propose a mechanism for the growth of graphene in the ambient-air process, based on depth profiling of the as-grown film, analyses of the ambient-air composition in the reaction chamber and reaction pathways for precursor reforming into graphene. The functionality of the graphene films was demonstrated through its direct integration as an electrochemical genosensor, in which sensitive and selective bio-detection was realized. Importantly, the ambient-air synthesis of graphene films from renewable precursors offers numerous advantages and opportunities for future streamlined integration into large-scale production infrastructures and the realization of diverse graphene-enabled technologies.Graphene films demonstrate excellent functional properties and are promising for diverse applications. However, the high cost and complexities associated with graphene production impede its commercial viability. To this end, we present a novel method for the synthesis of graphene films, in an atmospheric-pressure, compressed-gas-free ambient-air environment utilizing safe, low-cost renewable precursors. This ambient-air method offers numerous advantages over conventional thermal CVD techniques for graphene synthesis, which critically rely on resource- and time-consuming procedures . Graphen−1. This was followed by holding at 800 °C for 3 min. After the growth step, the sample was immediately removed from the heating zone to enable a rapid cooling (at approximately 25 °C min−1) to segregate the homogeneous and continuous graphene films. Owing to the evaporation and thermal expansion of the precursor material, a small build-up in pressure within the tube was observed. Throughout the heating stage (200 to 800 °C), atmospheric pressure was maintained in the quartz tube by allowing this build-up of gases to exit via the exhaust of the tube. A controlled gas environment was created in the tube through enabling the circulation of gases produced by precursor evaporation. Following the heating stage, pressure within the quartz tube was observed to be stabilized at atmospheric pressure. No additional gases were introduced into the quartz tube throughout the entire growth process.The growth of graphene was carried out in a thermal CVD furnace  with a quartz tube . Polycrystalline Ni foils  were used as the growth substrate. The experimental schematic is shown in −1 of PMMA  was spin-coated onto the as-grown graphene on Ni foil . The sample was then dried in open air for 12 h. Subsequently, the underlying Ni foil was dissolved in 1 M FeCl3 in 30 min. The PMMA/graphene film then floated to the surface. This was washed several times with deionized (DI) water. Next, the PMMA/graphene was lifted off from the DI water bath and transferred onto a glass substrate. The PMMA was then dissolved with acetone, and the sample was repeatedly washed with DI water. The graphene on glass was then used for subsequent microscopy and electrical characterization.A poly (methyl methacrylate) (PMMA)-assisted transfer of graphene was adopted. Briefly, 46 mg ml2. The XPS spectra were recorded with a Specs SAGE 150 spectroscope with Mg Kα excitation at 1,253.6 eV. Both survey scans and narrow scans of C 1 s and Ni2p3/2 were conducted. The Ni and graphene/Ni surfaces were progressively etched through Ar bombardment to create a depth profile of the material. The TEM images were obtained with a JEOL 2200FS TEM microscope operated at 200 kV.Raman spectroscopy was performed using a Renishaw inVia spectrometer with Ar laser excitation at 514 nm and a probing spot size of about 1 μm2 was used, and optical spectra were recorded in the wavelength range from 300 to 800 nm.Optical images were obtained with an Olympus BX51 optical microscope. Transmittance measurements were obtained using a Varian Cary 5000 ultraviolet–visible spectrophotometer. A graphene area of 4 cm2 was used. Four-point probe measurements were conducted at room temperature.Silver paint was applied to the graphene transferred onto glass. A graphene area of 1 cm2O3 holders, and were heated to required temperatures  at 10 °C min−1 heating rate under air purge gas. Correction/blank runs were carried out for each temperature range with empty reference and sample pans before sample thermal analysis. Evolved Gas Analysis was carried out by coupling the Netzsch system to a Thermostar Pfeiffer Quadrupole Mass Spectometry to determine gases and vapours evolving in the atomic mass range of up to 200 a.m.u. (plotted as mass to charge ratio m/z).The Netzsch STA 449 F1 instrument equipped with S-type DTA sensor was used for simultaneous thermogravimetric/differential thermal analysis of the soybean oil precursor samples. Soybean oil samples were placed in Al2 plasma  to introduce carboxylic functional groups on its surface. The sample was placed flat and 2 cm below the plasma generation zone. The size of each sensing substrate was 2 × 1 cm2. Then, the plasma-actived graphene was treated with 0.05 M N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) and 0.03 M N-hydroxysulfosuccinimide (NHS) in phosphate-buffered saline  for 15 min. This enabled the formation of active ester intermediates via carbodiimide chemistry. Next, the surface of graphene was washed several times with PBS and DI water to remove excess EDC/NHS. Next, the surface of graphene was washed several times with PBS  and DI water to remove excess EDC and NHS. Then, NH2-conjugated miRNAs  were diluted in PBS to 0.2 μM, and 50 μl was pipetted onto the EDC-treated surface. This was left to incubate overnight in a wet environment and at room temperature. Next, the sensing surface was washed with 0.05% sodium dodecyl sulfonate (Sigma-Aldrich) in 0.04 M hydroxylamine solution (Sigma-Aldrich) to deactivate the remaining carboxylic functional groups and to remove non-specifically bound probe miRNAs. Then, 0.01 M polyethylene glycol (Sigma-Aldrich) was loaded on the sensing surface to block the exposed areas of graphene to reduce further nonspecific binding. Next, the (biomarker) miRNA sequence  was dissolved in human serum  to obtain dynamic concentrations of 1 nM to 0.1 pM, which were pipetted onto the sensing surface. This was left to incubate at 45 °C for 20 min to induce hybridization between the complementary probe and target sequences. Finally, a washing step with PBS/DI water was used to remove remaining non-specifically bounded target miRNAs. To demonstrate sensing specificity, a similar protocol was adopted by replacing the target sequence with a single-base mismatched miRNA sequence . This fully assembled device was then utilized in a three-electrode electrochemical cell for biosensing measurements.The as-grown graphene on Ni foil was treated with a low-temperature O6 in 0.1 M Na2SO4 at room temperature. A three-electrode cell configuration was used. The three-electrode cell used the as-grown graphene on Ni as the working electrode, a Pt wire as the counter electrode, and an Ag/AgCl reference electrode. The EIS measurements were conducted in the frequency range from 500 kHz to 1 kHz, using a BioLogic VSP 300 potentiostat/galvanostat instrument. The charge-transfer resistance (Rct) of the sensing electrode was determined by the diameter of the semi-circle region in the EIS plots. The Rct of the sensor following incubation with the target miRNA was expressed as a percentage of Rct in the reference (blank) case, which was incubated in the human serum medium in the absence of target miRNAs. To evaluate the contribution of nonspecific interactions, the interfering analytes  were diluted in the FeCN6/Na2SO4 electrolyte before the electrochemical measurements. Further, linear regression analysis was utilized to estimate a detection limit for the sensor. From the plot of ΔRct versus concentration, a relation of ΔRct=90.89+6.04 log10 (Concentration [M]) was deduced (R2=0.99) for sensing the target sequence. The limit of quantification was calculated by 10Sy/b, with Sy as the standard deviation of the y-intercept (Sy=7.24) and b as the slope of the linear fit .Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.Supplementary Figures, Supplementary Tables, Supplementary Notes and Supplementary References


When used as anode materials in lithium-ion batteries, the composite exhibited good cyclic stability and decent specific capacity of 677 mA·h·g−1 after 50 cycles. CuO NWs can enhance the lithium-ion storage of the composites while the f-graphene effectively resists the volume expansion of the CuO NWs during the galvanostatic charge/discharge cyclic process, and provide a conductive paths for charge transportation. The good electrochemical performance of the synthesized CuO/f-graphene composite suggests great potential of the composite materials for lithium-ion batteries anodes.The copper oxide (CuO) nanowires/functionalized graphene (f-graphene) composite material was successfully composed by a one-pot synthesis method. The f-graphene synthesized through the Birch reduction chemistry method was modified with functional group “–(CH Therefore, they have been widely applied in telephones, personal computers, and electric vehicles ,2,3,4,5.enignity ,7,8,9,10enignity . For inst method . Among tt method ,14. Thest method ,16,17. Ht method ,19. Addit method ,21,22. WRecently, CuO and graphene composites with various morphologies have been fabricated by using different synthetic processes ,25,26,272)5COOH” groups were introduced onto f-graphene sheets via the Birch reduction chemistry method, which function as the nucleation sites for the formation of CuO nanowires (NWs) without adding any surfactants, according to previous literature [In most of these studies, rGO sheets were used. The rGO sheets were obtained by oxidizing graphene into graphene oxide first, and reducing it in the following step. However, the oxidation step will always damage the mircrostructure and molecular structure of graphene, and the reduction process could not completely restore its electrical conductivity behaviour . Here interature . This meterature ,25,28,302)5COOH” groups and the detailed processes were shown as follows [2  was added and reacted for 50 min. The mixed solution was stirred overnight. After the liquid ammonia evaporated completely, the product in the flask was transferred and mixed with hexane, and then washed by NaOH solution (pH = 11) three times to remove impurities. Finally, the CuO/f-graphene composite was dried at 60 °C overnight. The schematic of the synthesis procedure of the CuO/f-graphene composite is depicted in 2, and the pure CuO material was synthesized by the same method without adding graphene.The CuO/f-graphene composite was successfully synthesized via a one-pot chemistry method. The f-graphene was prepared through the Birch reduction chemistry method to yield “– was tested at a heating rate of 10 °C·min−1 in air from room temperature to 800 °C by using a NETZSCH TG-DTA/DSC analyzer . The Raman spectrum was measured on a DXR Raman Microscope  via a 633 nm He-Ne laser.The morphology of CuO NWs were characterized by using the field-emission scanning electron microscope  at 30 kV. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were measured on a JEOL JEM-2100F TEM at 200 kV . The crystalline phases of the composite were studied by an X-ray diffractomer  scanning from 10° to 80° with Cu K−2. The assembly of coin cells was performed in an argon-filled glove box by using CR 2025 coin-type cells with lithium foil counter-electrodes, Celgard 2400 membranes as separators, and 1.0 M LiPF6 in ethyl methyl carbonate (EMC)/ethylene carbonate (EC)/dimethyl carbonate (DMC) (volume ratio 1:1:1) as electrolyte. The galvanostatic charge/discharge performances were measured on a multichannel battery tester  with a voltage range from 0.01 to 3.0 V at room temperature. The cyclic voltammetry (CV) and electrochemical impendence spectroscopy (EIS) measurements were carried out on an electrochemical workstation .The anode electrodes were made up of the CuO/f-graphene composite, polyvinylidene fluoride (PVDF), and conducting acetylene black with a weight ratio of 80:10:10 dissolved in N-methyl-2-pyrrolidinone (NMP) solvent. Then, the slurry was coated on a Cu foil and heated at 120 °C for 12 h in a vacuum drier. The average mass coated on the electrodes is about 1 mg·cm−1 and 1600 cm−1. The former one, named D band, reveals the defect of the C atomic lattice while the latter peak called G band represents the stretching vibration of C atom sp2 hybrid plane. The intensity ratio (D/G ratio) shows an obvious increase after functionalization. The result suggests that the functional groups “–(CH2)5COOH” were successfully attached to the graphene and the sp3 defect centers were introduced [−1 in the Raman spectrum of the CuO/f-graphene composite is in agreement with the Raman signal of the monoclinic CuO, which gives the CuO NWs a priority to react on these defective positions.The Raman spectrum of f-graphene b shows ttroduced ,33. MoreThe SEM, TEM, and HRTEM images of raw graphite, the f-graphene, pure CuO, and the CuO/f-graphene composite are shown in 2 have reacted completely.2O phase and the decomposition of Cu2O into Cu [2O and CuO, respectively [ into Cu ,27,36. Iectively ,37. The From the second cycle to the fourth cycle, the CV curves of the CuO/f-graphene composite have higher extent overlapping than the CV curves of pure CuO and other CuO/graphene composite reported before , suggest−1 with voltage range from 0.01 to 3.0 V. In the first cycle, three voltage plateaus at about 2.0–2.3 V, 1.2–1.5 V, and 0.5–0.8 V are observed. This indicates that during the conversion process, multi-step electrochemical reactions have taken place between CuO and lithium, which correspond to the three cathodic peaks of the CuO/f-graphene composite in the CV curves . It suggests that the introduction of functional groups “–(CH2)5COOH” can increase the specific surface area of graphene to some extent compared with graphite, thus enhancing the capacity of lithium storage. The pure CuO shows a distinct capacity decline from 716 mAh·g−1 to 331 mAh·g−1. Contrast this with the f-graphene and pure CuO, where the initial charge and discharge capacities of the CuO/f-graphene composite are 912 mAh·g−1 and 778 mAh·g−1, respectively. Due to the various irreversible processes mainly including the ineluctable formation of SEI film and electrolyte decomposition, the capacity of the CuO/f-graphene composite has a reasonable loss in the first cycle. After the second cycle, the discharge capacity stabilizes at 677 mAh·g−1 during the whole cyclic process. The initial coulomb efficiency of the CuO/f-graphene composite is 85%, which is much higher than previous reports [2)5COOH” functional groups has increased the interlayer spacing of graphene sheets, and the expanded graphene sheets are highly conducive and leave enough space for the copper oxide to be inserted between the f-graphene sheets, which leads to the structural stability after several galvanostatic charge-discharge cycles. In addition, the “–(CH2)5COOH” groups can provide nucleation sites for the formation of well-dispersed CuO nanocrystals. −1. As we can see, the discharge capacities of the CuO/f-graphene composite are 659, 595, 467, 357, and 244 mAh·g−1, respectively at current densities of 0.1, 0.2, 0.5, 1.0, and 2.0 A·g−1. When the current density is restored to 0.1 A·g−1, the discharge capacity goes back to 572 mAh·g−1, making it clear that the CuO/f-graphene composite has a decent structural stability. On the other hand, the f-graphene exhibits an excellent stability at the same current densities since the specific capacity varies from 438 mAh·g−1 at 0.1 A·g−1 to 177 mAh·g−1 at 2 A·g−1 during the first 25 cycles and recover to 403 mAh·g−1 at 0.1 A·g−1 in the last five cycles. We may safely draw the conclusion that the stability of the CuO/f-graphene composite is attributed to the f-graphene. reports ,26. And  reports ,24,26,29ct), which engenders between the liquid electrolyte and the active materials, is denoted by the medium-frequency semicircle in the EIS [w), is ascribed to lithium diffusion within the electrodes. Apparently, the CuO/f-graphene composite has a smaller semicircle compared with the pure CuO before cycling, which indicates a lower Rct of the CuO/f-graphene composite than that of the pure CuO. Comparing to the pure CuO, the CuO/f-graphene composite has a better electronic conductivity and charge-transfer performance with the addition of conductive f-graphene [Finally, the electrochemical impedance spectroscopy (EIS) was carried out to investigate the kinetics, electric double layers, and diffusion of the electrode reaction process. As depicted in  the EIS . At low graphene .−1 at first cycle at a current density of 100 mA·g−1 and a good electrochemical stability with the capacity of 677 mAh·g−1 after 50 cycles. The introduction of functional groups “–(CH2)5COOH” has increased the interlayer spacing of graphene sheets, and the expanded graphene sheets are still conducive and leave enough space for CuO to be inserted between f-graphene sheets, which leads to the structural stability after galvanostatic charge-discharge cycles. In addition, “–(CH2)5COOH” groups provide nucleation sites for the formation of well-dispersed CuO nanocrystals. Therefore, this method can be a general approach to prepare anode materials for LIBs.In summary, the CuO/f-graphene composite material have been successfully synthesized by a one-pot wet chemistry method. The CuO NWs were well-dispersed in the f-graphene sheets with sizes ranging from 300 nm to 500 nm in length and 10 nm to 20 nm in width. As an anode material in LIBs, the CuO/f-graphene composite displays improved electrochemical performance compared to the pure CuO counterpart. It shows a high capacity of 912 mAh·g


Many newly observed FQHE features do not agree with a conventional model of composite fermions and reveal a different hierarchy in comparison to monolayer graphene or GaAs 2DEG. We explain the peculiarity of the FQHE hierarchy in the bilayer system in the framework of a topological approach, which includes the composite fermion model as its special case. Inclusion of a topological effect caused by the hopping of electrons between the two sheets in the bilayer system allowed for an explanation of the FQHE hierarchy in the graphene bilayer in satisfactory accordance with the experimental observations.Recent experimental progress in Hall measurements in bilayer graphene in the so-called open-face configuration of boron nitride encapsulated samples, together with the earlier technique of suspended samples, allows for precise observation of the fractional quantum Hall effect (FQHE) in all 4 subbands of the Lowest Landau level (with  It is commonly acknowledged that in the induced by the interaction formation of nonlocal specific correlations in FQHE, the central role is played by an exceptional topology of the planar continuum. An examination of FQHE in graphene is especially challenging. Graphene is perfectly two dimensional but with a pseudo-relativistic band structure. The band electron dynamics in graphene are dominated by the Dirac-like points in the corners of the hexagonal Brillouin zone, where the locally conical-shaped valence band meets the similarly conical-shaped conduction band, resulting in a linear-in-momentum local Hamiltonian2. This leads to non-equidistant LLs structure in the graphene monolayer, with energy proportional to n is number of the LL) instead of the ~n dependence in conventional 2DEG. In bilayer graphene, an interlayer tunnelling of electrons restores the parabolic local energy and almost-equidistant LLs, 3. The specific graphene pseudo-relativistic band structure close to the Dirac points, however, does not influence the topological constraints imposed on trajectories , because the band structure is induced by a local electric interaction-type crystal field, which does not perturb the path topology, and the FQHE is observed in graphene, similarly to conventional semiconductor 2DEG systems.The fractional quantum Hall effect (FQHE) is one of the most spectacular and mysterious quantum phenomena in condensed matter. Despite intensive experimental and theoretical studies of FQHE since the 80 s of the last century, the effect still eludes complete understanding. The FQHE apparently exceeds the conventional framework of local quantum mechanics and displays a trade-off between the Coulomb interaction induced localization and disorder8 reveal significant distinctions from FQHE manifestation in the graphene monolayer12. This is in conflict with a conventional imagination that FQHE is a manifestation of hypothetical composite fermions (CFs)13, i.e., electrons dressed with even number of localized on particles flux quanta of some auxiliary magnetic field. According to CF theory, such effective quasiparticles should be present both in monolayer and bilayer Hall systems, what however, does not agree with experimental observations in bilayer graphene8.In recent years, advances in the manufacturing methods of monolayer and bilayer ultra-clean graphene samples accelerated the development of the Hall experiment in this material, and several new observations of FQHE have been reported. Remarkably, the observations of FQHE in bilayer graphene12 and by the mastering of an independent method for reducing substrate perturbations of graphene layers in samples supported by hexagonal boron nitride (hBN) crystal substrate10. The absence of a substrate (for suspended samples) or the avoidance of lattice mismatch (for hBN substrate) favour the delicate correlations induced by the interaction of 2D electrons, resulting in FQHE manifestation. The triggering role for FQHE organization is played by high electron mobility, well exceeding 100,000 cm2/(Vs) in both abovementioned experimental setups for Hall measurement in graphene.Important progress in the Hall experiment in graphene has been achieved by the invention of a measurement technique for suspended graphene small scrapings (both monolayer and bilayer)2. Moreover, for Dirac points, the specific Berry phase-like shift for chiral 2D carriers additionally influences the LL spectrum, which finally results in the 2. These plateaus in the monolayer graphene occur at the centres of the consecutive LLs (not completely filled LLs)14. In bilayer graphene, an extra degeneracy of the n = 0 and n = 1 oscillatory states in the LLL occurs and the twice as large Berry phase for chiral carriers shifts the IQHE plateau positions to the edges of LLs3. LLs in bilayer graphene are also four-fold spin-valley degenerate, except for the eight-fold degenerate lowest LL (LLL) (due to n = 0 and n = 1 degeneracy in the LLL)15. In the case of monolayer graphene, FQHE features are observed in the first six subbands of LLs with n = 0 and n = 112, which reproduce a hierarchy similar to that in conventional semiconductor 2DEG. In bilayer graphene, observation of FQHE reaches even subbands with n = 2, revealing a different and unexpected FQHE hierarchy there10. Especially interesting are observations of unusual even-denominator fillings for FQHE in bilayer graphene in the LLL, including the most pronounced feature at 4, which does not find any counterpart in monolayer systems. In particular, this state cannot be explained with the CF approach, as for CFs the Hall metal state is predicted at 13.A graphene sheet has regular planar hexagonal crystalline structure with two equivalent sublattices (two carbon atoms in the Bravais cell). This feature, together with the vanishing of the forbidden semiconductor gap at Dirac points, results in the four-fold spin-valley degeneracy of LLs in graphene monolayer18. Within this topological nonlocal braid group approach, we explain the structure of fractional fillings of LL subbands in accordance with experimental data and explain the reason for the insufficiency of the CF model in the bilayer graphene case. The topological braid group approach, formerly developed in refs20, gives the hierarchy of FQHE in agreement with the available experimental data for monolayer Hall systems and can be extended to the bilayer graphene case via identification of topological differences between mono and bilayer situations.In the present paper, we summarize the recent and controversial experimental observations of FQHE in bilayer graphene and compare them with the data for graphene monolayer. We identify the specific topological features that can explain the oddness of the correlated multi-particle states in the bilayer system in accordance with experimental observations. We propose an explanation for the exotic even-denominator fractions for FQHE in the LLL and the whole FQHE hierarchy in bilayer graphene in the framework of the topological commensurability approach3, and is equal to B is the external magnetic field, S is the sample surface, and 2. The Zeeman splitting in graphene is small21 and the valley splitting is small as well2, which results in the 4-fold approximate spin-valley degeneracy (referred to as SU(4) band symmetry). The LLL subbands are divided between particles and holes from the conduction and valence bands2. Hence, the bottom of the LLL is shifted upward by 2 (in terms of the filling factor). Conventionally, filling rates for holes from the valence band are assigned as negative numbers and are mirror reflections of the positive numbers denoting filling rates for electrons in the conduction band. An additional opportunity in graphene, beyond the ability of conventional 2DEG, is a possible control over the transition between particles and holes by the shifting of the Fermi level passing the Dirac point. Experimentally, it is realized by application of a relatively small lateral voltage , which determines the filling rate independently of the magnetic field strength.The massive degeneracy of each LL subband in graphene is the same as in the conventional 2DEG, despite the different LL structure3. As usual in graphene, the division of the LLL subbands equally between particles and holes causes the bottom, for uniformly charged carriers (electrons or holes), to be located in the centre of the 8-fold degenerate LLL. This extra degeneracy of the LLL is caused by the vanishing of energy of both the n = 0 and n = 1 oscillatory Landau states in the bilayer graphene, in contrast to the monolayer one. In the bilayer graphene, the Berry phase shift for chiral particles is also different (twice as large) in comparison to the graphene monolayer and is equal to 2π2. Hence, the consecutive plateaus of IQHE are located in bilayer graphene at integer filling rates, whereas in monolayer graphene were located at half-fillings of LLs3.Due to the interlayer electron hopping the local Hamiltonian for bilayer graphene re-attains the quadratic form with respect to the momentum. Hence, the LL spectrum in bilayer graphene resembles that of the ordinary 2DEG, but with four subbands for each LL level except for the LLL, which has eight-fold degeneracyN < N0, the filling rate, v = N/N0, is fractional  to the conduction band and the magnetic field is strong enough that 22. To implement braid group generators, the cyclotron orbit must be commensurate with the interparticle separation (the details are presented in SI). An archetype of the commensurability is S is the sample surface, N is the number of electrons, and N0 is LL degeneracy), as for 22.To decipher the FQHE hierarchy in this subband in graphene monolayer, we apply the braid group topological approach developed for the ordinary 2DEG systemIn the case of graphene, an important property follows from the fact that cyclotron orbits in graphene are defined by the bare kinetic energy 22 . The commensurability condition, in this case, is as follows: q is an odd integer17). For the LL subband holes, the particle-hole symmetric filling rates Therefore, the cyclotron orbit size in the subband lth particle separation (similarly to in lth LL), whereas the q − 1 antecedent loops take away an integer number of flux quanta (which are commensurate with nearest-neighbouring particles). For lth particles (next neighbours). In this manner, we obtain the hierarchy of fillings for FQHE in this LLL subband in the following form (the same as for the CF model): The next possible commensurability occurs when the last loop of the multi-loop cyclotron orbit is commensurate with every 23, inspired by its fractal-like character and by the Hofstadter’s butterfly picture24, on the other hand. The latter displays the commensurability of 2D cyclotron orbits with the crystalline cell, what, however, requires giant magnetic fields (~105 T), which are out of reach in the experiment24. The commensurability with larger spatial scale, which in case of a diluted Wigner lattice is comparable with the magnetic length, Let us notice that the hierarchy of FQHE filling factors in the LLL of monolayer graphene is similar to the FQHE hierarchy in the conventional 2DEG (GaAs), due to the same commensurability structure in both cases. The role of the commensurability in identification of the FQHE filling factor hierarchy has been noted earlierq-loop orbit q − 1 loops are adjusted to every xth particle . It is noticeable, however, that this series of exotic FQHE filling fractions have not yet been observed in the LLL in graphene, though they are observed in the first LL in monolayer graphene (as will be discussed below).One can also observe that other variants of commensurability may concern multi-loop orbits. Namely, each loop of the multi-loop structure may in principle be adjusted to particle separation in a different and mutually independent manner, matching nearest or next-nearest neighbours under various schemes. One such possibility may correspond to the situation in which n = 0.For lower magnetic fields, the next subband, the last one in the LLL, n = 1. This level has four, electron type subbands. The bare kinetic energy in this LL  is equal to q-loop orbits satisfy the commensurability condition q is an odd integer, which defines the main series for FQHE (multi-loop) in this subband, n = 1 LL subband.In an analogous way, one can consider fillings of the following LLs. The nearest one corresponds to x = 1, 2, 3, i.e., when the cyclotron orbit size exceeds the particle separation. Then, the single-loop orbit (large enough in this subband) can fit with every xth particle (x-order next-nearest neighbours). From this new commensurability opportunity, one finds fractions Simultaneously, in the central part of this higher LL subband, a new type of commensurability is possible, which is not accessible in the LLL. This new commensurability occurs when p-like pairing due to the spin polarization in this subband).Let us note that the special case of the commensurability, n = 1. Moreover, an interesting new possibility for commensurability occurs for q-loop orbits with next-nearest neighbours. The sizes of particular loops in the multi-loop structure may, in general, be adjusted to the interparticle spacing in an independent way, resulting in new filling rates. In particular, this results in the hierarchy n = 1 LL in monolayer graphene at ultra-low temperatures10—cf. Fig. A similar scheme of commensurability may be applied to the following subbands with In bilayer graphene, the topology of braid trajectories changes considerably in comparison to the monolayer system. The bilayer graphene is not strictly two dimensional and this opens a new possibility for the topology of the trajectories, as illustrated in Fig. Two sheets of the bilayer graphene lie at a close distance and electrons can hop between them. Multi-loop cyclotron orbits (and related braids) may thus reside in both layers simultaneously, i.e., loops may be distributed among both sheets. This makes a difference in comparison to the monolayer case because each sheet contributes to the total flux of the external magnetic field independently with its own surface, which strongly affects the cyclotron orbit size and braid commensurability condition. cf. Fig. .4 and cannot be explained by the CF model , and q is an odd integer . After omitting a single loop, the next loops must duplicate the former ones, no matter in which way the loops are distributed between both sheets. Thus, only q − 1 loops take part in the enhancement of the effective q-loop cyclotron orbit size in bilayer graphene, taking into account the same instances of commensurability as in the monolayer case.In general, in a bilayer system, loops of a multi-loop orbit may be located partly in both 2D sheets. To account for this effect in topological terms, adjusted to braid trajectories and commensurability requirements, one must neglect the contribution of a single loop in the multi-loop structure when the total flux of the external field is divided into fractions per loop. This single loop captures its own flux, whereas the remaining loops will share an identical flux—the one which passes through any cyclotron orbit in the monolayer case. Removal of the single loop must be performed independently of how the loops are distributed among two sheets. When we consider a selected loop located in the opposite sheet with respect to the antecedent loop, the next loops must fill both sheets of the bilayer structure as additional loops, regardless their specific distribution. Thus, all these loops, except one, take part in the division of the external field flux in exactly the same manner as in the monolayer case, provided that the selected loop is omitted together with the flux passing through this loop. This trick reduces the bilayer system to a monolayer one in the braid-loop topology sense. Thus, we can write the commensurability condition in the bilayer graphene in the case of too short single-loop cyclotron orbits in the following form  in the first particle-type subband of the LLL, i.e., in the subband 4.It must be emphasized that for multi-loop orbits in bilayer graphene, the total number of loops is still ondition ). Therefmentclass2pt{miniml > 1 describes the lth-order next-nearest neighbours commensurate with the last loop of the q − 1 loops, similarly to the monolayer case  next-nearest neighbours, For holes in this subband , we can write n due to the same size of the cyclotron orbits). A novelty occurs, however, in the next two subbands of the LLL, n = 1, the FQHE main series in the first of these subbands of the LLL, In the following subbands of the LLL, The generalization of this main series for holes in the subband and to the full FQHE hierarchy in this subband is formulated as follows: for subband holes, n = 1 in monolayer graphene), which allows single-loop commensurability with next-nearest neighbours. For x = 1, 2, 3, one obtains the fillings rates x = 1.5 in the above formula, which corresponds to the perfect commensurability of cyclotron orbits of electron pairs with the separation of these pairs at the electron filling rate n = 1, the cyclotron orbits have the same size and the FQHE hierarchy is only shifted by 1 from the antecedent subband.In the subband n = 2, which gives the cyclotron orbit size n = 2 may be larger than the particle separation , the commensurability of this orbit with the next-nearest neighbours ought to be taken into account. As in the monolayer graphene subband with n = 2, one can expect the presence of four (2n) satellite FQHE (single-loop) states, symmetrically located around the central paired state. In the subband n = 2, 1, ↑, these satellite states occur at n = 2—cf. ref.25, whereas in bilayer graphene, the experimental picture is different5. This peculiarity is again caused by the specific topology of the double-sheet structure.The situation changes significantly, however, in the next LL (the first one beyond the LLL). The cyclotron orbits are determined here by the bare kinetic energy with smaller than the orbit size n = 2. Orbits can change only by integer numbers of flux quanta, thus for the initial nominal flux for n = 2, n = 2 in bilayer graphene5—cf. Figs not the particle and hole partners (like the particle n = 2 LL correspond to single-loop braid commensurabilities of nearest and next-nearest (every second) neighbours, respectively. This is confirmed by the asymmetry in the corresponding local minima of Rxx for these pairs, which is observable experimentally5 and illustrates the situation that in states at Rxx at n = 2 and the disappearance of a half-octet of FQHE features in the third subband, together with no features being registered in the fourth subband with n = 2 5, are consistent with this explanation .To solve this puzzle, let us note that in the bilayer system, distinct topological realizations of single-loop orbits may occur that are impossible in the monolayer system. This new opportunity is visualized in Fig. x = 4, 5, 6, 7. Some traces of these features are noticeable in the experiment, as marked in Fig. The orbits reduced due to flux leakage to Bilayer graphene has a different subband structure than monolayer graphene and conventional semiconductor 2DEG, as illustrated in Table n = 0 and n = 1 states results in 8-fold degeneration of the LLL, which is twice the 4-fold spin-valley degeneracy of the LLL in the monolayer case3. The Coulomb interaction causes mixing of the n = 0 and n = 1 states via various schemes induced by stress, deformation, structural imperfections and magnetic field enhancement , which lifts their degeneracy in the LLL in bilayer. After the degeneracy lifting, the order of the subbands with n = 0 and n = 1 occurs to be of particular importance. The sequences n = 0, 1 and n = 1, 0 lead to different FQHE hierarchies. The FQHE hierarchy for the sequence n = 0, 1 is described in paragraph 1.2. However, in the opposite case n = 1, 0, when the n = 1 subband is filled earlier than the n = 0 subband, the hierarchy is different: for the first subband n = 1 and n = 0. The comparison of reverted orderings of the first two LLL subbands is summarized in Table n = 0 is filled earlier than the subband with n = 1. In the inverted ordering of these subbands, the state 4, is shown in Fig. In bilayer graphene, the extra degeneracy of the n = 0, 1 states is lifted in such a way that both levels cross at a certain filling factor v* < 1 . Let us assume, for an example, that the n = 1 subband 5.More precise observations of FQHE in graphene have been recently obtained through improvements of sampling and measurement techniques, including freely suspended graphene sample measurementsn = 1) deviates from the CF picture12. In the bilayer graphene, the incompatibility of the CF model with experimental observations is manifested both in the LLL4 and in higher LLs5. Various scenarios of breaking of the approximate SU(4) spin-valley symmetry in graphene do not solve this problematic situation despite many theoretical attempts, which evidences the insufficiency of the CF model in this case.While the sequence of FQHE fillings in the LLL of monolayer graphene well fits the CF predictions, an explanation of the FQHE filling structure in the next subbands , the following doublets of fillings are observed: 12. The number of centrally located filling rates for FQHE (single-loop) grows with the LL number as 2n  states is of similar strength to that of the IQHE states and is higher in comparison to the FQHE (multi-loop) states, as shown in Fig. The effectiveness of the CF model in the LLL of graphene monolayer is linked with the fact that exclusively in the LLL, cyclotron orbits are always shorter than the interparticle spacing and additional loops are necessary to exchange neighbouring particles along cyclotron braids. These additional loops can be simulated by auxiliary fictitious field flux quanta attached to CFs (as detailed in SI). However, in the case when the more complicated commensurability conditions support particular FQHE states even in the LLL , recently reported10 at In the 4. The commensurability braid group approach for bilayer graphene reproduces all the experimentally observed FQHE hierarchies in the LLL, including the pronounced state at In bilayer graphene, the manifestation of FQHE deviates from the CF picture also in the LLL due to the peculiarity of the double-layer topology caused by interlayer hopping of electrons. As was presented in the paragraph 1.2, in the lowest subband of the LLL in bilayer graphene, even-denominator filling fractions for FQHE appear28, which is also consistent with the commensurability braid group predictions and evidences that this non-CF fraction is caused by the double-layer topology and not by specific material properties of bilayer systems.Let us emphasize that the FQHE state at 8. We propose to explain this effect by the commensurability braid group approach, noting that the occurrence of the Surprisingly, the FQHE state at entclass1pt{minimaentclass1pt{minima5 for the first LL beyond the LLL, i.e., for n = 2 in bilayer graphene . We have explained these astonishing unexpected features, distinct in comparison to conventional 2DEG in n = 2 LLs25, by a specific double-layer topology of bilayer graphene and by an effective leakage of flux due to electron interlayer hopping, as described in paragraph 1.2. The resulting commensurability hierarchy for FQHE in the first LL with n = 2 in the bilayer system (as derived in paragraph 1.2) is perfectly consistent with the experimental data5. We have obtained agreement with topological predictions not only for fractions with denominators 3 and 5 but also with denominators 2 and 4  are not of CF type, because all correspond to single-loop commensurability instances (as is presented in SI in more detail).The most spectacular observations of FQHE in bilayer graphene were reported recently7 for bilayer graphene that is fully encapsulated between two hBN layers, with perpendicular electric field applied by additional bottom and upper electrodes  and they should be completely washed out by the blocking of interlayer hopping, in favour of monolayer-type features with denominator 5 (for n = 2).An interesting opportunity to verify the exceptional bilayer FQHE filling structure due to interlayer hopping of braid trajectories arose from a new architecture in Hall measurement, in which additional vertical voltage is applied to the basal bilayer plane. By varying this voltage, the interlayer hopping of electrons in bilayer graphene can be tuned. The applied voltage can open a band gap at the charge-neutrality point and may change the topology of multi-loop trajectories in the bilayer case, reducing them to instances available in the monolayer case. Such an experiment has been performedx–subband number). For n > 1, these hole partners’ are not actually hole partners, but rather electron single-loop states with every second electron braided. The uncorrelated electrons in these states can scatter and enhance Rxx, in contrast to dual states with single-loop correlation of all electrons. The gradual diminishing of FQHE strength is visible in all subbands with n = 1 of the monolayer graphene10, and in all subbands with n = 2 of the graphene bilayer5. The FQHE energy gain (the activation energy) due to the lowering of the fraction of correlated electrons decreases and eventually drops below the disorder; then the FQHE features disappear in the experiment, as occurred in the fourth subbands of the n = 1 and n = 2 LLs in the monolayer and the bilayer graphene, respectively10, at least down to the lowest temperature range in the experimental setup. In both experiments10, the lowest temperature was 0.5 K. It is quite probable, however, that these very delicate FQHE features might be exposed at mK temperatures. Note also that some FQHE features predicted by the theory may be washed out in experiments by the IQHE re-entrance effect if they are too close to integer fillings (this may concern the poorly visible states at x is the subband number in n = 2 LL subbands in bilayer graphene).The commensurability braid group approach can also be used to explain the experimental observation of the reduction of the FQHE inter-subband relative strength with growing subband number, and of the intra-subband relative strength, when one compares the so-called electron-hole pairs. Both effects correspond to the lowering of the fraction of electrons participating in correlations. This fraction of electrons is further reduced when there are correlated next-nearest electrons, as occurs for ostensible hole partners, e.g., at n = 1 in monolayer graphene, and in the LLL and the first subband (with n = 2) in the bilayer system.We have explained the FQHE hierarchy in graphene in accordance with the recent experimental observations of correlated states, up to the sixth subband in monolayer graphene and up to the eighth subband in its bilayer, revealing deviations from hierarchy schemes known from conventional GaAs 2DEG and apparently going beyond the standard CF model, for subbands with The commensurability of cyclotron braids with interparticle spacing in homogeneous 2D charged systems in a magnetic field is utilized to verify the possibility of arrangement of correlated quantum multiparticle Hall states and to decipher the hierarchy of filling rates for FQHE. By identifying specific topology instances for braids in bilayer graphene caused by the interlayer tunnelling of electrons, we have successfully explained the recent experimental observations of FQHE in the bilayer system. The peculiarity of the FQHE hierarchy, evidenced experimentally in the bilayer graphene in comparison to monolayer graphene and conventional 2DEG, has been clarified in the first eight subbands of the bilayer LL structure.n = 1 there can be present correlated states with single-loop braids that are not equivalent to CFs. The predictions of the braid group commensurability approach reproduce one to one the experimentally observed features in these subbands (n = 1). Simultaneously, the relative strengths of the features, mutually compared intra- and inter-subbands, agree with the theory.In the monolayer graphene, it has been demonstrated that in subbands with n = 2 spin-valley subbands in bilayer graphene is also explained by the same topological arguments, specific to this material. An experimentally observed peculiarity of the FQHE hierarchy in the subbands of the first LL in bilayer graphene with n = 2 (different than in monolayer systems for n = 2 subbands) has been successfully explained in terms of the specific bilayer system topology caused by the interlayer hopping of electrons. By tuning or even blocking the interlayer tunnelling of electrons by application of voltage perpendicularly to the basal plane of graphene bilayer, the predicted phase transition in the FQHE hierarchy has been experimentally demonstrated, which positively evaluated the topological braid group commensurability approach.A similar consistency between the commensurability braid group theory and the experimental observations holds also in the case of the bilayer graphene. The new opportunities for braid group commensurability in the LLL and in higher LLs were identified in the double-sheet system and attributed to the interlayer hopping of electrons, which leads to a different topology than in the monolayer case and in the ordinary FQHE. The even-denominator main line of the fractional filling hierarchy in the LLL of bilayer graphene is derived in this way, in accordance with experimental observations. The unconventional hierarchy of FQHE that was observed recently in The applied braid group commensurability approach to monolayer and bilayer graphene generalizes the conventional CF model. It is confirmed by up-to-date available experimental FQHE observations in graphene on BN substrate, as well as in suspended samples including monolayer graphene up to the sixth spin-valley subband and bilayer graphene up to the eighth spin-valley subband.Supplementary Information