Graphene synthesized via chemical vapor deposition (CVD) on copper foil appears promising for this purpose, but residues from the polymethyl methacrylate (PMMA) layer, used for the wet transfer of CVD graphene, drastically affect the electrical properties of graphene. Here, we demonstrate a scalable and green PMMA removal technique that yields high-mobility graphene on the most common technologically relevant silicon (Si) substrate. As the first step, the polarity of the PMMA was modified under deep-UV irradiation at λ = 254 nm, due to the formation of ketones and aldehydes of higher polarity, which simplifies hydrogen bonding in the step of its dissolution. Modification of PMMA polarity was confirmed by UV and FTIR spectrometry and contact angle measurements. Consecutive dissolution of DUV-exposed PMMA in an environmentally friendly, binary, high-polarity mixture of isopropyl alcohol/water  resulted in the rapid and complete removal of DUV-exposed polymers without the degradation of graphene properties, as low-energy exposure does not form free radicals, and thus the released graphene remained intact. The high quality of graphene after PMMA removal was confirmed by SEM, AFM, Raman spectrometry, and by contact and non-contact electrical conductivity measurements. The removal of PMMA from graphene was also performed via other common methods for comparison. The charge carrier mobility in graphene films was found to be up to 6900 cm In a free-standing graphene layer, the electron mobility can even reach 200,000 cm2/(V·s) at room temperature, the highest value ever known in pure semiconductors [3 to 104 cm2/(V·s), decreased to 2 × 102–2.5 × 103 cm2/(V·s) after the transfer and PMMA removal in acetone [Graphene is a unique material with distinctive characteristics that has shown great potential for a wide range of applications, particularly involving its electronic structure and transport properties ,2,3. Thenductors ,6. Unfornductors , and thanductors ,9,10. Tonductors ,12. Thisnductors ,15,16,17nductors ,19. Aftenductors . It has nductors  that thenductors , even stnductors , acetic nductors , chlorobnductors , and chlnductors . Graphennductors ,27,28,29 acetone . Therefo3–4 × 103 cm2/(V∙s), which until now was the upper limit of the devices fabricated of CVD-grown graphene [Various strategies have been proposed to ensure effective PMMA removal after graphene transfer and preservation of the unique properties of graphene by maintaining its structural integrity ,32,33. Ographene .p-doping into graphene, changing its electrical properties in an undesirable way.In order to ensure the stability of graphene’s chemical composition and structure, and achieve reasonable mobility, scientists have turned attention to the degradation of the polymer under relatively mild processing conditions . As earlOn the other hand, regarding the quality of graphene detected after the removal of PMMA, an aqueous solution of isopropyl alcohol (IPA) looks promising as a solvent, since by its nature it does not introduce additional residuals that dope graphene, as it can be seen after using other solvents for PMMA removal . The aquIn this work, we propose a new approach for the efficient removal of the DUV-exposed PMMA from the surface of wet transferred CVD graphene. Traditionally, the removal of the PMMA film during wet transferring of the CVD graphene implies the dissolution of the polymer (a chain of compounds of the ester type) or the MMA monomer, after thermal or radiational decomposition, with solvents such as acetone (refers to the type of ketones). We propose here to modify this scheme by dissolving the DUV-exposed PMMA with a binary polar solvent of isopropyl alcohol and water. We show that complete dissolution of PMMA is achieved on CVD graphene. As far as we know, the investigation of modification in the polarity of the PMMA under the action of DUV ,47,48 as2 substrates of 1 mm thickness . To expose PMMA to DUV we have employed commercial crosslinker  equipped with 254 nm illumination source (UVC Philips TUV T5 lamps), with exposure time of 8 h at the distance between a source and a sample of 16 cm. To characterize the change in the polarity of the exposed PMMA, the optical contact angle meter  was used to assess the degree of hydrophilicity of the surface.To investigate the effects of DUV exposure on PMMA, 996 K molar mass PMMA  layers were prepared by spin coating a 4% PMMA solution (0.53 g/10 mL) in anisole  to the desired substrate and drying at 180 °C resulting in PMMA film of about 250 nm. For various experimental investigations we have used different substrates. The pristine and DUV-exposed PMMA samples were prepared on a 2 mm-thick fused silica substrates  for the investigation of absorbance spectra in UV spectrum range using a UV/VIS spectrometer  in the transmission geometry. Changes in IR absorbance in PMMA after DUV exposure were investigated using the FTIR spectrometer  in the transmission geometry with 1 mm aperture in a vacuum environment with PMMA samples on CaF−1. For each sample, 10 spectra were recorded with an integration time of 60 s and used for statistical analysis. The electrical characteristics of graphene were investigated using contactless optical and contact methods. For optical contactless characterization, terahertz time-domain spectroscopy (THz-TDS) was performed with the commercial THz-TDS spectrometer  in the transmission geometry of a focused beam with a spot size around 2–3 mm. Since THz-TDS measurements only provide information about the conductance of the graphene sheet, contact Hall measurements in a 0.5 T magnetic field  were also carried out to gain insight into the doping type of the samples.Finally, sets of graphene samples were prepared for a proof-of-concept of the proposed approach by taking a commercial monolayer CVD graphene synthesized on a copper foil with protective PMMA coating  and transferring it on float zone high resistivity (HR) (>10 kΩ∙cm) silicon wafers . The IPA , acetone  and chloroform  were used as solvents. The quality of the prepared graphene samples was determined by optical microscopy, SEM, atomic force microscopy (AFM), Raman spectroscopy, THz time-domain spectroscopy (TDS), and Hall effect measurements. Scanning electron microscopy images were obtained using secondary electrons at 2 kV and 25 pA beam current in a dual-beam system . The conductive microscopy was performed using scanning probe microscope system . Sample bias was set to value of 20 mV using tunneling AFM (TUNA) module under ambient conditions. For these measurements the PtIr cantilever, 300 um length and 0.8 N/m spring constant (type RMN-12PT300B) was used. The samples were characterized by a Raman spectrometer  using a 1800 lines/mm grating, a microscope equipped with a 50×/0.8 NA objective, and a continuous-wave 532 nm excitation laser operating at a power of 0.6 mW. The beam was focused to the size of a spot with a diameter of 0.8 μm on the sample surface. The position of the Raman spectrum bands on the wavenumber axis was calibrated by a silicon peak at 520.7 cmOne of the main points of the proposed method is the change in the properties of PMMA, both chemical and physical, when the polymer is exposed to UV radiation. We show that deep-UV irradiation with a wavelength of 254 nm, used for this purpose, leads not only to photodegradation of the polymer due to the main-chain scissions, as occurs with more powerful irradiation sources, but also the appearance of new species, the formation of which is more pronounced in the case of photodegradation at 254 nm.Since DUV exposure of PMMA takes longer due to the lower energy of irradiation, some products formed after main-chain scissions further absorb UV photons and contribute to the degradation of the polymer by side-chain scissions that are occurring in parallel with the main-chain scissions. As a result, new chemical species are formed, including ketone-type and aldehyde-type carbonyl compounds . To conf3 and CH2 groups , C=O stretching (1729 cm−1), and stretching vibration of the C−O−C group (1148 and 1193 cm−1). The vibrational spectrum of PMMA has been analyzed in detail in previous publications [–1), the relative intensity of the 1148 cm−1 band associated with the symmetric stretching vibration of the C−O−C group decreases the most, indicating DUV-radiation-induced cleavage of ester bonds. The negative-going feature at 1729 cm–1 due to the C=O stretching vibration of the ester group confirms this scenario. In the C−H stretching vibration spectral region, one can find direct evidence of radiation-induced destruction of CH2 groups, as two intense negative-going bands at 2851 and 2919 cm−1, associated with symmetric and asymmetric stretching vibrations of the methylene group, respectively, appear in the difference spectrum. In addition, the negative-going band, due to CH2 scissoring deformation vibration, is visible near 1486 cm–1. These spectral changes indicate cleavage in the vicinity of the –CH2−moiety (main chain). The positive-going feature near 1710 cm−1 reveals the DUV-exposure-induced formation of new species, most likely containing C=O of aldehyde and/or ketone functional groups. The positive-going broad feature near 1618 cm−1 is consistent with the formation of sp2-hybridized carbon bonds, aromatic carboxyl groups, and hydroxyl groups [−1 support the formation of compounds containing C−O bonds or/and hydroxyl groups. Earlier works investigating similar FTIR spectra of DUV-exposed PMMA also concluded that bands of newly produced species were observed in the IR spectrum, and were attributed to ketone-type and aldehyde-type compounds [To gain insight into the molecular changes of DUV exposure induced in PMMA film, we performed an analysis of FTIR transmission spectra . The domications ,72,73,74ompounds .Chemical changes in the exposed PMMA structure are manifested in the modification of the physical properties of the final products after the photochemical reaction, specifically in polarity. Namely, the increase in polarity is the first basis of the improved solubility mechanism of PMMA exposed to DUV. After exposure, the newly produced ketone and aldehyde type compounds with a polarity higher than that of the original ester functional group can form H-bonds more efficiently, when acting as an acceptor, namely a carbonyl oxygen acceptor, upon subsequent dissolution.Assessing the polarity of the material is not an easy task, but the water contact angle has been proven to be directly linked to the polarity of the surface . Contact3H6O 0.355), chloroform (CHCl3 0.259), anisole (C7H8O 0.198), or toluene (C7H8 0.099). However, it is known that PMMA is practically insoluble in water at ambient temperature [Since higher polarity products form hydrogen bonds, which are much easier than those of pristine PMMA upon subsequent dissolution, it is expected that this will result in the improved removal of PMMA when using a solvent of suitably high polarity. One could expect that the most effective dissolution will be achieved when the solvent with the highest polarity is used, namely, water (relative polarity 0.998) instead of solvents historically used for this purpose such as acetone  were studied via SEM and AFM. SEM images of graphene films prepared by different PMMA removal methods are shown in To compare the discussed method of PMMA removal, additional PMMA/graphene samples were prepared using the same wet transfer process (steps 1–3), but with PMMA removed with common solvents: acetone and chloroform. A total of five samples were prepared: three samples with DUV treatment and development in aqueous IPA (samples DUV1–DUV3), and one sample each for PMMA removal for 18 h at 23 °C with acetone and chloroform, respectively. As a reference, the standard commercially transferred graphene film to SiO−1 (G peak) and 2674 cm−1 (2D peak). It is worth noting that the D peak at around 1350 cm−1 falls into elevated background, and was not included in the analysis. To obtain the precise position and FWHM of G and 2D lines, a Lorentz function was used to fit each peak obtaining the mean and standard deviation values of peak intensity and FWHM. The results for all the samples are provided in −1, respectively. The samples prepared using chloroform and acetone exhibited a high 2D/G intensity ratio (>2.4), but their FWHM was larger in comparison with DUV samples, namely, FWHM ≥ 30 cm−1. To consider the repeatability of our process in the fabrication of DUV samples, we fabricated three DUV samples over two separate processing runs, the results of which are listed in the −1. Additionally, the fitted positions of the 2D and G lines are used in correlational position analysis, between the 2D and G peaks, which makes it possible to investigate strain and doping in graphene films [0; 2D0) of free-standing undoped graphene is marked with a large black cross, the position of which is at 1581, 2671 cm−1. The distribution of positions extends to a line in undoped graphene under biaxial strain, and is plotted as a black line, which is the usual case for graphene transferred onto Si [p-doped and under biaxial strain, this will cause the G peak position to move towards higher Raman shifts and parallel to the strain line. Since the data of the samples prepared in this study  are distributed between the theoretical lines of undoped graphene and 5 × 1012 cm−2 doping, this shows a low doping of the prepared graphene samples. A different behavior is observed for a commercially transferred graphene sample. A significant shift in the data points indicates a high doping of graphene films, which was found to be close to 2 × 1013 cm−2, demonstrating a low sheet resistance of the graphene according to the manufacturer data sheet.The Raman spectra for the selected sample DUV3 are shown in ne films . The resAny future applications of CVD graphene require contactless methods of graphene film electrical properties that can conduct large-area mapping and function rapidly . One of kness dS ,85,87. TS, sheet carrier density  NS, and carrier mobility µ, were found from fitting results using the respective definitions:Relevant electrical properties of the graphene films, such as sheet resistance R12 cm−2 and mobilities higher than 2410 cm2/(V·s). The best overall result was achieved for sample DUV3, which demonstrated very low residual doping and very high mobility values, found to be at the level of 0.8 × 1012 cm−2 and 6900 cm2/(V·s), respectively.The results for all samples are summarized in p-type conductivity (DUV1 and DUV2), while the last one demonstrated n-type conductivity (DUV3). Samples prepared using chloroform and acetone solvents showed n and p-type conductivity, respectively. The varying conductivity type for the DUV samples could be a result of slight unintentional doping during PMMA removal, since for all the samples analyzed, carrier density was below 2.5 × 1012 cm−2. These results indicate that DUV-assisted PMMA removal in an IPA/water solution makes it possible to obtain clean CVD graphene with high charge carrier mobility values, which are required in the field of high-frequency electronics.Remote THz characterization is a powerful tool; however, it does not provide information on the type of free-charge carriers that interact with THz radiation. To gain more insight into this, we added Ag epoxy contacts to each corner of the rectangular graphene samples and performed Hall experiments. Two of the three samples prepared using DUV treatment exhibited In conclusion, a green and cost-efficient method has been developed for PMMA supportive layer removal from the surface of CVD graphene wet transferred onto an application-compatible substrate of choice, which allows one to obtain scalable graphene with high electron mobility for the needs of high-frequency graphene-based electronics and optoelectronics. In terms of the method, we propose to first modify the polarity properties of PMMA via exposure to deep-ultraviolet (DUV) radiation with a wavelength 254 nm, so that not only the decomposition of PMMA polymer to MMA monomer occurs, as typically happens after thermal or photo-irradiation, but also the formation of final products  with polarities higher than those of the initial products (esters). Such products form hydrogen bonds much more easily upon subsequent dissolution, which would allow for better removal of PMMA using a solvent of high polarity. We propose to use a binary solvent mixture of isopropyl alcohol and water, which is not only extremely polar, but is also a more environmentally friendly solvent. Generally, an aqueous alcohol—such as ethanol—can be used, especially since it has no environmental impact at all. Another advantage of the method is that low-energy irradiation does not form free radicals, thus the released graphene remains intact, unlike in higher-energy PMMA decomposition methods, such as with an electron beam or even DUV at 195 nm.2/(V·s), which makes the proposed method suitable for removing PMMA from the graphene surface in the industry of high-performance large-scale electronic devices based on graphene.The high quality of graphene after the removal of PMMA using our method was confirmed with SEM, AFM, and Raman spectrometry. Electrical transport properties of released graphene, which are of special interest to current research, were fulfilled by means of contactless optical (THz-TDS) and contact  techniques. It was found that the mobility of charge carriers in graphene films reaches up to 6900 cmN.A. and I.K. are inventors on a provision patent application filed by the Valstybinis mokslinių tyrimų institutas Fizinių ir technologijos mokslų centras .


Larrea tridentata (gobernadora) and Capsicum Chinense (habanero). Graphene oxide was synthesized by the modified Hummers’ method and subsequently reduced using natural extracts to obtain a stable and environmentally friendly graphene precursor. Consequently, the gobernadora aqueous extract was found to have a better reducing power than the habanero aqueous extract. This opportunity for green synthesis allows the application of RGO in photocatalysis for the degradation of the methylene blue dye. Degradation efficiencies of 60% and 90% were obtained with these materials.In the present work, reduced graphene oxide was obtained by green synthesis, using extracts of  Nowadays, as a consequence of industrialization, the world faces problems with air, soil, and water pollution. This problem is becoming increasingly important despite the existence of pollutant removal treatments and waste reduction and disposal programs. In many of these processes, the problem is only partially eliminated, so pollution of rivers and seas is increasing, and the damage this is causing is of an unimaginable magnitude. In the last two decades, the organic pollutants discarded by industries have no control, which has led to water pollution being severely affected. The World Bank estimates that 17–20% of industrial water pollution comes from textile dyeing. Wastewater from textile industries is a major problem for conventional treatment plants worldwide. The release of these wastewaters into natural environments is very problematic for aquatic organisms. The wastewater generated by the textile industries is known to contain considerable quantities of non-fixed dyes, especially azo dyes, and a large number of inorganic salts. It has been estimated that more than 10% of the total dye is used in dyeing processes while the rest is released to the environment. Therefore, it is necessary to study new processes that allow the efficient elimination of pollutants, which are affecting the environment so much ,4.2 ..Larrea TCapsicum Chinense (habanero pepper) is an herbaceous plant with a high source of phytochemicals or bioactive compounds that have shown benefits to human health. The main compounds of Capsicum Chinense are phenolic compounds, capsaicinoids, flavonoids, vitamin C, carotenoids and tocopherols. The capsaicinoids present in the chili fruits of the genus Capsicum Chinense have various functional properties such as: antioxidant, anti-inflammatory, antimicrobial and antitumor capacity, among others. Additionally, natural capsaicin with a high level of purity is of great economic importance and appreciated in the pharmaceutical, food and chemical industries  natural extract—deionized water. The behavior of the extract concentration and it is reducing power in graphene oxide was analyzed.To prepare the gobernadora extract, 30 g of v/v). Subsequently, the solutions were heated at 80 °C for 12 h under constant agitation in a reflux system. After 2 h of heating, the color began to gradually change from brown to black, indicating the start of graphene oxide reduction. After the reduction was complete, the color turned dark black and this indicated the reduction of graphene oxide and the formation of reduced graphene oxide (RGO). To complete the green synthesis, the mixtures were centrifuged and washed with deionized water several times and finally dried at 60 °C for further characterization.Once the aqueous extracts were prepared, the graphene oxide solutions were exfoliated and mixtures of the aqueous extract solutions with GO were prepared in a ratio of 4:1 (% 0) of the solutions was noted before photodegradation. Dye degradation was carried out sequentially by individual dye solutions of MB.For the photocatalytic degradation study, dye selected was methylene blue (MB). UV light (365 nm) irradiation was applied to find out a suitable as well as effective way to eliminate the maximum percentage of dye. For photodegradation, the dye solution was prepared in deionized water at the concentration of 10 mg/L. Further, 20 mg/L of RGO is added to the prepared dye solution. After, these mixtures were subject to low shaking for 20 h under dark conditions for the adsorption and desorption of dye molecules onto the surface of RGO. At the end of the dark exposure period, each mixture was subjected to UV–Vis spectrophotometer analysis and the initial concentration . Dye degradation could be calculated from the absorbance values using the following formula ,31,32,33−1. To determine each of the carbon members, Raman spectroscopy using the LabRam VIS-633 equipment was used. The measurements were made in the spectral range between the wave numbers 1000 and 3500 cm−1. Finally, the morphology of our material was determined using a transmission electron microscope with a filament of lanthanum hexaboride at a scale of 100 and 200 nm.The XRD technique allows monitoring the oxidation process of graphite. The diffraction patterns of the GO and RGO were performed in a Miniflex II model, Rigaku brand diffractometer (λ = 1.5418), the measurements of the samples were made in a 2Θ range of 5 to 70°. To determine the reduction of graphene oxide the following techniques were used: UV–Vis, FT-IR and Raman. The interaction of the samples with the electromagnetic radiation was determined by UV–V is spectroscopy with a Perkin Elmer spectrophotometer, scanning wavelengths from 248 to 400 nm, the measurements were made in quartz cells of a 1 cm optical path over aqueous suspensions of graphene The presence of the characteristic bonds as well as the loss of oxygenated groups was determined by means of the FT-IR spectra of the samples with a Perkin Elmer Paragon 1000 spectrometer, the measurements were made in the spectral range between the wave numbers 500 and 4000 cmIn this work, six samples of a colloidal suspension of graphene oxide (GO) were reduced with different natural aqueous extracts (habanero and gobernadora). UV–VIS allowed the determination of whether suspensions contained transient products of GO and if it had been partially reduced (RGO) as the natural extract concentrations increased. In this technique only five samples were analyzed: (a) GO, (b) HAB1, (c) HAB2 (d) HAB3, (c) GOB1, (f) GOB2 and (g) GOB3.Larrea Tridentata extract is a better candidate as a GO-reducing agent compared to Capsicum Chinense extract [During the oxidation of graphite, oxygen adheres to the graphene layers, thus increasing the polarity of the layers which in turn increases its solubility in water. This results in a change in the color of the solution from yellow to brown. depending on the GO concentration, the brown color can be of different intensities. The GO that is formed has an absorption maximum at 225 nm for a well-oxidized material . TheUV–V extract ,36,37,38The reduction of the GO leads to the loss of oxygenated functional groups, so it was decided to apply FT-IR spectroscopy to verify if there are differences between the amount and type of functional groups in the samples. The analyzed FT-IR spectra are presented in −1 and was attributed to the C-OH stretch bands of the hydroxyl group. The second peak of less intensity was located at approximately 1620 cm−1 and was attributed to the skeletal vibration C=C. A third peak was located at approximately 1050 cm−1 and was attributed to the C-O alkoxy stretching vibration. Finally, a peak of very low intensity of approximately 1730 cm−1 was attributed to the vibration of the carbonyl group C=O [−1 and was attributed to the stretching vibration of the epoxy group C–O–C [−1 and was attributed to the skeletal vibration C=C of the graphene planes [−1, was attributed to the stretching vibrations C–OH of a hydroxyl group [2 carbon bonds, as seen by the increase in the band at 1620 cm−1, corresponding to the C=C links. In addition, in all the samples a two-diminution of intensity was observed in the peaks of the functional groups C–O–C and C–OH [Of all the FT-IR transmittance spectra of the samples analyzed, peaks attributed to the oxidation of graphite and graphene oxide can be observed See . Oxidizeroup C=O ,38,39. Tup C–O–C . The nexe planes ,42. A thyl group ,44,45. Tand C–OH ,38,39  and the D-peak (~1355 cm−1) arising from the mode of respiration of photons of the K symmetry point A1g [Raman spectroscopy is considered a popular technique for characterizing the structural and electronic properties of graphene, including disordered and defective structures, defective density and doping levels. Raman spectroscopy is very sensitive to structure for the characterization of carbon-based materials, especially C=C double bonds that lead to high-Raman intensities. The Raman spectrum of graphene is generally characterized by two main characteristics: the G-peak, which arises from the first-order dispersion of the Eoint A1g ,38,43.−1 while the D-band appeared in the range of 1342–1350 cm−1. Interestingly, the Raman spectrum of GO after reduction with natural extracts had higher intensities than GO, these high intensities could indicate the introduction of sp3 defects after functionalization and incomplete recovery of the graphene structure. The variation of the relative intensities of the G-band and the D-band in the GO Raman spectra during the reduction generally reveals the state change of the electronic conjugation. In this work an increase in the number of sp2 domains was indicated after GO reduction [Our results  show thaeduction ,20,44  GOB3 RGO-Larrea 20%.On the other hand, it is well known that the Raman dispersion of two phonons (2D) of graphene-based materials is a valuable band for differentiating monolayer graphene from double layer or multilayer graphene, since it is highly perceptive to the stacking of graphene layers. Usually, a Lorentzian peak is observed for the 2D band of the monolayer graphene sheets at 2697 cmayer RGO ,46. FiguD/IG) and will be used to compare the way in which the structural disorder grows in the graphitic network. The locations of both D- and G-bands and the ratio between their intensities are consistent with the characteristic values reported elsewhere. When pristine graphite was oxidized to GrO, the ID/IG ratio of the resulting material significantly increased indicating a higher level of structural disorder and a larger number of defects in the graphene layers due to the oxidation process. After sonication to obtain GO, ID/IG relationship in the resulting material slightly increased, indicating that the exfoliation process also incorporated further defects into the structure. Logically, the distance between defects (determined as 2) decreased from graphite to both GrO and GO [O and GO ,49,50,51The XRD technique allows for controlling the oxidation process of graphite. The data reported in the literature show that graphite has a reflection peak at approximately 2ϴ = 26°, which corresponds to a spacing d of 0.335. Upon oxidizing graphite, the reflection peak (002) changes to the angle 2ϴ = 10° (space d = 0.906). This increase in the d-space is largely due to the intercalation of water molecules and the formation of functional oxygen-containing groups in the graphite layers ,51,52. OThis characterization technique was used to observe the morphology and size of layers of graphene or graphene oxide, as well as their sizes and imperfections. The samples were prepared by dispersion in alcohol and then sonicated for 10 h. A drop of the suspension was deposited on to a copper grid to analyze it. 16H18N3Cl1S1 and a molecular weight of 319.85 g/mol. Its maximum absorbance is at 663 nm [Methylene blue (MB), also called methylthionine chloride, is an organic dye with the molecular formulation Ct 663 nm . The abso) with the absorbance values obtained at specific time intervals (Ct) (The degradation efficiency (%) was calculated from the absorbance values obtained for the initial dye concentration  .The first step of the photocatalysis is the activation of the photocatalyst by the reconstruction of the photocatalyst surface via electromagnetic radiation illumination. The electromagnetic radiations interact with the surface plasmons of the photocatalyst and excite the electrons into the higher states. Upon the excitation of the negatively charged electron (e−), the positively charged hole (h+) is created in its place. These e−/h+ pairs are responsible for the photocatalytic capability of the photocatalyst. These generated e−/h+ can undergo recombination reactions via relaxation processes which lead to the deactivation of the photocatalyst ,56,57.From the sample of RGO with gobernadora extract a, it is The efficiency of photocatalytic degradation of MB with a photocatalyst was calculated from absorbance values and is presented in The previously studied reduced graphene was compared with other studies on the removal of MB dye from similar light sources . Numerouv/v), the better the reduction of GO. Using Raman spectroscopy, we noticed that both GO and RGO obtained had a multilayer structure, possibly due to the lack of exfoliation time in the ultrasound period before and after the graphene oxide reduction. Prior to characterization by TEM microscopy, RGO was exfoliated for 10 h and monolayers were obtained. The TEM images reaffirmed the multilayer structure in RGO samples prepared by our eco-friendly route of synthesis.Based on these results, we obtained that the concentrations of the extract directly affect the reduction of our material, so we conclude that the higher the concentration of the natural extract  and Capsicum Chinense (habanero). We believe that the reduction is largely due to natural-reducing agents such as ascorbic acid, carotenes, polyphenols and capsicum contained in plants. In addition, we can also say that the Larrea Tridentata extract acts as the best GO reducer, according to the results obtained from the FT-IR, UV–Vis and XRD characterization techniques. On the other hand, it was possible to verify that the RGO reduced with natural extracts can act as a photocatalyst for the degradation of MB dye [Reduced graphene oxide (RGO) was obtained through an eco-friendly synthesis applying a green chemistry methodology and using natural extracts of f MB dye ,69,70,71The use of eco-friendly reducing agents to synthesize graphene garners great interest thanks to the great potential of applications that they can have. It is considered as one of the most versatile methods. These kinds of reagents are shown to be an alternative to inorganic compounds, such as hydrazine or other non-biocompatible or toxics reducing agents, as well as with better catalytic properties compared to other organic reducers, such as glucose. They are also safe to handle and the reaction co-products are biocompatible.


Although sarcoidosis is an established cause of multiorgan dysfunction, acute presentation with thrombotic microangiopathy resulting in severe renal and hematological sequelae has not been reported. We describe the case of a patient presenting with hypercalcemia, pancreatitis, and acute renal failure, followed by microangiopathic hemolytic anemia. Although there were no significant respiratory symptoms, thoracic radiology and mediastinal lymph node biopsy results were in keeping with sarcoidosis as the underlying cause of this multisystem presentation. Corticosteroids were commenced with clinical and biochemical improvement. This novel case highlights the need to consider sarcoidosis as part of the differential diagnosis for unusual multiorgan presentations and for early multidisciplinary involvement in such cases to permit optimal treatment. Sarcoidosis-associated kidney dysfunction in particular is usually attributable to granulomatous nephritis  or as a direct consequence of hypercalcemia .A 31-year-old man presented to the ED with epigastric pain and nausea, associated with generalized malaise and fatigue. The patient also described 2 days of mild, and 1 night of profuse, nonbloody diarrhea approximately 3 weeks before their attendance. He was a current smoker, working as a delivery driver, with no significant medical history and no regular prescribed medications. Over-the-counter medications included a multivitamin supplement and loperamide taken after the episode of profuse diarrhea. He had no history of illicit drug use. Initial investigations indicated acute kidney injury (Cr 241 μM) with hemoproteinuria, a raised amylase (191 U/L), and widespread pulmonary infiltrates visible on initial chest radiograph . The radTwo days after admission, the patient developed anemia (105 g/L) and thrombocytopenia  alongside an inflammatory response (c-reactive protein > 100 mg/L). A bone profile test revealed hypercalcemia . In this context, a blood film was performed, which showed red cell fragmentation (more than four per high-powered field), consistent with a microangiopathic hemolytic anemia . The patGiven the diagnostic uncertainty and multiorgan involvement, cross-sectional imaging was undertaken, showing marked perilymphatic ground-glass changes and nodularity in the midzones of both lungs, mediastinal lymphadenopathy, and splenomegaly . InvestiTransfusion of packed RBCs and platelets allowed a percutaneous kidney biopsy to be performed, which showed severe acute thrombotic microangiopathy (TMA), with no evidence of granulomata or interstitial nephritis A. Given Mycobacteria. Critically, the lymph node biopsies identified non-necrotizing granulomata consistent with sarcoidosis  and BAL of his middle lobe. The BAL, performed after the endobronchial ultrasound-guided biopsy, was blood-stained without prominent hemosiderin (indicating post-biopsy acute hemorrhage). The differential cell count was, as a result, difficult to interpret . BAL microscopy and culture was negative, including for coidosis B and, asEscherichia coli or Streptococcus pneumoniae, sarcoidosis has more frequently been linked to previous infection with Mycobacteria and Propionibacteria.,,To establish a final diagnosis for this case, we must consider whether the patient’s confirmed significant findings of granulomatous inflammation and TMA could be attributed to any other underlying condition. Both TMA and sarcoidosis can be associated with infection, but although hemolytic uremic syndrome is usually secondary to ,Given the widespread features of acute sarcoidosis and the sequence of events, a plausible explanation is that sarcoidosis represents the primary underlying pathology of this patient’s multiorgan dysfunction. We propose that sarcoidosis-driven hypercalcemia resulted in acute pancreatitis , which in turn led to TMA. Both sarcoidosis-induced hypercalcemia resulting in pancreatitis and this pathology leading to TMA are rare, but they have been described previously.Collaborative input from a multidisciplinary team including hematologists, nephrologists, respiratory physicians, histopathologists, and thoracic radiologists was critical to managing this case. We would therefore advocate early specialist input in such unusual cases of multiorgan pathology to permit optimal treatment to be provided and good clinical outcomes achieved.


This work proposes a novel design composed of graphene nanoribbons-based optofluidic tweezers to manipulate and sort bio-particles with radii below 2.5 nm. The suggested structure has been numerically investigated by the finite difference time domain (FDTD) method employing Maxwell's stress tensor analysis (MST). The finite element method (FEM) has been used to obtain the electrostatic response of the proposed structure. The tweezer main path is a primary channel in the center of the structure, where the microfluidic flow translates the nanoparticle toward this channel. Concerning the microfluid's drag force, the nanoparticles tend to move along the length of the main channel. The graphene nanoribbons are fixed near the main channel at different distances to exert optical forces on the moving nanoparticles in the perpendicular direction. In this regard, sub-channels embedding in the hBN layer on the Si substrate deviate bio-particles from the main path for particular nanoparticle sizes and indices. Intense hotspots with electric field enhancements up to 900 times larger than the incident light are realized inside and around the graphene ribbons. Adjusting the gap distance between the graphene nanoribbon and the main channel allows us to separate the individual particle with a specific size from others, thus guiding that in the desired sub-channel. Furthermore, we demonstrated that in a structure with a large gap between channels, particles experience weak field intensity, leading to a low optical force that is insufficient to detect, trap, and manipulate nanoparticles. By varying the chemical potential of graphene associated with the electric field intensity variations in the graphene ribbons, we realized tunability in sorting nanoparticles while structural parameters remained constant. In fact, by adjusting the graphene Fermi level via the applied gate voltage, nanoparticles with any desired radius will be quickly sorted. Moreover, we exhibited that the proposed structure could sort nanoparticles based on their refractive indices. Therefore, the given optofluidic tweezer can easily detect bio-particles, such as cancer cells and viruses of tiny size. Nevertheless, the vulnerability of cells under highly intense fields, low speed, and buffer incompatibilities impairs the efficiency of conventional microfluidic designs. Another technique to manipulate and sort cells in hydrodynamic flow control is based on either on-chip or off-chip, which is utilized to sort living cells due to less vulnerability of cells under a high electric field. However, this method suffers from the slow cycle time of the mechanical switch and the relatively large volume of fluids in each cycle5.The development of microfluidic and optofluidic systems is going to trigger a revolution in different fields such as physics, biology, chemistry, medicine, and photonics. The unique characteristics of such fluidic systems include fast and non-destructive performance, low cost, high efficiency, multiple applications, and compact footprint. Also, microfluidic cell sorting systems have received much attention with a variety of methods for active control of cell movements or flow, such as electrokinetic mobilization of fluids for bacterial cell sorting6. The radiation pressure of a focused laser beam resulting from the light momentum variations has been investigated to trap or push a single cell or particle in a fluidic medium without any physical contact. The imposed force on a particle depends on the size and optical properties of the particle as well as the surrounding fluidic medium. This optically-induced method opened a new promising approach to cell sorting networks in a microfluidic medium. The first single-cell sorting system was introduced at7, allowing the single cells to be trapped or sorted by imposed optical forces. Hence, this technique solved the problems mentioned regarding its non-invasive nature and ability to operate with a single cell.In this line of research, optical tweezers for cell trapping and manipulation were first introduced by Ashkin et al. in 19878 is based on optical far-field interactions. In these tweezers, the focal spot of a big numerical aperture (NA) objective has been used along prolonged paths to be more effective at far distances. However, these prolonged trap paths lead to drawbacks. First, observing the dynamic response of single molecules is impossible, and second, the diffraction limit restricts the sub-wavelength design of these tweezers. Therefore, an optical tweezer based on a near field or evanescent wave was developed to solve this limitation9. In the context of optical tweezers, it has been demonstrated that the optical force of an evanescent field is adequate to manipulate and trap microparticles at the interface of two media with different refractive indices, such as glass/water interfaces.The operation principle of conventional optical tweezers in the literature11.Nevertheless, such evanescent waves are not strong enough to trap and manipulate nanoparticles. Therefore, a metallic tip or nanoaperture has been employed for exciting surface plasmons waves (SP) to improve near-field enhancement. However, despite their ability to displace nanometer-sized single cells, the induced surface plasmons in a metallic tip introduce huge absorption losses reducing trapping stability16, modulator18 photodetectors23. Especially in the recent years graphene plasmonics applications in optical tweezers (PT)31, have been introduced to address mentioned drawbacks and have been utilized in optofluidic systems to sort nanoparticles. For instance, in25, active graphene plasmonic tweezers and size/RI-based nanoparticle trapping and sorting with radii in the range of 5–50 nm is proposed. The structure is illuminated by a laser beam in the mid-IR frequency range of 4–8 µm and its wavelength and intensity are kept constant even for sorting functionality. Each unit cell of the structure is composed of a graphene layer on top of a metallic nanoring which is embedded in SiO2. Strong hotspots with field enhancements reaching values as high as 150 are obtained inside the rings with no need for sharp edges conventional in plasmonic structures. Graphene, as a two-dimensional material, with superior optoelectronic characteristics such as broad-band light absorption, high electrical and thermal conductivity, ultrafast charge carrier dynamics, and gate tunable charge carrier density is a promising alternative to metallic counterparts for designing plasmonic structures. However, the unique features of graphene are vulnerable to its substrate, originating from the interaction of each graphene atom with the surrounding medium32.In recent decades, graphene plasmonic-based applications have been attracted significant attention such as sensors33, Ni34, Ru35, Pt36, SiC38, and SiO2 for graphene have been studied so far. Reports demonstrate that SiO2 as a conventional and widely used graphene substrate deals with problems such as carrier mobility reduction via scattering in the charged surface states, impurities, substrate surface roughness, and surface optical phonons. Therefore, a substrate is required for graphene-based structures without limiting its unique properties. Meanwhile, studies show that  hBN with promising features as the graphene substrate40 can surpass other materials.To improve graphene performance, different substrates, such as Co40. This improvement originated from graphene mobility due to the higher reduction of surface impurities associated with the low lattice mismatch between the graphene and its hBN substrate. The graphene/hBN lattice mismatch is only 1.7% which is ten times smaller than graphene's conventional substrates like SiO240. The flat surface of hBN, no dangling bonds, and no trap charges on the hBN surface make it a perfect substrate for a 2D graphene sheet41. High carrier mobility improves the plasmonic wave propagation and the optical response of graphene42. In addition, hBN has excellent physical properties such as high-temperature stability, corrosion resistance, sizeable optical absorption43, neutron capture interface, ultra-long carrier lifetime39, and significant negative electron affinity44. The unique feature of hBN/ graphene sandwich is investigated thoroughly in the graphene plasmonics Fabry–Perot wave interferometer photodetector19 in which by using hBN as an substrate for graphene in compare with the conventional substrates such as SiO245. In this work we represented that using hBN instead of SiO2 reaches the responsivity of photodetector more than 10 times larger, more over due to high graphene mobility on hBN, the photodetector bandwidth experienced an immense improvement as well as photodetection speed. However, using hBN due to 2D nature of this material causes some irregularities on graphene features which is completely studied at our previous work46.Dean et al. demonstrated the first graphene-based transistors using the hBN substrate with significant improvementsx), thus directing toward the adjacent nanoribbons where the electric field is significantly confined. The electric field’s hot spots on the graphene nanoribbons are 900 times larger than the incident one. The electric field enhancement on the graphene nanoribbons is significantly sensitive to graphene chemical potential. Therefore, the optical forces in the vertical (x) direction on nanoparticles can be tuned by correctly choosing the gate bias and the optimized gap distance between the main channel and graphene nanoribbons. Thus, a desired deviation of the nanoparticle allows us to direct it toward the outlet branches. The resonance wavelength of graphene ribbons is adjusted by tuning the graphene Fermi level, allowing us to determine the operating wavelength interval of the proposed optofluidic system. Finally, repetition of this process leads to individual particles with desired sizes or refractive indices being sorted and directed to outlet branches.This study proposes a novel structure composed of graphene nanoribbon embedded in hBN to trap nanoparticles with radii in the 2.5–50 nm range and sort below R = 2.5 nm nanoparticles. The principal mechanism of nanoparticle manipulation relies on exciting graphene plasmon with a parallel-polarized incident light concerning the graphene surface. An extra optical force is exerted on nanoparticles via graphene nanoribbons perpendicular to the liquid drag force. The moving nanoparticles inside the liquid deviate from their original path in the main channel in response to exerted optical force in the vertical direction (Fn = 1.57 for radii in the range of 2.5 nm to 50 nm. The fluidic medium is considered to be water with n = 1.33. The electromagnetic wave simulation using the Maxwell Stress Tensor (MST) method is performed to calculate the imposed optical forces numerically. The primary channel is where the nanoparticles with a liquid are pushed in, as seen in Fig. Figure 1), all the particles are placed in the middle of the ribbon as indicated by the dashed line in Fig. 1 in the x direction (Fx). Nanoparticles continue to move under the influence of liquid force in the y-direction without deviation in the x-direction. However, when the particle moves in the y-direction and reaches closer to the sub-channel graphene ribbon (GR2), the particles experience a gradient force in the x-direction exerted by the GR2, leading to deviation of a specific (larger) nanoparticle in the x-direction. Large particles sense stronger forces in the x direction, so the deviation of a large particle is more significant than the smaller ones. Therefore, the larger particle changes its path toward the GR2 and is filtered out from the main channel. Due to interaction with the GR2 (which is shown later) the Fx component of force felt by the nanoparticle became zero but it still has Fy to push the nanoparticles toward outlet.1.From Fig. 3) is placed in the main channel to push back undesired deviation to the center of the main channel.It is worth mentioning, despite that sorting the larger particle in step.1 the smaller nanoparticles also felt force in the x direction and experienced a small deviation from the center of the main channel. Therefore, another graphene nanoribbon  method and Perfectly Matched Layers (PMLs) are employed in all direction in our simulations. The simulation domain's height  is 5 µm, and the plane wave source is placed 2 µm above the graphene surface.In the optical analysis, we consider a total field-scattered field (TFSF) plane wave source with a constant intensity of 0.6 mW/ µm47, its surface conductivity is described by Random Phase Approximation (RPA) which is given by: ħ is the reduced Plank constant, T is the temperature, ω is the angular frequency, μc is the chemical potential, Γ is the phenomenological scattering rate that is assumed to be independent of energy εσ, and fd (εσ) is the Fermi–Dirac distribution function. Real and imaginary parts of the Surface conductivity of graphene versus chemical potential are illustrated in Fig. Graphene is modeled as a two-dimensional sheet in FDTD analysis, and according toentclass1pt{minimang = Cg (Vg-Vdirac)/q, in which Cg is the gate capacitance, Vdirac is the applied gate voltage corresponding to Ef = 0 in graphene, Vg is the applied voltage to the gate and q is the unit charge. Accumulating charge carriers in the graphene shift the Fermi level so that this shift versus the gate voltage can be calculated via Eq.  are extracted from42. Also, the permittivity of the Si is taken from51 and illustrated in Fig. In the given nanoparticle sorter, the hBN is modeled as anisotropic bulk material with parallel and perpendicular real and imaginary parts of permittivity functions obtained from Eq. . This ma52. To fabricate graphene nanoribbon on an hBN surface a mechanical transfer method52 to deposit graphene on hBN substrates can be used which is a special method to transfer graphene from one substrate to an exact location on another substrate (in this case an hBN flake). this method can be used to fabricate multilayer graphene nanoribbons53. In this method, extreme care is taken to reduce water residues and this is named the “dry transfer method”. They adopted the dry transfer method to our needs. A dry transfer method consists mainly of four steps as illustrated In step A the PMMA (carrying the graphene) is suspended in a plastic window that has been attached to the chip by using double-sided tape to the PMMA side. Next in step B, sacrificial PVA film is dissolved in DI water to release the PMMA film from its substrate. The graphene is on top of the PMMA so it will never be in contact with water. In step C they adhered the PMMA membrane to an aluminum transfer slide, which is clamped to a mask aligner modified. During the transfer process, they fix the hBN-containing substrate on the holder. In step D, using the optical mask micro-manipulators, they align the graphene flake to the hBN crystal and lower the polymer side onto the substrate. When the polymer touches the substrate, it makes strong contact with the SiO2 substrate. Then, they turn off the nitrogen valve of the mask aligner and down the holder substrate along with the PMMA polymer attached to it. They finally put the substrate with target hBN flake on a custom-made heater that they set to 110˚C to enhance adhesion between graphene and hBN for at least 10 min. Next, the sample is allowed to cool down and the PMMA is removed with acetone and isopropanol (IPA). As chemical cleaning with organic solvents always leaves some residues, they anneal the samples as well. At this stage, they heat the samples slowly to 400˚C in a tube oven in forming a gas environment and anneal them there for ∼3 h before slowly cooling them down to room temperature. This treatment is very effective in removing polymer residues from the transfer.The graphene-hBN stack can be created by dry-transferring graphene over thick mechanically cleaved hBN crystal, as described in2.Since this fabrication method requires only one cleaning step, it allows for fast device preparation of graphene on hBN with little bubbles and wrinkles. Electrical transport measurements of the graphene devices on hBN have mobilities and carrier inhomogeneity that are almost an order of magnitude better than devices on SiO54. The exerted average optical force is given by:S enclosing the particle, and TM is the Maxwell stress tensor obtained by Eq.  the scattering force is negligible. In order to evaluate optical forces acting on a particle at first, we integrate MST on the surface of the particle55, which is described by:µf, v, a, and h are the viscosity of water taken to be 0.89 mPa.s at the room56, the particle velocity, particle radius, and the distance between the surface and the center of the particle, respectively.When the particle is guided by the evanescent field and moves along a planar substrate in a flow channel and is pushed by a scattering force depending on its radius and distance from the substrate, it experiences the Stokes dragAs discussed earlier, an increment of the graphene Fermi level makes the plasmonic effect more robust and enhances the electric field at the surface of the ribbon. Figure According to Fig. x exerted on nanoparticles of different sizes, which are fixed at the center of the main channel, where the graphene ribbon in the second channel has a 117 nm gap from the main channel. Larger particles experience a more significant force. In Fig. x is calculated for the constant source wavelength of 4.44 µm, which is the plasmonic resonance wavelength of graphene ribbons. For nanoparticles with different sizes, the value of µc is constant. Figure Here, we suppose a structure with only two channels for analyzing the sorter's function. One of these channels is the main and, and the other is located at the substrate with a definite gap and their width are 120 nm in x-direction. Figure Figure x and Fz have maximum values at the center of the ribbon. In addition, Fy is almost negligible in the y-direction. It is worth mentioning that here the dynamic analysis is not investigated yet, and the figures show that particles of any size can be trapped by nanoribbons. The dynamic state of the proposed system will be vastly investigated in the next section.Figure x for five various nanoparticles when they are fixed at x = y = 0. This figure shows that the force decreases by increasing the distance between the nanoparticle and ribbon from 10 to 170 nm. Furthermore, the width and length of the graphene nanoribbon can impose an electric field enhancement such that the exerted force of the nanoparticle is affected, which is shown in Fig. x exerted on the nanoparticle has the maximum value in the x-direction. In addition, particle size and optical forces can vary the drag force felt by nanoparticles induced by microfluidic flow in the inlet. Figure The gap between nanoparticles and graphene ribbon significantly affects the optical force experienced by nanoparticles moving in the main channel. The exerted force increases by decreasing the gap between them. Figure x on a nanoparticle, it experiences a different trajectory. However, when the gap is fixed to its optimized value, the nanoparticle is trapped above the ribbon. In contrast, nanoparticle keeps moving at the main channel at large gaps.We have statically investigated the parameters that affect the manipulation of nanoparticles. In the following, dynamic structure simulations are evaluated, giving us more exciting information about the designed structure. Here we investigate the particle's movement along the channel regarding time for differing gaps and sizes. Since the gap variations affect the induced Fx increases, and the particle deviates from the main channel and moves toward the ribbon. At the small gap, Fx reaches a high value.Figure x has damped the x-direction movement of the particle, and it became constant. In other words, the ribbon electromagnetic field traps it. After the particle is trapped, it moves along the y-direction concerning the drag force shown in Fig. x has the maximum positive value, which means the particle felt force in the + x direction. However, due to the large gap and low exerted force on the particle, the particle's position has no considerable change in the x-direction and keeps moving in the main channel.The particle passes through the ribbon due to the particle's momentum, similar to Fig. x in comparison to the trapped particle, it remains at the main channel, as shown in Fig. Notably, when the larger particle is sorted, the smaller particle deviates from its main path. However, due to minor Fx takes more time to reaches steady-state, in another word particle 2 or 3 times path the ribbon until it trapped at the center of the ribbon according to Fig. z reaches its maximum value therefore Fz peaks each time the particle paths the center of the nanoribbon. Figure Figure One of the notable features of this structure is sorting tiny particles. As shown in Fig. BT for both particles. On the other hand, the potential chemical peaks at around 120 and 90 nm, equal to the G of both particles, which means the trapping potential has the maximum value at the left side of the ribbon. Likewise, the force change sign at potential chemical peaks means that when the particle path on the left side of the ribbon Fx tries to pull back to the ribbon, it takes more negative force to overcome its initial momentum due to the particle velocity. It is clear from both figures that the negative sign of force is larger than the positive sign, resulting from the initial momentum of the particles.Figure Figure th to 140 nm, the smaller particle which has a radius of R = 15 nm owns an undesired deviation of Δx = 25 nm, and as can be seen, it reaches to the edge of the main channel, which is not desirable. Figure As shown in Fig. X, it returns to the left of the ribbon, and the nanoparticle experiences a negative velocity. Eventually, the speed direction reverses, and particles fall into the trap in a sinusoidal pattern by repeating these steps; the particle with R = 15 nm and G = 125 nm is damped, and its velocity reaches zero as expected at the center of the ribbon. In contrast, the inset of Fig. We analyzed the impact of nanoparticles' refractive index (RI) variation in manipulation. by decreasing the nanoparticle's RI, the differential between medium RI and nanoparticle decreases, which leads to a weak electromagnetic field and so that the exerted force on the nanoparticle decrease. as Fig. Finally, the threshold gaps between various particle sizes are explored. Figure c, about 1.15 eV. Nevertheless, the optical force dropped sharply by increasing or decreasing µc from 1.15 eV. It means that a minor change in graphene chemical potential results in changes in optical force felt by nanoparticles. Therefore, the proper and suitable graphene chemical potential can be obtained by adjusting the biased gate voltage. Figure As we claimed at first, the proposed structure can also sort nanoparticles only with one subchannel or nanoribbon at a constant gap. The physical mechanism is the same as the threshold gap examined previously; however, instead of changing the gap to control exerted force on the nanoparticles, the shift in graphene chemical potential by applying a gate voltage to the Si substrate has been used to control exerted force for each nanoparticle. To clarify the algorithm for sorting particles with fermi energy, Fig. By analyzing the threshold gaps and the graphs obtained from them, an equation can be proposed for both methods stated in this article, in which only with an error of less than 2.5 nm, the threshold gap and the potential energy of the graphene threshold for sorting all obtained nanoparticles with the desired radius. But not only for particles with a certain radius such as 30, 20, 15, etc. Rather, for any desired radius, one can easily find the threshold gap as well as the threshold form for sorting that specific radius. Equations th represents the threshold gap shown in Fig. –3 and c = −1695.In Eq. c represents the threshold graphene nanoribbons’ chemical potential for sorting and deviating any specific nanoparticles with radii of R. the value of a1, b1, and c1 are constant and are equal to a1 = 43 × 10–3 b1 = 8 × 10–3 and c1 = 1.574.Moreover, to the gap threshold as shown in Fig. This article presents a structure for manipulating and sorting nanoparticles using the optical and electrical advantages of graphene nanoribbons embedded in the hBN substrate. In this structure, two methods are used to separate the particles, one is through the distance of the ribbon with the main channel in x direction , and the other is through the chemical potential of graphene. It was also shown that the presented structure could sort particles with a radius below 2.5 nm, making it one of the few structures that can trap and sort nanoparticle particles below 5 nm in diameter. In addition, both methods showed that the presented structure could sort the particles entering the liquid according to their refractive index. The primary physical mechanism of both methods in the proposed structure is to control the force on the particle moving inside the channel, which can be done through the gap between the ribbon and the channel or the potential chemical level of the graphene. The presented structure can be one of the most used structures and open a door for the future of nano-biosensors. Also, this structure makes it possible to sort and manipulate all kinds of viruses or any desired particles in the liquid with very high accuracy of 1 nm. Another advantage of the proposed design is its facility to fabricate, and there is no difficulty in the fabrication process of the proposed structure, or second-order effects and irregularities arise from errors in the fabrication process of the structure. furthermore, by using several animations in the main text and as supplemental information the performance and physical mechanisms of the understanding of the proposed structure became very clear. .Supplementary Information 1.Supplementary Information 2.Supplementary Information 3.Supplementary Video 1.Supplementary Information 4.Supplementary Information 5.Supplementary Information 6.Supplementary Information 7.Supplementary Information 8.Supplementary Information 9.Supplementary Video 2.


Long Interspersed Element-1 (LINE-1 or L1) is the only autonomously active human retrotransposable element shown to mobilize in cancers, which can disrupt normal gene function or regulation . HoweverFOXR2 overexpression  [FOXR2 activation may have driven tumorigenesis and the observed methylome profile.We identified an infant high-grade glioma  . HoweverFOXR2. The reads contained a poly-A or L1 5’UTR sequence, indicating an L1 insertion event . PCR amplification of the genomic sequence revealed a ~ 3 kb somatic insertion . Targeted PacBio sequencing identified a 5’ inverted L1 insertion with a nearly intact L1 5’UTR, which contains an RNA pol-II promoter in the same orientation as FOXR2 but inverted with respect to the remaining truncated L1 sequence, where a partial L1 open reading frame (ORF2) was present, followed by the L1 3’UTR, a 31 bp poly-A tail, a 29 bp transduction sequence, and a 96 bp poly-A tail .The tumor’s whole genome sequencing (WGS) data revealed a cluster of soft-clipped (SC) reads containing sub-regions unmapped to the reference genome located within intron 1 of FOXR2 transcription as we identified a chimeric L1/FOXR2 transcript spanning the first 97 bp of L1 5’UTR from a known L1 splice donor site to the acceptor site of exon 2 of a non-canonical FOXR2 isoform . To further confirm promoter activity of the FOXR2 L1, we performed bisulfite sequencing on its 5’UTR. We observed hypomethylation of all CpG sites profiled, while the source 6p24.1 L1 5’UTR remained hypermethylated  .Molecular profiling of serial tumor samples projected the temporal order of mutation acquisition as follows Fig. f: a somaFOXR2 fusion, likely due to low L1 activity in CNS tumors [Our study presents the first example of L1 promoter “donation” as a novel cancer-initiating mechanism, as compared to previously reported L1-mediated disruption of tumor suppressors or oncogene repressors . We screS tumors . NeverthS tumors , on globSupplementary file1 (XLSX 58 KB)Supplementary file2 (PDF 7561 KB)Below is the link to the electronic supplementary material.


Mott-VRH, Efros–Shklovskii-VRH and activation energy supported VRH. On the basis of transport behavior and confirmed by characterization analyses, the RGO film is modeled as GQD arrays where graphitic (sp2) domains behave as QDs and oxygenated (sp3) domains between interdots act as tunneling barriers. Temperature dependent resistance and current–voltage (I–V) characteristics indicate high sensitivity where sensor resistance changes by almost six orders of magnitude as the temperature is varied between 300 and 12 K. In convection mode, the developed temperature sensor shows a temperature coefficient of resistance (TCR) of ∼−1999% K−1 in the 300–77 K temperature range, which is much higher than the TCR values reported so far. Additionally, the sensor exhibits an extremely fast response (∼0.3 s) and recovery (0.8 s) time; and such high TCR leads to ultra high resolution of ∼ μK. The sensor shows excellent repeatability with negligible drift over several cycles. These studies are crucial for modern day thermal management and sensitive cryogenic applications.We report an ultra-sensitive temperature sensor derived from graphene quantum dots (GQDs) embedded in a self-standing reduced graphene oxide (RGO) film. The GQDs are obtained as a natural derivative during synthesis of GO to RGO. A fundamental study on low temperature transport mechanisms reveals the applicability of temperature zone specific ‘variable range hopping (VRH)’ conduction models,  We report an ultra-sensitive temperature sensor derived from graphene quantum dots (GQDs) embedded in a self-standing reduced graphene oxide (RGO) film. Irrespective of the dot size, graphene quantum dots (GQDs) possess distinctive graphene structures inside the dots which endows them with some of the remarkable properties of graphene;22–26 rendering them ideal systems for observing a novel quantum phenomena and building blocks for futuristic electronic devices in sensor applications.24,26,27 Nonetheless, the handling and device fabrication pose challenges, thereby necessitating the search for alternative graphene like materials which are easy to fabricate and possess properties close to graphene. An enormous quality research study is underway to search for such materials with mass production and ease of device fabrication.Since its inception, carbon nanotechnology has opened new prospects for the synthesis and analysis of one- and two-dimensional materials wherein fundamental physics converges with device applications.28–32 One such route is a chemical synthesis technique where exfoliated graphene oxide (GO) is produced in the first step and then reduced to obtain reduced graphene oxide (rGO).33–36 This technique is most suitable for economic and large scale synthesis of rGO. Despite having lowered electrical and thermal properties in comparison to pristine graphene, rGO is interesting owing to its unique properties which are an amalgamation of properties similar as well as dissimilar to those of pristine graphene.37,38 Various functional groups, such as epoxy (–O–) and hydroxyl (–OH) covalently attach on the basal plane, whereas carboxylic (–COOH) and carbonyl  scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z M0 280 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z"/></g></svg>O) groups primarily append at the sheet edges.18 Besides, sp3 → sp2 carbon transformation in rGO is not hundred percent complete and causes considerable defects or disorders which can trap charge carriers.39 Additionally, the conductivity of an rGO film can be controlled by varying the film thickness which in turn depends upon the synthesis parameters .3 Thus, rGO has gained immense scientific interest due to – (a) large scale production; (b) modifiable properties which can be controlled by tuning the sp2 to sp3 carbon ratio; and (c) a possibility of further modifying the rGO structure (and hence its properties) via functionalization with different nanoparticles as well as organic molecules.40 This behavior is attributed to the presence of significant disorders on the rGO films. Thus, a comprehensive study needs to be undertaken to analyze the effect of synthesis conditions on all these parameters.The most successful routes to synthesize such materials rely on using graphite as the precursor.41–43 Although a substantial amount of work has been done on the carrier transport mechanism in graphene,17,38,44–48 hardly any studies are available on the development of temperature sensors either from graphene or GQD arrays, exploiting their carrier transport properties. In the case of carrier transport in graphene or 2D materials, the current flow is controlled by scattering events;49–52 whereas in GQDs, the current will exist only if carriers overcome the Coulomb blockade potential.53,54 The temperature dependent differential change in resistance/current in the circuit is the key factor for the development of a highly sensitive temperature sensor. Two major sensing parameters, i.e. temperature coefficient of resistance (TCR) and thermal hysteresis (HTh) are very crucial since both of them control the quantification of heat sensing characteristic parameters including sensitivity, response- and recovery-time, resolution and repeatability. Interestingly, not many reports are present on GQD based temperature sensors and no concrete report is presented so far.Interestingly, much of the initial work on graphene based devices, in general, has been on field effect transistors (FETs). Development of a smart temperature sensor from graphene is a relatively new area of research.vis-à-vis its room temperature value. The rGO film has been converted into nanometre sized graphitic zones (termed as graphene quantum dots or GQDs) caged within insulating zones (barrier). The GQDs, distributed in disordered arrays, demonstrate elevated temperature (T ∼ 300 K) activated hopping, and direct quantum tunneling depending on the spatial interdot separation and operating temperature. The temperature sensor fabricated from this film shows TCR values of −7946.5% K−1 and −1999.8% K−1 in the temperature ranges of 300–12 K and 300–77 K, respectively. Such a high TCR leads to the achievement of ultra-resolution of ∼ μK, and a response-and recovery-time of 0.3 s and 0.8 s respectively in convection mode. Cycling tests conducted at 77 K show negligible drift over several cycles. Additionally, this work presents an example of reversible metal–insulator transition in a solid-state system implying the prospects of producing novel solid-state materials, based on GQDs, wherein the electronic band structure of the material can be ‘tailored’ by adjusting the electronic wave function overlap between neighboring dots.In this article, we present the rich transport phenomena observed in the rGO/alumina self-standing film where the resistance can be tuned over more than six orders of magnitude 2.2.1.via a chemical conversion technique has surfaced as a convenient method to produce graphene like monolayers with considerable yield.51,52,55 Modified Hummers’ method based oxidative treatment of natural graphite flakes was performed to prepare graphite oxide.56 Unlike pristine graphite, GO is highly oxidized having oxygenated epoxide bonds on the basal plane, whereas carbonyl and carboxyl groups are present at the sheet edges. Single- to few-layered GO sheets were obtained by exfoliation of graphite oxide in DI using a bath sonicator (90 minutes). The presence of oxygen moieties makes GO sheets readily soluble in DI, resulting in stable aqueous suspensions of nearly 1 nm thick sheets under mild sonication conditions.57 GO was then washed and dried under ambient conditions. Chemical reduction of the GO powder was carried out by dissolving 500 mg GO in 500 mL DI followed by 1 h of sonication. To this mixture, 50 μL hydrazine hydrate was mixed and the solution was refluxed at a constant temperature (98 °C) for varying time periods . At this point, the color changed from yellowish brown to black, indicating the conversion of GO to rGO. The RGO powder was obtained by suction filtering and washing the suspension with DI followed by subsequent drying at 60 °C in an inert (N2) ambient atmosphere for 10 h.51,52 The reduction process removes epoxy groups from the basal plane resulting in regeneration of C–C bonds.55Transformation of graphite to graphene oxide (GO) 58 where three out of four valence electrons from each C atom are covalently bound to three neighboring C atoms. These bound electrons are called σ-electrons and the corresponding bonds are termed as σ-bonds or C–C bonds. The fourth electron from each C atom (termed as π-electron) is free to move around the graphene layer, and thus acts as a charge carrier. In the hexagonal lattice of graphene, these π-electrons occupy six individual corners of the first Brillouin zone .58 During oxidation, each oxygen (O) atom uses two π-electrons from two C-atoms and meets its octet requirements, thereby forming epoxy bonds. However, neither σ-electrons nor σ-bonds are altered to fulfill octet requirements because the bond energy of C–O (358 kJ mol−1) is much lower vis-à-vis C–C (473 kJ mol−1) in graphene.58–60 Four types of oxygenated functional groups exist in GO, these are61To understand the mechanism of the above reactions, we can consider a graphene lattice,(a) Epoxide (–O–): attached to the basal plane.(b) Hydroxyl (–OH): along the basal plane.O): distributed along the edges.(c) Carbonyl (–C(d) Carboxyl (–COOH): attached to the edges.38 During reduction by a chemical route or thermal treatment, the C–O bonds break, thereby again freeing the π-electrons. In this way, graphene oxide recovers its pristine state by clearing the oxygen debris created during the oxidation process. Further, there was no apparent involvement of either σ-electrons or σ-bonds (or C–C bonds) unless aggressive oxidation/reduction is pursued. Thus, the graphene lattice is usually intact and no considerable point defects are introduced. Additionally, carbonyl and carboxyl groups cannot be removed without destroying the graphene basal plane.62Out of these, epoxide and hydroxyl groups dominate the total oxygen functionalities glued to GO sheets.3 to sp2 bonding. The graphene region (sp2 bonding) shows semi-metallic behavior whereas the remaining sp3 region is insulating. Physical properties of rGO are considerably affected by the sp2/sp3 hybridized carbon ratio, and the presence of different functional moieties. Therefore, the electrical conduction process through the rGO sheet becomes complex and it shows the Coulomb blockade phenomena for charge transport, specifically at low temperatures.23,55,63,64 Growth of QDs in the rGO film have been studied by several groups,23,63–66 where the degree of reduction during the synthesis process and atomic scale features are studied and characterized with various microscopic and spectroscopic techniques.GO to rGO transformation leads to the creation of graphene quantum dots (GQDs) within the rGO maze and their sizes vary from a few nm to 100 nm depending on the degree of conversion from sp2.2.2.2.1.3 defects alter the intrinsic π state of sp2 sites,35,55,62,67,68 residual sp2 carbon fraction becomes a vital clue for rGO sheets and is often described as the reduction efficiency. O bond ; and (4) the C(O)O or OC–OH bond . 2 carbon fraction, while the oxygenated functional moieties present at the basal plane of the sheets and sheet edges signify sp3-hybridized carbon fraction.38,67,69,70 The sp2 carbon fraction is obtained from the ratio of the integrated peak areas of the C–C peak to the total area under the C1's spectrum:40The changes in carbon and oxygen groups were analyzed by studying the gradual removal of oxygen containing functional groups by employing X-ray photoelectron spectroscopy (XPS). Since sp2 carbon fraction (or reduction efficiency) of the rGO sheet increases from ∼57% for GO (0 h) to ∼80% for rGO treated for 5 h.The results in 2.2.2.2 C–C bonds. Nevertheless, a continuous sp2 phase is not observed, rather these sp2 zones remain spatially separated by ‘islands’ of sp3 clusters. Thus, the reduction of GO creates numerous sp2 clusters of small size.71 This has been observed by Erickson et al. in 2 zones appear to be surrounded by disordered sp3 domains. The size of these sp2 zones is found to vary from 2 to 6 nm.As indicated in 2.2.3.−1, 1580 cm−1, and ∼2700 cm−1 respectively.38,73 The D-band arises from disorders in atomic arrangement, edge effects, ripples, or charge puddles of the graphene sheet. A broad D-band having a higher intensity than that of the G-band signifies high disorderness of rGO. The G-band arises from in-plane vibrations of sp2-hybridized carbons, whereas the 2D-band is due to the second order Raman scattering and is particularly dominant in graphene vis-à-vis bulk graphite.74 The intensity ratio (ID/IG) of D- and G-bands can be used to quantify disorders, as represented by the sp2/sp3 carbon ratio.73,7538,40,76 relating the ID/IG ratio and crystallite size of the graphitic sp2 domain, it is found that the rGO sheets embrace ordered graphitic zones having a size of 3.3 nm (for 5 h reduction treatment) enclosed by domains of oxidized carbon atoms or point defects.38The most remarkable peaks in Raman spectra of graphene and alternative graphitic materials comprise D, G, and 2D peaks at ∼1350 cm2.2.4.51,52 This peak initially remains narrow with increasing reduction time up until 3 h of treatment and then starts broadening .Chemical reduction was performed to convert GO to rGO and the degree of transformation was monitored by XRD studies . As can 2.2.5.51 The gradual increase in areal intensity endorses the gradual restoration of C–C bonding with the increase in reduction time. Besides, there is a gradual red-shift of the peak at 239 nm (corresponding to GO) with the reduction time and the shift virtually saturates at the reduction time of around 5 h (267 nm).51,52UV-Vis spectra, obtained at different reduction steps of the chemically driven sample are shown in 2.3.via sol–gel processing where 0.6 wt% rGO powder was mechanically added to 99.4 wt% alumina sol as elaborated in The rGO (treated for 5 h) prepared in Section 2.1 was used for temperature sensor fabrication. A self-standing film of the rGO/alumina nanocomposite was prepared 3.3.1.I–V) characteristics of the fabricated sensor were studied in a four probe helium cryostat (Oxford Instruments) where cryo-pumping maintained the base pressure at ∼10−7 torr throughout the experiment. Proper care was taken to prevent stray radiation and condensation of residual moisture on the rGO film mounted inside the cryostat. The system is designed for low current measurements of the order of picoampere (pA). Current and voltage sweeps were programmed via LabView programme.Current–voltage  and disorders in rGO.38,80–89 Several distinct regions are clearly observed (as demonstrated in the TEM image), similar to disordered semiconductors.80,85The resistance i.e. Mott variable range hopping (Mott-VRH),38,86 Efros–Shklovskii variable range hopping (ES-VRH),55,87,88 and thermal activation52,89 supported VRH – also known as Arrhenius type; and these are highly temperature zone specific. While looking into the theoretical aspects, there is a serious disagreement on the temperature scaling factor even for an identical temperature range; and this is because the results were obtained with different sample geometries, reduction processes, reduction temperatures and the reduction routes.88 Therefore, the transport mechanism in GQD arrays in rGO is an important subject in the field of graphene based electronics.On the basis of XPS and Raman data, the rGO sheet may be considered as a two-dimensional (2D) array of GQDs where graphitic domains behave as QDs while oxygenated domains act as tunnel barriers. The temperature dependent charge-transport mechanism in rGO is generally supported by three independent theories, 38,88 theory relies on three specific criteria – (1) localized defect states are created near the Fermi level during GO to rGO conversion; and carrier transport occurs via hopping from one state to another by taking energy either from a phonon or directly from an externally applied electric field; (2) at low temperatures, the nearest neighbor hopping will not dominate; rather the hopping electron will always try to achieve the lowest activation energy (ΔE) and shortest hopping distance. Generally, these two conditions are not fulfilled simultaneously; and there exists an optimum hopping distance rhop, corresponding to maximum hopping probability; and (3) there is no Coulomb interaction between the localized states. The standard Mott-VRH relation is:40R0 is the resistance at zero temperature and T0 is the Mott characteristic temperature. The scaling factor p depends upon the dimensions of the system or the shape of density of states (DOS).85,90 This concept results in the mathematical expression where R is proportional to (T)−1/3.The temperature dependent resistance behavior shown in via hopping and there is Coulomb interaction among carriers. This idea results in R scaling as (T)−1/2.40,90Efros–Shklovskii (ES) proposed that defect states are localized around the Fermi level, transport occurs p turns out to be −1 in the case of Arrhenius theory of activation energy induced hopping and the relation is:80The scaling factor  in the temperature range of 90–12 K pointing toward ES-VRH as a plausible charge-transport phenomenon in rGO layers consisting of GQD arrays. The other fitted values are  in the 146–90 K temperature range where Mott-VRH is applicable. The temperature range of 273–146 K comes under Arrhenius type of conduction via activation energy where p = 1 is the best fit. The temperature range of 100–80 K may be a mixed zone where ES-VRH and Mott-VRH both coexist.Best linear fits were obtained for ξ by plotting R against T−1/2 in a semi-log scale  as a function of temperature. Here, ΔR = R(T) − R; R denotes resistance at 273 K and R(T) denotes the resistance of the sensor at a set temperature of T °C. The sensor exhibits an exceptionally high change in resistance leading to an ultra high TCR.The ES-VRH suggests strong localization of wave functions in GQDs. Its further analysis allows the calculation of localization length og scale .91–93 Fr3.2.The temperature sensing measurement was conducted in a two probe system fitted with a liquid nitrogen closed cycle system . The hea3.3.i.e. thermal (κ) and electrical (σ) conductivities; and both are responsible for heat and carrier transportation. Their interdependence determines the temperature coefficient of resistance (TCR) and thermal hysteresis loss (HTh), thereby playing an important role in efficient operation of the sensing device. A large TCR is critical for improved sensitivity, resolution, drift, and response- and recovery time.52,77,78In a temperature sensor, we encounter two interdependent physical properties of the material, i.e. convection mode  the de-Haas van Alphen effect under a magnetic field,96 and (3) the superposition of a group of waves having slightly different wavelengths from each other while propagating in a medium.97 Notably, the oscillations of the envelope as well as the wave pattern within the envelope were found periodic and their frequency of oscillation is 0.61 Hz and 10 Hz respectively. In the present case, the first two cases can be discarded as there is neither a high frequency (carrier wave) source nor any magnetic field applied to the sensing system. Therefore, the last one is most probable and needs further explanation.Interestingly, the envelope pattern resembles – (1) the superposition of the signal and carrier frequency as seen in the case of amplitude modulation in communication engineering,98–100 The ratio of interdot separation (D) and size (L) of the QD clearly measures the coupling strength between dots. While assuming L as a constant, the coupling strength may be classified in terms of D as followsWe propose these to be the Coulomb blockade effects in terms of tunneling strength between coupled dots. The type of coupling between QDs influences the character of the electronic states and the nature of transport through the QD array. Theoretical prediction supports phase transition for tunneling in coupled GQD arrays.D, there is no interaction among QDs and the CB of individual QDs is preserved, i.e. the number of peaks is equal to the number of energy levels within a single QD. Each peak signifies the addition of electrons to the array, one to each GQD at the same time.(1) For a large D is the intermediate, the CB of individual QDs is lifted and a combined CB effect across the QD array materializes.(2) When D, original energy levels split in subbands; these will cross each other and the CB will be completely diluted.(3) For low 99–104Due to the formation of high density QDs, there is a possibility to have charge particle interactions between the dots and it may be supported from the second point (2) mentioned above. As a result, the de-Broglie waves of the electrons may superimpose and the oscillatory envelope function may evolve from individual to collective electronic states in a dense QD assembly.D and L parameters are taken as average values because GQDs were self-created as a consequence of the chemical reduction process. Therefore, the Coulomb force due to interdot coupling is affected by the dilution effect arising from high temperature as well as high bias voltage. At a high bias voltage, the charging energy becomes negligible and the envelope disappears. Similarly, when the temperature is very high, the Coulomb force between GQDs gets diluted resulting in the disappearance of the envelope.In our case, 3.5.T) is micro-tuned to reach the targeted temperature and the corresponding change in resistance (ΔR) was measured accordingly. At a target temperature of 77 K, ΔR was found to be ∼MΩ for ΔT = 0.1 K (after extrapolation of the curve). For a gross simplification, if we assume the measurable signal strength to be within the 10–100 Ω range, then the signal obtained for ΔT = 0.1 K will correspond to a measurable temperature resolution of ∼μK. Measurements beyond 0.1 K change could not be carried out in our system due to the limitation of the temperature controller employed. As seen from 105–117 A comparison is presented in vis-à-vis some of the recently reported temperature sensors.The performance of the fabricated sensor is found to be much better than most of the existing sensors reported so far.4.i.e. an ultra-sensitive low temperature thermometer with very high resolution along with the fastest response and recovery. TCR and thermal hysteresis loss are considered as the main characteristic parameters that control the quality of most of the sensor parameters and the sensor ratings. Surprisingly, both of them appeared to be exceptional in making the sensing device ultra-sensitive both in cryogenic and high temperature measurement. The cycling test revealed that the sensor is stable for over 50 cycles with an ultra-fast response time. A highly sensitive temperature sensor is in great demand for cryogenic temperature measurements in industry, healthcare, and R&D laboratories; and the proposed sensor may fulfill the need of these sectors. An interesting fact is that the sensors are cheap and reproducible. Identical rGO sheets were developed and tested successfully to justify our claim. Further, no such comprehensive report is available in the literature on the development of graphene quantum dot based temperature sensor to date.GQD arrays, developed in the rGO film during the chemical reduction process from GO to rGO, act as a maze where poly-dispersed graphene QDs are semimetallic, and the interdot space is an insulating zone, called the tunnel barrier. Coulomb blockade and charge carrier tunneling through the tunnel barrier is largely associated with metal and semiconductor quantum dots. The carrier transport is explained using suitable VRH models where the ESH–VRH model fits well in the low temperature regime. The average QD size or the electron localization length was found to be ∼3.2 nm. This has allowed us to translate these phenomena into making a real device, There are no conflicts to declare.


Polyimide matrix nanocomposites have gained more attention in recent years due to their high thermal stability, good interfacial bonding, light weight, and good wear resistance and corrosion, factors that make them find great applications in the field of aerospace and advanced equipment. Many advancements have been made in improving the thermal, mechanical, and wear properties of polyimide nanocomposites. The use of nanofillers such as carbon nanotubes, graphene, graphene oxide, clay, and alumina has been studied. Some challenges with nanofillers are dispersion in the polymer matrix and interfacial adhesion; this has led to surface modification of the fillers. In this study, the interaction between clay and graphene to enhance the thermal and thermal-oxidative stability of a nanocomposite was studied. A polyimide/graphene nanocomposite containing ~12.48 vol.% graphene was used as the base nanocomposite, into which varying amounts of clay were added (0.45–9 vol.% clay). Thermogravimetric studies of the nitrogen and air atmospheres showed an improvement in thermal decomposition temperature by up to 50 °C. The presence of both fillers leads to increased restriction in the mobility of polymer chains, and thus assists in char formation. It was observed that the presence of clay led to higher decomposition temperatures of the char formed in air atmosphere (up to 80 °C higher). This led to the conclusion that clay interacts with graphene in a synergistic manner, hence improving the overall stability of the polyimide/graphene/clay nanocomposites. Polyimide is an engineering polymer that finds wide applications in the fabrication of aircraft structures and microelectronic devices. It has excellent chemical, thermal, and mechanical properties . In receThe incorporation of small loadings of nanoscale filler materials in polymers leads to substantial property enhancements compared with the conventional micro- and macroscale composites ,5. The s2 hybridized carbon atoms [Among the various nanofillers, graphene has been widely used due to its exceptional thermal, mechanical, and electrical properties ,7,8,9. Ion atoms ,11. Grapon atoms ,13,14. Gon atoms .Liu et al. investigated the gas barrier and thermal properties of polyimide/graphene and polyimide/clay nanocomposites. They reported decreased water vapor transmission rates and improvement in the temperature of decomposition at 5% weight loss, concluding that addition of these nanofillers improved the thermal stability of the polyimide ,17. WangPolymer/layered silicate nanocomposites have attracted attention because of the improvement in material properties when compared with the virgin polymer. These include increased strength and heat resistance ,18, highVarious property enhancements due to the addition of graphene and clay nanoplatelets have been studied and reported. The thermal stability studies have mostly focused on the temperature at onset of decomposition as a determinant factor for the improvement or lack thereof in thermal stability. However, few/no studies exist that delve further into the mechanisms of decomposition of these polyimide/graphene or polyimide/clay nanocomposites. Factors such as the effect of the nanofillers on the rate of decomposition of the polymer and the nature and mechanism of char decomposition have not been thoroughly investigated. These are important factors in elucidating the mechanism of flame retardancy.In previous research work by this group, polyimide/graphene nanocomposites containing 10–50 wt.% graphene were fabricated, and various properties were reported ,30,31. TNanographene sheets of 98.48% purity were purchased from Angstron Materials, Dayton, OH, USA. The graphene sheets were 70–100 nm thick, with a lateral dimension of 2–7 µm. Montmorillonite organomodified Cloisite 30B clay of 100–200 nm thickness and 2–13 µm length was purchased from Southern Clay Products, Inc., Gonzales, TX, USA. Ammonium ion (III) was used in the Cloisite 30B, as the exchange cation is methyl, octadecyl, and bis-2-hydroxyethyl ammonium ion. 4,4-oxydianiline (ODA-98% purity), pyromellitic dianhydride (PMDA-99% purity) and N-methyl-pyrrolidone (NMP-99% purity) were purchased from Sigma Aldrich, St. Louis, MO, USA.The fabrication of the composites occurred in three stages. The first step involved the synthesis of the poly(amic acid)–graphene solution. The second step was the synthesis of the poly(amic acid)–clay solution. In each case, 5.2 g of ODA was added to 100 mL of NMP contained in a round bottomed flask, followed by mechanical stirring until the solid completely dissolved in the solvent. For the poly(amic acid)–graphene solution, a graphene quantity corresponding to ~12.48 vol.% of total solids was added to the ODA solution, and stirring continued for 8 h. PMDA was then added to the mixture, followed by stirring for 12 h, the temperature of the reactants being maintained at 10 °C. For the poly(amic acid)–clay solution, varying concentrations (0.45–9 vol.%) of clay were added to each solution, and the rest of the process was similar to that of the poly(amic acid)–graphene synthesis procedure. These solutions were then mixed in varying concentrations of clay (0–9 vol.%), while maintaining the amount of graphene at ~12.78 vol.%. The poly(amic acid)–graphene–clay mixtures were cast onto a glass substrate, followed by curing in a vacuum at 120 °C for 2 h and 200 °C for 1 h to obtain PI/graphene/clay composite films (PI–NGS–Clay).Thermogravimetric analysis was used to investigate the mechanism of decomposition and thermal stability. The films were subjected to heating rates of 30 °C/min from 25 °C to 1000 °C in air and nitrogen in a TGA Q50 Thermal Analyzer purchased from TA Instruments, New Castle, DE, USA.The films were subjected to heating rates of 10 °C/min from 25 °C to 725 °C in nitrogen atmospheres in a DSC Q20 thermal analyzer purchased from TA instruments, New Castle, DE, USAEnvironmental Scanning Electron Microscopy (ESEM), model FEI XL30 FEG , was used to study the morphology of the composite films. The samples were coated with silver to improve their conductivity.Scanning electron microscopy with EDAX was used to obtain images of the decomposed char in nitrogen and its elemental composition. This is shown in The thermogravimetric degradation profiles of neat PI, graphene and Cloisite 30B clay are shown in In the The char performance of the 0.45 vol.% clay sample is similar to that of the 0 vol.% clay sample, but the former also shows a remarkable increase in the onset temperature of degradation. This goes to show that with just a small quantity of clay added to the PI-NGS nanocomposite, the thermal stability of the system can be enhanced, while saving on cost and preserving and/or improving on the properties of the polymer, because the dispersibility of the filler in the matrix is still excellent at low loadings of clay.max) is observed to have an overall shift towards higher temperatures. This is shown in The temperature at maximum rate of decomposition  is shown to decrease in height with increasing clay content, confirming the effect of clay on the degradation of graphene char. The decrease in the rate of degradation of graphene is therefore as a direct result of the increasing clay content.The rate of degradation of the three regions in air is shown in x group in clay.DSC thermograms in The behavior of the samples in air as measured by DSC is different from the nitrogen trends shown above. In The temperature at the onset of degradation, shown in The thermal degradation and stability of PI–NGS–Clay nanocomposites was investigated. Cloisite 30B clay was observed to maintain high char content (~70%) in both inert and oxidizing atmosphere. The addition of clay to the PI–NGS nanocomposite was shown to increase the onset degradation temperature in both atmospheres, as observed in TGA and DSC. The thermal stability of the system is therefore enhanced by the addition of clay. DSC results show that the char for the hybrid system degrades at much higher temperatures. A synergistic effect is observed between graphene and clay, as the presence of clay tends to shift the temperature of degradation of graphene char to higher temperatures. It was demonstrated that incorporating a small amount of clay into a polyimide–graphene system would enhance the thermal stability of the system. Higher loadings of graphene to achieve greater stability would decrease the ability of the nanofiller to homogenously disperse in the polymer matrix. This would lower certain characteristics of the system. This can therefore be counteracted by using a graphene quantity to the level of optimal dispersibility and then adding small quantities of clay to further enhance the thermal stability of the system without affecting the dispersibility of the nanofillers in the polymer.