The electrochemical voltage generated by the flexible jelly electrolyte sensors was also investigated. It was found that the initial open-circuit voltages were equal to 201 mV and increased slightly, by 5–10% under the effect of humidity and temperature as well. The short-circuit currents under the effect of humidity and temperature increased by 2–3 times. The Al/Gr-Jelly/Cu electrochemical sensors may be used as prototypes for the development of the jelly electronic-based devices.Here we present the fabrication of graphene and jelly (superabsorbent polymer) electrolyte composite-based shockproof flexible electrochemical sensors (Al/Gr-Jelly/Cu) and their properties under the effect of humidity and temperature. A layer of graphene mixed in jelly electrolyte was drop-casted onto porous rubber substrates between preliminary fixed aluminum (Al) and copper (Cu) electrodes followed by rubbing-in. It was observed that the graphene and jelly mixture was mechanically soft and flexible, similar to jelly. Electrically, this mixture (graphene and jelly) behaved as a flexible electrolyte. It was observed that under the effect of humidity ranging from 47 to 98%, the impedances of the sensors decreased by 2.0 times on average. Under the effect of temperatures ranging from 21 to 41 °C the impedances decreased by 2.4 times. The average temperature coefficient of impedances was equal to −0.03 °C As is known, humidity sensors are used in different areas of modern technology and their properties have been described in detail in the literature. Ref.  presenteFor environmental monitoring the organic semiconductor copper phthalocyanine-based illumination and humidity sensors and their properties were described in Ref. . The proDuring the past few years, number of graphene-based electronic devices have been designed and fabricated. The graphene-based electrochemical sensor and biosensors were fabricated and investigated by Shao et al. . In Ref.Moreover, a number of electrochemical sensors were designed, fabricated, and investigated based on graphene as well. The electrochemical sensors fabricated on paper (where the paper was used as a scaffold to create electrodes of porous carbon nanotubes) were investigated in Ref. . The conIn pursuance of our work on the sensors, in this paper we are presenting the data about the fabrication and investigation (of the electric properties) of Al/Gr-Jelly/Cu-rubber composite-based shockproof flexible solid electrochemical humidity and temperature sensors. RH) the impedance decreased: in particular, 2.02 times (at 100 Hz), 2.04 times (at 1 kHz), 2.05 times (at 10 kHz), 1.89 times (at 100 kHz), and 2.0 times (at 200 kHz). It was also seen that on increasing the frequency the impact of humidity on the impedance or on the sensor was approximately the same. On average, the change of the impedances was equal to 2.0. The influence of humidity on the properties of the sensor was estimated by the humidity coefficient of impedance (HCI):Z is the impedance change with the change in humidity (relative) (ΔRH in %). By calculation it was found that the average HCI is equal to 1.32 kΩ/%. TCR), the temperature coefficient of impedance (TCI) can also be introduced:Analogous to the temperature coefficient of the resistance (TCI) were equal to (−0.030) °C−1 for 0.1 kHz, (−0.031) °C−1 for 1 kHz, (−0.030) °C−1 for 10 kHz, (−0.026) °C−1 for 100 kHz and (−0.026) °C−1 for 200 kHz.The values of the temperature coefficient of impedance , copper (0.0039) and aluminum (0.0043)) showed that the resistance-temperature behavior of the graphene–jelly composite was similar to that of semiconductors rather than that of metals. Comparison of these values of the temperature coefficient of impedance with the ocV (open-circuit voltage) and scI (short-circuit current) of the sensor on humidity. The ocV increased by 5% and scI increased by 2 times on increasing the relative humidity from 47 to 98%.It was found that the fabricated Al/Gr-Jelly/Cu electrochemical sensors generated voltage. ocV and scI of the Al/Gr-Jelly/Cu electrochemical sensor on temperature. It was seen that the ocV and the scI of the sensor depended on the temperature as well  and hydroxide ions (OH) finally results in the separation of (H+) and (OH−) (as shown in Equation (3)) and causes the concentration of charges to increase.The literature survey allowed disclosure of the following information concerning the investigations regarding the effect of humidity and temperature on the impedance and voltage of Al/Gr-Jelly/Cu-rubber composite-based flexible electrochemical sensors. Concerning the humidity effect on the electric properties of the materials two mechanisms may be considered. First of all, diffusion of water molecules into the material increases the dielectric permittivity. Secondly, the self-ionization of water molecules into protons  and their ratio; second, the fabrication technology; and third, the structure of the sensors allowed us to realize the shockproof flexible humidity and temperature sensors. Because of the simplicity of fabrication technology these sensors can be used in practice and as a teaching aid as well. Our preliminary investigations and estimations showed that the sensors are not costly, having practically acceptable sensitivity and stability of the properties. Much graphene-related research work has shown that this organic material is environmentally friendly; no negative effect was observed by us as well. Our preliminary experiments showed that in this sensor the copper can be replaced by CNT , which can make it cheaper and acceptable for utilization in practice.To fabricate the Al/Gr-Jelly/Cu-rubber composite-based flexible electrochemical sensor the graphene was purchased from the Sigma Aldrich , while the jelly and the rubber substrates were purchased from the market. The graphene’s structure and its disorders were discussed in Ref. . Figure http://www.miracle-chemical.com/Products.asp?ClassID=115, accessed on 6 December 2021) . The addition of other materials such as graphene, CNTs, or orange dye makes the gel conductive or semiconductive. Moreover, it is also important that the gel should be like glue.The gel used for these sensors is made of superabsorbent polymers such as cross-linked sodium polyacrylate, cross-linked sodium carboxymethyl cellulose, etc. This gel is inodorous, non-edible, environmentally friendly, and used for fairy crafts for kids and indoor plantations. It is commercially available with a trade name of Rainbow Crystal Clay  electrodes was kept to 1 mm. The sizes of the rubber substrates were the following: length, width and thickness were equal to 20:10:10 mmThe micrographs were taken using an Evo-15 W filament scanning electron microscope at an accelerating voltage of 5 KeV. A secondary electrons detector was used to obtain the micrographs.The MT 4090  was used for the measurement of the impedance at various frequencies ranging from 100 Hz to 200 kHz. For the measurements of the voltage the DT 4253 multimeter was used. Humidity and temperature were measured by the TECPEL 322. The testing was done in a special chamber with a built-in heating system.


Moreover, the FS‐GFF can be further attached to various shaped objects by a simple rewetting manipulation with negligible changes of electric conductivity. Based on the advanced fabric structure, excellent electrical property, and high infrared emissivity, the FS‐GFF is thus assembled into a flexible device with tunable infrared emissivity, which can achieve the adaptive camouflage ability in complicated backgrounds. This work provides an infusive insight into the fabrication of large‐scale freestanding graphene fabric films, while promoting the exploration on the flexible infrared camouflage textiles.Graphene films, fabricated by chemical vapor deposition (CVD) method, have exhibited superiorities in high crystallinity, thickness controllability, and large‐scale uniformity. However, most synthesized graphene films are substrate‐dependent, and usually fragile for practical application. Herein, a freestanding graphene film is prepared based on the CVD route. By using the etchable fabric substrate, a large‐scale papyraceous freestanding graphene fabric film (FS‐GFF) is obtained. The electrical conductivity of FS‐GFF can be modulated from 50 to 2800 Ω sq A freestanding graphene film is reported by etching graphene‐coated substrate with fabric structure. Moreover, the large‐scale papyraceous freestanding graphene fabric film (FS‐GFF) can be further attached to various shaped substrates and showing a superior electrical conductivity. Meanwhile, the FS‐GFF based infrared camouflage flexible textile device exhibits superior infrared camouflage performance. The synthetic strategies of GF can be mainly divided into two routes: 1) top‐down synthesis from the assembly of graphene flakes and its derivative; this method enables the GF production with relatively low cost, but suffers from the dilemma of graphene thickness uncontrollability and tedious fabrication procedures; 2) bottom‐up synthesis from carbon source molecule by chemical vapor deposition (CVD) method. The as‐fabricated graphene film owns merits of high quality and high uniformity. But the tight integration between graphene film and substrate limits further structure design, while the inevitable tedious transfer process could also cause defects and degrade the properties of graphene.Graphene film (GF) with high mechanical flexibility, superior electrical conductivity, and high specific surface area shows great potentials in supercapacitors,3, 42 fiber by CVD method, a flexible papyraceous freestanding graphene fabric film (FS‐GFF) was designed. In case of using nickel/copper fiber as growth substrate, the large diameter (≈100µm) of metal fiber and the loose structure of common metal mesh may cause a degradation of its original fabric structure and make it unable to be freestanding. In this work, the dense structure of SiO2 fiber with a small diameter of 6 µm ensured that the FS‐GFF can maintain its original fabric structure after the SiO2 fiber was etched. Furthermore, a large‐scale FS‐GFF can be obtained based on the size of SiO2 fabric. Moreover, the flexible FS‐GFF can be attached to various shaped objects by a very simple rewetting process.Herein, by virtue of our graphene growth experience on SiOD method,28 a fBased on this novel FS‐GFF, a unique adjustable infrared camouflage (AIC) flexible textile device was fabricated. Benefiting from the substrate‐independent character of the FS‐GFF material, the AIC device can be easily transferred onto any shaped target and operated conveniently compared with other reported works on AIC devices.34The infrared emissivity the FS‐GFF‐based AIC device can be modulated from 0.79 to 0.68 by applying a low input voltage of 5 V. Based on a specially designed multielectrode structure, this unique AIC textile device shows excellent infrared camouflage ability under complicated infrared backgrounds.22 fabric with size about 800 cm × 40 cm  was chosen as the flexible substrate for graphene growth  condition. Since the concentration of active carbon species decreased along the gas flow direction, thickness of the graphene film was gradually reduced, resulting in a nonuniform graphene@SiO2 fabric (G@SF) sample with lower sheet resistance near the gas‐in direction and higher sheet resistance near the gas‐out direction  (≈3.4) indicate the large‐scale uniformity and high quality of the as‐fabricated graphene film  characterization in Figure Raman spectra of the G@SF were collected along the rolling direction from positions marked in Figure m Figure . The repm Figure . C 1s peFigure 2 fiber substrate in hydrofluoric acid solution, the extremely soft and wet graphene film was thus obtained floating on water  as the ionic liquid electrolyte. By applying voltage between the FS‐GFF (U‐high) and the back electrode (D‐low), the ionic motion was induced. When increasing the applied voltage, the infrared reflectance (Rinfrared) of the as‐fabricated AIC flexible textile device increases due to the increase of Fermi energy and the optical conductance of FS‐GFF, which is relevant to the intercalation of ions . Since the FS‐GFF is impermeability to the infrared light with a transmittance (T) of zero, the infrared emissivity (ε) can be calculated by the equation of ε = 1 − Rinfrared. Therefore, the infrared reflectance of the AIC device in the infrared atmospheric window can be consequently improved through increasing the applied voltage =(2πεhc2)/(λ5(exp(hcλkBT)−1)), where E, ε, T, and λ are spectral radiation power of gray body, emissivity, temperature, and wavelength, respectively; h, c, and kB are the Planck constant, speed of light, and the Boltzmann constant, respectively, which shows that the FS‐GFF can be regarded as a representative gray‐body radiation. Based on this adjustable emissivity, the flexible device was attached onto a human finger . Typical growth conditions were 200 sccm of Ar, 100 sccm of H2, and 20 sccm of CH4 at 1050 °C. The thickness of graphene could be modulated by tailoring the growth time from 2 to 10 h.A roll of SiO2 fabric. Afterward, the G@SF collapsed into graphene ribbons and then was washed by deionized water and ethanol to remove the residual chemical reagents. Then, the soft graphene fabric film was transferred to pretreated filter paper. Surface of the filter paper was swept by nitrogen for 30 min and the FS‐GFF was then separated from the filter paper.G@SF was diffused in hydrofluoric acid solution (20 wt%) for hours to remove the SiOFirst, a piece of FS‐GFF larger than the surface area of the target object was tailored. Second, surface of the target object could be wiped by proper organic solvent. Then, the FS‐GFF was layered on the top of the target object and tiny amount of proper organic solvent was splashed onto the FS‐GFF by nebulizer.The finite element analysis was conducted to further elaborate the dispersion process. Basic unit of a single graphene ribbon was 20 nm × 9 µm × 2 mm, modulus of elasticity was set as 1.0 TPa, and the number of stacked layers was chosen as 20, 15, 10, 5, and 1.6) was applied onto the fabric separator layer which acted as both the separator and ionic conductive layer.The fabric separator layer (cellulose paper) was adhered to the electrode (sputtered gold). The other electrode was fixed on the fabric separator layer by conducting resin. Then, the FS‐GFF was attached to the surface of the fabric separator layer by rewetting process, forming the complete device. After the flexible AIC device was transferred to human finger, the ionic liquid electrolyte , optical microscopy (Olympus DX51), Keithley 2001 multimeter , and Fourier transform infrared (Nicolet 6700) spectrometer equipped with integrating sphere.The samples were characterized by Raman spectroscopy , SEM , XPS (Kratos Analytical Axis‐Ultra spectrometer using a monochromatic Al KThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.Supplemental Video 1Click here for additional data file.Supplemental Video 2Click here for additional data file.


FOXC2 mutations cause Lymphedema-distichiasis syndrome (LD). Recently, a natural antisense was identified, called lncRNA FOXC2-AS1, which increases FOXC2 mRNA stability. No studies have evaluated FOXC2 and FOXC2-AS1 blood expression in LD and healthy subjects. Here, we show that FOXC2 and FOXC-AS1 expression levels were similar in both controls and patients, and a significantly higher amount of both RNAs was observed in females. A positive correlation between FOXC2 and FOXC2-AS1 expression was found in both controls and patients, excluding those with frameshift mutations. In these patients, the FOXC2-AS1/FOXC2 ratio was about 1:1, while it was higher in controls and patients carrying other types of mutations. The overexpression or silencing of FOXC2-AS1 determined a significant increase or reduction in FOXC2 wild-type and frameshift mutant proteins, respectively. Moreover, confocal and bioinformatic analysis revealed that these variations caused the formation of nuclear proteins aggregates also involving DNA. In conclusion, patients with frameshift mutations presented lower values of the FOXC2-AS1/FOXC2 ratio, due to a decrease in FOXC2-AS1 expression. The imbalance between FOXC2 mRNA and its lncRNA could represent a molecular mechanism to reduce the amount of FOXC2 misfolded proteins, protecting cells from damage.Forkhead-box C2 (FOXC2) is a transcription factor involved in lymphatic system development.  Lymphedema-distichiasis syndrome LD, OMIM 153400) is an autosomal dominant rare disorder in which the lymphatic system, responsible for the production and transport of fluids and immune cells throughout the body, does not develop correctly 53400 is . The ageFOXC2 gene (MIM 602402), a member of the Forkhead-box (FOX) family [FOXC2 is located on the long arm of chromosome 16, positive strand, and consists of a single exon. It encodes a transcription factor (FOXC2), composed of 501 amino acids, regulating the development of some systems during embryogenesis, particularly the lymphatic and blood vascular system. FOXC2 has several functional regions: two transactivation domains, AD-1 and AD-2, located in the N- and C- terminal parts, respectively; a forkhead DNA binding domain , which contains the first nuclear localization signal ; a second NLS ; and an inhibition domain (ID2) located in the C- terminal region [LD is associated with mutations in the e MIM 60202, a mem) family . FOXC2 iwww.hgmd.cf.ac.uk accessed on 15 July 2020). Most of them, being complex rearrangements, deletions, insertions, or nonsense mutations, should result in a partial or total loss of FOXC2 function. However, functional studies have shown that some variations, particularly missense mutations, located outside the FHD domain lead to an increase in transcription factor activity [Almost 110 LD-causing mutations have been identified  and 8 healthy age-matched subjects , using ethylenediaminetetraacetic acid (EDTA) as anticoagulant. The clinical and genetic information of the LD patients were reported in previous studies ,14. The −ΔΔCt method, after normalization with Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) expression. RNA obtained from HeLa cells was used as positive control.Peripheral blood mononuclear cells (PBMCs) were isolated from the EDTA-treated peripheral blood by density gradient centrifugation using Histopaque, following the manufacturer’s instructions. RNA was extracted with Trizol solution and reverse transcription was performed after treating 2 μg of RNA with DNAse I . QuantitIn addition, semi-quantitative RT-PCR was performed as previously described , using tGFP-FOXC2 recombinant plasmids were previously obtained ,18. FOXCTM Coomassie (Bradford) Protein Assay Kit  and separated by electrophoresis on 10% SDS-polyacrylamide gel . Then, they were transferred to a polyvinylidene difluoride (PVDF) membrane (Biorad) and, after blocking with 5% nonfat dry milk, the membrane was incubated with primary antibodies against GFP  and GAPDH . The immune signals were examined using the SuperSignal West Pico Complete Detection Kit (Pierce) containing ImmunoPure Peroxidase Conjugated Goat anti-Mouse . After 48 h, the cells were lysed using NP40 buffer containing protease inhibitors. Total proteins were quantified using a PierceIn addition, HeLa cells were simultaneously transfected as described above, then fixed and analyzed with a LeicaMB5000B microscope and a confocal microscope Leica TCS SPE equipped with 40× and 63× oil immersion objectives. t-test . Linear correlations were performed using the Pearson product moment method (significant set at p < 0.05). The ratio of FOXC2-AS1/FOXC2 expression was compared using the Kruskal–Wallis test . SPSS v.19 package  was utilized to carry out all statistical analysis. qRT-PCR results were tested comparing the values with Student’s https://robetta.bakerlab.org accessed on 15 July 2020). The investigation of the secondary and three-dimensional structure of FOXC2 mutant proteins was performed using Robetta software , a nonsense mutation (p.Y109*), and two frameshift mutations (p.H199Pfs264* and p.I213Tfs18*). These were localized in various protein domains , while a moderate correlation was identified in the LD patients   (FOXC2 expression tended to 1:1 and it was significantly lower (p < 0.05) than that detected in control subjects and all the other patients  B,C. Neve≤ 0.001) D. Finallpatients E. FOXC2 and FOXC2-AS1 expression was significantly higher in the female population compared to male population , but not in females   B, consisFOXC2 and FOXC2-AS1 were expressed in blood cells, a semi-quantitative RT-PCR analysis was carried out in the control and LD patients. FOXC2 and FOXC2-AS1 RT-PCR fragments of 384 and 319 nt, respectively, were obtained. No FOXC2 amplification products were observed in -RT samples. The sequencing of FOXC2 and FOXC2-AS1 RT-PCR products confirmed the expression of both genes in peripheral blood  did not affect protein nuclear localization 9* did no.Immunofluorescence analysis evidenced that p.Y109* showed a cytoplasmic localization, missense mutations  maintained a homogeneous nuclear distribution, similar to native FOXC2, and frameshift mutations H199Pfs264* and I213Tfs18* were able to enter the nucleus and induced intranuclear protein aggregates . To better clarify if these nuclear aggregates could interact with DNA, confocal microscope analysis was performed. The nuclear images of cells transfected with GFP-FOXC2(H199Pfs264*) or GFP-FOXC2(I213Tfs18*) clearly showed an uneven DNA staining which colocalized with mutant FOXC2 protein aggregates .FOXC2 frameshift mutations cause the production of mutant proteins (p.H199Pfs264* and p.I213Tfs18*) in which a stretch of amino acids can be found that is different from native FOXC2 sequence. Bioinformatic investigation revealed secondary structure modifications not only of amino acids localized in the central region but also in some residues of the FHD domain  and GFP-FOXC2(I213Tfs18*) lost their ability to divide, increasing cell death [FOXC2 frameshift mutations might block mitosis. However, it might be hypothesized that nuclear protein aggregations play an important role in the inhibition of cell cycle progression. Here, we demonstrated by confocal analysis that these aggregates colocalized with DNA, showing a non-uniform staining. As chromatin assembly is essential to regulate transcription factor-DNA interaction and gene expression [As it was previously reported, p.I213V, p.V228M, and p.A492V preserved the correct nuclear localization, while could cause both a loss (p.V228M) and gain (p.I213V and p.A492V) of FOXC2 activity ,18. p.Y1pression , the varIn silico investigation showed that nuclear aggregates formation could be associated with dramatic structural alterations of FOXC2 mutant proteins. In the previous study, we investigated secondary and tertiary structures of both mutant proteins using i-Tasser tool . i-TasseFOXC2 and FOXC2-AS1 in blood samples from control and LD subjects. Conversely, a sex-based regulation of both genes was identified. Moreover, a strong positive correlation between both RNAs amount was identified in all participants, except in females carrying FOXC2 frameshift mutations. In these LD patients, FOXC2-AS1 amount was lower than in other control and LD subjects, determining an imbalance between FOXC2 and FOXC2-AS1 expression. Confocal and bioinformatic investigations seemed to indicate that frameshift mutations dramatically modify FOXC2 tertiary structure and DNA binding. Our in vitro studies showed that ectopic FOXC2-AS1 over or under expression directly regulates FOXC2 protein production. Likewise, endogenous FOXC2-AS1 down-regulation might be a molecular mechanism useful to protect the cell, decreasing misfolded proteins production. Since a small number of blood samples were analyzed, additional studies should be performed on larger number of healthy and LD subjects to better clarify the relationship between FOXC2 and FOXC2-AS1 expression.In conclusion, we showed that there were similar expression levels of


Graphene, synthesized either epitaxially on silicon carbide or via chemical vapor deposition (CVD) on a transition metal, is gathering an increasing amount of interest from industrial and commercial ventures due to its remarkable electronic, mechanical, and thermal properties, as well as the ease with which it can be incorporated into devices. To exploit these superlative properties, it is generally necessary to transfer graphene from its conductive growth substrate to a more appropriate target substrate. In this review, we analyze the literature describing graphene transfer methods developed over the last decade. We present a simple physical model of the adhesion of graphene to its substrate, and we use this model to organize the various graphene transfer techniques by how they tackle the problem of modulating the adhesion energy between graphene and its substrate. We consider the challenges inherent in both delamination of graphene from its original substrate as well as relamination of graphene onto its target substrate, and we show how our simple model can rationalize various transfer strategies to mitigate these challenges and overcome the introduction of impurities and defects into the graphene. Our analysis of graphene transfer strategies concludes with a suggestion of possible future directions for the field. Graphene, a two-dimensional hexagonal carbon allotrope, boasts a number of electronic, mechanical, thermal, and optical properties that make it very attractive for incorporation into next-generation electronic and optical devices ,2,3,4,5.Although both epitaxial and CVD growth can produce high-quality single-layer graphene, it is often desirable or even necessary to transfer graphene from its original growth substrate onto a different substrate for the material to be useful in device applications. This is most apparent with CVD-grown graphene, where the graphene sits atop a metal substrate. A conductive, opaque metal substrate precludes many applications and therefore must be exchanged for another substrate which is more practical . Epitaxial growth does not have this problem explicitly, as SiC is an insulator. However, due to uneven growth patterns and step edges on epitaxially grown graphene, it is also often desirable to consider transfer of graphene to an more suitable substrate .In this review, we present current knowledge concerning the transferring of graphene from one substrate to another. A number of reviews have appeared recently which focus on various aspects of the graphene transfer process ,10, inclExisting reviews tend to divide graphene transfer methods into etching and non-etching, based on whether graphene is separated from its substrate physically or whether the substrate is chemically etched away to create freestanding or polymer supported graphene. We have chosen not to divide the methods this way, but have instead considered the transfer process as consisting of two main parts: (1) delamination of graphene from its original substrate, and (2) relamination of graphene onto its target substrate . We haveThe remainder of this paper is structured as follows. In A note about terminology: in general, graphene does not explicitly form covalent bonds with its underlying substrates. Several covalently bound carbon morphologies are present during epitaxial growth of graphene on silicon carbide, but even in this case, the carbon overlayer is generally not considered graphene until no covalent bonds exist between it and the underlying “buffer layer” . We willThe promise of incorporating graphene into electronics runs up against several practical issues, but the two most important points related to graphene transfer are those of cleanliness and structural integrity. The superlative electronic properties of graphene are extraordinarily sensitive to chemical doping as well as crystal defects ,19,20,2113 atoms·cm−2, regardless of the extensiveness of the post-etching cleaning procedure . T. Tx with2O3 and an adhesive  layer of Aladhesive a. The au2 bubbles formed during bubble transfer  as well as mechanical and mechanochemical methods involving pressure-sensitive and thermal release adhesives.Since these strategies do not strictly employ chemical etching of the original substrate, metallic contamination tends to be less of an issue for them. However, as mentioned above, electrochemical strategies might release a small amount of metal ions, which must be accounted for in high precision experiments. Regardless, the graphene transferred using these methods tends to be cleaner and more free from dopants than in the case where the substrate is etched away.The main drawback of methods increasing graphene-substrate distance is that physical force is applied to the graphene to separate it from its original substrate. This force can cause tears and cracks to form in the graphene e.g., a. The maIntercalation methods seek to insert atoms and molecules in the space between the graphene and the substrate. Graphite intercalation compounds are well-known, especially with respect to alkali metal intercalation compounds . SeveralOther more involved intercalation schemes have been explored. Recently, Guo et al. have demonstrated intercalative growth of silicon oxide between graphene and a ruthenium metal growth layer. The presence of silicon oxide increases the distance between the graphene and the metal substrate. However, the researchers did not use the separator to facilitate transfer; they used the intercalated silicon oxide as a new substrate on which to build graphene devices directly . Ma et a2 bubble formation between the graphene and the metal, physically increasing the distance between the graphene and its substrate. Strictly speaking, as there is no water between the graphene and the metal to begin with, water must somehow intercalate between graphene and metal at the graphene edge [Electrochemical methods pioneered by Wang et al. involve immersing the graphene on copper in water and applying a bias to the copper substrate a 33]. T. T33]. Tene edge , so thesene edge .2 bubbles are generated between the graphene and copper substrate.Bubble transfer can also be combined with other methods such as mechanical stamping . These two effects contribute to the complete wrinkle-free delamination of the graphene from its substrate , tuning of the intrinsic graphene interaction, and manipulation of the distance between graphene and substrate, where a close conformal contact between graphene and the target substrate will tend to mitigate issues arising specifically during relamination such as wrinkles.Physically, relamination of graphene is simply the inverse of delamination, so that promoting strong adhesion to the target substrate is largely a matter of inverting the conditions that one would promote for weakening adhesion during delamination. In reality, the processes are not complete inversions of one another. For instance, instead of strengthening the substrate interaction coefficient for relamination, it is much more common to delaminate graphene onto a temporary substrate which strongly adheres to it and subsequently find ways to weaken the adhesion to this temporary substrate in favor of the permanent target substrate. This strategy manifests itself most clearly in the form of a temporary polymer support applied during graphene delamination, which is subsequently removed upon relamination.However, support removal can leave polymer residues which change the properties of the graphene, and therefore a number of techniques have been developed to limit the initial amount of residue left behind by polymer support during transfer, with the goal of obviating the need for extended cleaning procedures. Ren et al. reported a modification of the standard chemical etching with polymer support technique in 2012, where they omitted the PMMA step completely, simply allowing unsupported graphene to float freely on the etchant bath . HoweverAs mentioned above, the most widely used graphene transfer techniques employ a temporary polymer substrate. This is both to support the graphene mechanically when its original substrate is removed and to facilitate the transfer by being, in effect, a substrate which exhibits tunable adhesion to graphene. The most prominent example is the use of PMMA as a polymer support. While the PMMA adheres strongly to graphene when it is in a solid state, dissolving it in acetone causes its adhesion to drop dramatically and makes it easily removable from the graphene surface.It has been shown that PMMA and other support polymers leave behind physisorbed and chemisorbed species after being dissolved off graphene with acetone. Lin et al. showed that PMMA residues remain even after annealing at high temperatures in forming gas . Therefo2O2, which would agitate and possibly damage the single layer graphene. Sun et al. determined using Raman spectroscopy that the main PMMA-based contaminant remaining after thermal annealing was non-covalently bonded methoxycarbonyl side chain material, and they used this finding to develop an electrolytic cleaning technique [2 bubbles generated from electrolyzed water aid in liftoff of the polymer residues, in a mechanism similar to the bubble transfer technique for lifting off graphene. Park et al. later showed that the formation of bubbles was not strictly necessary, by performing a bubble-free electrochemical cleaning procedure in nonaqueous solution [In the same spirit, Liang et al. developed a “modified RCA” cleaning procedure , by adapechnique . The grasolution .Another technique to limit polymer residue is the use of releasing layers, which are polymer support layers composed of material that only weakly or tunably adheres to graphene. It has been shown that polymers such as polystyrene or polyisobutylene have relatively weak interaction with graphene . When thThis releasing layer idea can be taken a step further by using thermal release tape  109,110110. ThisCalado et al. showed that wrinkling of graphene was minimized when the target substrate was hydrophobic. They hypothesized that water plays an important role in the formation of wrinkles, and that wrinkles provide a conduit through which water drains from between graphene and target substrate upon relamination . A hydrog. Whereas, in general, covalent functionalization of the graphene decreases Cg and therefore weakens the adhesion of graphene to its substrate, removing covalent functionalities from chemically modified graphene can strengthen Cg and allow previously delaminated graphene to adhere tightly to a new substrate. Whitener et al. have shown that hydrogenated graphene that has been delaminated onto a water surface can be dehydrogenated in situ by briefly exposing the material to bromine gas. The relaminated dehydrogenated graphene then adheres strongly to a target substrate, without further delamination upon introduction of water [As mentioned earlier with respect to delamination, the ability to chemically modify graphene gives us control over Cof water . A non-cof water . This trOne of the earliest graphene transfer methods to eschew a polymer support was demonstrated by Regan et al. in 2010, who reported a direct transfer of graphene from a copper growth substrate to a TEM grid by placing a drop of isopropanol between the grid and the copper substrate . The evaAvoidance of wrinkling of the 2D sheets during relamination has driven much of the advancement in transfer strategies seeking to decrease the graphene-substrate distance during relamination. In particular, many strategies focus on the use of very soft polymer supports which can be easily melted and are thus conformable simultaneously to flat graphene and to the target substrate ,118,119.A similar soft polymer approach was advanced by Zhang et al., who replaced PMMA in the standard transfer with a commercially available 3M Nexcare liquid bandage (LB) . The mecIn the same vein is the use of pressure sensitive adhesive as a polymer support. This technique ultimately has its roots in the Scotch Tape micromechanical cleavage method that Novoselov et al. used to isolate graphene in 2004 . Kim et 2/Si wafer, and then etching away the copper chemically. This etching forms voids in the copper which adhere the graphene to the underlying SiO2 via capillary forces. Such a process would naturally form wrinkles where the voids connect the SiO2 and the graphene, but the authors avoid wrinkle formation by modulating the surface tension of the water through addition of isopropyl alcohol. This technique allows an ultrasmooth, single-wafer transfer of CVD graphene [An unusual single-wafer transfer technique employed a remarkable method to avoid introduction of wrinkles to the graphene. Gao et al. reported growth and transfer of CVD graphene on the same wafer by first growing graphene on an ultrathin layer of copper on a specially treated SiOgraphene .The transfer of graphene is an indispensable step in graphene-based device fabrication. As we have seen, a great deal of progress has been made to mitigate many of the issues that arise during graphene transfer. Delamination and relamination each bring their own challenges, and understanding them and graphene-substrate interaction on a mechanistic level enables a rational, holistic approach to solving problems associated with each step of transfer.Each transfer strategy comes with benefits and drawbacks, and the most effective transfers appear to be the ones which combine the strengths of several different strategies to mitigate many issues at once. At least part of the future of graphene transfer at a basic research level will likely be continuing to evaluate new combinations of strategies for cleanliness and integrity of the final product. From the standpoint of incorporating graphene into commercializable devices, however, there needs to be an examination of the tradeoff between complicating the transfer process by combining many strategies and reducing cost by simplifying the process. This tradeoff could see great progress in the use of automation specifically for transfer. Tight control of conditions during transfer would provide reproducibility, and an automated system could perform tasks such as mechanical peeling much more slowly and systematically, thereby introducing less strain into the graphene and hence less mechanical damage. Other techniques which are very promising commercially include clean delamination of graphene and recycling of substrates. Chemical etching is destructive and adds to cost, but a simple recycling scheme could make the transfer process and ultimately, graphene incorporation into devices, more economical.In a less pragmatic, but more fundamental way, studies on graphene transfer can advance basic graphene science by probing graphene-materials interactions systematically. The physics outlined in In principle, the model that we have introduced is applicable not only to graphene transfer, but to transfer of any 2D material. Van der Waals heterostructures display an astonishing versatility of properties, including superconductivity magic-angle twisted bilayer graphene , long-li


This paper provides modeling and simulation insights into field-effect transistors based on graphene (GFET), focusing on the devices’ architecture with regards to the position of the gate , substrate , and the graphene growth . These aspects are explored and discussed in order to facilitate the selection of the appropriate topology for system-level design, based on the most common topologies. Since most of the GFET models reported in the literature are complex and hard to understand, a model of a GFET was implemented and made available in MATLAB, Verilog in Cadence, and VHDL-AMS in Simplorer—useful tools for circuit designers with different backgrounds. A tutorial is presented, enabling the researchers to easily implement the model to predict the performance of their devices. In short, this paper aims to provide the initial knowledge and tools for researchers willing to use GFETs in their designs at the system level, who are looking to implement an initial setup that allows the inclusion of the performance of GFETs. Despite the promising results at cryogenic temperatures, the FET mobility at room temperature remains low for TMDCs. Because of that, graphene (a monolayer of carbon atoms in a honeycomb lattice) is being widely pursued as an enabling material; it has amazing properties at room temperature, such as high saturation velocity and high carrier mobility, which make this material suitable for radiofrequency (RF) applications, for example.The development of CMOS  transistors is achieving its performance limit, due to the maximum downscaling according to Moore’s law. Several new materials have appeared with the potential to overcome silicon devices’ performance; most of these rely on two-dimensional (2D) materials. Those families of materials feature dangling-bond free surfaces exhibiting excellent electronic and optical properties. Such materials range from graphene to other 2D materials, such as the transition metal dichalcogenides (TMDCs). TMDCs have a finite bandgap, which is essential to enable low-power digital electronics. The state of the art of the TMDC transistors and silicon transistors is similar, as reported in , where MSince the discovery of graphene by Geim and Novoselov in 2004 ,4, and f2 V−1 s−1 was observed at low temperature , suggesting the possibility of the use of this material in very fast analog electronics, due to the very short carrier transit time. However, it must be noted that the properties of graphene—mainly its high mobility—change with the substrate where the graphene lays, as suggested in [2 substrate, which suggests that high mobility can be achieved even after the graphene’s transfer to a substrate [From initial measurements, performed on monolayer graphene, a very high mobility of about 20,000 cmested in . High moubstrate . DespiteThe good potential of graphene in GFETs—mainly in radiofrequency, where graphene’s high mobility is essential to achieve a good performance—is demonstrated by the cutoff frequency  and their applications, along with discussion of how they can be modeled for use in tools that allow circuit- and/or system-level simulation, in order to assess the performance of electronic or sensing circuitry based on such GFETs. This paper is divided into four sections: firstly, a discussion of the different architectures for the graphene transistors is presented; then, the different fabrication techniques are presented and discussed; in the third section, the different substrates for GFET fabrication are addressed; finally, a model of the graphene transistor is presented, and its potential use discussed. This model was implemented in MATLAB, Verilog in Cadence, and VHDL-AMS in Simplorer, which are three tools widely used for electronic circuit simulation.DS) a current (IDS) flows through the channel, from drain to source. By applying a potential (VGS) on the third terminal (the gate), this current can be modulated by adjusting the charge of the channel through the induced electric field—the basic operation of the field-effect transistors. A GFET is a particular implementation of the above description, where the channel is implemented using a graphene layer. A field-effect transistor is a device characterized mainly by its three terminals : the drain, the source, and the gate. The drain and the source are interconnected by the graphene channel. The gate is isolated from the channel by a gate dielectric. The channel is characterized by its length (L) and its width (W). For a given drain-source voltage  films to act as a gate dielectric. The h-BN film has a dielectric constant of ~3.4; however, due to the similarity with the hexagonal graphene’s structure, it is the suitable oxide to be used together with graphene due to the absence of dangling bonds on its surface, which makes this a chemically inert material. With this approach, the graphene’s mobility could be improved by one order of magnitude when compared with other approaches. In Top-gated graphene transistors are a suitable approach to applications where a thin oxide layer gate is required. This is necessary to exert more control over the electrostatically doped carriers in the channel and, consequently, a lower gate bias is required to modulate the channel. Despite all the advantages of this approach, the difficulty of growing an oxide on top of the graphene, without damaging its lattice and degrading its mobility, remains a problem. To solve this, several approaches have been developed, such as the physical transfer of a nanowire with an oxide shell to act as a gate electrode . StandarAnother very widely used structure for GFET devices is the back-gated topology. From the literature, this group of GFETs is mostly used in biosensors ,25 or phThese devices  are very useful, mainly in RF applications, given the small achievable gate capacitance, reducing the parasitic capacitance, which increases the RF performance. In this approach, the common issues associated with the growth of an oxide on top of the graphene are avoided. In For several applications, it is necessary to shift the Dirac point in order to electrostatically dope the graphene, adjusting the operation of the transistor. With this purpose, back gates are added to top-gated transistors. In fact, since graphene transistor research is only in the early stages, most of reported top-gated graphene transistors have back gates. Such devices are useful to tune all of the transistors to the same point , reducing the variability between GFETs, which is a big drawback of GFETs today. In After presenting a set of GFETs in each topology, briefly discussing their applications and performance, this section will present the issues related to the fabrication aspects that are necessary to consider while selecting one of the previous options to obtain 2D electronic circuits.Despite the promising properties of GFETs, several issues need to be solved to increase the performance of such devices to the required levels, e.g., the low on/off ratio of the graphene devices is a big limitation on the use of these devices for logic applications . HoweverBeing the fundamental material to support the device characteristics, the methodology to obtain the graphene and transfer it to the fabrication steps has been widely explored. Several methods to obtain graphene have been developed, with the most common growing solutions being CVD on a metal foil , CVD on In addition to the final performance considerations, the chosen method to obtain graphene constrains the GFET fabrication process and, eventually, the transistor’s topology. For example, when the graphene is obtained via mechanical exfoliation, the flake needs to be identified, and the structures of the source, drain, and gate are then fabricated , which mThe selection of the appropriate methodology will be dependent on the available processing methods at each facility, on the required application, and on the integration level and scalability desired.Another relevant aspect that has an impact on the performance and/or fabrication steps, as well as integration potential, is the base substrate that is used to fabricate the GFET devices. The substrate may be imposed by the fabrication facilities, by the integration methodology required, or by the graphene fabrication and processing steps, with the latter being the topic of the next discussion.2 [2, due to their compatibility with the standard fabrication processes and the easy optical identification of the graphene on SiO2. This property makes these the most suitable substrates for the fabrication of high-quality CVD-grown graphene devices after graphene transfer. The presence of a thick layer of SiO2 on top of the Si substrate makes this substrate also very useful in RF applications, decreasing the parasitic substrate capacitances. SiC substrates are often used for the epitaxial growth of graphene for electronics applications, with the advantages of the use of the conventional top-down lithography techniques well established in nanotechnology [Graphene transistors can be fabricated on several substrates, with the most common being Si/SiO2 , SiC [592 . Graphen2  or polye2 . These a2 . The moschnology . In contchnology .From the above analysis, it is possible to conclude that the fabrication of graphene transistors remains a challenging task. For different purposes, several aspects should be taken into consideration in order to ensure that the best design can be selected. Final performance can be a quantitative means of selecting a GFET solution, but there are other aspects to take into consideration. Before fabricating new devices or systems, it is highly desirable to have models that can predict the behavior of the devices, allowing, for example, the performance assessment of full electronic systems. Hence, this section will describe how to implement a model for monolayer/bilayer graphene transistors, using different tools, as well as how such a model can be used in DC analysis. Since the reported model describes the intrinsic behavior of the GFET, making the presented analysis valid for DC or low-frequency, adding external parasitic capacitances can further extend the model to specific applications, such as the performance of the GFET in high-frequency applications. The implemented model can be integrated in circuits such as frequency multipliers—a very common application of GFETs, used in many cases to validate the performance of the fabricated GFETs. More complex circuits can be simulated, such as inverters—a very important building block in logic circuits. The implemented model was obtained from ,65. In [DS–VGS characteristic curve, when VDS is constant, is shown in GS value were the GFET has its minimum IDS. As will be further shown, this point is obtained by setting VGS0 and VBS0 in Equation (2) (for top-/back-gated graphene transistors). These values are obtained empirically, extracted from the GFET transfer curve of the real device that is intended to be modulated. DS–VDS) for a graphene transistor. It is possible to observe two regions in the figure: firstly, the conduction is performed through electrons, when VGS > V0 with IDS and VDS positive, and secondly, conduction performed by holes, when VGS < V0 with IDS and VDS negative. The electron conduction is composed of three regions—namely, the triode region, the unipolar saturation region, and the ambipolar saturation region—along with the charge interaction in the channel. For hole-based conduction, these three regions are also present. These DC characteristic curves can be obtained by using the implemented model, which indicates the correct behavior of the model and its ability to be useful, mainly in DC simulations, as will be shown in the next section. The general IAs was previously mentioned, this model was implemented in MATLAB, VHDL-AMS in Simplorer, and in Verilog to be used in Virtuoso from Cadence. The models are available as Among the several possible applications of GFETs, one is to use this device as a frequency doubler, due to the V-shaped I–V output characteristic curve of GFETs. To show the correct behavior of the model, a frequency doubler was implemented using Simplorer and Cadence, as shown in As can be shown, since the GFET rectifies the input signal, the output signal is a wave with new frequency components—namely, the double frequency. In this way, it is shown that we can use this model to rectify a signal, or as a multiplier.Despite the graphical aspects related to the model display, which are straightforward in each tool, it is necessary to define a solution to implement the model for each desired GFET (how to set the specific GFET parameters into the model), as well as to define how the calculations will be performed.q), substrate thickness (Hsub), top-gate dielectric thickness (tox), channel width (W), gate length (L), back-gate dielectric constant at the Dirac point (BS0V), top-gate voltage at Dirac point (GS0V), charge density (topn), critical electric Field (Ec) and electron/hole mobility (µ), back-gate dielectric thickness (Hsub), top-gate dielectric constant (ℇt), series resistance (Rs), and the reduced Planck’s constant (h). As soon as the user writes all the necessary data, as a first step, the program must calculate the capacitances and the voltages. After that, a comparison between VGS and V0 (threshold voltage) is performed to select the adequate conduction region, performed by holes or electrons. The surface potential of the channel (Vc) is also calculated. Then, a validation is performed to evaluate in which region the GFET is being operated , the back-gate capacitance (backC), and the channel capacitance, which are dependent on the quantum capacitance (qC) and the capacitance between gate and channel (eC). Those parameters are calculated following the expressions in Equation (1) [To model the top-/back-gated transistor, it is necessary to compute the capacitances of the device—namely, the effective gate capacitance (tion (1) :(1){CtopcV) depends on the critical electric field (Ec) and the gate length (L), while the threshold voltage (Vo) depends of the gate voltage at the Dirac point (GS0V), the capacitance between the back gate and the channel (backC), the effective gate capacitance (topC), the back-gate voltage at the Dirac point (BS0V) and the back-gate voltage (BSV). These relationships are presented in Equation (2):The surface potential of the channel (GSV) and the threshold voltage (0V) must be performed. If (GSV > 0V), the transistor is working via hole conduction; otherwise, the transistor works in electron conduction.As previously mentioned, to select the region where the graphene FET is being operated, a comparison between the gate voltage  [β < 1.4 as a constant to help in the fitting of real data.tion (3) :(3){Vds−The output current is presented in Equation (4) for the different regions ,65:(4)IDIn this paper, an overview of different graphene transistor topologies was presented, looking for the most common gate topologies present in the literature, and taking into consideration the base substrate and the fabrication technology. It was found that top-gated transistors are more widely used for applications where the fine control of the graphene channel is required, such as high-frequency applications. Back-gated devices, including the buried gated devices, were found to be widely used for applications in sensors, photodetectors, and biosensors, due to the full exposure of the graphene to the entity that will be transduced. Buried gates are very useful in RF applications, presenting the advantages of top-gated devices while reducing the parasite capacitances, which are a known limiting factor in the RF performance of the devices. The top-/back-gated devices are very useful due to the addition of the possibility of the tuning of the Dirac point by adding a back gate to the top-gated devices, useful to set different transistors for approximately the same work regions at the same voltages, reducing the variability between devices. 2 as a substrate, due to its advantageous compatibility with standard fabrication processes. Another substrate that is used is SiC, which has the advantage that graphene developed on SiC substrates does not require the transfer steps, and can be used in high-temperature applications. The other types of insulating substrates, such as glass or quartz, have the advantage of allowing a much-reduced parasitic capacitance, which decreases the RF losses associated with the substrates. Regarding the graphene growth, despite the better quality of exfoliated graphene from graphite, CVD-grown graphite is the preferred method, since it has a good quality and enables the growth of large areas, being suitable for large-scale fabrication, while the epitaxial graphene grown on SiC remains expensive. Thus, it is possible to conclude that the fabrication of graphene transistors remains challenging. For different purposes, several aspects should be taken into consideration in order that the best design can be selected. In general, for RF applications, top-gated transistors or buried gates are preferable, since they enable better control of the graphene’s channel. For sensors (biosensors and photodetectors), the most common topology reported in the literature is back-gated devices, due to the existence of an exposed graphene gate owing to its easy functionalization, as well as allowing for liquid top-gated devices.Graphene FETs are generally fabricated using Si/SiOFinally, this paper presents a tutorial to be used in simulation tools and to allow the performance assessment of GFETs using a model of graphene transistors using MATLAB, VHDL-AMS, and Verilog. Those models are available in the


The KO2-assisted hydrothermal treatment was proven to be a high-yield method for forming graphene nanoribbons and dots or sub-micro-sized graphene nanosheets. Starting with functionalized MWCNTs, the method produces water-dispersible graphene nanoribbons with characteristic photoluminescence depending on their width. Using pristine graphene, the hydrothermal treatment with KO2 produces nanosized graphene sheets and graphene quantum dots with diameters of less than 10 nm. The latter showed a bright white photoluminescence. The effective hydrothermal unzipping of MWNTs and the cutting of large graphene nanosheets is a valuable top-down approach for the preparation of graphene nanoribbons and small nanographenes. Both products with limited dimensions have interesting applications in nanoelectronics and bionanotechnology.The dual use of potassium superoxide (KO Graphene and carbon nanotubes (CNTs) are the two most well-studied carbon nano allotropes . They ar4−2) [GNRs can be made, among other ways, by the unzipping of CNTs, which means making a cut in the longitudinal direction. Usually, their width ranges between 10 and 100 nm, and their lengths are related to that of the starting CNTs ,20,21. T4−2)  are char4−2) . Bottom-4−2) ,25,26,272) has been proven to be an effective method to produce GQDs from GO [Similar cutting methods have been also developed recently for graphene, leading to small-sized graphenic pieces with interesting optical properties: the so-called graphene quantum dots (GQDs) ,29,30. T from GO .2 to unzip functionalized water-dispersible multiwalled carbon nanotubes (MWCNTs) under hydrothermal conditions to create GNRs. Furthermore, we show that the same reaction is highly effective, as well, at cutting pristine graphene nanosheets to produce nanographenes and GQDs. The method is simple and eco-friendly, and can be performed at a large scale with good yield.In this article, we explore the ability of KOPotassium superoxide purchased from Sigma-Aldrich, MWNT-f-OH, were prepared according to . GraphenFTIR spectra were obtained with an ATR technique on a Fourier transform spectrometer . Raman spectra were collected both with a Raman System T-64000 and a LabRam-HR Mirco Raman spectrometer  using a laser excitation line at 514nm. The laser power was 1.082 mV. XRD was conducted with a D8 Advance Bruker diffractometer  using a CuKa (lD 1.5418) radiation source  and a secondary beam graphite monochromator. Diffraction patterns were recorded in the 2-theta (2′) scale from 2° to 80°, in steps of 0.02° and with a counting time of 2 s per step. The optical absorption spectra were obtained with a Hitachi Digilab, Model U2800-Double Beam-UV/Vis .−1. The Si wafers  used in the AFM imaging were cleaned before use for 20 min in an ultrasonic bath (160 W) with water, acetone , and ethanol .Surface roughness was measured by using AFM atomic force microscopy (AFM) images that were collected in tapping mode with a Bruker Multimode 3D Nanoscope  using a microfabricated silicon cantilever type TAP-300G, with a tip radius of <10 nm and a force constant of approximately 20–75 N m−9 mbar with a SPECS GmbH spectrometer equipped with a monochromatic Mg Kα source (hv = 1253.6 eV) and a Phoibos-100 hemispherical analyzer . Spectral analysis included a Shirley background subtraction and peak separation using Gaussian–Lorentzian functions in a least squares fitting software package (Winspec) developed at the LISE laboratory, University of Namur, Belgium.X-ray photoelectron spectroscopy (XPS) measurements were performed in an ultra-high vacuum at a base pressure of 6 × 10The sheet resistance of the samples was measured on circular spots made from the samples after being compressed at 2 tn by a 4-point probe system  and Keithley 2400 Source Meter. The thickness was estimated to be 5 μm . 2O by sonication for 30′, and then 50 mg of KO2 was added, followed by stirring for another 30′. After that, the mixture was heated hydrothermally overnight at 185 °C in an autoclave Teflon. For this step, 5 mg of catechol-functionalized MWCNTs  or pure 1) and the precipitate (NR2). The brown-to-yellow-colored supernatant was purified with dialysis membrane, while the precipitate was washed and isolated by centrifugation  and redispersed in water. The supernatant was left for a week on a filtration membrane to remove by-products. Carbon nanotubes: The product of the hydrothermal reaction was separated in two parts by precipitation: the supernatant  (NG). The final brown-to-yellow supernatant was purified with a dialysis membrane (GQDs).2 in water and heated hydrothermally overnight at 185 °C. The mixture of the hydrothermal heating after sedimentation was separated in two parts: the supernatant (NR1) and the precipitate (NR2)  showed no fluorescence under the same excitation  dispersed in water were mixed with an excess of KONR2) see a. The brcitation c.AFM images. The AFM images of the sample NR1 reveal that it contains elongated single-layered nanoribbons with a thickness of 0.86 nm or some thicker few layers nanoribbons (~4 nm) and a mean width close to 40  of the samples NR1 and NR2 was evaluated using PL spectroscopy, as shown in 1 and NR2 were similar and show a broad absorption with a maximum at 263 nm, which corresponds to the π,π* transition and a very broad, and weak absorption around 350 nm that corresponds to the n,π* transition  is attributed to the added functional groups. Comparing the values for the ID/IG ratio, which is 0.36 and 0.64 for the spectra of products NR2 and NR1, respectively, the much lower value recorded for NR2 reflects the increased ratio between the sp2 carbon atoms at the core and the sp3 carbon atoms at the edges, due to the much larger width of the NR2 product [The Raman spectra of products NRf-OH see . The cha product .2 showed the different functional chemical groups , carbonyl (4.1%), and carboxyl (3.2%) groups. The pi–pi* interactions may derive from the few layers nanoribbons while interacting together via aromatic systems.The XPS analysis of the sample NRoups see . The mai2 was estimated to be 1075 S m−1 (sheet resistance: 186 Ohm sq−1) and increased to 1835 S m−1 (sheet resistance: 109 Ohm sq−1) after the reduction of the product with NaBH4. The conductivity of the nanoribbons was lower than that of the starting MWCNT-f-OH, which was measured to be 2940 S m−1 (sheet resistance: 68 Ohm sq−1); however, it was remarkably higher compared with similar nanoribbons in the literature and suitable for applications in nanoelectronics. In the literature, several procedures for the unzipping of MWCNTs have been described. Unfortunately, few reports presented a common description of the nanoribbon product, which usually contains the dimensions, dispersibility, conductivity or sheet resistance, yield, etc. In 2-assisted hydrothermal treatment is one of the most eco-friendly, low-cost, and high-yield methods. Apparently, it is the only one that can produce simultaneously narrow nanoribbons with intense photoluminescence and wide nanoribbons with an electrical conductivity between the highest points, especially after reduction.The electrical conductivity of large nanoribbons NR2 was also performed successfully. The products of the reaction, after the removal of the unreacted material or the large graphene nanosheets, were also divided by the material that was dispersed in the supernatant and the precipitate. As revealed by TEM analysis  and between 450 and 550 nm . The photoluminescence spectra of the GQD sample at several excitation wavelengths showed two different luminescence bands. The first with λ0 nm see . Interes0 nm see b. The di0 nm see c.−1, respectively. Both products have an increased ID/IG ratio compared to that of pristine graphene nanosheets, due to the increased number of sp3 carbon atoms at the edges of the much smaller GQDs and NGs. The difference between the ID/IG ratio of the two products, as shown in 3 carbon atoms due to the existence of defects at the core apart from the edges.The Raman spectra of the two products showed the characteristic peaks of the D, G, and 2D bands at 1360, 1570, and 2737 cmThe XPS analysis of nanographene showed different types of oxygen functional groups see . The mai2-assisted hydrothermal treatment for both substrates was indicated by the relatively high yield from unzipping MWCNT-f-OH or cutting graphene nanosheets. For the first procedure, the yield was above 90%, as indicated by the limited number of unreacted MWCNT-f-OH that was observed in the TEM images. As regards the hydrothermal cutting of graphene, the KO2 assistance resulted in a remarkable yield that reached 50%. The KO2-assisted hydrothermal treatment has proven to be an effective top-down method for the preparation of nanosized carbon structures from different graphenic precursors, such as carbon nanotubes, pristine graphene, or graphene oxide [2 and nanographenes NG (50–100 nm). The first could be used for the preparation of transparent conductive films in several applications, such as photovoltaics, smart screens, etc. Finally, nanographenes seems to have the suitable size to be used in bioapplications, such as drug delivery, biosensing, etc.The effectiveness of the KOne oxide . PrelimiThe mechanism. The mechanism of this effective cutting of graphenic layers or unzipping carbon nanotubes has been already proposed by Zhao et al., who showed that KO2 hydrothermally cut GO into very small pieces, thus producing GQDs with yellow PL emission [2 in water produces an intermediate superoxide anion O2−, and finally OH− and O2. The mechanism proposed by Zhao et al. is based on the existence of epoxy groups along lines on the GO surface or the formation of new lines of epoxy groups by the strongly oxidative superoxide anion O2−, and the dissociation of the underlying C-C bonds by OH− during the hydrothermal heating. In our work, functionalized MWCNTs and pristine graphene—without epoxy groups—were used, which means that epoxy lines should be formed exclusively during the KO2 treatment of the starting material (see emission . It is krial see .2 in water under sonication for a few minutes, and the product was separated and washed repeatedly to remove by-products. The KO2-treated graphene and MWCNT-f-OH were characterized by FTIR spectroscopy, which showed in both cases the formation of a strong band at 1350 cm−1 and a broad band at 3150–3200 cm−1 (see To support this hypothesis, pristine graphene and MWCNT-f-OH were mixed with an excess of KOcm−1 see .2 treatment of graphene or MWCNT-f-OH, and before the hydrothermal heating in the presence of OH−, which favors the cutting or unzipping of the epoxy or hydroxy functionalized graphene or MWCNT-f-OH surface.The latter can be attributed to OH stretching vibrations and the former to C-O bending vibrations or epoxy groups. The lack of any other characteristic peak in the FT-IR spectra of both samples indicates the formation of epoxy groups, which probably was partly hydrolyzed to C-OH during the KO2 leads to the effective unzipping and production of GNR. The same reaction was successfully applied to pristine graphene, creating nanographenes and GQDs. In both cases, there is a hydrophilic emissive nanostructure that was isolated by the water phase—narrow GNRs or GQDs—and a less hydrophilic, non-emissive part that isolated a precipitate that contains larger GNRs or nanographenes. Interestingly, narrow GNRs and GQDs are emissive nanostructures and, significantly, GQDs emit white light after excitation at 350 nm.The hydrothermal treatment of hydrophilic-functionalized MWCNTs with KO


Optimal geometries, adsorption energies, and projected density of states (PDOS) are computed using a DFT method. We show that nitrene reactive intermediates, formed by thermal or photo splitting of arylazides – p-carboxyphenyl azide (1a), p-carboxyperfluorophenyl azide (1b), and p-nitrophenyl azide (1c) – react with graphene to yield functionalized derivatives, with reaction energies >−1.0 eV and barriers of the order of 2.0 eV, and open a ∼0.3 to 0.5 eV band gap which is in principle apt for applications in sensing and electronic devices. The interaction between the amines and functionalized graphene, as demonstrated from the calculations of charge density differences showing regions of charge gain and others of charge depletion between the involved groups, occurs through hydrogen bonding with interaction energies ranging from −0.04 eV to −0.76 eV, and induce charge differences in the system, which in the case of p-carboxyperfluorophenyl azide (1b) are sizeable enough to be experimentally observable in sensing.Food quality is of paramount importance for public health safety. For instance, fish freshness can be assessed by sensing the volatile short chain alkylamines produced by spoiled fish. Functionalized graphene is a good candidate for the design of gas sensors for such compounds and therefore of interest as the basic material in food quality sensor devices. To shed theoretical insight in this direction, in the present work we investigate  Simulations show that the total volatile basic amines (TVB) from spoiled fish can be sensed by aziridine-functionalized graphene nanomaterials to induce substantial changes in the physical properties. Indeed, computational and theoretical studies showed that the pristine graphene functionalization with p-azidoperfluorophenyl carboxylic acid leads to a conductivity decrease by ca. 50%.19,24Pristine graphene, a one atom thick layer of carbon arranged in a honeycomb shape 2D crystal, is extensively investigated from theoretical and experimental point of views to unveil its potential applications.25 and nitrogen-doped graphene decorated with noble metals such as, Rh, Pt, Pd, etc. have been used to develop gas sensors to detect volatile gases such as CH4, H2S, N2, CO2.26 The organic-functionalized graphene can be obtained via chemical and physical adsorption of organic compounds on the graphene surface and be used for gas sensing. For instance, Tang et al. used 2,3,5,6-tetrafluorohydroquinone to modify pristine graphene to successfully detect formaldehyde with a good discrimination to ethanol and acetone.27 Interestingly, Xu et al. designed wearable sensors based on porphyrin-modified graphene and exploited it to detect eight volatile organic compounds (VOCs) using an array of electrodes. The chemoresistance of the devices varies up to 60% in presence of 100 ppm of the VOC vapours.28 Non-covalently modified pristine graphene with N-substituted triphenylene was successfully used to detect dimethyl methylphosphonate (DMMP), a simulant of the sarin nerve gas, through hydrogen bonding involving the target and the sensing surface. The addition of as low as 1.3 ppm of DMPP induces a variation of the chemoresistance by 10%.6Graphene modified with transition elements 29–33 such as xanthine employing biosensors,30–39 but also by detecting total volatile basic amines (TVB) such as ammonia, methylamine, dimethylamine and trimethylamine, that result from bacterial spoilage, enzymatic lysis and deamination of seafood.40 Developing graphene-based sensors with chemical functionalities represents a promising path in this direction since functionalized graphene can lead to a favourable interaction with specific VOCs thanks to the matching chemical characteristics that may result in highly sensitive and specific sensors.Fish freshness can be assessed using a series of biomarkersvia theoretical and computational simulations, investigating: (1) the chemical functionalization of graphene nanosheets with aryl nitrenes, obtainable from the decomposition of aryl azides, to yield chemically modified graphene, and (2) the interaction of such chemically modified graphene with typical TVB compounds. In particular, we focused on three modifiers: p-azidophenyl carboxylic acid (1a), p-azidoperfluorophenyl carboxylic acid (1b), and p-nitrophenyl azide (1c), and we found that the functionalization reaction energy is sizeable (>−1.0 eV) for these compounds depending on the added functional groups. Moreover, the formation energy barrier of aziridine-functionalized graphene, estimated via a NEB approach, shows transition states at 2.01 to 2.15 eV. The functionalized graphene interacts with MA, DMA and TMA species through hydrogen bonding with energies ranging from −0.04 eV to −0.76 eV (i.e. −3.7 kJ mol−1 to −73.3 kJ mol−1), and the interaction-induced charge differences are appreciable, and in particular in the case of (1b) are of the order of ±0.03/0.06 atomic charge units, correspond to an induced sizeable dipole of few tenths of a Debye, thus being sufficiently large to give rise to an experimentally observable effect.Aiming at providing insight in this direction, in this work, we explore this route The article is organized as follows. In Section 2,41 was used to carry out the ab initio calculations. For all the DFT calculations, a semi empirical Grimme's DFT-D3 Van der Waals correction was applied.42 Projector augmented wave (PAW) basis sets and periodic boundary conditions were employed in the calculations. A generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional was used. The plane-wave energy cutoffs (ecutwfc) for the wave functions and the charge density (ecutrho) were respectively set at 49.14 Ry and 442.32 Ry (9 × ecutwfc). The latter was optimised for different values of the wave function energy cutoffs (ecutrho = n × ecutwfc) where the difference (4 − n) × ecutwfc stabilizes (see ESIQuantum ESPRESSO (v6.4.1 or v6.5) packages see ESI.k-point grid and the orbital energies are broadened using a Methfessel–Paxton smearing of 0.01 eV, having tested that these parameters give converged results for band structure and electronic properties. For calculating the projected density of states (PDOS), we use a doubled 6 × 6 × 1 Monkhorst–Pack k-point grid and a tetrahedron integration method with homogeneous weights on tetrahedra. Atomic coordinates are optimized until the maximum force on ions is less than 0.001 eV Å−1 for all systems.Each simulated system consists of a supercell corresponding to a 5 × 5 or 6 × 6 graphene unit cells with the three different azide modifiers physically or chemically adsorbed onto it, in the latter case including or not the amine TVB compounds. In the structure relaxation, the Brillouin zone is sampled using a 3 × 3 × 1 Monkhorst–Pack 43,44 implemented in the simulation package, connecting the initial and the final equilibrium structures using 21 intermediate images connected with springs. Each image is optimized till the maximum force on ions is less than 0.01 eV Å−1 for all systems.Minimum Energy Paths (MEP) for the reaction between aryl nitrenes and graphene supercell were determined using the Nudged Elastic Band (NEB) method,The charge density differences were calculated from the individual charge densities for fully relaxed, minimal energy systems of the adsorbates, substrates and adsorbate/substrate complexes using 45All atomic and charge density visualisations were made using VESTA software.Eads, was computed as the difference between the energy of system (Eadsorbate+graphene) and the energies of the adsorbate (Eadsorbate) and graphene (Egraphene) fragments according to Starting from fully relaxed, minimal energy configurations of the adsorbates, the 5 × 5 graphene supercell and the adsorbate/graphene, the adsorption energy of phenylazides and phenylnitrenes, A selection of graphene/adsorbate optimized geometries are displayed in p-azidoperfluorophenyl carboxylic acid (1b), which the most electron deficient species due to electron withdrawing by the fluorine atoms. Moreover, we can observe that all the nitrene intermediates lie at a shorter distance from the graphene surface ca. 3.1–3.2 Å when they are in atop, bridge and hollow positions. In the parallel position, the intermediates are lying at a slightly larger distance from the surface (ca. 3.8–3.9 Å) because of larger repulsion between the electronic clouds. Energetically, the parallel position yields the strongest adsorption energies comparatively to the other configurations because a larger number of atoms from the absorbates are facing the graphene. The 2b nitrene gives the highest adsorption energies because of the fluorines on the aromatic ring. Finally, the parallel configuration seems to favour adsorption compared to the vertical configuration , which is consistent with reaction energies reported in literature.47 These high values are indicative of a chemical reaction occurring between graphene C PBM data was replaced with SVG by xgml2pxml:<glyph-data id="z.dbd" format="PBM" resolution="300" x-size="8" y-size="10" xml:space="preserve">00000000000000000000000000000000111111110000000011111111000000000000000000000000</glyph-data><svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="13.200000pt" height="16.000000pt" viewBox="0 0 13.200000 16.000000" preserveAspectRatio="xMidYMid meet"><metadata>Created by potrace 1.16, written by Peter Selinger 2001-2019</metadata><g transform="translate 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>C and the nitrogen from the nitrene intermediates to give three atom rings via a [2 + 1] cycloaddition reaction. The most electron deficient nitrene intermediates 2b and 2c seem to react more favourably with the graphene surface than 2a to form g55/3a–c since the Eads for the latter is 60 meV lower than the two others. For instance, 2a is more stable than 2b since the latter bears four electron withdrawing fluorine atoms and is formed at slightly higher energy than 2a  projected onto various carbon atoms (PDOS) illustrated in To achieve a deeper understanding of the changes in transport properties of graphene brought about by chemical functionalization, we analyse in detail the band structure of the systems. ca. 40% of the reaction path with an energy of ca. 2.1 eV corresponding to the splitting of the azylazide into arylnitrene and nitrogen, which in fair agreement with the experimental value of the formation of arylnitrene from arylazide determined in liquid phase 49 – liquid phase effects in experiment will likely reduce the gas-phase energy barrier we determine here. A second transition state corresponding to the approach of arylnitrene to graphene is located at 55% of the reaction path and an energy of 2.0 eV. Finally, a descendent path leads to the final products, which lie at a higher energy with respect to the starting reagents. This confirms that an initial energy activation (by photolysis or thermolysis) is necessary to overcome the energetic barrier of the arylnitrene formation,50 which reacts rapidly with the carbon–carbon double bond from graphene to yield the final products. In experiment, the products are stabilized by the evolution of nitrogen gas and the associated free-energy gain (more than 1 eV at 400 °C), which overcomes the electronic energy cost of the functionalization reaction. It is worth mentioning that in case of the g55/3b adduct the barrier is lower by 14.5 kJ mol−1 (0.15 eV) comparatively to the two others due to electronic effect induced by the fluorine atoms.In order to gain more insights into the path leading to the formation of aziridine–graphene adducts, we determined the NEB profiles for the different reactions . The plo42 The relaxed structures, pictorially illustrated in 2H, –NO2) interact with N–H or C–H groups from the amines through hydrogen bonding. The lengths of such hydrogen bonds are comprised between 1.6 Å and 2.8 Å respectively, being O–H⋯N in the case of N-tetrafluoroaphenyl aziridine and N–H⋯ON in the case of N-nitrophenyl aziridine. Furthermore, as shown in O from the carboxylic acid, respectively. Finally, it is noteworthy that the tertiary amine interacts more strongly with the carboxylic acid group from the phenyl carboxylic acid and perfluorophenyl carboxylic acid. The weakest hydrogen bond was noticed with g55/3c substrate which does not present and acidic group.The sensing properties of the aziridine-appended graphene substrates as materials to construct sensing devices have been investigated using DFT augmented by D3-Grimme for long range dispersion corrections.e on the H closest to the O of the CO2H group can be observed.51 Somewhat larger differences were found for g55/3c where N and the two H closest to the NO2 lost −0.006 and −0.004e, respectively, in favour of the 2H (+0.004e) farthest from the aromatic functionalizer. Finally, for g55/3b, we found that the CO2H group gets a large additional electron charge , yielded −0.05e from N and −0.06 from a H of the methyl groups far from the aromatic functionalizer, corresponding to an induced significant dipole of few tenths of a Debye and therefore to a local drop in electrostatic potential of several tens of mV, sufficiently large to give rise to an experimentally observable effect. Although also the g55/3c pair can be of interest, the g55/3b pair thus seems the most favourable case for sensing as it exhibits the largest adsorption-induced dipole, both in terms of absolute values of the charge differences and in terms of distances between the so-generated charges.Next, we focus on a Lowdin charge analysis following the adsorption process to extract information on the sensing capability of the proposed systems. We analysed the charge density differences between the system before and after adsorption of the tertiary amine as a prototypical case, and found that for g55 substrate only minor differences of −0.0022H and NO2 groups involved in the hydrogen bonding concomitantly with regions of charge depletion (blue colour) on the hydrogen from the NH groups of MA and DMA. In case of the interaction between g55/3c and TMA, the charge depletion occurs on the acidic hydrogen from the graphene substrate, while the charge gain is observed on the nitrogen from the TMA adsorbate. The effect is less pronounced in case of g55/3a with MA and g55/3b where the isovalues of the charge density difference read several times lower than the case of g55/3b with TMA (highest HB energy). These results are in good agreement with the computed thermodynamic data and Lowdin charges.Furthermore, to evidence the interactions between the different amines and the aziridine-modified graphene derivatives, we start from fully relaxed, minimum-total-energy configurations and we compute the charge density difference for the three cases depicted in e.g. in the detection of volatile (short-chain) amines for food safety. In the present work, we show that pristine graphene can be modified with various nitrene intermediates, generated from the decomposition of azides, to yield the corresponding aziridine-modified graphenes, representing a novel path to functionalized graphene materials. Such reactions are thermodynamically favoured and occur with a reaction energy ranging from −1.04 to −1.10 eV. A combined band-structure and PDOS analysis show the opening of an energy band gap yielding a semi-conducting state of graphene, which make it suitable for transistor applications, however pointing to a dependence of this phenomenon upon the density of modifiers as a key parameter. Our modelling finally suggests that some of the resulting materials  can be used to sense short-chain aliphatic amines: their interaction via hydrogen bonding with the functional group anchored onto the graphene surface induce appreciable charge differences upon adsorption which should be experimentally detectable, i.e., generate electrostatic perturbations strong enough to be a good candidate for sensing applications. The concept here explored can be extended to a whole class of host–receptor pairs adsorbed or chemically linked to the graphene surface, thus representing an appealing path to exploit the unique properties of 2D graphene-based materials.Graphene functionalization is of great interest in current physico-chemical research in view of sensing applications, with many potential applications such as There are no conflicts to declare.RA-011-D0RA09964C-s001