Poly(methyl methacrylate) (PMMA) is widely used for graphene transfer and device fabrication. However, it inevitably leaves a thin layer of polymer residues after acetone rinsing and leads to dramatic degradation of device performance. How to eliminate contamination and restore clean surfaces of graphene is still highly demanded. In this paper, we present a reliable and position-controllable method to remove the polymer residues on graphene films by laser exposure. Under proper laser conditions, PMMA residues can be substantially reduced without introducing defects to the underlying graphene. Furthermore, by applying this laser cleaning technique to the channel and contacts of graphene field-effect transistors (GFETs), higher carrier mobility as well as lower contact resistance can be realized. This work opens a way for probing intrinsic properties of contaminant-free graphene and fabricating high-performance GFETs with both clean channel and intimate graphene/metal contact.The online version of this article (doi:10.1007/s40820-016-0093-5) contains supplementary material, which is available to authorized users. Beingctronics –6. UnforTo fabricate graphene field-effect transistors (GFETs), graphene grown by chemical vapor deposition (CVD) need to be transferred from a metal foil to an insulating substrate using a polymer such as poly(methyl methacrylate) (PMMA) as a support layer. PMMA is also commonly used as a mask material for electron beam lithography (EBL). Yet, a thin layer of PMMA residues (1–2 nm) after organic solvent  cleaning cannot be completely removed due to strong physical  or chemical  adsorption effects .2 atmosphere or vacuum [Previous studies show that polymer residues left on graphene surfaces result in shift of the Fermi level and decrease of carrier mobility , 5. Liker vacuum , 10, 11.2 plasma treatment is aggressive and needs to be operated with extremely low plasma density and delicate time control [However, previous studies of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electrical measurements reveal that thermal annealing still cannot remove the polymer residues thoroughly. Furthermore, high-temperature heating process may intensify graphene/substrate and graphene/atmosphere interactions, causing graphene to be highly doped with severe mobility degradation –13. In a control , 18; ult control , 20.Here we propose a new technique using a laser beam to eliminate polymer residues and recover clean graphene surfaces. Our laser cleaning technique, unlike previous methods, can be specially applied to targeted positions without introducing additional contaminants and defects. In the following contexts, detailed descriptions on laser cleaning process and optimization conditions are given. Then the laser cleaning technique is applied to GFETs, which shows that higher carrier mobility as well as lower contact resistance can be realized. Finally, mechanisms of laser cleaning are discussed in three ways: agglomeration, decomposition, and expulsion.2 layer. The CVD graphene films were grown on polycrystalline copper foil  in a gas mixture of methane, hydrogen, and argon at 1000 °C. Then graphene films were transferred to a Si/SiO2 substrate. To describe the process of laser cleaning, both the exfoliated and CVD graphene films on Si/SiO2 substrate were intentionally spin-coated with a 270-nm-thick PMMA layer (Allresist AR-P 679.04), baked at 170 °C for 2 min, cooled to room temperature, and then placed in an acetone bath for 2 h to dissolve PMMA. The number of layers was first characterized by optical microscopy (Olympus BX51) and then confirmed by Raman spectroscopy  and atomic force microscope  in air.Graphene was prepared using both mechanical exfoliation and CVD methods. The exfoliated graphene films were peeled off from natural flake graphite using an adhesive tape (3 M) at ambient conditions and transferred onto a heavily doped Si wafer coated with a 300-nm-thick thermally grown SiOBack-gated GFETs were fabricated in a top-down process. The graphene channels were patterned using e-beam lithography (EBL) followed by inductively coupled plasma reactive ion etching (ICP-RIE). The source (S) and drain (D) electrodes were fabricated by EBL, e-beam metal evaporation, and subsequent lift-off process. The exfoliated and CVD graphene films as the channel were contacted with Ti/Au (10/70 nm) and Pd/Au (20/60 nm), respectively. The structure of GFETs was inspected by optical microscope and AFM at tapping mode. All electrical measurements of GFETs were carried out on a probe station (Signatone WL-210E) using an Agilent B1500A semiconductor device analyzer under ambient conditions.2 substrate were 0.695, 1.041, and 4.826 nm, respectively . The PMMA residues on CVD graphene surfaces were introduced during the transfer process from Cu foil to SiO2 surface.Figure  . Also a piezoelectric multi-axis stage with variable step size  was mounted to locate or scan the graphene samples , which indicates that a nearly complete removal of polymer residues is achieved. The higher the exposure power, the faster the Rq decreases and saturates. However, it may induce defects at higher power . The dotted red boxes indicate the regions where the disorder-induced Raman D peak occurs. Figure −1 indicates that there is no significant damage to the sp2 hybridized carbon structure under a moderate exposure power of 30 mW for 180 s [−1 for monolayer GFETs to realize fast, effective, and noninvasive removal of polymer residues.To save time, we increase the exposure power of laser. The dependence of or 180 s . HoweverThis laser cleaning technique has also been applied to CVD mono-, bi-, and trilayer graphene, as shown in Fig. S3. The polymer residues left on CVD graphene samples are apparently removed, except at the ripples formed in wet transfer process where few residues may still remain due to increased chemical activity at these sites .2 substrate. Figure Vbg of the GFET before and after laser cleaning of the channel. Total resistance in our two-probe measurements is calculated from the transfer characteristics with Vbg swept from −40 to 40 V (Vds = 0.1 V). The as-fabricated GFET exhibited a shift of the charge neutrality point  to 26.4 V, owing to the hole doping by polymer residues from EBL process [Rtotal is the total resistance; Rcontact is the contact resistance; L and W are the channel length and width, respectively; μ is the carrier mobility; n0 is the carrier density at the Dirac point; n = Cbg(Vbg−VD) is the carrier density away from the Dirac point; and Cbg is the back-gate capacitance. There is a good agreement between measured data and theoretical fits as shown in Fig. 2 (Vs)−1, respectively. The electron–hole asymmetry is generally attributed to charge transfer at the interface of graphene/metal contact, which forms p–n or p–p junctions for electron or hole cases and results in different transport properties [VD shifted to 7.6 V, indicating reduction in hole doping. The near-zero yet non-zero VD is attributed to oxygen or moisture adsorption from ambient atmosphere [2 (Vs)−1, respectively. We measured eight GFETs before and after laser exposure. Histogram of electron (red) and hole (blue) mobility of these GFETs is shown in Fig. In the following, we demonstrate how this laser cleaning technique can be harnessed to remove PMMA contaminants from the graphene channel and graphene/metal contact in GFETs. For clarity, the effects of laser cleaning on graphene channel and contact were investigated independently. For the case of laser cleaning of the graphene channel, an exfoliated monolayer graphene was contacted by Ti/Au 10/70 nm) electrodes via EBL and lift-off metallization process to form a GFET. Figure  process . The ele process , 30:Fig.operties , 32. Aftmosphere , 33, 34./70 nm elThe laser cleaning technique can also be used to remove the polymer residues from the contact regions of GFETs as defined by EBL prior to metal deposition. The previous thermal or current annealing methods, however, are not possible to remove the residual PMMA layer that is already covered by metal. To form intimate graphene/metal contact without polymer residues, generally there exist two kinds of processes in previous reports: the resist-free process and the resist-involved process. However, the resist-free process includes complex steps of non-polymer mask fabrication and alignment , 35. The2 substrate by a PMMA layer and cut into a 1.4-μm-wide strip via EBL and inductively coupled plasma (ICP) etching. Then subsequently EBL was re-performed to define the electrode array. As shown in the middle inset of Fig. 12 and GFET34 with Vbg grounded. The device structure is shown in the lower inset of Fig. 12 with uncleaned contacts, the Id–Vd curve of GFET34 with cleaned contacts exhibits a steeper slope indicating a lower total resistance. As the two GFETs are fabricated adjacently from a same graphene strip with nearly identical geometry, the reduction in contact resistance is supposed to be the main contributor to the reduction in total resistance. Contact resistance, extracted from total resistance  is 390.1 and 87.8 Ω μm for uncleaned and cleaned GFETs, respectively. We measured five GFET groups with similar structure using the above local cleaning process. Figure CVD monolayer graphene was used to demonstrate the laser cleaning effects on contacts. The cleaning process at graphene contacts is as follows: first, a CVD graphene was transferred onto a SiOectively , 37. As It is worth noting that this laser cleaning technique may also be used in contact area with size smaller than 1 μm. The contact region shown in Fig. Besides PMMA residues, our laser cleaning is also effective for other polymer residues, such as novolak-based negative resist (AR-N 7520). After cleaning by 532 nm laser at 30 mW for 180 s, the residual negative-resist residues can also be completely removed, as shown in Fig. S4.Rq, as shown in Fig. 2, CO, CO2, CH4, C2H4) in trace amounts [The mechanism of our laser cleaning process can be understood based on laser ablation phenomenon and PMMA behavior under laser exposure. Laser ablation (commonly by ultraviolet or near-infrared pulse lasers) has been widely used and thoroughly investigated for polymer micro-machining since the early 80s . Here we amounts , 46, 47.On the other hand, during photon absorption, polymer residues not only gain energy but also momentum. Driven by monomer vapor pressure as well as laser light pressure, expulsion of liquid PMMA particles or even ejection of solid PMMA fragments occurs, thus facilitating removal of polymer residues , 48, 49.In summary, we have proposed a facile and reliable technique to remove polymer residues on graphene surfaces without generating defects using a visible laser from Raman system. After laser cleaning of the channel in GFETs, carrier mobility has been improved by a factor of 1.5–2.6. Moreover, this technique can be particularly applied to the contact regions as defined by EBL prior to metal deposition to eliminate the polymer residues, which is impossible by previous annealing methods. The contact resistivity of GFETs with cleaning at contacts can be reduced to 1/5–1/3 of those of GFETs without cleaning. This work provides an efficient route to get access to intrinsic properties of polymer residue-free graphene and fabricate high-speed GFETs with high carrier mobility and low contact resistance.Supplementary material 1 (PDF 805 kb)Below is the link to the electronic supplementary material.


Here we report on a miniaturized optical interferometer in one fiber based on two mismatched nodes. The all-fiber structure shows stable performance of temperature and humidity sensing. For temperature sensing in large ranges, from 40 to 100 °C, the sensor has a sensitivity of 0.24 dB/°C, and the adjusted R-squared value of fitting result reaches 0.99461 which shows a reliable sensing result. With carbon nanotubes coating the surface of the fiber, the temperature sensitivity is enhanced from 0.24561 to 1.65282 dB/°C in a small region, and the performance of humidity sensing becomes more linear and applicable. The adjusted R-squared value of the linear fitting line for humidity sensing shows a dramatic increase from 0.71731 to 0.92278 after carbon nanotube coating, and the humidity sensitivity presents 0.02571 nm/%RH. The detection of environmental parameters, including physical and chemical changes, has become increasingly important for process control, security monitoring, and human protection. Temperature and humidity are the key parameters in these applications because of their great influence on food safety, manufacturing accuracy, and the service lives of precise instruments. Various methods have been used for temperature or humidity sensing, such as physical methods ,2,3,4,5,2-hybridized carbon atoms [Carbon nanotubes (CNT), which were first discovered by Iijima in 1991, are known as 1D nanostructures with spon atoms . The stron atoms . CNT maton atoms ,26. Beneon atoms ,29,30,31A mismatched structured fiber was successfully fabricated to serve as our miniaturized optical fiber interferometer (MOFI). The offset of the two single fibers was around 20 μm, and the distance between the two nodes was about 2 cm. The multi-walled CNT were bought from a commercial corporation. The CNT were dispersed in ethanol solvent and attached to the fiber structure using the drop-cast method. In order to make sure that the CNT adhered to the fiber firmly, an annealing process was conducted from the temperature of 100 °C to room temperature (24 °C).To test the performance of the achieved mismatched fiber, and to explore the diverse potential applications based on light modulation by environment change, the experiments and comparison between the bare mismatched fiber and the CNT-assisted mismatched fiber were conducted on temperature and humidity sensing. The range of the temperature was controlled between 40 and 125 °C at an interval of 5 °C. The relative humidity (RH) sensing experiment was conducted by tuning RH between 45% and 95% at an interval of 10% at room temperature (24 °C). For each testing step of temperature and RH, extra observation time of 25 min was guaranteed to make sure that the results were stable and reliable. A wideband laser device (1300–1650 nm) was utilized as the light source, and the optical spectrum analyzer was used for spectra capture. The simulation work of the mismatched fiber structure was conducted, and the results are shown in Based on the MOFI structure, we can realize sensing performance through tuning light interference between the core mode and cladding modes which can be stably excited in the mismatched fiber structure. L is the interference length.L in Equation (3)), the wavelength shifting can also be attributed to alteration of the RI difference between core mode and cladding modes. The interference intensity will also be influenced by energy redistribution of core mode and cladding modes which is induced by RI change of fiber core and cladding. Based on the observation in the experiment process, the fiber condition can be stabilized within 90 s following the external environment change, which means that the response time of temperature sensing can be estimated to be 90 s. The sensitivity is calculated to be 0.2165 nm/°C which is almost four times higher than 0.0575 nm/°C reported by Dong et al. [The destructive interference condition is shown in the following equations :(2)2π⋅(ne rising . Howevere rising . This meg et al. . It was To increase the sensitivity of temperature sensing performance, the CNT material was utilized to alter the cladding modes modulation of the MOFI structure. As can be seen from Based on cladding modes modulation, this mismatched fiber structure can also be used for humidity sensing, as shown in Based on the above results, it is manifested that both the core mode and cladding modes can be excited in the mismatched fiber structure. This structure shows good and stable sensing performance of temperature and humidity which is due to the modulation of cladding modes by the external environment. Due to the dominant cladding modes, the all-fiber sensor shows good sensing reliability and sensitivity.In conclusion, a mismatched fiber structure was successfully created and simulated that demonstrated its application for sensing temperature and humidity based on cladding modes modulation. The sensing experiments were conducted with the structured fiber, and it displayed good temperature and humidity sensing performance. With CNT attached to the fiber, the sensitivity of temperature detection in small ranges was enhanced from 0.24561 to 1.65282 dB/°C, and the humidity sensing became more reliable for real application. The combination of the manufactured MOFI structure and CNT achieved cost-effective, sensitive, and reliable sensing for both temperature and humidity.


Discourse and argumentation are effective techniques for education not only in social domains but also in science domains. However, it is difficult for some teachers to stimulate an active discussion between students because several students might not be able to develop their arguments. This paper proposes to use WordNet as a semantic source in order to generate questions that are intended to stimulate students’ brainstorming and to help them develop arguments in a discussion session. In a study including 141 questions generated by human experts and 44 questions generated by a computer system, the following research questions have been investigated: Are system-generated questions understandable? Are they relevant to given discussion topics? Would they be useful for supporting students in developing new arguments? Are understandable and relevant system-generated questions predicted to be useful for students in order to develop new arguments? The evaluation showed that system-generated questions could not be distinguished from human-generated questions in the context of two discussion topics while the difference between system-generated and human-generated questions was noticed in the context of one discussion topic. In addition, the evaluation study showed that system-generated questions that are relevant to a discussion topic correlate moderately with questions that are predicted as useful for students in developing new arguments in the context of two discussion topics and understandable system-generated questions are rated as useful in the context of one specific discussion topic. An argument is an artifact that is created to articulate and justify claims, explanations, or viewpoints, and argumentation is the process of generating these artifacts  and Freebase (https://www.freebase.com/) to facilitate learners’ self-directed learning. Using this system, students in self-directed learning are asked to build a timeline of events of a history period with causal relationships between these events given an initial document. The student develops a concept map containing a chronology by selecting concepts and relationships between concepts from the given initial Wikipedia document to deepen their understanding. While the student creates the concept map, the system also generates its own concept map by referring to semantic information from DBpedia and Freebase. The system’s concept map is updated with every modification of the student’s one and enriched with related concepts that can be queried from both linked open data sources. Thus, the system’s concept map always contains more concepts than the student’s map. Using these related concepts and their relationships, the system generates questions for the student to lead to a deeper understanding without forcing to follow a fixed path of learning.In contrast to traditional approaches to generating questions using text as input and deploying various natural language processing techniques for creating questions, the fifth class of educational applications of question generation exploits linked open data that are a part of the semantic web  With respect to the technical issue, while Jouault and Seta adopted ontology and linked open data techniques to eliminate the difficulty of the natural language understanding problem in the learning domain , this paper suggests an approach to deploy natural language techniques  in order to extract important concepts from a discussion topic and using WordNet to query related concepts that are relevant for discussion; 2) With respect to learning goals, Jouault and Seta proposed to use automatic generated questions for enhancing students’ knowledge in history whereas our approach focuses on helping students develop new arguments for the argumentation process.The catastrophe at the Fukushima power plant in Japan has shocked the world. After this accident, the Japanese and German governments announced that they are going to stop producing nuclear energy. Should we stop producing nuclear energy and develop renewable energy instead?In this section, we describe conceptually how questions can be generated in our approach. A more detailed technical description of the approach is presented in Le et al. . In ordecatastrophe, Fukushima power plant, nuclear energy, renewable energy. This step is described in more details in the following subsection.From the discussion topic, we note that the following noun phrases can serve as starting points to generate questions: In order to automatically recognize key concepts of a discussion topic, a natural language parser is used to analyze the grammatical structure of a sentence into its constituents. The language parser analyzes a text and identifies the category of each constituent . This parsing process results in a parse tree. Since nouns and noun phrases can be used as key concepts in a discussion topic, we select from the parse tree of the parsed discussion text only constituents which are tagged as nouns (NN) or noun phrases (NP) cf. Fig. . Since tWhat does <X> remind you of?What are the properties of <X>?What is an example of <X>?Using the extracted key concepts, we are ready to generate questions. The next issue that needs to be addressed is to determine the types of questions to be generated. According to Wilen , there ehttps://www.wikipedia.org/) provides descriptions of concepts. While Wikipedia might contain incorrect information due to its contribution mechanism, one of the advantages of Wikipedia is that the description of many concepts is available in many different languages. If we want to develop a question generation for different languages, Wikipedia might be an appropriate source. WordNet  responded to Europe's debt crisis by flooding banks with cheap money…ECB President has reduced the main interest rate to its lowest level in history, taking it from 0.5 to 0.25 percent” , this might make it difficult for discussion participants to initiate a discussion or for human experts to think of questions to be generated:From our eight experts, we received 54 questions for topic 1, 47 questions for topic 2, and 40 questions for topic 3.For each discussion topic, the system generated several hundred questions , because from each discussion topic several key concepts were extracted, and each key concept was extended with a set of hyponyms queried from WordNet. For each key concept and each hyponym, fourteen questions have been generated based on the question templates in Table Then, we mixed human-generated questions with automatic generated questions and asked human raters to identify whether each question from the mixed set of questions had been generated by the system or by a human expert. For topic 1, we had three raters, and for each of the last two topics, we could only get two raters. Note that these human raters were not the same human experts who generated questions. Also, they did not know about the proportion between human-generated questions and system-generated questions.Is that an automatic system-generated question (Yes/No)? We use the balanced F-score to evaluate and to analyze the ratings of humans. The F-score is calculated based on precision and recall using the following formula:First, we evaluated the soundness of system-generated questions. For this purpose, we asked human raters to answer the following question: F-score is high, it shows that the system-generated questions and the human-generated questions are easy to distinguish. Otherwise, a low F-score indicates that it is difficult for human raters to distinguish between system-generated and human-generated questions.The precision for a class is the number of true positives  divided by the total number of elements labeled as belonging to the positive class, while the recall for a class is the number of true positives divided by the total number of elements that actually belong to the positive class. If the F-scores of each human rater. It shows that for topic 1, it was difficult for rater 1 (F = 0.33) and moderately difficult for rater 2 (F = 0.51) to distinguish the authorship of questions. The kappa value (0.086) indicates a low agreement between two raters—which means that even if each of the graders correctly classified some questions, their ratings would not be consistent with each other. With respect to topic 2, the F-score of both raters is moderate (0.5 and 0.52). The Kappa value for their agreement was 0.233, which can be considered as fair. This shows that for topic 2, it was easier to distinguish between human-generated and system-generated questions than in the context of topic 1. With respect to topic 3, for both raters, it was relatively difficult to identify the authorship of the questions (F-score is between 0.40 and 0.44) and the agreement between the raters was fair (0.263).Table What is cheap money?” was generated by a human expert and by the system identically. This question was assumed by both human raters as a system-generated question. Thus, this question was not included in the statistical evaluation for topic 3.Interestingly, in the context of topic 3, one question “In summary, we have learned that for all raters it was not easy to identify system-generated questions from the set of mixed questions. This indicates that system-generated questions are sound as human-generated questions. The agreement between raters was slight or fair. This strengthens the indication that it was difficult for human raters to distinguish between system-generated and human-generated questions.The goal of the following evaluation is to empirically investigate the first three research questions specified in the “The first three research questions were also given literally to human raters who were asked to rate the mixed set of questions using the scale from one to three scores . First, we investigate these research questions in the context of each specific discussion topic, then we normalize the evaluation result for each topic and investigate these research questions in general.In the context of topic 1, Table What do you have in mind when you think about tsunami?What do you like when you think of/about catastrophe?What does Fukushima remind you of?What does power plant remind you of?What features does catastrophe have?Analyzing the system-generated questions in the context of topic 1, we learned that there was no question that was rated with score 1  on average. The list of system-generated questions that have the rating score of 1.33 on average with respect to “Usefulness” follows:Should we stop producing nuclear energy and develop renewable energy instead”). If the questions were more specific, for example, “What does the catastrophe at the Fukushima power plant in Japan remind you of?”, this could be more useful.The low usefulness of these questions might be attributed to the fact that these questions are very general and have little relation to the question in the discussion topic 1 (“t = 3.01), relevance (t = 3.93), and usefulness (t = 3.29). Thus, the research hypothesis that system-generated questions are understandable, relevant to a given discussion topic, and useful for developing new arguments as human-generated questions cannot be confirmed in the context of topic 2.In the context of topic 2, Table deflation be used today?” It is not common for us that deflation can be “used” (unless we are economy experts). The other problem with these questions is that these “non-meaningful” nouns/noun phrases are extracted from the discussion topic  and from the hyponym set provided by WordNet . This is a limitation of the question generation approach presented in this paper. In the current version, the system is not implemented with a mechanism to identify meaningful noun phrases from the set of noun phrases that are extracted from a discussion topic and from the hyponym set of WordNet.We investigated the system-generated questions which had least mean score, i.e., the rating mean score over the raters is 1. Table Similar to topic 1, in the context of topic 3, Table (opposite-) problems” that is generated by the system using a pre-specified question template. The question could be more understandable if it were constructed like this: “How could problems of the central bank be stopped?” Thus, the pre-specified question template should be optimized accordingly. The problems with the two least relevant questions can be explained by the noun phrases “ECB president” and “central bank” that are not as relevant as other noun phrases “debt crisis” and “cheap money” in topic 3. Again, the problem here is to determine the most important noun phrases in a discussion topic before applying question templates for constructing questions. The least useful question “What features does ECB president have?” was also rated as least relevant. In In the “We analyze the system-generated questions with the lowest scores. We identified one least understandable, two least relevant, and one least useful question(s) Table . The leaWhat is cheap money?” that was generated identically by a human expert and by the system was rated by both human raters as very understandable. However, with respect to the criteria “Relevance” and “Usefulness”, there was disagreement between raters as Table The question “Overall, when considering the quality of system-generated questions over all three topics, we can learn from Table In this section, we investigate the fourth research question: Are understandable and relevant system-generated questions also useful for students?r = 0.76). A similar tendency can be found for human-generated questions (r = 0.81). Both correlation values are significant. However, the understandable system-generated questions are weakly correlated with the criterion of usefulness (r = 0.31), whereas for human-generated questions the correlation between the criteria understandability and usefulness is higher (r = 0.57).In the context of topic 1 . Yet, correlation values show that understandable questions (either system-generated or human-generated) are moderately correlated with the criterion of being useful questions (r = 0.52–0.53) and these correlation values are significant.In contrast to topic 1, in the context of discussion topic 2 (cf. Table r = 0.39–0.43). However, it indicates a weak relationship between understandable questions and useful questions. The correlation between the relevance of a question and its usefulness (r = 0.53–0.62) is moderately positive and means there is a tendency that relevant questions will be useful for students. Note, except the correlation coefficient between the criteria understandability and usefulness for system-generated questions, all other correlation values are significant.In the context of topic 3  are significantly correlated with useful questions, except the system-generated questions for topic 3. Relevant questions (both system-generated and human-generated questions) are significantly correlated with useful questions, except for topic 2.The question generation approach has been evaluated using three discussion topics from the domains of energy (topic 1) and economy (topics 2 and 3). Each topic was presented by two sentences that describe the problem of a topic, followed by a discussion question. With two discussion domains, we still cannot conclude about the coverage of scope of discussion domains that can be supported by the question generation system using WordNet. However, the results of the evaluation study give us some information about the quality of system-generated questions. In the context of topic 1, the human-generated questions were not significantly better than system-generated questions over three criteria “Understandability” and “Relevance” . In the context of topic 3, the difference between human-generated questions and system-generated questions was not significant over three criteria. Only in the context of topic 2, which is about increasing fear of deflation in Europe and US, the difference between human-generated and system-generated questions was statistically significant, i.e., the quality of human-generated questions was better than of system-generated questions. Of course, the effectivity of our approach relies on the set of hyponyms provided by WordNet and on the accuracy of the algorithm that extracts nouns/noun phrases from a discussion topic.In the current implementation of the system, the algorithm for extracting nouns/noun phrases from a discussion topic has the limitation that it is not able to rank the importance of a noun/noun phrase. In order to determine the relevance of a concept, several effective approaches have been devised in the area of information retrieval, e.g., document frequency  for evaluation without having clear selection criteria. The small number of selected system-generated questions and the ratio 1:3 between system-generated questions and human-generated questions might not reflect fully the quality of system-generated questions. We might think of increasing this ratio. Yet, possibly too many system-generated questions might bias human graders—this needs to be investigated.This paper presented a question generation approach using WordNet for supporting students during argumentation processes. The approach extracts important concepts from a discussion topic and query hyponyms of these concepts from WordNet. Questions are constructed by either using important concepts from a given discussion topic or using hyponyms of the extracted concepts.Although the evaluation results show that system-generated questions were as sound as human-generated questions in two discussion topics, the question generation approach presented in this paper certainly still has some limitations. First, it generates too many questions for a discussion topic. Second, the algorithm for extracting relevant concepts is not yet able to determine the grade of importance for each noun/noun phrases. These two issues are our short-term future work.As long-term future work, we intend to use system-generated questions and human-generated questions of highest quality to test whether they are actually useful for students in the argumentation process. After that, we intend to identify and model characteristics of useful questions for argumentation purposes. Using this model, appropriate question templates will be defined for question generation.


In earlier studies, much research has focused on increasing the efficiency of heat exchanger fields. Therefore, in this study, graphene nanofluid was fabricated for use as a heat transfer medium for a heat exchanger. Graphene has excellent electrical conductivity, mechanical properties, and heat transfer properties. It is expected that the heat transfer efficiency will be improved by fabricating the nanofluid. However, graphene is prone to sedimentation, because of its cohesion due to van der Waals binding force. In this experiment, a nanofluid was fabricated with enhanced dispersibility by surfactant and the ball-milling process. The zeta potential, absorbance, and thermal conductivity of the nanofluid were measured. As a result, when using the ratio of 2:1 (graphene:sodium dodecyl sulfate (SDS)), a higher thermal conductivity was obtained than in other conditions. As the industry has developed, heat exchangers have been increasingly used in a variety of fields, including food, cooling and heating, shipbuilding, and chemistry. Thus, if the efficiency of the heat exchanger can be increased, the energy consumed and the generation of carbon dioxide can both be reduced ,2. Commo2/g and purity of 99.9% was purchased from Graphene supermarket, and surfactant SDS and SDBS were purchased from Junsei Chemical Co., Ltd.  (SDS), TOKYO Chemical Industry Co., Ltd.  (SDBS) was used. First, 0.1 g of graphene was pulverized with a ball size of 1 mm, a ball-milling speed of 200 rpm, and a ball-milling time of 60 min using (a) the planetary ball mill instrument. After that, the ratio of graphene (0.1 wt %) dissolved in the water and the surfactant SDS and SDBS were prepared for adding in ratios of 1:3, 1:2, 1:1, 2:1, and 3:1. Furthermore, ultrasound excitation was carried out for 40 min to make the graphene nanofluids, and the degrees of nanoparticle dispersion were measured by using UV spectroscopy.In this study, DW (distilled water) was used for the base fluids that were produced through the membrane-type DW maker, which maintained a water quality under 10 ppm for the total dissolved solids (TDS). Graphene with 7-nm thickness and a 40-nm size with a specific surface area of 100 mThe equipment used in this experiment is shown in The thermal conductivity measuring system LAMBDA in A graph of the zeta potential, which was measured using a ZetaSizer Nano ZS instrument, is shown in The mean thermal conductivity of the graphene nanofluids according to the amount of surfactant added is shown in In this study, graphene was grinded using a planetary ball mill instrument to stably disperse and the graphene nanofluid; (0.1 wt %) graphene nanofluid was prepared by adding surfactant to each condition. In order to measure the dispersion and dispersion stability, the zeta potential and the absorbance through UV were measured. The thermal conductivity was measured using the transient hot-wire method, and the following conclusions were obtained.(1)The absorbance was measured to confirm the dispersibility. The highest absorbance was obtained when 0.3 g of SDS and SDBS were used, and the lowest absorbance was obtained when 0.034 g of SDS and SDBS were used. As a result, as the surfactant ratio increases, the nanofluid containing SDS and SDBS produced higher absorbance values.(2)The zeta potential was measured to figure out the dispersion stability. Absolute values of 30 mV or more were obtained under all of the conditions, and it could be judged that the value of the dispersion stability was sufficiently high. In this experiment, SDBS showed that the zeta potential value was higher than SDS, and had a higher dispersion stability as the amount of surfactant was increased.(3)The thermal conductivity was measured in comparison with distilled water. Graphene nanofluid with SDS added showed a higher thermal conductivity than when SDBS was added. SDS showed a higher thermal conductivity than distilled water at the ratio of graphene to surfactant of 2:1 (0.05 g) and 3:1 (0.034 g) and generally, SDBS showed a lower thermal conductivity than distilled water at all of the conditions. When the mean thermal conductivity of the two surfactants was compared, SDS showed a higher increase in thermal conductivity than the SDBS as the amount of surfactant decreased. When the ratio of graphene to SDS was 2:1 (0.05 g), it showed the highest thermal conductivity. As a result of thermal conductivity measurement, it was confirmed that the thermal conductivity becomes smaller according to the amount of the surfactant.


Efficient reduction of graphene oxide to obtain high-quality graphene nanosheets is desirable for energy storage, catalysis, electronics and environmental remediation. In this brief review, we mainly focus on the microwave-assisted production of reduced graphene oxide in three categories: (1) microwave-assisted chemical reduction of graphene oxide; (2) microwave-assisted thermal reduction of graphene oxide; (3) microwave-assisted simultaneous thermal exfoliation & thermal reduction of graphite oxide. We also summarize common techniques for characterizing reduction efficiency and quality of as-obtained rGO. In general, there are mainly two strategies used for graphene oxide reduction: chemical reduction and thermal reduction, both of which are facing certain challenges. In chemical reduction methods, the reduction efficiency is unsatisfactory, requiring long treating time and yielding rGO with oxygen content usually higher than 15%  pattern of graphene/graphite oxide usually shows a characteristic diffraction peak at 2θ = 10.9° with the corresponding d-spacing of 0.81 nm  could help to obtain qualitative and quantitative analysis results of the content of oxygenated groups. For example, the carbon/oxygen atomic ratio (C/O ratio) could be evaluated from the areas of C1s and O1s peaks and the atomic sensitivity factor. Usually, the C/O ratio of graphene oxide is ~2.2–2.7  solution. Zhao et al.  is usually required, which is not only very energy consuming but also leads to the formation of defects in the graphene basal plane because of the evolution of the oxygen functional groups during reduction, like nanoscopic holes brought by carbon loss as CO or CO2 and Stone-Wales types of defects lead by rearrangement of carbon atoms in the graphene basal plane. Besides, the reducing efficiency is always suppressed by the highly stable ether and carbonyl groups formed between the oxygen functional groups.In conventional thermal reduction process, long-time high-temperature treatment in a protecting atmosphere  of rGO prepared by 800°C annealing. They further examined the Raman spectra of graphene-triggered microwave reduction at different positions, and found the part of graphene oxide located nearest to the trigger was not reduced the best, as shown in Jiang et al.  further Instead of putting a small piece of graphene as the trigger, Wan et al.  put a fuD/IG in the Raman spectrum of the product decreased from 2.89 to 1.56 and C/O derived from XPS results increased from 7.8 to 17.5. In addition, microwave-enabled exfoliation leading to thinner pieces was also observed in their work.Low-temperature reduction of graphene oxide is of great importance when graphene oxide film was deposited on glass or plastic substrates. Han et al.  demonstrD/IG values, the high C/O values and the conductivity values of most as-derived rGO. It is worth to note that rGO containing only 4% oxygen and exhibiting pristine CVD graphene-like features in the Raman spectrum was successfully fabricated via this reducing strategy. Besides, owning to the ultra-rapid treating process, protecting atmosphere is not always necessary. However, too long treatment time would result in re-oxidation and consequently rGO with worse quality when the reduction is done in the air. Since the amounts of GO samples and the microwave heating chambers in different work were different, which would affect the power intensity imposed on the GO, it is also difficult to draw a conclusion regarding the effect of microwave power here.The characteristics of the as-obtained rGO products derived from different microwave-assisted thermal reduction of graphene oxide methods are summarized and listed in −1.Beside of direct reduction of graphene oxide to yield rGO, thermal shock like flash-assisted simultaneous exfoliation and reduction of graphite oxide at temperatures up to 1,050°C has also been used. Theoretically, microwave heating which is well-known for its rapid heating feature is very promising in enabling simultaneous exfoliation and reduction of graphite oxide. In 2010, Zhu et al.  treated Under microwave irradiation, graphite oxide itself might not be heated to a high enough temperature to cause its exfoliation and reduction efficiently due to its inferior microwave absorption ability. Scientists have tried several ways to come over this problem.2+Ar (1:9) showed a C/O ratio of 3.6, 11.45, 18.5, respectively and ID/IG values of 0.853, 0.842, and 0.785, respectively in Raman spectra, respectively. The rGO prepared in Ar, H2+Ar showed a conductivity of 7.41 × 102 and 1.25 × 103 S m−1, respectively. Hydrogen containing atmosphere is the most effective because H2O was formed instead of CO2, which prevents the formation of vacancies and defects due to the loss of carbon atoms.Park et al.  mixed gr4 at 95°C for 2 h, and subsequently made into a film, which was microwave irradiated at 5.8 GHz with a power of 1,400 W for 10 min in N2. After NaBH4 treatment, a C/O value of 3.84, an ID/IG value of 1.05 in Raman, and a conductivity of 1.41 × 102 S m−1 were obtained. During the microwave treatment, the sample expanded to a loose floc and transmitted bright orange light, leading to ultrathin sheets with a C/O ratio of 10.33, an ID/IG ratio of 1.07 in the Raman spectrum and a conductivity of 1.19 × 104 S m−1. Sole microwave irradiation at 5.8 GHz with a power of 1,400 W for 10 min without a preceding chemical reduction process gave yield to a C/O of 7.24 and an ID/IG of 0.89 in Raman spectrum. This demonstrated that solid-state microwave irradiation not only removed oxygen-containing groups, but also repaired defects on the graphene sheets while NaBH4 though effective for removing oxygen-containing groups may induce more defects. Further, through XPS analysis of content of C-O and C = O groups, they found that microwave irradiation removed C = O more readily than C-O while the chemical reduction method removed C-O more efficiently.Wen et al.  applied 2 without becoming red. The expanded graphite oxide had a C/O of 2.42. However, it was so loose that microwave could not concentrate on a definite area for further reduction of graphite oxide. Hence, in the second step, the expanded graphite oxide was collected and then exposed to additional microwave irradiation for 1 and 2 min, resulting in rGO showing a C/O ratio of 5.78 and 10.39, respectively.Pokharel et al.  developeD/IG values, mass loss temperatures and conductivities, simultaneous exfoliation and reduction was not able to yield rGO with as high quality as those obtained from thermal reduction of graphene oxides. However, when combined with reducing atmosphere  or pretreatment with strong reducing reagents (NaBH4), the reduction degree could be greatly enhanced.The characteristics of the as-obtained rGO products derived from different microwave-assisted simultaneous thermal exfoliation and reduction of graphite oxide methods are summarized and listed in It is expected that the explored methods for microwave-assisted reduction of graphene/graphite oxide into high-quality rGO could be extended to fabrication of graphene composites. The microwave-induced arc facilitated short reaction time at high temperature is not only beneficial for getting high-quality rGO, but also promising in facilitating the formation of high-quality nanomaterials  with advanced performance. In addition, the methods could be extended to fabrication of other conductive materials that could trigger sparks under microwave irradiation, like graphene does.All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


LINE‐1 or L1) reactivation is linked to poor prognosis in non‐small‐cell lung carcinoma (NSCLC), but the molecular bases of this response remain largely unknown. In this report, we show that challenge of human bronchial epithelial cells (HBECs) with the lung carcinogen, benzo(a)pyrene (BaP), shifted the L1 promoter from a heterochromatic to euchromatic state through disassembly of the nucleosomal and remodeling deacetylase (NuRD) complex. Carcinogen challenge was also associated with partial displacement of constituent proteins from the nuclear to the cytoplasmic compartment. Disruption of NuRD corepression by genetic ablation or carcinogen treatment correlated with accumulation of L1 mRNA and proteins. Mi2β bound directly to the L1 promoter to effect retroelement silencing, and this response required the DNA‐ and ATPase‐binding domains of Mi2β. Sustained expression of L1 in HBECs was tumorigenic in a human–SCID mouse xenograft model, giving rise to tumors that regressed over time. Together, these results show that functional modulation of the NuRD constituent proteins is a critical molecular event in the activation of L1 retrotransposon. L1 expression creates a microenvironment in HBECs that is conducive to neoplasia and malignant transformation.Long interspersed nuclear element‐1 ( BaPbenzo(a)pyreneHBECshuman bronchial epithelial cellsLine‐1/L1L1)long interspersed nuclear element‐1 L1 is ~6 kb and consists of an internal promoter located within the 5′untranslated region (5′UTR), two open reading frames (ORFs) encoding ORF1p and ORF2p, and a 3′UTR with a poly(A) tail and signal  at 711 (t/c), both of which differentiate Ta‐1d from the Ta‐Ind, Ta‐0, and Pre‐Ta families  or trans‐ (minor) preference to bind L1 mRNA or SINEs and other cellular mRNAs, to form ribonucleoprotein particles (RNPs) pyrene (BaP) through a process that is orchestrated by the aryl hydrocarbon receptor (AHR) and retinoblastoma (RB) family of proteins to influence the epigenetic machinery , as seen in non‐small‐cell lung cancers (NSCLCs)  through a signaling cascade initiated by TGF‐β1  multiprotein complex is enriched in the 5′untranslated DNA sequence of L1 in human and murine cells. Further, genetic ablation of RB proteins destabilizes interactions within the NuRD complex, and mediates nuclear rearrangement of Mi2β, an ATP‐dependent helicase subunit with nucleosome remodeling activity ; methyl‐CpG‐binding domain proteins 1/2/3 (MBD1/2/3); metastasis‐associated proteins 1/2/3 (MTA1/2/3); histone‐binding proteins , histone deacetylases 1/2 (HDAC1/2), and nuclear zinc finger proteins (Gata2a/2b(p66α/β))  vector using infusion cloning and primers listed in Table CTR or pB015WT using Lipofectamine, as previously described. The pB015WT and pB001CTR  vectors were used to create stably transfected HBECs constitutively expressing L1‐ORF1 and ORF2 proteins, as confirmed by indirect immunofluorescence.Mi2β wild‐type (WT) and a biologically inactive W508A chromodomain mutant were kind gifts from J. Hagman at the University of Colorado . A polyclonal antibody against L1‐ORF1 generated by New England Peptide and validated in previous studies was used in all experiments  is a nontransformed HBEC line immortalized with a replication‐defective SV‐40/adenovirus 12 hybrid . Despite the presence of T‐antigen in replication‐defective lines . Chromatin immunoprecipitation assay (ChIP) was conducted as described before , vortexed briefly, and incubated at room temperature for 15 min with gentle rotation. The eluate was combined with 20 μL of 5M NaCl and incubated at 65 °C for 4 h to reverse formaldehyde cross‐linking of DNA/protein complexes. DNA was recovered by phenol/chloroform extraction and ethanol precipitation. DNA was resuspended in nuclease‐free H2O and quantified by Cytation 3 machine. Serial dilutions were completed to confirm a linear relationship while accounting for proper amplification of template to ensure equal amounts of starting template for all samples. RT‐PCR was used to determine enrichment for L1‐5′UTR sequences using tiling primers (P1‐P4) that span the 5′UTR promoter region of L1. The specificity of NuRD target recognition was examined in previous studies  supplemented with protease and phosphatase inhibitor cocktails (Cat#: 539‐134‐1SET) before being scraped and pelleted for 5 min at 800 g at 4 °C and resuspended in DPBS. Two 500‐μL aliquots of lysate were set aside for RNA analysis and input control. A total of 500 μL of lysate was resuspended in FAIRE lysis buffer  and sonicated as described for 30 sec and cooled in ice for ~5 min. Unbound DNA and DNA cross‐linked to proteins were separated by phenol/chloroform extraction. Unbound DNA in the aqueous phase was ethanol precipitated with 1/10 of 3M sodium acetate (NaAc) and 2.5X of 95% ethanol (ETOH) overnight followed by centrifugation at 14000 g for 20 min. DNA was washed with 70% ETOH once, air‐dried, and resuspended in 50 μL of sterile nuclease‐free H2O. Total DNA was quantified and serial dilutions of 2.5, 5, and 10 ng used for RT‐PCR analysis using a primer set (P4) that spans the CpG shore region of the L1 promoter . Total gDNA for use as input control was isolated using Purelink genomic DNA isolation kit (Cat#: K1820‐01).Formaldehyde‐assisted isolation of regulatory elements (FAIRE) was used to study m HEPES/150 mm NaCl, pH 7.05). Retroviral packaging vectors (pSPAX‐2 and pVSV‐G) were a kind gift from Schenten at the University of Arizona . An aliquot of 42 μL of PEI (1.0 μg/μL) was added to each transfection and incubated at room temperature for 15 min. DNA/PEI complexes were added to the cells and incubated for 18 h. Transfection media were removed and new media containing 10% FBS added. The viral supernatant was collected the next day and filtered through 0.45‐μm PES filter tubes. Viral titer was incubated with one volume of X‐concentrator (Clontech) overnight and centrifuged at 1500 g for 45 min. The supernatant was removed and virus resuspended in 100 μL PBS to make 10X viral concentrate. A total of 10 μL of viral titer was used to transiently transduce transfected cells. HBECs were grown to 70% confluence and transiently transfected with 0.75 μg of luciferase and 0.25 μg of Renilla vectors. Transfection media were removed 18 h later. Cells were allowed to recover for 24 h and then transduced with Mi2βWT or mutant retroviral vectors or cotreated with BaP and retroviral vectors for 24 h. Cells were lysed passively for 15 min at room temperature and luciferase and Renilla luminescence measured using a Cytation 3 machine. Relative luminescence units (RLU) were calculated as a ratio of firefly luciferase to Renilla.HEK293T‐17 cells were used to generate virus titers for subsequent transduction of the virus containing Mi2β and mutant plasmids into BEAS‐2B cells. HEK293T‐17 cells were grown to 90% confluence and transfected with Mi2βWT/mutants retroviral vectors (6 μg), combined with pSPAX‐2 packaging vector (3 μg) and pVSV‐G envelope vector (1.5 μg) diluted in 500 μL of dilution media (10 m6) cells stably expressing control (pB001ctr) or wild‐type (WT) L1 plasmids (pB015wt) were mixed with Matrigel and injected subcutaneously into anesthetized SCID mice at the University of Arizona Cancer Center Core Facility. Mouse weights and tumor burden were monitored twice weekly for up to 90 days, with tumor volumes estimated using the following formula: [(width)2 × length]/2. A 1 : 50 dilution of ORF1p antibody was used to monitor L1‐ORF1 protein in tumors derived from grafted cells or human tissues by immunohistochemistry (IHC). Images were taken using an Axiovision inverted microscope at 40 ×  magnification.HBECs  and histone‐4 lysine‐20 trimethylation (H4K20Me3) . Marked reductions in enrichment for Mi2β, MBD2/3, and MTA2 were seen 12 h after carcinogen challenge, indicating that BaP displaces NuRD macromolecular complex constituents from the L1 promoter. Next, FAIRE was employed to separate unbound and bound DNA sequences based on their relative affinities for the aqueous and organic phases, respectively . Increased fluorescence intensity for cytoplasmic Mi2β and MTA2 was observed in cells treated with BaP compared to DMSO controls  that spanned the complete L1‐Ta 5′UTR promoter sequence coupled with antibodies specific to Mi2β  were transiently transfected into HBECs. Cells recovered from transfection for 24 h before treatment with retroviral vectors encoding Mi2βWT or mutants for an additional 24 h. Transduction efficiency was optimal 24 h after exposure (data not shown). A significant, but modest, reduction in L1 reporter activity was seen in Mi2β WT‐transfected cells  or a constitutively active wild‐type L1 construct (pB015WT) (n = 15)  and flag‐myc double tags, respectively . L1 was tumorigenic in SCID mice, with tumor burden first detected one week after inoculation and sustained for up to eight weeks . Representative samples are shown in Fig. L1‐ORF1 protein were detected in p53 null tissue, but not in normal lung. These findings demonstrate that activation of L1 in HBECs creates a microenvironment that supports oncogenic transformation and implicate molecular interactions between L1 and p53 as critical players in lung cancer.The final set of experiments examined the oncogenic potential of 8 h Fig. , an in vely Fig. A. A cytoeks Fig. B. No tument Fig. B. The exype Fig. C. L1‐ORFL1‐Ta reactivation, and malignant transformation in HBECs challenged with the lung carcinogen BaP. These findings build upon earlier reports by our group showing that L1 reactivation involves the following: 1) enrichment of activating H3K4Me3 and H3K9Ac marks; 2) increased histone H3 acetylation of the 5′UTR; 3) reduced DNMT1 recruitment; and 4) CpG hypomethylation in both transformed and nontransformed epithelial cells . As such, constitutive AHR may support critical protein–protein interactions that are disrupted in the presence of BaP to facilitate disassembly of the NuRD repressor complex. Furthermore, AHR interacts with TGF‐β1, an upstream regulator of L1 and inducer of EMT in HBECs  pathway (Wylie et al., L1‐encoded ORF‐1p was increased in human lung tumors null for p53, a finding consistent with previous reports (Wylie et al., L1 can induce tumors in athymic mice that outgrow those induced by wild‐type L1 (Reyes‐Reyes et al., L1 pose significant restrictions on the tumorigenic process. This is an area worthy of exploration as novel chemotherapeutic agents can be designed to exploit this property in the clinical management of lung tumors.Interestingly, tumor growth in mice grafted with cells expressing L1‐Ta promoter from a heterochromatic to euchromatic state through disassembly of the NuRD complex and partial displacement of constituent proteins from the nucleus to the cytoplasm. Disruption of NuRD corepression correlates with accumulation of L1 mRNA and proteins and tumorigenesis.In conclusion, evidence is presented here showing that challenge of HBECs with the lung carcinogen BaP shifts the KSR conceived the study, KSR and PBJr designed the study, PBJr acquired the data, KSR and PBJr analyzed and interpreted the data, and KSR and PBJr wrote the manuscript.Fig. S1. Optimization of L1‐ORF1 in HBECs by Western analysis.Fig. S2. Time‐dependent analysis of L1 mRNA accumulation in HBECs challenged with 0.1 μm BaP.Fig. S3. DNA and Sequence analysis of L1‐5′UTR sequences.Fig. S4. Analysis of CYP1A1 expression after 12 h of BaP treatment by indirect immunofluorescence.Click here for additional data file.


Graphene, a single atom thick layer of two-dimensional closely packed honeycomb carbon lattice, and its derivatives have attracted much attention in the field of biomedical, due to its unique physicochemical properties. The valuable physicochemical properties, such as high surface area, excellent electrical conductivity, remarkable biocompatibility and ease of surface functionalization have shown great potentials in the applications of graphene-based bioelectronics devices, including electrochemical biosensors for biomarker analysis. In this review, we will provide a selective overview of recent advances on synthesis methods of graphene and its derivatives, as well as its application to electrochemical biosensor development. We believe the topics discussed here are useful, and able to provide a guideline in the development of novel graphene and on graphene-like 2-dimensional (2D) materials based biosensors in the future.  This feature includes a high surface area, excellent electrical conductivity, strong mechanical strength, unparalleled thermal conductivity, and ease of surface functionalization  layer of a hexagonal structure consisting of splization  . Th. Th2O2 coflowers . The golng cells . A simplhydrogel . The devDifferently, Lee et al., utilized graphene-Au hybrid nanoelectrode array (NEAs) to monitor stem differentiation in a non-destructive real-time manner  89]. Ty. Ty89]. It is evident that the exceptional physicochemical properties of graphene and its derivatives make them compelling for various electrochemical biosensor applications. The development and wide application of the electrochemical sensing based on these materials were hindered by the lack of facile and reproducible synthesis method of these materials with defined properties. In order to make it compatible to develop various electrochemical sensors, numerous efforts have been devoted to controllable and scalable production of graphene and its derivatives. Mechanical exfoliation method was first used to obtain graphene; however, the poor controllability and low production were the limiting factors. To achieve scalable production, LPE based methods were developed to obtain a dispersed solution of these materials and its products has been the most widely utilized for the electrochemical biosensors. More or less, recently CVD method was also adopted to synthesize graphene with controllable properties; however, limited scale production of graphene and its derivatives still hinders its applications. For example, various oxygenated surface functional groups provide a relatively high surface area, while it inhibits the performance of electrochemical biosensor as an insulator. Thus, a novel synthesis method which can consistently produce graphene and its derivatives with defined properties  in a large scale (high yield) and cost-effective manner is still required for future commercialization of graphene and its derivatives based electrochemical biosensors.During the past years, many different strategies have been also explored to develop novel graphene and its derivatives based electrochemical biosensors for analyzing bio/chemical molecules. It is clear that the optimization through the selection of a suitable surface functionalization method still needs to be revealed, in order to develop a highly effective and reproducible electrochemical biosensors. In addition, the combination with functional materials, such as ionic liquids, nanomaterials and polymers, have provided numerous choices to take the synergistic effect to enhance the electroanalytical performances. However, designing and finding the appropriate combinatorial structure with functional materials must be addressed for each biomolecule to maximize the performance of electrochemical biosensors. Although extensive studies have been made to design and fabricate novel electrochemical biosensors, long-term stability of combinatorial structure and functionalized surfaces (with receptor), in complexed real sample matrices, should be considered. Real biological fluids, such as blood and plasma, always contain various molecules and ions which can cause the interference through nonspecific binding events and undermine the performance of electrochemical biosensors. Furthermore, to adopt graphene and its derivatives for recently arisen in situ live cells and in vivo sensing strategies, more effort, such as long-term toxicity of graphene and its derivatives, as well as incorporated functional materials, should be also discovered. Moreover, since graphene and its derivatives can serve as both the sensing component and transducer, utilization to flexible electrode and miniaturization in size by forming free-standing structures via self-assembly would be an excellent approach for developing an implantable (flexible) and portable (lightweight) sensors as well. However, the lack of a suitable power source is a limiting factor.In addition, owing to the advantages of specific planar morphology, graphene-like 2D nanomaterials have attracted significant attention as emerging materials for electrochemical sensor approaches. Taking the advantages of diverse composition and structural effect, graphene-like 2D nanomaterials also have promoted great efforts to improve the performance of electrochemical biosensors. Similar to graphene and its derivatives, the defined synthesis method for high quality graphene-like 2D nanomaterials with controllable sizes and thickness, as well as tunable properties, and surface functionalization method is highly desirable for their practical application to electrochemical biosensor development as well. In witness of their current attention, we also endeavor that further improvement of graphene and its derivatives, as well as graphene-like 2D nanomaterial-based electrochemical biosensors, will lead to a significant advance in analytic applications for the highly effective and reliable detection of biomarker and open new avenues in biological and medical fields.


Nanocarbon-based materials, such as carbon nanotubes (CNTs) and graphene have been attached much attention by scientific and industrial community. As two representative nanocarbon materials, one-dimensional CNTs and two-dimensional graphene both possess remarkable mechanical properties. In the past years, a large amount of work have been done by using CNTs or graphene as building blocks for constructing novel, macroscopic, mechanically strong fibrous materials. In this review, we summarize the assembly approaches of CNT-based fibers and graphene-based fibers in chronological order, respectively. The mechanical performances of these fibrous materials are compared, and the critical influences on the mechanical properties are discussed. Personal perspectives on the fabrication methods of CNT- and graphene-based fibers are further presented. E), unparalleled thermal and electricity conductivity, and ultrahigh electron mobilities [σ) and E are widely used in aerospace, aviation, automobile, electronic, mechanical, chemical, textile, and other civilian industry. However, the electrical and thermal conductivities of carbon fibers are not satisfied. One-dimensional (1D) macroscopic architecture of CNTs and graphene, namely CNTs fibers (CFs) and graphene fibers (GFs), are analogous to carbon fibers in constitution and structure. Moreover, the combined performances including good flexibility and excellent electrical and thermal conductivities make them potential as structural–functional integrated materials. As more attentions have been attracted to the macroscopic fibers of 1D CNTs and 2D  graphene, it is the time to give a correlative review about CFs and GFs together. We think that this insightful review can help researchers to have a better systematic understanding of the whole developing journey of macroscopic assembled fibers. In this mini review, we firstly introduce the assembly strategies of CFs and GFs and then compare the mechanical performance of fibers made from different approaches. Finally, we present our perspectives on the future of CFs and GFs.Nanocarbon-based materials, such as carbon nanotubes (CNTs) and graphene, are extensively investigated due to their outstanding properties such as large theoretical specific area, high Young’s modulus  if they can attain the extraordinary mechanical and electrical properties of individual CNTs. This requires that the CNTs in the fibers are sufficiently long, highly aligned, and packed in an arrangement, and is nearly free of defects. Until now, the strategies for assembling CNTs to CFs can be classified into liquid- or solid-state spinning approaches. Liquid-state spinning approaches involve the dispersing of CNTs in a suitable solvent and shaping in coagulation bath. Solid-state spinning approach circumvents the dissolution problem either by drawing a fiber from a vertically grown CNT array or by drawing directly from an aerogel in the furnace .Liquid-state spinning approaches generally include polymer-based coagulation spinning method, liquid crystalline (LC) spinning method, polymer-free spinning method, and dip-coating method. Among them, polymer-based coagulation spinning method is first introduced to achieve CFs.σ and 15 GPa for E [The history of CFs fabrication dates back as far as 17 years ago. In 2000, Poulin’s group dispersed single-wall carbon nanotubes (SWNTs) in sodium dodecyl sulfonate (SDS) solutions, recondensed the nanotubes in the flow of poly (PVA) solution to form a nanotube mesh, and then collated this mesh to a nanotube fiber  [By utilizing SWNTs synthesized from carbon monoxide and lithium dodecyl sulfate as a surfactant, Baughman’s groups first produced mechanically strong gel fibers. After post-treatment with acetone-washing bath, continuous, multifunctional dry CFs were achieved. The resultant CFs showed a dramatically increased 0 J g−1) , 10 Besi0 J g−1) . The res0 J g−1) .The main challenge of producing CFs is to disperse the CNTs at high concentration for efficient alignment. Using surfactant is an effective approach to disperse CNTs into solutions, yet there is a loss in the properties of CFs due to the decreased van der Waals interaction between the neighboring CNTs. So super-acid (100% sulfuric acid) was introduced to increase the dispersity of CNTs. The protonated SWNTs in the super-acid behave as rigid-rod-like liquid crystals (LC) and exhibit an isotropic-to-nematic phase transition with an increased concentration Fig. a, b 12––12–14. BE and 116 MPa for σ) and electrical (5000 S cm−1) properties.Ericson et al.  improved−1) of these fibers were two orders of magnitude higher than that of fibers made by polymer-based coagulation spinning method (0.2 S cm−1).Unlike the LC spinning method, polymer-free spinning process using dilute, low-viscosity CNT dispersions (0.6 wt%) as spinning dope. By adjusting the pH (pH > 13 or pH < 1), polymer-free, surfactant-stabilized CNTs were flocculated/coagulated rapidly and uniformly to afford continuous CNTs gel fibers  can yield LC phase due to its high aspect ratio (or width/thickness ratio) and sufficient dispersibility/solubility with the solution concentration up to 30 mg mL−1 –49. This−1 . The gelpacitors , 51.Fig.−1 were also be spun by Yu’s group. They injected GO dispersion into CATB solution, and the curliness-fold formation mechanism of GO fibers was proved by SEM observations  and poly (glycidyl methacrylate) (PGMA) chains were covalently and uniformly grafted onto GO surfaces via a simple free radical polymerization process , 58. Theσ = 652 MPa, E = 20.9 GPa). A deformation mechanism model was also proposed based on the SEM observation  approach and wet-spinning technology to continuously fabricate biomimetic composites fibers Fig. a–g. Theyion Fig. h–j. Besiion Fig. k–m, reacanowires , bismuthanowires  and mont2 and was hold by glass slides for drying in air [3O4 and TiO2 and obtained functional GFs with magnetic and photoelectric  response [3O4 functionalized GFs was then acted as both substrate and catalyst for CVD growth of CNTs. The subsequent 1D CNTs and 2D graphene hybrid fibers with a large surface area (ca. 79.5 m2 g−1) and high electrical conductivity (1200 S m−1) were achieved [Besides the above wet-spinning method, Qu’s group developed a one-step dimensionally confined hydrothermal strategy to prepared GFs . They ing in air . To endoresponse . The Fe3achieved . This stachieved .Reduced GO nanoribbon (GONR) fibers were also fabricated by using an electrophoretic self-assembly method without any polymer or surfactant. Specifically, a graphitic tip as a positive electrode was immersed into the chemically reduced GONR colloidal solution in a Teflon vessel containing the counter electrode. The distance between two electrodes is ca. 5 mm, and the fiber is drawn out under a constant voltage ranging from 1 to 2 V. After annealing treatment, the fiber showed superior field emission performance with a low potential for field emission and a giant field emission current density when compared with vertically aligned few-layer graphene and single-layer graphene films prepared by electrophoretic deposition .Different from the above three methods using GO as precursors, self-assembly method directly utilizes graphene films to fabricate GFs. The 1D fiber-like structures were self-assembled from 2D graphene films in an organic solvent  and then dried to give the porous and crumpled structure , 71. Theσ and 1.25 to 397 GPa for E , it is fundamentally important to probe the critical factors affecting the mechanical properties of CFs. The CNT structures  [σ and E would reduce with increasing twisting MWNT fibers to a larger extent [Based on the assembly approaches, the mechanical properties of CFs show a broad range from 109 to 8800 MPa for ntation)  and CF gntation) . The larr extent .Table 1SE of CFs. To solve this problem, strong interaction between the tubes must be introduced. Electron beam irradiation is an effective approach to cause stable links between neighboring CNT within bundles. The mechanical properties showed a 30-fold increase in the bending modulus due to the formation of stable crosslinks that effectively eliminate sliding between the nanotubes [Owing to the weak van der Waals interaction between the neighboring CNT, the CNT can easily slide on each other, resulting in a low anotubes .−1, far superior to commercially used high-strength fibers [−1, far exceeding spider dragline silk (165 J g−1) and Kevlar (78 J g−1) [Besides the electron-beam-induced crosslinking approach, a method based on filtration-twisting was proposed to fabricate CNT-based composite fibers . The strh fibers . Further8 J g−1) .σ from 0.55 to 0.91 GPa compared with the pure fibers. After crosslinking at 120 °C for 2 h, σ and E of the fibers increased to 2.2 GP and 120 GPa, respectively  [σ is raised from 124 to 214 MPa and E reaches 47 from 14 GPa. To decreasing the structural defects, large-sized GO were used as building block [σ ranged from 214 to 501 MPa. To enhance the interlayer interaction, PVA [σ of 199, 652, 452, and 500 MPa, E of 17.1, 20.9, 8.31, and 18.8 GPa, respectively (as shown in Table The first GFs show a ht knots . Compare1.1 TPa) –83, a pl1.1 TPa) , 85. The1.1 TPa) . When drng block , 86, 87.ion, PVA , HPG [59ion, PVA , PGMA [5ion, PVA , and SA ion, PVA  were intσ break through 1 GPa for the first time. In 2015, Lian’s group improved the mechanical performance of GFs to 1.15 GPa by combining the large-sized graphene with small-sized graphene, aided by flowing-stretching and high-temperature graphitization treatment [High-temperature graphitization process is a more effective method to achieve high-performance GFs since the structural defects were removed or restored. The reatment . Recentlreatment –91.Many methods are developed to assemble CNTs and graphene into macroscopic fibers. For CNT fibers, on account of the entanglement nature between individual nanotubes, the approach of drawing CNT out from superaligned CNT arrays or aerogels is promising in achieved continuous, high-strength and high-electrical-conductive fibers. For GFs, considering the excellent dispersity of GO in water and organic solvent, liquid-state spinning approaches may be more competitive in the future.σ of CFs and GFs both exceed 1 GPa, comparable to that of the universal carbon fibers. In order to improve the performance of macroscopic CFs and GFs, defects such as voids and disordered orientation should be minimized.Although great progress has been made to improve the mechanical performance of macroscopic CFs and GFs, a wide gap still exists considering the intrinsic properties of CNT and graphene building blocks. Until now, the To further upgrade the combined performance of CFs and GFs, especially the mechanical strength and electrical conductivity, much work is waiting to be explored and more sophisticated understandings about the relationship between the structure and performance is of significant important from the viewpoints of both fundamental research and real application. On the one hand, we should establish a real-time system to monitor the structural evolution of the basic CNTs/graphene units during the fiber-forming process, which will contribute to the structure controlling of the fibers. On the other hand, the processing techniques  used to enhance the performance of polymeric fibers and carbon fibers should be borrowed to optimize the fabrication process throughout.


X-ray photoelectron spectroscopy (XPS) revealed the relative extension of the graphene sheets π-system and the type of nitrogen chemical functions present in the lattice structure. Scanning Electron microscopy (SEM), Transmission Electron microscopy (TEM) and Raman spectroscopy were applied to determine morphological and structural characteristics of the sheets. Optical emission and FT-IR spectroscopy were applied for characterization of the high-energy density plasma environment and outlet gas stream. Electrochemical measurements were also performed to elucidate the electrochemical behavior of NG for supercapacitor applications.Direct assembling of N-graphene, i.e. nitrogen doped graphene, in a controllable manner was achieved using microwave plasmas at atmospheric pressure conditions. The synthesis is accomplished via a single step using ethanol and ammonia as carbon and nitrogen precursors. Tailoring of the high-energy density plasma environment results in a selective synthesis of N-graphene (~0.4% doping level) in a narrow range of externally controlled operational conditions, i.e. precursor and background gas fluxes, plasma reactor design and microwave power. Applying infrared (IR) and ultraviolet (UV) irradiation to the flow of free-standing sheets in the post-plasma zone carries out changes in the percentage of sp Among the possible doping agents, nitrogen has drawn a considerable amount of attention because its atomic radius is comparable to that of carbon and contains five valence electrons available to form strong covalent bonds. The conjugation between the nitrogen lone-pair electrons and the graphene π-system modifies graphene physical and chemical properties. The substitution of carbon atoms by nitrogen ones influences the atomic charge distribution on the graphene scaffold and creates “active sites” thus significantly increasing the electrochemical activity of nitrogen-doped graphene, known as N-graphene (NG)4.Beyond its unique set of physico-chemical properties, graphene can be considered as a robust, atomic scale scaffold from which other 2D materials can be derived through the attachment of foreign atoms and functional groups5 predicted modified electronic and chemical properties of nitrogen-doped graphene, which is being supported by numerous experimental investigations. Indeed, there is significant experimental evidence of the advanced properties of the NG-based materials in respect to already practically implemented ones5. For instance, NG has been tested in fuel cells either as the catalyst or carbon supports. The “active sites” can be engaged in catalytic reactions, such as oxygen reduction reaction (ORR), or can be used as a scaffold for other catalysts8. NG demonstrates better chemical reactivity and sheet-to-sheet separation than the pristine graphene9. To this end, N-doping is a very promising approach for the development of metal-free carbon-based catalysts with even better performance than commercially available Pt-based electrodes, with prospective impact on fuel cells’ commercialisation. However, the lack of an appropriate synthesis route providing both high quality and quantity of NG hinders its practical implementation.The theoretical studies5. The influence of the N-bonding configuration on the carrier concentration and consequently on the electronic properties of graphene was studied in10.Graphitic, pyridinic and pyrrolic are the three common N-bonding configurations. Graphitic N can facilitate electron transfer by lowering charge-transfer resistance of the electrode. Being electrochemically active, pyridinic and pyrrolic N offer high pseudocapacitance−1), excellent life number of cycles , suitable to operate with flexible substrates and various electrolytes were developed in11 using nitrogen-doped graphene. Moreover, N-doped graphene has been hybridized with different metal compounds to enhance electronic and ionic conductivity12.N-doped graphene display interesting properties for charge storage applications. Supercapacitors with high capacitance , spintronics, etc.26. The sensing ability of NG was investigated for certain dyes by a new surface analysis technique, i.e. graphene-enhanced Raman scattering15. It was demonstrated that NG can be used to efficiently detect trace amounts of certain molecules.N-doped graphene nanoribbons were also tested as conductive host materials in lithium-sulfur (Li-S) batteries, demonstrating stronger fixation of sulfur-containing species and higher stability, as compared with pristine graphene nanoribbons27. The battery exhibited an open-circuit voltage of 1.46 V, a specific capacity of 873 mAhg−1, and a peak power density of 65 mWcm−2, that can be continuously charged-discharged with an excellent cycling stability.Rechargeable zinc-air battery with the nitrogen-doped graphene nanoribbons used as an air electrode in a two-electrode configuration was assembled in5 can be categorized into in-situ direct methods and post-treatment approaches. In situ approaches characterized by simultaneous graphene synthesis and N-doping include CVD, ball milling, solvothermal synthesis, etc19 CVD involves growth of N-graphene on a preheated structure  in the carbon and nitrogen-containing environment. Although CVD is one of the most common methods for in-situ NG synthesis, it suffers from metal interference. Post-treatment methods include wet chemical methods, thermal annealing of graphene oxides (GO) with heteroatom precursors and plasma-based treatments38. These methods present several drawbacks, such as degradation of the nanostructure properties due to the transition metals used, the requirement of expensive and/or hazardous catalysts, vacuum systems and very high temperatures, and lengthy/complex batch procedures. Although, in principle, direct synthesis may have the potential to create homogeneous doping throughout the bulk material, the results reported up to now fail to indicate so. As a rule, graphene oxide (GO), in the presence of N-precursors, has been frequently used for N-graphene synthesis. However, chemical reduction of GO requires the use of reducing toxic agents. Although it is a low-cost method to produce N-graphene in a relatively large scale, the materials obtained exhibit only relatively low electrical conductivity due to the contaminants, saturated sp3 bonds and bonded oxygen groups30. Thus, restoration of the high conductivity of N-graphene sheets is an issue.Numerous methods for synthesis of N-graphenehttps://graphene-supermarket.com/) show variable physical properties, thus limiting their use. Generally, the fabrication of N-graphene meets significant unresolved problems such as: i) uncontrolled N bonding type and distribution; ii) N doping at non-specific positions and untuned doping content. Most importantly, the greatest challenge on the path towards either graphene or N-graphene commercialization is the controllable production of high quality material on a large scale, at low cost and in a reproducible manner. To this end, plasmas and their ability to control energy and matter at an atomic scale level appear as powerful tools to tackle this challenge3. Plasma assisted growth of nanostructures can be achieved without the use of catalysts due to plasma’s unique ability to activate the surface, thus creating favorable conditions for nucleation and growth processes.Graphene/N-graphene´s properties vary strongly as a function of its synthesis method and their intrinsic properties are drastically dependent on the structural quality. A good spatial control of the energy and mater fluxes at a nanoscale, is indispensable in enabling a cost-effective and environmentally friendly synthesis process and constitutes one of the main challenges of the above-mentioned conventional methods. Existing commercial products  was achieved using low pressure RF nitrogen plasma treatment39. Similarly, microwave N2-Ar post discharge plasma was used for N-doping of free-standing graphene, with a maximum level of doping achieved of 5.6%32. Gas-phase controllable doping of graphene by ammonia plasma exposure, with maximum doping level of about 0.4% has been reported in32. However, the large percentage of oxygen, common for post-treatment approaches, is to be noticed. Generally, plasma-based post-treatment approaches can provide higher levels of N-doping compared to direct ones, but these processes have some disadvantages. They are two-step processes, slower, more complex and expensive, and are commonly performed at low-pressure conditions. Furthermore, plasma post-treatment affects only the surface of the sample, which significantly reduces its effectiveness.The successful synthesis of N-graphene consisting of multiple layers with 1% level of doping using a DC arc-discharge with carbon electrodes in an atmosphere of ammonia, was reported inin-situ direct synthesis of free-standing N-graphene flakes at a relatively high yield (~ 1.3 mg min−1), was achieved in a single step by employing microwave plasma  operating at atmospheric pressure conditions44. An ethanolic solution of ammonia (4 wt %) was used as precursor of both carbon and nitrogen. Argon was used as a background gas. The plasma properties have been tailored to achieve selective synthesis of free-standing N-graphene sheets. The flowing sheets were submitted to UV and IR irradiation in the post-plasma zone during their flight to the collecting system to further improve their structural quality40. Raman spectroscopy, SEM and TEM and XPS were used to characterize the morphology, microstructure and chemical properties of the synthesized material. The outlet gas stream was analyzed by Fourier-Transform Infrared spectroscopy (FT-IR) to detect the generated by-products. The electrical conductivity of the synthesized NG samples was determined using the Van der Pauw method45. Electrochemical measurements were also performed to elucidate the electrochemical behavior of NG for supercapacitor applications. Optical emission spectroscopy (OES) was used to detect the emission of plasma generated “building units” and to determine the gas temperature.In the present work, 2, C, CN, N) and to determine important plasma parameters such as the gas temperature in the “hot” zone of the plasma reactor, emission spectroscopy has been applied. Optical emission spectroscopy allows the identification of the active carbon/nitrogen species in the plasma that are the “building units” for the synthesis and growth of the nanostructures in the mild plasma zone43. The detected argon/ethanol/ammonia plasma emission spectra in the visible range (240–750 nm) are shown in Fig. 2Σ → X2Σ), C2 , CH band, the hydrogen Balmer-alpha line Hα (656.3 nm) and several Ar lines. These species are formed as a result of ethanol/ammonia decomposition and intensified chemistry in the “hot” plasma zone. As it can be seen in Fig. 2 molecular band, i.e. the Swan system, with heads band at 473.7, 516.5 and 558.6 nm were detected. The typical green colour of the plasma  is due to C2 emission caused by the radiative decay of the excited state C2*(A3Πg). Electron impact and three body recombination processes, involving carbon and argon atoms, are responsible for the excitation of the ground state C2 molecules to the C2*(A3Πg) excited state, while CN species are formed according to the reaction C + N + Ar → CN*(B2Σ) + Ar44.To identify the species of interest  (3000–3200 Å) band was used to estimate the rotational temperature, which at atmospheric pressure conditions is nearly equal to the gas temperature. The OH spectrum detected in the range 307.5–315 nm,  at axial distance z = 2.5 cm from the launcher in the “hot” plasma domain is shown on Fig. 44. An exemplification of the 2D map of the temperature as obtained by an infrared-sensitive thermal imager (FLIR camera) is shown in Fig. 40 can be clearly distinguished. The temperature corresponding to the position of the marker is 437 °C.The gas temperature in the plasma, particularly in the “hot” zone, is an essential parameter regarding plasma kinetics. In gas discharges, the gas temperature can be usually assumed equal to the rotational temperature of diatomic molecular species−1 and 1000 cm−1, which are “fingerprints” of the ethanol and the ammonia molecules, respectively. With the plasma turned on, these lines are not present, clearly indicating that the ethanol and ammonia molecules are decomposed in the plasma environment. At the same time, the absorption peaks of CO at around 2170 cm−1; C2H2 and/or HCN at around 720 and 3300 cm−1, and C2H2 at around 1350 cm−1 are detected  of the 2D peak in the synthesized samples is typically 50 cm−1, suggesting that graphene dominantly consists of several layers. For the sample obtained without application of IR and UV irradiations, the intensity ratio of the D-band to G-band at different locations on the sample vary significantly, as seen from Fig. As seen from the figures the spectra are dominated by three peaks, attributed to the D, G and 2D bands at about ~1332 cmEx-situ XPS analysis has been performed to study the relative extension of the delocalized system, the amount and type of nitrogen atoms doping the graphene and the amount of oxygen.40. However, N 1s spectrum shown in Fig. 52 and/or nitrogen atoms bound to oxygen, like nitroso groups.Nitrogen was detected in all the samples. The detailed XPS regions Fig.  show dif2 carbon atoms in highly delocalized C-C bonds, and the expected features due to the energy losses associated to π-π* excitations. This energy losses region can extend roughly from 287 eV to over 295 eV, superposing to much less intense photoelectron peaks assigned to carbon bound to oxygen , which, as attested by O 1s region (not shown), is in a residual amount  and also has the largest relative amount of nitrogen (N/C ~ 0.4%) and is the least oxidized (O/C = 1.5%). The sequence of UV irradiation and relatively low heating (i.e. 200 °C) slightly increases the sp2%. Additionally, changes in the relative amount of the different nitrogen groups are observed, such as an increase of the amounts of pyridinic and pyrrolic nitrogen. This might be caused by activation of the defects due to additional heating, with the subsequent bonds reorganization. The fact that these changes are small, however, makes it difficult to assess the validity of this assumption and further investigation to analyze this influence is an ongoing work. The small decrease of oxygen/carbon ratio from 0.021 to 0.015 can be attributed to the kicking-out of the oxygen groups by UV irradiation with a photon energy of ~3 eV.The results in Table The electrical conductivity of the N-graphene sheets was measured on pressed disc pellets of 8 mm diameter and thickness between 1.2 and 3.2 mm. A four-contact configuration with pinching point contacts located on the periphery of the pellet, was used, providing longitudinal conductivity measurements for the current lines parallel to the pellet surface. For the current ranging from 0.5 to 3.5 mA, the current-voltage characteristics and reconfirmation of the Ohmic contact character were obtained.54.The values of electrical conductivity presented in Table QAr = 1200 sccm, QAr/Et/Am = 120 sccm and submitted to IR and UV irradiation, was tested as electrode for supercapacitor applications by performing cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS) in 1 M H2SO4 electrolyte. The measurements were performed in a three-electrode electrochemical cell using Pt and Standard Calomel Electrode (SCE) as counter and reference electrodes, respectively.N-graphene, produced at P = 2 kW, vs. SCE at varying scan rates, are presented in Fig. −1. Such rectangular features and high reversibility can be attributed to the high and easily accessible active surface area of the N-graphene.The CV curves obtained in the potential window of 0–0.8 V −1 , ∆t is discharge time (s), and ∆V is working potential window. The specific capacitance of 8.87 Fg−1 was obtained at current density of 0.1 Ag−1 which retained ~100% of the capacitance on increasing the applied current ten times higher i.e. at 1 Ag−1  to study the resistive nature of the synthesized N-graphene. The spectra along with the equivalent circuit proposed to fit the data are illustrated in Fig. 2 obtained from fitting suggest negligible charge transfer resistance.Nyquist plot gives the information about the charge transfer resistance at high frequency and capacitive at low frequency. The absence of a semi-circle in the high frequency region, as can be noticed from magnified plot shown in inset of Fig. o in the mid frequency region represents the diffusion of ions dependent on frequency. A well-defined and short Warburg region portion, with phase angle of around - 45° (n = 0.51), evidences the short and equal diffusion path length of the ions in the electrolyte. Also, the Warburg resistance value of 0.386 Ωcm2 was very low. The very low charge transfer resistance and the decreased diffusion effect can be the reason for very fast reversible processes at the interface, which explains the rectangular CV, the rectangular nature retention even at high scan rates and the linear profiles of GCD plots. At very low frequency, the presence of almost vertical line and phase angle close to - 90°  and ultraviolet (UV) irradiation to the flow of free-standing sheets in the post-plasma zone carries out changes in the percentage of spElectrodes assembled with the produced N-graphene showed good electrochemical response with negligible interfacial resistance, even at low percentage of N-doping in the graphene, evidencing high potential for supercapacitor applications.By optimizing the microwave plasma reactor performance, along with detailed modelling of the plasma environment and formation of the main “building units”, well controlled synthesis of carbon/nitrogen atom lattices can be generated. Further investigations are underway in these directions, including the use of other carbon/nitrogen precursors such as methane, air, pyridine etc., to achieve further advancements in this technique, and increase the yield along with reduction of the cost via scaling-up the plasma reactor. Focus will be on mastering the process by achieving control on both the level of doping and bond configuration.The method is highly scalable and versatile: carbon precursors in liquid, gas and solid state can be used and different graphene derivatives can be synthesized using the same plasma reactor. Moreover, customization is possible, i.e., depending on the target application one can tailor N-graphene sheets in a suitable form and required quality.Supplementary Material