Among a growing body of research that examined the contradictory role of written corrective feedback (WCF) in development of L2 writing accuracy, this study investigated the possible impact of focused metalinguistic WCF on discourse markers (DMs) in writing performance of an intact group of 42 Iranian English as a Foreign Language (EFL) learners over an eight-week period. In an authentic, situated, and personalized learning platform, giving and receiving WCF were made possible only through the mobile-mediated application of WhatsApp. Before participants wrote on selected elicitation topics, they had taken part in a 2004 version of Oxford Preliminary Test in order to be screened for their initial differences in writing performance. After receiving metalinguistic WCF on their scripts, participants were required to work on the coded feedback and try to eliminate the DM errors in their revised writing assignment. After collecting the scripts over an eight-week period, the content of written assignment was thematically analyzed using NVivo 21 Software for the additive, adversative, causal and temporal DMs, following Halliday and Hasan’s  typology. In a convergent mixed-methods design, the content analysis of the qualitative data showed a larger distribution of additive DM than adversative, causal, and temporal DMs in all participants’ written scripts. Exploring the possible impact of metalinguistic WCF on improving the DMs accuracy, analysis of the frequency count data with Statistical Package for the Social Sciences (SPSS) multivariate Chi-square test reported the fluctuation and unsystematic patterns of distribution for four types of DMs with no sign of significant long-term improvement in DMs accuracy after receiving metalinguistic WCF. These findings implied further research on practicing alternative WCF strategies focused on variety of error types in actual and virtual L2 writing environments. Many studies verified the viability of WCF in improving L2 learners writing  in second/foreign language (L2) contexts does not protect any language teachers from losing sight of how to interpret the contradictory research findings and how to take actions to apply them in real classroom context. For many L2 teaching professionals, the critical concern about WCF has never been whether it is useful, but In the absence of serious examination of WCF long-term efficacy, well-designed and valid experimental studies, the challenge over WCF benefits still persists. Within the WCF advocates party, a group of researchers have been interested in the extent to which different WCF strategies and their amount of explicitness may have divergent impacts on L2 writers’ accuracy  pandemic. Online initiatives, resources and educational programs have emerged and evolved quickly in the absence of face-to-face teacher mediation, wherein the L2 writers can still benefit from WCF. It is through computer-mediated writing assignment or online classroom tasks that the teachers’ suggested notes or corrective feedback can easily be transmitted to the L2 writers. Therefore, it is believed that using modern technological devices such as smart phones, iPads or even desktop computers might create a platform to bring to the L2 learners the advantages of immediate and more favorable types of WCF  learners progressed in fluency, communicative abilities, and their confidence in using French, they commonly failed to master French grammar use even after years of extensive exposure  slims the chance of bewilderment that students will usually experience if they fail to recollect the received indirect feedback; (2) grants them a toolkit to predict and prevent future errors; and eventually, (3) seems more intriguing and immediate to the students in writing classrooms  WCF if they have to attend to all committed errors at the same time. While to several researchers, unfocused WCF is detailed and authentic; many more blamed it as an unsystematic WCF strategy which overloads L2 writers’ working memory capacity  has made entrance to most educational settings, especially L2 learning/teaching context. So far, the power of wireless technologies has improved markedly, “especially with smart mobile phones which have incorporated the functionality of hand-held computers and audio-video recorders and players”  consented to voluntary participation among whom three volunteers were excluded after administering the Oxford Preliminary Test (2004 version) as the placement test in this study. Within the age range of 19 to 45 and average of 28, the 42 candidates enrolled in a virtual course of English paragraph writing at a private language institute in Karaj, Iran which lasted for eight consecutive weeks. The participants were undergraduate university students majoring in engineering (27%), medical sciences (22%), accounting (22%), Russian literature (16%) and architecture (13%), whose general English proficiency was determined at advanced levels of C1 and C2, trusting their range of obtained scores (48–60) on the OPT.OPT is a standard test of general English proficiency with a six-point rating scale. As stated in www.oxfordenglishtesting.com , OPT “meα = 0.883). Eventually, 42 students whose OPT scores assigned them to levels of C1 and C2 were selected as the final research sample.At the outset of the experiment, to minimize the odds of initial differences among the participants in terms general English proficiency, the researchers administered a 2004 version of OPT with 100 multiple-choice items and reasonable measure of inter-item reliability  whose scores were below the advanced level of language proficiency . The final 42 selected candidates were informed that in the following 8 weeks they were required to write a 150–200 word paragraph on every selected topic and send it to the instructor through WhatsApp Messenger. Next, they received detailed instructions on four types of DMs  referred the students to the following explanations in the DMs glossary sheet:and, also, moreover, in other words, is used to repeat or emphasize the previous information or add relevant new ideas or expressions to them.ADD = Additive DM, such as yet, though, however, in any case, instead, is used to express contrasts and comparisons between sentences or corrections in relation to foregoing discourse.AD = Adversative DM, such as so, then, therefore, because, is used to signal the results or consequences of what is being stated.CD = Causal DM, such as next, when, secondly, is used to reflect the chronological, logical or sequential relationship between discourse units. No further error categories were corrected or received coded feedback.TD = Temporal DM, such as Once a DM error was located by the researchers, it was highlighted and an abbreviation above the error , including and, however, before, so, if, 10 of which were additive DM. Among additive DM, and was overused. Table Imagine a day without the Internet, smart phones or computers. How would your life most likely become?As Table n = 14) were used more reasonably and frequently. Moreover, AR started to use less frequent DMs, such as initially, since, and as well as which show some degree of adjustment in her writing performance. Still, AR used more additive DM (n = 7) than other three DM types. Finally, as Table Why do most people still want to live in cities rather than country sides?In Table n = 0), the instances of other types of DMs, such as although, because of, and, also, and so were accomodated accurately with similar frequency rates (n = 14). To sum up, the frequency distribution of four types of DMs in AR’s writing was different in every session, with no sign of considerable improvement over 8 weeks of receiving metalinguistic WCF. Similar unsystematic and fluctuating patterns of DMs distribution were retrieved and reported in other participants’ writing.According to Table obligatory occasion analysis). For instance, in a written script, the three correct usage of the additive DM from 10 obligatory occasions was calculated as 30% accuracy rate.Following Ellis and Barkhuizen , accuracFor frequency analysis of the collected quantitative data, the IBM SPSS 21 descriptive statistics was deployed. The obligatory occasions for the DMs were identified and noted in all the written scripts by each candidate on the eight assigned writing tasks. The interrater reliability was checked across the current researchers’ ratings to ensure the credibility of the content analysis and it had the index of 0.815 in terms of Cohen’s kappa coefficient. The measures of mean and standard deviation for four types of DMs were summarized in Table the extent to which metalinguistic WCF affects EFL learners’ accuracy of four types of DMs in their writing performance, the measures of mean and SD demonstrated fluctuating patterns of distribution across four types of DMs, despite the participants constantly using additive DM more than the three other DM types along eight sessions of metalinguistic WCF. In other words, through the treatment sessions, no considerable progress in the DMs accuracy could be seen in participants’ writing after receiving metalinguistic WCF. Figure As it can be seen in Table As Fig. how metalinguistic WCF would affect EFL learners’ accuracy of DMs in their writing performance over an eight-week period, or in another terms, the significance of fluctuations in DMs accuracy along the metalinguistic WCF intervention sessions, the frequency pattern for every type of DMs was cross-examined in a contingency table , p = 0.000, Cramer’s V = 0.910 (indicating a strong effect size)]. To sum up the findings, the frequency counts of the four types of DMs showed different distributions in the participants’ writing, with the additive DM as the most frequent (n = 4651) and temporal DM as the least (n = 1393) overall. However, such fluctuating patterns of occurrence seemed consistent and non-significant along the eight-week period of treatment rendering no accountable sign of improvement in participants’ writing performance through and after receiving metalinguistic WCF.Summarized in Table This study aimed at investigating the extent and the quality of metalinguistic WCF possible impacts, specifically focused on EFL learners’ use of discourse markers in a mobile-mediated language learning platform. Qualitative data analysis in this study indicated a considerable divergence in the frequency patterns of four types of DMs  in the participants’ writing performance. To be precise, the additive DM had an outnumbered appearance over adversative, causal and temporal DMs. Much to the chagrin of the current researchers, however, despite a significant difference in the frequency distributions of the DMs, the statistical data analysis failed to support a meaningful improvement in the participants’ DMs accuracy along an eight-week period of receiving metalinguistic WCF. There is a growing body of research which still examines such nuances and niches in applying WCF. Despite ample empirical evidence, it is still unclear whether specific error types are more sensitive to WCF than others (Bitchener, temporarily but they hardly advance their internal grammar which is acquired and internalized over time and only through natural and extensive exposure to L2. In other words, regarding the constructive role of feedback, positive evidence is a trigger for progressive change; negative evidence seems irrelevant in a long shot.Conforming to Truscott’s  stark dito correct or not to correct their students’ written performance are left in the middle of contention.There have been abiding debates between those who strongly support the advantages of WCF to natural improvement of L2 learners’ writing performance and those who are against them. Likewise, Guénette  argued tScholars like Truscott and Hsu , who belIn L2 research domain, several studies found corrective feedback even harmful rather than simply ineffective (Farrokhi et al., Although attempts were made to minimize the probable lapses in research design, data collection and content analysis in this study, there are some limitations and implications which should be pointed out once further research is designed in the future. The focus of metalinguistic WCF in this study was only on locating and responding to discourse markers, which can be both a source of strength and a cause of restraint to the generalizability of the findings. Adopting DM lenses made it possible to focus on the EFL learners’ accuracy of cohesive devices; however, further research is needed to estimate the extent to which the findings in this study are applicable to other non-treatable error categories as well.Further research is also needed to investigate whether alternative means of data collection, such as writing tasks of different genres or various strategies of WCF might change the algorithm of DMs occurrences in EFL learners’ writing. It should also be noted that the participants in this study were Iranian EFL learners at the advanced level of English language proficiency who studied English in the formal educational setting and had received some earlier instructions to the use of DMs in academic English writing and grammar courses. Further research seems necessary to determine whether a variety of WCF strategies would help the elementary or less proficient EFL learners to develop accuracy in using DMs in their writing performance.Finally, as several incompatibilities were earlier reported between the WCF empirical research findings and real classroom practice (e.g., Hobbs,


Graphene and its derivatives, with their unique two-dimensional structures and excellent physical and chemical properties, have been an international research hotspot both in the research community and industry. However, in application-oriented research in the oil and gas industry they have only drawn attention in the past several years. Their excellent optical, electrical, thermal and mechanical performance make them great candidates for use in oil and gas exploration, drilling, production, and transportation. Combined with the actual requirements for well working fluids, chemical enhanced oil recovery, heavy oil recovery, profile control and water shutoff, tracers, oily wastewater treatment, pipeline corrosion prevention treatment, and tools and apparatus, etc., this paper introduces the behavior in water and toxicity to organisms of graphene and its derivatives in detail, and comprehensively reviews the research progress of graphene materials in the upstream oil and gas industry. Based on this, suggestions were put forward for the future research. This work is useful to the in-depth mechanism research and application scope broadening research in the upstream oil and gas industry. With the continuous growth of population and the rapid development of economy, the global energy demand is increasing. Oil and natural gas, as the most important current energy sources for human society, will not be replaced on a large scale, at least during the first 50 years of the 21st century. The oil and gas industry is a multibillion-dollar market that affects the lives of anyone who has ever driven a car, used electricity, walked on asphalt-paved roads or used polymer products such as plastics [In recent years, nanomaterials application research in biology, medicine, electronic engineering and other fields has made rapid progress, which also provides new ideas for the development of the upstream oil and gas industry. The relatively high cost of nanomaterials is a major challenge for their application in the oil and gas industry, but scholars and oil companies around the world are still actively carrying out research on the applications of nanomaterials in the oil industry. The most widely studied nanomaterials are carbon nanotubes, carbon nanofibers, nano-oxides, and nano-clays .2 hybridized, and there are dangling bonds on the edges. However, because graphene needs to be stable in the natural environment, the hanging bonds on the edges of such nanoscale graphene sheets are occupied by other chemical bonds, therefore, in practical applications, it is always a three-dimensional graphene material composed of nanoscale graphene sheets. In this paper, the application of graphene and its derivatives in petroleum engineering is reviewed, and their development directions in the upstream oil and gas industry are proposed.As a special nanomaterial, the application of graphene and its derivatives in the field of oil and gas industry has attracted more attention. However, compared with its extensive application in other fields , the application of graphene in oil and gas exploration and production is still at the initial stage. Although its research time is short, the effects of graphene and its derivatives in oil exploration and development are obvious, so many scholars and engineers believe that they will have a better application prospects in the upstream oil and gas industry. Although in theory, graphene should be large in size and large in area, each carbon atom is sp2 hybridization. Its basic structural unit is the most stable benzene-like six-membered ring structure. Its theoretical thickness is only 0.35 nm, which is the thinnest two-dimensional material discovered so far [In 2004, Novoselov and Geim at the University of Manchester in the UK obtained the first graphene sheet by a mechanical exfoliation method, and since then graphene has become a research hotspot in the scientific community around the world . The uni4 cm2·V−1·s−1, which is twice that of indium antimonide material  and 10 times higher than that of the commercial silicon wafers. Under certain conditions , the mobility can even be as high as 2.5 × 105 cm2·V−1·s−1. The thermal conductivity of graphene can reach 5 × 103 W·m−1·K−1, which is three times that of diamond. In addition, graphene has excellent chemical stability and adsorption properties [Graphene has many excellent physical and chemical properties. For example, the strength of graphene is the highest among the tested materials, reaching 130 GPa, which is more than 100 times that of steel. Its carrier mobility is 1.5 × 10operties ,7,8,9.2 hybrid state to sp3 hybrid state, and then peeled layer by layer [Graphene derivatives generally include graphene oxide (GO), reduced graphene oxide (rGO), graphene quantum dots (CQDs), doped graphene and modified graphene, among which graphene oxide is the most widely used graphene derivative. Graphene oxide is a kind of single-layer two-dimensional material, obtained by the oxidizing and intercalating modification treatment of graphene, which changes part of carbon atoms from spby layer . The strby layer ,12,13,14The industrial applications of graphene and its derivatives are mainly in the fields of surface coating and preparation of nanocomposites, in which graphene and its derivatives participate the whole process mainly in the dispersion form. The research on the behavior of graphene and its derivatives in water is involved in the fields of chemistry, materials science, environmental science and biomedicine ,16. In t−1, GO began to coagulate rapidly. Furthermore, the influence of divalent metal ions on the average electrophoretic mobility and the hydraulic diameter was stronger than that of univalent metal ions. Moreover, the humic acid had a significant effect on the stability of GO in the solution. When the concentration of humic acid increased from 0 to 10 mg·L−1, the hydraulic diameter of GO decreased from 500 nm to 250 nm, and the stability was significantly improved [The solubility of graphene in water is very low. Due to the effect of van der Waals forces, it easily forms agglomerates or even accumulates to form turbostratic carbon in aqueous solution . The zetimproved . In addiimproved .With the rapid growth of the application scope and usage of graphene materials, it is inevitable they will leak into the environment at some point during the whole cycle of production, storage, transportation, use, disposal and recycling. Although graphene nanomaterials have relatively good biocompatibility, they still have certain biological toxicity. Therefore, the impact of graphene nanomaterials on organisms and the environment has attracted more and more attention . The oilCytotoxicity is one of the important indexes used to evaluate the safety of pollutants. Studies have shown that graphene nanomaterials have certain cytotoxicity, and their toxicities are closely related to their physical and chemical properties and the types of cells, and it also has a significant concentration dependence. The mechanism of the cytotoxicity of graphene is not very clear at present, but studies have shown that oxidative stress and inflammatory reaction are the main mechanisms leading to cell death. Graphene materials have high surface activity, which can produce a lot of reactive oxygen radicals (ROS) after aggregation on the surface or inside of cells. These ROS further lead to DNA fragmentation, cell membrane damage and mitochondrial dysfunction . Qu et aCaenorhabditis elegans, which can damage its gonad development [Graphene materials have also shown some toxic effects on animals. At present, most of the studies focus on mammals such as rats and mice. The lower protozoa and nematodes, as well as zebrafish and other aquatic animals have also been studied. The toxicity of graphene materials to animals is closely related to its action position, action mode and action concentration, as well as the size of itself and the types of surface functional groups. The toxicity of graphene to mammal is manifested as low acute toxicity. GO is more toxic to the lungs of mammals than graphene, however, the surface modification can avoid the toxic effects of GO. The size of graphene material is also a major factor affecting its toxicity ,29,30,31elopment . Chen etelopment .Arabidopsis thaliana, and found that GO had no significant effect on seed germination, seed development, seedling root development and flowering time. The above studies indicate that the toxic effect of graphene on plants may be related to oxidative stress, but the detailed mechanisms need further study [Raphidocelis subcapitata from the aspects of ROS, membrane damage and chlorophyll content, and the results showed that GO could lead to the increase of ROS and membrane damage in green algae cells, and the accumulation of graphene would also affect the lighting efficiency of green algae [Chlorella vulgaris and found that GO could accumulate on the surface of algal cells, significantly reduce the permeability of cell membrane, and cause a degree of extent oxidative stress, resulting in algal cells damage [Graphene materials are toxic to both terrestrial plants and algae. Begum et al. studied the toxic effects of graphene on a variety of vegetables, from the aspects of growth, biomass, shape, cell death and active oxygen level of their roots and buds. The results showed that higher concentrations of graphene could significantly inhibit plant growth and biomass increase. In addition, different kinds of plants and different parts of plants have different reactions after exposure to the action of graphene . Zhao ster study . Nogueiren algae . Ouyang s damage . The aboEscherichia coli while showing less cytotoxicity. Graphene paper sheet obtained by simple vacuum filtration using graphene suspension also had good antibacterial effect [In the aspect of antibacterial activity, Hu et al. first reported the antibacterial activity of GO and rGO, and found that the graphene-based nanomaterials can effectively inhibit the growth of l effect .In conclusion, the toxicity of graphene materials to cells, animals, and plants is relatively low, and they can show good biocompatibility after surface modification. Graphene has a good antibacterial effect on microorganisms. However, Schinwald et al. found that GO could interact with proteins in the plasma to form GO-protein composite particles. Graphene sheets could easily become inhalable particles, enter the lungs and deposit into the alveoli, and produce toxic effects on the lungs, causing severe pulmonary fibrosis and cysts. In addition, the particles may accumulate in the lung, liver, spleen and kidney. What makes matters worse is that it cannot be removed from the kidney . TherefoExploratory research for applying graphene and its derivatives in the fields of well working fluids, chemical enhanced oil recovery, heavy oil recovery, profile control and water shutoff, tracer, and oily wastewater treatment, etc., was conducted in the past three years. Meanwhile, they have also been applied in tools, sensors and pipelines. Although the above research is still in the initial stages, we have reasons to believe that graphene and its derivatives will certainly provide new breakthroughs in their application in the oil and gas industry, because of their widely application research in many fields such as biomedicine, nanotechnology, electronics, photonics, heat transfer and so on, through which the similar mechanisms could be found.Drilling engineering is an important step in establishing a connection channel between the ground production system and the underground reservoir, which refers to the rock stratum with pores, fractures or holes, where oil or natural gas are stored and flow. The performance of the working fluid directly affects the construction work. Drilling fluid in the broad sense is all fluids  that help to produce and remove cuttings from the wellbore during drilling process. The functions of drilling fluid mainly include flushing the bottom of the well, carrying cuttings, balancing formation pressure, cooling and lubricating the drill bit, stabilizing the well wall, protecting oil and gas reservoir, and transmitting the ground power, etc. Monteiro et al. pointed out that graphene particles can effectively improve the fluid fluidity, filtration, rheology, stability, lubricity, electrical properties, thermal properties, viscosity and other properties, therefore it can be added to drilling fluid, completion fluid, cementing fluid, etc. . This seDrilling fluids can be filtered into the reservoir at a certain temperature and pressure difference. The filtration loss property of a drilling fluid refers to the property of whether a drilling fluid can be easily filtered into the formation or not. A large amount of filtrate invading into the reservoir will block the oil/gas flow channels and cause damage to the reservoir. At the same time, the thick filter cake  may cause drilling accidents such as undergauging of holes, increased friction, bit freezing, and well leakage. Therefore, it is necessary to add a fluid loss control agent to drilling fluids to ensure the formation of high-quality mud cake and prevent the filtrate from invading the formation during the drilling process .Submicrometer-thick membranes made from graphene oxide can be completely impermeable to liquids, vapors, and gases, including helium, but these membranes allow unimpeded permeation of water . If it cGraphene oxide, as a kind of nanomaterial with the same lamellar structure as graphene, is more suitable for use in water-based drilling fluid than graphene because its surface is rich in polar groups and it has good water dispersibility . During 2 and the diameter of 9 cm at room temperature and 0.689 MPa pressure for 30 min. Compared with standard bentonite , the best filtration loss property was achieved when the mass ratio of flaky GO to powdered GO was 3:1, and the results were that the API filtration loss was 6.1 mL and the filter cake thickness was 20 μm [Kosynkin et al. believed that even if GO was added to a water-based drilling fluid at a dosage as low as 0.2 wt %, it still showed good filtration loss control performance. American Petroleum Institute (API) filtration loss is a commonly used parameter to describe the filtration performance of drilling fluids. API filtrate loss refers to the filtration loss of drilling fluid permeated through the filter paper with the cross-sectional area of 45.8 cmas 20 μm . Xuan etas 20 μm .Graphene has excellent self-lubricating properties, so it can be used to improve the lubricity of drilling fluids. Zhao et al. studied the lubrication and wear properties of graphene particles as lubricant additives added into the PAO4 lubricating oil by means of a UTM-2 tribometer via ball on plate contact reciprocating sliding. The results showed that the friction coefficient and the wear rate can be reduced by 78% and 95%, respectively, when graphene was added .Taha et al. developed nanographene particles that can enter the pores of metals where they crystallize under high pressure to form a protective film, and prevent the formation of balled bits. The tests showed that the extreme pressure lubrication coefficient of water-based polymer drilling fluid could be reduced by 80% after adding graphene with a volume fraction of 1–5%, while it as only reduced by 30–40% after the addition of a common ester-based lubricant. In addition, graphene also can significantly improve the reservoir protection performance of the well completion fluid. After the interaction of graphene-based completion fluid with the reservoir, the reservoir permeability recovery rate reached 41%, while it was only 5% for a conventional completion fluid. After adding 2% graphene into the drilling fluid of a pilot well in Myanmar, the penetration rate increased from 3.0–4.0 to 9.0 m/h, while the friction resistance decreased by 70–80%. Meanwhile, the bit life was extended by 75%, the bit wear was small, and no mud was found on the bit surface. The wear rate of the drill bit was reduced, and no balled bit were seen ,53.Furthermore, Liu et al. pointed out that GO had a better effect on improving the lubricating properties and friction reduction of drilling fluid than graphene. A field application test in Northeast China showed that when 0.075 wt % GO was added to an oil-based drilling fluid, the lubrication factor of the drilling fluid was reduced by 15.6%, the reduction rate of the friction coefficient was increased by 24.3%, and the aluminum disk wear was reduced by 20.5% .Halliday et al. pointed out in their patent that adding graphene particles to the drilling fluid could improve the rheological properties of drilling fluids, such as plastic viscosity, yield pint, gel strength, apparent viscosity, and so on. Using graphene particles 80 mesh size (the particle size distribution was greater than 65%) they could prepare a drilling fluid system with excellent rheological properties, while particles of 120 mesh could be used to prepare a stuck-freeing spotting fluid .Borehole wall stability refers to the ability of the face of a well to maintain its original state. Shale inhibitors are often used to inhibit shale expansion and maintain borehole wall stability. Graphene and its derivatives can also improve the shale stability ,57,58. ACementing fluid is the working fluid used in well cementation. During the process of cementing, the cementing fluid is injected from the casing pipe to the annulus space  pointed out in their patent that both nanographene and nano-GO can be used as crosslinkers for fracturing fluids. When a composite crosslinker system based on the above materials and crosslinkers was used to conduct fracturing, the shear resistance of fracturing fluids was improved by the synergistic effect between nano-GO or nanographene and cross-linking agents . Lv et ant areas . The aboFossil energy sources such as oil and natural gas, are non-renewable energy forms. How to maximize the oil or gas recovery is of great significance to the sustainable development of the global economy, and the enhanced oil recovery (EOR) technology has attracted worldwide attention, in which chemical enhanced oil recovery (CEOR) is one of the most effective ways. The construction of oil flooding systems based on new materials has always been the main direction of the development of chemical flooding for oil recovery. The application of nanoparticles in CEOR, which has developed rapidly in the past two decades, provides the basis for the application of graphene materials in CEOR ,80,81,82Nanofluid flooding technology shows great application prospects in CEOR. The term nanofluid refers to a homogeneous liquid obtained by highly dispersing nanomaterials  in water or other liquid phases (such as ethanol). Compared with the conventional chemical flooding , the nanofluid flooding mechanism is more diversified, including conventional mechanisms such as mobility control, low interfacial tension, wetting reversal, as well as the unique interfacial effects of nanoparticles ,84,85.+ cations acted as a bridge between the two negatively charged surface of the sandstone and GO sheets, and the bridging effect of Na+ was not as much as the effect of pH at low salinities [It is found that graphene oxide can be used in CEOR due to its surfactant-like properties, such as changing wettability, emulsifying property and reducing interfacial tension. Radnia et al. studied the adsorption behavior and mechanism of GO on the sandstone surface  in improving oil recovery, as shown in Namin et al. pointed out that functionalized nitrogen-doped graphene could disperse stably in water in the condition of high salt and high temperature and could reduce the oil/water interfacial tension by 49.2%. Wettability reversal could be achieved by its adsorption on sandstone and limestone surfaces. In addition, when functionalized nitrogen-doped graphene was used as oil displacement agent, the oil recovery could be increased by 16.42%, which they believed was mainly due to its ability to reduce the interfacial tension .2 nanohybrid by the sol-gel method, and pointed out that the Pickering emulsion stabilized by this nano-porous graphene/SiO2 nanohybrid remained stable in a reservoir with a salt content of 1%, the temperature of 25–120 °C, and the pH value of 7–10. It is also pointed out that the composite material can reduce the oil/water interfacial tension, improve the rheology of the injecting fluid, and could be used in chemical flooding [AfzaliTabar et al. prepared rGO/SiOflooding . Tajik eflooding .Polymer flooding, which employs polymers as flooding agents, is a commonly used technique to improve oil recovery. The oil displacement mechanism is to reduce the water-oil mobility ratio and increase the sweep efficiency of the flooding fluid, thereby improving the crude oil recovery ,96. The Haruna et al. prepared graphene oxide/partially hydrolyzed polyacrylamide materials (GO/HPAM) and studied the influence of GO nanosheets on the rheological properties and thermal stability of HPAM. The results show that hydrogen bonds were formed between GO and HPAM. The addition of GO significantly improved the long-term thermal stability of the material, as well as the storage modulus and loss modulus of HPAM. In addition, GO/HPAM composite has good performance under high salt conditions . Lyu et 2 foam flooding to improve oil recovery, in order to improve the foam stability, the stabilizer needs to be quickly migrated onto the surface of the liquid film to form a stable foam boundary, and slow down the drainage of the liquid film of the foam [In the process of COthe foam . The comthe foam ,107,108.the foam ,110,111.2/water emulsion, as shown in 2 flooding. The results show that graphene oxide played a stabilizing role in the CO2/simulated seawater foam system due to the formation of hydrogels and graphene oxide accumulation effect. rGO could not stabilize the foam due to its small size, which increased the hydrophilicity. rGO with the content of 13–22% could not stabilize the foam, which was different from the results obtained by Liu. This may be due to the high reduction degree of the particles, and the increase of oxygen content would enhance the hydrophilicity and reduce the CO2-affinity [Liu et al. demonstrated that partially reduced graphene oxide (rGO) can effectively stabilize COaffinity .Thermal oil recovery is the main method of heavy oil production, which refers to the method of injecting heat from the ground to the stratum or generating heat underground to achieve underground crude oil extraction ,115,116.2O3, NiO, CuO, ZnO, Al2O3, TiO2 and WO3, Fe2O3 exhibited the best viscosity reduction effect. However, if the same heavy oil viscosity reduction rates were achieved, the price of GO was 10–15% lower than that of Fe2O3. Therefore, they claimed that GO not only had a significant viscosity reduction effect for heavy oil, but also was economically feasible, and can be applied to all methods of heavy oil production  [Elshawaf et al. studied the application of GO in heavy oil recovery. They pointed out that when the temperature was 40–70 °C and the GO dosage was 0.02–0.08 wt %, the viscosity of heavy oil can be significantly reduced by 25–60%. By comparing the viscosity reduction of heavy oil treated by other nano particles, such as Fed, etc.) ,125.3O4) have strong magnetic loss to microwave. Therefore, by combining graphene with magnetic nanoparticles, graphene/magnetic nanocomposites with both electrical loss and magnetic loss can be obtained, which is conducive to widening the absorption band and impedance matching, and improving the microwave absorption capacity [The use of microwave irradiation to extract heavy oil has the advantages of continuous heating, being unaffected by buried depth, easy to control, and a low-level of environmental pollution. At present, many countries and oil companies are carrying out relevant research and experiments. However, due to the small dielectric constant of heavy oil, the penetration depth of microwave in heavy oil reservoirs is limited, which affects the viscosity reduction effect ,128,129.capacity ,137,138.Xu et al. prepared magnetic graphene oxide (MGO) by a self-assembly method and conducted microwave-assisted enhanced recovery research. The results showed that MGO had good dispersibility in water. With the increase of microwave radiation time, the dispersibility weakened and formed magnetic reduced graphene oxide (MrGO), showing better lipophilicity and better microwave absorption ability when compared with MGO. MGO-assisted microwave irradiation showed good performance in reducing the viscosity of heavy oil. After microwave treatment for 10 min, the viscosity reduction rate reached 43.61%. In addition, the adsorption of MrGO onto the crude oil droplets could also reduce the viscosity. Compared with conventional water flooding, MGO assisted microwave flooding increased the recovery efficiency by increasing the sweep ratio, as shown in The heterogeneity of the formation makes the injected water directly flow into the oil well along a high permeable layer. The washing action of water to the high permeability layer further aggravates the heterogeneity, which makes it easier for water to break into the oil well along the high permeability layer ,141,142.Profile control and water shutoff are indispensable both in secondary oil recovery  and tertiary oil recovery . The mechanism of profile control and water shutoff to improve oil recovery is to improve the sweep efficiency ,146,147.2/rGO nanocomposite as the crosslinking agent. The novel polymer/graphene nanocomposite had a uniformly distributed three-dimensional network structure. The small size of the gel grid holes made the network structure thermally stable and firmly locked the water in the gel, even at high temperature. The improvement in the properties of this material was mainly due to the high specific surface area provided by graphene at the nanoscale, which increasing the interface interaction between the polymer and graphene. The experimental results of core flooding showed that the pressure drop of sandstone cores with high permeability (Berea sandstone with the permeability of 1000 × 10−3 μm2 and porosity of 21%) increased significantly after treatment. The material had good shear resistance and thermal stability. It can significantly enhance the plugging effect in high-temperature reservoir with lower cost, compared with the existing polymer gel [Almoshin et al. prepared a kind of gel by using low molecular weight polyacrylamide , and ZrOymer gel .Ye et al. found that GO had the function of adjusting the injection volume, plugging the high permeability layer and improving the sweep efficiency, making it can be used as profile control agent in water injection in the oilfield. Flooding experiments in the single core showed that the injection of GO dispersion into the core had two effects, one was to increase the injection pressure of the water phase, the other was to reduce the permeability due to the adsorption and retention of GO. As a result, the mobility of the displacement phase in the core was greatly reduced. Flooding experiments in the two parallel cores showed that in the stage of injecting GO dispersion, it preferentially entered the core with high permeability, and the adsorption of GO in the layer with high permeability caused physical plugging, which increased the injection pressure of high permeability core  have significant quantum confinement effect and boundary effect due to their ultra-small size. They have adjustable band gap and can emit stable fluorescence when stimulated. They are new nano carbon materials with fluorescence properties, in which graphene quantum dots (GQDs) is a special CQDs . MurugesOily wastewater in oilfields refers to all kinds of sewage generated during the process of drilling, production, and transportation, mainly including drilling sewage, wastewater separated from crude oil and other types of oily wastewater ,168,169.Materials with adsorption and separation abilities are often used in oily wastewater treatment ,177,178.6 and 3 × 106 L/(m3·h), respectively [Nguyen et al. prepared graphene nanosheets-based sponges with high oil absorption, good selectivity and recyclability by a dip coating method. The material had super-hydrophobicity and super-lipophilic characteristics, and the adsorption capacity was up to 165 times of its own weight. It was suitable for oil and organic solvent absorption . Also, Qectively .2/GO/rTAc membrane by introducing GO and TiO2 coating into cellulose triacetate (TAC) membrane by electrophoretic deposition. The oil-water separation rate could reach up to 98.9%, exhibiting broad application prospect in oil-water separation [2O3 membrane using GO as the modifier by vacuum transfer method, which has longer service life and better separation performance compared with the unmodified membrane [By adjusting the surface roughness and surface energy, Yang et al. designed a graphene foam material with super hydrophobic characteristics, which had good adsorption properties for both oil and a variety of organic solvents . The enhparation . Hu et amembrane .In the process of oil-gas storage and transportation, crude oil, refined oil and natural gas are all corrosive to equipment and pipelines. With the development of reservoirs with harsh conditions such as high temperature and high salinity, higher requirements are put forward for related metal materials and rubber materials, such as abrasion resistance, corrosion resistance and higher strength ,193.The application of nanotechnology in oil and gas equipment and pipelines is attracting increasing attention in the field of oil and gas industry, especially the application research of nanocomposites. The discovery of carbon nanotubes and graphene with higher strength makes the application of nanocomposites in the field of oil and gas industry become a new hotspot. Nanocomposites refer to the complex system that was prepared based on resin, rubber, ceramic and metal as the continuous phase, and metal, semiconductor, rigid particles and other inorganic particles, fibers, carbon nanotubes and other modifiers as the dispersion phase. The modifier is evenly dispersed in the matrix material by an appropriate preparation method. The equipment and apparatus prepared based on nanocomposite materials have the characteristics of light weight, corrosion resistance, fire resistance, durability and high strength. Nanocomposites can replace some of the metal material components in the oil and gas industry , or as sealing materials , or as coating agent or lubricants ,197,198.Graphene has been widely used in anticorrosive coatings due to its advantages of large specific surface area, good toughness and good self-lubricating property. The graphene-modified coating has a tight structure with improved corrosion resistance and wear resistance. Graphene-modified anticorrosive coatings are a good choice for oil pipe protection ,200,201.During the drilling process, drill bit and downhole power apparatus are the main tools used to break rocks. The harsh environment of high temperature and high pressure put forward higher requirements for drilling tools. Graphene coatings have excellent mechanical properties, which can optimize the surface morphology and characteristics of metal, improve the wear resistance, corrosion resistance and impact resistance of drilling tools, and prevent the tool surface from oxidation and rusting. Chakraborty et al. coated the surface of diamond particles with a graphene film and applied it to PDC  drilling bit, which extended the drilling life, and meanwhile the temperature resistance reached 1200 °C . KeshavaRubber failure is one of the common failures of downhole tools in petroleum engineering. Ocsial company added graphene nanotubes concentrated solution with a mass fraction of 1.7% to nitrile rubber, which increased the tensile modulus of nitrile rubber by about 30%. When the modified nitrile rubber was applied to the rubber stator used in the screw drilling tools, the wear resistance of rubber stator was increased by 20% and the mechanical drilling speed was also increased by more than 20% .Sensors are crucial for finding new oilfields in the process of exploration, safety monitoring in the process of stimulation treatments and data collecting in oil and gas production . In oil 1/2 [In order to ensure the quality of spatial resolution, it is often necessary to use multiple acoustic sensors at the same time in oil exploration. The development of acoustic sensors is directly affected by the development of lightweight diaphragm materials ,214. At 1/2 ,217.The poor conductivity of oil-based drilling fluids could block the direct current, resulting in the unavailability of resistivity logging while drilling. Magnetic graphene nanoribbon stacks (MGNRs) are quasi-one-dimensional graphene-based materials. Their special edge confinement effect makes their properties flexible and adjustable. For example, the magnetic graphene material cannot be used directly because there is no gap between the conduction band and valence band, but it can be applied to the field effect transistor (FET) when it is cut into a smaller scale MGNRs ,219. Gen−1 (45 times higher than that of the silicon piezoresistive pressure sensor) in a wide pressure range (0–50 kPa). The response time under high pressure reached 0.4 ms, which can be promoted in the field of oil and gas exploration [Graphene, as a functional reinforcement material, can enhance the conductivity of composite materials. Compared with other conductive materials, graphene has excellent conductivity, certain degree of flexibility, and good compatibility with organic polymers. It is an ideal material for the preparation of flexible conductive composite materials with organic polymer. Graphene flexible sensors enhance the selectivity of commonly used sensors in oil and gas exploration ,222,223.loration .2 and H2S in natural gas well will gradually exceed the critical value. The corrosion medium will lead to fracture and dropout of rod or tube phenomena, and even cause the scrapping of oil and gas wells. Therefore, the detection of CO2, H2S and other gases is worthy of attention. The graphene-based gas sensor had ultra-high sensitivity and ultra-low detection limit because every atom was able to interact with gas molecule, providing a new choice for oil field gas sensor [There are many types of pipelines used in oil and gas production, and the performance requirements for pipelines are various according to the different construction situations. When the oil field enters the middle or high water cut stage, the properties of produced fluid in oil well has changed, and the partial pressure of the corrosive gas such as COs sensor ,228,229.In the medical field, bones and tissue structures can be distinguished by contrast agents. Similarly, in the field of oil and gas field exploration and development, the fluids and reservoir rock skeletons can also be distinguished by contrast agents, so that the direction of fluid flows can be analyzed and the three-dimensional fracture morphology of the reservoir can be identified. The research of contrast agents based on graphene and its derivatives is one of the hotspots in the biomedical field. Many scholars have shown that the contrast agents based on graphene and its derivatives has good stability, high relaxation rate and easy to monitor and trace. Therefore, contrast agents based on graphene and its derivatives can also be extended to the field of oil and gas industry, expanding their application scope ,231,232.As new materials, the development of graphene and its derivatives needs to go through a gradual process from laboratory discovery to large-scale application, and this should follow the development rules of emerging industries. The application of graphene and its derivatives in the upstream oil and gas industry is still in the initial exploring stage, but with its excellent mechanical, chemical, electrical and optical properties, graphene and its derivatives have broad application prospects in hydrocarbon exploration, oil and water well stimulation, downhole operation, enhanced oil recovery, oilfield wastewater treatment, tools and apparatus, and other aspects. Limited by the cost and the depth of the research, there is still a certain gap between the applications of graphene in the oil and gas industry.In order to promote the application of graphene and its derivatives in the oil and gas industry, further research should be conducted in the following aspects: (1) clarification of the microscopic mechanisms, such as the role of graphene materials in chemical enhanced oil recovery; (2) broadening the research scope in the oil and gas industry, such as the application of graphene materials in shale gas production; (3) revealing the compatibility with other additives, such as the compatibility of graphene materials with surfactant in chemical flooding; (4) putting forward performance requirements for graphene and its derivatives used in the oil and gas industry, such as functional modification of graphene for different purposes in profile control and water shutoff treatments. In addition, how to reduce the cost of industrial application of graphene in the oil and gas industry is particularly important given the current low oil price situation.


The aim of this paper was to improve the fire retardancy of beech wood by graphene. Six fire properties, namely time to onset of ignition, time to onset of glowing, back-darkening time, back-holing time, burnt area and weight loss were measured using a newly developed apparatus with piloted ignition. A set of specimens was treated with nano-wollastonite (NW) for comparison with the results of graphene-treated specimens. Graphene and NW were mixed in a water-based paint and brushed on the front and back surface of specimens. Results demonstrated significant improving effects of graphene on times to onset of ignition and glowing. Moreover, graphene drastically decreased the burnt area. Comparison between graphene- and NW-treated specimens demonstrated the superiority of graphene in all six fire properties measured here. Fire retardancy impact of graphene was attributed to its very low reaction ability with oxygen, as well as its high and low thermal conductivity in in-plane and cross-section directions, respectively. The improved fire-retardancy properties by the addition of graphene in paint implied its effectiveness in hindering the spread of fire in buildings and structures, providing a longer timespan to extinguish a fire, and ultimately reducing the loss of life and property. Based on the improvements in fire properties achieved in graphene-treated specimens, it was concluded that graphene has a great potential to be used as a fire retardant in solid wood species. Wood is a versatile material with a myriad of applications and therefore, its plantation and harvesting are vastly studied all over the world ,2. The iImproving the effects of nanotechnology on different materials has been vastly and intensively elaborated ,19,20,21In this connection, graphene is a one-atom-thick planar sheet of a hexagonally arranged carbon atoms and therefore, it is considered a nano-material. These sheets are densely packed in a honeycomb crystal lattice. Graphene has got appreciable attention over the last two decades due to its special structure and exceptional properties ,35. ThesFagus orientalis) were purchased from the Khavaran Wood Bazar . The density of beech specimens was measured to be 0.62 g·cm−3. Boards were kept in the wood workshop of Shahid Rajaee Teacher Training University  for four months before cutting . They were then cut to size, 220 mm in length, 140 mm in width (plain sawn), and 5 mm in thickness. Specimens were free from any fungal or insect attack, checks or cracks, and knots. Twenty specimens were selected and divided into four treatments; for each treatment, five replicate specimens were prepared. Treatments included: control , painted, NW+painted (nano-wollastonite was mixed in paint and applied on the surface of specimens), and NG+painted  and the anode electrode of graphite foil (2 × 10 cm2). Two electrodes were placed at a distance of 2.7 cm from each other. NiCl2.6H2O powder (98.0% Merck) was dissolved in water  to prepare electrolyte. To provide expansion, exfoliation of graphite, and deposition of Ni, a voltage of 10 V was applied. The Pt electrode was washed every 20 min with HCl and water to avoid the accumulation of the product on the cathode. Finally, the products were collected using vacuum filtration, and then they were washed with water. The end product was dispersible for sonication in water. In the electrochemical exfoliation mechanism, hydroxyl ions (OH) were first produced in the cathode region by applying the voltage between the electrodes, and then the ions accelerate towards the anode and hit the graphite surface. The collision of OH ions with graphite and oxidation at the edge sides and grain boundaries lead to expansion of the graphite layers, penetration of Cl ions through the graphite layers, and reduction of Cl ions to finally produce Cl gas. An excessive force exerted to graphite layers upon Cl gas caused the separation of the graphite layers [2+ ions and proceeded towards the negative electrode under an electric field. Finally, black composite on the Pt electrode was created. Generation of hydroxyl at cathode via ionization of water is as follows [Electrochemical exfoliation of graphite was performed in a system with a cathode electrode of platinum 2 as crystalline layers were deposited on graphene flakes (G-flakes). The final product in form of powders was pressed (under a pressure of 5 MPa for 30 min) into pellets. The average dimensions were 6.5 mm (radius) and 1 mm (thickness), approximately.The OH generation together with other electrons and ions lead to formation of Ni and Ni(OH)2, Ni-oxides) were randomly distributed on graphene sheets. The size of Ni and Ni(OH)2 nanocrystals obtained by TEM and XRD patterns were found to be 30–40 nm. The brightness of graphene sheets appearing in TEM images showed a small thickness (1.2 μm) of graphene sheets [The characterization of Ni-graphene composite was done by X-ray diffraction  radiation, X-ray photoelectron spectroscopy , tunneling electron microscopy (TEM-Philips model CM120), and dynamic light scattering . TEM and XRD patterns of Ni-graphene represented that the nano-crystals e sheets .4 (90–98%). The producer reported that other hydrocarbons accompanied methane . The gas flew steadily at the rate of 0.097 lt/s through a Bunsen type burner hold vertically and the specimen is mounted at a 45° angle to it. The internal diameter of the burner was 11 mm. The Bunsen-type burner provides a fairly mild and localized fire exposure to the testing specimens. The time from the point of burner application that it takes for the specimen to develop a visible flame that is sustained for more than one second will be registered as the “time to onset of ignition”; and the time from the point of burner application that it takes for the specimen to sustain glowing for more than one second will be registered as the “time to onset of glowing”. The higher the amount of time of these two properties, the better from the viewpoint of fire-safety. As the burning continues, the back face of the specimen nearest to the flame of the burner starts blackening and after some more time, a small hole or split appears. These times are also registered as back-blackening and back-holing times. The test is terminated once the back-holing occurs. Then, the burnt area, as well as weight loss, is measured. The whole apparatus is put in a three-wall-compartment in order to protect the burning flame from wind and air movements.Fixed Fire Test Apparatus (FFTA) was designed and built, using piloted ignition, as depicted in Density functional theory (DFT) calculations were carried out for graphene and oxygen molecule with OpenMX3.8 package to calculate the adsorption energy of oxygen molecule on graphene ,45,46. TIn the present simulations, one model for pure graphene flake (G-flake) was investigated. The fully optimized atomic structure of pure G-flake is shown in The adsorption energy, Statistical analysis was carried out by a SAS software, version 9.2 . One-way analysis of variance (ANOVA) was performed on the average values to ascertain significant differences at the 95% level of confidence. Hierarchical cluster analysis, including dendrograms and Ward methods , was carried out using SPSS/18, version 18 . The scaled indicator on top of cluster analysis shows similarities and differences between treatments; lower scale numbers show more similarities while higher ones show dissimilarities. Contour and surface plots were designed in Minitab software, version 16.2.2 .Results demonstrated outstanding improving effects of graphene (NG) on both times to onset of ignition and to the onset of glowing . NG resu−1·K−1, at room temperature [−1·K−1, and that of a purified diamond can be up to 50% higher. However, the thermal conductivity of graphene in cross-section direction  is as low as only 6 W·m−1·K−1 [The improvement in fire properties by graphene can be elaborated from its thermal conductivity as well. With regard to its two-dimensional structure, the thermal conductivity of graphene can also be studied in two directions. The in-plane thermal conductivity of graphene is reported to be one among materials the highest thermal conductivity, about 2000–4000 W·mperature . For com·m−1·K−1 . This ex·m−1·K−1 ,38. OverPainted specimens showed a little bit of decrease in time values, though the decreases were not statistically significant. The decrease, which is not favorable as far as fire retardancy is concerned, was attributed to the easier ignitability of the chemical ingredients of the paint applied on the surface of specimens. The addition of NW to the paint resulted in an increase in both times to onset of ignition and glowing in comparison to the unpainted specimens, though the increase was not statistically significant in time to onset of glowing. The increase was partially attributed to the mineral and unignitable nature of wollastonite. In fact, NW acted as an insulating layer, too, towards the penetration of the piloted fire from the Bunsen burner, protecting the wood substrate beneath the paint.Results of assessing the back of specimens showed that both NG and NW increased the times to back-darkening and to back-holing , showingMeasurement of the burnt area illustrated that NG was very effective in hindering the spread of fire throughout specimens . The sprThe weight measurement of specimens before and after being exposed to fire showed that the lowest weight losses occurred in specimens treated with NG . The weiA significant direct relationship was calculated between most of the fire properties. The highest R-square (99%) was found between the two times to onset of ignition and glowing. Contour and surface plots also illustrated a direct trend among different properties; for instance, weight loss increased as the two times to onset of glowing and ignition increased A,B.The cluster analysis based on all six fire properties studied in the present project demonstrated the distinct difference of specimens treated with graphene in comparison to the other three treatments  . This inFire properties of beech specimens were tested by a newly developed apparatus using piloted fire. Specimens were prepared to be surface-treated by graphene to investigate its improving effects on fire properties. Graphene was mixed at 5% with water-based paint and applied on the front and back surfaces of specimens. As a basis for comparison, three separate groups of specimens were prepared, including specimens without any paint (the control group), painted with no nano-material mixed with it, and painted with 5% nano-wollastonite. Results showed significant improving effects of graphene on all six fire properties studied in the present project. Graphene demonstrated outstanding improvement in times to onset of ignition and glowing, as two very important properties that determine the ignitability of materials. Moreover, graphene illustrated a high impact on decreasing the burnt area. The decrease was also important from the viewpoint of the spread of fire to other surrounding parts in an area. Overall, the improved fire properties provide fire-fighters with a larger timespan to extinguish the fire, ultimately saving both life and property. It was concluded that graphene has a great potential to be used as an effective fire-retardant in wood and wood-composite materials for surface protection against fire. Therefore, further studies should be carried out to investigate graphene from other perspectives, including FT-IR analysis.


Ions in the electrolytes are used to configure electric-double-layers (EDLs) that induce p- and n-type regions in graphene. These EDLs are locked in place by two different electrolytes with distinct mechanisms: (1) a polyethylene oxide (PEO)-based electrolyte, PEO:CsClO4, is locked by thermal quenching ), and (2) a custom-synthesized, doubly-polymerizable ionic liquid (DPIL) is locked by thermally triggered polymerization that enables room temperature operation. Both approaches are gateless because only the source/drain terminals are required to create the junction, and both show two current minima in the backgated transfer measurements, which is a signature of a graphene p-n junction. The PEO:CsClO4 gated p-n junction is reconfigured to n-p by resetting the device at room temperature, reprogramming, and cooling to T < Tg. These results show an alternate approach to locking EDLs on 2D devices and suggest a path forward to reconfigurable, gateless lateral p-n junctions with potential applications in polymorphic logic circuits. A gateless lateral  Orization . After pp-n junction formation and ion-locking are shown in p-n junctions, the highest concentration of ions (~2.4 × 1021 cm−3 at 1.5 V) builds up near the electrode surface and then dissipates with distance away from the electrode, meaning that a more abrupt junction can be expected with decreasing channel length. Note that the device channel lengths reported here are 100 times larger than those modeled in reference [TFSI] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), which has been successfully used as an ion gate ,60, but BG, which means that the DPIL was causing an overall n-type doping of the graphene channel. Note that such an n-type shift was not observed on the bare graphene device , the signature of a p-n junction and an indication that the ions were locked into place. However, unlike the PEO:CsClO4-gated device, I12 also exhibited two current minima . At first blush, a p-n junction would not be expected between electrodes 1 and 2. However, as discussed above, the cations of the DPIL seemed to have affinity for the graphene surface, which means that they would also preferentially accumulate near electrode 1, which was floated during programming and locking. Thus, the preferential accumulation of cations to the graphene surface can explain the additional p-n junction located between electrodes 1 and 2. In the future, the p-n junction between electrodes 1 and 2 can be avoided by further material optimization to avoid preferential adsorption of one type of ion over the other. The corresponding band diagrams are shown in 4, except for the prominent n-type shift observed for DPIL. Focusing again on p-n junction serve as proof-of-concept that alternate triggers can be used to semi-permanently dope 2D devices for room temperature operation. In fact, we have also recently shown that incorporation of thermally-labile linkers into polymerizable ionic liquids allows ions to be released after the materials are polymerized, which we anticipate will enable DPILs that can be locked and then unlocked with a second trigger [n-type doping caused by DPIL polymerization, locking and unlocking the EDLs on demand to demonstrate reconfigurability, and extending the concept to 2D semiconductors to show rectifying behavior. The results of the chemically locked, gateless, graphene  trigger . This typ-n junction is demonstrated on 4-electrode graphene devices by ion-locking using two different solid polymer electrolytes. PEO:CsClO4 is locked by lowering the operating temperature to 220 K , while DPIL is locked by heating to 353 K to polymerize the anions and cations, and then operating the device at room temperature. In both cases, the signature of the p-n junction is double current minima—consistent with what is expected for graphene. For the PEO:CsClO4, reconfigurability of the p-n junction is also demonstrated by resetting the device at room temperature, reversing the polarity of the applied bias, and cooling the temperature to 220 K to create a n-p junction. While the chemical trigger using DPIL is more practical than the low-temperature approach, preferential n-type doping is observed and attributed to the affinity of the cation over the anion for the graphene surface. Overall, this study provides proof-of-concept that triggerable electrolytes can lock-in p-n junctions in graphene, and this approach can be extended to other 2D material, for electronic and optoelectronic applications. A gateless lateral


By exploiting the tunable functionality of graphene, a two-dimensional material, efficient deposition from a chemical was achieved. Ozone-generated defects in the graphene were shown to be required to enhance the morphology and quality of the material and comprehensive characterization of the seed layer and the Sb2S3 film were applied to design an optimal deposition process. The resulting material exhibits efficient carrier transport and high photodetector performance as evidenced by unprecedented responsivity and detectivity in semiconductor/graphene/glass vertical heterostructures. .Despite significant progress in the fabrication and application of semiconductor materials for optical emitters and sensors, few materials can cover the cyan-gap between 450 and 500 nm. We here introduce a robust and facile method to deposit amorphous Sb To fulfill the missing cyan emission component in the PL spectrum, it is urgent to find a semiconductor material with the bandgap at 2.8 eV that can fill the cyan gap presents in the high-quality white light. GaN possesses a bandgap at 2.8 eV but also has a 3.27 eV bandgap for the ultraviolet emission4. Zincblende ZnSs also has a 2.8 eV bandgap structure, but it needs to be under 10 K environment to adjust the bandgap from 2.7 to 2.8 eV4. MnS is another wide-gap semiconductor when its structure is rocksalt configuration, but the bandgap energy is a range of 2.8–3.2 eV5. Semiconductors mentions above have the necessary bandgap at 2.8 eV, but none of them have a good absorption coefficient in the cyan gap.Solid-state light emitters have improved the efficiency, availability, and comfort of lighting in our daily lives. Through a combination of red, green and blue emissions white light can be generated but the quality of color-rendering is not good enough due to the missing cyan emission around 450–500 nm, which is also called the cyan gap2S3 is a promising semiconductor material with different phase structures  depending on the process. Whereas the stibnite phase has a direct energy gap ranging from 1.7 to 1.8 eV, the amorphous phase has a direct energy gap ranging from 1.7 to 2.8 eV8. In the amorphous phase, it has a very high absorption coefficient (1.8 × 105 cm−1)9 at a wavelength of 450 nm. Different from many other semiconductors, Sb2S3 films can be deposited by a variety of facile, inexpensive and scalable methods such as thermal evaporation method10, sputtering method11, polyol reflux method12, chemical vapor deposition method13, spray-lysis method14, hydrothermal method15, and chemical bath deposition method19. However, the formation of amorphous material with stable band-gap properties remains elusive.In chalcogenide semiconductors, Sb2S3 from a chemical bath by utilizing functionalized graphene as a substrate. Since graphene has a poor lattice mismatch with crystalline Sb2S3, only amorphous Sb2S3 can be deposited on functionalized graphene21. To increase the efficiency of deposition, UV ozone irradiation is utilized to functionalize the surface of graphene. Upon optimized deposition, the amorphous Sb2S3 exhibits high morphological stability and good electrical properties. Optoelectronic characterization reveals a bandgap of 2.85 eV and high sensitivity to blue light irradiation yielding high photo-responsivity values (112 A/W), and detection rate . The presented robust and scalable deposition of Sb2S3 on graphene (SSG) opens up new routes for large bandgap optoelectronic devices in light emission and solar cells.We here demonstrate the robust deposition of amorphous Sb22. The growth pressure was kept constant at 10 Torr and the flow rate ratio of H2/CH4 was fixed at 20 resulting in identical partial pressures for various flow speeds. A standard wet-chemical transfer process was employed to remove graphene from the growth substrate and deposit it on a 300 nm Si/SiO2 substrate for further characterization23.Graphene was grown on untreated Copper foil  following previous reports2S3 film was made from the literature published by PK Nair et al. in 199722. We used sodium thiosulfate (Na2S2O3·5H2O) and antimony trichloride (SbCl3) as the source of sulfur ions and the source of cerium ions when antimony trichloride (SbCl3) is reacted with sodium thiosulfate (Na2S2O3) and deionized water (DI Water). Absorbance, A%, and Transmittance, T% were measured by Thermo Scientific UV–Vis spectrophotometer, I–V and I–T measurements were conducted in Keithley 2636B on macroscopic (1 cm2) samples using silver paint electrodes. Raman spectroscopy was carried out in a homebuilt confocal setup using a 532 nm excitation and PL spectra were measured in Acton Series (SP-2156) spectroscopy. X-ray diffraction analysis was carried out in BRUKER D2 PHASER X-ray diffractometer. SEM images were carried out in Hitachi S-480 Scanning Electron Microscope.SbIt can be seen that the surface morphology of graphene before and after UV irradiation is not much different in Figs. D/IG and the high I2D/IG ratio of unmodified graphene  corroborate the presence of single-layer graphene with few defects . The incident source of the excitation element is a 405 nm laser. The incident light intensity is 10–60 mW/cm2 and the measurement voltage is 1–15 V. The SSG composite components grown for 2–8 h were compared by 405 nm illumination I–V measurement, and it was found that the illumination current was significantly improved at a growth time of 6 h in Fig. 2S3 film on the UV irradiated graphene due to the oxygen functional group on the graphene surface, the graphene defects are increased, and the graphene high carrier mobility is sacrificed26. Therefore when an electron–hole pair is generated after illumination, the photocarrier is trapped by the modified graphene defect before being injected into the pure graphene layer, compared to no illumination condition, as schematically shown in Fig. The dimensions of the components are glass (1.5 cm × 1.5 cm), graphene (1 cm × 1 cm) and Sb27.A comparison of the signal peak, photocurrent and rise time of the atmosphere and vacuum in Fig. When unilluminated, part of the photocarriers are still trapped by the modified graphene defects, making the photocarriers difficult to recombine and prolonging the excitons recombination time, cause additional a few seconds needed for the rise and fall times to complete the on/off action in the SSG.2) in the atmosphere that will attract electrons that jump to high energy states, producing negatively charged oxygen atoms , P is the incident light intensity of the xenon lamp, and S is the effective illumination area. Because our growing material area is larger than the illumination spot area, we do not need the area item in this experiment.2. In the ultraviolet band, when the light of the wavelength of 350 nm is irradiated. The optical response of the component is also 69.76 AW−1. When the wavelength of light absorbed by Sb2S3 exceeds 568 nm, the photo-responsivity value immediately drops to zero and there is no absorption at all. Therefore, it can be found that Sb2S3 is only in the ultraviolet to the visible range for photo-responsivity to occur, and the best photo-responsivity value in the visible light band will also confirm the argument that the Sb2S3 enthalpy gap deposited in this study is about 2.2 eV. The detection rate corresponding to the response value can be calculated by the following formula.When the light of the wavelength of 450 nm is utilized, the optical response is 112 A/W when the optical power intensity is 1 μW/cm–19 C. After calculation by the above formula, it has the highest response value at 450 nm and the highest detection rate, which is 2.01 × 1012 Jones, shown as Fig. R is the spectral response value, Id is the dark current measured by Xenon lamp, S is the effective illumination area, and e is 1.609 × 102S3 can be deposited on graphene after UV irradiation for 5, 10, and 20minutes. In the measurement of photoelectric characteristics, no photocurrent and switching characteristics were found from 5 and 20 min of UV irradiation. Therefore, in this study, the modified 10-min graphene was used as the best parameter for Sb2S3 film deposition. The effects of different Sb2S3 film deposition time from 2 to 8 h on the photoelectric properties of graphene were compared. It was found that the film thickness was not proportional to the photocurrent increase. Due to the increase in film thickness, the charge was transferred during the transfer process due to the graphene defect trap produced via UV irradiation. Influenced by the scattering between the particles, thus increasing the chance of carrier recombination and slowing down the rise time. Finally, the UV ozone irradiation was modified for 10 min and after 6 h of Sb2S3 film deposition, which had the best rise time of 27.05 ms for the 405 nm laser. Optimal photo-responsivity value 112 A/W and detection rate 2.01 × 1012 Jones, demonstrating that semiconductor Sb2S3 materials can increase the photo-responsivity of graphene.Using graphene with different UV irradiation times to find the best growth parameters, we found that SbSupplementary information.


Hybrid transparent contacts based on combinations of a transparent conductive oxide and a few graphene monolayers were developed in order to evaluate their optical and electrical performance with the main aim to use them as front contacts in optoelectronic devices. The assessment of the most suitable strategies for their fabrication was performed by testing different protocols addressing such issues as the protection of the device structure underneath, the limitation of sample temperature during the graphene-monolayer transfer process and the determination of the most suitable stacking structure. Suitable metal ohmic electrodes were also evaluated. Among a number of options tested, the metal contact based on Ti + Ag showed the highest reproducibility and the lowest contact resistivity. Finally, with the objective of extracting the current generated from optoelectronic devices to the output pins of an external package, focusing on a near future commercial application, the electrical properties of the connections made with an ultrasonic bonding machine (sonic welding) between the optimized Ti + Ag metal contacts and Al or Au micro-wires were also evaluated. All these results have an enormous potential as hybrid electrodes based on graphene to be used in novel designs of a future generation of optoelectronic devices, such as solar cells. Although graphite, one of the crystallographic forms of carbon, has been relatively well known for a long time, its two-dimensional version—graphene—is a much more recent object of research. The lamellar structures of graphite and of thermally reduced graphite oxide were already known in the mid-19th century . Despite2 hybrid orbitals of the mutually-bonded carbon atoms. It is therefore a two-dimensional material (2D). Such an atomic arrangement and its two-dimensional structure are the factors conferring extraordinary properties to graphene.Graphene is defined as the material made of a single layer of carbon atoms distributed in the vertexes of a hexagonal network. This hexagonal shape (honeycomb) results from the covalent bonds generated by the overlap of the sp2⋅V−1⋅s−1. A single layer of graphene absorbs 2.3% of incident light, allowing around 97.7% to pass through [Graphene is also a zero-gap semiconductor. Its electron mobility is extremely high, of the order of 150,000–200,000 cm through . As a ru2:F) abbreviated as FTO, indium tin oxide (In2O3:SnO2) abbreviated as ITO, and aluminum doped zinc oxide (ZnO:Al2O3), abbreviated as AZO. They usually play the role as transparent electrodes, and thus, they must have n-type conductivity [Many of the described properties of this new material are outstanding in many senses, but for the purpose of the present work, the above-mentioned electrical and optical features are particularly relevant. The possibility of obtaining an excellent sheet conductance in combination with a very low absorption of light (for one or a few atomic layers), added to an extremely low reflection to visible light, all of this without adding more than a few angstrom to device thickness, makes graphene an excellent candidate for those optoelectronic applications in which low sheet resistances, exceptional responses at high frequencies, low contact resistances or reduced light absorption are required. A wide range of optoelectronic devices such as light emitting diodes, photodiodes, liquid-crystal displays, touch screens or solar cells require transparent or semi-transparent contacts having such properties . In addiuctivity . The TCOuctivity . Among tuctivity . For theAmong the TCO materials, ITO is currently the most commonly used in silicon heterojunction solar cell (SHJ) technology. This semiconductor material is well-known from its mass production and exhibits very suitable optoelectronic properties. Generally, ITO is deposited by direct current (DC) magnetron sputtering on large areas . Otherwi13 cm−2. Tests involving different metals, surface treatments and innovative architectures have also been reported. Among them, Cr/Pd/Au (1/15/50 nm) metal stack fabricated by e-beam evaporation on CVD graphene using a pre-plasma treatment presenting ~270 Ωµm contact resistivity [On the other hand, to efficiently extract the current in the SHJ device, a front metal grid must be evaporated finally. Therefore, it is essential to achieve low resistive metal contacts. As the graphene atomic layers are part of the hybrid electrode concept, appropriated metal stacks with ohmic character deposited on top of graphene also play a vital role in the device operation. In graphene-based technology, several investigations have been devoted to check different metals with proper work functions for electronic devices such as field-effect transistors . These sistivity , Ni/Au  or gold (Au) micro-wires to Ti + Ag front contacts could modify the contact resistance of the metal/graphene interface were also carried out. At this stage, the ideal Ti + Ag thickness layer and the setting of the parameters used in the semiautomatic wedge-wedge bonding machine were calculated to minimize the resistance of the sonic welding and to avoid interface damage. The results derived from this investigation have a considerable potential for the development of advanced transparent or semitransparent electrodes based on graphene and its application in novel designs of optoelectronic devices. The research of such a combination and of adequate preparation protocols is the kernel of the present paper.The hybrid transparent contacts described in this work are based on the combination of a common TCO and 1 to 3 graphene monolayers. In most optoelectronic devices, an ohmic low-contact-resistance metal electrode is essential in order to extract current with the lowest power losses. Hence, this metal stack plays a relevant role in device operation. The choice of the metallization is a critical step in outlining the cost and efficiency of solar cells and is considered as a vital factor for achieving high efficiencies. For this reason, strategies to reduce the metal contact resistance were also developed in this work. 4 precursor, prepped for transfer with polymethyl methacrylate (PMMA) coating, and finally transferred to the desired substrate. The CVD fabrication technique was preferred because it can produce relatively high-quality and high-purity graphene and potentially on a large scale. More details about the graphene fabrication can be found in reference [The graphene monolayers were grown by the Spanish company Graphenea S.L. by chemical vapor deposition (CVD) on copper foil from CHeference .2O3  commercial target subject to radio-frequency (RF), and indium tin oxide (ITO) was obtained from a ceramic 4-inch In2O3:SnO2  commercial target subject to direct current (DC). Argon of a purity of 99.999% was used as the inert gas in the sputtering process, and the control of its flux was carried out by means of a mass-flow controller. All the TCO films were deposited at low temperature in order to work in conditions compatible with the preparation of different kinds of optoelectronic devices having a particular sensitivity to high temperatures.The TCO materials were fabricated using a commercial Leybold UNIVEX 450B magnetron sputtering system . Aluminum-doped zinc oxide (AZO) was deposited by using a ceramic 4-inch ZnO:AlDifferent combinations of TCO and graphene were tested, with different deposition and transfer sequences in order to assess technological paths taking into account the mutual compatibility of the processes involved as well as the properties of the resulting multilayers.2 quartz to make electrical measurements, 2 cm × 2 cm Corning glass to produce samples for testing transparency, and 2 cm × 2 cm silicon substrates yielding samples suitable for the assessment of their antireflecting capability. The latter is considered an essential property in the specific case of front transparent contacts for silicon-based solar cells.Three different substrates were used: 1 × 1 cmThe metal stacks were evaporated by thermal evaporation on the graphene-based transparent contacts by using a commercial UNIVEX 300 system. The metals tested in the different schemes were aluminum (Al), palladium (Pd), nickel (Ni), titanium (Ti) and silver (Ag), respectively. This choice was done based on metal costs, except for Pd, which was used because it is one of the most commonly used metals in high-efficiency photovoltaic device technology. cρ) and the current transfer length (TL) were determined for the metal stacks, as well as the sheet resistance (sR) of the transparent contacts, by using the transmission line method (TLM) [TR. Then, TR was plotted as function of the contact spacing d to extract parameters such as the TL, measured from the intersection of the TR curve for TR = 0, and the ρc, usually obtained from the plot using the extracted TL and the sheet resistance sR [To determine the electrical parameters, four metal coplanar parallel electrodes of 0.1 cm width and 1 cm length unequally spaced  were deposited by thermal evaporation onto the samples. These monolayers had been previously transferred onto 1 cm × 1 cm quartz substrates. These measurements were carried out by testing 4-point electrical resistance between all the possible electrode pairs with two contacts on each electrode. The electrodes were contacted by means of 4 micro-positioners, a power supply was used to bias the samples, an electrometer measured currents and a voltmeter provided voltages. The overall system is pictured in od (TLM) . These Ttance Rs .To determine the fraction of light transmitted by the different layers that compose the transparent contact, optical transmission maps were obtained by using an experimental optical-transmittance-mapping (OTM) system that combines a focused white-light lamp, an X-Y linear-positioner set, a pair of current pre-amplifiers, a reference photodiode and a pair of digital voltmeters. Finally, the optical total  reflectance of the transparent contact as function of the wavelength was measured using a UV/Visible/NIR Perkin Elmer Lambda 1050 spectrophotometer, equipped with a 6-mm-diameter integrated sphere.The ultrasonic wire bonding technique is considered as one of the most flexible and cost-effective to assemble the vast majority of semiconductor packages. It commonly uses either Au or Al wires with tens of micrometers of diameter to interconnect integrated circuits (IC) or other semiconductor devices, and to package during the semiconductor device fabrication. Hence, it can be very useful to connect an IC to other electronics, or to connect from one printed circuit board (PCB) to another.To extract the current generated by the optoelectronic device is mandatory to interconnect the optoelectronic device to the supporting board, as it is depicted in In this work, the ultrasonic wire bonding technique (labeled as sonic welding) was chosen to make the connections. For this purpose, the bonding machine used was the 5632DA model from F&S BONDTEC Semiconductor GmbH  . Three mTo measure sonic welding contact resistance, a four-wire technique was used with the home-made system pictures in c of the conventional metal stacks previously described was determined for the different metal stacks tested. The metal stacks were evaporated at room temperature on graphene monolayers, bilayers and trilayers, respectively, previously transferred onto quartz substrates at the common transfer process conditions used by the supplier of the graphene monolayers (www.graphenea.com) [The contact resistivity ρnea.com) . The metnea.com) . Al and cρ and transfer length TL depending on the metal stack used. In addition, the sheet resistance sR of the graphene material underneath was estimated in each case.It was found that the contact resistivity to graphene monolayers was lower if using Ti + Ag and Ni + Al metallic combinations. Pd and Al contacts were much more resistive. The sheet-resistance data obtained by the graphene monolayer using Al for the contact were very disparate, as seen in the out-of-range value of 843 Ω/sq and its wide error bar. This value was far from that given by the supplier  and thosT calculated, the longest value was reached by the Ti + Ag contacts. That implies that electrons travel a longer distance in the graphene beneath the contact before flowing up into it. A possible explanation about why the metal stack based on Ti presents a better electrical performance could be related to the positive difference of the work function at the graphene/Ti interface, close to 0.15 eV [From the results in  0.15 eV . A charg2 plasmas and UV-O3 gentle activation steps. The high temperature regime includes processing steps at a temperature range from 200 to 450 °C, that is, annealing in vacuum at 200 °C, the use of temperature up 450 °C in inert atmosphere, or both; while the low temperature regime avoids those steps and the temperature is not superior to 120 °C [sR, measured with the system presented in 2/Si substrates [The compatibility between the conditions used in the graphene transfer method  and the temperature applied to fabricate the cell material was evaluated. It is very important to perform these analyses because the hybrid transparent contact based on graphene is incorporated at the last manufacturing step. Hence, parameters such as the temperature and the environment used in the transfer process could negatively affect the performance of the material located underneath and that constitutes the device. For this reason, low- and high-temperature transfer procedures were mutually compared; avoiding Oo 120 °C . Table 2bstrates .sR, a slight electrical improvement was observed in the graphene material transferred at low temperature. This work undergone so far clearly suggests the possibility of reducing the temperature in that process while the material performance is maintained. In addition, the low substrate temperature would also benefit the deposition of the hybrid transparent contacts based on a TCO by reducing the possible damage to it.It can be noticed that the average white-light transmission values were in agreement with the theoretical predictions made according to the number of graphene monolayers . TherefoThe second step consisted of evaluating the position where the graphene monolayers should be placed within the hybrid transparent contact structure. This required the study of the possible damage to graphene material produced by the bombardment of the high-energy sputtered particles during the TCO deposition. For that, three graphene monolayers were placed in two positions: (i) transferred onto the already TCO-coated resistive glass  where the graphene material was transferred at low temperature. AZO and ITO materials were incorporated into the contact to enhance both the optical and electrical device performance. From the optical point of view, the main role of the TCO is to act as an antireflection coating diminishing the amount of light reflected on the solar-cell surface; that means, to eliminate unwanted reflection and increase the overall transparency. Hence, the thickness of the TCO must be fitted so that the wavelength in the dielectric material is one quarter the wavelength of the incoming wave, according to formula (1)spectrum . TherefoFrom the electrical point of view, the TCO must present the lowest possible resistivity to reduce device resistance and to extract the current in the most efficient way. Under these considerations, the performance of the hybrid transparent contacts was evaluated from the figure of merit (FOM) y Haacke  given by2-size TCO-coated silicon wafers, and the TLM mask used in this work with the further TLM structure based on Ti + Ag evaporated on graphene monolayer transferred onto quartz  for the bare ITO layer. This almost negligible difference was considered within the measurement error; therefore, the addition of the graphene material into the transparent contact would not affect its AR capability. 2 substrate were around 40 ± 12 mΩ. These values are found to be typical for sonic welding at ambient temperatures using AlSi wires and Ag substrates; this is a very promising result for the applications of the graphene-based technology. So far, no tests have been done on solar cells with the hybrid transparent electrodes, but they are foreseen in the near future. In depth studies about damage produced by the wire bonding on graphene/metal interface should be done.With the future goal of integrating the optoelectronic device based on the optimized hybrid graphene/TCO transparent electrode described above into a PCB, it is necessary to minimize the resistance connections of the wire bonding used. For this reason, the contact resistance of the welding Ti + Ag metal contact-AlSi wire, made with the ultrasonic wire bonding machine showed in This work presents the optimization of a metal stack combination being a candidate to make ohmic contacts for silicon-based photovoltaic devices. The metal combinations tested were Ti + Ag, Al, Ni + Al and Pd, being the first one that showed the most reliable and reproducible data with the lowest specific contact-resistance value.The evaluation of the preparation protocols used in the fabrication of the hybrid transparent contacts based on a common TCO and graphene monolayers was also studied. The first parameter evaluated was the temperature used during the graphene transfer process. Reduced sheet-resistance values of the graphene monolayers were obtained at low temperature. The optimum spatial configuration of the layers forming the hybrid transparent contacts was also determined. A strong effect on electrical properties of graphene due to the bombardment of the highly-sputtered atoms during the sputtering process of the TCO thin film was observed. Hence, adequate preparation conditions should include transferring the graphene monolayers onto the TCO and not the opposite. A correlation between the avoidance of aluminum  and good and repeatable electrical properties was found. Combinations of graphene with ITO were systematically better than those of graphene and AZO.Therefore, a suitable combination of graphene and ITO thin film in a hybrid transparent contact deposited on silicon was found, showing appropriate performance for it to be used as an electrode in optoelectronic devices, more specifically, for silicon-heterojunction solar cells. Finally, 25 µm-thick AlSi bonding wires were used to connect the samples with Ti + Ag contacts to a PCB. The contact resistances of such wires were around 40 ± 12 mΩ, resulting in suitable values for this type of wire bonding at ambient temperature.All these approaches have an enormous potential to open new horizons to achieve the definitive take-off of graphene technologies for electrical standard and transparent contacts.


Sarcoidosis is an idiopathic systemic granulomatous disease that presents with noncaseating granulomas most commonly affecting the lungs and mediastinal lymph nodes. Patients often have nonspecific symptoms, including cough of unknown cause, fever, shortness of breath, fatigue, or weight loss. The diagnosis for sarcoidosis is relatively challenging in the sole presence of swollen lymph nodes and the absence of the aforementioned symptoms. We present a case of unilateral axillary lymphadenopathy found on routine mammography; ultimately proven to be an atypical symptom of sarcoidosis. Our goal is to highlight radiologic features that help distinguish sarcoidosis from potential malignancy. Palpable lymph nodes when present are more related to benign than malignant disease processes . The difDiagnosis for sarcoidosis requires data from clinical features, radiologic findings, histologic evidence of noncaseating granulomas, and exclusion of other causes. However, many patients are asymptomatic and thus are incidentally diagnosed with the presence of hilar lymphadenopathy during chest radiography. Sarcoidosis may also present with peripheral lymphadenopathy in approximately 2% to 25% of patients, which is also a common initial finding of several malignant diseases, such as breast carcinoma and lymphoma [A 66-year-old woman with a past medical history of pulmonary sarcoidosis presented for her routine screening mammography. Her family history was significant for a daughter having papillary carcinoma with bone metastasis. The patient self-reported as a past smoker. Her routine mammography showed scattered areas of fibro-glandular density in bilateral breasts and right axillary lymphadenopathy Figure . There wDue to the patient's past medical history of sarcoidosis and the suspicion of malignancy, a CT scan of the thorax was performed to further evaluate the accurate diagnosis. The CT scan of the chest showed hilar and mediastinal lymphadenopathy Figure . BilaterA tissue biopsy of the right axillary lymph node was performed for a definitive diagnosis. The histological findings showed non-necrotizing granulomas composed of epithelioid cells with scattered Langerhans giant cells and lymphocytes Figures , 5B. StaThe above findings were consistent with her history of pulmonary sarcoidosis and hence, she was recommended to follow-up with her pulmonologist.The presence of generalized lymphadenopathy almost always indicates a significant systemic disease process, such as lymphoma, sarcoidosis, mononucleosis-type syndromes, tuberculosis, human immunodeficiency virus infection, and hepatitis. On the other hand, localized lymphadenopathy means only one area is involved and often indicates a local infection or malignancy . OftentiSarcoidosis can be confused with many other diseases, especially in the absence of its typical presentations, such as cough, constitutional symptoms, uveitis, and erythema nodosum. On imaging, 90% of the cases show hilar, paratracheal, and mediastinal lymphadenopathy which is often bilateral and can progress to interstitial lung disease . PeripheMalignancy is an important differential diagnosis to rule out in the sole presence of adenopathy. Malignant causes of axillary lymphadenopathy include breast cancer, lymphoma, melanoma, or metastases from other sites. Metastatic breast cancer may present with an initial spread to bilateral anterior and central axillary lymph nodes . ImagingDiagnosis for sarcoidosis requires combined information from clinical features, radiologic findings, and histologic evidence. Sonographic findings of axillary sarcoidosis include hypoechoic, oval, or round lymph nodes with well-circumscribed margins and a homogenous echotexture . The afoSarcoidosis lymphadenopathy often presents bilaterally in multiple regions. As a result, the unilaterality of the lymph node involvement and the absence of active sarcoidosis symptoms in our case can make the accurate diagnosis a challenging task. The differential diagnosis for unilateral axillary adenopathy is broad, including both benign and malignant causes. Malignancies such as metastatic breast cancer and lymphoma must be excluded. Therefore, multiple imaging modalities and tissue biopsies are warranted to assist with the diagnostic process.