Conveyor CVD to high-quality and productivity of large-area graphene and its potentiality

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However, the chemical vapor deposition (CVD) systems previously studied for graphene production face bottlenecks in terms of quality, speed, and reproducibility. Herein, we report a novel conveyor CVD system that enables rapid graphene synthesis using liquid precursors. Pristine and nitrogen-doped graphene samples of a size comparable to a smartphone (15 cm × 5 cm) are successfully synthesized at temperatures of 900, 950, and 1000°C using butane and pyridine, respectively. Raman spectroscopy allows optimization of the rapid-synthesis conditions to achieve uniformity and high quality. By conducting compositional analysis via X-ray photoelectron spectroscopy as well as electrical characterization, it is confirmed that graphene synthesis and nitrogen doping degree can be adjusted by varying the synthesis conditions. Testing the corresponding graphene samples as gas-sensor channels for NH 3 and NO 2 and evaluating their response characteristics show that the gas sensors exhibit polar characteristics in terms of gas adsorption and desorption depending on the type of gas, with contrasting characteristics depending on the presence or absence of nitrogen doping; nitrogen-doped graphene exhibits superior gas-sensing sensitivity and response speed compared with pristine graphene. Graphene Synthesis Doping Chemical Vapor Deposition Conveyor Productivity Gas sensor Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Since the discovery of graphene [ 1 – 3 ] , there has been continuous research on the synthesis of large-area graphene. [ 4 , 5 ] Conventional batch-type methods for graphene synthesis can be segmented into the following processes: heating, annealing of catalyst metal surface, graphene growth, and cooling; each process is executed independently. [ 6 , 7 ] However, these methods, despite yielding satisfactory graphene at the laboratory level, are not competitive in terms of future industrial applications owing to the slow production speed. To overcome these bottlenecks, we focused on improving conventional chemical vapor deposition (CVD) methods, including both systems and recipes. The roll-to-roll CVD system has been consistently reported for scaling up graphene production. [ 8 – 10 ] In this process, a copper foil roll, which acts as the catalyst metal, is transported within a chamber filled with hydrocarbon gas; a thin carbon film is deposited on the copper surface as it moves to the high-temperature zone. The catalyst metal is continuously moved into and out of the CVD reaction zone, allowing the sequential execution of heating, surface annealing and reduction, growth, and cooling. This process enables the synthesis of large-area graphene in a short time. However, the individual processes cannot be controlled independently. Furthermore, when the metal foil moves continuously, it is exposed to the carbon precursor at a lower temperature than the target temperature in areas far from the reaction zone, resulting in the deposition of an amorphous carbon film. Additionally, the mechanical forces applied to the metal foil during its transportation between the high- and low-temperature zones cause alternating tensile and compressive stresses, creating defects in the graphene. [ 8 , 9 ] As a result, synthesizing high-quality materials in this system is challenging. Furthermore, because graphene is synthesized on a metal catalyst roll, only flexible substrates must be used, greatly limiting the substrate scope. Efforts have been made to overcome these challenges, such as mechanically separating the annealing and growth zones, [ 11 , 12 ] or attempting to maintain consistent tension by moving the foil vertically. [ 10 ] However, the quality of graphene synthesized has not improved sufficiently. Although numerous studies have reported on the mass production of high-quality large-area graphene, challenges such as the formation of graphene defects and nonuniformities such as adlayers still persist. In addition, for the practical application of graphene, research on property modulation through doping is crucial. Various methods have been employed for the synthesis of doped graphene, including the plasma post-treatment of pristine graphene and the CVD of dopant-containing carbon precursors. However, the former is prone to a relatively high level of defects and requires multiple processes, [ 13 ] whereas the latter results in nonuniform doping. [ 14 , 15 ] Furthermore, research on the mass production of doped graphene has not yet been conducted. Therefore, the development and optimization of systems and processes that overcome the drawbacks of the existing roll-to-roll CVD system are crucial for the mass production of high-quality graphene with desired properties, which in turn is key for the industrialization of graphene. In this study, to overcome the drawbacks of the roll-to-roll CVD system, we developed a novel conveyor-type CVD system and optimized its mass-production process (Fig. 1 a.). As mentioned earlier, conventional batch-type CVD allows high-quality graphene synthesis but is challenging for mass production, whereas roll-to-roll CVD allows mass production but suffers from insufficient quality. The conveyor system retains the advantages of independent process control from segment-based batch-type CVD and continuous production from roll-to-roll CVD, while eliminating the respective drawbacks of low productivity and reduced quality caused by decreased process control flexibility. In our system, while the desired temperature is maintained at the reaction zone for annealing and growth, the substrate prepared in the cartridge sample holder is transported to the reaction zone by a conveyor belt. The process gas is then toggled according to each process segment, completing annealing and growth. After growth, the substrate is transported to the opposite cartridge holder. Importantly, only the carbon-containing precursor is injected during the synthesis, whereas the residual carbon gas is removed during the other processes. This iterative method enables the continuous synthesis of high-quality graphene. Furthermore, it is versatile, allowing for the use of various substrates, such as flexible substrates, rigid wafers, metal foams, and powders (Fig. 1 b., Figure S1 . ). Various carbon sources of all phases have been utilized as graphene precursors, with the growth time and temperature conditions varying significantly depending on their phase. [ 16 ] Dehydrogenation of the carbon source is particularly crucial in determining the growth time. 17 For example, traditional CVD with methane gas, which is common for graphene synthesis, requires a prolonged synthesis time of over 10 min at temperatures around 1000 ℃ owing to the high C–H bonding energy. [ 4 , 5 , 18 – 20 ] Therefore, to achieve mass production of graphene, it is essential to identify suitable carbon precursors and synthesis conditions that allow rapid synthesis. We previously reported the high-speed synthesis of pristine graphene using LPG [ 21 ] and nitrogen-doped graphene using pyridine, a nitrogen-containing organic solvent. [ 22 ] Based on prior research, we applied these methods to our conventional CVD system, utilizing pure liquefied butane for pristine graphene synthesis and pyridine for N-doped graphene synthesis; consequently, our conveyor CVD system achieved the desired quality of graphene with high productivity and reproducibility. Furthermore, we used the N-doped graphene to enhance the properties of other 2D materials. [ 23 ] We optimized the synthesis conditions, namely the growth temperature and time, for the mass production of pristine and N-doped graphene. Finally, we demonstrated the potential application of these pristine and doped samples as gas sensors for various applications. 2. Experiment 2.1 Graphene Synthesis Pristine and nitrogen-doped graphene were synthesized using pure butane (99% purity, n-Butane; Sigma-Aldrich) and pyridine (99.8% purity, anhydrous; Sigma-Aldrich), respectively, on a copper foil (99.8% purity, 25 µm thickness; Alfa Aesar) using the conveyor CVD system; various high-speed synthesis conditions were investigated to determine the optimal conditions for the desired quality or dopant content of graphene. The sample was heat treated at the target temperatures for a constant 1 min duration of hydrogen treatment at 50 sccm and 380 mTorr. After heat treatment, pristine graphene synthesis using butane (3 sccm; 170 mTorr) or nitrogen-doped graphene synthesis using pyridine (100 mTorr) was conducted over various synthesis times (30, 45, 60, and 90 s) to optimize the synthesis time. Twelve substrates, each sized at 15 cm × 5 cm, were transported from the cartridge holder and subjected to 1 min of heat treatment ( Figure S3 . ) and 1 min of growth, resulting in the synthesis of 12 samples in 1 h (Fig. 1 b.). A supplementary video related to this process can be found at https://doi.org/?(to be updated). The synthesized graphene, supported with a PMMA layer on the top surface, was spin-coated and electrochemically delaminated to separate it from the copper foil, [ 24 – 26 ] then transferred onto a SiO 2 substrate for evaluation of its optical and electrical characteristics, among other properties. 2.2 Characterization The graphene samples synthesized on copper foil under various conditions were transferred onto 300-nm SiO 2 substrates for Raman spectroscopy, which was performed on 30 points for each sample, both before and after transfer, using the Renishaw inVia Raman microscope with a 514-nm laser. Additionally, the graphene samples on gold film deposited SiO 2 substrates were subjected to X-ray photoelectron spectroscopy (XPS) to analyze their elemental compositions and bonding structures. The graphene samples transferred onto 300 nm-thick SiO 2 substrates were then used to fabricate back-gate field-effect transistors (FETs) with 10 µm × 10 µm graphene channels. These devices were loaded into a vacuum chamber (pressure below 3×10 –3 Torr) and interfaced with a source measure unit (SMU; Keithley 236 & 237) using a LabVIEW program. The electrical response characteristics were measured as functions of the gate voltage and source-drain current. To demonstrate the potential applications of the graphene samples, both pristine and nitrogen-doped samples were exposed to NH 3 and NO 2 , and their electrical characteristics were measured. The gas sensitivity was evaluated using the response properties calculated from the resistance and current changes in each sample channel as a function of gas type, gas concentration, and exposure time. 3. Result and Discussion 3.1 Raman Spectroscopy Figure 1 a. shows the conveyor CVD system process. The substrate was first loaded into the left cartridge and placed on the copper metal foil; the foil acted as a conveyor belt and transported the cartridge to the center of the furnace, where the substrate underwent heat annealing and growth. It was then transported to the right cartridge. Simultaneously, during transport of the substrate from the loading chamber to the growth area, the temperature increased rapidly from room temperature. As reaction with a carbon source during transport can cause the deposition of amorphous carbon, synthesis gas was not supplied, and only hydrogen was supplied for reduction. The furnace was operated at various target temperatures—850, 900, 950, and 1000 ℃—for a 1 min hydrogen treatment to optimize the heat treatment temperature. The heat treatment time was varied to find the minimum temperature for rapid synthesis ( Figure S2 . ). Figure 1 c. shows the Raman spectra of pristine and nitrogen-doped graphene synthesized on copper at 900 and 1000°C, respectively, for 60 s. For the pristine graphene, the G peak appeared at ∼1588 cm –1 , and the 2D peak at ∼2698 cm –1 . Meanwhile, for the nitrogen-doped graphene, the G peak appeared at ∼1595 cm –1 , and the 2D peak at ∼2724 cm –1 ; both the G-peak and 2D peak exhibited blue shifts of approximately 7 cm –1 and 6–7 cm –1 , respectively. To determine the maximum graphene area achievable through conveyor-type CVD synthesis, graphene samples were synthesized at various positions along the furnace; the temperature was measured at each position, and the synthesized graphene samples were analyzed using Raman spectroscopy (Fig. 2 .). Using a 45-cm furnace as the reference, we confirmed the synthesis of high-quality graphene in an area measuring 5 cm × 15 cm, approximately equal to the size of a smartphone screen. Figure 3 . shows the Raman spectra of pristine and nitrogen-doped graphene synthesized using butane and pyridine as precursors, respectively, and transferred onto SiO 2 /Si substrates. Figure 3 a. shows the Raman spectra for pristine graphene synthesized using butane at varying temperatures of 850, 900, 950, and 1000 ℃ for 60 s, while Fig. 3 c. shows the Raman spectra for pristine graphene synthesized at 900 ℃ for varying growth times of 30, 45, 60, 90 s. Figure 3 b. and d. show the corresponding data for nitrogen-doped graphene synthesized under the same conditions using pyridine as the precursor. Notably, the high-speed synthesis conditions afforded both pristine and doped graphene in just 60 s at a growth temperature of 900 ℃, and were applicable even when using a Si substrate with a thin copper film deposited on top (300-nm-Cu/SiO 2 /Si). This demonstrated the suitability of these conditions for device fabrication processes ( Figure S1 . ). As shown in Fig. 3 a., pristine graphene samples synthesized at temperatures above 900 ℃ exhibited almost identical characteristics to that synthesized at 900°C, indicating the high quality of the synthesized monolayer of pristine graphene. For N-doped graphene synthesized under the same conditions, the D/G ratio decreased and the 2D/G ratio increased with increasing temperature (Fig. 3 c.). While there is no clear relationship between synthesis time and Raman data for pristine graphene at 900 ℃ and N-doped graphene at 1000 ℃ (Fig. 2 c, d.), examining the peak ratio based on synthesis time for pristine graphene reveals that a low D/G ratio and high 2D/G ratio were achieved only at a synthesis time of 60 s, indicating the synthesis of high-quality and uniform graphene with small error bars ( Figure S2 . ). Considering cost and energy efficiency, as well as the potential for mass production and industrial competitiveness, the most suitable conditions for the synthesis of pristine graphene are 900 ℃ and 60 s. For nitrogen-doped graphene, the conditions at 1000 ℃ resulted in the highest 2D peak. However, the optimal conditions must be adjusted based on the required qualities and application purpose; this can be achieved by combining XPS and electrical property evaluation, considering factors such as the nitrogen content and charge neutrality point (Dirac point). Based on the Raman data, additional analyses were conducted on the graphene samples synthesized at 900, 950, and 1000 ℃ for 60 s. For pristine graphene, the analysis was focused on the sample synthesized at the lowest temperature, 900 ℃, as the results did not differ significantly with varying temperatures. In other words, when the growth temperature was sufficiently high and the characteristics were saturated, there was minimal variation in the samples with temperature. In Fig. 4 ., the G peaks and 2D peaks for pristine and doped graphene synthesized at 900, 950, and 1000 ℃ were compared using Raman data measured at 30 spots for each sample. For pristine graphene, the G peak and 2D peak were located at approximately 1583 and 2684 cm –1 , respectively, independent of growth temperature. Meanwhile, for doped graphene, at growth temperatures of 900, 950, 1000 ℃, the G peak was located at approximately 1595, 1594, and 1589 cm –1 , respectively, and the 2D peak at approximately 2704, 2694, and 2688 cm –1 , respectively. The purple dots represent the reference values for exfoliated freestanding graphene unaffected by strain or doping (G peak: 1581.6 ± 0.2 cm –1 , 2D peak: 2676.9 ± 0.7 cm –1 ). 23 The gray lines indicate the Raman changes due to strain, with a slope of 2.2 ± 0.2 (Pos(2D)/Pos(G)). 23 For graphene synthesized using butane, three distinct graphene clusters were formed near the reference points, indicating uniform pristine graphene. According to previous research, hole doping causes Raman spectra to exhibit a linear shift toward higher frequencies at a slope of 0.70 ± 0.05 (Pos(2D)/Pos(G)) and blue shifts toward higher frequencies. [ 27 ] However, studies on the effect of electron doping on the Raman spectra are relatively limited, though they have been reported as nonlinear shifts. [ 28 , 29 ] Additionally, a previous study utilized freestanding graphene in top-gate transistors, making it challenging to directly compare and explain our Raman results for nitrogen-doped graphene, in which the dopant replaced carbon. In case of N-doped graphene using pyridine, both the G and 2D peaks exhibited a blue shift and nonlinear changes with decreasing synthesis temperature. 3.2 X-Ray Photoelectron Spectroscopy Figure 5 . shows the XPS data obtained for the elemental analysis of each graphene sample. Figure 5 a. shows the XPS spectrum of pristine graphene synthesized at 900 ℃, while Fig. 5 b–d. show the XPS spectra of nitrogen-doped graphene synthesized at 1000, 950, and 900 ℃, respectively. The C1s spectra for both graphene types include a dominant peak at 284.7 eV corresponding to the C–C bond, a small oxide bond that can occur during the process at 286.3 eV corresponding to the C–O bond, and peaks at 287.5 and 289.0 eV corresponding to the O–C = O and C = O bonds, respectively. [ 13 – 15 , 20 , 30 – 32 ] For nitrogen-doped graphene, there was an additional clear peak corresponding to the C–N bond at 285.7 eV, and all C1s peaks exhibited overall broadening. The N1s spectra can comprise three main peaks corresponding to three different bonds: the pyridinic N bond (398.6 eV) and pyrrolic N bond (400.3 eV) represent the bonding of one and two nitrogen atoms, respectively, with carbon through π bonds, and the graphitic N bond at 401.5 eV corresponds to the substitution of carbon with nitrogen. [ 13 , 14 ] Although all three bonds involve nitrogen and carbon, pyridinic N and pyrrolic N contribute to p-type doping, whereas graphitic N contributes to n-type doping. [ 33 , 34 ] These peaks are not present for pristine graphene, indicating the absence of nitrogen. Meanwhile, all doped graphene samples were confirmed to contain nitrogen owing to the presence of all three peaks, with the nitrogen content being similar independent of the synthesis temperature; however, as the synthesis temperature decreased from 1000 to 900 ℃, the ratio of graphitic-N increased. 3.3 Electrical Properties Figure 6 a. shows the transfer curve of pristine graphene with respect to the growth temperature. Pristine graphene synthesized at three different temperatures exhibited Dirac points ranging from 0 to + 1 V, and the values of the source-drain current with respect to the gate voltage were similar. As observed from the Raman data, the electrical properties of pristine graphene were nearly identical when synthesized at growth temperatures above 900 ℃. This is consistent with Fig. 5 (a), in which the absence of C–N and N1s is logically presented. The electron mobility was calculated to be 1430–1498 cm 2 V –1 s –1 at a charge concentration of n = + 1e 12 , and the hole mobility was calculated to be 1468–1572 cm 2 V –1 s –1 at n=–1e 12 . In the case of N-doped graphene, the Dirac point voltage was consistently below 0 V, indicating n-type behavior. For graphene samples synthesized at 900, 950, and 1000°C, the Dirac point voltages were − 117, − 82, and − 51 V, respectively, electron mobilities at n = + 1e 12 were calculated as 253, 317, and 402 cm 2 V –1 s –1 , respectively, and hole mobilities at n=–1e 12 were calculated as 255, 326, and 404 cm 2 V –1 s –1 , respectively. As the growth temperature decreased, the relative abundance of graphitic N increased, leading to a larger absolute value of the Dirac point voltage in the negative direction. However, overall, the graphitic structure decreased, and the increased scattering sites resulted in a reduction in mobility ( Figure S4. ). 3.4 Gas Sensing Application Figure 7 . shows the potential applicability of gas sensors using pristine graphene synthesized at 900 ℃ and N-doped graphene synthesized at 1000 ℃. The two types of graphene were transferred onto SiO 2 substrates to create simple FET devices, which were then applied as gas-sensor channels for NO 2 and NH 3 at room temperature and atmospheric pressure. Typically, CVD-grown graphene, the dominant carriers are holes, is a p-type channel; NO 2 absorbed onto the graphene surface withdraws free electrons such that the resistance increases, while NH 3 donates free electrons to the graphene surface, thus the resistance decreases. Meanwhile, nitrogen-doped graphene, the dominant carriers are electrons, is an n-type channel that exhibits the opposite electrical response characteristics. This leads to opposite changes in the reaction characteristics. The graphene-based gas sensors were exposed to NO 2 and NH 3 gases for 9 min each, and the resistance changes were measured repeatedly. Pristine graphene exhibited a polarity characteristic similar to that of a previous study, [ 35 ] showing adsorption and desorption based on the gas type. In contrast, the N-doped graphene exhibited reversed polarity. Figure 8 a. shows the second cycle of the graphs in Fig. 7 ., grouped according to graphene and gas types. Pristine and N-doped graphene exhibited reactivities of − 25% and 79%, respectively, when exposed to NO 2 for 9 min, and reactivities of 18% and − 12%, respectively, when exposed to NH 3 for 9 min. Figure 8 b. shows the reactivity of the graphene samples after 2 min of exposure to each gas; nitrogen-doped graphene exhibited higher sensitivity and faster response compared to pristine graphene for both gases. 4. Conclusion To enhance the potential for the industrial synthesis of graphene, we developed a conveyor CVD system for the highly productive synthesis of high-quality graphene. By optimizing the synthesis conditions, we successfully synthesized pristine and nitrogen-doped graphene using the liquid precursors butane and pyridine, respectively; 12 samples were synthesized in 1 h, confirming the potential for rapid synthesis. This system not only allows for the simultaneous synthesis of numerous graphene samples, but enables the synthesis of graphene with the desired qualities by using various precursors and different recipes. In addition, it can accommodate flexible foils, rigid substrates, and powder catalysts for graphene synthesis. At synthesis temperatures above 900°C, we achieved high quality prisitine graphene samples that exhibited low D/G and 2D/G ratios in their Raman spectra. XPS analysis indicated dominant C–C peaks, excluding oxides formed during the transfer process, and no N1s peaks. The Dirac point voltage ranged from 0 to 5 V, exhibiting characteristics of neutral CVD graphene. Meanwhile, for the nitrogen-doped graphene samples, decreasing the growth temperature blue-shifted the G-peak and 2D-peak in the Raman spectra, increased the ratio of graphitic-N in the XPS spectra, and decreased the Dirac point voltage and mobility with a unidirectional tendency. Therefore, for future research and development applications, synthesis closer to 900°C may be preferred for synthesizing graphene with a higher level of nitrogen doping, while synthesis closer to 1000°C can be selectively employed if graphene with lower nitrogen doping and better mobility is needed based on the specific objectives. Declarations Acknowledgements Not applicable Availability of data and material The datasets used during the current study are available from the corresponding author on reasonable request. Competing interests The authors declare that they have no competing interests Funding This research was supported from the National Research Foundation of Korea (NRF) grant, funded by the Korea government (MSIT). (No. 2019R1A2C1009963) And also this research supported by Global Research Development Center Program (No. 2018K1A4A3A01064272) and Basic Science Research Program (No. 2021R1A4A1031900) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (MSIT). Authors’ contributions DYL, JN, and AJ performed experiments. DYL, JN, AJ, and KSK conducted the experiments and analyzed the data. AJ and KSK supervised the research. All authors discussed the experimental results. DYL, JN, AJ, and KSK wrote and edited the paper. References KS Novoselov, D Jiang, F Schendin, TJ Booth, VV Khotkevich, SV Morzov, AK Geim, Proc. Natl. Acad. Sci. 102 (30), 10451-10453 (2005). KS Novoselov, AK Geim, SV Morozov, D Jiang, MI Katsnelson, IV Grigorieva, SV Dubonos, AA Firsov, Nature 438, 197-200 (2005). Y Zhang, TW Tan, HL Stormer, P Kim, Nature 438, 201-204 (2005). C Berger, Z Song, X Li, X Wu, N Brown, C Naud, D Mayou, T Li, J Hass, AN Marchenkov, EH Conrad, PN First, WA Heer, Science 312 (5777), 1191-1196 (2006). KS Kim, Z Yue, H Jang, SY Lee, JM Kim, KS Kim, JH Ahn, P Kim, JY Choi, BH Hong, Nature 457, 706-710 (2009). DS Choi, KS Kim, H Kim, Y Kim, TY Kim, SH Rhy, CM Yang, DH Yoon, WS Yang, ACS Applied Materials & Interfaces 6 (22), 19574-19578 (2014). J Seo, J Lee, AR Jang, Y Choi, U Kim, HS Shin, H Park, Chemistry of Materials 29 (10), 4202-4208 (2017). T Yamada, M Ishihara, J Kim, M Hasegawa, S Iijima, Carbon 50 (7), 2615-2619 (2012). T Kobayashi, M Bando, N Kimura, K Shimizu, K Kadono, N Umezu, K Miyahara, S Hayazaki, S Nagai, Y Mizuguchi, Y Murakami, D Hobara, Appl. Phys. Lett. 102, 023112 (2013). G Zhong, X Wu, L D'Arsie, KBK Teo, NL Rupesinghe, A Jouvray, J Robertson, Appl. Phys. Lett. 109, 193103 (2016). ES Polsen, DQ McNerny, B Viswanath, SW Pattinson, AJ Hart, Sci. Rep. 5, 10257 (2015). PR Kidambi, DD Mariappan, NT Dee, A Vyatskikh, S Zhang, R Karnik, AJ Hart, ACS Appl. Mater. Interfaces 10 (12), 10369-10378 (2018). M Rybin, A Pereaslavtsev, T Vasilieva, V Myasnikov, I Sokolov, A Pavlova, E Obraztsova, A Khomich, V Ralchenko, E Obraztsova, Carbon 96, 196-202 (2016). D Wei, Y Liu, Y Wang, H Zhang, L Huang, G Yu, Nano Lett. 9 (5), 1752-1758 (2009). M Deifallah, PF McMillan, F Corà, The Journal of Physical Chemistry C112 (14), 5447-5453 (2008). M Zhu, Z Du, Z Yin, W Zhou, Z Liu, SH Tsang, EHT Teo, ACS Appl. Mater. Interfaces 8 (1), 502-510 (2016). JH Choi, Z Li, P. Cui, X Fan, H Zhang, C Zeng, Z Zhang, Sci. Rep.3, 1925 (2013). J Nam, DC Kim, H Yun, DH Shin, S Nam S, WK Lee, JY Hwang, SW Lee, H Weman, KS Kim, Carbon 111, 733-740 (2017). KS Kim, Physics & High technology 28 (5), 31-38 (2019). J Nam, J Yang, Y Zhao, KS Kim, Curr. Appl. Phys. 61, 55-70 (2024). I Lee, DJ Bae, WK Lee, CM Yang, SW Cho, J Nam, DY Lee, AR Jang, HS Shin, JY Hwang, S Hong, KS Kim, Carbon 145, 462-469 (2019). SJ Park, I Lee, DJ Bae, J Nam, YH Han, BJ Park, KS Kim, KEPCO Journal on Electric Power and Energy 1 (1), 169-174 (2015). D Seo, DY Lee, J Kwon, JJ Lee, T Taniguchi, K Watanabe, GH Lee, K S Kim, J Hone, YD Kim, HJ Choi, Appl. Phys. Lett. 115, 012104 (2019). Y Wang, Y Zheng, X Xu, E Dubuisson, Q Bao, J Lu, KP Loh, ACS Nano 5(12), 9927-9933 (2011). CT Cherian, F Giustiniano, I Martin-Fernandez, H Andersen, J Balakrishnan, B Özyilmaz, Small 11 (2), 189-194 (2015). I Roh, SH Goh, Y Meng, JS Kim, S Han, Z Xu, HE Lee, Y Kim, SH Bae, Nano Converg. 10, 20 (2023). JE Lee, G Ahn, J Shim, YS Lee, S Ryu, Nat. Comm. 3, 1024 (2012). A Das, S Pisana, B Chakraborty, S Piscanec, SK Saha, UV Waghmare, KS Novoselov, HR Krishnamurthy, AK Geim, AC Ferrari. AK Sood, Nat. Nanotech. 3, 210-2015 (2008). A Das, B Chakraborty, S Piscanec, S Pisana, AK Sood, AC Ferrari, Physical Review B 79 (15), 155417 (2009). B Xiong, Y Zhoua, R O’Hayrec, Z Shao, Applied Surface Science 266, 433-439 (2013). GV Bianco, A Sacchetti, M Grande, A D’Orazio, A Milella, G Bruno, Sci. Rep. 12, 8703 (2022). H Xu, L Ma, Z Jin, J. Energy Chem. 27 (1), 146-160 (2018). L Zhao, R He, KT Rim, T Schiros, KS Kim, H Zhou, C Gutiérrez, SP Chockalingam, CJ Arguello, L Palova, D Nordlund, MS Hybertsen, DR Reichman, TF Heinz, P Kim, A Pinczuk, GW Flynn, AN Pasupathy, Science 333 (6045), 999-1003 (2011). T Schiros, D Nordlund, L Palova, D Prezzi, L Zhao, KS Kim, U Wurstbauer, C Gutierez, D Delongchamp, C Jaye, D Fischer, H Ogasawara, LGM Pettersson, DR Reichman, P Kim, MS Hybertsen, AN Pasupathy, Nano Lett. 12 (8), 4025-4031 (2012). F Schedin, AK Geim, SV Morozv, EW Hill, P Blake, MI Katsnelson, KS Novoselov, Nat. Mater. 6, 652-655 (2007). Supplementary Files Additionalfile1SIFigureNanoConvergenceConveyorCVD.docx Additional file 1: Figure S1. Supporting Figures show comparison of conventional and rapid synthesis of graphene on thermally deposited copper film (300 nm) on SiO 2 /Si substrate. Figure S2. Raman peak ratio of pristine graphene synthesized at 900 ℃ by growth time. Figure S3. Correlation between Dirac Voltage and mobility of the graphene by growth temperature and doping. Figure S4. Annealing time dependence Raman spectra of pristine graphene at 1000 ℃ (S4). Additionalfile2ConveyorCVDmovieNanoConvergence.mp4 Additional file 2: Movie S1 Conveyor CVD process. GraphicalAbstract.png Cite Share Download PDF Status: Published Journal Publication published 14 Aug, 2024 Read the published version in Nano Convergence → Version 1 posted Editorial decision: Minor revision 05 Jun, 2024 Reviewers agreed at journal 13 May, 2024 Reviewers invited by journal 13 May, 2024 Editor assigned by journal 29 Apr, 2024 First submitted to journal 27 Apr, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4336389","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":301854830,"identity":"0f7871a8-bee8-4cc9-b7d6-48a98e8319dd","order_by":0,"name":"Dong Yun Lee","email":"","orcid":"","institution":"Sejong University","correspondingAuthor":false,"prefix":"","firstName":"Dong","middleName":"Yun","lastName":"Lee","suffix":""},{"id":301854831,"identity":"886c991e-15f5-49c9-815c-e97dc1ba3bf6","order_by":1,"name":"Jungtae Nam","email":"","orcid":"","institution":"Sejong University","correspondingAuthor":false,"prefix":"","firstName":"Jungtae","middleName":"","lastName":"Nam","suffix":""},{"id":301854832,"identity":"22a67843-9438-41c9-8a79-ea8aa266404a","order_by":2,"name":"Gil Yong Lee","email":"","orcid":"","institution":"Sejong University","correspondingAuthor":false,"prefix":"","firstName":"Gil","middleName":"Yong","lastName":"Lee","suffix":""},{"id":301854833,"identity":"bb461be4-bcb2-4b0f-8795-54fff6fcb98b","order_by":3,"name":"Imbok Lee","email":"","orcid":"","institution":"Kongju National University","correspondingAuthor":false,"prefix":"","firstName":"Imbok","middleName":"","lastName":"Lee","suffix":""},{"id":301854834,"identity":"e22146df-e922-44e7-bb4f-6d4a89cf7b66","order_by":4,"name":"A-Rang Jang","email":"","orcid":"","institution":"Kongju National University","correspondingAuthor":false,"prefix":"","firstName":"A-Rang","middleName":"","lastName":"Jang","suffix":""},{"id":301854835,"identity":"5062b700-f701-4493-93b1-236e893b1d7b","order_by":5,"name":"Keun Soo Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBUlEQVRIie3RMWrDMBSA4ScC9mLQ+oyhZxAY2gZCchUFgyZ191ZNngxZHXIJH6CDGkG8GLqmkMFenKVDIUunUqUdSoao6Vao/kkS+pDgAfh8fzCEADTkk/tFqI67r4j6kbSCLEv9CwKkWJO64t+nThIvNvP1NtAjFu/77jbfTVVoOrJ8OE8SFNrIaBfcJDJl2A6ZigQj9XCeXGGojMQhGq9kgHFhMgAJpNMOQhtLmEH23OzfPgl9cZMEjh/jhrEtXIMlU0D7Su0gcSW4kVrwuJQpYmt4gAN7rBwEnzbp4e59wmnY9AfMzYzSrO9LBzlpZEc5L+ziUmAn+Aowu/i2z+fz/Zs+ANIRWL8rzK94AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-4901-6156","institution":"Sejong University","correspondingAuthor":true,"prefix":"","firstName":"Keun","middleName":"Soo","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2024-04-28 06:07:39","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4336389/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4336389/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40580-024-00439-0","type":"published","date":"2024-08-14T15:57:28+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57451538,"identity":"209738cd-0cbc-4f5b-9173-cefe1f511561","added_by":"auto","created_at":"2024-05-30 20:52:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":635001,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e Schematic of conveyor CVD system. \u003cstrong\u003e(b)\u003c/strong\u003e Photograph of twelve as-synthesized graphene samples. \u003cstrong\u003e(c)\u003c/strong\u003e Raman spectra of as-grown pristine and n-doped graphene on copper foil synthesized at 900 ℃ and 1000 ℃, respectively.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/cb13b0a314fca4a883b3ce3f.png"},{"id":57451537,"identity":"a2b52c26-b520-4f66-976f-ff9a3e1e2784","added_by":"auto","created_at":"2024-05-30 20:52:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":174855,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003eThermal profile of CVD furnace and \u003cstrong\u003e(b)\u003c/strong\u003e Raman spectra of graphene synthesized at various furnace positions.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/1ea751cd5981da2a8f2107fb.png"},{"id":57451540,"identity":"f3c2fd1b-2df8-415b-8448-9973000b1caf","added_by":"auto","created_at":"2024-05-30 20:52:03","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":74984,"visible":true,"origin":"","legend":"\u003cp\u003eGrowth temperature dependence Raman spectra of \u003cstrong\u003e(a)\u003c/strong\u003epristine and \u003cstrong\u003e(b)\u003c/strong\u003e N-doped graphene. Growth time dependence Raman spectra of \u003cstrong\u003e(c)\u003c/strong\u003e pristine and \u003cstrong\u003e(d)\u003c/strong\u003e N-doped graphene.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/c5246ef02ae4b1c7d281cdc6.png"},{"id":57451541,"identity":"579d6dd4-a039-4015-a3a7-d894601b90ff","added_by":"auto","created_at":"2024-05-30 20:52:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":62337,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between the positions of the G and 2D Raman modes of graphene. The data were obtained from the Raman mapping of six graphene samples at 30 spots each. The purple dots represent the results for a freestanding graphene sample.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/6d3ba88f0bcca7e84d37f7de.png"},{"id":57452340,"identity":"3bdd6eca-52af-4891-9d63-29575e996190","added_by":"auto","created_at":"2024-05-30 21:00:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":93343,"visible":true,"origin":"","legend":"\u003cp\u003eXPS C1s spectra (left) and N1s spectra (right) of \u003cstrong\u003e(a)\u003c/strong\u003epristine graphene synthesized at 1000 ℃ and N-doped graphene synthesized at \u003cstrong\u003e(b\u003c/strong\u003e) 1000 ℃, \u003cstrong\u003e(c)\u003c/strong\u003e 950 ℃, \u003cstrong\u003e(d)\u003c/strong\u003e and 900 ℃. The C 1s peak can be split into five peaks at 284.7, 285.7, 286.3, 287.5, and 289.0 eV, which correspond to and are labeled as C–C (green), C–N (blue), C–O (purple), C=O (orange), and O–C=O (brown), respectively. The N 1s peak can be split into three peaks at 398.6, 400.3, and 401.5 eV, which correspond to and are labeled as pyridinic N (green), pyrrolic N (blue), and graphitic N (purple), respectively.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/7322b67a8539336c0696523a.png"},{"id":57451544,"identity":"bd032c35-4e20-4de9-b2d2-7c39cfb45827","added_by":"auto","created_at":"2024-05-30 20:52:03","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":96592,"visible":true,"origin":"","legend":"\u003cp\u003eElectrical properties of \u003cstrong\u003e(a, c)\u003c/strong\u003e pristine and \u003cstrong\u003e(b, d)\u003c/strong\u003e N-doped graphene. \u003cstrong\u003e(a, b)\u003c/strong\u003e I\u003csub\u003eDS\u003c/sub\u003e–V\u003csub\u003eGS\u003c/sub\u003e characteristic of pristine graphene synthesized at various growth temperatures and \u003cstrong\u003e(c, d)\u003c/strong\u003e carrier mobilities calculated from \u003cstrong\u003e(a)\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/f34365059a3067047dca13be.png"},{"id":57451547,"identity":"fe1b32fe-c469-4172-97a2-2253fac4b1db","added_by":"auto","created_at":"2024-05-30 20:52:03","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":60039,"visible":true,"origin":"","legend":"\u003cp\u003eNO\u003csub\u003e2\u003c/sub\u003e and NH\u003csub\u003e3\u003c/sub\u003e gas response characteristics of \u003cstrong\u003e(a)\u003c/strong\u003e pristine graphene and \u003cstrong\u003e(b)\u003c/strong\u003e N-doped graphene.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/64254cc672ae4a76bb7b2242.png"},{"id":57451545,"identity":"795b8d83-76f5-4148-a164-d7bba88e2bff","added_by":"auto","created_at":"2024-05-30 20:52:03","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":39190,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) \u003c/strong\u003eNO\u003csub\u003e2 \u003c/sub\u003eand NH\u003csub\u003e3\u003c/sub\u003e gas response characteristics of pristine and N-doped graphene for one cycle and \u003cstrong\u003e(b)\u003c/strong\u003e magnified absolute sensitivity for 2 min.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/2fcdf23264bdd625746bf913.png"},{"id":63071301,"identity":"a4833962-1a08-437f-a779-b73616e5b602","added_by":"auto","created_at":"2024-08-22 20:06:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1726580,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/1e335659-46b2-47b2-99ec-a0757715e3d5.pdf"},{"id":57452339,"identity":"7e31bac9-536b-46cf-a927-9007f125a996","added_by":"auto","created_at":"2024-05-30 21:00:02","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":646516,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdditional file 1:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure S1. \u003c/strong\u003eSupporting Figures show comparison of conventional and rapid synthesis of graphene on thermally deposited copper film (300 nm) on SiO\u003csub\u003e2\u003c/sub\u003e/Si substrate. \u003cstrong\u003eFigure S2. \u003c/strong\u003eRaman peak ratio of pristine graphene synthesized at 900 ℃ by growth time. \u003cstrong\u003eFigure S3. \u003c/strong\u003eCorrelation between Dirac Voltage and mobility of the graphene by growth temperature and doping. \u003cstrong\u003eFigure S4.\u003c/strong\u003e Annealing time dependence Raman spectra of pristine graphene at 1000 ℃ (S4).\u003c/p\u003e","description":"","filename":"Additionalfile1SIFigureNanoConvergenceConveyorCVD.docx","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/e094387ce4d83c55f18782b2.docx"},{"id":57451546,"identity":"568c37c2-5b53-4e69-aee9-15560c38c5eb","added_by":"auto","created_at":"2024-05-30 20:52:03","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":19969451,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdditional file 2: Movie S1\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConveyor CVD process.\u003c/p\u003e","description":"","filename":"Additionalfile2ConveyorCVDmovieNanoConvergence.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/af84ac1be5bc4f6931c2a435.mp4"},{"id":57451542,"identity":"b2617f30-7864-4ba7-898e-12f537a232b9","added_by":"auto","created_at":"2024-05-30 20:52:03","extension":"png","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":632431,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.png","url":"https://assets-eu.researchsquare.com/files/rs-4336389/v1/18f6cb52596494f5912d6b19.png"}],"financialInterests":"","formattedTitle":"Conveyor CVD to high-quality and productivity of large-area graphene and its potentiality","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSince the discovery of graphene\u003csup\u003e[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e, there has been continuous research on the synthesis of large-area graphene. \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e Conventional batch-type methods for graphene synthesis can be segmented into the following processes: heating, annealing of catalyst metal surface, graphene growth, and cooling; each process is executed independently. \u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e However, these methods, despite yielding satisfactory graphene at the laboratory level, are not competitive in terms of future industrial applications owing to the slow production speed. To overcome these bottlenecks, we focused on improving conventional chemical vapor deposition (CVD) methods, including both systems and recipes.\u003c/p\u003e \u003cp\u003eThe roll-to-roll CVD system has been consistently reported for scaling up graphene production. \u003csup\u003e[\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e In this process, a copper foil roll, which acts as the catalyst metal, is transported within a chamber filled with hydrocarbon gas; a thin carbon film is deposited on the copper surface as it moves to the high-temperature zone. The catalyst metal is continuously moved into and out of the CVD reaction zone, allowing the sequential execution of heating, surface annealing and reduction, growth, and cooling. This process enables the synthesis of large-area graphene in a short time. However, the individual processes cannot be controlled independently. Furthermore, when the metal foil moves continuously, it is exposed to the carbon precursor at a lower temperature than the target temperature in areas far from the reaction zone, resulting in the deposition of an amorphous carbon film. Additionally, the mechanical forces applied to the metal foil during its transportation between the high- and low-temperature zones cause alternating tensile and compressive stresses, creating defects in the graphene. \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e As a result, synthesizing high-quality materials in this system is challenging. Furthermore, because graphene is synthesized on a metal catalyst roll, only flexible substrates must be used, greatly limiting the substrate scope.\u003c/p\u003e \u003cp\u003eEfforts have been made to overcome these challenges, such as mechanically separating the annealing and growth zones, \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e or attempting to maintain consistent tension by moving the foil vertically.\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e However, the quality of graphene synthesized has not improved sufficiently. Although numerous studies have reported on the mass production of high-quality large-area graphene, challenges such as the formation of graphene defects and nonuniformities such as adlayers still persist.\u003c/p\u003e \u003cp\u003eIn addition, for the practical application of graphene, research on property modulation through doping is crucial. Various methods have been employed for the synthesis of doped graphene, including the plasma post-treatment of pristine graphene and the CVD of dopant-containing carbon precursors. However, the former is prone to a relatively high level of defects and requires multiple processes, \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e whereas the latter results in nonuniform doping. \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e Furthermore, research on the mass production of doped graphene has not yet been conducted.\u003c/p\u003e \u003cp\u003eTherefore, the development and optimization of systems and processes that overcome the drawbacks of the existing roll-to-roll CVD system are crucial for the mass production of high-quality graphene with desired properties, which in turn is key for the industrialization of graphene.\u003c/p\u003e \u003cp\u003eIn this study, to overcome the drawbacks of the roll-to-roll CVD system, we developed a novel conveyor-type CVD system and optimized its mass-production process (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea.). As mentioned earlier, conventional batch-type CVD allows high-quality graphene synthesis but is challenging for mass production, whereas roll-to-roll CVD allows mass production but suffers from insufficient quality. The conveyor system retains the advantages of independent process control from segment-based batch-type CVD and continuous production from roll-to-roll CVD, while eliminating the respective drawbacks of low productivity and reduced quality caused by decreased process control flexibility. In our system, while the desired temperature is maintained at the reaction zone for annealing and growth, the substrate prepared in the cartridge sample holder is transported to the reaction zone by a conveyor belt. The process gas is then toggled according to each process segment, completing annealing and growth. After growth, the substrate is transported to the opposite cartridge holder. Importantly, only the carbon-containing precursor is injected during the synthesis, whereas the residual carbon gas is removed during the other processes. This iterative method enables the continuous synthesis of high-quality graphene. Furthermore, it is versatile, allowing for the use of various substrates, such as flexible substrates, rigid wafers, metal foams, and powders (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb., \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eVarious carbon sources of all phases have been utilized as graphene precursors, with the growth time and temperature conditions varying significantly depending on their phase.\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e Dehydrogenation of the carbon source is particularly crucial in determining the growth time.\u003csup\u003e17\u003c/sup\u003e For example, traditional CVD with methane gas, which is common for graphene synthesis, requires a prolonged synthesis time of over 10 min at temperatures around 1000 ℃ owing to the high C\u0026ndash;H bonding energy.\u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e Therefore, to achieve mass production of graphene, it is essential to identify suitable carbon precursors and synthesis conditions that allow rapid synthesis. We previously reported the high-speed synthesis of pristine graphene using LPG\u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e and nitrogen-doped graphene using pyridine, a nitrogen-containing organic solvent.\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e Based on prior research, we applied these methods to our conventional CVD system, utilizing pure liquefied butane for pristine graphene synthesis and pyridine for N-doped graphene synthesis; consequently, our conveyor CVD system achieved the desired quality of graphene with high productivity and reproducibility. Furthermore, we used the N-doped graphene to enhance the properties of other 2D materials.\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e We optimized the synthesis conditions, namely the growth temperature and time, for the mass production of pristine and N-doped graphene. Finally, we demonstrated the potential application of these pristine and doped samples as gas sensors for various applications.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Graphene Synthesis\u003c/h2\u003e \u003cp\u003ePristine and nitrogen-doped graphene were synthesized using pure butane (99% purity, n-Butane; Sigma-Aldrich) and pyridine (99.8% purity, anhydrous; Sigma-Aldrich), respectively, on a copper foil (99.8% purity, 25 \u0026micro;m thickness; Alfa Aesar) using the conveyor CVD system; various high-speed synthesis conditions were investigated to determine the optimal conditions for the desired quality or dopant content of graphene. The sample was heat treated at the target temperatures for a constant 1 min duration of hydrogen treatment at 50 sccm and 380 mTorr. After heat treatment, pristine graphene synthesis using butane (3 sccm; 170 mTorr) or nitrogen-doped graphene synthesis using pyridine (100 mTorr) was conducted over various synthesis times (30, 45, 60, and 90 s) to optimize the synthesis time. Twelve substrates, each sized at 15 cm \u0026times; 5 cm, were transported from the cartridge holder and subjected to 1 min of heat treatment (\u003cb\u003eFigure \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e.\u003c/b\u003e) and 1 min of growth, resulting in the synthesis of 12 samples in 1 h (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb.). A \u003cb\u003esupplementary video\u003c/b\u003e related to this process can be found at \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/?(to\u003c/span\u003e\u003cspan address=\"https://doi.org/?(to\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e be updated). The synthesized graphene, supported with a PMMA layer on the top surface, was spin-coated and electrochemically delaminated to separate it from the copper foil,\u003csup\u003e[\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e then transferred onto a SiO\u003csub\u003e2\u003c/sub\u003e substrate for evaluation of its optical and electrical characteristics, among other properties.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Characterization\u003c/h2\u003e \u003cp\u003eThe graphene samples synthesized on copper foil under various conditions were transferred onto 300-nm SiO\u003csub\u003e2\u003c/sub\u003e substrates for Raman spectroscopy, which was performed on 30 points for each sample, both before and after transfer, using the Renishaw inVia Raman microscope with a 514-nm laser. Additionally, the graphene samples on gold film deposited SiO\u003csub\u003e2\u003c/sub\u003e substrates were subjected to X-ray photoelectron spectroscopy (XPS) to analyze their elemental compositions and bonding structures. The graphene samples transferred onto 300 nm-thick SiO\u003csub\u003e2\u003c/sub\u003e substrates were then used to fabricate back-gate field-effect transistors (FETs) with 10 \u0026micro;m \u0026times; 10 \u0026micro;m graphene channels. These devices were loaded into a vacuum chamber (pressure below 3\u0026times;10\u003csup\u003e\u0026ndash;3\u003c/sup\u003e Torr) and interfaced with a source measure unit (SMU; Keithley 236 \u0026amp; 237) using a LabVIEW program. The electrical response characteristics were measured as functions of the gate voltage and source-drain current. To demonstrate the potential applications of the graphene samples, both pristine and nitrogen-doped samples were exposed to NH\u003csub\u003e3\u003c/sub\u003e and NO\u003csub\u003e2\u003c/sub\u003e, and their electrical characteristics were measured. The gas sensitivity was evaluated using the response properties calculated from the resistance and current changes in each sample channel as a function of gas type, gas concentration, and exposure time.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Result and Discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Raman Spectroscopy\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. shows the conveyor CVD system process. The substrate was first loaded into the left cartridge and placed on the copper metal foil; the foil acted as a conveyor belt and transported the cartridge to the center of the furnace, where the substrate underwent heat annealing and growth. It was then transported to the right cartridge. Simultaneously, during transport of the substrate from the loading chamber to the growth area, the temperature increased rapidly from room temperature. As reaction with a carbon source during transport can cause the deposition of amorphous carbon, synthesis gas was not supplied, and only hydrogen was supplied for reduction. The furnace was operated at various target temperatures\u0026mdash;850, 900, 950, and 1000 ℃\u0026mdash;for a 1 min hydrogen treatment to optimize the heat treatment temperature. The heat treatment time was varied to find the minimum temperature for rapid synthesis (\u003cb\u003eFigure \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e.\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. shows the Raman spectra of pristine and nitrogen-doped graphene synthesized on copper at 900 and 1000\u0026deg;C, respectively, for 60 s. For the pristine graphene, the G peak appeared at \u0026sim;1588 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, and the 2D peak at \u0026sim;2698 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. Meanwhile, for the nitrogen-doped graphene, the G peak appeared at \u0026sim;1595 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, and the 2D peak at \u0026sim;2724 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e; both the G-peak and 2D peak exhibited blue shifts of approximately 7 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e and 6\u0026ndash;7 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively.\u003c/p\u003e \u003cp\u003eTo determine the maximum graphene area achievable through conveyor-type CVD synthesis, graphene samples were synthesized at various positions along the furnace; the temperature was measured at each position, and the synthesized graphene samples were analyzed using Raman spectroscopy (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.). Using a 45-cm furnace as the reference, we confirmed the synthesis of high-quality graphene in an area measuring 5 cm \u0026times; 15 cm, approximately equal to the size of a smartphone screen.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. shows the Raman spectra of pristine and nitrogen-doped graphene synthesized using butane and pyridine as precursors, respectively, and transferred onto SiO\u003csub\u003e2\u003c/sub\u003e/Si substrates. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. shows the Raman spectra for pristine graphene synthesized using butane at varying temperatures of 850, 900, 950, and 1000 ℃ for 60 s, while Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec. shows the Raman spectra for pristine graphene synthesized at 900 ℃ for varying growth times of 30, 45, 60, 90 s. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. and \u003cb\u003ed.\u003c/b\u003e show the corresponding data for nitrogen-doped graphene synthesized under the same conditions using pyridine as the precursor. Notably, the high-speed synthesis conditions afforded both pristine and doped graphene in just 60 s at a growth temperature of 900 ℃, and were applicable even when using a Si substrate with a thin copper film deposited on top (300-nm-Cu/SiO\u003csub\u003e2\u003c/sub\u003e/Si). This demonstrated the suitability of these conditions for device fabrication processes (\u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea., pristine graphene samples synthesized at temperatures above 900 ℃ exhibited almost identical characteristics to that synthesized at 900\u0026deg;C, indicating the high quality of the synthesized monolayer of pristine graphene. For N-doped graphene synthesized under the same conditions, the D/G ratio decreased and the 2D/G ratio increased with increasing temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec.). While there is no clear relationship between synthesis time and Raman data for pristine graphene at 900 ℃ and N-doped graphene at 1000 ℃ (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, d.), examining the peak ratio based on synthesis time for pristine graphene reveals that a low D/G ratio and high 2D/G ratio were achieved only at a synthesis time of 60 s, indicating the synthesis of high-quality and uniform graphene with small error bars (\u003cb\u003eFigure \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e.\u003c/b\u003e). Considering cost and energy efficiency, as well as the potential for mass production and industrial competitiveness, the most suitable conditions for the synthesis of pristine graphene are 900 ℃ and 60 s. For nitrogen-doped graphene, the conditions at 1000 ℃ resulted in the highest 2D peak. However, the optimal conditions must be adjusted based on the required qualities and application purpose; this can be achieved by combining XPS and electrical property evaluation, considering factors such as the nitrogen content and charge neutrality point (Dirac point).\u003c/p\u003e \u003cp\u003eBased on the Raman data, additional analyses were conducted on the graphene samples synthesized at 900, 950, and 1000 ℃ for 60 s. For pristine graphene, the analysis was focused on the sample synthesized at the lowest temperature, 900 ℃, as the results did not differ significantly with varying temperatures. In other words, when the growth temperature was sufficiently high and the characteristics were saturated, there was minimal variation in the samples with temperature.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e., the G peaks and 2D peaks for pristine and doped graphene synthesized at 900, 950, and 1000 ℃ were compared using Raman data measured at 30 spots for each sample. For pristine graphene, the G peak and 2D peak were located at approximately 1583 and 2684 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively, independent of growth temperature. Meanwhile, for doped graphene, at growth temperatures of 900, 950, 1000 ℃, the G peak was located at approximately 1595, 1594, and 1589 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively, and the 2D peak at approximately 2704, 2694, and 2688 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively. The purple dots represent the reference values for exfoliated freestanding graphene unaffected by strain or doping (G peak: 1581.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, 2D peak: 2676.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e).\u003csup\u003e23\u003c/sup\u003e The gray lines indicate the Raman changes due to strain, with a slope of 2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 (Pos(2D)/Pos(G)).\u003csup\u003e23\u003c/sup\u003e For graphene synthesized using butane, three distinct graphene clusters were formed near the reference points, indicating uniform pristine graphene.\u003c/p\u003e \u003cp\u003eAccording to previous research, hole doping causes Raman spectra to exhibit a linear shift toward higher frequencies at a slope of 0.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05 (Pos(2D)/Pos(G)) and blue shifts toward higher frequencies.\u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e However, studies on the effect of electron doping on the Raman spectra are relatively limited, though they have been reported as nonlinear shifts.\u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e Additionally, a previous study utilized freestanding graphene in top-gate transistors, making it challenging to directly compare and explain our Raman results for nitrogen-doped graphene, in which the dopant replaced carbon. In case of N-doped graphene using pyridine, both the G and 2D peaks exhibited a blue shift and nonlinear changes with decreasing synthesis temperature.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 X-Ray Photoelectron Spectroscopy\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. shows the XPS data obtained for the elemental analysis of each graphene sample. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea. shows the XPS spectrum of pristine graphene synthesized at 900 ℃, while Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb\u0026ndash;d. show the XPS spectra of nitrogen-doped graphene synthesized at 1000, 950, and 900 ℃, respectively. The C1s spectra for both graphene types include a dominant peak at 284.7 eV corresponding to the C\u0026ndash;C bond, a small oxide bond that can occur during the process at 286.3 eV corresponding to the C\u0026ndash;O bond, and peaks at 287.5 and 289.0 eV corresponding to the O\u0026ndash;C\u0026thinsp;=\u0026thinsp;O and C\u0026thinsp;=\u0026thinsp;O bonds, respectively.\u003csup\u003e[\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e For nitrogen-doped graphene, there was an additional clear peak corresponding to the C\u0026ndash;N bond at 285.7 eV, and all C1s peaks exhibited overall broadening. The N1s spectra can comprise three main peaks corresponding to three different bonds: the pyridinic N bond (398.6 eV) and pyrrolic N bond (400.3 eV) represent the bonding of one and two nitrogen atoms, respectively, with carbon through π bonds, and the graphitic N bond at 401.5 eV corresponds to the substitution of carbon with nitrogen.\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e Although all three bonds involve nitrogen and carbon, pyridinic N and pyrrolic N contribute to p-type doping, whereas graphitic N contributes to n-type doping. \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e These peaks are not present for pristine graphene, indicating the absence of nitrogen. Meanwhile, all doped graphene samples were confirmed to contain nitrogen owing to the presence of all three peaks, with the nitrogen content being similar independent of the synthesis temperature; however, as the synthesis temperature decreased from 1000 to 900 ℃, the ratio of graphitic-N increased.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Electrical Properties\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea. shows the transfer curve of pristine graphene with respect to the growth temperature. Pristine graphene synthesized at three different temperatures exhibited Dirac points ranging from 0 to +\u0026thinsp;1 V, and the values of the source-drain current with respect to the gate voltage were similar. As observed from the Raman data, the electrical properties of pristine graphene were nearly identical when synthesized at growth temperatures above 900 ℃. This is consistent with Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e (a), in which the absence of C\u0026ndash;N and N1s is logically presented. The electron mobility was calculated to be 1430\u0026ndash;1498 cm\u003csup\u003e2\u003c/sup\u003e V\u003csup\u003e\u0026ndash;1\u003c/sup\u003e s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e at a charge concentration of n\u0026thinsp;=\u0026thinsp;+\u0026thinsp;1e\u003csup\u003e12\u003c/sup\u003e, and the hole mobility was calculated to be 1468\u0026ndash;1572 cm\u003csup\u003e2\u003c/sup\u003e V\u003csup\u003e\u0026ndash;1\u003c/sup\u003e s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e at n=\u0026ndash;1e\u003csup\u003e12\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn the case of N-doped graphene, the Dirac point voltage was consistently below 0 V, indicating n-type behavior. For graphene samples synthesized at 900, 950, and 1000\u0026deg;C, the Dirac point voltages were \u0026minus;\u0026thinsp;117, \u0026minus;\u0026thinsp;82, and \u0026minus;\u0026thinsp;51 V, respectively, electron mobilities at n\u0026thinsp;=\u0026thinsp;+\u0026thinsp;1e\u003csup\u003e12\u003c/sup\u003e were calculated as 253, 317, and 402 cm\u003csup\u003e2\u003c/sup\u003e V\u003csup\u003e\u0026ndash;1\u003c/sup\u003e s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively, and hole mobilities at n=\u0026ndash;1e\u003csup\u003e12\u003c/sup\u003e were calculated as 255, 326, and 404 cm\u003csup\u003e2\u003c/sup\u003e V\u003csup\u003e\u0026ndash;1\u003c/sup\u003e s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively. As the growth temperature decreased, the relative abundance of graphitic N increased, leading to a larger absolute value of the Dirac point voltage in the negative direction. However, overall, the graphitic structure decreased, and the increased scattering sites resulted in a reduction in mobility (\u003cb\u003eFigure S4.\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Gas Sensing Application\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. shows the potential applicability of gas sensors using pristine graphene synthesized at 900 ℃ and N-doped graphene synthesized at 1000 ℃. The two types of graphene were transferred onto SiO\u003csub\u003e2\u003c/sub\u003e substrates to create simple FET devices, which were then applied as gas-sensor channels for NO\u003csub\u003e2\u003c/sub\u003e and NH\u003csub\u003e3\u003c/sub\u003e at room temperature and atmospheric pressure. Typically, CVD-grown graphene, the dominant carriers are holes, is a p-type channel; NO\u003csub\u003e2\u003c/sub\u003e absorbed onto the graphene surface withdraws free electrons such that the resistance increases, while NH\u003csub\u003e3\u003c/sub\u003e donates free electrons to the graphene surface, thus the resistance decreases. Meanwhile, nitrogen-doped graphene, the dominant carriers are electrons, is an n-type channel that exhibits the opposite electrical response characteristics. This leads to opposite changes in the reaction characteristics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe graphene-based gas sensors were exposed to NO\u003csub\u003e2\u003c/sub\u003e and NH\u003csub\u003e3\u003c/sub\u003e gases for 9 min each, and the resistance changes were measured repeatedly. Pristine graphene exhibited a polarity characteristic similar to that of a previous study,\u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e showing adsorption and desorption based on the gas type. In contrast, the N-doped graphene exhibited reversed polarity. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea. shows the second cycle of the graphs in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e., grouped according to graphene and gas types. Pristine and N-doped graphene exhibited reactivities of \u0026minus;\u0026thinsp;25% and 79%, respectively, when exposed to NO\u003csub\u003e2\u003c/sub\u003e for 9 min, and reactivities of 18% and \u0026minus;\u0026thinsp;12%, respectively, when exposed to NH\u003csub\u003e3\u003c/sub\u003e for 9 min. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb. shows the reactivity of the graphene samples after 2 min of exposure to each gas; nitrogen-doped graphene exhibited higher sensitivity and faster response compared to pristine graphene for both gases.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eTo enhance the potential for the industrial synthesis of graphene, we developed a conveyor CVD system for the highly productive synthesis of high-quality graphene. By optimizing the synthesis conditions, we successfully synthesized pristine and nitrogen-doped graphene using the liquid precursors butane and pyridine, respectively; 12 samples were synthesized in 1 h, confirming the potential for rapid synthesis. This system not only allows for the simultaneous synthesis of numerous graphene samples, but enables the synthesis of graphene with the desired qualities by using various precursors and different recipes. In addition, it can accommodate flexible foils, rigid substrates, and powder catalysts for graphene synthesis.\u003c/p\u003e \u003cp\u003eAt synthesis temperatures above 900\u0026deg;C, we achieved high quality prisitine graphene samples that exhibited low D/G and 2D/G ratios in their Raman spectra. XPS analysis indicated dominant C\u0026ndash;C peaks, excluding oxides formed during the transfer process, and no N1s peaks. The Dirac point voltage ranged from 0 to 5 V, exhibiting characteristics of neutral CVD graphene. Meanwhile, for the nitrogen-doped graphene samples, decreasing the growth temperature blue-shifted the G-peak and 2D-peak in the Raman spectra, increased the ratio of graphitic-N in the XPS spectra, and decreased the Dirac point voltage and mobility with a unidirectional tendency. Therefore, for future research and development applications, synthesis closer to 900\u0026deg;C may be preferred for synthesizing graphene with a higher level of nitrogen doping, while synthesis closer to 1000\u0026deg;C can be selectively employed if graphene with lower nitrogen doping and better mobility is needed based on the specific objectives.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eAvailability of data and material\u003c/p\u003e\n\u003cp\u003eThe datasets used during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis research was supported from the National Research Foundation of Korea (NRF) grant, funded by the Korea government (MSIT). (No. 2019R1A2C1009963) And also this research supported by Global Research Development Center Program (No. 2018K1A4A3A01064272) and Basic Science Research Program (No. 2021R1A4A1031900) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (MSIT).\u003c/p\u003e\n\u003cp\u003eAuthors’ contributions\u003c/p\u003e\n\u003cp\u003eDYL, JN, and AJ performed experiments. DYL, JN, AJ, and KSK conducted the experiments and analyzed the data. AJ and KSK supervised the research. All authors discussed the experimental results. DYL, JN, AJ, and KSK wrote and edited the paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKS Novoselov, D Jiang, F Schendin, TJ Booth, VV Khotkevich, SV Morzov, AK Geim, Proc. Natl. Acad. Sci. 102 (30), 10451-10453 (2005).\u003c/li\u003e\n\u003cli\u003eKS Novoselov, AK Geim, SV Morozov, D Jiang, MI Katsnelson, IV Grigorieva, SV Dubonos, AA Firsov, Nature 438, 197-200 (2005). \u003c/li\u003e\n\u003cli\u003eY Zhang, TW Tan, HL Stormer, P Kim, Nature 438, 201-204 (2005).\u003c/li\u003e\n\u003cli\u003eC Berger, Z Song, X Li, X Wu, N Brown, C Naud, D Mayou, T Li, J Hass, AN Marchenkov, EH Conrad, PN First, WA Heer, Science 312 (5777), 1191-1196 (2006).\u003c/li\u003e\n\u003cli\u003eKS Kim, Z Yue, H Jang, SY Lee, JM Kim, KS Kim, JH Ahn, P Kim, JY Choi, BH Hong, Nature 457, 706-710 (2009).\u003c/li\u003e\n\u003cli\u003eDS Choi, KS Kim, H Kim, Y Kim, TY Kim, SH Rhy, CM Yang, DH Yoon, WS Yang, ACS Applied Materials \u0026amp; Interfaces 6 (22), 19574-19578 (2014).\u003c/li\u003e\n\u003cli\u003eJ Seo, J Lee, AR Jang, Y Choi, U Kim, HS Shin, H Park, Chemistry of Materials 29 (10), 4202-4208 (2017).\u003c/li\u003e\n\u003cli\u003eT Yamada, M Ishihara, J Kim, M Hasegawa, S Iijima, Carbon 50 (7), 2615-2619 (2012).\u003c/li\u003e\n\u003cli\u003eT Kobayashi, M Bando, N Kimura, K Shimizu, K Kadono, N Umezu, K Miyahara, S Hayazaki, S Nagai, Y Mizuguchi, Y Murakami, D Hobara, Appl. Phys. Lett. 102, 023112 (2013).\u003c/li\u003e\n\u003cli\u003eG Zhong, X Wu, L D\u0026apos;Arsie, KBK Teo, NL Rupesinghe, A Jouvray, J Robertson, Appl. Phys. Lett. 109, 193103 (2016).\u003c/li\u003e\n\u003cli\u003eES Polsen, DQ McNerny, B Viswanath, SW Pattinson, AJ Hart, Sci. Rep. 5, 10257 (2015).\u003c/li\u003e\n\u003cli\u003ePR Kidambi, DD Mariappan, NT Dee, A Vyatskikh, S Zhang, R Karnik, AJ Hart, ACS Appl. Mater. Interfaces 10 (12), 10369-10378 (2018).\u003c/li\u003e\n\u003cli\u003eM Rybin, A Pereaslavtsev, T Vasilieva, V Myasnikov, I Sokolov, A Pavlova, E Obraztsova, A Khomich, V Ralchenko, E Obraztsova, Carbon 96, 196-202 (2016).\u003c/li\u003e\n\u003cli\u003eD Wei, Y Liu, Y Wang, H Zhang, L Huang, G Yu, Nano Lett. 9 (5), 1752-1758 (2009).\u003c/li\u003e\n\u003cli\u003eM Deifallah, PF McMillan, F Cor\u0026agrave;, The Journal of Physical Chemistry C112 (14), 5447-5453 (2008).\u003c/li\u003e\n\u003cli\u003eM Zhu, Z Du, Z Yin, W Zhou, Z Liu, SH Tsang, EHT Teo, ACS Appl. Mater. Interfaces 8 (1), 502-510 (2016).\u003c/li\u003e\n\u003cli\u003eJH Choi, Z Li, P. Cui, X Fan, H Zhang, C Zeng, Z Zhang, Sci. Rep.3, 1925 (2013).\u003c/li\u003e\n\u003cli\u003eJ Nam, DC Kim, H Yun, DH Shin, S Nam S, WK Lee, JY Hwang, SW Lee, H Weman, KS Kim, Carbon 111, 733-740 (2017).\u003c/li\u003e\n\u003cli\u003eKS Kim, Physics \u0026amp; High technology 28 (5), 31-38 (2019).\u003c/li\u003e\n\u003cli\u003eJ Nam, J Yang, Y Zhao, KS Kim, Curr. Appl. Phys. 61, 55-70 (2024).\u003c/li\u003e\n\u003cli\u003eI Lee, DJ Bae, WK Lee, CM Yang, SW Cho, J Nam, DY Lee, AR Jang, HS Shin, JY Hwang, S Hong, KS Kim, Carbon 145, 462-469 (2019).\u003c/li\u003e\n\u003cli\u003eSJ Park, I Lee, DJ Bae, J Nam, YH Han, BJ Park, KS Kim, KEPCO Journal on Electric Power and Energy 1 (1), 169-174 (2015).\u003c/li\u003e\n\u003cli\u003eD Seo, DY Lee, J Kwon, JJ Lee, T Taniguchi, K Watanabe, GH Lee, K S Kim, J Hone, YD Kim, HJ Choi, Appl. Phys. Lett. 115, 012104 (2019).\u003c/li\u003e\n\u003cli\u003eY Wang, Y Zheng, X Xu, E Dubuisson, Q Bao, J Lu, KP Loh, ACS Nano 5(12), 9927-9933 (2011).\u003c/li\u003e\n\u003cli\u003eCT Cherian, F Giustiniano, I Martin-Fernandez, H Andersen, J Balakrishnan, B \u0026Ouml;zyilmaz, Small 11 (2), 189-194 (2015).\u003c/li\u003e\n\u003cli\u003eI Roh, SH Goh, Y Meng, JS Kim, S Han, Z Xu, HE Lee, Y Kim, SH Bae, Nano Converg. 10, 20 (2023).\u003c/li\u003e\n\u003cli\u003eJE Lee, G Ahn, J Shim, YS Lee, S Ryu, Nat. Comm. 3, 1024 (2012).\u003c/li\u003e\n\u003cli\u003eA Das, S Pisana, B Chakraborty, S Piscanec, SK Saha, UV Waghmare, KS Novoselov, HR Krishnamurthy, AK Geim, AC Ferrari. AK Sood, Nat. Nanotech. 3, 210-2015 (2008).\u003c/li\u003e\n\u003cli\u003eA Das, B Chakraborty, S Piscanec, S Pisana, AK Sood, AC Ferrari, Physical Review B 79 (15), 155417 (2009).\u003c/li\u003e\n\u003cli\u003eB Xiong, Y Zhoua, R O\u0026rsquo;Hayrec, Z Shao, Applied Surface Science 266, 433-439 (2013).\u003c/li\u003e\n\u003cli\u003eGV Bianco, A Sacchetti, M Grande, A D\u0026rsquo;Orazio, A Milella, G Bruno, Sci. Rep. 12, 8703 (2022).\u003c/li\u003e\n\u003cli\u003eH Xu, L Ma, Z Jin, J. Energy Chem. 27 (1), 146-160 (2018).\u003c/li\u003e\n\u003cli\u003eL Zhao, R He, KT Rim, T Schiros, KS Kim, H Zhou, C Guti\u0026eacute;rrez, SP Chockalingam, CJ Arguello, L Palova, D Nordlund, MS Hybertsen, DR Reichman, TF Heinz, P Kim, A Pinczuk, GW Flynn, AN Pasupathy, Science 333 (6045), 999-1003 (2011).\u003c/li\u003e\n\u003cli\u003eT Schiros, D Nordlund, L Palova, D Prezzi, L Zhao, KS Kim, U Wurstbauer, C Gutierez, D Delongchamp, C Jaye, D Fischer, H Ogasawara, LGM Pettersson, DR Reichman, P Kim, MS Hybertsen, AN Pasupathy, Nano Lett. 12 (8), 4025-4031 (2012).\u003c/li\u003e\n\u003cli\u003eF Schedin, AK Geim, SV Morozv, EW Hill, P Blake, MI Katsnelson, KS Novoselov, Nat. Mater. 6, 652-655 (2007).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nano-convergence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ncon","sideBox":"Learn more about [Nano Convergence](https://www.springer.com/journal/40580)","snPcode":"40580","submissionUrl":"https://www.editorialmanager.com/ncon/default2.aspx","title":"Nano Convergence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Graphene, Synthesis, Doping, Chemical Vapor Deposition, Conveyor, Productivity, Gas sensor","lastPublishedDoi":"10.21203/rs.3.rs-4336389/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4336389/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe mass production of high-quality graphene is required for industrial application as a future electronic material. However, the chemical vapor deposition (CVD) systems previously studied for graphene production face bottlenecks in terms of quality, speed, and reproducibility. Herein, we report a novel conveyor CVD system that enables rapid graphene synthesis using liquid precursors. Pristine and nitrogen-doped graphene samples of a size comparable to a smartphone (15 cm \u0026times; 5 cm) are successfully synthesized at temperatures of 900, 950, and 1000\u0026deg;C using butane and pyridine, respectively. Raman spectroscopy allows optimization of the rapid-synthesis conditions to achieve uniformity and high quality. By conducting compositional analysis via X-ray photoelectron spectroscopy as well as electrical characterization, it is confirmed that graphene synthesis and nitrogen doping degree can be adjusted by varying the synthesis conditions. Testing the corresponding graphene samples as gas-sensor channels for NH\u003csub\u003e3\u003c/sub\u003e and NO\u003csub\u003e2\u003c/sub\u003e and evaluating their response characteristics show that the gas sensors exhibit polar characteristics in terms of gas adsorption and desorption depending on the type of gas, with contrasting characteristics depending on the presence or absence of nitrogen doping; nitrogen-doped graphene exhibits superior gas-sensing sensitivity and response speed compared with pristine graphene.\u003c/p\u003e","manuscriptTitle":"Conveyor CVD to high-quality and productivity of large-area graphene and its potentiality","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-30 20:51:58","doi":"10.21203/rs.3.rs-4336389/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Minor revision","date":"2024-06-05T04:09:08+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-05-13T11:24:47+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-13T11:06:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-29T04:27:33+00:00","index":"","fulltext":""},{"type":"submitted","content":"Nano Convergence","date":"2024-04-28T02:07:32+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nano-convergence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ncon","sideBox":"Learn more about [Nano Convergence](https://www.springer.com/journal/40580)","snPcode":"40580","submissionUrl":"https://www.editorialmanager.com/ncon/default2.aspx","title":"Nano Convergence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ef0b9d7e-46c5-4ffe-9c48-bc532b64b43a","owner":[],"postedDate":"May 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-22T19:35:51+00:00","versionOfRecord":{"articleIdentity":"rs-4336389","link":"https://doi.org/10.1186/s40580-024-00439-0","journal":{"identity":"nano-convergence","isVorOnly":false,"title":"Nano Convergence"},"publishedOn":"2024-08-14 15:57:28","publishedOnDateReadable":"August 14th, 2024"},"versionCreatedAt":"2024-05-30 20:51:58","video":"","vorDoi":"10.1186/s40580-024-00439-0","vorDoiUrl":"https://doi.org/10.1186/s40580-024-00439-0","workflowStages":[]},"version":"v1","identity":"rs-4336389","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4336389","identity":"rs-4336389","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}