I. INTRODUCTION Section: Choose Top of page ABSTRACT I.INTRODUCTION << II.EXPERIMENTAL III.RESULTS IV.DISCUSSION V.SUMMARY REFERENCES CITING ARTICLES

Graphene is a crystalline monolayer of sp2-bonded carbon atoms arranged in a regular hexagonal pattern. This structure is the reason for the remarkable mechanical, electronic, thermal, optical and chemical properties of graphene. Optical transparence of up to 97% and electron mobility above 15000 cm2/Vs has been reported 1 8, 1815 (2010). 1. S. J. Wang, Y. Geng, Q. B. Zheng, and J. K. Kim, Carbon, 1815 (2010). https://doi.org/10.1016/j.carbon.2010.01.027 2/Vs for free-standing graphene 2 103, 053702 (2008). 2. A. Akturk and N. Goldsman, J. Appl. Phys., 053702 (2008). https://doi.org/10.1063/1.2890147 graphene's acoustic phonons. However, these values are limited by the quality of the graphene itself and the type of substrate. Due to these properties graphene is getting much attention from fundamental as well as applied science and technology. One problem that still detained this material from a broad technological implementation is the challenge to synthesize a defect-free graphene layer on larger scale, which is essential for its industrial use for example in energy applications (batteries, fuel cells) and semiconductor technology. is a crystallineof sp-bondedatoms arranged in a regular hexagonal pattern. This structure is the reason for the remarkable mechanical, electronic, thermal, optical and chemical properties ofOptical transparence of up to 97% and electron mobility above 15000 cm/Vs has been reportedwith theoretically potential limits as high as 200.000 cm/Vs for free-standinglimited by the scattering ofacoustic phonons. However, these values are limited by the quality of theitself and the type of substrate. Due to these propertiesis getting much attention from fundamental as well as applied science and technology. One problem that still detained this material from a broad technological implementation is the challenge to synthesize a defect-freelayer on larger scale, which is essential for its industrial use for example in energy applications (batteries, fuel cells) and semiconductor technology.

graphene was the method of mechanical exfoliation that was also used by the Nobel price laureates K. S. Novoselov and A. K. Geim using Scotch tape to pull apart the layers of a piece of highly oriented pyrolytic graphite and transfer layers from the graphite onto a SiO 2 substrate. 3 306, 666 (2004). 3. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, Science, 666 (2004). https://doi.org/10.1126/science.1102896 First methods to produce a sample ofwas the method of mechanical exfoliation that was also used by the Nobel price laureates K. S. Novoselov and A. K. Geim using Scotch tape to pull apart the layers of a piece of highly oriented pyrolytic graphite and transfer layers from the graphite onto a SiOsubstrate.One can easily see that this method is slow and limited in size by the dimension of the highly oriented crystal, making this method expensive and not suitable for industrial applications.

graphene is the use of chemical vapor deposition (CVD), in particular thermal CVD, which allows to deposit rather large areas with graphene of high quality. 4 9, 30 (2009). 4. A. Reina, X. Jia, J. Ho, D. Nezich, H. Son, V. Bulovic, and M. S. Dresselhaus, J. Kong, Nano Letters, 30 (2009). https://doi.org/10.1021/nl801827v CVD process, reactive gas species (mostly H 2 and CH 4 ) are fed into a hot-wall reactor (temperatures at around 1000 °C) for chemical reactions. Most of these CVD processes use copper as substrates and take advantage of the catalytic influences of the copper and hydrogen. 5,6 324, 1312 (2009). 5. X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, and R. S. Ruoff, Science, 1312 (2009). https://doi.org/10.1126/science.1171245 5, 6069 (2011). 6. I. Vlassiouk, M. Regmi, P. Fulvio, S. Dai, P. Datskos, G. Eres, and S. Smirnov, ACS Nano., 6069 (2011). https://doi.org/10.1021/nn201978y temperature for the catalytic reaction of methane causes significant evaporation of the substrate material even at temperatures far below the melting point of copper 5 324, 1312 (2009). 5. X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, and R. S. Ruoff, Science, 1312 (2009). https://doi.org/10.1126/science.1171245 defects in the growing graphene likely to occur. The main reason for this effect is the strong increase of copper's vapor pressure with an increasing temperature at the conditions used for the CVD of graphene. One of the most promising alternatives to synthesize larger areas of high qualityis the use of chemical vaporin particular thermalwhich allows torather large areas withof high quality.During the low-pressureprocess, reactive gas species (mostly Hand CH) are fed into a hot-wall reactorat around 1000 °C) for chemical reactions. Most of theseprocesses useas substrates and take advantage of the catalytic influences of theand hydrogen.However the high activationfor the catalytic reaction of methane causes significant evaporation of the substrate material even atfar below the melting point ofmaking the process hard to control andin the growinglikely to occur. The main reason for this effect is the strong increase ofvaporwith an increasingat the conditions used for theof

In combination with the slow increase of temperature in a typical thermal CVD reactor (thus long process time) the process will be affected by the evaporation of a notable amount of copper. In sharp contrast, the synthesis of graphene by plasma-enhanced CVD (PECVD) can circumvent this problem by substantially shortening the process time and the prospect of lowering the substrate temperature. The reduced thermal load and the possibility to industrially scale-up the PECVD process makes it a very attractive alternative to the thermal CVD process with respect to future's graphene production.

temperature including the use of microwave plasma CVD to synthesize graphene on nickel foil, 7 8, 263106 (2011). 7. Y. Kim, W. Song, S. Y. Lee, C. Jeon, W. Jung, M. Kim, and C. Y. Park, Appl. Phys. Lett., 263106 (2011). https://doi.org/10.1063/1.3605560 plasma CVD to synthesize graphene at low temperatures in the range of 300 °C to 400 °C on large area conductive electrodes 8,9 8, 091502 (2011). 8. J. Kim, M. Ishihara, Y. Koga, K. Tsugawa, M. Hasegawa, and S. Iijima, Appl. Phys. Lett., 091502 (2011). https://doi.org/10.1063/1.3561747 8, 2815 (2012). 9. G. Kalita, K. Wakita, and M. Umeno, RSC Adv., 2815 (2012). https://doi.org/10.1039/c2ra00648k deposition of graphene on copper foils at temperatures down to 600 °C. 10–12 8, 285 (2013). 10. S. H. Chan, S. H. Chen, W. T. Lin, M. C. Li, Y. C. Lin, and C. C. Kuo, Nanoscale Res. Lett., 285 (2013). https://doi.org/10.1186/1556-276X-8-285 19, 305604 (2008). 11. A. Malesevic, R. Vitchev, K. Schouteden, A. Volodin, L. Zhang, G. van Tendeloo, A. Vanhulsel, and C. Van Haesendonck, Nanotechnology, 305604 (2008). https://doi.org/10.1088/0957-4484/19/30/305604 58(1), 53 (2011). 12. J. H. Kim, E. J. D. Castro, Y. G. Hwang, and C. H. Lee, J. Korean Phys. Soc.(1), 53 (2011). https://doi.org/10.3938/jkps.58.53 PECVD is a promising method for the synthesis of graphene, the resulting carbon structures often lack of quality being FLG with considerable amount of defects. 11,12 19, 305604 (2008). 11. A. Malesevic, R. Vitchev, K. Schouteden, A. Volodin, L. Zhang, G. van Tendeloo, A. Vanhulsel, and C. Van Haesendonck, Nanotechnology, 305604 (2008). https://doi.org/10.1088/0957-4484/19/30/305604 58(1), 53 (2011). 12. J. H. Kim, E. J. D. Castro, Y. G. Hwang, and C. H. Lee, J. Korean Phys. Soc.(1), 53 (2011). https://doi.org/10.3938/jkps.58.53 defect density in PECVD graphene is referred to energetic particles from the plasma interacting with the growing surface. Nevertheless there have been experiments proving that SLG of good quality can be deposited by plasma-assisted methods. 10 8, 285 (2013). 10. S. H. Chan, S. H. Chen, W. T. Lin, M. C. Li, Y. C. Lin, and C. C. Kuo, Nanoscale Res. Lett., 285 (2013). https://doi.org/10.1186/1556-276X-8-285 plasma reactor. According to their process, a distance must be maintained between the plasma initial stage and the deposition stage to allow the plasma to diffuse to the substrate. The deposition is therefore not taken place in the direct plasma but downstream. While that leads to a much lower defect density in the SLG it makes an additional furnace necessary to heat the sample. Another disadvantage of this method is the relatively low pressure that the deposition is taking place (0.5 torr). There have been some reports of plasma-based methods to decrease the processincluding the use of microwaveto synthesizeon nickel foil,surface waveto synthesizeat lowin the range of 300 °C to 400 °C on large area conductive electrodesand the plasma-assistedofonfoils atdown to 600 °C.Although these works show thatis a promising method for the synthesis ofthe resultingstructures often lack of quality being FLG with considerable amount ofThe highdensity inis referred to energetic particles from theinteracting with the growing surface. Nevertheless there have been experiments proving that SLG of good quality can beby plasma-assisted methods.In this work the authors used a pulsed DCreactor. According to their process, a distance must be maintained between theinitial stage and thestage to allow theto diffuse to the substrate. Theis therefore not taken place in the directbut downstream. While that leads to a much lowerdensity in the SLG it makes an additional furnace necessary to heat the sample. Another disadvantage of this method is the relatively lowthat theis taking place (0.5 torr).