石墨烯擁有卓越的電性，在各種電子應用中成為有前途的材料。為了能夠大規模合成石墨烯，化學氣相沉積被視為最有效率的生產方式，但不可避免地產生多晶石墨烯並包含晶界。晶界被認為會降低電傳輸。然而，很少有系統的實驗來仔細探索晶界數量對石墨烯電學性能的影響。
本實驗利用化學氣相沉積方法生長單層多晶石墨烯，在不同的生長溫度（760 °C - 1000 °C）下產生的多晶石墨烯中的晶界數量可以通過使用後處理在實驗上可視化晶界來計算。通過拉曼光譜觀察多晶石墨烯晶格中的缺陷。利用微影製程、乾蝕刻及蒸鍍系統製作了Van der Pauw的幾何形狀，並進行Van der Pauw和電化學阻抗頻譜的電性量測。結果表明，多晶石墨烯的薄層電阻和遷移率與晶界數量有關，晶界數量的增加會阻礙電子在石墨烯中的運動，當晶界達到臨界數量，晶界的影響會變得很微小。而進一步通過穿透電子顯微鏡觀察和計算分形維度，發現晶界的不同型態也會影響電荷的累積，良好域間連通性的晶界對電性是有利的。

Graphene possesses excellent electrical properties and has become a promising material in various electronic applications. Chemical vapor deposition is considered the most efficient production method for large-scale graphene synthesis. However, it inevitably results in polycrystalline graphene with grain boundaries. Grain boundaries are believed to reduce electrical conductivity. Nevertheless, there have been few systematic experiments to carefully explore the impact of grain boundary quantity on the electrical performance of graphene.
In the experiment, monolayer polycrystalline graphene is grown using the chemical vapor deposition method. The quantity of grain boundaries in the polycrystalline graphene produced at different growth temperatures (760 °C - 1000 °C) was calculated by visualizing the grain boundaries using post-processing techniques. Defects in the graphene lattice were observed through Raman spectroscopy. Van der Pauw's geometry was fabricated using photolithography, dry etching, and evaporation systems, enabling electrical measurements via Van der Pauw and electrochemical impedance spectroscopy. The results indicate that the sheet resistance and mobility of polycrystalline graphene are correlated with the quantity of grain boundaries. An increase in grain boundary quantity impedes electron motion in graphene, but their impact becomes minimal when the grain boundaries reach a critical quantity. Furthermore, by observing and calculating the fractal dimension through transmission electron microscopy, it was discovered that different types of grain boundaries also affect charge accumulation, with well-connected grain boundaries benefiting electrical properties.

[1] Biró, László P., and Philippe Lambin. "Grain boundaries in graphene grown by chemical vapor deposition." New Journal of Physics 15.3 (2013): 035024.
[2] Kim, Philip. "Across the border." Nature materials 9.10 (2010): 792-793.
[3] Yasaei, Poya, et al. "Chemical sensing with switchable transport channels in graphene grain boundaries." Nature communications 5.1 (2014): 4911.
[4] Liu, Jia-Ming, and I-Tan Lin. Graphene photonics. Cambridge University Press, 2018.
[5] Novoselov, Kostya S., et al. "Electric field effect in atomically thin carbon films." science 306.5696 (2004): 666-669.
[6] Novoselov, Kostya S., et al. "Two-dimensional atomic crystals." Proceedings of the National Academy of Sciences 102.30 (2005): 10451-10453.
[7] Geim, Andre K., and Konstantin S. Novoselov. "The rise of graphene." Nature materials 6.3 (2007): 183-191.
[8] Hass, J., W. A. De Heer, and E. H. Conrad. "The growth and morphology of epitaxial multilayer graphene." Journal of Physics: Condensed Matter 20.32 (2008): 323202.
[9] Mishra, Neeraj, et al. "Graphene growth on silicon carbide: A review." physica status solidi (a) 213.9 (2016): 2277-2289.
[10] Li, Dan, et al. "Processable aqueous dispersions of graphene nanosheets." Nature nanotechnology 3.2 (2008): 101-105.
[11] Li, Xuesong, et al. "Large-area synthesis of high-quality and uniform graphene films on copper foils." science 324.5932 (2009): 1312-1314.
[12] Bets, Ksenia V., Vasilii I. Artyukhov, and Boris I. Yakobson. "Kinetically determined shapes of grain boundaries in graphene." ACS nano 15.3 (2021): 4893-4900.
[13] Vicarelli, Leonardo, et al. "Controlling defects in graphene for optimizing the electrical properties of graphene nanodevices." ACS nano 9.4 (2015): 3428-3435.
[14] Read, William T., and W. J. P. R. Shockley. "Dislocation models of crystal grain boundaries." Physical review 78.3 (1950): 275.
[15] Liu, Yuanyue, and Boris I. Yakobson. "Cones, pringles, and grain boundary landscapes in graphene topology." Nano letters 10.6 (2010): 2178-2183.
[16] Huang, Pinshane Y., et al. "Grains and grain boundaries in single-layer graphene atomic patchwork quilts." Nature 469.7330 (2011): 389-392.
[17] Kim, Kwanpyo, et al. "Grain boundary mapping in polycrystalline graphene." ACS nano 5.3 (2011): 2142-2146.
[18] Gao, Li, Jeffrey R. Guest, and Nathan P. Guisinger. "Epitaxial graphene on Cu (111)." Nano letters 10.9 (2010): 3512-3516.
[19] Gargiulo, Fernando, and Oleg V. Yazyev. "Topological aspects of charge-carrier transmission across grain boundaries in graphene." Nano letters 14.1 (2014): 250-254.
[20] Vancsó, Péter, et al. "Effect of the disorder in graphene grain boundaries: A wave packet dynamics study." Applied Surface Science 291 (2014): 58-63.
[21] Van Tuan, Dinh, et al. "Scaling properties of charge transport in polycrystalline graphene." Nano letters 13.4 (2013): 1730-1735.
[22] Zhang, Hengji, et al. "Grain boundary effect on electrical transport properties of graphene." The Journal of Physical Chemistry C 118.5 (2014): 2338-2343.
[23] Koepke, Justin C., et al. "Atomic-scale evidence for potential barriers and strong carrier scattering at graphene grain boundaries: a scanning tunneling microscopy study." ACS nano 7.1 (2013): 75-86.
[24] Nemes-Incze, Péter, et al. "Electronic states of disordered grain boundaries in graphene prepared by chemical vapor deposition." Carbon 64 (2013): 178-186.
[25] Rutter, Gregory M., et al. "Scattering and interference in epitaxial graphene." Science 317.5835 (2007): 219-222.
[26] Jauregui, Luis A., et al. "Electronic properties of grains and grain boundaries in graphene grown by chemical vapor deposition." Solid State Communications 151.16 (2011): 1100-1104.
[27] Cummings, Aron W., et al. "Charge transport in polycrystalline graphene: challenges and opportunities." Advanced Materials 26.30 (2014): 5079-5094.
[28] Ma, Teng, et al. "Tailoring the thermal and electrical transport properties of graphene films by grain size engineering." Nature communications 8.1 (2017): 14486.
[29] Malard, Leandro M., et al. "Raman spectroscopy in graphene." Physics reports 473.5-6 (2009): 51-87.
[30] Ferrari, Andrea C., and Denis M. Basko. "Raman spectroscopy as a versatile tool for studying the properties of graphene." Nature nanotechnology 8.4 (2013): 235-246.
[31] Ni, Zhenhua, et al. "Raman spectroscopy and imaging of graphene." Nano Research 1 (2008): 273-291.
[32] Ferrari, Andrea C., et al. "Raman spectrum of graphene and graphene layers." Physical review letters 97.18 (2006): 187401.
[33] Lucchese, Márcia Maria, et al. "Quantifying ion-induced defects and Raman relaxation length in graphene." Carbon 48.5 (2010): 1592-1597.
[34] Cançado, L. G., et al. "General equation for the determination of the crystallite size L a of nanographite by Raman spectroscopy." Applied Physics Letters 88.16 (2006): 163106.
[35] Ago, Hiroki. "CVD growth of high-quality single-layer graphene." Frontiers of Graphene and Carbon Nanotubes: Devices and Applications (2015): 3-20.
[36] Reina, Alfonso, et al. "Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition." Nano letters 9.1 (2009): 30-35.
[37] Li, Xuesong, et al. "Large-area synthesis of high-quality and uniform graphene films on copper foils." science 324.5932 (2009): 1312-1314.
[38] Mattevi, Cecilia, Hokwon Kim, and Manish Chhowalla. "A review of chemical vapour deposition of graphene on copper." Journal of Materials Chemistry 21.10 (2011): 3324-3334.
[39] Gelb, Alan, and Mark J. Cardillo. "Classical trajectory study of the dissociation of hydrogen on copper single crystals: II. Cu (100) and Cu (110)." Surface Science 64.1 (1977): 197-208.
[40] Zhang, Y. I., Luyao Zhang, and Chongwu Zhou. "Review of chemical vapor deposition of graphene and related applications." Accounts of chemical research 46.10 (2013): 2329-2339.
[41] Zhou, Weilie, and Zhong Lin Wang, eds. Scanning microscopy for nanotechnology: techniques and applications. Springer science & business media, 2007.
[42] Levinson, Harry J. Principles of lithography. Vol. 146. SPIE press, 2005.
[43] Grant, David J., and Siva Sivoththaman. "Electron-beam lithography: From past to present." University of Waterloo, Canada (2003).
[44] Chung, Chen-Kuei. "Plasma etching." Encyclopedia of Microfluidics and Nanofluidics. New York: Springer Sci-ence+ Business Media (2014): 1-18.
[45] Awan, Tahir Iqbal, Almas Bashir, and Aqsa Tehseen. Chemistry of nanomaterials: fundamentals and applications. Elsevier, 2020.
[46] Werner, Florian. "Hall measurements on low-mobility thin films." Journal of Applied Physics 122.13 (2017): 135306.
[47] Rietveld, Gert, et al. "DC conductivity measurements in the Van Der Pauw geometry." IEEE transactions on instrumentation and measurement 52.2 (2003): 449-453.
[48] Instruments, Gamry. "Basics of electrochemical impedance spectroscopy." G. Instruments, Complex impedance in Corrosion (2007): 1-30.
[49] Fultz, Brent, and James M. Howe. Transmission electron microscopy and diffractometry of materials. Springer Science & Business Media, 2012.
[50] Kim, HoKwon, et al. "Activation energy paths for graphene nucleation and growth on Cu." ACS nano 6.4 (2012): 3614-3623.
[51] Červenka, J., and C. F. J. Flipse. "Structural and electronic properties of grain boundaries in graphite: planes of periodically distributed point defects." Physical Review B 79.19 (2009): 195429.
[52] Tsen, Adam W., et al. "Tailoring electrical transport across grain boundaries in polycrystalline graphene." Science 336.6085 (2012): 1143-1146.
[53] Tian, Jifa, et al. "Direct imaging of graphene edges: Atomic structure and electronic scattering." Nano letters 11.9 (2011): 3663-3668.
[54] Rasool, Haider I., et al. "Atomic-scale characterization of graphene grown on copper (100) single crystals." Journal of the American Chemical Society 133.32 (2011): 12536-12543.
[55] Yu, Qingkai, et al. "Control and characterization of individual grains and grain boundaries in graphene grown by chemical vapour deposition." Nature materials 10.6 (2011): 443-449.
[56] Childres, Isaac, et al. "Raman spectroscopy of graphene and related materials." New developments in photon and materials research 1 (2013): 1-20.