Wu Zehao, Zhang Xuewei, Das Atanu, Liu Jinglan, Zou Zhenxing, Zhang Zilong, Xia Yang, Zhao Pei, Wang Hongtao
Center for X-Mechanics and Institute of Applied Mechanics, Zhejiang University Hangzhou 310012 P. R. China
Institute of Microelectronics, Chinese Academy of Sciences Beijing 100029 China.
RSC Adv. 2019 Dec 16;9(71):41447-41452. doi: 10.1039/c9ra09268d. eCollection 2019 Dec 13.
Transfer acts as a crucial bridge between the chemical vapor deposition (CVD) synthesis of large-scale graphene and its applications, but the quality evolution of a graphene film during transfer remains unclear. Here we use scanning Raman spectroscopy to monitor as-grown graphene during each step of wet transfer including floating on etchant solution, loaded onto a target substrate, and with additional annealing. Results show that the etchant solution results in strong compressive strain and p-type doping to floating graphene, but both are significantly reduced after the sample is loaded and rinsed especially for the doping. An annealing treatment increases the compressive strain in graphene but hardly its doping level. Moreover, when a poly(methyl methacrylate) (PMMA) layer is used to assist the transfer, it does not only increase the p-type doping of floating graphene but also lowers the crystalline quality of annealed graphene. Therefore, to obtain graphene with better quality, besides the attempts of improving CVD synthesis for its larger domain sizes, universal and easy-to-use polymer-free transfer techniques must be developed as well.
转移是大规模石墨烯化学气相沉积（CVD）合成与其应用之间的关键桥梁，但转移过程中石墨烯薄膜的质量演变仍不清楚。在此，我们使用扫描拉曼光谱在湿法转移的每个步骤中监测生长态石墨烯，包括漂浮在蚀刻剂溶液上、加载到目标衬底上以及进行额外退火。结果表明，蚀刻剂溶液会对漂浮的石墨烯产生强烈的压缩应变和p型掺杂，但在样品加载和冲洗后，尤其是掺杂，两者都显著降低。退火处理会增加石墨烯中的压缩应变，但几乎不会提高其掺杂水平。此外，当使用聚甲基丙烯酸甲酯（PMMA）层辅助转移时，它不仅会增加漂浮石墨烯的p型掺杂，还会降低退火后石墨烯的晶体质量。因此，为了获得质量更好的石墨烯，除了尝试改进CVD合成以获得更大的畴尺寸外，还必须开发通用且易于使用的无聚合物转移技术。
