Graphene Annealing: How Clean Can It Be?
Graphene Annealing: How Clean Can It Be?
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DOI：
10.1021/nl203733r
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发表时间：
2012-01-01
期刊：
影响因子：
10.8
通讯作者：
Chiu, Po-Wen
中科院分区：
文献类型：
--
作者：
Lin, Yung-Chang;Lu, Chun-Chieh;Chiu, Po-Wen
长期以来，聚合物残留物的表面污染一直是探索石墨烯的固有性质以及在表面化学、生物技术和超高速电子设备中使用石墨烯的关键问题。聚甲基丙烯酸甲酯(PMMA)是一种常用的大分子，用于石墨烯转移和器件加工，留下一层薄薄的残留物，通过退火法进行经验清理。本文利用透射电子显微镜结合拉曼光谱系统地研究了PMMA在石墨烯上的分解及其对石墨烯本征性质的影响。透射电子显微镜图像显示，物理吸附的PMMA在热处理过程中经历了两个失重步骤，并且在石墨烯敏感温度下不能在断裂前完全去除。拉曼光谱分析表明，退火后石墨烯的2D模发生了显著的蓝移，表明存在缺陷的石墨烯中存在退火态的能带结构调制。用密度泛函理论计算表明，在石墨烯缺陷上，碳从sp(2)到sp(3)的局部再杂化可能发生在高分子链的随机断裂中，并解释了拉曼2D模的蓝移。
Surface contamination by polymer residues has long been a critical problem in probing graphene's intrinsic properties and in using graphene for unique applications in surface chemistry, biotechnology, and ultrahigh speed electronics. Poly(methyl methacrylate) (PMMA) is a macromolecule commonly used for graphene transfer and device processing, leaving a thin layer of residue to be empirically cleaned by annealing. Here we report on a systematic study of PMMA decomposition on graphene and of its impact on graphene's intrinsic properties using transmission electron microscopy (TEM) in combination with Raman spectroscopy. TEM images revealed that the physisorbed PMMA proceeds in two steps of weight loss in annealing and cannot be removed entirely at a graphene susceptible temperature before breaking. Raman analysis shows a remarkable blue-shift of the 2D mode after annealing, implying an anneal-induced band structure modulation in graphene with defects. Calculations using density functional theory show that local rehybridization of carbons from sp(2) to sp(3) on graphene defects may occur in the random scission of polymer chains and account for the blue-shift of the Raman 2D mode.