Rapid Selective Etching of PMMA Residues from Transferred Graphene by Carbon Dioxide

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• 作者：Cheng Gong ; Herman Carlo Floresca ; David Hinojos ; Stephen McDonnell ; Xiaoye Qin ; Yufeng Hao ; Srikar Jandhyala ; Greg Mordi ; Jiyoung Kim ; Luigi Colombo ; Rodney S. Ruoff ; Moon J. Kim ; Kyeongjae Cho ; Robert M. Wallace ; Yves J. Chabal
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：November 7, 2013
• 年：2013
• 卷：117
• 期：44
• 页码：23000-23008
• 全文大小：640K
• 年卷期：v.117,no.44(November 7, 2013)
• ISSN：1932-7455

文摘

During chemical-vapor-deposited graphene transfer onto target substrates, a polymer film coating is necessary to provide a mechanical support. However, the remaining polymer residues after organic solvent rinsing cannot be effectively removed by the empirical thermal annealing in vacuum or forming gas. Little progress has been achieved in the past years, for little is known about the chemical evolution of the polymer macromolecules and their interaction with the environment. Through in situ Raman and infrared spectroscopy studies of PMMA transferred graphene annealed in nitrogen, two main processes are uncovered involving the polymer dehydrogenation below 200 掳C and a subsequent depolymerization above 200 掳C. Polymeric carbons over the monolayer graphitic carbon are found to constitute a fundamental bottleneck for a thorough etching of PMMA residues. The dehydrogenated polymeric chains consist of active C鈺怌 bonding sites that are readily attacked by oxidative gases. The combination of Raman spectroscopy, X-ray photoemission spectroscopy, and transmission electron microscopy reveals the largely improved carbon removal by annealing in oxidative atmospheres. CO₂ outperforms other oxidative gases (e.g., NO₂, O₂) because of its moderate oxidative strength to remove polymeric carbons efficiently at 500 掳C in a few minutes while preserving the underlying graphene lattice. The strategy and mechanism described here open the way for a significantly improved oxidative cleaning of transferred graphene sheets, which may require optimization tailored to specific applications.