title: Graphene annealing: how clean can it be?
abstract: 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.
authors.affiliation: Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: Yung-Chang
authors.initials: YC
authors.lastname: Lin
authors.forename: Chun-Chieh
authors.initials: CC
authors.lastname: Lu
authors.forename: Chao-Huei
authors.initials: CH
authors.lastname: Yeh
authors.forename: Chuanhong
authors.initials: C
authors.lastname: Jin
authors.forename: Kazu
authors.initials: K
authors.lastname: Suenaga
authors.forename: Po-Wen
authors.initials: PW
authors.lastname: Chiu
mesh_terms: D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D006108:Graphite / Q000737:chemistry*; D006244:Hardness; D006358:Hot Temperature; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D006108:Graphite; D019904:Polymethyl Methacrylate