title: Negligible environmental sensitivity of graphene in a hexagonal boron nitride/graphene/h-BN sandwich structure.
abstract: Using Raman spectroscopy, we study the environmental sensitivity of mechanically exfoliated and electrically floating single-layer graphene transferred onto a hexagonal boron nitride (h-BN) substrate, in comparison with graphene deposited on a SiO(2) substrate. In order to understand and isolate the substrate effect on graphene electrical properties, we model and correct for Raman optical interference in the substrates. As-deposited and unannealed graphene shows a large I(2D)/I(G) ratio on both substrates, indicating extremely high quality, close to that of graphene suspended in vacuum. Thermal annealing strongly activates subsequent environmental sensitivity on the SiO(2) substrate; such activation is reduced but not eliminated on the h-BN substrate. In contrast, in a h-BN/graphene/h-BN sandwich structure, with graphene protected on both sides, graphene remains pristine despite thermal processing. Raman data provide a deeper understanding of the previously observed improved graphene electrical conductivity on h-BN substrates. In the sandwich structure, the graphene 2D Raman feature has a higher frequency and narrower line width than in pristine suspended graphene, implying that the local h-BN environment modestly yet measurably changes graphene electron and phonon dispersions.
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Zheyuan
authors.initials: Z
authors.lastname: Chen
authors.forename: Cory R
authors.initials: CR
authors.lastname: Dean
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.forename: Louis E
authors.initials: LE
authors.lastname: Brus
authors.forename: James
authors.initials: J
authors.lastname: Hone
mesh_terms: D001896:Boron Compounds / Q000737:chemistry*; D004553:Electric Conductivity; D004579:Electron Transport; D006108:Graphite / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D013499:Surface Properties
chemical_list: D001896:Boron Compounds; D046911:Macromolecular Substances; C017282:boron nitride; D006108:Graphite