Near-edge x-ray absorption fine structure spectroscopy studies of charge redistribution at graphene/dielectric interfaces
(Color online) Raman spectra acquired using 514.5 nm laser excitation for as-grown SLG/Cu, transferred SLG on SiO2, and double-oxide dielectric/graphene/SiO2 heterostructures where the top layer is ZrO2, TiO2, TiN, or HfO2. All spectra have been baseline corrected and normalized to the G band. An increase in the intensity of the D band is representative of a large number of defect-induced states; corroborated with a diminished 2D band.
(Color online) Carbon K-edge NEXAFS spectra collected at several angles for transferred graphene, and graphene–dielectric interfaces. (a) Single-layered graphene at all angles, where the relative intensities of the π* and σ* resonances denote a high degree of anisotropy after transfer on 300 nm SiO2/Si. (b)–(d) NEXAFS spectra of graphene interfaces acquired for graphene on SiO2 with ZrO2, TiO2, TiN, and HfO2 overlayers. The spectra are compared at three different angles of the incident x rays: (b) 25°, (c) 54.7°, and (d) 85°.
(Color online) Ab initio excited-state core–hole (XCH) spectra calculated for a neutral 200 atom graphene supercell and upon the addition of electrons (3 − , 2 − , 1 − ) or holes (1 + , 2 + , 3 + ). The alignment of the spectra is discussed in the Methods section. The subtle shifts in intensity and peak position of the π* resonance denote changes to the unoccupied density of states near the Fermi level as discussed in the Results and Discussion Section B.
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