Strong Charge-Transfer Doping of 1 to 10 Layer Graphene by NO₂

Abstract

We use resonance Raman and optical reflection contrast methods to study charge transfer in 1-10 layer (1L-10L) thick graphene samples on which NO(2) has adsorbed. Electrons transfer from the graphene to NO(2), leaving the graphene layers doped with mobile delocalized holes. Doping follows a Langmuir-type isotherm as a function of NO(2) pressure. Raman and optical contrast spectra provide independent, self-consistent measures of the hole density and distribution as a function of the number of layers (N). At high doping, as the Fermi level shift E(F) reaches half the laser photon energy, a resonance in the graphene G mode Raman intensity is observed. We observe a decrease of graphene optical absorption in the near-IR that is due to hole-doping. Highly doped graphene is more optically transparent and much more electrically conductive than intrinsic graphene. In thicker samples, holes are effectively confined near the surface, and in these samples, a small band gap opens near the surface. We discuss the properties and versatility of these highly charge-transfer-doped, few-layer-thick graphene samples as a new class of electronic materials.

Changes in work function due to NO2 adsorption on monolayer and bilayer epitaxial graphene on SiC(0001)

“…This is in agreement with previous DFT calculations [19] and angle-resolved photoemission spectroscopy (ARPES) experiments showing that NO 2 acts as a strong charge acceptor despite its relatively weak binding to the graphene surface [12]. Crowther et al find that 0.012e per C atom is transferred to NO 2 monolayers adsorbed on both sides of an isolated graphene sheet, using a Langmuir adsorption isotherm [39]. This is in good agreement with our calculations which have eight C atoms per unit cell and molecular adsorption on only one side of the graphene layer.…”

“…We find an adsorption energy of −108 meV for NO 2 adsorbed on 1LG. The low adsorption energy suggests that NO 2 is physisorbed on the graphene surface, in agreement with Raman spectroscopy experiments [39]. This value is considerably smaller than that extracted from thermal desorption spectra of 0.4 eV [40,41].…”

“…This value is considerably smaller than that extracted from thermal desorption spectra of 0.4 eV [40,41]. The high experimental binding energy could be explained by the existence of defects in the graphene layer [42] or the presence of other, unknown, species on the surface [39]. Another possibility is that ripples or ridges are present on the graphene surface [17,43].…”

Li Intercalation into Graphite: Direct Optical Imaging and Cahn–Hilliard Reaction Dynamics

“…Similar two-peak Raman spectra have been recently observed in few layer graphenes with adsorbed NO2, which is a strong electron acceptor. 5 For stage 2 GIC, in which all graphene layers are equivalent, there is only one G peak with weaker intensity. It is softened to a lower frequency than the direct contact G peak in stage 3, indicating a higher doping level in stage 2, explained by an in plane lattice expansion accompanying such higher doping 6 .…”

“…1 Lithium intercalated graphite shows a rich phase diagram and is widely used as the anode in batteries and other electrochemical energy storage systems. Understanding Li intercalation is a critical technological problem that has been studied principally using electrochemical methods: [2][3][4][5][6][7][8] potentiostatic intermittent titration (PITT), galvanostatic intermittent titration (GITT), electrochemical impedance spectroscopy (EIS), and slow scan rate cyclic voltammetry(CV). Additional information on elementary atomic hopping steps of Li transport has also been obtained from nuclear magnetic resonance.…”