Abstract
We present a detailed study of gaseous Br2 adsorption and charge transfer on graphene, combining in situ Raman spectroscopy and density functional theory (DFT). When graphene is encapsulated by hexagonal boron nitride (h-BN) layers on both sides, in a h-BN/graphene/h-BN sandwich structure, it is protected from doping by strongly oxidizing Br2. Graphene supported on only one side by h-BN shows strong hole doping by adsorbed Br 2. Using Raman spectroscopy, we determine the graphene charge density as a function of pressure. DFT calculations reveal the variation in charge transfer per adsorbed molecule as a function of coverage. The molecular adsorption isotherm (coverage versus pressure) is obtained by combining Raman spectra with DFT calculations. The Fowler-Guggenheim isotherm fits better than the Langmuir isotherm. The fitting yields the adsorption equilibrium constant (∼0.31 Torr-1) and repulsive lateral interaction (∼20 meV) between adsorbed Br2 molecules. The Br2 molecule binding energy is ∼0.35 eV. We estimate that at monolayer coverage each Br 2 molecule accepts 0.09 e- from single-layer graphene. If graphene is supported on SiO2 instead of h-BN, a threshold pressure is observed for diffusion of Br2 along the (somewhat rough) SiO 2/graphene interface. At high pressure, graphene supported on SiO2 is doped by adsorbed Br2 on both sides.
Original language | English (US) |
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Pages (from-to) | 2943-2950 |
Number of pages | 8 |
Journal | ACS nano |
Volume | 8 |
Issue number | 3 |
DOIs | |
State | Published - Mar 25 2014 |
Keywords
- Raman spectroscopy
- adsorption isotherm
- band gap
- bromine
- charge transfer
- graphene
- hexagonal boron nitride
ASJC Scopus subject areas
- General Engineering
- General Materials Science
- General Physics and Astronomy