Physical adsorption and charge transfer of molecular Br2 on graphene

Zheyuan Chen*, Pierre Darancet, Lei Wang, Andrew C. Crowther, Yuanda Gao, Cory R. Dean, Takashi Taniguchi, Kenji Watanabe, James Hone, Chris A. Marianetti, Louis E. Brus

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

60 Scopus citations

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 languageEnglish (US)
Pages (from-to)2943-2950
Number of pages8
JournalACS nano
Volume8
Issue number3
DOIs
StatePublished - 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

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