Opening an electrical band gap of bilayer graphene with molecular doping

Wenjing Zhang, Cheng Te Lin, Keng Ku Liu, Teddy Tite, Ching Yuan Su, Chung Huai Chang, Yi Hsien Lee, Chih Wei Chu, Kung Hwa Wei, Jer Lai Kuo, Lain Jong Li*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

219 Scopus citations


The opening of an electrical band gap in graphene is crucial for its application for logic circuits. Recent studies have shown that an energy gap in Bernal-stacked bilayer graphene can be generated by applying an electric displacement field. Molecular doping has also been proposed to open the electrical gap of bilayer graphene by breaking either in-plane symmetry or inversion symmetry; however, no direct observation of an electrical gap has been reported. Here we discover that the organic molecule triazine is able to form a uniform thin coating on the top surface of a bilayer graphene, which efficiently blocks the accessible doping sites and prevents ambient p-doping on the top layer. The charge distribution asymmetry between the top and bottom layers can then be enhanced simply by increasing the p-doping from oxygen/moisture to the bottom layer. The on/off current ratio for a bottom-gated bilayer transistor operated in ambient condition is improved by at least 1 order of magnitude. The estimated electrical band gap is up to ∼111 meV at room temperature. The observed electrical band gap dependence on the hole-carrier density increase agrees well with the recent density-functional theory calculations. This research provides a simple method to obtain a graphene bilayer transistor with a moderate on/off current ratio, which can be stably operated in air without the need to use an additional top gate.

Original languageEnglish (US)
Pages (from-to)7517-7524
Number of pages8
JournalACS Nano
Issue number9
StatePublished - Sep 27 2011
Externally publishedYes


  • Raman spectroscopy
  • band gap opening
  • bilayer grapheme
  • doping
  • on/off current ratio
  • transistor
  • triazine

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy


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