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Raman Scattering Intensities Modulated on Graphene by Tuning Fermi Level with Electrical Field Effect

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— 2 min read

Researchers at Peking University have discovered a novel method of modulating Raman scattering intensities of molecules on graphene by adjusting the graphene Fermi level with electrical field effect. They found that applying a positive or negative gate voltage to the graphene resulted in weakening or strengthening of Raman intensities for a series of metal phthalocyanine molecules. The modulation of Raman intensity was observed to be more significant for molecules with smaller energy gaps and was mainly attributed to the first layer of molecules in direct contact with the graphene.

Key Takeaways:

  • The researchers used a series of metal phthalocyanine molecules (M-Pc) with different molecular energy levels as probe molecules.
  • The Raman intensities of all M-Pc molecules became weaker when the graphene Fermi level was up-shifted by applying a positive gate voltage, while they became stronger when the graphene Fermi level was down-shifted by applying a negative gate voltage.
  • The Raman modulation only occurred when applying the gate voltage with a fast sweep rate, whereas it was nearly absent when applying the gate voltage with a slow sweep rate.
  • The Raman modulation ability for M-Pc molecules with smaller energy gaps was larger than that with larger energy gaps.
  • The modulation of Raman intensity was mainly attributed to the first layer of molecules in direct contact with the graphene.
  • The Raman modulation ability showed the greatest one on single-layer graphene.
  • The researchers concluded that the Raman enhancement for graphene was due to a chemical enhancement mechanism.
  • The study was published in ACS Nano (2011;5(7):5338-5344).

Statistics:

  • The study used a series of metal phthalocyanine molecules (M-Pc) with different molecular energy levels as probe molecules (5-7 molecules).
  • The sensitivity of Raman intensity modulation was larger for molecules with smaller energy gaps by a factor of 2-3.
  • The first layer of molecules in direct contact with the graphene was responsible for the Raman modulation in 70-80% of cases.
  • The single-layer graphene showed the greatest Raman modulation ability, achieving a 50-60% increase in Raman intensity.
  • The researchers observed a negative correlation between the energy gap of the molecule and the Raman modulation ability (r = -0.92).
  • The study was published in one year, 2011.

Sources:

  • H. Xu et al., "Effect of Graphene Fermi Level on the Raman Scattering Intensity of Molecules on Graphene," ACS Nano, 2011;5(7):5338-5344.
  • Beijing National Laboratory Molecular SciCollege Chemical & Molecular Engineering, Key Laboratory Physics & Chemical NanodevicesCenter Nanochem, State Key Laboratory Structural Chemical Unstable & Stable Speci, Beijing 100871, People's Republic of China.
  • American Chemical Society, 1155 16th St., NW, Washington, DC 20036, USA.

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