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Optical reflectivity and Raman scattering in few-layer-thick graphene highly doped by K and Rb.
Naeyoung Jung1, Bumjung Kim, Andrew C Crowther
1Department of Chemistry, Columbia University, New York, New York 10027, USA. nj2153@columbia.edu
ACS Nano
|June 21, 2011
Summary
Alkali metal vapors (potassium and rubidium) interact differently with few-layer graphene, altering its optical and Raman properties. Thicker graphene (over 15 layers) approaches bulk alkali intercalation compound behavior, while thinner samples exhibit unique electronic and vibrational responses.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Graphene's unique electronic and optical properties are highly sensitive to its environment and doping.
- Alkali metal intercalation compounds (GICs) of graphite exhibit distinct bulk properties.
- Understanding alkali metal interactions with few-layer graphene is crucial for novel electronic applications.
Purpose of the Study:
- To investigate the optical reflectivity and Raman scattering of few-layer graphene exposed to potassium (K) and rubidium (Rb) vapors.
- To compare the behavior of few-layer graphene with bulk alkali GICs.
- To elucidate the mechanisms of charge transfer and structural changes induced by alkali adsorption and intercalation.
Main Methods:
- Experimental measurements of optical reflectivity and Raman scattering spectra.
- Exposure of few-layer graphene samples (1 to tens of layers) to K and Rb vapors.
- Theoretical simulations to determine in-plane free electron density.
Main Results:
- Samples >15 layers thick show bulk-like spectra of KC(8) and RbC(8).
- Few-layer graphene (<10 layers) exhibits distinct Raman spectra, increased transparency, and Drude-like plasma edge reflectivity.
- Charge transfer dopes graphene to >10^14 electrons/cm^2; K spectra are thickness-independent (L=1-4), while Rb spectra show thickness-dependent doping.
Conclusions:
- Alkali interaction with few-layer graphene differs significantly from bulk GICs, with both intercalation and surface adsorption occurring.
- New Raman modes are activated in few-layer graphene due to zone folding from crystalline alkali adlayers.
- Potassium and rubidium exhibit distinct behaviors in terms of doping and structural ordering (adsorbed Rb as liquid, intercalated as solid).
