Raman Radiation Patterns of Graphene

Area of Science:

• Materials Science
• Condensed Matter Physics
• Spectroscopy

Background:

• Graphene's unique electronic properties are often studied using Raman spectroscopy.
• The interpretation of Raman spectra, particularly intensity ratios like I(2D)/I(G), is crucial for determining graphene's doping levels.
• Understanding light emission patterns is key for accurate measurements, especially in microscopy.

Purpose of the Study:

• To investigate the angular distribution of G and 2D Raman scattering from graphene on glass.
• To determine how factors like numerical aperture and collection angle affect Raman emission patterns and polarization.
• To provide a foundation for accurate quantitative analysis of Raman intensities in graphene.

Main Methods:

• Detection of back focal plane patterns to analyze angular distributions of Raman scattering.
• Modeling Raman emission as combinations of incoherent point dipoles.
• Parameter-free calculations to compare with experimental radiation patterns.

Main Results:

• G Raman emission modeled as two orthogonal dipoles; 2D emission modeled as three or two dipoles.
• Experimental and calculated radiation patterns show excellent agreement.
• The 2D polarization ratio and I(2D)/I(G) intensity ratio are dependent on the microscope objective's numerical aperture.
• Polarization contrast and intensity ratios are affected by light depolarization and polarization mixing at the substrate interface.

Conclusions:

• The study clarifies the angular distribution of G and 2D Raman scattering from graphene.
• Findings highlight the influence of experimental conditions (microscope NA, collection angle) on measured Raman signals.
• Results are critical for accurate quantitative Raman spectroscopy of graphene, especially for doping analysis and understanding plasmonic antenna effects.