Mid-Infrared Mapping of Four-Layer Graphene Polytypes Using Near-Field Microscopy

Area of Science:

• Condensed matter physics
• Materials science
• Photonics

Background:

• Mid-infrared (MIR) spectral region is crucial for chemical analysis.
• Few-layer graphene (FLG) offers broad absorption and tunable optical properties in the MIR range.
• Noncentrosymmetric ABCB/ACAB tetralayer graphene structures possess intrinsic bandgaps and polarization.

Purpose of the Study:

• To investigate the MIR optical response of three tetralayer graphene polytypes.
• To compare experimental results with theoretical predictions from a tight-binding model.
• To assess the potential of these polytypes in MIR photonic devices.

Main Methods:

• Scattering-scanning near-field microscopy (s-SNOM) was used to measure optical responses.
• Measurements were conducted in the 8.5-11.5 μm MIR range.
• A finite dipole model was employed to analyze optical conductivity, comparing it to tight-binding calculations.

Main Results:

• Significant discrepancies were observed between the experimental MIR optical conductivity and theoretical predictions for different tetralayer graphene polytypes.
• The experimental results indicate unique optical behaviors for each polytype not fully captured by the tight-binding model.
• The study highlights differences in MIR optical conductivity among the polytypes.

Conclusions:

• Tetralayer graphene polytypes exhibit distinct MIR optical properties.
• The observed discrepancies suggest limitations of current theoretical models for predicting their behavior.
• These unique polytypes hold significant promise for advanced photonic devices in MIR chemical sensing and infrared imaging.