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

Daniel Beitner, Shaked Amitay, Simon Salleh Atri, Andrew McEllistrim, Tom Coen, Vladimir I. Fal’ko, Shachar Richter, Moshe Ben Shalom and Haim Suchowski

Nano Letters 23, 10758 (2023)

The mid-infrared (MIR) spectral region attracts attention for accurate chemical analysis using photonic devices. Few-layer graphene (FLG) polytypes are promising platforms, due to their broad absorption in this range and gate-tunable optical properties. Among these polytypes, the noncentrosymmetric ABCB/ACAB structure is particularly interesting, due to its intrinsic bandgap (8.8 meV) and internal polarization. In this study, we utilize scattering-scanning near-field microscopy to measure the optical response of all three tetralayer graphene polytypes in the 8.5–11.5 μm range. We employ a finite dipole model to compare these results to the calculated optical conductivity for each polytype obtained from a tight-binding model. Our findings reveal a significant discrepancy in the MIR optical conductivity response of graphene between the different polytypes than what the tight-binding model suggests. This observation implies an increased potential for utilizing the distinct tetralayer polytypes in photonic devices operating within the MIR range for chemical sensing and infrared imaging.