Nano-infrared imaging and spectroscopy of epitaxial graphene on SiC

Epitaxial graphene on silicon carbide (SiC) is one of the most important types of graphene for technological applications due to its scalability, high quality, and potential for generating new electronic properties. In this work, we demonstrate that scattering-type scanning near-field optical microscopy (s-SNOM) is a powerful and efficient technique for characterizing epitaxial graphene due to its capability of high-resolution infrared (IR) imaging and spectroscopy. With nano-IR imaging, we were able to map microscopic graphene domains with various thicknesses and doping. With nano-IR spectroscopy, we found the mapped graphene domains have distinct IR contrasts at different spectral regions due to their interactions with the optical phonon resonance of SiC. Furthermore, we performed quantitative modeling of the nano-IR spectra, based on which we were able to estimate the Fermi energy of the different graphene domains. Our work uncovered new IR responses and surface properties of epitaxial graphene on SiC and paved the way for future large-scale applications of epitaxial graphene in wafer-scale electronics and optoelectronics.