Synchrotron-Based Nanoscale Spectroscopy of Free Electrons in Semiconductors and Graphene

Synchrotron light provides a much broader infrared spectrum than tabletop sources, making it a powerful platform for spectroscopy at the nanoscale. In this talk, we use synchrotron-based infrared nano spectroscopy (nano-FTIR) to probe free carriers in semiconductors and 2D materials. In doped silicon, analysis of the near-field spectra yields the carrier density and mobility, showing that near-field spectroscopy can retrieve dielectric-function parameters with nanometer spatial resolution. For graphene/CrI₃ heterostructures, the spectra reveal graphene plasmons due to pronounced charge transfer from CrI₃ to graphene. Due to the broad bandwidth, we also observe a feature near 200 cm^-1 arising from coupling between a CrI₃ phonon and graphene plasmonic polariton modes. Together these results demonstrate the advantages of synchrotron-based nano-spectroscopy for quantifying charge carrier properties. They also outline clear pathways to follow-on experiments, including nanoscale photocurrent spectroscopy based on the same platform.