Anisotropic dielectric function of graphite probed by far- and near-field spectroscopies

Abstract

Graphite is a cornerstone material for novel technologies, from energy storage to two-dimensional materials. Despite its foundational role, the predictive power required for engineering emergent optical behavior in van der Waals heterostructures is severely constrained by persistent discrepancies in reported graphite optical constants. We resolve this long-standing ambiguity. A multi-modal approach synergizes far-field spectroscopic ellipsometry with nanoscale near-field optical probing (scattering-type scanning near-field optical microscopy) and micro-reflectance spectroscopy of graphite. We establish a new, self-consistent set of optical constants (n and k) for both in-plane and out-of-plane crystallographic directions across the ultraviolet-to-near-infrared spectrum. This definitive reference provides the essential foundation for the quantitative modeling and engineering of light–matter interactions in the evolving landscape of carbon-based nanophotonics.