Exploring Surface Roughness in Epsilon-Near-Zero Materials

The practical application of materials with epsilon-near-zero (ENZ) characteristics heavily depends on the quality of real-world ENZ materials, considering factors like material losses and surface roughness. These materials have drawn interest due to their strong nonlinear responses and unique behavior. In this study, an experimental examination of how surface roughness affects ENZ substrates is presented. We employed silicon carbide (SiC) substrates deliberately engineered to exhibit different levels of roughness, enabling us to analyze samples spanning from a few to hundreds of nanometers in size scales. Substrates with nanoscale roughness experience adverse effects due to longitudinal phonon coupling and strong ENZ fields, while at larger roughness scales, the ENZ band demonstrates to be more robust compared to dielectric and surface phonon polariton (SPhP) bands.