Nanoscale Characterizations of Plasmon-Mode Superposition in Iron-Filled Multiwalled Carbon Nanotubes

The coaxial plasmonic waveguide structure has unique advantages in nanophotonics. This study provides insight into high-resolution images of the plasmonic near-field of iron-filled multiwalled carbon nanotubes, as observed through photon-induced near-field electron microscopy. The images reveal plasmon interference between the iron core and the carbon nanotube and the superposition of polarization-dependent plasmon modes. Under specific phase differences between plasmon modes, these modes show asymmetric near-field contrast when the dipole field is perpendicular to the electron beam and a pronounced low-intensity channel when parallel. Finite-element simulations further support the analysis, providing insights into the plasmon-mode superposition within the coaxial structure. This comprehensive understanding of plasmon modes in metal-filled nanotubes paves the way for advanced applications in nanosensors and nanowaveguides.