Para-hexaphenylene (p-6P) nanofibers for polarization-insensitive surface plasmon polariton excitation

Developing micro- and nano-scale systems with defined active elements acting as local sources of surface plasmons polaritons (SPPs) is crucial for future plasmonic circuitry. We demonstrate excitation of SPPs, exploiting fluorescent light from crystalline organic para-hexaphenylene nanofibers. The fibers were fabricated utilizing two scenarios, epitaxial growth on crystalline substrate and random growth directly on a metal surface. The excited SPPs are characterized using angle-resolved leakage radiation spectroscopy, in the excitation wavelength range 420 – 675 nm, corresponding to nanofibers photoluminescence band. To support experimental results, we developed a theoretical model based on finite-difference-time-domain (FDTD) method, where we introduced the excited nanofibers as polarized electric dipole sources on the dielectric/silver interface. We characterized the influence of the angular position of the dipoles to asymmetrical excitation of SPPs, which are related to fibre molecular alignment and possible changes due to the transfer process. These results were compared to LRS signals from randomly oriented p-6P nanofibers grown directly on Ag surface. Directly grown nanofibers reveal optical properties very similar to the transferred ones, while demonstrating polarization-insensitive plasmonic excitation and very good agreement with theoretical models. This opens a new way of integrating organic nanofibres into optoelectronic applications by direct deposition of the p-6P material onto desired substrates and avoids distortion of the fibre structure and introducing impurities during a transfer process.