Metallo-dielectric nanophotonic materials via direct laser writing and electroless metallization

Interest in three-dimensional (3D) metallo-dielectric photonic crystals (MDPCs) has grown considerably given their potential applications in optics and photonics. MDPCs can exhibit intriguing and potentially useful optical properties, including ultra-wide photonic bandgaps, engineered thermal emission, and negative refractive index. Yet experimental studies of such materials remain few because of the difficulties associated with fabricating 3D micron- and sub-micron-scale metallic structures. We report a route to MDPCs based on metallization of a 3D polymeric photonic crystal (PC) fabricated by multi-photon microfabrication (MPM). Polymeric PCs having face-centered tetragonal symmetry and micrometer-scale periodicity were created using a cross-linkable acrylate or epoxide pre-polymer. The resulting PCs were metallized by electroless deposition of silver or copper. Analysis of the metallized structures in cross-section by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy shows that silver deposited conformally onto the entire micro-porous lattice. The dielectric and metallized PCs were characterized by Fourier transform infrared (FTIR) spectroscopy. The polymer photonic crystals exhibit a stop band with strong reflectance near 4 to 6 microns, depending upon the lattice period. In contrast, FTIR spectra of the metallized PCs show widened stop bands of nearly 6 microns and greater and maximum reflectance exceeding 90%. The appreciable broadening of the stop band due to the presence of the deposited metal is a result consistent with previously reported theoretical and experimental data for all-metallic 3D PCs. Thus, the approach reported here appears suitable for fabricating 3D MDPCs of many symmetries and basis sets and provides a path for integrating such structures with other micron-scale optical elements.