Additive manufacturing of titanium dioxide for dielectric photonic crystals

Abstract

Fabrication of 3D dielectric photonic crystals in the visible and in the infrared range typically requires sub-micron structural features and high-refractive index materials. We developed a template-free additive manufacturing (AM) process based on direct laser writing (DLW) that can create complex 3D architectures out of titania (TiO_2) with ~100 nm resolution. In this process, we synthesize hybrid organic-inorganic materials that contain titanium clusters coordinated with acrylic ligands to prepare a photoresist that is amenable to two-photon lithography (TPL). We sculpt a pre-ceramic architecture using TPL and then pyrolyze in air at 900°C to remove the organic constituents to produce a replica of the original structure with ~70% reduced linear dimensions. Energy-Dispersive Spectroscopy (EDS) and Raman spectroscopy confirm the constituent solid to consist predominantly out of rutile titania. We demonstrate this process by fabricating titania woodpile structures with lateral dimensions of 70 × 70 μm and lateral periodicities between 1.0 and 1.3 μm. Fourier Transform Infrared (FTIR) spectroscopy reveals passive tuning of the reflectance peak between 1.7 and 2.3 μm, which agrees with Plane Wave Expansion simulations. This titania AM process offers a promising pathway to efficiently fabricate complex 3D nano-architectures out of a high-index material for 3D dielectric photonic crystals in the visible and the infrared.