3D Printed Silica with Nanoscale Resolution

SiO₂ (silica) is one of the most widely used inorganic materials that demands fabrication methods with nanoscale resolution. Fabricating silica with designed three-dimensional nanostructures is an exciting yet challenging area of research and industrial application. The emerging technology of additive manufacturing (AM) can create fine structures through layer-by-layer deposition to generate complex architectures and simplify fabrication processes. AM of fused silica glass was realized via stereolithography with the resolution of tens of microns. However, the relatively low spatial resolution limits their applications in micro-electronics, MEMS, and micro-photonics. To address the limitation, we propose an approach to 3D print silica nanostructures with sub-200 nm resolution via two-photon polymerization. The technique involves 2PP enabled AM of functionalized colloidal silica nanocomposite ink, followed by pyrolysis and sintering, where the post-processing procedure determines the crystallinity of the structures produced, which can be either amorphous glass or polycrystalline cristobalite. In this technique, making a suitable “ink” containing silica nanoparticles (NPs) and two-photon polymerizable precursor is the dominating factor. The nanocomposite ink has low viscosity, high transparency, and high heat conductivity. The 3D printed nanostructures demonstrate attractive optical properties. The fabricated microtoroid optical resonators can reach quality factors (Q) over 10⁴. Moreover, doping and co-doping of rare earth salts such as Er³⁺, Tm³⁺, Yb³⁺, Eu³⁺ and Nd³⁺ can be directly implemented in the printed SiO₂ structures, showing strong photoluminescence at the desired wavelengths. Especially for Er³⁺, the final printed structures exhibit photoluminescence around 1.55 µm, making the proposed technology a powerful tool for optical telecommunication applications. It is also envisioned that arbitrary 3D structure of crystalline silicon can be fabricated by magnesium reduction of printed crystalline silica, making the dream of 3D printing silicon chips a reality.