Crack-free 3D hybrid microstructures from photosensitive organosilicates as versatile photonic templates

We fabricated diamond-like microstructures from epoxy-functionalized cyclohexyl polyhedral oligomeric silsesquioxanes (POSS) through four-beam interference lithography. The 3D structure was maintained when calcined at a temperature up to 1100 degrees C, and crack-free samples over a large area ( approximately 5 mm in diameter) were obtained when the POSS films were heated at 500 degrees C under an Ar environment or treated with a low intensity oxygen plasma. In the latter, the volume fraction of the 3D porous structures could be fine-tuned by plasma etching time and power. Both Fourier transform infrared (FT-IR) spectroscopy and energy-dispersive X-ray (EDX) spectroscopy analysis suggested that the presence of carbon materials in the films enhanced the crack resistance of 3D POSS structures treated under Ar or oxygen plasma. Since POSS and its derivatives could be easily removed by HF solution at room temperature, we demonstrated high fidelity replication of the 3D porous structures to biocompatible poly(glycidyl methacrylate) (PGMA) and elastomeric poly(dimethylsiloxane) (PDMS). Importantly, the whole fabrication process (template fabrication, infiltration, and removal) was carried out at room temperature. Finally, we illustrated the application of 3D PDMS film as a reversible and repeatable color-changing, flexible photonic crystal.