3D Printing of Hierarchical\nStructures Made of Inorganic\nSilicon-Rich Glass Featuring Self-Forming Nanogratings

Hierarchical structures are abundant in nature, such\nas in the\nsuperhydrophobic surfaces of lotus leaves and the structural coloration\nof butterfly wings. They consist of ordered features across multiple\nsize scales, and their advantageous properties have attracted enormous\ninterest in wide-ranging fields including energy storage, nanofluidics,\nand nanophotonics. Femtosecond lasers, which are capable of inducing\nvarious material modifications, have shown promise for manufacturing\ntailored hierarchical structures. However, existing methods, such\nas multiphoton lithography and three-dimensional (3D) printing using\nnanoparticle-filled inks, typically involve polymers and suffer from\nhigh process complexity. Here, we demonstrate the 3D printing of hierarchical\nstructures in inorganic silicon-rich glass featuring self-forming\nnanogratings. This approach takes advantage of our finding that femtosecond\nlaser pulses can induce simultaneous multiphoton cross-linking and\nself-formation of nanogratings in hydrogen silsesquioxane. The 3D\nprinting process combines the 3D patterning capability of multiphoton\nlithography and the efficient generation of periodic structures by\nthe self-formation of nanogratings. We 3D-printed micro-supercapacitors\nwith large surface areas and a high areal capacitance of 1 mF/cm<sup>2</sup> at an ultrahigh scan rate of 50 V/s, thereby demonstrating\nthe utility of our 3D printing approach for device applications in\nemerging fields such as energy storage.