Inorganic microstructured materials are ubiquitous in nature. However, their formation in artificial self-assembly systems is challenging as it involves a complex interplay of competing forces during and after assembly. For example, colloidal assembly requires fine-tuning of factors such as the size and surface charge of the particles and electrolyte strength of the solvent to enable successful self-assembly and minimize crack formation. Co-assembly of templating colloidal particles together with a sol–gel matrix precursor material helps to release stresses that accumulate during drying and solidification, as previously shown for the formation of high-quality inverse opal (IO) films out of amorphous silica. Expanding this methodology to crystalline materials would result in microscale architectures with enhanced photonic, electronic, and catalytic properties. This work describes tailoring the crystallinity of metal oxide precursors that enable the formation of highly ordered, large-area (mm2) crack-free titania, zirconia, and alumina IO films. The same bioinspired approach can be applied to other crystalline materials as well as structures beyond IOs.
K.R.P. and T.S. contributed equally to this work. The authors acknowledge Dr. Alison Grinthal and Dr. Michael Aizenberg for thoughtful discussions and assistance with the manuscript. K.R.P. acknowledges support from a graduate fellowship from the Department of Defense. T.S. acknowledges support from the Weizmann Institute of Science-National Postdoctoral Award Program for Advancing Women in Science. The materials design aspects of this work are supported by the National Science Foundation (NSF) Designing Materials to Revolutionize and Engineer our Future program under Award No. DMR 1533985. Electron microscopy and other characterizations were performed in part at the Harvard University Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Coordinated Infrastructure Network (NNCI), which is supported by the National Science Foundation under NSF ECCS Award No. 1541959.