We describe low-index porous alumina thin films deposited from aqueous solutions containing flat-Al clusters and the nonionic block copolymer Pluronic F127. The films exhibit surface roughness as low as 0.5 nm, a characteristic useful for the fabrication of multilayer optical devices. We have investigated the chemical, optical, and structural properties of the films and their formation by Fourier transform infrared spectroscopy, temperature programmed desorption, spectroscopic ellipsometry, transmission electron microscopy, atomic force microscopy, and X-ray diffraction. By varying the Pluronic F127 concentration, film porosities can be tuned to produce refractive indexes between n = 1.26 and 1.54 (λ = 550 nm).
Perkins, C. K.; Mansergh, R. H.; Ramos, J. C.; Nanayakkara, C. E.; Park, D.-H.; Goberna-Ferrón, S.; Fullmer, L. B.; Arens, J. T.; Gutierrez-Higgins, M. T.; Jones, Y. R.; et al. Low-index, smooth Al2O3 films by aqueous solution process. Opt. Mater. Express 2017, 7 (1), 273