Porous anodic aluminum oxide (AAO) is a unique platform for many high-tech nanotechnology, nanophotonics, and membrane science applications. Although scanning electron microscopy is the technique most widely used to measure the pore diameters of an AAO structure, this method accesses only a limited area of the structure and provides data with limited statistics. The AAO characteristics, averaged over the entire thickness of a porous film, can be measured by optical spectroscopy. In our paper [1], we demonstrate that the angular dependence of the transmittance of AAO porous films has several features caused by birefringence, which is used to measure the porosity of AAO. This method of measuring porosity is accurate, precise, cheap, and does not require specific sample preparation procedures. The suggested approach can be applied to measure the porosity of other optically transparent materials, containing aligned cylindrical channels, such as anodic titanium oxide, porous silicon oxide, track-etched membranes, and porous films based on diblock copolymers.
This work was supported by Russian Science Foundation (grant № 18-73-10151) and Russian Foundation for Basic Research (grant № 20-33-90084).
A.A. Noyan, K.S. Napolskii, Birefringence in anodic aluminum oxide: an optical method for measuring porosity // Materials Advances, 2022, v. 3, pp. 3642–3648. DOI: 10.1039/D2MA00111J.