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Pulse anodization of aluminum is a promising method to produce porous photonic crystals (PCs) with tunable photonic stopbands (PSBs) by a fully programmable change of electrochemical conditions. The spectral position of the PSBs is mainly determined by thickness and porosity of alternate layers forming the periodic structure. Temperature is one of the most important factors influencing the growth of porous anodic alumina (PAA). It alters the rate of PAA formation and the porosity of PAA layers. In this work, the effect of the anodizing temperature on the characteristic PSBs of graded-index PCs produced by sinusoidal pulse anodization (SPA) is analyzed. Two different anodization periods (tp) of the sinusoidal function were used whereas the amplitude and the number of cycles were kept constant. It was revealed that upon increasing the temperature from 5 to 30 °C the ion transport from electrolyte reservoir to the pore base becomes progressively hindered by increasing total PAA thickness which was manifested in the delayed current recovery to the initial values. As an effect, the periodic structures with inhomogeneous layers' thickness were formed providing broad and irregular PSBs in optical spectra. The quality of PSBs can be, however, significantly improved by post-processing pore broadening. Well-resolved and intensive peaks, which shift towards red part of the spectrum with increasing temperature and tp, could be then obtained. After a proper modification of the pulse sequence (e.g. application of the current density-controlled mode) the PCs can be used in optical sensing platforms operating from UV to NIR spectral range.
Keywords: Anodization, porous anodic alumina, anodizing temperature, gradient-index filters, optical properties© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.