Ferroelectric Photonic Crystals from Anodic Aluminum Oxide Filled with Sodium Nitrite
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oelectric Photonic Crystals from Anodic Aluminum Oxide Filled with Sodium Nitrite V. S. Gorelika, b, * and P. P. Sverbila aP.N.
Lebedev Physical Institute, Russian Academy of Sciences, Moscow, 119991 Russia
bBauman Moscow State Technical University (National Research University), Moscow, 105005 Russia
*e-mail: [email protected] Received April 22, 2020; revised June 15, 2020; accepted June 23, 2020
Abstract—One-dimensional ferroelectric photonic crystals have been produced by filling porous anodic aluminum oxide with sodium nitrite. Introducing sodium nitrite into the pores of the photonic crystals has been shown to cause a 40-nm bathochromic shift in the spectral position of their bandgap. The results of this study demonstrate the feasibility of using aluminum oxide-based composite photonic crystals as narrow-band selective mirrors. Keywords: ferroelectric photonic crystal, bandgap, pore filling, narrow-band filter, reflection spectrum DOI: 10.1134/S0020168520110023
INTRODUCTION A characteristic property of photonic crystals (PCs) is that their energy spectrum contains so-called bandgaps [1–4] where electromagnetic radiation is strongly reflected. This opens up the possibility of producing new types of selective mirrors and light filters with controlled optical properties. Previous research dealt with the optical properties of porous opal PCs built up in the form of a face-centered cubic lattice of densely packed silica (SiO2) spheres [5–24]. In recent years, electrochemical oxidation (anodizing) of aluminum [25–31] was used to produce one-dimensional porous anodic aluminum oxide PCs. The lattice parameter of such crystals can vary from 100 to 500 nm, depending on etching conditions. The properties of such PCs, with their pores free of crystalline nanoparticles, have been the subject of extensive studies [31–41]. The objectives of this work were to study reflection spectra of porous aluminum oxide-based composite PCs having pores filled with sodium nitrite and examine the feasibility of using such PCs as narrow-band selective mirrors. Sodium nitrite is a bioactive material present in some biological objects. In addition, it is a piezoelectric and ferroelectric and is of interest for gaining insight into nonlinear optical processes. Similar properties are characteristic of noncentrosymmetric biological structures: triglycine sulfate, Rochelle salt, chiral crystalline amino acids, proteins, and others. Sodium nitrite was chosen for this study because it
is easy to incorporate into porous aluminum oxide owing to its high water solubility. EXPERIMENTAL PROCEDURE AND RESULTS In our measurements, we used PCs in the form of thin multilayer aluminum oxide films produced by electrochemical oxidation (anodizing) of aluminum [25–31, 42]. During the sample preparation process, a periodically varying current with a density from 0.4 to 1.2 A/cm2 at a voltage of 20 V was passed through an aluminum substrate immersed in an acid mixture. This led to the formation of an anodic oxide on the aluminum surface, in which pores (chan
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