On the Precise Tuning of Optical Filtering Features in Nanoporous Anodic Alumina Distributed Bragg Reflectors

Abstract

This study presents a nanofabrication approach that enables the production of nanoporous anodic alumina distributed Bragg reflectors (NAA-DBRs) with finely engineered light filtering features across the spectral regions. The photonic stopband (PSB) of these NAA-based photonic crystal (PC) structures is precisely tuned by an apodization strategy applied during stepwise pulse anodization with the aim of engineering the effective medium of NAA-DBRs in depth. We systematically assess the effect of different fabrication parameters such as apodization function (i.e. linear positive, linear negative, logarithmic positive and logarithmic negative), amplitude difference (from 0.105 to 0.420 mA cm−2), current density offset (from 0.140 to 0.560 mA cm−2), anodization period (from 1100 to 1700 s), and pore widening time (from 0 to 6 min) on the quality and central wavelength of the PSB of NAA-DBRs. The PSB’s features these PC structures are demonstrated to be highly tunable with the fabrication parameters, where a logarithmic negative apodization is found to be the most effective function to produce NAA-DBRs with high quality PSBs across the UV-visible-NIR spectrum. Our study establishes that apodized NAA-DBRs are more sensitive to changes in their effective medium than non-apodized NAA-DBRs, making them more suitable sensing platforms to develop advanced optical sensing systems.

Anodic Alumina Photonic Crystals as Refractive Index Sensors for Controlling the Composition of Liquid Mixtures

“…Based on these data, we could calculate the refractive index sensitivity of our samples ∆λ/∆n = 142 nm/RIU. This value is greater than ones reported in [25,26] (see Table 1) and comparable with that in [28], but lower than the sensitivity demonstrated in [27] by using the graded-lattice AAO PCs (441 nm/RIU) and the one obtained in [29] by using apodized samples (390 nm/RIU). An additional chemical etching was applied to enhance the porosity and corresponding volume fraction of analyzed liquid in [27,29].…”

“…Over the past decade, much attention has been devoted to sensors based on anodic aluminum oxide (AAO) one-dimensional PCs [18]. AAO PCs with the special functionalization can be applied to detect heavy metals, biomolecules, and drugs [19][20][21][22][23][24], whereas non-functionalized AAO PCs can be used to determine the refractive index of liquids filling the pores in their structures [23][24][25][26][27][28][29]. For instance, changes in the transmittance and stop band position for AAO PCs soaked in water, ethanol, ethylene glycol, and glycerol have been reported in [26].…”

“…However, the authors in [23,[25][26][27]29] have demonstrated only the fundamental possibility of AAO PCs utilization as refractive index sensors, but have not shown the results of testing of any liquid mixtures. More detailed studies have been carried out in [24,28]: the applicability of AAO PCs refractive index sensors for the detection of the composition of ethanol-isopropanol mixtures has been demonstrated [24], and linear correlation between the stop band spectral position and glucose concentration has been established [28].…”

Rational Management of Photons for Enhanced Photocatalysis in Structurally-Colored Nanoporous Anodic Alumina Photonic Crystals

“…4 NAA-PCs have distinctive PSBs, the features of which can be readily tuned across the spectral regions by engineering the effective medium of NAA in a multi-dimensional fashion, through various anodization approaches. 45,[47][48][49][50][51][52] These NAA-PC platforms include optical microcavities 47,48 , distributed Bragg reflectors 5 (DBR) 45,49 , linear variable bandpass filters 50 , gradient-index filters 51 , and hybrid PCs 52 . These PC structures provide new opportunities to rationally utilize the "slow photon" effect to attain an efficient management of photons at the nanoscale for photocatalytic applications.…”

Light-Confining Nanoporous Anodic Alumina Microcavities by Apodized Stepwise Pulse Anodization

“…Recently, we identified sharp resonance bands within the photonic stopband (PSB) of NAA-PCs produced by stepwise pulse anodization when a logarithmic negative apodization function was applied under certain conditions. 60 Motivated by these results, we decided to explore this nanofabrication approach to develop high-quality NAA-µCVs. Figure 1.…”