Fabrication of Porous Anodic Alumina (PAA) by High-Temperature Pulse-Anodization: Tuning the Optical Characteristics of PAA-Based DBR in the NIR-MIR Region

Abstract

In this work, the influence of various electrochemical parameters on the production of porous anodic alumina (PAA)-based DBRs (distributed Bragg reflector) during high-temperature-pulse-anodization was studied. It was observed that lowering the temperature from 30 to 27 °C brings about radical changes in the optical performance of the DBRs. The multilayered PAA fabricated at 27 °C did not show optical characteristics typical for DBR. The DBR performance was further tuned at 30 °C. The current recovery (iamax) after application of subsequent UH pulses started to stabilize upon decreasing high (UH) and low (UL) voltage pulses, which was reflected in a smaller difference between initial and final thickness of alternating dH and dL segments (formed under UH and UL, respectively) and a better DBR performance. Shortening UH pulse duration resulted in a progressive shift of photonic stopbands (PSBs) towards the blue part of the spectrum while keeping intensive and symmetric PSBs in the NIR-MIR range. Despite the obvious improvement of the DBR performance by modulation of electrochemical parameters, the problem regarding full control over the homogeneous formation of dH+dL pairs remains. Solving this problem will certainly lead to the production of affordable and efficient PAA-based photonic crystals with tunable photonic properties in the NIR-MIR region.

Charge Density-Versus Time-Controlled Pulse Anodization in the Production of PAA-Based DBRs for MIR Spectral Region

“…It was demonstrated before that the time-controlled mode leads to a continuous reduction of the total amount of charge taking part in the anodization reaction that occurs under each UH and UL pulse [25,29]. As an effect, the dH and dL layers formed under the UH and UL pulses, respectively, become thinner with the anodization cycles.…”

“…In the transmittance spectrum of the sample PAA_2989-5017 the λ1 peak is presumably shifted above 6000 nm and thus is not visible, whereas the peak at around 3500 nm is the second order the PSB (λ2). It was demonstrated before that the time-controlled mode leads to a continuous reduction of the total amount of charge taking part in the anodization reaction that occurs under each U H and U L pulse [25,29]. As an effect, the d H and d L layers formed under the U H and U L pulses, respectively, become thinner with the anodization cycles.…”

“…In our previous works [25,29], free-standing DBR structures were prepared by immersion entire samples in the CuCl 2 /HCl solution to remove remaining Al foil after the electrochemical process. This method most possibly resulted in upper layers' delamination and exfoliation.…”

“…In Figure 3, the transmittance (T) spectra of the PAA_600-60 sample are shown for different tp. The vertical, red, dotted line in all transmittance spectra denotes the OH group vibrations coming from adsorbed water [25,29]. As can be seen, the λ1 shifts towards blue part of the spectrum as the immersion time of the PAA_600-60 in- The PAA-based photonic structures were studied by a field-emission scanning electron microscope FE-SEM (AMETEK, Inc., Mahwah, NJ, USA).…”

“…Recently, we have analyzed the photonic properties of PAA based DBRs synthesized under relatively high anodizing temperature (30 • C) [25]. Selected DBRs demonstrated distinct peak in 3500-6000 nm spectral range which was ascribed to the first order PSB (λ 1 ).…”