Abstract
In this work, the influence of a wide range anodizing temperature (5–30 °C) on the growth and optical properties of PAA-based distributed Bragg reflector (DBR) was studied. It was demonstrated that above 10 °C both structural and photonic properties of the DBRs strongly deteriorates: the photonic stop bands (PSBs) decay, broaden, and split, which is accompanied by the red shift of the PSBs. However, at 30 °C, new bands in transmission spectra appear including one strong and symmetric peak in the mid-infrared (MIR) spectral region. The PSB in the MIR region is further improved by a small modification of the pulse sequence which smoothen and sharpen the interfaces between consecutive low and high refractive index layers. This is a first report on PAA-based DBR with a good quality PSB in MIR. Moreover, it was shown that in designing good quality DBRs a steady current recovery after subsequent application of high potential (UH) pulses is more important than large contrast between low and high potential pulses (UH-UL contrast). Smaller UH-UL contrast helps to better control the current evolution during pulse anodization. Furthermore, the lower PSB intensity owing to the smaller UH-UL contrast can be partially compensated by the higher anodizing temperature.
Highlights
Porous anodic alumina (PAA) is a multifunctional porous ceramic coating prepared by anodization of aluminum
PAA with long-range hexagonally ordered and parallel pores is usually formed under self-ordering regimes, which are defined by narrow process windows characteristic for a given electrolyte [3,4]
The PAA-based distributed Bragg reflector (DBR) is formed by applying a series of potential pulses, comprising high potential pulse (UH = 50 V and tH = 360 s) followed by a low Materials 2020, 13, x FOR PEER REVIEW
Summary
Porous anodic alumina (PAA) is a multifunctional porous ceramic coating prepared by anodization of aluminum Its geometrical parameters, such as interpore distance (Dc ) and pore diameter (Dp ), can be controlled by electrochemical conditions including type and concentration of electrolyte, temperature, applied voltage, and anodization time [1,2]. PAA with long-range hexagonally ordered and parallel pores is usually formed under self-ordering regimes, which are defined by narrow process windows characteristic for a given electrolyte [3,4]. Out of these regimes, the pore arrangement strongly deteriorates. The applied voltage determines mostly the Dc [8,9], while temperature—both
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