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

Abstract

A robust and reliable method for fabricating porous anodic alumina (PAA)-based distributed Bragg reflectors (DBRs), operating in mid-infrared (MIR) spectral region, is presented. The method relies on application of high (UH) and low (UL) voltage pulse sequence repeated in cycles. PAA-based DBR consists of alternating high-(dH) and low-porosity (dL) layers translated directly into periodically varied refractive index. Two anodization modes were used: time- and charge density-controlled mode. The former generated dH + dL pairs with non-uniform thickness (∆d) and effective refractive index (∆neff). It is supposed, that owing to a compensation effect between the ∆d and ∆neff, the photonic stopbands (PSBs) were symmetrical and intensive (transmittance close to zero). Under the charge density-controlled mode dH + dL pairs of uniform thickness were formed. However, the remaining ∆neff provided an asymmetrical broadening of PSBs. Furthermore, it is demonstrated that the spectral position of the PSBs can be precisely tuned in the 3500–5500 nm range by changing duration of voltage pulses, the amount of charge passing under subsequent UH and UL pulses, and by pore broadening after the electrochemical synthesis. The material can be considered to be used as one-dimensional transparent photonic crystal heat mirrors for solar thermal applications.

Influence of Anodization Mode and Temperature on the Optical Properties of Photonic Crystals Based on Porous Anodic Alumina

“…It was shown previously that the photonic stopbands (PSBs) in the PCs produced under the U q mode (using trapezoidal pulse sequence) are unsymmetrically broadened and split at the blue edge as compared to symmetrical and intensive PSBs generated by the PCs formed under the U t mode. 28 The results suggested that the optical periodicity is better sustained when the decreasing layer thickness is accompanied by the decreasing porosity, and thus increasing refractive index of the respective layers grown in subsequent anodization cycles. Hence, the question arises which of the anodization modes is actually best suited for the production of the porous filters with optimal optical qualities.…”

Structural stability and optical properties of 1D photonic crystals based on porous anodic alumina after annealing at different temperatures

“…Since 2006 [21] various highlyordered PAAs with periodically modulated pore diameters along the pore axes have been produced [7,[22][23][24][25][26]. It has been demonstrated that photonic crystals can be tailored-engineered to modulate light in the UV (10-400 nm) [22,23,25], visible (400-700 nm) [22,23,25,27], near-infrared (700-2500 nm) [23,25,28,29], and mid-infrared (MIR) (2500-25 000 nm) [28,29] spectral region. Periodic modulation of refractive index in PAA originates from the alternate application of low (U low ) and high (U high ) voltage pulses.…”

“…In general, the refractive index profile of the PAA-based photonic crystal follows the shift of voltage/current density. Therefore, the effective medium of PCs can be precisely tailored by the application of a variety of pulse anodization modalities such as pseudo-sinusoidal (triangular and trapezoidal) [23,28,30], sinusoidal [25,31], or Gaussian-like [24,32] pulse shape.…”

“…The recent studies shown that the optical transparency in MIR spectral region of PAA (defined as the wavelength range where the decrease of transmittance does not exceed 25%) anodized in the oxalic acid electrolyte is restricted by the two broad transmittance dips [28,29,35]. The O-H symmetric stretching vibration coming from H 2 O molecules incorporated into the alumina during the anodization (usually between 2740 and 3125 nm) causes the presence of first dip [36][37][38].…”

Self-Ordered Porous Anodic Alumina with Large Pore Intervals: Review on Experimental and Theoretical Research

“…[1][2][3][4][5] These templates are also commercially available. However, to expand the applicability of porous alumina in the field of optics (photonic crystals), 30 plasmonic devices, 31 anti-reflection sheets, 32 diodes, 33 nanocontainers, 34 separation filters, 35 and other nanotools, highly ordered porous membranes with larger cell diameters that correspond to visible-IR light wavelengths are required. It is widely accepted that the D c is proportional to the anodization voltage.…”