(Invited) Engineering Anodic Porous Alumina-Based Photonic Structures and Prospective Applications
Authors: Acosta Laura K. , Ferre-Borrull Josep , Xifre-Perez Elisabet , Marsal Lluis F. 
Published: December 2024

Nanoporous anodic alumina (NAA) has become a popular material because of cost-competitive fabrication processes and fully scalable process compatible with conventional micro- and nanofabrication approaches. NAA is a nanostructured material that under specific conditions, their porous structure presents a self-ordering defined by a close-packed hexagonal array of well-defined cylindrical nanopores. The outstanding set of properties of NAA such as self-organized nanoporous structure, straight cylindrical nanopores of high aspect ratio, optical properties, chemical resistance and thermal stability and intrinsic photoluminescence demonstrate its versatility and potential [1]
NAA is produced by electrochemical etching of aluminum, and their geometric characteristics such as pore diameter and length and separation distance between pores can be precisely tuned by the anodization conditions (voltage and time of anodization, temperature, and electrolyte) and by post-anodization treatments (etching and annealing). The highly effective surface area (hundreds of m2/cm3) makes of NAA an interesting platform for sensing and loading and releasing of active agents. Recently, different anodization approaches have been proposed to create new structures and pore geometries such as cone-like, funnel-like, modulated, tip-like, etc. [2-4].
NAA has been used to fabricate photonic structures with the aim to control, enhance or inhibit the propagation of light. Photonic properties can be obtained by engineering the pore shape. For instance, the application of periodic variations of current or voltage during the anodization is transferred to the material as the periodic variation of the pore diameter and consequently, it is possible design, 3D structures and photonic structures with stop bands tunable within the UV-VIS-NIR range [5]. The fabrication of new photonic structures with single or multiple narrow photonic stopbands at different spectral positions, remains a challenge. These photonic structures can be obtained by using non-conventional pulse anodization for example, averaging the sum of multiple sinusoidal waves, Gaussian-like pulse or combining a gold coating layer on top of a NAA−photonic structure to create a hybrid metal−dielectric structure (Tamm plasmon resonance) [6-8]
In this work, will show recent advances in the design and fabrication of nanoporous anodic alumina and their photonic and optic applications such as optical encoding tags, optical sensing, photonics and photovoltaics. We will analyze different technological parameters and its effect on the structure and future applications.

Acknowledgements

This work was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN/FEDER) PDI2021-128342OB-I00, by the Agency for Management of University and Research Grants (AGAUR) 2021-SGR-00739 and by the Catalan Institution for Research and Advanced Studies (ICREA) under the ICREA Academia Award 2021.

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