Growth and Morphological Evolution of Porous Anodic Alumina via Two-Step Anodization in 0.3 M Oxalic Acid

Abstract

Porous anodic alumina (PAA) films were fabricated via a two-step anodization process in 0.3 M oxalic acid at 40 V. This study systematically investigates the effect of anodization duration on the morphology, pore diameter, surface roughness, and crystallographic texture of PAA using atomic force microscopy (AFM) and the Harris equation. Results demonstrate that increasing anodization time from 30 min to 4 h facilitates the formation of highly ordered hexagonal pore arrays. Specifically, the mean pore diameter increased from 45 ± 6 nm to 72 ± 4 nm, while surface roughness (Ra) decreased from 8.3 nm to 4.1 nm. Furthermore, the texture coefficient TC(111) increased from 2.1 to 9.0, indicating a strong preferred orientation. The sample anodized for 4 h exhibited optimal self-ordered morphology with straight pore channels and minimal structural defects. These findings confirm that anodization time is a critical parameter for achieving steady-state growth, providing quantitative guidelines for the fabrication of high-quality templates for nanophotonic and sensing applications