Easy preparation of anodic aluminum oxide photonic crystal films with tunable structural colors

Abstract

Anodic aluminum oxide (AAO) photonic crystal films with Sn nanoparticles electrodeposited at the bottom were prepared using a pseudo-sine-pulse anodization technique followed by an alternating current electrodeposition. Moreover, a pore-widening post-treatment was performed for the Sn electrodeposited films. The phase structure, microstructure and structural color properties of the specimens with different preparation histories were examined. The Sn electrodeposition enabled production of brightly colored AAO photonic crystal films after a short-duration anodization (40 anodization cycles) in a sulfuric acid electrolyte solution at a temperature (around 20 °C) near to room temperature, which is technology-friendly relative to the conventional anodization conditions when using sulfuric acid electrolyte solutions, e.g., after 80–300 anodization cycles at around 0 °C. Moreover, the pore-widening treatment was demonstrated to be convenient and controllable in tuning the porosities and structural color properties of the Sn electrodeposited films. The peak wavelengths of the reflectance spectra were nearly linearly blue-shifted from 681 to 574 nm with increasing pore-widening time from 0 to 8 min, concomitant with a structural color change from bright-red to yellowish-green. Meanwhile, the peak reflectances were linearly enhanced from 59 to 84%, corresponding to an increase of the brightness of the films. The linearly varied peak wavelengths and peak reflectances were related to a linear increase of the porosities of the stem and branched layers in the films with pore-widening time.