Method for preparing invisible anodic aluminum oxide pattern

A method for preparing invisible anodic aluminum oxide patterns comprising:

• providing an aluminum substrate;
• performing a first anodizing of the aluminum substrate to form a first anodic aluminum oxide (AAO) on a surface of the aluminum substrate, said first AAO having a first anodized surface;
• defining a pattern on the first AAO by performing photolithography, said pattern having a first portion of the first AAO covered with a photoresist and a second portion of the first AAO free of the photoresist;
• performing a second anodizing of the second portion of the first AAO free of the photoresist on the aluminum substrate to form a second AAO on the first AAO, said second AAO having a second anodized surface;
• removing the photoresist from and exposing said first portion of the first AAO, thus establishing a first operational mode having said second anodized surface of the second AAO forming an invisible pattern with said first portion of the first AAO exposed upon removal of the photoresist;
• and
• transferring said first operational mode into a second operational mode wherein the invisible pattern is rendered visible by at least one operational process selected from a group consisting of:
• (a) annealing said invisible pattern, and subsequently exposing the annealed invisible pattern, to ultraviolet (UV) light;
• or
• (b) treating said invisible pattern by pore-widening, and subsequently performing droplet addition on the pore-widened invisible pattern.