Porous Layers Composed of Oxide Crystallites Formed by the Combination of Laser Ablation and Anodization of Metal

Self-limiting and self-organizing high voltage anodization is well known for making oxide nanostructures such as porous alumina and TiO₂ nanotubes. The formation mechanisms of both of these materials involve an intricate balance between oxide growth and dissolution in which pore initiation and propagation is convoluted with the need for strain relief because of the expansion inherent to oxide formation. Laser ablation with a nanosecond pulsed Nd:YAG laser operating at 532 nm produces texture in the form of arrays of pillars, macropores and ripples. Nanoparticles produced in the ablation plume can also be deposited on the target or a remote substrate. These substrates are anodized in solutions typically used for porous film and nanotube production (including viscous fluoride containing electrolytes). Results for a number of metals including Al, Sn, Ti and Zn will be discussed. Laser pre-texturing results in the formation of structures unattainable by conventional anodization. Deposited nanoparticles, of e.g. Al, are found to act as seeds for the growth of oxide crystallites that fuse into porous films composed of these crystallites, as shown in the image below.