Fabrication Of Metal Nanowires Using AAO Template

The porous anodic alumina template has attracted due attention because of its special characters including uniform highly oriented pores and these pores parallel to each other. This template fabricated by anodizing the aluminum in oxalic acid, sulfuric acid or phosphate acid has different pore diameter which range from 10nm to 200nm and different pore length which range from 20nm to 5μm. The diameter and length of pores depend on the anodization conditions, generally, the higher the anodized voltage is, the larger the pore diameter of porous alumina is; the longer the time is, the thicker the membrane is. A layer named barrier layer can be created at the interface of oxide layer and metal during the process of oxidation, its thickness remains constant at a given voltage and proportional to the voltage. This layer will resist the cathodic current during the course of electrodeposition because of its insulation. To make it easier for the cathodic current pass through this layer, we need to increase the cathodic current or dissolve both the aluminum and this layer by the method of chemical erosion, but these two ways are not efficient. The over high cathodic current causes some hydrogen evolution, which may inhibit the process of deposition. Using appropriate chemical solution to move the aluminum substrate and the barrier layer may influence the pore structure of the anodic alumina template. Therefore, it is necessary to thin the barrier layer without destroying the metalsubstrate by applying current limited anodized steps. The current limited anodized method can produce a comparative thin barrier layer which owns a lower thickness about 10nm. This thin layer can be broken by thermal shock during electrodeposition easily. Using this method, the metal and metallic alloy can be deposited into pores of porous alumina membrane successfully.