Nanoscale Surfaces : Anodic Aluminum Oxide (AAO)

Anodic alumina is a self-organized nanostructured material containing a high density of uniform cylindrical pores that are aligned perpendicular to the surface of the materials and penetrate its entire thickness (see figure). A regular porous structure is formed when aluminum is electrochemically oxidized (anodized) in certain solutions. A thin dense alumina barrier layer separates the pores from the aluminum. The pore diameter is tunable from 5 nm to several hundred nm, with the corresponding pore density in the range from 1012 to 109 cm-2. Dimensions of this porous structure are defined by the synthetic conditions, providing a convenient way to precision engineer the nanoscale morphology. On the low end, the pore diameter approaches the mean free path of selected metal and semiconductors, suggesting that quantum confinement effects might be realized. 

The structure of this material has been known since late 1960-s. Following pioneering work in 1970 and 1980's by Moskovits in Canada and Masuda in Japan, in the last 15 years this material has gained a wide popularity as a template for "bottom-up" nanofabrication.

Anodic alumina is optically transparent, electrically insulating, thermally and mechanically robust and chemically inert. AAO processing is compatible with microfabrication and scaleable to high volume production. Synkera's well-establishe

meters and pore length from 0.1 up to 300 microns, covering the size domain of interest to nanotechnology. Different architectures of AAO are developed and used in our product development efforts, including AAO attached to Al foil, free-standing AAO wafers and AAO nanotemplates integrated onto various non-Al substrates, such as Si wafers and glass to name a few.

Various materials synthesis approaches - electrodeposition, polymerization, sol-gel, chemical vapor deposition and others - can be used for templated nanofabrication of high-density arrays of prepackaged nanostructures inside the pores of the AAO. Intrinsic anisotropic morphology and chemistry of anodic alumina enables unique opportunities for micromachining this nanostructured ceramic, providing extensive opportunities for development of nano- and microdevices.

Web Site: http://www.synkera.com/Technology/aao.html

ANGGIE M. NAVAS G. CRF