A new route for the formation of self-organized anodic porous alumina in neutral electrolytes

The present work reports the formation of regular porous aluminum oxide layers in neutral fluoride containing (NH4)2SO4 electrolytes. For a fluoride free (NH4)2SO4 electrolyte only irregular and thin porous alumina layers can be grown under these conditions. Upon addition of small amounts of fluorides highly regular, smooth high aspect ratio pore arrays can be produced. Pores with a typical diameter of approximately 50 nm and a length of several micrometers are formed. This finding significantly widens the spectrum of synthesis routes for ordered porous alumina structures and templates.