Did you know that hexagonal pore ordering in anodic aluminum oxide was discovered by Rummel already in 1936? Or that under similar anodization conditions, titanium gives rise to nanotubular titanium oxide?
A recent mini-review on the subject delineates mechanisms, chemical and physical, by which these nanotubes are created. The authors claim that over 3000 papers have been published on the subject in the last decade. Their own citation list (79 references) includes both overviews and reviews.