Simply being nanoporous, however, is not enough if you want to use these materials for transmission applications. The nanotubes also need to be hollow and free of internal obstructions.

In a recent issue of Nantotechnology, researchers at the University of Melbourne, Australia, described novel ways of fabricating and characterizing such electron transparent, nanotubular arrays in alumina. The group demonstrated that the nanotube arrays are extremely well aligned to each other, which allows the membrane to act as an electron collimator or a physical sieve. Even small angular offsets (<1°) of the membrane were sufficient to block electron transmission, which is indicative of the extremely high aspect ratios that can be achieved (>300:1).

Looking ahead, the authors hope to create two-dimensional arrays of coupled nitrogen vacancy centre quantum dots in diamond by placing the nanotubular arrays in the path of low-energy ion beams. Other applications may include the templated growth of nanotube and nanowire arrays.