Postgrowth processing of carbon nanotube arrays-enabling new functionalities and applications

Highly ordered carbon nanotube arrays were fabricated by pyrolysis of acetylene using anodic-aluminum-oxide templates. To avoid the natural tendency of the nanotubes sticking together and forming haystack-like bundles when exposing the nanotubes from the growth template, a new postgrowth treatment process using a mixture of 6 wt% phosphoric acid and 1.8 wt% chronium oxide as the etchant, and 0.1 wt% Gum Arabic or 5 wt% polymethacrylic acid as the dispersant, was developed yielding for the first time well aligned and spatially free-standing carbon nanotube arrays. The dispersants can be adsorbed on both the surface of carbon nanotubes and that of the alumina film resulting in the elimination of aggregation of exposed carbon nanotubes, a more uniform dissolution of alumina, and a lower, thereby, more controllable etching rate. The as-prepared carbon nanotube arrays, which are vertically aligned and well separated could be used for many applications such as mechanical oscillators, field emission, and sensors, and the exposed nanotubes offer a good platform for study on collective behavior of electrical and magnetic nano arrays.