Templates yield nano branches

Researchers from Rensselaer Polytechnic Institute have devised a way to make highly branched nanostructures from many different types of materials.

The researchers' prototypes include a single branch that splits into as many as 16 branches, and a branch that subdivides as many as four times. The approach works for a wide range of materials, including metals, semiconductors, carbon, polymers and insulators, according to the researchers.

The method could eventually be used to make molecular-size electronics, drug delivery systems, devices that filter molecules by size, sensors, and relatively complicated nanoscale materials, according to the researchers.

To make the structures the researchers first made a template of a series of nanopores inside aluminum oxide. To make the templates the researchers anodized aluminum foil by immersing it in acid and applying an electrical voltage so that a layer of aluminum oxide containing pores formed on the foil.

The templates can be used to make structures from any material that can coat or fill the pores, and allows for precise control of the dimensions and branching of the nanostructures. The researchers made branched carbon nanotubes and metallic nanowires.

Researchers had previously made Y-shaped nanostructures using aluminum oxide templates. The trick to making multiply-branched and hierarchically-branched structures turned out to be stepping down the voltage used to form the aluminum oxide.

The researchers' next step is to use the templates to build structures that combine different materials -- nanotubes, metal nanowires, and polymers.

The method could be used practically in two to ten years, depending on the application, according to the researchers.

The work appeared in the May 17, 2005 issue of the Proceedings of the National Academy of Sciences (Controlled fabrication of hierarchically branched nanopores, nanotubes and nanowires).