Many prospective nanotech uses of carbon nanotubes depend upon separating semiconducting from metallic nanotubes—for example, semiconducting nanotubes to make transistors, and metallic nanotubes to make transparent conducting materials for solar cells and displays. An international team of scientists has shown that semiconductor nanotubes can be attracted to and aligned on surfaces chemically modified with amino groups, while surfaces with phenyl groups attract metallic nanotubes. From “Nanotubes get sorted“, as reported by Belle Dumé at nanotechweb.org (requires free registration):
When single-walled carbon nanotubes are made, a mixture of both metallic and semiconducting nanotubes is produced. This is a problem for those trying to make electronic devices from nanotubes, who need pure samples of either semiconducting or metallic tubes (depending upon the application), not both. Now, researchers in the US and South Korea have a developed a new and simple technique that not only efficiently separates the two types of nanotube but also allows them to be patterned onto a substrate as thin films. These films could be used to make electronic devices with desirable properties, and could even replace silicon as the material of choice for integrated circuits.
Single-walled nanotubes are essentially rolled up sheets of graphite just one atom thick and can be metallic or semiconducting depending on the direction in which the sheet has been rolled. They have enormous potential as the building blocks in nanoscale electronics, and are often touted as being the perfect alternatives to silicon thanks to their tiny size and their ability to carry large currents. Metallic tubes could function as transparent conducting leads, while semiconducting tubes could make good nanoscale transistors.
Although researchers have already proposed several techniques to separate nanotubes, most of these have proved difficult to perform on an industrial scale. However, help may be at hand: recent experiments have shown that specific molecules tend to interact selectively with metallic or semiconducting tubes in solution. Now, new work, by Zhenan Bao of Stanford University and colleagues, builds on this work by using such molecules to create a special surface that interacts selectively with nanotubes (Science abstract).