Credit: © 2008 AAAS

Single-walled carbon nanotubes are considered potential building blocks for future nanoscale electronics. For example, nanotubes that are semiconducting can be electrically switched on and off as field-effect transistors. Methods for growing carbon nanotubes, however, produce collections of metallic and semiconducting materials. Hence, precise control over the separation of the nanotubes is critical. Furthermore, for such devices to be practical, the nanotubes must also be arranged into dense, aligned structures.

There are techniques that can carry out these steps separately or on a small scale, but not in ways that could be easily scaled-up. Now, Zhenan Bao and colleagues1 at Stanford University and Samsung Advanced Institute of Technology have developed a straightforward route to fabricating single-walled carbon nanotube field-effect transistors in which the alignment and type of nanotube is controlled simply through surface chemistry. The transistors are fabricated by spin-coating solutions of nanotubes onto silica surfaces that are functionalized with silanes. By altering the nature of the end group on the silane, Bao and co-workers can dictate whether metallic or semiconducting nanotubes bind to the surface.

By using a surface that selectively adsorbs semiconducting nanotubes, which are aligned and densely packed, they can create devices that exhibit promising transistor behaviour, with on/off ratios as high as 900,000.