Feb 20, 2009
Saw-toothed sapphire helps build ordered polymer arrays
Producing ultra-dense, orderly arrays of nanoscale elements for next-generation microelectronics is no easy task, but researchers at the University of Massachusetts Amherst and the University of California Berkeley have now shown that they can do just this. The new technique involves layering a film of block copolymers onto the surface of a commercially available sapphire wafer, which rearranges the polymer atoms into a regular saw-toothed pattern. The process produces large area films of highly patterned and densely packed nanostructures that are almost defect free.
The technique could lead to dramatic improvements in the data-storage capacity of electronic media, say Tom Russell and Ting Xu.
The new work relies on the fact that molecules in the thin films of block polymers – two or more chemically dissimilar polymer chains linked together – will self-assemble into ordered patterns when spread out on a surface. The only problem is that the order seems to break down as the area increases. This lack of order means that you can no longer write to or read individual domains, which means they cannot be used for data storage.
Russell, Xu and colleagues have overcome this problem by layering the film of copolymers onto the surface of a commercially available "miscut" sapphire crystal (a crystal cut at an angle). When this crystal is heated to between 1300 and 1500 °C for 24 hours, its surface reorganizes into a highly ordered patterned of saw-toothed ridges that can then be used to guide the self-assembly of the block copolymers.
Using their technique, the researchers succeed in making almost defect-free arrays measuring more than 3 × 3 cm2 that contain nanoscopic elements with feature sizes as small as 3 nm. This translates into densities of 10 terabits per square inch, which is more than 15 times higher than that achieved to date.
Although sapphire was used in this work, Russell and Xu explain that other single-crystalline off-the-shelf materials, like silicon, can be employed to guide self-assembly too.
The technique is also better than using "top down" methods of nanopatterning, such as nano-photolithography, which is expensive, environmentally unfriendly (it uses harsh chemicals) and rapidly approaching the resolution limits of light.
The researchers, who have filed a joint patent on their technology, reported their work in Science.
About the author
Belle Dumé is contributing editor at nanotechweb.org