An experiment that University of Chicago physicists conducted just for fun has unexpectedly led them to a new technique for producing nanoscale structures.
The Chicago physicists have built simple electronic devices using the new technique, which precisely controls the growth of metal wires along tiny scaffolds that automatically assemble themselves.
‘This is perhaps the first time that it has been possible to assemble large numbers of parallel, continuous wires that are truly nanometer scale in cross-section,’ said Heinrich Jaeger, Professor in Physics at the University of Chicago.
Conventional methods for building smaller, faster computer components involve chiselling fine structures out of a larger piece of material. Self-assembly, in contrast, builds up larger structures from smaller building blocks.
The nanowires that Jaeger’s colleague, Ward Lopes of Arryx Inc, fabricated during the course of his Ph.D. research at the University measure 30 nanometers by 10 nanometers in diameter. Lopes also fabricated ‘nanochains,’ tiny strings of metal beads of similar size that could serve as switches.
The most perfect wirelike structures are formed with silver, Jaeger said. ‘Silver is unique in that it forms the wires. Essentially all other metals like gold, copper, tin, lead and bismuth form nanochains under normal conditions.
‘We can also form nanochains with silver, but the exciting advance of Ward’s research is that he was able to combine experimental results with computer simulations to get a feeling of what it is about a particular metal that makes it behave in a wirelike fashion or the chainlike fashion.’
This productive line of research began surreptitiously.
In his experiment, Lopes attempted to see if silver would chemically react to certain copolymers (synthetic compounds) the way gold did, as would be expected. Lopes noticed that the silver exhibited strange behaviour. All other metals formed balls on the copolymers and, if he added too much metal the balls would bond to each other and ignore the template.
When he added enough silver he expected the silver to ignore the copolymer template, but the silver spheres had become long and thin. Potential applications for the technique include the production of high-density computer disks, and to make lenses for X-ray lithography, a process for transferring ultra small patterns to silicon computer chips.
The Chicago physicists used commonly available copolymers and simple methods with an eye toward easing the transfer of their results to potential applications.
‘The plastics in the copolymer we used are standard, everyday plastics,’ Lopes said. ‘One was polystyrene, which is used to make Styrofoam, and the other, polymethylmethacrylate is familiar from Plexiglas.’
‘The technology for making these structures is extremely straightforward. It’s not high technology in some sense,’ added Jaeger. ‘That’s the beauty of this.’