US team succeeds in growing new materials from nanorods

A team of researchers from Florida University’s department of chemistry has developed a technique for growing new materials from nanorods.

Such materials have the potential to be used in applications including data processing and human medicine, according to the university, but attempts to assemble nanoscale objects into sophisticated structures have largely been unsuccessful.

In a statement, the university said its study represents a major breakthrough in the field, showing how thermodynamic forces can be used to manipulate the growth of nanoparticles into superparticles with unprecedented precision. The study is published in the 19 October edition of the journal Science.

In the Florida University study, a synergism of fluorescent nanorods, sometimes used as biomarkers in biomedical research, resulted in a superparticle with an emission polarisation ratio that could make it a candidate for use in creating a new generation of polarised light-emitting diodes (LEDs).

‘The technology for making the single nanorods is well established,’ said Tie Wang, a postdoctoral researcher at Florida University and lead author of the study. ‘But what we’ve lacked is a way to assemble them in a controlled fashion to get useful structures and materials.’

The team is said to have bathed the individual rods in a series of liquid compounds that reacted with certain hydrophobic regions on the nanoparticles and pushed them into place, forming a larger, more complex particle.

Two different treatments yielded two different products.

‘One treatment gave us something completely unexpected: these superparticles with a really sophisticated structure unlike anything we’ve seen before,’ Wang said.

The other yielded a less complex structure that Wang and his colleagues were able to grow into a small square of polarised film about a quarter of the size of a postage stamp.

The researchers said that the film could be used to increase efficiency in polarised LED television and computer screens by up to 50 per cent, using currently available manufacturing techniques.

‘I’ve worked in nanoparticle assembly for a decade,’ said Dmitri Talapin, an associate professor of chemistry at Chicago University who was not involved in the study. ‘There are all sorts of issues to be overcome when assembling building blocks from nanoscale particles. I don’t think anyone has been able to get them to self-assemble into superparticles like this before.

‘They have achieved a tour-de-force in precision and control,’ he said.