Researchers build nano 'trees'

Swedish researchers have managed to grow leaves on nano trees. These branching networks of nanoscale wires have huge potential in solar cells, low energy lighting and sensors, the researchers say. It might even be possible to make the trees mimick photosynthesis.

This announcement follows a similar breakthrough in the US: Charles Lieber and his colleagues at Harvard speculate the technology could lead to "three-dimensionally interconnected computing structures analogous to the brain".

Both teams of researchers found a way to make grow branches from nanoscale semiconductor wires. Lieber et al repeated the process twice, creating tree-like structures. The Swedish team, led by Professor Lars Samuelson, have managed a third iteration, and have grown tertiary branches which, in keeping with the tree analogy, they call 'leaves'. "This opens the possibility of producing ever more complex structures on the nano scale," Samuelson said.

Building a tree is an iterative process. To begin, the researchers use chemical deposition of a vapour of a semiconducting material - silicon, indium arsenide or gallium hosphide, for instance - on catalytic gold seeds. The semiconductor crystals form directly on the gold seeds. The more time the deposition phase gets, the longer the wires will be. To get the branches, just spray the wires with gold dust, and repeat the process.

Professor Samuelson suggests a new line of research could be growing branches out of different materials that the trunks. It may be possible that the properties of the trees could be tailored so that they could convert sunlight to electricity. Theresearchers also suggest the trees could be used to make efficient lighting systems.

More basic research must be done: certainly the manufacturing process will need to get cheaper if these applications are to have a commercial future. However, the team is confident they can make it happen and have formed a spin off company - QuMat Technologies AB - to investigate the possibilities. ®

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