Tiny metal pine trees with a twist

SEM micrographs of PbS pine tree nanowires, illustrating branch epitaxy on the tree trunk. [Image courtesy of AAAS/Science]

Some things-like iPods and laptop computers-just keep getting smaller and smaller. And scientists are trying to shrink these kinds of gadgets even further, using parts that can be as tiny as the width of a human hair. But as researchers are finding out, it can be tricky to create building blocks that stack into neat patterns at this small size.

Now, Matthew Bierman and his fellow researchers have built an extremely tiny wire with a beautiful pattern in their chemistry lab at the University of Wisconsin. The wire looks a lot like a pine tree, with a trunk and branches that swirl around the trunk like a spiral staircase. The scientists were able to grow a whole forest of these metal trees, which stand hundreds of micrometers tall. Well, maybe not so tall-a human hair is about 100 micrometers wide, so maybe as tall as a few hairs stacked on top of each other!

The scientists think they know why the trees seem to grow into this shape all on their own, without the help of any other chemicals. There is a tiny break in the middle of each tree trunk, where the trunk is twisted like a screw. Bierman and colleagues think the twist encourages any growing branches to wrap around the trunk in the unusual pattern.

This study appears in the 1 May issue of the journal Science.

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