Tiny diamonds aid nanowire assembly

Researchers in the US have used the world’s smallest diamonds to help assemble nanowires just three atoms wide, which could have a range of useful applications.

Reported in the journal Nature Materials, the work involved scientists from Stanford University and the Department of Energy's SLAC National Accelerator Laboratory. They used tiny diamonds, known as diamondoids, to prompt the nanowires to self-assemble in a solution. According to the researchers, this is the first time nanowires with a solid core and good electronic properties have been made in this way.

"What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves," said Hao Yan, a Stanford postdoctoral researcher and lead author of the paper.

"The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It's almost as if the diamondoids know where they want to go."

Diamondoids are tiny, interlocking cages of carbon and hydrogen that are found naturally in petroleum fluids, and which are strongly attracted to each other by van der Waals forces. The researchers started with the smallest possible diamondoids - single cages that contain just 10 carbon atoms - and attached a sulphur atom to each. Floating in a solution, each sulphur atom bonded with a single copper ion, creating the basic nanowire building block. The building blocks then drifted toward each other, drawn by the van der Waals attraction between the diamondoids, and attached to the growing tip of the nanowire.

"Much like LEGO blocks, they only fit together in certain ways that are determined by their size and shape," said Stanford graduate student Fei Hua Li. "The copper and sulphur atoms of each building block wound up in the middle, forming the conductive core of the wire, and the bulkier diamondoids wound up on the outside, forming the insulating shell."

The team has already used diamondoids to make one-dimensional nanowires based on cadmium, zinc, iron and silver, including some that grew long enough to see without a microscope. The cadmium-based wires are similar to materials used in optoelectronics such as LEDs, and the zinc-based ones are like those used in solar applications and in piezoelectric energy generators, which convert motion into electricity.