Researchers are reporting development of the world’s thinnest electrical wires, made of chalcogenide and diamondoids (the smallest possible bits of diamond). The study appears in the journal Nature Materials.
Fuzzy white clusters of nanowires on a lab bench, with a penny for scale. Assembled with the help of diamondoids, the nanowires can be seen with the naked eye because the strong mutual attraction between their diamondoid shells makes them clump together, in this case by the millions. At top right, an image made with a scanning electron microscope shows nanowire clusters magnified 10,000 times. Image credit: SLAC National Accelerator Laboratory / Hao Yan / SIMES.
The needle-like nanowires have a semiconducting core — a combination of copper and sulfur known as a chalcogenide — surrounded by the attached diamondoids, which form an insulating shell.
“Their minuscule size is important because a material that exists in just one or two dimensions – as atomic-scale dots, wires or sheets – can have very different, extraordinary properties compared to the same material made in bulk,” said co-author Dr. Nicholas Melosh, from Stanford University.
“What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves,” added co-author Dr. Hao Yan, also from Stanford.
“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.”
The diamondoids the team used as assembly tools are tiny, interlocking cages of carbon and hydrogen. Found naturally in petroleum fluids, they are extracted and separated by size and geometry in a lab.
For the study, the scientists took advantage of the fact that diamondoids are strongly attracted to each other, through what are known as van der Waals forces.
They started with the smallest possible diamondoids – single cages that contain just 10 carbon atoms – and attached a sulfur atom to each. Floating in a solution, each sulfur atom bonded with a single copper ion. This created 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 co-author Fei Hua Li, a graduate student at Stanford.
“The copper and sulfur 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 researchers have 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, and they have experimented with carrying out the reactions in different solvents and with other types of rigid, cage-like molecules, such as carboranes.
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.
“You can imagine weaving those into fabrics to generate energy,” Dr. Melosh said.
“This method gives us a versatile toolkit where we can tinker with a number of ingredients and experimental conditions to create new materials with finely tuned electronic properties and interesting physics.”