Researchers from Stanford University and Department of Energy’s SLAC National Accelerator Laboratory have discovered away to coax diamondoids – the smallest possible bits of diamond, naturally occurring in petroleum fluids – to assemble atoms into electrical wires just three atoms wide.
“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 on 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.”
While techniques for making materials to self-assemble have been around for a while now, this is the first time it has led to a functional nanowire with a solid, crystalline core that has good electronic properties.
The semi-conducting core is a combination of copper and sulfur, known as chalcogenide, that’s surrounded by an insulating shell made of tiny fragments of diamond. Thanks to their minuscule size, the wires posses extraordinary properties far beyond those of materials made in bulk.
To trigger self-assemblage, the researchers attached a sulfur atom to a number tiny diamondoids – each made of only 10 carbon atoms – and submerged them in a solution, where each sulfur atom bonded together with a single copper ion, forming the basic nanowire building block.
Then, the microscopic structures started to drift towards each other via the Van der Waals forces – the residual attractive or repulsive forces between molecules or atomic groups that arise not from covalent or ionic bonds, but through quantum interactions with zero-point field.
“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, who played a critical role in synthesizing the tiny wires and figuring out how they grew. “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 team has already used diamondoids to make one-dimensional nanowires based on cadmium, zinc, iron and silver, including some that grew long enough to be seen without a microscope, and experimented with carrying out the reaction in different solvents and with other types of rigid, cage-like molecules, such as carboranes.
According to study-co-author Nicholas Melosh, this method gives researchers a versatile toolkit for tinkering with a number of ingredients and experimental conditions to develop new materials with precise electronic properties and interesting physics.