The world's narrowest silicon wires with a cross section of a mere four atoms by one atom have been created by a team of developers from the University of New South Wales, the University of Melbourne and Purdue University. The wires are fully functioning, with current-carrying capacity equivalent to that of a microprocessor's copper cable, despite being 20 times thinner - and 10,000 times narrower than a human hair.
The team adopted a very different approach to circuit construction in order to develop wires at this scale. "Typically we chip or etch material away, which can be very expensive, difficult and inaccurate," said Gerhard Klimech, a professor of electrical and computer engineering at Purdue University. "But this experimental group built devices by placing atomically thin layers of phosphorus in silicon and found that with densely doped phosphorus wires just four atoms wide it acts like a wire that conducts just as well as metal."
The traditional technique of stripping back metal wires hits a limit once you get down to a width of 20 atoms, Klimech explained. The team's breakthrough came building circuits of phosphorous atoms in silicon crystal an atom at a time. It's an approach that would have been impossible without a technique known as "scanning tunneling microscopy," which allowed the team to both view and manipulate individual atoms.
As well as real-world experiments, supercomputer simulations were run to establish the current-carrying properties of atomic-scale cables. The team discovered that the resistivity of the wires is not dependent on wire width, and that Ohm's Law (which describes the relationship between current, potential difference and resistance in a conductor) still holds.
"It is extraordinary to show that such a basic law still holds even when constructing a wire from the fundamental building blocks of nature - atoms," said PhD student Bent Weber of the University of New South Wales, and lead author of the study.
The team hopes that their discovery will pave the way for practical silicon-based quantum computing using single-atom transistors, a goal to which atomic-scale wiring has previously been a barrier.