Searching for the Thinnest Metallic Wire

Searching for the Thinnest Metallic Wire
by Robert Schreiber
Lausanne, Switzerland (SPX) Jun 12, 2024

Researchers from the Laboratory for Theory and Simulation of Materials at EPFL in Lausanne, part of the NCCR MARVEL, have used computational methods to identify what could be the thinnest possible metallic wire, as well as several other unidimensional materials with properties that could prove interesting for many applications.

Unidimensional (or 1-D) materials are made of atoms aligned in the form of wires or tubes. Their electrical, magnetic, and optical properties make them suitable for applications ranging from microelectronics to biosensors to catalysis. While carbon nanotubes have received significant attention, they have proved challenging to manufacture and control. Scientists are searching for other compounds to create nanowires and nanotubes with similar properties but easier handling.

Chiara Cignarella, Davide Campi, and Nicola Marzari used computer simulations to analyze known three-dimensional crystals, looking for those that could be easily "exfoliated," peeling away a stable 1-D structure. This method has been used in the past to study 2-D materials, but this is the first application to their 1-D counterparts.

The researchers started with a collection of over 780,000 crystals from various databases. They applied an algorithm to identify wire-like structures and calculate the energy required to separate the 1-D structure from the rest of the crystal.

"We were looking specifically for metallic wires, which are supposed to be difficult to find because 1-D metals, in principle, should not be sufficiently stable to allow for exfoliation," says Cignarella, who is the first author of the paper.

They identified 800 1-D materials and selected the 14 best candidates, compounds that have not been synthesized as actual wires yet but that simulations suggest as feasible. They computed their properties in detail to verify stability and electronic behavior.

Four materials - two metals and two semi-metals - stood out as the most interesting. Among them is the metallic wire CuC2, a straight-line chain composed of two carbon atoms and one copper atom, the thinnest metallic nanowire stable at 0 K found so far. "It's really interesting because you would not expect an actual wire of atoms along a single line to be stable in the metallic phase," says Cignarella. The scientists found that it could be exfoliated from three different parent crystals (NaCuC2, KCuC2, and RbCuC2). It requires little energy to be extracted and its chain can be bent while preserving its metallic properties, making it interesting for flexible electronics.

Other interesting materials found in the study, published in ACS Nano, include the semi-metal Sb2Te2, which may allow the study of an exotic state of matter predicted 50 years ago but never observed, called excitonic insulators. Then there are Ag2Se2, another semi-metal, and TaSe3, a well-known compound that has already been exfoliated in experiments as a nanowire, used as a benchmark.

For the future, Cignarella explains that the group wants to team with experimentalists to synthesize the materials and continue computational studies to see how they transport electric charges and behave at different temperatures, fundamental for real-world applications.

Research Report:Searching for the Thinnest Metallic Wire