A chain of copper and carbon atoms may be the thinnest metal wire

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

One-dimensional (or 1-D) materials are one of the most exciting products of nanotechnology and are made of atoms aligned in the form of wires or tubes. Their electrical, magnetic, and optical properties make them excellent candidates for applications ranging from microelectronics to biosensors to catalysis.

While carbon nanotubes are the materials that have received most of the attention so far, they have proven to be very difficult to make and control, so scientists are eagerly looking for other compounds that could be used to create nanowires and nanotubes with equally interesting properties, but simpler. manage.

So Chiara Cignarella, Davide Campi and Nicola Marzari thought they would use computer simulations to analyze known three-dimensional crystals and look for those that – based on their structural and electronic properties – looked like they could be easily “peeled off”, essentially peeling off . have a stable 1-D structure. The same method has been used successfully in the past to study 2D materials, but this is the first application to their 1-D counterparts.

The researchers drew on a collection of more than 780,000 crystals taken from various databases found in the literature and held together by van der Waals forces, a type of weak interaction that occurs when atoms are close enough that their electrons overlap. They then used an algorithm that considered the spatial organization of their atoms, looked for those that contained wire-like structures, and calculated how much energy would be required to separate this 1-D structure from the rest of the crystal.

“We specifically looked for metal wires, which are thought to be difficult to find because 1-D metals should not, in principle, be stable enough to allow exfoliation,” says Cignarella, who is the first author of the paper.

In the end, they came up with a list of 800 1-D materials, from which they selected 14 of the best candidates—compounds that have not yet been synthesized as real wires but that simulations suggest are feasible. They then proceeded to calculate their properties in more detail to check how stable they would be and what kind of electronic behavior could be expected from them.

Four materials – two metals and two semi-metals – stood out as the most interesting. Between them is a CuC metal wire₂a straight chain composed of two carbon atoms and one copper atom, the thinnest metal nanowire stable at 0 K yet found.

“It’s really interesting because you wouldn’t expect an actual wire of atoms along a single line to be stable in the metal phase,” says Cignarella. The researchers found that it could be exfoliated from three different parent crystals, all known from experiments (NaCuC₂KCuC₂ and RbCuC₂). It requires little power to be extracted from them, and its chain can be bent while retaining its metallic properties, which would make it interesting for flexible electronics.

Other interesting materials found in the study, which is published in ACS Nanobelongs to semi-metal Sb₂You₂, whose properties may enable the study of an exotic state of matter predicted 50 years ago but never observed, called excitonic insulators, one of those rare cases where quantum phenomena become visible on a macroscopic scale. Then there are Ag₂Se₂another half metal and TaSe₃a well-known compound that is the only one that has already been exfoliated in experiments as a nanowire, and which scientists used as a benchmark.

As for the future, Cignarella explains that the group wants to work with experimenters to actually synthesize the materials, while continuing computational studies to see how they transport electrical charges and how they behave at different temperatures. Both of these will be critical to understanding how they would work in real-world applications.

Provided by the National Center of Competence in Research (NCCR) MARVEL