Researchers have compressed copper phthalocyanine crystals to pressures of more than 21 gigapascals, transforming them into long, single-atom copper chains wrapped in a carbon shell. The structure is stable and anisotropically conductive—but the road to industrial application is still a long way off.
How thin can an electrical wire be? At a fundamental level, the limit is a chain in which the atoms are arranged one after the other, the width of a single atom.
Researchers from China have now succeeded in creating single-atom chains of copper Which reach micrometers in length – more than 4,000 atoms in a row – using extreme pressure on a material much more familiar from nanoelectronics: copper phthalocyanine, a blue compound used, among other things, as a pigment.
The study, published inScience, presents a new way to produce long, stable single-atom metal chains. However, it is important to emphasize: This is not yet a tiny industrial “copper wire” that is ready to replace wiring in chips. The pressures required are enormous, and the electrical conduction in the structure stems largely from the carbon-nitrogen framework surrounding the copper atoms.
The one-dimensional boundary of a metallic material
Monoatomic chains of metal, which are called SMACs – Single-Metal-Atom Chains – are considered extreme one-dimensional structures.
They are interesting not only because they are extremely thin, but also because in such systems the electronic, magnetic, and catalytic properties can be very different from those of a regular metal block.
The problem was always production.
Solution chemical methods can create short chains, but as they get longer, they become more difficult to stabilize. The ligands – the molecules that hold the metal atoms in place – become less soluble and growth stops.
Therefore, most of the chains produced in the past were very short. According to the researchers, the previous record reached only about 28 atoms.
Start with a blue pigment
The team chose β-copper phthalocyanine, or β- for short.CuPc.
In this crystal, each molecule contains a copper atom at the center of a flat organic ring. The molecules are arranged one above the other in a structure that resembles a stack of coins.
When the crystals were compressed in a diamond anvil chamber to a pressure of more than 21 gigapascals – about 200 times atmospheric pressure – the distances between the copper atoms were greatly reduced.
At the same time, the organic rings around them polymerized, forming a rigid carbon shell.
The result: a core in which copper atoms are arranged along a single line, wrapped in a protective organic-carbon structure.
More than 4,000 atoms in a row
The chains formed reached lengths of micrometers.
That may sound tiny, but on an atomic scale, it’s a huge leap. The researchers estimate that each chain contains more than 4,000 copper atoms in a row—two to three orders of magnitude more than previous single-atom chains.
The distance between the copper atoms is maintained at around 2.57 angstroms.
The study also reports creation on a milligram scale, a significant figure relative to a field where tiny structures are sometimes produced in only a limited number.
Three-layer atomic cable
The structure is not simply "bare copper wire."
The researchers describe it as a kind of tiny coaxial cable with three layers:
In the center – a monoatomic chain of copper atoms.
Environment – a ring framework of carbon and nitrogen.
And on the outside – a more rigid carbon shell, based on an sp3 network.
It is this shell that stabilizes the structure and allows it to be isolated without the chain immediately breaking apart.
Stable in air and in acid
One of the surprises was the stability.
The chains remained stable in air and even survived for hours in a strong acidic solution while ultrasound was being applied.
The researchers were also able to separate the structures from the material using an acid-assisted exfoliation process.
For one-dimensional atomic systems, such a level of stability is particularly important, because such structures often tend to be very sensitive to the environment.
The transmission is not "plain copper"
The measurements showed anisotropic conduction: electricity moves more easily along the chain than across it.
In actual samples, the conduction along the structure was more than ten times higher than the conduction in the transverse direction.
Computational models indicate that in an ideal, flawless structure, the difference may be as much as a thousand times greater.
But here comes an important point: the copper atoms themselves do not behave like a regular metallic copper wire.
The direct bond between the copper atoms is very weak, and according to calculations, the effective conduction along the structure comes largely from the overlap between the orbitals of the carbon and nitrogen atoms in the framework surrounding the core.
That is, "a monatomic copper chain" is a structurally correct description - but it does not mean that the current flows in it like in a macroscopic copper wire.
Also magnetic properties
The researchers also found evidence of antiferromagnetic interactions between the copper atoms.
In such a situation, the magnetic moments of neighboring atoms tend to align in opposite directions.
The combination of one-dimensional structure, directional conduction, and magnetic properties also makes such systems interesting for research in spintronics – a field in which not only the electric charge but also the spin of electrons is used.
Still far from the chip
The research presents a synthetic breakthrough, but does not solve the implementation problem.
The pressure required—over 21 gigapascals—requires specialized equipment such as a diamond anvil chamber. It is not a process currently suitable for chip production lines or industrial-scale wiring.
The question of how to place, connect, and control such chains within a real device is also still open.
Therefore, it is more correct to see the study as proof that it is possible to create long, stable single-atom chains, rather than a ready-made nanoelectronic product.
Why is this still important?
In extreme one-dimensional systems, almost every atom is part of the “surface.” Defects, vibrations, and chemical bonds directly affect the electronic properties.
Long enough chains make it possible to measure behavior that cannot be seen in chains of only a few atoms.
They also provide a platform for research into quantum conduction, one-dimensional magnetism, electronic interactions, and future possibilities for nanoelectronics.
And in this case, the path to the atomic boundary began with a familiar blue material – and ended with more than 4,000 copper atoms arranged in a single row.
Questions and Answers
Is this really a wire one atom thick? The copper core is a single-atom chain, but it is wrapped in an organic framework and a carbon shell, so the overall structure is wider than a single atom.
How many copper atoms are there in the chain? More than 4,000 atoms in a chain that is micrometers long.
Does electricity flow through the copper atoms themselves? Not primarily. The calculations indicate that the significant conduction comes from the framework of carbon and nitrogen that surrounds the chain.
Can this already be used in chips? No. Production requires a pressure of more than 21 gigapascals, so this is a research stage and not an available production technology.
The scientific article
מקור
Phys.org – Extreme pressure turns blue pigment into record-long single-atom copper chains
More on the subject on the science website
- So what do they do there at the university? Chapter 8: One molecule, that's all it takes – on nanoelectronics
- A molecule in a circle
- Yissum will present nanometric ink at the "Nano Israel 2014" exhibition
- Just mix and serve – conductive nanomaterials
- The first step to developing a quantum wire
For the original publication: Opening the original publication
