This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: As the electronics in our technology keep shrinking, traditional silicon-based chips are approaching their fundamental physical limits. Yet the wires connecting them might be able to shrink beyond conventional dimensions, as scientists have created one of the longest single-atom copper chains to date that could serve as molecular wires.
The researchers began with copper phthalocyanine (CuPc), a compound used to make the commonly used blue pigment phthalo blue. Under high pressure—more than 21 gigapascals, roughly 200,000 times normal atmospheric pressure—they converted the CuPc crystals into copper atomic chains stretching for micrometers, each encased in a carbon sheath. The resulting sheathed single-metal-atom chains (sSMACs) resembled a household power cord on an atomic scale, with three distinct layers.
The wires exhibited strong anisotropy, meaning electricity flows easily along the wire but has a hard time traveling sideways across it. With more than 4,000 copper atoms strung into a single chain, the structure was two to three orders of magnitude longer than any single-atom chain made before. The previous record stood at just 28 atoms.
The 1D SMACs, considered the thinnest possible metal wires, are gaining attention because of their unusual electronic, magnetic and catalytic properties. Beyond their applications, these structures also give scientists a way to study how matter behaves at the smallest scales. Scientists have successfully created single-atom chains before, but the method has been highly impractical for making longer ones.
SMACs are traditionally grown in liquid solutions containing ligands—chemical wrappers that support the metal atoms. The trouble begins when the chains get longer and the wrappers needed to stabilize them become insoluble in the liquid. This brings the synthesis to a halt, resulting in atomic wires that are fewer than 10 atoms long, a problem encountered in almost all previously made SMACs.
The researchers overcame these limitations by eliminating the liquids entirely and using a high-pressure solid-state reaction. They started with copper phthalocyanine, whose flat, ring-like molecules, each containing a single copper atom, naturally stacked one above another like a column of coins. They placed the pigment crystals inside a tiny, high-pressure device called a diamond anvil cell, which triggered the transformation inside the solid material.
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