| Oct 30, 2025 |
New method creates ultra-thin carbon nanowires packed with atomic chains
Scientists developed the smallest, densest carbon nanowires ever made, opening the door to explore the remarkable strength and conductivity of long carbon chains.
(Nanowerk News) Carbon comes in many forms—diamond, graphite, graphene, and even long atomic chains known as carbynes. These long linear carbon chains, or LLCCs, are predicted to be stronger and conduct heat better than any other known material. But there’s been a catch: they fall apart easily.
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To study them, scientists have learned to protect these fragile chains by sealing them inside carbon nanotubes, forming what are known as carbon nanowires. Until now, most attempts produced nanowires that were slightly too wide to hold the most stable and dense LLCCs.
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A research team has now solved that problem with a new way to make small-diameter single-walled carbon nanowires packed with a record number of LLCCs (Chemical Physics Letters, "Highly efficient synthesis of small-diameter single-walled carbon nanowires through transformation of polyyne molecules into long linear carbon chains inside single-walled carbon nanotubes").
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“Recently, it has been shown that by encapsulating polyyne in single-walled carbon nanotubes, it is possible to achieve small-diameter carbon nanowires,” said the study’s lead researcher. “Building on this, we have synthesized single-walled carbon nanowires with even smaller diameters, while also achieving significantly higher LLCC concentrations.”
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| Single-walled carbon nanowires (SWCNWs) are synthesized by inserting polyynes (C2nH2) as a carbon source into SWCNTs, followed by annealing under high vacuum. This proposed approach successfully yields small diameter single-walled carbon nanowires, with a high density of LLCCs. This will allow researchers to probe the properties of LLCCs experimentally, paving the way for new advancements. (Image: Takahiro Maruyama)
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To make these ultra-thin nanowires, the team mixed open-ended single-walled carbon nanotubes with a solution of n-hexane containing purified polyyne molecules. After heating the mixture at 80°C under pressure for 24 hours, the polyyne molecules slipped inside the nanotubes. The filled nanotubes were then heated to 700°C in a vacuum, converting the polyynes into long carbon chains.
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Using Raman spectroscopy, the researchers confirmed both the successful encapsulation of the molecules and their transformation into nanowires. They found that the denser the starting polyyne solution, the higher the final concentration of LLCCs—allowing them to reach record densities.
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The resulting nanowires had diameters between 0.73 and 0.77 nanometers, smaller than those ever reported before. The tiny size came from the narrow shape of the polyyne molecules used as the carbon source. “In our experiments, polyyne molecules with a slender linear shape were used as the carbon source, exhibiting a diameter nearly the same as the van der Waals diameter of carbon atoms,” said the lead researcher. “In contrast, previous studies used relatively larger precursor molecules, resulting in nanowires with diameters larger than 0.9 nanometers.”
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The Raman data also showed a record L-band to G-band ratio of 3.6, confirming the high density of LLCCs inside these narrow nanotubes.
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“Our method for synthesizing high-density small-diameter carbon nanowires will help researchers probe the exact properties of long linear carbon chains,” the researcher said. “This can lead to breakthroughs in many fields ranging from nanotechnology to sensors and energy storage.”
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This achievement marks an important advance toward understanding and harnessing one of carbon’s most extraordinary forms.
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