| Sep 17, 2025 |
Heat localization in carbon nanotube arrays explained by reduced dimensionality
Research reveals how reducing dimensionality can trap heat, opening the door to high-efficiency energy devices.
(Nanowerk News) Thermal energy conversion technologies, such as thermionic and thermoelectric devices, require materials that can sustain steep temperature gradients without compromising electrical conductivity. One surprising candidate is the carbon nanotube (CNT) forest — many individual nanotubes grown upright on a surface, resembling a dense collection of trees in a forest, though at the nanoscale. Each tube is just nanometers wide and micrometers to millimeters long.
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Imagine shining a tiny light — with just tens of milliwatts of power — onto such a CNT forest. Almost instantly, the spot heats up to thousands of degrees, with temperature changes of hundreds of degrees across distances smaller than the width of a human hair.
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Researchers at the University of British Columbia have now uncovered the mechanism behind this effect (Physical Review B, "Heat localization through reduced dimensionality"). The team has shown that arrays of one-dimensional structures, such as CNT forests, can confine heat very effectively — even when those materials are typically good thermal conductors — a finding with important implications for thermionic and thermoelectric energy conversion.
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Their research shows that when a CNT forest is illuminated with power levels of just tens of milliwatts, it can reach temperatures exceeding 2000 K and gradients of hundreds of kelvins per micrometer. As the authors note in their paper, “extremely high temperatures of thousands of kelvins and gradients of hundreds of K/µm may thus be obtained in a conductor using a modest local power source such as a laser pointer.”
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This occurs due to a combination of strong anisotropic thermal conductivity and a positive feedback loop where increasing temperature leads to decreasing thermal conductivity, further intensifying local heating. Such extreme local heating can reach the threshold for processes like thermionic emission, highlighting the potential of CNT forests not only in energy conversion applications, but also in areas like vacuum electronics, electron emission devices, and nanoscale thermal engineering.
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The study identifies reduced dimensionality as the key factor: in one-dimensional systems, heat cannot easily dissipate in transverse directions, allowing energy to build up rapidly. Unlike traditional approaches that rely on materials with inherently low thermal conductivity, this mechanism enables thermal confinement through the macroscopic assembly of one-dimensional structures — even when those materials are normally good thermal and electrical conductors. This unique combination is crucial, since it allows precise control of heat without sacrificing electrical performance. As a result, the findings have important implications for energy conversion technologies such as thermionic and thermoelectric devices, as well as for nanoscale heating, optoelectronics, and photonic emitters.
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Importantly, the phenomenon is not exclusive to CNTs. Similar behaviors are expected in arrays of other low-dimensional materials, such as silicon nanowires and black phosphorus, indicating that heat confinement may be a general feature of reduced-dimensional systems.
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These insights may be utilized in future designs and applications of thermionic and thermoelectric devices, as well as other technologies where thermal confinement is important without sacrificing electrical conductivity.
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The research was conducted by Mike Chang, Harrison D. E. Fan, Mokter M. Chowdhury, George A. Sawatzky, and Alireza Nojeh from the University of British Columbia’s Departments of Electrical and Computer Engineering, Physics and Astronomy, Chemistry, and the Quantum Matter Institute.
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