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How the shrinking method works
Yong Cheng, Pei Li, Qiaobao Zhang and corresponding author Ming-Sheng Wang, at Xiamen University, reported a top-down way to reduce the diameter of existing few-walled carbon nanotubes (CNTs). Rather than growing a tube at a target diameter, the researchers exposed it to an electron beam while heating it, removing carbon as the tube contracted.
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The team synthesized tubes by arc discharge, then placed them on a thin silicon nitride film mounted on a MEMS-based heating chip. They studied the tubes in an FEI Talos F200s TEM using an FEI-NanoEx heating holder. The electron beam was 200 kV; the holder provided temperature control up to 1200 °C. The samples were mostly double-walled CNTs, with a small number of one-, three- and four-walled tubes. The 2019 study in Nanoscale describes the experimental setup and results.
What the researchers observed
A measured reduction in one double-walled tube
In a representative experiment, a tube with an initial outer diameter of 4.32 nm was irradiated at 1200 °C with a beam dose of 20 A cm−2. After 10 minutes, its outer diameter was 2.36 nm—about 45% smaller. A separate imaged example reached an outer diameter of approximately 1.04 nm. These are outcomes from the reported experiments, not guaranteed results for other tubes or settings.
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Contraction along the tube
The authors observed regular kinks moving along the tube as it narrowed. In representative lattice images, they reported no visible disorder from irradiation and described the contraction as seamless and uniform. Their explanation is that moving atomic-scale kinks help remove carbon in an organized way.
More specifically, the authors propose that the kinks are associated with climb motion of 5|7 dislocation cores, rather than dislocation glide. This is the mechanism they offer to explain their observations; it should not be treated as a universal, independently established account of how CNTs shrink.
How far a nanotube can shrink
The shrinking rate depended strongly on beam dose and annealing temperature, which the authors say makes it possible to control the final diameter. For tubes with n shells, where n ≥ 2, the paper gives an approximate lower-diameter relation:
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The researchers report shrinking ultrathin one- to four-walled tubes toward their respective diameter limits. In a double-walled tube, the inner shell reached about 3.2 Å in diameter; below that, the tubes broke apart. Chemistry World’s 2019 coverage also summarizes this reported stability limit.
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- 【Visual Design】: This 3D carbon nanotube model forms a rounded cylindrical shape with an open lattice structure, offering views of internal connecting from multiple angles for demonstrations and study.
- 【Application Purpose】: Developed as a manual on teaching model, it supports classroom instruction, research facility reference, demonstrations, and individual study by making abstract nanoscale science tangible and viewable.
- 【Product Identity】: This carbon nanotube high density structure model is a three dimensional teaching tool built from glossy black spherical particle representations connected by white cylindrical linking rods, designed and materials science learning.
- 【Construction Style】: Built as a ball and model, it uses distinct black spheres for particles and white rods for relationships, creating a clear, easy to distinguish representation of the nanotube's interconnected framework.
- 【Educational Function】: As a dedicated high density model, it visually demonstrates the open lattice arrangement of carbon particles, helping learners understand connecting patterns and the unique geometry of carbon nanotube structures.
What “uniform” does—and does not—mean
Here, uniformity means that a given tube contracted evenly along its length while retaining a near-perfect lattice in the images described by the authors. It does not mean that the researchers produced a batch of nanotubes with identical diameters. The study focused on manipulating individual few-walled tubes in an in-situ TEM experiment.
The paper contrasts its approach with earlier shrinking methods based on tensile loading or Joule heating, which it says could manipulate only one nanotube at a time and often produced nonuniform shapes. In this experiment, multiple tubes were placed on the heating-chip membrane. That setup is not evidence of high-throughput production: the reported work remained a laboratory microscopy demonstration.
Why diameter control matters—and what remains unproven
Diameter and chirality both matter to potential CNT applications, including transistors and photoelectronic devices. The value proposed for this method is that it could tune the diameter of an already-grown tube instead of relying only on synthesis to produce a desired diameter. However, the study demonstrates diameter manipulation—not arbitrary chirality selection—and does not report a finished transistor, photoelectronic device or commercial manufacturing process made using shrunken tubes.
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The authors characterize their method as a reliable way to control the diameter of individual few-walled CNTs. That claim applies to the laboratory method and the tubes studied; it is not a claim that mass production or commercial deployment has been established.
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