For more than 25 years, physicists have predicted that shrinking some semiconducting nanotubes to extreme dimensions would fundamentally change their electronic behavior.
The problem was proving this. Structures of this size are very difficult to fabricate, because they become unstable long before they reach the sizes required for experimental verification. Researchers in The University of Tokyo has now overcome this challenge by creating atomically precise molybdenum disulfide nanotubes that are only one nanometer in diameter, about 100,000 times thinner than a human hair. Beyond creating one of the world’s smallest semiconducting nanotubes, this achievement solves a long-standing theoretical question about how electronic properties change at the nanoscale and provides a new platform for the design of ultra-miniaturized electronic components in the future.
How molybdenum disulfide nanotubes could transform transistors and future quantum devices
Nanotubes have attracted scientific interest since the early 1990s because their cylindrical atomic structures can exhibit unusual electrical, optical, and mechanical properties. While carbon nanotubes have become the main focus of research, scientists have also predicted that inorganic semiconducting nanotubes could offer advantages for future electronics if their atomic structure can be precisely controlled.
This was followed in 1995 by the successful high-rate gas-phase growth of inorganic fullerenes and interconnected MoS2 nanotubes.
Advances in functional properties
As the field progressed, research turned toward understanding the unique physical properties of these materials: Superconductivity and photovoltaics: Investigations into related chiral nanotubes led to the discovery of superconductivity in 2017 and an enhanced intrinsic photoelectric effect in tungsten disulfide nanotubes in 2019.Theoretical predictions: Theoretical studies, such as those conducted in 2000 and 2002, predicted that the electronic properties and stability of MoS2 nanotubes would change dramatically as their diameters decreased, and specifically predicted that the band gaps would shrink as the diameter decreased.The paper, “Contrained growth of armchair MoS2 nanotubes at the 1 nm limit,” suggests that the challenge lies in size.
Conventional fabrication methods generally produce nanotubes larger than 10 nm in diameter, often with multiple walls and structural irregularities. Theoretical models developed more than two decades ago suggested that smaller, single-walled nanotubes should exhibit measurable changes in their electronic bandgap, a property that determines how semiconductors conduct electricity. To date, these expectations have remained largely untested.According to Associate Professor Yusuke Nakanishi, Kashiwa Department of Advanced Materials Science, University of Tokyo:“We have achieved the synthesis of atomically precise semiconductor nanotubes with nanometer diameters. These tiny nanotubes have been identified as an ideal platform for transistor nanochannels.”The team’s measurements showed that the band gap decreases as the diameter of the nanotubes becomes smaller, directly confirming theoretical predictions proposed more than a quarter century ago.
Building a stable nanotube with a width of only one nanometer
To achieve this breakthrough, the researchers used boron nitride nanotubes as protective outer molds. Within these confined nanospaces, molybdenum disulfide (MoS₂) atoms are assembled into highly ordered single-walled nanotubes approximately one nanometer wide.Historically, these tiny nanotubes were considered unstable or inaccessible due to the extreme stress caused by their high curvature. The researchers achieved stability using spatially confined interactions within insulating nanotubes of boron nitride (BN).Advanced electron microscopy and chemical mapping confirmed the structures and revealed exceptionally well-defined atomic arrangements. The surrounding boron nitride served as a stabilizing shell, allowing the ultra-thin semiconducting nanotubes to form without collapsing.The resulting structures differ significantly from many existing nanotube systems. Instead of relying on multiple concentric walls or supporting materials inside the tube, the new structure keeps the semiconductor channel precisely clean at the atomic level.Yusuke Nakanishi, lead author and correspondent, explained:“Their biggest advantage is structural control at the atomic level. This specific structure is seen as a promising path toward creating true transistor nanochannels.”
Why this discovery is important for future electronics
As silicon transistors continue to approach the limits of physical measurement, engineers are exploring alternative materials capable of maintaining predictable behavior in extremely small dimensions.
Small structural defects increasingly impact performance as devices shrink, creating one of the major hurdles facing semiconductor technology in the future.Newly developed nanotubes provide a potential solution because their atomic structure can be controlled with much greater precision than conventional semiconductor channels. The researchers believe that the coaxial arrangement, in which a semiconducting MoS₂ nanotube is surrounded by an insulating boron nitride nanotube, could eventually be useful for engineering universal gate transistors, one of the most advanced designs currently pursued by the semiconductor industry.Although practical devices are still a long way off, this work establishes a new path to constructing semiconducting nanotubes with predictable electronic properties. This approach can also be extended to magnetic, superconducting, and other inorganic materials, potentially expanding the scope of nanotube science beyond carbon-based systems.More importantly, this achievement closes a chapter that began with theoretical calculations more than 25 years ago. What was once a prediction limited to mathematical models can now be measured directly inside a nanotube only a billionth of a meter wide.