Carbon nanotube

Carbon nanotubes (CNTs) are hollow, tube-shaped structures made of carbon atoms joined in a hexagonal, graphene-like network. A single-walled carbon nanotube consists of one such cylindrical wall; a multi-walled nanotube contains multiple nested or rolled layers. For single-walled tubes, the way the atomic lattice is wrapped around the cylinder—often described by its chirality—helps determine its diameter and electronic behaviour.

Nanotubes can have useful electrical, thermal and mechanical characteristics, but these are not identical for every sample. Diameter, atomic arrangement, defects, purity, surface chemistry, aggregation and processing can all affect measured performance. For example, single-walled nanotubes with different lattice arrangements can behave as conductors or semiconductors. Claims about exceptional strength or conductivity therefore depend on the particular nanotube and the way it is assembled into a usable material.

Several methods can produce carbon nanotubes, including chemical vapour deposition and other high-temperature techniques. Manufacturing conditions influence tube structure and can leave impurities or mixtures of different nanotubes. Researchers use characterization and separation methods to assess properties and distinguish types; this remains important because a material’s performance depends on which nanotubes are present and how they are arranged.

Carbon nanotubes are studied for applications that exploit their nanoscale structure and material properties, including composite materials, electrical components, sensors and biomedical research. NASA has investigated vertically aligned multi-walled nanotubes as very low-reflectance coatings for spacecraft instruments, while the U.S. National Nanotechnology Initiative describes carbon-nanotube sheets for possible use in next-generation aircraft, including electromagnetic shielding and thermal management. These are specific research and engineering uses, not evidence that all proposed applications are commercially mature.

Potential benefits must be considered alongside health and environmental questions. Toxicity studies report that effects can depend on a nanotube’s dimensions, surface chemistry, dose, purity and route of exposure. Risk assessment therefore requires attention to the particular material and its production and handling, rather than assuming that all carbon nanotubes have the same biological effects.