Carbon nanotubes are a type of carbon material that have been studied extensively since 1991. They can be single-walled, double-walled, or multi-walled. Scientists have used various methods to create and study different types of nanotubes, including speciality ones like junction nanotubes. Researchers have also modified nanotubes chemically by adding elements like boron and nitrogen, or by attaching metal nanoparticles to them. These nanotubes have unique properties that make them potentially useful in electronics, displays, energy devices, and even medical applications.