Scanning tunneling microscopes can deposit individual atoms on surfaces, enabling researchers to study and modify nanostructures. Such microscopes do not have continuous capabilities, though, so are limited in transporting atoms, molecules or ions. Carbon nanotubes could make excellent conduits for atoms, but a scanning tunneling microscope could not act as the pump mechanism. Adjusting the phase difference between their coherent radiation creates a net current that can selectively induce the flow of atoms in the desired direction.
Developers can control the tubes' diameters and electrical conductivity.
Although nanotubes have found several applications, some have been limited. For example, an electric current passing through the structure creates a force that will push atoms and molecules through the center of the tube. But it is difficult to make electrical contacts to the nanotubes. A schematic shows a carbon nanotube that is only 1.4 nm in diameter. Many atoms and molecules fit inside, as indicated by the red spheres, and could be pumped through these miniature pipes using two laser beams.