Confinement of selenium inside carbon nanotubes. Structural characterization by X-ray diffraction and X-ray absorption spectroscopy

In order to study the effect of confinement on crystallographic arrangement, selenium (Se) was introduced into carbon nanotubes with average diameters of 12, 23 and 50 Å. The evolution of the Se long-range crystallographic arrangement and the Se short-range atomic surroundings was characterized by X-ray diffraction and X-ray absorption spectroscopy, respectively. A transition from an initially disordered trigonal structure, where part of the chains are not well connected, to a structure exhibiting well-organized rings was observed when the tube diameter was of the order of 12 Å. Se–C bonds, detected when nanotube average diameters were of the order of 20 Å and less, might play a role in the structural transition.