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A vapor phase method was developed to fill different kinds of nanotubes (including multiwall and singlewall nanotubes), which inner diameters range from 200 down to 1.5 nm. Experiments were performed with selenium in a sealed reactor in order to control the selenium partial pressure. This process allows a full control of the nanotube filling (partial or complete), i.e., either a selective diameter filling or a full filling rate. The weight gain of all the samples was plotted for different reaction temperature as a function of selenium pressure. Experimental isotherms are characteristic of capillary condensation of selenium, which occurs at first in the smallest nanotube inner diameters. X-ray diffraction data show that selenium confined in nanotubes with diameters larger than 3 nm keeps its trigonal structure.

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Filling of carbon nanotubes with metals or semi-metals (such as Se, Bi, . . .) raises the possibility of novel nanomaterials synthesis with technologically interesting properties on a nanometric scale. Indeed it offers the possibility to enhance the physical properties of both the encapsulated and encapsulating materials. In the present study, multi-walled nanotubes, synthesized by thermic decomposition of propylene in alumina membrane and catalytic decomposition of acetylene on solid solution and single-walled nanotubes (from Rice University, Houston, Texas, USA) were filled with selenium, in order to study the influence of confinement on Se structure and the nanocomposite properties. The filling was performed in the vapor phase in a sealed reactor, and the control of selenium pressure allows us to control the nanotube filling rate, which depends also on the nanotube diameter. A filling rate up to 90% could be reached with this method.