The unexpected complexity of filling double-wall carbon nanotubes with iodine-based 1D nanocrystals

A variety of iodine-based 1D nanocrystals were introduced into double-wall carbon nanotubes using the molten phase method, as an intermediate step for ultimately obtaining encapsulated metal nanowires. Based on HRTEM observations using different imaging modes (bright field, dark field, STEM) and associated analytical tools (EELS), it is revealed that the reality of nanotube filling is much more complex than expected. For some halides (typically Nih), earlier decomposition during the filling step was observed, which could not be anticipated from the known data on the bulk material. Others (e.g., iodine) show a variety of atomic structuration inside and outside the CNTs which is driven by the available space being filled, and was ascertained by modelling. Overall, the whole study reveals a variety of filling efficiencies, the reason of which is discussed.