The Unexpected Complexity of Filling Double-Wall Carbon Nanotubes With Nickel (and Iodine) 1-D Nanocrystals

A variety of iodine-based one-dimensional (1-D) nanocrystals were introduced into double-wall carbon nanotubes (DWCNTs) using the molten phase method, as an intermediate step for ultimately obtaining encapsulated metal nanowires. Based on high-resolution transmission electron microscopy (HRTEM) observations using different imaging modes (bright field, dark field, and scanning TEM) and associated analytical tools (electron energy loss spectroscopy), it is revealed that the reality of nanotube filling is much more complex than expected. For some iodides (typically NiI 2), earlier decomposition during the filling step was observed, which could not be anticipated from the known data on the bulk material. Other filling materials (e.g., iodine) show a variety of atomic structuration inside and outside the CNTs, which is driven by the available space being filled. Most of the encapsulated structures were confirmed by modeling.