This research would not have been possible without the invaluable samples and expertise of Asst. Prof. Jeremy Sloan of the University of Warwick. Jeremy's group in Warwick fills the ~1nm central cavity of single walled carbon nanotubes with another material to form extreme nanowires whose diameter is 1 or 2 times the unit cell of the parent material. Nanowires with these dimensions often crystallise in a different structure to the parent which are not stable in bulk form, i.e. they are entirely novel materials with new properties different from their parent materials.
Fully characterising the structure of these materials requires extremely high quality Transmission Electron Microscopy which is a speciality of the Warwick group. Shown below are some images of filled carbon nanotubes taken with at TEM.