ABSTRACT
Since their discovery by Iijima [1], the specific morphology ofnanotubes with an empty cylindrical core space and the presence of large surface areas on both outer and inner sides of the walls, has captured the interest of many researchers who have demonstrated many types of fillings, coatings or graftings with gases, molecules or solid compounds. In particular, new families of nano-objects have been identified, such as nanowires, nanocontainers, peapods. They offer strong potentialities for exhibiting novel properties and for developing new applications as transport components, storage devices or reaction chambers. On the other hand, the combination of intense electron probes of near-atomic dimension (in a STEM microscope) with highly efficient 2D detectors for recording electron energy-loss spectra (EELS) within a few milliseconds, has provided quite powerful tools to explore individual nanostructures with unprecedented spatial and energy resolutions. In particular, the identification of single atoms encaged in fullerene molecules along peapods structures was demonstrated [2], and the technique has been extended to the analysis of trapped molecules or single crystals within SWNTs [3]. Here, we demonstrate that beyond chemical mapping, the electronic states in such nanostructures can be locally investigated by mapping the EELS fme structures observed on core edges. Two examples are reported: the mapping of B chemical bond in complex BN nanotubes samples and the detection of pentagonal defects in highly defective multiwall carbon nanotubes.
