X-ray diffraction and electron microscopy of as-produced pristine SWCNT. Panel a: X-ray diffraction pattern of a SWCNT powder placed in a glass capillary. The image is made of two patterns recorded for different durations, allowing the visualization of intense peaks (left part of the image) as well as much weaker ones (right). The two dotted arrows point towards diffraction peaks, around 0.5 and 0.9 Å-1, from the CNT bundles, the large bump (star) comes from the glass capillary and peak 1, at wave-vector Q ~ 3 Å-1, can be attributed to both CNT and iron-based nanoparticles. The three plain arrows point toward diffraction peaks characteristic of cementite Fe3C (see e.g. ). The widths of the peaks are resolution-limited and they correspond to particle sizes of about 5 nm and above: one mainly probes here the bigger particles (Φ ≥ 5 nm). Panel b: HAADF-STEM image showing tiny white spots corresponding to iron-based nanoparticles covering lightly contrasted bundles of SWCNT deposited on a TEM grid coated with a lacey carbon film. Nanoparticle diameters range from 1 to 10 nm. Panel c: HRTEM image of bundles of SWCNT. Arrows show iron-based catalyst nanoparticles on the sidewalls of CNT.