Increased chemical reactivity of single-walled carbon nano-tubes on oxide substrates: In situ imaging and effect of electron and laser irradiations

We studied the oxygen etching of individual single-walled carbon nano-tubes on silicon oxide substrates using atomic force microscopy and high-temperature environmental scanning electron microscopy. Our in situ observations show that carbon nano-tubes are not progressively etched from their ends, as frequently assumed, but disappear segment by segment. Atomic force microscopy, before and after oxidation, reveals that the oxidation of carbon nano-tubes on substrates proceeds through a local cutting that is followed by a rapid etching of the disconnected nano-tube segment. Unexpectedly, semiconducting nano-tubes appear more reactive under these conditions than metallic ones. We also show that exposure to electron and laser beams locally increases the chemical reactivity of carbon nano-tubes on such substrates. These results are rationalized by considering the effect of substrate-trapped charges on the nano-tube density of states close to the Fermi level, which is impacted by the substrate type and the exposure to electron and laser beams. (authors)