We have performed a detailed transmission electron microscopy study of the tip of carbon nanotubes prepared by chemical vapor deposition (CVD) and by arc discharge. We found that a large proportion of the CVD-grown tubes have well-formed caps but that the graphitization of the walls is far from perfect. The tip shapes are also more rounded and the tip radius is higher when compared to arc-discharge tube tips. These features are discussed in relation with the growth mechanism and with the consequences they might have for applications in scanning probe microscopies.
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