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Top ends of aligned carbon nanotubes were opened via room-temperature sputter etching of the nanotubes in the same chemical-vapor deposition (CVD) chamber that the nanotubes were grown. The mechanism of the sputter etching process involves incident positive ions in the plasma, such as hydrogen or argon, colliding with the nanotube material and preferentially eroding the nanotube walls around the catalyst metal particles. The cut-off nanotube segments are removed from the sample in the CVD chamber together with the catalyst particles. This process is entirely physical in nature with no wet chemical processing steps involved. The sputter etching process is found to be faster with larger ion size, higher applied voltage forming the plasma, and higher pressure of the sputtering gas. [ABSTRACT FROM AUTHOR]