Vertically aligned carbon nanotubes (CNTs) are grown by plasma enhanced chemical vapor deposition and are analyzed by high-resolution transmission electron microscopy. With this process, the growth of vertically aligned and densely packed CNTs can only be obtained with an Fe catalyst on an Si3N4 support or with an Ni catalyst on a TiN support. The authors observe that base- and tip-growth modes occur simultaneously for the Fe/Si3N4 system, whereas in the Ni/TiN system only the base-growth mode is observed. When using the multilayer catalyst FeNi (2:1), growth occurs on both supports. These structures are quite similar to those obtained with a pure Fe or Ni catalyst on their corresponding support. Growth at lower temperatures, down to 550 °C, shows that at temperatures high enough to just activate the catalyst, the structures obtained are not significantly influenced by the growth temperature, but rather by the catalyst-support system and other growth conditions.