Plasma-enhanced chemical vapor deposition (PECVD) was used to prepare vertically well-aligned carbon nanotube arrays on atomic layer deposition (ALD) of zinc oxide (ZnO) films with acetylene (C2H2) and ammonia (NH3). The mechanisms of their nucleation and initial growth were analyzed on ZnO films, and the activation energy was also calculated to be about 60.7 kJ/mol. Generally, the reactivity of NH2 radicals was higher than that of H2 molecules and H radicals, so the activation energy was lower for the nucleation and initial growth of vertically aligned carbon nanotube arrays (VACNTs) with NH2 radicals, compared with H radicals and H2 molecules.