Growth of a dense forest of vertically-aligned carbon-nanotubes (VA-CNTs) by a hot filament chemical vapor deposition (HFCVD) method was investigated. The growth of very pure VA-CNTs via the bottom growth mechanism was extremely fast during the initial few minutes, but it slowed down and reached the terminal height of a couple of millimeters. The different temporal variations of the VA-CNT height and growth rates corresponding to different growth stages indicated that a temperature-mediated thermodynamic model, precursor diffusion, and catalyst deactivation were responsible for the VA-CNT growth in respective stages. (C) 2009 Elsevier B.V. All rights reserved.