The characteristics of nanotubes (nanorods) converted from diamond films were investigated. The microstructures and Raman spectroscopy are markedly altered when the diamond films were coated with a thin layer of Fe/Co films (<10 nm) and then postannealed at high enough temperature (>950 degreesC), which is owing to the formation of carbon nanotubes (nanorods) resulted from the heat treatment. The same phase transform behavior was observed no matter whether the starting materials are diamond nuclei, nanodiamonds, or faceted diamonds. The main reaction is presumably the dissolution and reprecipitation of carbon species in the diamond films through the Fe-Co catalyst layer. The carbon nanotubes (nanorods) derived from faceted diamonds show electron field emission current density I order of magnitude larger than those converted from diamond nuclei, that is, (J(e))(nuclei) = 320 muA/cm(2) and (J(e))(diamond) = 3800 muA/cm(2) , with the turn-on field about the same [(E-0) = 5.2- 7.2 V/mum]. (C) 2003 American Vacuum Society.