Aligned carbon nanotube arrays were synthesized on Fe-coated Si substrates using thermal chemical vapor deposition (TCVD) method by pyrolysis of C2H2 The results show that carbon nanotube arrays with two layers were obtained after growth for 60 min, which were connected to each other through iron catalyst particles. A possible growth model for the layered carbon nanotube arrays is proposed. In addition, the results show that the time of catalyst pretreatment in NH3 affected greatly the morphologies of the layered carbon nanotube arrays and the reason for this was discussed. (c) 2005 Elsevier B.V. All rights reserved.