Metal-catalysed reactions between atomic H and C nanopowders in a modified CVD reactor are used to generate ordered arrays of aligned nanotubes. The technique allows to produce either deposits consisting of aligned bundles of nanotubes laying along the substrate or dense arrays of nanotubes oriented at variable angles with respect to the substrate surface. Moreover, controlled growth of densely packed nanotube arrays can be obtained at given locations of substrates by means of a process sequence which exposes patterned layers of thermally grown SiO2 onto Si(1 0 0) wafers to the reactant flows. This procedure has been successfully used to realize specific architectures, such as the selected-area growth of rather long (30-50 mum) and vertically aligned nanotubes bundles along the crossing lines of regularly shaped features. (C) 2002 Elsevier Science B.V. All rights reserved.