© 2005 The Royal Microscopical Society Journal of Microscopy, Vol. 219, Pt 2 August 2005, pp. 69– 75 Received 23 December 2004; accepted 23 May 2005 Blackwell Publishing, Ltd. Cross-sectional TEM investigation of nickel-catalysed carbon nanotube films grown by plasma-enhanced CVD Y. YAO, L. K. L. FALK, R. E. MORJAN,* O. A. NERUSHEV* & E. E. B. CAMPBELL* Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden *Department of Physics, Göteborg University, SE-412 96 Göteborg, Sweden Key words. CNT film, cross-sectional TEM, interface, metal dusting, Ni-catalyst, nucleation. Received 23 December 2004; accepted 23 May 2005 Summary Nickel-catalysed multiwall carbon nanotubes synthesized by plasma-enhanced chemical vapour deposition on a silicon substrate with acetylene and ammonia at 700 °C have been characterized by high-resolution and analytical transmission electron micro- scopy. The nucleation of the carbon nanotubes occurs as a con- sequence of the carburization and dusting of supported preformed nickel- and silicon-rich particles. This process yields disintegrated silicon-containing nickel particles dispersed in dome-shaped carbon islands adherent to the substrate. The particles act as catalysts for tube growth, resulting in aligned multiwall carbon nanotubes with a bamboo-like structure anchored to the dome- shaped carbon islands. The bottom part of the carbon islands contains bundles of graphene sheets orientated parallel to the substrate. The nanotubes are capped with fcc nickel particles containing dissolved silicon. Most of these particles have a conical shape orientated with a <110> direction along the tube growth axis, and with {110} and {111} planes as exposed faces. Introduction In light of the possible applications of carbon nanotubes (CNTs) for nano-electronic devices and electron field-emission sources, plasma-enhanced chemical vapour deposition (PECVD) has attracted considerable attention in recent years. The PECVD technique provides a promising synthesis method to satisfy the demands for micro/nano-electronic devices, e.g. highly ordered orientation, low defect level, reproducibility and controllable properties. A uniform and high growth rate of CNT films using different plasma CVD techniques has been achieved with con- trolled alignment, precise positioning, and controlled height and diameter of the structures (Ren et al., 1998; Choi et al., 2000, 2003; Merkulov et al., 2000; Chowalla et al., 2001; Chang et al., 2002; Morjan et al., 2004). Generally, nickel-catalysed CNTs grown by PECVD show a tip- growth behaviour, which has been explained by the weak inter- action between the nickel catalysts and the silicon substrate. The generally accepted mechanism for tip growth (Baker et al., 1972) suggests that the carbon from decomposed hydrocarbon stock gas is dissolved at the front surface of the catalytic particle causing oversaturation, diffusion and precipitation on the rear surface to form graphene sheets with a tubular structure. The detailed structure at the base of the CNTs at the interface with the substrate, which contains the essential information on nucleation and growth, is, however, usually disregarded in the literature. This is because CNTs are usually characterized using dispersed CNT samples in transmission electron microscopy (TEM). In this paper we report cross-sectional TEM observations and local analyses at the base of nickel-catalysed CNT films synthesized by PECVD. The purpose is to characterize fully the interface between the silicon substrate and the film of tip-grown CNTs, and to develop a better understanding of the nucleation and growth of CNTs on the microscopic scale. Materials and methods A nickel thin film with nominal thickness of 30 nm was depos- ited on polished silicon (002) wafers by electron beam evapo- ration at room temperature. The substrate was ultrasonically cleaned in isopropanol before deposition, and dried in flowing nitrogen. The coated substrate was then transferred into a CVD chamber and heated at 700 °C for 15 min in flowing argon and hydrogen. The nanotubes were thereafter grown in an acetylene : ammonia = 1 : 5 atmosphere at a pressure of 4 torr for 1, 5 and 10 min. A DC voltage of 400 V was supplied for plasma production with a current density of 0.5–1 mA cm -2 . Samples taken for characterization after heat treatment only and after nanotube growth were furnace cooled in a mixture of flowing argon and hydrogen. The reaction products were characterized by scanning electron microscopy (SEM) of the exposed surfaces. The nanotubes grown Correspondence to: Professor Lena K. L. Falk. E-mail: lklfalk@fy.chalmers.se