Growth of novel carbon phases by methane infiltration of free-standing single-walled carbon nanotube films Artur Bo ¨ ttcher a, * , Frank Hennrich b , Harald Ro ¨ sner b , Sharali Malik b , Manfred M. Kappes a,b, * , Sven Lichtenberg c , Gu ¨ nter Schoch c , Olaf Deutschmann c a Institut fu ¨ r Physikalische Chemie, Universita ¨ t Karlsruhe, Fritz-Habel-Weg 4, D-76128 Karlsruhe, Germany b Institut fu ¨r Nanotechnologie, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany c Institut fu ¨ r Technische Chemie und Polymerchemie, Universita ¨ t Karlsruhe, 76131 Karlsruhe, Germany Received 21 June 2006; accepted 8 December 2006 Available online 30 January 2007 Abstract High-temperature methane infiltration of thin, free-standing films of acid-treated single-walled carbon nanotubes (SWCNT) has been studied by means of scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. In the early stages of infiltration, carbon nuclei form predominantly at SWCNT bundle intersections. Further growth proceeds via the formation of graphite nanosheets – without further influence of the nanotube support. Both sheet edges and their structural imperfections act as reaction cen- ters for subsequent deposition, likely giving rise to autocatalytic deposition kinetics. In contrast, infiltration with a H 2 :CH 4 (24:1) mixture leads to the reductive activation of residual Ni/Co impurities embedded in the precursor SWCNT-felt. This is associated with a different predominant carbon deposition mode in which multiwalled carbon nanotubes grow out from the substrate. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction Thin films of partially oriented single-walled carbon nanotube (SWNT) bundles, may be thought of as a new class of essentially monodispersed all-carbon materials [1]. They exhibit high-temperature stability [2] as well as surprisingly high tensile strength [3]. The corresponding Young’s modulus can range up to at least 24 MPa, making these films and particularly composites derived from them, potentially interesting for applications [4]. We have shown that thin, free-standing films of SWCNT bundles (=SWCNTF) can be readily generated from aqueous SWCNT suspensions by filtration through nanopore filters [5]. Careful removal of the deposited material from the fil- ter results in large area (10 cm 2 ), free-standing films which are homogeneous on length scales greater than 200 nm. This was demonstrated both for as-prepared and for nitric acid-treated (reduced metal content) SWNT materials [5]. Film thickness can be controlled over the range from 200 nm up to several lm by varying the suspension vol- ume/concentration. In free-standing SWCNTF samples, bundles lie preferentially in the plane of the film but are otherwise aligned randomly. Mass densities are approxi- mately 1 g/cm 3 [4]. Varying the rate of solvent removal dur- ing filtration, results in some vertical layering which is associated with slight density differences between layers. The mechanical properties of more conventional porous carbon materials can often be significantly strengthened by methane gas infiltration/pyrolitic carbon deposition at high substrate temperatures [6]. This motivated us to perform analogous experiments with methane infiltration of SWCNTF. Additionally, we were interested in the associ- ated elementary reaction steps and how these differ from reactions occurring at graphite single crystal surfaces under 0008-6223/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.12.008 * Corresponding authors. Address: Institut fu ¨r Physikalische Chemie, Universita ¨t Karlsruhe, Fritz-Habel-Weg 4, D-76128 Karlsruhe, Germany. Tel.: +49 7216083254; fax: +49 7216087232. E-mail addresses: artur.boettcher@chemie.uni-karlsruhe.de (A. Bo ¨ ttcher), manfred.kappes@chemie.uni-karlsruhe.de (M.M. Kappes). www.elsevier.com/locate/carbon Carbon 45 (2007) 1085–1096