Growth of multi-wall and single-wall carbon nanotubes with in situ high vacuum catalyst deposition

Abstract

In the last few years, carbon nanotubes (CNTs) haveattracted a great interest, due to their unique electronicand mechanical properties [1]. The growth via chemicalvapor deposition (CVD) allows obtaining high qualityCNTs at a large scale [2–8]. Generally a metal catalyst isneeded for the synthesis and, by choosing the appro-priate growth conditions, it is possible to obtain single-or multi-wall carbon nanotubes with controlled averagediameter and length [1,2,5]. The catalyst metallicity iscrucial for the CNTs growth, and generally the CNTsdiameter depends on the catalyst cluster dimensions.The catalyst may be pre-deposited on the surface (sur-face CVD) before the CVD process [2–9], or may beintroduced into the flowing carrier gas (gas phase CVD)[10–13]. In CVD with a supported catalyst film, it ispossible to reduce the nanotubes diameter by reducingthe catalyst film thickness: single-wall carbon nanotubes(SWCNTs) are obtained, even if they are generallymixed with multi-wall carbon nanotubes (MWCNTs)[9]. An efficient film for SWCNTs growth was obtainedstarting from a solution containing metal nanoparticlesof the catalyst [3–5]. This method is time-consuming inthe catalyst preparation, implying heating of the catalystsolution for hours and grinding into powder of nano-metric scale. SWCNTs were observed during carbonevaporation on a thin pre-deposited catalyst film in ultrahigh vacuum conditions [17]. However the tubes grownwith this method are very short (50 nm) and theresulting growth yield is low. The gas phase CVD [10–13]results also very efficient for SWCNT growth.Here we describe an efficient procedure for the syn-thesis of multi- and/or single-wall carbon nanotubes. Itis based on CVD process using merely acetylene asprecursor gas and starting from a catalyst film depositedunder high vacuum (HV) conditions (base pressure: 10