On-line detection of single-walled carbon nanotube formation during aerosol synthesis methods Anna Moisala a , Albert G. Nasibulin a , Sergei D. Shandakov b , Hua Jiang c , Esko I. Kauppinen a,c, * a Department of Engineering Physics and Mathematics Center for New Materials, Helsinki University of Technology, P.O. Box 1602, FIN-02044 VTT, Finland b Kemerovo State University, General Physics Department, ul. Krasnaja 6, 650043 Kemerovo, Russia c Aerosol Technology Group, VTT Processes, P.O. Box 1602, FIN-02044 VTT, Finland Received 29 September 2004; accepted 11 March 2005 Available online 12 May 2005 Abstract Differentialelectricalmobility(DMA)methodfortheon-linedetectionofsingle-walledcarbonnanotubes(SWCNTs)formation wasusedforthefirsttime.Threedifferentgas-phasesynthesisprocesseswereusedtoproduceSWCNTsviaCOdisproportionation inthepresenceofcatalystnanoparticlesformedeitherbyahotwiregeneratormethodorviathermaldecompositionofferroceneor iron pentacarbonyl. The typical product measured with the DMA method was bundles of SWCNTs, which further agglomerated prior to the measurement. Despite the different product morphology and concentration, the on-line measurement was able to dis- tinguishSWCNTformationineachexperimentalset-upasanincreaseinthegeometricmeanparticlediameterandasadecreasein the total particle number concentration. Furthermore, information regarding the relative SWCNT concentration can also be obtainedfromtheDMAmeasurement.Atheoreticalapproachtothemobilityofnonsphericalparticlesintheelectricfieldwassuc- cessfully developed in order to convert the electrical mobility size of the high aspect ratio SWCNTs measured with DMA to the physical size of the product. Size-selected SWCNTs were studied with transmission electron microscopy in order to find the corre- lation between the on-line DMA measurement data and the SWCNT morphology. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Carbon nanotubes; Pyrolysis; Transmission electron microscopy; Particle size 1. Introduction Carbon nanotubes (CNTs) have extraordinary phys- ical and chemical properties [1]. The existing and possi- ble applications together with abundant fundamental researchinteresthaveresultedindevelopmentofnumer- ous production methods for this unique material. The catalytic methods for SWCNT synthesis involve cata- lytic decomposition of carbon precursor molecules (e.g.hydrocarbons,carbonmonoxide(CO)oralcohols) on the surface of transition metal nanoparticles. In the supported chemical vapour deposition (CVD) method the catalyst nanoparticles are supported on a substrate. During the gas-phase (i.e. aerosol) process the catalyst nanoparticles form in the gas-phase prior to the SWCNT growth typically via thermal decomposition of catalyst precursors (e.g. [2]). The nucleation of the SWCNTshasbeenproposedtotakeplacewhenthelib- erated carbon diffuses into and on the catalyst particle surface and a carbon layer forms at the particle surface [3]. Both, the supported CVD and the gas-phase meth- ods have been used for selective SWCNT formation and both processes have shown great promise toward the synthesis of SWCNTs in large quantities [4,5]. Carbon 43 (2005) 2066–2074 www.elsevier.com/locate/carbon 0008-6223/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2005.03.012 * Correspondingauthor.Tel.:+35894566165;fax:+35894567021. E-mail address: esko.kauppinen@vtt.fi (E.I. Kauppinen).