| Abstract
| - The preparation of the catalyst is one of the key parameters which governs the quality of carbon nanotubes(CNTs) grown by catalyzed chemical vapor deposition (CVD). We investigated the influence of three differentprocedures of catalyst preparation on the type and diameter of CNTs formed under identical growth conditionsvia methane CVD. In the first one, chemically synthesized colloidal iron oxide or iron molybdenum alloynanoparticles were used, which were homogeneously deposited on silicon substrates by spin coating to preventthem from coalescence under CVD growth conditions. The obtained multiwall CNTs (MWNTs) exhibiteddiameters corresponding to the catalyst particle size, whereas no formation of single-wall CNTs (SWNTs)was observed. In the second method, commercial porous alumina nanoparticles were used in association withiron and molybdenum salts and the Fe/Mo catalyst was formed in situ. We determined that the aluminaconcentration significantly influenced the morphology of the catalyst and that below a critical value of therange of 1 g/L no CNTs were formed. While yielding nearly defect-free SWNTs, their diameter could not becontrolled using this procedure, resulting in a large distribution of tube sizes. In a third, new preparationmethod, associating alumina and iron-based nanoparticles, SWNTs of a different size and narrower diameterdistribution as compared to the second method were obtained. Our results are evidence of the essential roleof alumina particles in the formation of SWNTs, and the newly developed method opens up a way to thesynthesis of diameter-controlled SWNTs via catalyzed CVD.
|
