To investigate the effect of high and low magnetic fields on the control of structure and morphology of carbon nanotubes, a unique in-situ MOCVD (Metal Organic Chemical Vapor Deposition) facility is constructed and tested for a variety of conditions. The facility has been used to fabricate multi-wall carbon nanotubes (MWCNTs) and the final microstructures were characterized using advanced electron microscopy techniques.
It has been shown that conventionally synthesized CNTs could be oriented when subsequently placed in the presence of a strong external magnetic field. It is therefore anticipated that their growth, under such conditions would lead to large arrays of well-aligned CNTs. We have carried this effort a step further by synthesizing MWCNTs using the in-situ MOCVD facility to also examine the effect of high magnetic field on these as grown tubes. SEM and TEM analysis of in-field produced materials indicated a large increase (296% min. to 450% max.) in diameter of the CNTs, a sharp reduction in their contaminating metallic (Fe) particles and the formation of other structural arrangements (possible multilayered nanospherules) that have been, up to date, very rarely reported.
The results are interpreted in terms of magnetic force and reactor conditions, on the thermal decomposition of a xylene-ferrocene mixture allowed to condense in helium or argon atmospheres, with hydrogen gas as a reducing agent. Further parametric studies of both in and ex-situ CNT synthesis are being planned. Funding was provided by the National Science Foundation and the US Army.
