Towards Controlled Growth and Applications of Carbon Nanotubes

This thesis deals with growth, characterization and application of carbon nanotubes. The methods involved in the production of carbon nanotubes are thermal chemical vapor deposition (T-CVD) and plasma enhanced chemical vapor deposition (PE-CVD). Thermal-CVD has been successfully employed in synthesis of single wall carbon nanotubes (SWCNT) and multi wall carbon nanotubes (MWCNT). The understanding of the MWCNT growth was performed by studying the effects of influential parameters such as: carbon feedstock molec?les, size of catalytic iron (Fe) particles and temperature. A growth mechanism for MWCNT was proposed. Using the PE-CVD method we investigated the growth of MWCNT catalyzed by Fe and of vertically aligned carbon nanofibers (VACNFs) catalyzed by nickel (Ni). Using Fe as a catalyst, carbon nanotube carpet-like films were grown with exceptionally high growth rate. The selective growth of individual VANCFs within a hole etched in Si is demonstrated. The Ni catalyzed growth of VACNFs was investigated for different metal underlayers, namely: Pt, Pd, Ti, Mo, W and Cr. This study was carried out on continuous films and on patterned Ni dots. We observed that the Si/metal interaction occurring during growth plays a vital role in VACNFs formation on W, Mo, Pt and Pd metals. Structural and spectroscopic properties of the nanotube films were determined using electron microscopy (SEM and TEM) and Raman spectroscopy. All these results represents intermediate steps towards integration of MWCNT/ VACNFs into CNT-based devices. Making use of the thermal and electrical properties of carbon nanotubes, aligned MWCNT were tested in a microcooler channel device, while the VACNFs were involved in fabrication and measurement of nanoeletromechanical systems

Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part I: The silicon substrate/nanotube film interface

The interface between the silicon substrate and a carbon nanotube film grown by thermal CVD with acetylene (C2H2) and hydrogen at 750 or 900 \ub0C has been characterized by high resolution and analytical transmission electron microscopy, including electron spectroscopic imaging. Silicon (0 0 2) substrates coated with a thin (2.8 nm) iron film were heat treated in the CVD furnace at the deposition temperature in a mixture of flowing argon and hydrogen whereby nanosized particles of (Fe,Si)3O4 formed. These particles were reduced to catalytic iron silicides with the α–(Fe, Si), α2–Fe2Si and α1–Fe2Si structures during CVD at 900 \ub0C, and multi-wall carbon nanotubes grew from supported particles via a base-growth mechanism. A limited number of intermediate iron carbides, hexagonal and orthorhombic Fe7C3, were also present on the substrate surface after CVD at 900 \ub0C. The reduction of the preformed (Fe, Si)3O4 particles during thermal CVD at 750 \ub0C was accompanied by disintegration leading to the formation of a number of smaller

Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part I: The silicon substrate/nanotube film interface

The interface between the silicon substrate and a carbon nanotube film grown by thermal CVD with acetylene (C2H2) and hydrogen at 750 or 900 \ub0C has been characterized by high resolution and analytical transmission electron microscopy, including electron spectroscopic imaging. Silicon (0 0 2) substrates coated with a thin (2.8 nm) iron film were heat treated in the CVD furnace at the deposition temperature in a mixture of flowing argon and hydrogen whereby nanosized particles of (Fe,Si)3O4 formed. These particles were reduced to catalytic iron silicides with the α–(Fe, Si), α2–Fe2Si and α1–Fe2Si structures during CVD at 900 \ub0C, and multi-wall carbon nanotubes grew from supported particles via a base-growth mechanism. A limited number of intermediate iron carbides, hexagonal and orthorhombic Fe7C3, were also present on the substrate surface after CVD at 900 \ub0C. The reduction of the preformed (Fe, Si)3O4 particles during thermal CVD at 750 \ub0C was accompanied by disintegration leading to the formation of a number of smaller