Carbon nanotubes are one of the most exciting materials for emerging practical nanotechnologies. However, a significant issue for applications is the mixture of semiconducting and metallic tubes in all typical samples. One of the proposed solutions for this problem is to tailor the electronic structure by doping the lattice with heteroatoms, most notably nitrogen. In this thesis, nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were synthesized using an ambient pressure floating catalyst chemical vapor deposition method. A novel combination of precursors was used, with carbon monoxide (CO) acting as the carbon source and ammonia (NH3) as the nitrogen source. Experiments were conducted with two reactor setups, both utilizing iron nanoparticles as the catalysts. The material was deposited as grown directly from the gas phase as films on various substrates and subsequently characterized by a variety of microscopic and spectroscopic methods, as well as sheet resistance measurements. The sheet resistance measurements of the thin film samples revealed that the doped films had unexpectedly high resistances. To understand this effect, a resistor network model was developed, which allowed the disentanglement of the contribution of bundle-bundle contacts when combined with data for undoped films. Assuming doping does not significantly change the contacts, the increased resistances of the doped films are likely due to enhanced carrier scattering by defect sites in the nanotubes. This work represents the first experimental report on macroscopic N-SWCNT thin films. Finally, the mechanism of the initial stages of N-SWCNT growth was studied for the first time by tandem infrared and mass spectrometry gas measurements and first principles electronic-structure calculations. We investigated the bonding and chemistry of CO, NH3, and their fragments on a model Fe55 icosahedral cluster. A possible dissociation path for NH3 to atomic nitrogen and hydrogen was identified, with a reaction barrier consistent with an experimentally determined value. Both C-C and C-N bond formation reactions were found to be barrierless and exothermic, while a parasitic reaction of hydrogen cyanide formation had a large barrier of over 1 eV.
|Julkaisun otsikon käännös||Nitrogen-doped single-walled carbon nanotube thin films|
|Tila||Julkaistu - 2011|