Due to their novel properties, nanostructured carbon materials are concentrating more and more efforts within the scientific community. The latest members of this ever increasing family, carbon nanotubes, have been indicated as the most interesting and promising material both from a purely scientific and technological point of view. Field emission based devices are considered their closest to market technological application. Synthesis and characterization of such structures represents, therefore, key tasks in material science research. Within such framework, the three-year work reported in this thesis face the challenge in optimizing the deposition of Single Wall Carbon Nanotubes (SWNTs), synthesizing a new hybrid nanostructured material consisting of diamond and SWNTs and investigating their field emission properties. As for the synthesis step, a modified Hot Filament Chemical Vapor Deposition set-up was used. Carbon nanopowders were used as carbon feedstock, plain and lithographically patterned Si as substrates; different morphologies of SWNT bundles were obtained. By slightly varying the synthesis conditions and getting longer deposition times a new hybrid material constituted by a diamond outer phase and a SWNT inner phase was obtained. For both the plain (SWNTs) and hybrid (SWNTs-diamond) selected area growth onto predefinite areas was achieved. Field emission investigation was carried out by using a home-made set-up which enabled the I-V characterization of the samples. Being interested in the quantitative comparison of morphologically different samples, a simple, new and reliable measurement methodology has been set up. Procedures for the evaluation of interelectrode distance and emitting area are presented: as for the former, a capacimetric approach is described; as for the emitting area evaluation, an approximated analytical formula is proposed. A quantitative comparison among three samples showing different features is carried out: extraction fiel is found out to increase as the density of the SWNT bundles increase. The results are explained in term of mutual field screening. A preliminary study on the diamond/nanotubes hybrid material revealed favourable field emission properties. The novelty of such structures lead me to go deeper in the investigation: a study of the emission pattern and of the energy spectrum in systematically different experimental conditions was carried out. A unusual, never-seen spectrum consisting of many sharp peaks located within 500 eV from the Fermi level was recorded. We explained this behavior by invoking the highly resistive nature of diamond. We consider our results as referring to the truly intrinsic properties of the outer diamond. As a result of the field emission investigation two field emission devices are proposed: a triode and a X-ray tube.
Fiori, A. (2009). Sintesi e caratterizzazione delle proprietà di emissione di campo di materiali nanostrutturati a base carbonio.
|Titolo:||Sintesi e caratterizzazione delle proprietà di emissione di campo di materiali nanostrutturati a base carbonio|
|Data di pubblicazione:||2-feb-2009|
|Anno Accademico:||A.A. 2005/2006|
|Settore Scientifico Disciplinare:||Settore CHIM/07 - Fondamenti Chimici delle Tecnologie|
|Tipologia:||Tesi di dottorato|
|Citazione:||Fiori, A. (2009). Sintesi e caratterizzazione delle proprietà di emissione di campo di materiali nanostrutturati a base carbonio.|
|Appare nelle tipologie:||07 - Tesi di dottorato|