This dissertation presents experimental studies on the growth of carbon nanotubes (CNTs) by means of newly designed environmental transmission electron microscopy (ETEM). The ETEM is equipped with an environmental-cell of the differentially pumped aperture type which consists of several apertures and additional pumps. Using the ETEM, gas molecules can be localized only around a specimen at certain pressure while maintaining high vacuum in the other parts. Growth dynamics of CNTs has been studied by in situ observations of the growth of CNTs as well as electron energy-loss spectroscopy (EELS) of gases by ETEM.
Before the study using the ETEM, CNTs have been synthesized by a newly constructed chemical vapor deposition (CVD) system and observed ex situ by a conventional TEM. Single-walled CNTs (SWNTs) have been grown on silicon nanowires (SiNWs) by ethanol CVD with Co catalyst. It has been clarified that the surface SiOx layers of SiNWs inhibit the diffusion of Co into Si. By detailed TEM observations of the root of SWNTs, it has been found that the diameter of SWNTs correlates with that of catalyst nanoparticles. The diameter ratio of catalyst nanoparticles to SWNTs is 1.0 to 1.7 and there is no SWNT whose diameter is larger than that of catalyst nanoparticles.
Theory of ETEM image formation has been outlined and applied to simulating high-resolution TEM images of SWNTs in source gases for the investigation of the effect of gases on TEM images. It has been demonstrated that SWNTs can be observed under an actual growth condition. Thus, the ETEM is one of the promising tools for in situ observations of the growth of CNTs.
The growth of CNTs have been observed in situ by ETEM. A short multi-walled CNT was grown from a Co catalyst nanoparticle, and then transformed to a carbon onion. Its mechanism has been discussed. Discontinuous and rotational growth of CNT have also observed. When the CNT contacts with the substrate, the contact position repeats stick and slip; therefore the CNT grow discontinuously. It has been found that the growth direction of the CNT fluctuates hard when the CNT does not contact with the substrate.
EELS spectra of ethanol, methane, and acetylene, which are source gases of CNTs, have been measured using the ETEM. Features of the low loss spectra and the C-K energy-loss near edge structure (ELNES) depend on the kind of gases. We have also calculated the ELNES of gases by a first principles molecular orbital method. Calculated spectra for Slater's transition state have reproduced experimental ELNES. Moreover, we have observed the decomposition of ethanol molecules during the growth of CNT by EELS.