Cold wall CVD generation of single-walled carbon nanotubes and in situ Raman scattering measurements of the growth stage

Abstract

Catalytic CVD generation of high-purity single-walled carbon nanotubes (SWNTs) without use of an electric furnace or a hot-filament is demonstrated. High-purity SWNTs were generated from alcohol used as a carbon source with Fe/Co particles supported on zeolite by Joule-heating of a silicon base plate. This technique was applied for an in situ measurement of Raman scattering during the growth stage in a vacuum chamber equipped with an SPM/Raman detector. The surface temperature was measured by a systematic shift in the silicon signal and kept at 850 °C. The G-band intensity of the SWNT Raman spectrum increased nearly linearly with time in the growth stage after an initial rapid increase. IntroductionThe discovery of single-walled carbon nanotubes (SWNTs) [1] has invoked numerous research interests because of their unique physical properties [2] and hence remarkable potential as a new material for various applications. The generation technique of SWNTs has since been developed by demands for specimens with sufficient amount and quality. Followed by the landmark establishment of the synthesis method in macroscopic amounts by laser-furnace [3] and arc-discharge [4] methods, several techniques employing the CVD approach [5-13] have been proposed for improved efficiency or productivity in the bulk synthesis of SWNTs. At present, CVD approaches, including the high-pressure CO (HiPco) technique [6,7], have become dominant for the mass production of SWNTs.As a new approach for higher-purity and lower-temperature generation, we have proposed the use of alcohol, particularly ethanol and methanol, for the carbon feedstock [14,15]. The proposed alcohol catalytic CVD (ACCVD) method can produce high-quality SWNTs when combined with appropriate catalysts and experimental procedures. Furthermore, it was recently demonstrated that high-quality SWNTs could be synthesized on a mesoporous-silica coated substrate [16] or directly on a solid substrate such as silicon or quartz [17,18]. Detailed comparisons of HiPco and ACCVD products are found in our recent papers [19,20], and the generation mechanism is discussed based on molecular

The dynamics of the nucleation, growth and termination of single-walled carbon nanotubes from in situ Raman spectroscopy during chemical vapor deposition

“…To compare more directly with other in situ Raman studies, a roughly linearly increasing G band with time was observed by Chiashi et al [1]. However, the time resolution was lower, growth was halted before saturation was observed, and other bands were not visible in situ.…”

“…An early spectroscopic study reported a linear increase in the G band signal during CVD using a zeolite/Fe Co-based catalyst and ethanol vapor as the carbon source [1]. In a combined Raman spectroscopy global Raman imaging (GRI) study, we were able to detect SWNTs as they formed in the reactor and to trace out the D and G band evolution [2].…”

Phases of Carbon Nanotube Growth and Population Evolution from in Situ Raman Spectroscopy during Chemical Vapor Deposition

“…In previous in situ Raman studies of CVD growth, Chiashi et al reported a linear increase in G band intensity during growth. 1 In subsequent work, we observed an exponential initial stage, as well as a gradual saturation stage for both D and G bands during low-temperature growth. 7 A similar shape for the Raman evolution can be discerned in data from laser heating CVD experiments.…”

Distinct termination morphologies for vertically aligned carbon nanotube forests

“…Forests were grown in a cold-walled CVD reactor (which provides excellent optical access to the sample [27][28][29][30]) operated at atmospheric pressure as described previously [21], with additional details given in other references [27,28]. Forests were imaged in situ through a large glass window using a long focal length optical microscope and camera at an ∼5…”