Low-temperature catalyst activator: mechanism of dense carbon nanotube forest growth studied using synchrotron radiation
| Autor: | Akio Kawabata, Naoki Yokoyama, Eiji Ikenaga, Tomo Murakami, Masato Kotsugi, Mizuhisa Nihei, Takayuki Muro, Yudai Izumi, Takuo Ohkochi, Tomohiro Matsushita, Akito Takashima |
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| Rok vydání: | 2014 |
| Předmět: |
Absorption spectroscopy
Annealing (metallurgy) Photoemission spectroscopy Nanoparticle soft X-ray photoemission spectroscopy (SXPES) Carbon nanotube X-ray absorption spectroscopy (XAS) Biochemistry Catalysis law.invention law photoemission electron microscope (PEEM) General Materials Science hard X-ray photoemission spectroscopy (HAXPES) thermal chemical vapor deposition growth mechanism Crystallography synchrotron radiation Chemistry General Chemistry Condensed Matter Physics Research Papers dense vertically aligned carbon nanotubes Chemical state Photoemission electron microscopy Chemical engineering QD901-999 |
| Zdroj: | IUCrJ IUCrJ, Vol 1, Iss 4, Pp 221-227 (2014) |
| ISSN: | 2052-2525 |
| Popis: | The mechanism of dense vertically aligned carbon nanotube growth achieved by a recently developed thermal chemical vapor deposition method was studied using synchrotron radiation spectroscopic techniques. The mechanism of the one-order-of-magnitude increase in the density of vertically aligned carbon nanotubes (CNTs) achieved by a recently developed thermal chemical vapor deposition process was studied using synchrotron radiation spectroscopic techniques. In the developed process, a Ti film is used as the underlayer for an Fe catalyst film. A characteristic point of this process is that C2H2 feeding for the catalyst starts at a low temperature of 450°C, whereas conventional feeding temperatures are ∼800°C. Photoemission spectroscopy using soft and hard X-rays revealed that the Ti underlayer reduced the initially oxidized Fe layer at 450°C. A photoemission intensity analysis also suggested that the oxidized Ti layer at 450°C behaved as a support for nanoparticle formation of the reduced Fe, which is required for dense CNT growth. In fact, a CNT growth experiment, where the catalyst chemical state was monitored in situ by X-ray absorption spectroscopy, showed that the reduced Fe yielded a CNT forest at 450°C. Contrarily, an Fe layer without the Ti underlayer did not yield such a CNT forest at 450°C. Photoemission electron microscopy showed that catalyst annealing at the conventional feeding temperature of 800°C caused excess catalyst agglomeration, which should lead to sparse CNTs. In conclusion, in the developed growth process, the low-temperature catalyst activation by the Ti underlayer before the excess Fe agglomeration realised the CNT densification. |
| Databáze: | OpenAIRE |
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