Filament poisoning at typical carbon nanotube deposition conditions by hot-filament CVD
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We report on the poisoning of tungsten filaments during the hot-filament chemical vapour deposition process at typical carbon nanotube (CNT) deposition conditions and filament temperatures ranging from 1400 to 2000 °C. The morphological and structural changes of the filaments were investigated using scanning electron microscopy and X-ray diffraction, respectively. Our results conclusively show that the W-filament is not stable during the carburization process and that both mono- and ditungsten-carbides form within the first 5 min. Cracks and graphitic microspheres form on the carbide layer during the first 15 min at the temperatures ≥1600 °C. The microspheres subsequently coalesce to form a graphite layer, encapsulating a fully carburized filament at the temperature of 2000 °C after 60 min, which inhibits the catalytic activity of the filament to produce atomic hydrogen. The structural changes of the filament also induce variations in its temperature, illustrating the instability of the filament during the deposition of CNTs.
KeywordsCarburization Filament Temperature Silicon Thin Film Deposition Pressure Carbon Microsphere
The authors acknowledge the financial support of the Department of Science and Technology, the National Research Foundation and the Council for Scientific and Industrial Research (Project No. HGERA2S) of South Africa. The authors are especially thankful to Mr. Adrian Josephs (Microscopy Unit, University of the Western Cape) for his assistance with the SEM measurements and sample preparation.
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