High temperature activation and deactivation of single-walled carbon nanotube growth investigated by in situ Raman measurements

A decrease of nanotube yield is usually observed at high temperature. Here, we report on the origins of the activation and deactivation of the SWCNT growth in this high temperature range (between 700 °C and 850 °C) based on in situ Raman measurements. We observed that, at high temperature, carbon precursors such as ethanol and methane readily reduce metal oxide such as Co₃O₄. Once reduced, the size distribution of the catalyst particles quickly evolves at high temperature leading to a dramatic deactivation of the nanotube growth. An oxidizing pre-treatment has a stabilizing effect on the catalyst. In addition, we evidenced a threshold partial pressure of the carbon precursor to initiate the growth. This threshold partial pressure sets a second requirement for activating the nanotube growth in addition to the requirement of reducing the catalyst.