Ethanol-Promoted High-Yield Growth of Few-Walled Carbon Nanotubes

We report the use of a small concentration of ethanol in addition to ethylene as the carbon source for growth of dense vertically aligned forests of few-walled carbon nanotubes (CNTs) Through a detailed comparison of CNTs vi own with and without ethanol added to the C2H4/H-2 feedstock, we quantify several important effects of the ethanol addition We show that ethanol selectively reduces the number of CNT walls without changing the outer diameter, increases the catalyst lifetime more than 3-fold, and increases the rate of carbon conversion more than 5-fold Online dewpoint and mass spectrometry measurements of the exhaust stream suggest that ethanol decomposes into active carbon species that enhance growth, and into H2O, which counteracts the accumulation of amorphous carbon and thus prolongs the catalyst lifetime We performed a systematic study of the effect of the catalyst film thickness, and identify a set of conditions that provides growth of millimeter-tall double-walled CNT forests Importantly, our study reveals that the chemistry or the CVD atmosphere alone. plays a critical role in controlling the structure of CNTs, and that addition of ethanol results in few-walled CNTs over a broad range of growth conditions These findings ale an important step toward the ultimate goal of control of CNT chirality during synthesis as well as toward realization of important large-scale applications of aligned CNT films having high monodispersity and structural quality.