Effect of growth temperature on the synthesis of carbon nanotube arrays and amorphous carbon for thermal applications

Though carbon nanotube (CNT) arrays have tremendous potential due to their attractive mechanical, electrical, and thermal properties, the growth kinetics of CNTs are still not fully understood. Thus, we report on the effect of synthesis parameters, such as growth temperature, on the resulting arrays. In this work, CNT arrays were synthesized using catalytic chemical vapor deposition (CCVD) with furnace temperatures varying from 680 to 900 degrees C. Microscopy was used to investigate the effect of growth temperature on the structural properties, such as tube diameter, array length, and the amount of amorphous carbon produced at the top of the canopy as a growth by-product. Additionally, Raman spectroscopy was used to elucidate the effect growth temperature has on the resulting purity of the CNTs. It was then revealed that crystalline inhomogeneity exists along the length of the tubes with respect to crystallinity. Transmission electron microscopy (TEM) further determines the degree of tube crystallinity as well as the thickness of amorphous carbon coating around the nanotubes. Through both microscopy and spectroscopy, we found two distinct temperature regimes within the range of 680-900 degrees C. Below 800 degrees C, the growth of tube length and diameter remained relatively stagnant followed by a rapid growth rate above 800 degrees C with the highest tube crystallinity obtained within the regime of 800-840 degrees C. This indicates the presence of an important transitional temperature for CNT CCVD growth. Additionally, growth temperature was determined to play an important role in the amount of the resulting amorphous carbon by-product. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim