The effect of changes in synthesis temperature and acetylene supply on the morphology of carbon nanocoils

Carbon nanocoils (CNCs) with controlled shape, coil diameter and coil pitch have been synthesized in a chemical vapor deposition (CVD) system by changing the reaction temperature and acetylene flow rate. It is found that three-dimensional CNCs are produced at a lower temperature (700-770 °C), while a higher temperature (810 °C) leads to the growth of straight carbon nanofibers (CNFs). CNC-CNF hybrid structures are produced by increasing growth temperature from 750 to 810 °C during a single synthesis run, while CNF-CNC hybrid structures are produced by decreasing the temperature from 810 to 750 °C. Similarly, by changing growth temperature from 750 to 810 °C and then back to 750 °C during a single run, CNC-CNF-CNC complex hybrid structures can be obtained. During the CVD process, the pulsing of acetylene and the changing of acetylene flow rate are also found to be effective in controlling the structure of CNCs. CNCs with periodic helical structures can be produced by interrupting the acetylene flow or changing its flow rate periodically. It is found that the higher the flow rate of acetylene, the smaller the coil pitch and diameter of the grown CNCs.