The effects of temperature and catalyst grain sizes on the properties and characterization of CCVD grown CNTs investigated by micro-Raman spectroscopy

In order to investigate the optimum growth mechanism, carbon naotubes (CNTs) were grown on the Si(100) substrates by catalytic chemical vapor deposition (CCVD) using C2H2 as the carbon source. Various growth conditions were employed for the synthesis of vertically aligned CNTs by controlling the temperature of the CCVD reactor and also the grain sizes of the catalytic. The used catalytic was Y2O3 in three categories of sizes. In this study, we used C2H2 at fixed optimum pressure and temperature for the growth of CNTs. Carrier gases consisting of Ar and H-2 were used for the transport of the carbon source. The process involves passing a hydrocarbon vapor, typically for 5 minutes, through a tube furnace in which Y2O3 material on Si surface was present at sufficiently high temperature (850 degrees C) to decompose the hydrocarbon. Y2O3 powders with different nano-grain sizes were prepared by using co-precipitation technique. Raman scattering measurements showed that uniform CNTs with different dimensions were grown on the Si faces and the relative intensity and the position of some Raman peaks can be controlled by modulating the size of the catalytic particles in the thermal CVD. Effects of catalyst composition on morphology of CNTs were also studied by Raman spectroscopy. Our results shows that better quality CNTs can be achieved with smaller sizes of catalysts. The growing mechanism of CNTs was not totally clear in the process, what can be pictured is the crucial effect of catalyst on the initial stage of carbon atom deposition. The present results provide useful information for achieving diameter-controlled growth of CNTs. Nevertheless, it is still hard to control nanotube diameter or chirality, which is the ultimate issue to resolve if we are to maximize their potential as one-dimensional nanowire.