Temperature effect on the synthesis of carbon nanotubes and core–shell Ni nanoparticle by thermal CVD

• The CVD fabrication processes of carbon nanostructures is enhanced in order to obtain either core–shell nanoparticles or MWCNT with high efficiency
• The temperature may be a fine tune tool in order to differentiate the carbon product on the CVD process
• The relation between the diameter of the metal catalyst and the velocity of diffusion of the C is an important parameter in order to define the carbon nanostructure.

The synthesis of carbon nanostructures has been studied for the past two decades, not only for their excellent electrical, physical and thermal properties but also due to their potential applications on different kinds of sciences, including medical and biological ones. In this sense, the CVD technique has shown very good results in terms of quality and quantity in the synthesis of these nanostructures. Unfortunately, some problems have been presented in the successful fabrication of carbon nanotubes and Ni core–shell nanoparticles in terms of quality, quantity and separation of both nanostructures. For this reason, in this work carbon nanostructures were synthetized by CVD utilizing CH4 as the carbon precursor gas, on Ni/SiO2 catalytic substrates with different nickel thicknesses (15, 10, 5, 2 nm), at different temperatures (900 °C, 800 °C, 700 °C). The samples were analyzed by Raman spectroscopy, SEM and TEM; the results indicate a majority formation of multi-walled carbon nanotubes (MWCNT) at lower temperatures and Ni thickness, and a formation of Ni core–shell nanoparticles at higher temperatures, leaving a total control on the process in order to obtain both nanostructures only with a few variation of the temperature and avoiding the separation post-process.