Physical Methods for the Preparation of Cobalt Nanoparticles for Use in the Synthesis of Multiwalled Carbon Nanotubes

The aim of this work was to obtain cobalt nanoparticles through a physical method, which could be formed simultaneously during the Catalytic Chemical Vapour Deposition (CCVD) synthesis of carbon nanotubes, under conditions suitable for both carbon nanotube synthesis and Co-nanoparticle formation. Co nanoparticles were prepared by Physical Vapour Deposition (PVD) using a 0.05 m3 magnetron on two different substrates, SiO2/Si and C, followed by a reduction treatment in an H2 atmosphere. Transmission Electron Microscopy (TEM) and Field Enhanced Scanning Electron Microscopy (FE-SEM) were used to characterize the Co nanoparticles. On the SiO2/Si substrate, cobalt silicate is formed, which stabilizes the Co nanoparticles, while the nanoparticles obtained on the C-substrate are sometimes surrounded by a layer of Co3O4, which deactivates the cobalt nanoparticles. To obtain suitable Co nanoparticles for carbon nanotube synthesis, the optimal Co-layer thickness is between 20 and 30 Å, and the optimal reduction temperature is 800 °C and 450 °C for SiO2/Si and C substrates, respectively.