Magnetic properties of core-shell catalyst nanoparticles for carbon nanotube growth

Two types of core-shell nanoparticles have been prepared by laser pyrolysis using Fe(CO)5 and C2H2 or [(CH3)3Si]2O as precursors and C2H4 as sensitizer. The first type (about 4 nm diameter) – produced by the decomposition of Fe(CO)5 in the presence of C2H4 and C2H2 – consists of Fe cores protected by graphenic layers. The second type (mean particle size of about 14 nm) consists also of Fe cores, yet covered by few nm thick γ-Fe2O3/porous polycarbosiloxane shells resulted from the [(CH3)3Si]2O decomposition and superficial oxidation after air exposure. The hysteresis loops suggest a room temperature superparamagnetic behavior of the Fe-C nanopowder and a weak ferromagnetic one for larger particles in the Fe-Fe2O3-polymer sample. Both types of nanoparticles were finally used as a catalyst for the carbon nanotube growth by seeding Si(100) substrates via drop-casting method. CNTs were grown by Hot-Filament Direct. Current PE CVD technique from C2H2 and H2 at 980 K. It is suggested that the increased density and orientation degree observed for the multiwall nanotubes grown from Fe-Fe2O3-polymer nanoparticles could be due to their magnetic behavior and surface composition.