Magnetic Properties Of Core-shell Catalyst Nanoparticles For Carbon Nanotube Growth

摘要

Two types of core-shell nanoparticles have been prepared by laser pyrolysis using Fe(CO)_5 and C_2H_2 or [(CH_3)_3Si]_2O as precursors and C_2H_4 as sensitizer. The first type (about 4 nm diameter) - produced by the decomposition of Fe(CO)_5 in the presence of C_2H_4 and C_2H_2 - 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-Fe_2O_3/porous polycarbosiloxane shells resulted from the [(CH_3)_3Si]_2O decomposition and superficial oxidation after air exposure. The hysteresis loops suggest a room temperature super-paramagnetic behavior of the Fe-C nanopowder and a weak ferromagnetic one for larger particles in the Fe-Fe_2O_3-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 C_2H_2 and H_2 at 980 K. It is suggested that the increased density and orientation degree observed for the multiwall nanotubes grown from Fe-Fe_2O_3-polymer nanoparticles could be due to their magnetic behavior and surface composition.