Catalytical growth of carbon nanotubes/fibers from nanocatalysts prepared by laser pulverization of nickel sulfate

Dispersed nickel sulfate (NiS O4) microclusters on Si substrates were fragmented by pulsed excimer laser irradiation to serve as catalysts for carbon nanotube/nanofiber (CNT/CNF) growth. At proper fluences, NiS O4 clusters were pulverized into nanoparticles. The sizes of clusters/nanoparticles were found to be dependent on laser fluence and laser pulse number. By increasing the laser fluence from 100 to 300 mJ cm2, the size of disintegrated particles decreased drastically from several micrometers to several nanometers. It was found that laser-induced disintegration of as-dispersed NiS O4 clusters was mainly due to physical fragmentation by transient thermal expansion/contraction. Thermal melting of nanoparticles in a multipulse regime was also suggested. Hot-filament chemical vapor deposition (HFCVD) was used for growth of CNTs from the pulsed-laser treated catalysts. For samples irradiated at 100 and 200 mJ cm2, CNFs were dominant products. These CNFs grew radially out of big NiS O4 clusters, forming dendritic CNF bunches. For samples irradiated at 300 mJ cm2, dense multiwalled carbon nanotubes (MWCNFs) with uniform diameters were obtained. It is suggested that elemental Ni was formed through thermal decomposition of NiS O4 clusters/nanoparticles during HFCVD. The size and the shape of the Ni aggregation, which were determined by the initial size of NiS O4 clusters/nanoparticles, might affect the preference in the synthesis of CNTs or CNFs.