Laser synthesis of iron nanoparticles as effective catalysts for the growth of vertically aligned MWCNTs with amorphous shell.

Vertically aligned multi-walled carbon nanotubes (MWCNTs) are attractive for use in nanoelectronics, nanosensors, electrodes for energy storage and harvesting devices, composites, weaving yarns and many other devices. However, in order to reach practical relevance in these applications, the vertically aligned MWCNTs must be dense and sufficient height. Fulfilling those requirements is often challenging. Herein, we report production of high density vertically aligned MWCNTs with amorphous shell on iron nanoparticles by the modified CVD method in the tube flow reactor via catalytic pyrolysis of acetylene. The iron thin films of thickness from 0.5 to 68 nm were obtained by the pulsed laser deposition in droplet-free mode on single crystal silicon substrates (100). The obtained films of the thickness from 0.5 to 20 nm were arrays of nanoparticles with a size from 5 to 17 nm as a result of thermal annealing. These nanoparticles were used as catalysts for the growth of MWCNTs. SEM investigations have shown that height of the obtained vertically aligned MWCNTs depends on the thickness of the initial iron film. The height of the MWCNTs array of 42 µm was achieved on the iron nanoparticles obtained after annealing the metal film of 5 nm thickness. The growth temperature of the obtained MWCNTs array was 700 °C at the volume flow ratio of the CH and H(5%)/Ar gas mixture was 1:4. TEM investigations have shown that the diameter of the obtained MWCNTs reached 15-20 nm with amorphous shell thickness of 5-10 nm. Four distinguished Raman peaks at 1360, 1603, 2711, and 2932 cm- 1 correspond to the D-band, G-band, 2D-band, and (D + G)-band, respectively and confirm the formation MWCNTs with good graphitization.