Nanocrystallized steel surface by micro-shot peening for catalyst-free carbon nanotube growth

Nanocrystallized steel surface by micro-shot peening (MSP) were applied to carbon nanotube growth in this study. Micro-shot peening treatment severely deformed steel surface and nanocrystallized surface layer was formed by the plastic deformation. The grain sizes of the nanocrystallized layer were 10–30 nm after 300 s of MSP treatment. On the nanocrystallized surface, carbon nanotubes were formed with thermal chemical vapour deposition without catalysts. Before carbon nanotube growth, the nanocrystallized steel surface was reduced with H2/N2 gas at 600 °C. The carbon nanotube growth was performed at 600 °C with C2H2 gas carried by H2/N2 gas. The carbon nanotubes formed on the nano-structured surface was multi-walled carbon nanotube and the diameter was 10–20 nm. The reduction process before carbon nanotube growth was essential to form carbon nanotubes on the nanocrystallized surface with MSP.