Conclusions
In conclusion, an efficient and cost-effective method of
synthesizing highly aligned MWNTs directly on stainless steel
substrates is reported. XPS analysis reveals that the surface of
the as-received stainless steel is covered by a passive chromium
oxide film, which is not favorable for the growth of CNTs because
of catalyst poisoning. Treating the stainless steel in a strong
sulfuric acid for several minutes removes the passive layer and,
by enriching the surface with iron oxide, very much supports the
CNT growth. The density and alignment of the CNTs depend
on the ratio of the iron oxides to the chromium oxides and therefore
can be controlled by tuning the oxide ratio through chemical
treatment on the stainless steel surface. Controlled etching on
the substrate surface proves to be an effective method for the
site-selective growth of CNTs on electrically conductive substrates.