To understand the substrate effect on the CNT growth, all the
treated substrate samples along with the control substrate were
first heated in the CVD furnace up to the CNT growth temperature
of 700 °C and kept at that temperature for 30 min in an Ar
atmosphere without any chemical flow. These samples were
allowed to cool to room temperature in the Ar atmosphere, and
surface property analysis was carried out using the XPS technique.
The survey spectra of all the samples revealed that the peaks
were mainly contributed by the compounds of iron and chromium.
Nickel remained undetectable on all the surfaces of both the
as-received and the treated samples. Figure 2a,b shows the XPS
spectra of Cr 2p3/2 and Fe 2p3/2 for the as-received and 1, 5,
and 10 min treated stainless steel samples. An intense chromium
signal is observed on the surface of the as-received stainless
steel foil, with almost no detectable iron peak. This is due to the
presence of the chromium-rich passive oxide film on the surface
of the stainless steel.25 Generally, the chromium-rich passive
oxide film is believed to protect stainless steel from corrosion.
As the sample is treated in the 9 M sulfuric acid, a gradual
decrease in the intensity of the chromium signal and an increase
in the iron signal are noticed with the increase in the treatment
time from 1 min to 10 min. This suggests that chromium is being
depleted from the surface of the treated samples.