Biomedical Engineering Reference
In-Depth Information
concentration of carbon in oxidized form,
C
ox
, in consistency with alcohol, primary amine,
primary amide and ester functions. Accordingly,
O
org
= C
ox
- N = C
286.3
+ C
287.8
+ C
288.7
- N
tot
(1)
where the name of an element in italic designates its concentration and the number in
subscript designates the binding energy of the peak component. Errors would occur in case
of a high concentration of polysaccharides (
C
ox
/
O
= 6/5) or carboxyl (
C
ox
/
O
= 1/2) (Genet et
al., 2008 ; Landoulsi et al., 2008a).
The sum of the concentrations of the elements present in organic compounds is then given
by:
∑org = C
tot
+ O
org
+ N
tot
+ Si
org
= C
tot
+ C
ox
+ Si
org
(2)
For sake of uniformity, all spectral data involved in correlations below are ratioed to
∑org
(Table 2).
The concentration of the main elements or functions due to organic compounds, obtained at
photoelectron collection angle
θ
= 0°, is plotted in Figure 4 as a function of the same quantity
obtained at
θ
= 60°. A 1:1 relationship is obtained for all elements or functions and all
samples, indicating no significant effect of the photoelectron collection angle
θ
on the
relative contribution of the constituents of the organic adlayer.
4. Discussion
4.1 Passive film composition
Table 2 shows that the apparent concentrations of metal elements varied only slightly
according to the surface treatment. The main change concerned the decrease of the Fe
ox
concentration for sil+BS, sil+Gox and sil+BS+Gox samples. However, no change in the
shape of the Fe 2p
3/2
peak was observed (data not shown). For these samples, a significant
decrease of the molar concentration of
O
529.7
was also noticed (Table 2). It appears that the
oxide layer of SS passive film, after incubation in the aqueous medium for 48 h (nat sample),
was mainly constituted with a mixture of Fe and Cr oxides/hydroxides and small amounts
of partially oxidized Ni and Mo. This is in agreement with a previous study (Landoulsi et
al., 2008a), however in the latter, the stoichiometry of the passive film was not computed.
The O
1s component at 529.7 eV is due to metal oxides. By considering that Mo
ox
is in the
form of MoO
3
(Landoulsi et al., 2008a), the difference between the
O
529.7
concentration and
three times the Mo
ox
concentration should be due to Fe and Cr oxides. Figure 5 presents the
relation between this difference and the sum of Fe
ox
and Cr
ox
concentrations. All data show
reasonable linear regressions. The shift of the dots along the line when the photoelectron
collection angle changes from 0° to 60° is due to the presence of the organic constituents on
top of stainless steel. The average ratio between the
y
and
x
scales is 0.80 and 0.96 at
θ
= 0
and 60°, respectively; the slope of the regression lines is 1.03 (s.d. 0.23) and 1.42 (s.d. 0.12),
respectively. Thus, the ratio oxide/metal ions in chromium and iron oxyhydroxides is of the
order of 1 to 1.5.
The evaluation of the quantity of hydroxide associated to Fe and Cr is complex due to the
multiple chemical functions overlapping in the O
531.2
component. Ni
ox
is in the form of
Ni(OH)
2
(component at ~855.6 eV (Briggs & Seah, 1990, Zhou et al., 2006), spectra not
shown). The amount of oxygen associated to silane depends on the products of APTES
