Fig. 2 shows the XPS sputter depth profiles of the coating systems
produced by process paths A and B. The chemical composition mainly
differs in the oxygen and carbon contents within the films. The bulk of
the plasma polymer film, which undergoes a heat treatment at
environmental atmosphere (process path A) contains 28.3 at.% silicon,
36.7 at.% carbon and 33.8 at.% oxygen. The bulk of the plasma polymer
film, which is applied to the already alloyed metallic overlay (process
path B), contains 29.3 at.% silicon, 48.3 at.%carbon and 22.0 at.% oxygen.
The oxygencontent of heat-treated plasmapolymer films is significantly
higher than that of the not heat-treated plasma polymer. In contrast to
this, the carbon content is lower. Only the silicon content remains
approximately constant. The reasons for the presence of oxygen in the
not heat-treated film are versatile. On the one hand, the residual gas in
the vacuum chamber contains a significant part of oxygen containing
species resulting from desorption processes from the walls, parts of the
setup etc., this desorption becomes enhanced by the plasmaprocess. On
the other hand, the native oxide layer on the metal surface becomes
sputtered in the first seconds of the plasma process as well. It was
already shown by other groups, that these oxygen containing species
become re-incorporated in the film during the deposition process [15].
FT-IRRA spectra shown in Fig. 3 support the results of XPS. The peak
in the wave number region between 1045 cm−1 and 1100 cm−1,
indicating the Si–O–Si/Si–O–C-stretching vibrations, is much more
distinct in the spectrumof the plasma polymer film thatwas exposed to
the heat treatment (process path A) compared to the according peak of
the not heat-treated plasma polymer film (process path B). This
indicates a higher amount of oxygen-containing bonds in the heattreated
plasma polymer film. Inaccordance to this, the Si–CH3 stretching
as well as the Si–C rocking vibrations at 840 cm−1 are less prominent,
when plasma polymer was exposed to a heat treatment. At 2100 cm−1
the plasma polymer on the sample produced by process path B shows a
small peak revealing the stretching vibrations of Si–Hbonds. This peak is