Chemical interaction of Fe, Ni and Au with poly(vinyl chloride) and poly(tetrafluoroethylene) during thermal evaporation and the effect of post-metallization X-ray irradiation studied by in situ X-ray photoelectron spectroscopy - Polyimides and Other High Temperature Polymers - page 345

2. EXPERIMENTAL
Metal deposition and X-ray photoelectron spectroscopy (XPS) measurements
were carried out in the same ultrahigh vacuum (UHV) chamber. A typical base
pressure of 1 x 10 -8 Torr was maintained during data collection and of 5 x 10 -7
Torr during metal deposition. All XP spectra were acquired at 15 kV and 300 W
with a 45° take-off angle from the sample normal using a Mg K α source. Elemen-
tal scans used a pass energy of 44.75 eV and 0.125 eV/step. Binding energy scales
were referenced to literature values of known peaks in each elemental region (i.e.
CHCl in native PVC and CF 2 in native PTFE). XPS data fitting was performed
using 100% Gaussian line shapes using Shirley background subtraction [18]. In
situ post-metallization X-ray irradiation was performed using the same irradiation
source as used for data collection. PVC and PTFE substrates were prepared as de-
scribed in previous publications [16, 19].
The metal (Au, Ni, Fe) evaporation sources were prepared as described previ-
ously using a shrouded tungsten filament wrapped with the deposition metal and
heated using a DC power supply [16, 19]. The source was degassed until pure
metal (free of oxygen and carbon contamination) was deposited on a Au sample,
as determined by XPS. NiCl 2 (Aldrich, 98%), FeCl 2 and FeCl 3 (Aldrich, 98%)
reference samples were mounted on carbon tape prior to XPS analysis. In these
experiments, the position of the halide peak was used to calibrate the XPS binding
energy scale.
3. RESULTS
3.1. PVC
Figure 1 shows comparative spectra of the Cl(2p) region as well as the major
relevant metal transitions for the Au/PVC, Ni/PVC and Fe/PVC systems follow-
ing metallization of native PVC. In the native polymer, the Cl(2p) region consists
of a Cl(2p 3/2 /2p 1/2 ) doublet at 200.0 eV and 201.6 eV respectively, associated with
the CHCl groups present (not shown). During Au, Ni and Fe deposition, a reduc-
tion in the CHCl component in the C(1s) region was observed (not shown), in-
dicative of C-Cl bond cleavage during metallization. Metal deposition on PVC
also resulted in a broadening of the Cl(2p) envelope to lower binding energy con-
sistent with the formation of a new set of Cl(2p 3/2 /2p 1/2 ) peaks between 198-200
eV, indicative of Cl - formation (Figure 1) [20].
Although additional bands associated with Au + in the Au(4f) region are ob-
scured by the metallic envelope during Au deposition on PVC, the presence of Cl -
ions in the Cl(2p) region indicates production of AuCl [20, 21]. During Ni deposi-
tion on PVC, the Ni(2p 3/2 ) region exhibits two peaks (Figure 1(b)). On the basis of
literature values, the 852.0 eV peak is assigned to metallic nickel and the peak at
855.0 eV to Ni 2+ [20]. In conjunction with the changes observed in the Cl(2p) re-
gion, this indicates the formation of NiCl 2 during metallization. Figure 1(c) shows