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Degradation mechanisms of the molybdenum back contact
5.3.1.2 Visual degradation
The visual degradation of molybdenum occurs quickly and follows different paths
for the selenised and non-selenised samples. Photographs of the surface were taken
after each degradation step to see the visible changes on the surface of the samples.
The photographs taken after 17, 33 and 105 hours are depicted in Figure 5.3, Figure 5.4
and Figure 5.5 respectively.
Before degradation, no visual difference could be observed between the six samples,
except for a discolouration at the edge of the selenised samples. This discolouration
was caused by the sample holder used during selenisation, which covered the edge
of the samples, so these regions are not selenised. These regions therefore degraded
different from the rest of the samples, as can be seen in Figure 5.3 and are not
representative for the degradation of selenised molybdenum.
After 17 hours of degradation of 85°C/85% RH exposure, a clear difference could be
observed between the selenised and the non-selenised samples ( Figure 5.3). The non-
selenised samples had large degraded areas with layered colours, while the selenised
samples had only small spots on the surface and some larger coloured spots at the
edge. On the Mo15Se sample, dark spots from four point probe (4PP) measurements
could be seen, indicating this porous material was very easily damaged by mechanical
loads. This damage was not observed for the non-selenised Mo15 samples.
o
After 33 hours under 85C/85% RH conditions (Figure 5.4), the samples still showed
two distinctly different degradation patterns. The non-selenised samples showed the
layers of coloured molybdenum oxide surrounded by large grey areas on the edges,
Figure 5.3
Photographs of the samples (30x25 mm) after 17 hours exposure to 85°C/85% RH.
135
5.3.1.2 Visual degradation
The visual degradation of molybdenum occurs quickly and follows different paths
for the selenised and non-selenised samples. Photographs of the surface were taken
after each degradation step to see the visible changes on the surface of the samples.
The photographs taken after 17, 33 and 105 hours are depicted in Figure 5.3, Figure 5.4
and Figure 5.5 respectively.
Before degradation, no visual difference could be observed between the six samples,
except for a discolouration at the edge of the selenised samples. This discolouration
was caused by the sample holder used during selenisation, which covered the edge
of the samples, so these regions are not selenised. These regions therefore degraded
different from the rest of the samples, as can be seen in Figure 5.3 and are not
representative for the degradation of selenised molybdenum.
After 17 hours of degradation of 85°C/85% RH exposure, a clear difference could be
observed between the selenised and the non-selenised samples ( Figure 5.3). The non-
selenised samples had large degraded areas with layered colours, while the selenised
samples had only small spots on the surface and some larger coloured spots at the
edge. On the Mo15Se sample, dark spots from four point probe (4PP) measurements
could be seen, indicating this porous material was very easily damaged by mechanical
loads. This damage was not observed for the non-selenised Mo15 samples.
o
After 33 hours under 85C/85% RH conditions (Figure 5.4), the samples still showed
two distinctly different degradation patterns. The non-selenised samples showed the
layers of coloured molybdenum oxide surrounded by large grey areas on the edges,
Figure 5.3
Photographs of the samples (30x25 mm) after 17 hours exposure to 85°C/85% RH.
135
