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Chapter 5
5.3.2.4.3 XPS measurements
XPS was used to determine the chemical environment of the elements in order to
learn the molecular structure of the reaction products. The reported results are only
for the surface composition, due to the very low penetration depth of XPS.
The survey spectra of Mo25/2 before and after degradation and Mo25/15 after
degradation are displayed in Figure 5.24.
O 1s Na KLL
Na 1s O KLL Mo 3p Mo 3d
Mo 4p
Mo15 - degraded
Mo2 - degraded
10 4 counts/sec 10 5 Mo2 - non-degraded
0
1200 1000 800 600 400 200 0
Figure 5.24 Binding energy (eV)
The survey XPS spectra of the non-degraded Mo25/2 and Mo25/2 and Mo25/15 after 150 hours exposure to 85 o C/85% RH.
The non-degraded molybdenum sample as obtained by the lift-off process exhibits
molybdenum and selenium signals pointing out the presence of MoSe, which is
2
formed during the CIGSe growth. Furthermore, sodium and oxygen signals with a
very low intensity are observed. These elements were expected, since sodium was
also present on the molybdenum side after the CIGSe layer lift-off process on other
samples, while the oxygen is rapidly incorporated due to air exposure. Indium and
gallium were not detected on the molybdenum side, which is unlike results obtained
in a previous study [12].
Figure 5.25 and Table 5.8 show more in-depth information about the sodium signals
as measured by XPS. After damp heat exposure, the sodium signal intensity increased
due to diffusion of sodium through the molybdenum layer. The surface of the
degraded molybdenum samples contained the same amount of sodium, while the
chemical environment of the sodium for both the degraded and the non-degraded
samples were similar, since they all showed the same binding energy and line shape.
The similar binding energy and shape indicated that the sodium must be in the same
chemical environment before and after degradation. The modified Auger parameter
value α* is used to determine the composition of the sodium containing species.
156
5.3.2.4.3 XPS measurements
XPS was used to determine the chemical environment of the elements in order to
learn the molecular structure of the reaction products. The reported results are only
for the surface composition, due to the very low penetration depth of XPS.
The survey spectra of Mo25/2 before and after degradation and Mo25/15 after
degradation are displayed in Figure 5.24.
O 1s Na KLL
Na 1s O KLL Mo 3p Mo 3d
Mo 4p
Mo15 - degraded
Mo2 - degraded
10 4 counts/sec 10 5 Mo2 - non-degraded
0
1200 1000 800 600 400 200 0
Figure 5.24 Binding energy (eV)
The survey XPS spectra of the non-degraded Mo25/2 and Mo25/2 and Mo25/15 after 150 hours exposure to 85 o C/85% RH.
The non-degraded molybdenum sample as obtained by the lift-off process exhibits
molybdenum and selenium signals pointing out the presence of MoSe, which is
2
formed during the CIGSe growth. Furthermore, sodium and oxygen signals with a
very low intensity are observed. These elements were expected, since sodium was
also present on the molybdenum side after the CIGSe layer lift-off process on other
samples, while the oxygen is rapidly incorporated due to air exposure. Indium and
gallium were not detected on the molybdenum side, which is unlike results obtained
in a previous study [12].
Figure 5.25 and Table 5.8 show more in-depth information about the sodium signals
as measured by XPS. After damp heat exposure, the sodium signal intensity increased
due to diffusion of sodium through the molybdenum layer. The surface of the
degraded molybdenum samples contained the same amount of sodium, while the
chemical environment of the sodium for both the degraded and the non-degraded
samples were similar, since they all showed the same binding energy and line shape.
The similar binding energy and shape indicated that the sodium must be in the same
chemical environment before and after degradation. The modified Auger parameter
value α* is used to determine the composition of the sodium containing species.
156
