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Chapter 6
Since the current has to be transported millimeters in the lateral direction, against less
than a micrometer in the vertical direction, the grain size was determined only in the
horizontal direction. Since most of the grains have a columnar structure, the average
grain size was obtained by measuring only the cross-section at the surface. The axis of
the grains perpendicular to the surface has thus not been taken into account.
It was observed that not all the samples crack in a similar way. This can partly be
o
explained by etching conditions, but it was noted that the 200C sample broke in a
burst-like fashion, while the RT sample broke more homogeneously. This difference
might be caused by difference in grain size.
Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) imaging was performed
using an Ion-Tof TOF-SIMS IV instrument, operated in positive and negative mode,
+
using a high current 25 keV Bi beam of ~3 μm diameter. Depth profiling was only
+
performed in negative mode, using 2 keV Cs ions for sputtering. The depth scale
calibration was based on the thickness of the RT sample as determined by HIM.
Determination of the water content was executed by a Prodigy High Dispersion
Induced Coupled Plasma – Mass Spectrometer (ICP-MS).
6.3 Results
6.3.1 Damp heat treatment
6.3.1.1 Structural properties
ZnO:Al films were deposited by radio frequency (RF) magnetron sputtering for 50
min by room temperature (RT) and 200 C. These samples were studied and recorded
o
before, during and after degradation by camera, optical microscope, SEM-EDX and
HIM. In Table 6.2 , the deposition conditions and the initial material properties are
summarised. The grain sizes and thicknesses are obtained from the HIM photographs
shown in Figure 6.2 and Figure 6.3. These measurements showed that before
degradation, the thickness of the 200C sample (490 nm) was smaller than the RT
o
sample (620 nm). The grain size of the 200 C sample was larger than for the RT sample.
o
The roughness of the films was similar within the error margin.
The decreased deposition rate and increased grain size for the elevated deposition
temperature can be explained by the influence of the substrate temperature on the
mobility of the adsorbed atoms and therefore on the resulting structural development
of the film: a substrate with a low temperature has a low adatom (adsorbed atom)
mobility and tends to form crystallite structures that are highly porous, low in density
and have rough surfaces. Higher substrate temperatures on the other hand enhance
182
Since the current has to be transported millimeters in the lateral direction, against less
than a micrometer in the vertical direction, the grain size was determined only in the
horizontal direction. Since most of the grains have a columnar structure, the average
grain size was obtained by measuring only the cross-section at the surface. The axis of
the grains perpendicular to the surface has thus not been taken into account.
It was observed that not all the samples crack in a similar way. This can partly be
o
explained by etching conditions, but it was noted that the 200C sample broke in a
burst-like fashion, while the RT sample broke more homogeneously. This difference
might be caused by difference in grain size.
Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) imaging was performed
using an Ion-Tof TOF-SIMS IV instrument, operated in positive and negative mode,
+
using a high current 25 keV Bi beam of ~3 μm diameter. Depth profiling was only
+
performed in negative mode, using 2 keV Cs ions for sputtering. The depth scale
calibration was based on the thickness of the RT sample as determined by HIM.
Determination of the water content was executed by a Prodigy High Dispersion
Induced Coupled Plasma – Mass Spectrometer (ICP-MS).
6.3 Results
6.3.1 Damp heat treatment
6.3.1.1 Structural properties
ZnO:Al films were deposited by radio frequency (RF) magnetron sputtering for 50
min by room temperature (RT) and 200 C. These samples were studied and recorded
o
before, during and after degradation by camera, optical microscope, SEM-EDX and
HIM. In Table 6.2 , the deposition conditions and the initial material properties are
summarised. The grain sizes and thicknesses are obtained from the HIM photographs
shown in Figure 6.2 and Figure 6.3. These measurements showed that before
degradation, the thickness of the 200C sample (490 nm) was smaller than the RT
o
sample (620 nm). The grain size of the 200 C sample was larger than for the RT sample.
o
The roughness of the films was similar within the error margin.
The decreased deposition rate and increased grain size for the elevated deposition
temperature can be explained by the influence of the substrate temperature on the
mobility of the adsorbed atoms and therefore on the resulting structural development
of the film: a substrate with a low temperature has a low adatom (adsorbed atom)
mobility and tends to form crystallite structures that are highly porous, low in density
and have rough surfaces. Higher substrate temperatures on the other hand enhance
182
