Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 79
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near-field PL intensity and the presence of pits, however, are not sufficient to prove the
region is enhanced by the presence of Au NPs. In fact it is widely known that there can
be significant inhomogeneities in emission intensity and energy in InGaN quantum wells
[65-67]. One way of proving the presence of NPs is to correlate the spectral features of
the emission near the NP to those observed in the far-field. Specifically it is known that
there are strong changes in the strength of the electron-phonon coupling in the vicinity
of the Au NPs. Figure 5.13 shows the value of the Huang-Rhys parameter in the same
lx1 micron area imaged in Figure 5.12. This map is derived using the same fitting
algorithm used in the angle dependent measurements. It is clear that the area depicted
in Figure 5.12 region 3 has a much smaller value of S than that of Region 4. This
correlates well with the overall lower value of S for the Au NP sample when compared
with the reference, and hence suggests strongly that the emission near the pits is due to
5.9 Fluorescence Lifetime Imaging Microscopy
In order to clearly demonstrate the inhomogeneity of the lifetime and PL on a
small scale, I have made use of Fluorescence Lifetime Imaging Microscopy (FLIM) to
map the decay constant and intensity over a large region of the sample with ~300nm
resolution. Figure 5.14 demonstrates a clear difference between the homogeneity of
emission in the reference sample (panel c) and that of the Au NP sample (panel a).
Furthermore, the decay constants measured for the Au NP sample (panel b) show a
strong positive correlation between lifetime and intensity, whereas the decay constants
for the reference sample show no correlation with intensity at all. This inhomogeneity in
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Llopis, Antonio. Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures, dissertation, May 2012; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc115113/m1/89/: accessed April 29, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .