Biomedical Engineering Reference
In-Depth Information
Figure 14.5
Three-layer CNP performance characteristics. (a) Bulk gain
values,and(b)electricfielddistributionandthenormalizedPoyntingvector
field:
S
inc
+
S
ext
[17].
503.3 nm from 513.3 nm. Any metal coated IO design would
involve only a thin outer coating to not significantly change the
resonancefrequencyand,assuch,wouldbeamenabletofabrication
chemistries. As one observes in Fig. 14.5a, the addition of this
thin layer significantly improves upon the original active IO CNP's
performance characteristics. Similarly, the addition of a 5.0 nm Au
core to the original two-layer Ag/SiO
2
design yields a three-layer
design with two resonant frequencies. The first resonance occurs
with
κ
=−
0.291 at a wavelength of 504.4 nm, and the second
resonance occurs at a wavelength of 507.7 nm with
κ
=−
0.605.
Itsperformancecharacteristicsarequitecompetitivewiththeother
two-layerand three-layer nano-amplifierdesigns.
These successful multilayer geometries encouraged our consid-
eration [18] of realistic gain media in our active CNP designs. In
particular, quantum-dots (QDs) provide an exciting option for the
gain media because they possess large gain coe
cients resulting
from their extreme confinement effects. The optical properties of
core/shell QDs can be tuned by changing the relative size of the
core/shell, that is, by effectively changing their band gap structure.
Similarly, as noted previously, the resonance of a CNP can be
adjustedbychangingtherelativesizesofitslayers.Asshownin[18],
locating the QDs inside a resonant CNP structure is again optimal; it
greatly enhances the intrinsic amplifying behavior of the combined
QD-CNPsystem.
