Environmental Engineering Reference
In-Depth Information
(a)
(b)
0.25
2
D
M
MC−DS
DC−MS
2.1
1.8
0.2
1.6
0.15
2
1.4
0.1
1.9
1.2
0.05
1
0
1.8
400
500
600
700
800
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
(c)
(d)
1.5
D
M
MC−DS
DC−MS
r 1 =7.5
r 1 =10
r 1 =12.5
1
1
0.5
0.5
0
0
400
500
600
700
800
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 7.10 a The real and imaginary parts of the refractive index of the active material; b the
spectral enhancement factors for various nanospheres. D denotes the dielectric sphere (n ¼ 4,
k ¼ 0), M denotes the metal silver sphere, MC-DS denotes the metal core-dielectric shell sphere,
and DC-MS denotes the dielectric core-metal shell sphere. The SiO 2 and Ag as a dielectric and
metal layers are adopted for the core-shell spheres; c the scattering cross-section (SCS) of the
nanospheres; d the SCS of the DC-MS sphere as a function of the core radius (nm). 2011 OSA;
Ref. [ 33 ]
respectively. As seen in Fig. 7.10 b, c, the peaks of the enhancement factors agree
with those of the SCS well. The small dielectric nanosphere, although has no
loss and large refractive index ð n ¼ 4 Þ , is not a good concentrator for OSCs.
The dielectric nanosphere with positive refractive index cannot produce strong
dipole resonance compared to the metal nanosphere. Moreover, in contrast to the
DC-MS sphere that has a metal layer adjacent to different materials (SiO 2 and
polymer), the resonance of the MC-DS sphere is blue-shifted, because only one
material SiO 2 with lower refractive index is adjacent to the metal layer. The near
field of the MC-DS sphere confines to the shell layer and cannot sufficiently scatter
to the active layer. As a result, the optical enhancement by the MC-DS sphere is
very weak. Figure 7.10 d shows a tunable plasmon resonance by engineering the
geometry of the DC-MS sphere. The resonance is red shifted and becomes damped
as the core radius increases.
Second, we investigate the plasmonic silver cavity structure enclosing the
active polymer material. Here the nanosphere is excluded. Figure 7.11 a shows the
spectral enhancement factor by the plasmonic cavity. A broadband enhancement
 
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