Page 214 - Principles and Applications of NanoMEMS Physics

5. NANOMEMS APPLICATIONS: PHOTONICS 203

of 8 is observed. When the wave is incident normal to the major axis (as
indicated by the dashed arrow), a broad resonance is observed at
λ = 380 nm , with a gap field enhancement of 40 with respect to the incident
illumination. 400

400
400
Scattering Cross Section(nm) Scattering Cross Section(nm) Scattering Cross Section(nm) 300
300
300

200
200
200
100
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100
0 0 0
400
300
300 400 500
300
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400
Wavelength(nm)
Wavelength(nm)
Wavelength(nm)
Figure 5-8. Scattering cross section (SCS) calculation of 50 nm diameter cylinders with 5 nm
separation. Illumination is in two different directions, as indicated by the arrows in the inset.
The incident field polarization is in-plane, perpendicular to the arrows. The dotted curve
corresponds to a single cylinder. [220].
5.3.2.5 Plasmonic Waveguides
The concept of exploiting the coupling of resonant SP fields between
adjacent metal nanoparticles to realize plasmon waveguides was studied by
Maier et al. [211] via finite-difference time-domain (FDTD) simulations and
experimentally. The FDTD simulations involved exciting a linear array of 50
nm Au spheres with a center-to-center spacing d = 75 nm , and driven by a

source dipole placed before the first particle. The driving pulse was centered
at 2.4 eV, the resonance energy of an individual particle and corresponding
to k = π d 2 , the highest group velocity waveguide mode. The pulse had a

width of 30 fs, equivalent to 95% of the bandwidth of the dispersion relation
for each polarization, and 24% of the total simulation time. For a linear chain
of nine nanoparticles, the FDTD simulations predicted group velocities of
7 . 1 × 10 7 m s / and . × 10 6 m s / for field excitations of transverse and
7
5
longitudinal polarization, respectively. Similarly, energy decay lengths,
estimated by monitoring the maximum field amplitudes at the center of each
particle and at the longitudinally polarized source, of 6dB/280nm and