Biomedical Engineering Reference
In-Depth Information
Figure 15.19
(a) Representative 30
◦
tilt angle SEM image of stacked
optical antennas (single antenna dimensions: 250 nm
×
90 nm
×
60 nm;
interparticle gap: 9 nm; overlapping length: 50 nm) (scalebar: 200 nm);
(b) SOA lateral cross section; (c,d) 2D field-enhancement (ratio between
the local and incident electric field) plots generated, respectively at the
longer and shorter resonance wavelengths, on a profile plane that cuts the
structure in the center.
top-down fabrication techniques, typically lithographic approaches,
present lacks of accuracy control in the sub-10 nm regime. A
way to overcome the problem consists in expanding the gap along
the vertical direction (i.e., out of plane), by a double patterning
process interspersed with the deposition of a thin dielectric layer
working as spacer. This combined process results in an overlapped
configuration, that is, in the fabrication of stacked optical antennas
(SOAs).
ThedesignofSOAshasbeencarriedoutrecurringtoasimulation
software thatsolvesEMequationsby means ofafiniteelement(FE)
code. A lateral cross section of the nanostructures is sketched in
Fig. 15.19b which clearly elucidates the nanocavity configuration
under study. The evolution of the gap profile suggests in principle
this device could support both stationary and propagating elec-
tromagnetic modes and, besides, there could exist variability in
the response of the system as function of light incidence angle.
Simulations have been performed, at first, for normal incidence
incoming plane wave and polarization parallel to the structure long
