Biomedical Engineering Reference
In-Depth Information
[22] or structuring the metallic thin film's surface with a proper
grating [23-25], propagating SPPs can flow with respect to the
optical wave with own properties, with a propagation length up to
tensofmicron,dependingonlyonthemetalpropertiesthusoffering
the potentiality to guide light toward the active photo conversion
area, under external dark field illumination condition. Furthermore,
controlling the surface roughness and structure geometry, it is also
possible to stimulate local specific SPP damping channels [26-30],
anditispossibletoelecttheradiativelossesorthegenerationofhot
electrons as the primary decay channel at the apex. It can happen
stimulating the propagation of the TM or the HE mode, provided a
device with the proper geometry.
Here, we want to describe a specific photoexcitable plasmonic
device, characterizing it in terms of design and realization pa-
rameters for visible, 670 nm, radiation line. Then, we present
the far-field emission measurements, followed by the current to
voltage conduction characteristic recorded in the dark and under
illumination condition when it was shined with a laser light directly
on the coupler.
15.2.2
Description of the Device
The device is defined by a micrometric metallic cone with
nanometric apex supported by an AFM tip provided by a grating
coupler. The grating acts as unidirectional SPPs launcher allowing
the conversion between light and SPs. Coupled SPPs (the energy
reservoir) move down to the tapered guiding structure of the cone,
allowing the concentration of energy at the nanometric scale of its
apex where SPPs damp out.
The coupling surface used to harvest incident light into prop-
agating SPPs was directly realized milling with focused ion beam
(FIB)techniquesub-wavelengthgroovesonthefrontfacingpartofa
gold-coated pyramidal AFM tip (
μ
-masch snc38, n-type silicon tip,
height
=
20
μ
m, full tip cone angle 40
◦
). The sharp micrometric
cone (height: 2500 nm, base radius: 300 nm) was realized with
FIB-induced deposition technique, as a Pt-C cone structure with an
apex radius of about 10 nm. Subsequently, the whole structure was
coated with a metallic layer of controlled thicknesses by a plasma
