Biomedical Engineering Reference
In-Depth Information
lead to various applications such as chemical identification and
innovativeimaging techniques.
15.2 A Plasmonic Device for Multidisciplinary
Investigation
We address the problem of e
cient electromagnetic field energy
deliveryatnanoscaleandweproposeaplasmonicdevicethatmakes
use of photo-excited surface plasmon polaritons (SPPs) to harvest
and subsequently deliver electromagnetic (e.m.) energy, either as a
subdiffraction-limited bright photonic source or as a quasi DC ideal
current source, offering nanometric spatial resolution in both cases.
We report on the design, optimization, and characterization of such
nanoplasmonic device.
Light waves coupling to free electron oscillations at the metal
surface, that is, SPPs, overcome the fundamental propagation limit
given by the electron's mean free path in the metal, providing a
precious method to guide and localize e.m. [1, 2]. Tapered metallic
structures allow the energy concentration at the nanoscale with
minimal losses field [3-5]. The proposed device makes use of a
grating coupler tailored upon a convergent geometry to exploit the
e.m. field to SPPs coupling and a guiding cone structure to concen-
trate the e.m. field, hence acting as a subdiffraction-limited optical
focusing lens or as a sensing electrode. When posed in contact with
a planar semiconductor sample, it realizes a Schottky photodiode
[6]. The point contact geometry at the nanoscale strongly departs
on the 1D barrier potential model, leading to specific current
to voltage characteristic that reflects the cylindrical symmetry of
the electric problem [7-9]. The performance of such plasmonic
concentrator is qualitatively described in terms of radiative and
nonradiativelossesfortheexcitedSPPs.Radiatedenergyandexcited
energetic electrons can be observed in our originally developed
optoelectronicsetup.Validatingtheexpectations,thephotoemission
and the photocurrent depend on light polarization orientation and
result in linear proportion with the incident power, showing a
conversion e
ciency improvement for optimal grating coupling
condition. We performed specific numerical simulations to obtain a
