Download FIB – an easy tool for fabrication of high quality plasmonic structures

Application Example
FIB – an easy tool for fabrication
of high quality plasmonic
structures interference patterns
Surface Plasmon Polaritons (SPPs) are electromagnetic
waves of collective longitudinal oscillations of free
electrons propagating at metal-dielectric interfaces. This
dynamic effect results in formation of the electromagnetic
near-field zone which can be detected using Scanning
Near-field Optical Microscopy (SNOM). Surface plasmons
can be excited by illumination of nanostructured metaldielectric interfaces. For fabrication of these structures
one of the most suitable tools is Focused Ion Beam (FIB).
Preface
Surface Plasmon Polaritons present a
promising solution in subwavelength optics and lithography beyond the diffraction
limit. They also find their applications in
photonic data storage, light generation,
and bio-photonics.
SPPs cannot be excited directly by incident electromagnetic radiation. One of
the possible ways for their excitation is
scattering of an incident electromagnetic
wave on surface perturbations: holes,
grooves and slits. In this example, an
observation of interference of SPPs
on the slits prepared by FIB in a thin
gold layer on the quartz substrate is
1a
presented. Gold was used due to a
long SPPs propagation length and its
inert character.
To visualize SPPs the sample was illuminated from bottom through the quartz
substrate by a He-Ne laser (λ = 633 nm)
and the electromagnetic near field was
detected from top using SNOM in the
collection mode. Fig. 1a) shows the
topography of the prepared structures
and in Fig. 1b) the theoretical near field
distribution is presented.
cc Fig. 1a) SEM image of the sample topography with the excitation slits produced
by FIB taken by LYRA3 (5 x 5 μm). .
1b
Experimental conditions
Interference of SPPs was studied by
SNOM. Before the local milling of the
slits a 200 nm-thick Au layer was deposited on the quartz substrate with
a 3 nm Ti adhesion layer. Due to the
quality requirements on the excitation
grooves and the interface, the combination of FIB and SEM appears to be
the best solution.
The LYRA3 (Fig. 2), a combination of the
state-of-the-art electron microscope
and focused ion beam source, is an
instrument of choice for the preparation of the above mentioned structures. The instrument control software
includes a sophisticated DrawBeam
patterning module (see Fig. 3) which
offers an excellent control over the
whole lithographic process, including
the design of the desired structures.
A great advantage of the DrawBeam
is the possibility of importing bitmaps
or vector images. The software also
supports the application of several
drawing layers for the same project.
The layers enable an easy organization
of multistep processes.
cc Fig. 1b) FDTD simulation of the electromagnetic near-field distribution.
ff Fig 2.: The LYRA3 FEG instrument
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Application Example
FIB – an easy tool for fabrication of high quality plasmonic structures Interference Patterns
Near field electromagnetic intensity
measured by SNOM on slits arranged
in square patterns is depicted in Fig. 4
for different polarization of incident
light. Here, electromagnetic field can
be described by interference of SPPs.
Since the excitation of SPPs is very
sensitive to various defects, the clear
observation of interference patterns
confirms that the prepared patterns
are of a high quality.
Conclusion
The structures were fabricated using
a combined SEM and FIB instrument
TESCAN LYRA3. This device integrates
a high resolution Shottky FEG-SEM
column and a high performance FIB with
ultra-high resolution. This equipment
enables fast and accurate production
of excitation slits and other plasmonic
structures, crucial for experimental
detection using SNOM.
cc Fig 3: DrawBeam patterning module designed for the lithographic process control. EBL
and FIB milling in distinct layers were used for step by step fabrication of complex plasmonic structures. The parameters of electron exposition or FIB milling are displayed in the
DrawBeam process panel.
4a
4b
cc Fig 4: Measured interference patterns for two different polarizations of the incident light.
The light polarization is indicated on the left bottom part of the images.
TESCAN ORSAY HOLDING, a.s.
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(phone) +420 530 353 411 / (email) [email protected] / [email protected]
www.tescan.com
TESCAN ORSAY HOLDING reserves the right to change the document without notice. 2015.10.21
The presented experimental results
obtained by near-field scanning optical
microscopy shows that high quality
nanostructures can be prepared by
FIB. FIB is an ideal instrument for an
easy fabrication of nanostructures for
basic and applied research in various
scientific fields.