20 / 25
Page 64
Mater Sci Nanotechnol 2017 | Volume 1 Issue 2
allied
academies
Nanomaterials and Nanochemistry
November 29-30, 2017 | Atlanta, USA
International Conference on
C
omparative study has been performed on the spectral and
near-field properties of concave and convex nano-object-
patterns that can be fabricated via colloid-sphere lithography
(CSL) and via interferometric illumination of colloid sphere
monolayers (IICSM) by applying circularly polarized light.
Previous studies on hole- and disk-arrays in the literature
have shown that the s/p-polarized transmittance on the
former corresponds to the p/s-polarized reflectance on the
latter type of patterns, according to the Babinet principle.
In CSL hexagonal pattern of nano-ring and nano-crescent
shaped holes can be prepared via illuminating a hexagonal
monolayer of Au colloid spheres by perpendicularly and
obliquely incident circularly polarized beams, as a result two
and four geometrical parameters canbe tuned independently.
In IICSM mini-arrays composed of a central ring and satellite
nano-crescents can be fabricated via illuminating a hexagonal
monolayer of Au colloid spheres by two interfering circularly
polarized beams, and six geometrical parameters (p pattern
period, t nano-object distance, d nano-ring and nano-
crescent diameter,
ε
nano-crescent opening angle and
ω
orientation) can be tuned independently (Fig. 1a, b). When
the Au colloid sphere monolayers are aligned on thin Au
films, nanoholes of various shape can be directly fabricated,
while a lift-off procedure makes it possible to transfer the
pattern into analogous convex nano-objects. Both of the
concave and convex hexagonal patterns of nano-rings and
nano-crescents, as well as of the two different (p=300 nm
and p’=600 nm) rectangular patterns of mini-arrays were
re-illuminated by p-polarized light in different azimuthal
orientations to demonstrate their spectral engineering
capabilities. Our results have shown that in complementary
complex patterns illuminated by complementary beams
the reflectance and transmittance are interchanged. The
convex patterns indicate the cavity resonances of individual
nano-objects and the lattice resonances on their array,
while the optical response of the concave patterns is more
structured due to the Fano modulations originating from
coupled localized and propagating modes. The spectra on
the hexagonal pattern of nanorings did not show azimuthal
orientation dependence, while the spectra on the hexagonal
pattern of nano-crescents and on both rectangular patterns
composed of analogous miniarrays strongly depend on the
azimuthal orientation. The hexagonal pattern of nano-rings
indicates the “U-resonance” of crescent-shaped objects,
which is independent of the E-field oscillation direction
due to their symmetry properties. In contrast, on the
hexagonal pattern of nano-crescents the convex reflectance
in
γ
=0°/90° corresponds to the concave transmittance in
γ
=90°/0° azimuthal orientation (Fig. 1c). Similarly, on the
rectangular pattern of mini-arrays the convex reflectance in
30°/120° azimuthal orientation corresponds to the concave
transmittance in
γ
=120°/30° (Fig. 1e). On both rectangular
patterns ofminiarrays at smallwavelengthanalogous extrema
are observable, while the larger periodic rectangular pattern
exhibits additional extrema at larger wavelengths. The
charge distribution and corresponding near-field indicates
U / C1 and C2 resonance on the convex hexagonal array of
nano-crescents in
γ
=90°/0° azimuthal orientation, while on
the convex rectangular pattern analogous resonances appear
in
γ
=30°/120° (Fig. 1d, f). However, the charge and near-
field distribution on the complementary concave pattern is
perturbed by coupled localized and propagating modes.
e:
mcsete@physx.u-szeged.comComparativestudyonpatternsof roundedconcaveandconvexobjectsachievablevia integratedlithography
realized by circularly polarized light
Mária Csete
University of Szeged, Hungary