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Fractal Shaped Periodic Metal Nanostructures Atop Dielectric-Metal Substrates for SERS Applications
journal contribution
posted on 2020-07-03, 12:35 authored by Sergey M. Novikov, Sergejs Boroviks, Andrey B. Evlyukhin, Dmitry E. Tatarkin, Aleksey V. Arsenin, Valentyn S. Volkov, Sergey I. BozhevolnyiControlled and reliable field enhancement
(FE) effects associated
with the excitation of plasmons in resonant metal nanostructures constitute
an essential prerequisite for the development of various sensing configurations,
especially those utilizing surface-enhanced Raman scattering (SERS)
spectroscopy techniques. Leveraging advantages of random nanostructures
in providing strong collective resonances in a broad wavelength range
with the design flexibility of individual gap plasmon resonators,
we experimentally investigate fractal-shaped arrays of gap plasmon
resonators and characterize the occurring FE effects by mapping SERS
signals from uniformly spread Rhodamine 6G with high-resolution Raman
microscopy. In such a geometry, the total FE is expected to benefit
from both FE associated with gap plasmon excitation and FE due to
constructive interference of the surface plasmon modes reflected and
diffracted by fractal-shaped boundaries. Linear reflection imaging
spectroscopy is used to verify that the fabricated nanostructures
exhibit spatially distributed resonances (bright spots) close to the
excitation wavelengths used for the Raman microscopy. The positions
of bright spots are argued to be influenced by fractal-shaped boundaries,
particle dimensions, polarization, and wavelength of the incident
and scattered light. Experimentally obtained SERS images from similar
fractal (gold) structures fabricated with different dielectric SiO2 spacer thicknesses (0, 20, and 40 nm) featured diffraction-limited
bright spots corresponding to local SERS enhancements of up to ∼107 (relative to Raman signals obtained with a glass substrate)
for 40 nm thick SiO2 layers. Our results indicate that
the strategy of combining fractal array geometry with gap plasmon
resonances is promising for the design of highly efficient SERS substrates
for potential applications in surface-enhanced multichannel sensing,
including single-molecule spectroscopy.
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Keywords
Raman microscopymapping SERS signalswavelengthgap plasmon excitationgap plasmon resonancesgap plasmon resonatorsSERS Applications ControlledFEfractal array geometryLinear reflection imaging spectroscopySiO 2 layersPeriodic Metal Nanostructuresfractal-shaped boundariessurface plasmon modes40 nmspread Rhodamine 6 Gnanostructure
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