TY - JOUR

T1 - Fractal Shaped Periodic Metal Nanostructures Atop Dielectric-Metal Substrates for SERS Applications

AU - Novikov, Sergey M.

AU - Boroviks, Sergejs

AU - Evlyukhin, Andrey B.

AU - Tatarkin, Dmitry E.

AU - Arsenin, Aleksey V.

AU - Volkov, Valentyn S.

AU - Bozhevolnyi, Sergey I.

PY - 2020/7/15

Y1 - 2020/7/15

N2 - Controlled 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 a107 (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.

AB - Controlled 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 a107 (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.

KW - field enhancement

KW - fractals

KW - gap surface plasmons

KW - linear and nonlinear light scattering by nanostructures

KW - plasmonics

KW - scanning microscopy

KW - SERS

UR - http://www.scopus.com/inward/record.url?scp=85089197494&partnerID=8YFLogxK

U2 - 10.1021/acsphotonics.0c00257

DO - 10.1021/acsphotonics.0c00257

M3 - Article

AN - SCOPUS:85089197494

VL - 7

SP - 1708

EP - 1715

JO - ACS PHOTONICS

JF - ACS PHOTONICS

SN - 2330-4022

IS - 7

ER -