TY - JOUR

T1 - The role of a plasmonic substrate on the enhancement and spatial resolution of tip-enhanced Raman scattering

AU - Rahaman, Mahfujur

AU - Milekhin, Alexander G.

AU - Mukherjee, Ashutosh

AU - Rodyakina, Ekaterina E.

AU - Latyshev, Alexander V.

AU - Dzhagan, Volodymyr M.

AU - Zahn, Dietrich R.T.

PY - 2019/5/1

Y1 - 2019/5/1

N2 - Since the first report in the early 2000s, there have been several experimental configurations that have demonstrated enhancement and spatial resolution of tip-enhanced Raman spectroscopy (TERS). The combination of a plasmonic substrate and a metallic tip is one suitable approach to achieve even higher enhancement and lateral resolution. In this contribution, we demonstrate TERS on a monolayer of MoS2 on an array of Au nanodisks. The Au nanodisks were prepared by electron beam writing. Thereafter, MoS2 was transferred onto the plasmonic substrate via the exfoliation technique. We witness an unprecedented enhancement and spatial resolution in the experiments. In the TERS image a ring-like shape is observed that matches the edges of the nanodisks. TERS enhancement at the edges is about 170 times stronger than at the center of the nanodisks. For a better understanding of the experimental results, finite element method (FEM) simulations were employed to simulate the TERS image of the MoS2/plasmonic heterostructure. Our calculations show a higher electric field concentration at the edges that exponentially decays to the center. Therefore, it reproduces the ring-like shape of the experimental image. Moreover, the calculations suggest a TERS enhancement of 135 at the edges compared to the center, which is in very good agreement with the experimental data. According to our calculations, the spatial resolution is also increased at the edges. For comparison, FEM simulations of a tip-flat metal substrate system (conventional gap-mode TERS) were carried out. The calculations confirmed a 110 times stronger enhancement at the edges of the nanodisks than that of conventional gap-mode TERS and explained the experimental maps. Our results provide not only a deeper understanding of the TERS mechanism of this heterostructure, but can also help in realizing highly efficient TERS experiments using similar systems.

AB - Since the first report in the early 2000s, there have been several experimental configurations that have demonstrated enhancement and spatial resolution of tip-enhanced Raman spectroscopy (TERS). The combination of a plasmonic substrate and a metallic tip is one suitable approach to achieve even higher enhancement and lateral resolution. In this contribution, we demonstrate TERS on a monolayer of MoS2 on an array of Au nanodisks. The Au nanodisks were prepared by electron beam writing. Thereafter, MoS2 was transferred onto the plasmonic substrate via the exfoliation technique. We witness an unprecedented enhancement and spatial resolution in the experiments. In the TERS image a ring-like shape is observed that matches the edges of the nanodisks. TERS enhancement at the edges is about 170 times stronger than at the center of the nanodisks. For a better understanding of the experimental results, finite element method (FEM) simulations were employed to simulate the TERS image of the MoS2/plasmonic heterostructure. Our calculations show a higher electric field concentration at the edges that exponentially decays to the center. Therefore, it reproduces the ring-like shape of the experimental image. Moreover, the calculations suggest a TERS enhancement of 135 at the edges compared to the center, which is in very good agreement with the experimental data. According to our calculations, the spatial resolution is also increased at the edges. For comparison, FEM simulations of a tip-flat metal substrate system (conventional gap-mode TERS) were carried out. The calculations confirmed a 110 times stronger enhancement at the edges of the nanodisks than that of conventional gap-mode TERS and explained the experimental maps. Our results provide not only a deeper understanding of the TERS mechanism of this heterostructure, but can also help in realizing highly efficient TERS experiments using similar systems.

KW - SINGLE-MOLECULE

KW - OPTICAL-PROPERTIES

KW - CHEMICAL-ANALYSIS

KW - LOCALIZED STRAIN

KW - HOT-SPOTS

KW - SPECTROSCOPY

KW - SURFACE

KW - NANOSCALE

KW - MICROSCOPY

KW - CONTRAST

UR - http://www.scopus.com/inward/record.url?scp=85066496227&partnerID=8YFLogxK

U2 - 10.1039/c8fd00142a

DO - 10.1039/c8fd00142a

M3 - Article

C2 - 30839033

AN - SCOPUS:85066496227

VL - 214

SP - 309

EP - 323

JO - Faraday Discussions

JF - Faraday Discussions

SN - 1364-5498

ER -