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The Role of a Plasmonic Substrate on the Enhancement and Spatial Resolution of Tip-enhanced Raman Scattering

Abstract

Since the first report in early 2000s, there are several experimental configurations that demonstrated enhancement and spatial resolution in 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 MoS2 on an array of Au nanodisks. The Au nanodisks were prepared by electron beam writing. Thereafter MoS2 was transferred onto the plasmonic substrate using 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 which 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 that 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 deployed. The calculations confirmed a 110 times stronger enhancement at the edges of the nanodisks than that of conventional gap-mode TERS and explaining the experimental maps. Our results provide not only a deeper understanding of the TERS mechanism of this heterostructure, but they can also help in realizing highly efficient TERS experiments using similar systems.

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Publication details

The article was accepted on 07 Nov 2018 and first published on 07 Nov 2018


Article type: Paper
DOI: 10.1039/C8FD00142A
Citation: Faraday Discuss., 2018, Accepted Manuscript
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    The Role of a Plasmonic Substrate on the Enhancement and Spatial Resolution of Tip-enhanced Raman Scattering

    M. Rahaman, A. G. Milekhin, A. Mukherjee, E. E. Rodyakina, A. Latyshev, V. Dzhagan and D. R. Zahn, Faraday Discuss., 2018, Accepted Manuscript , DOI: 10.1039/C8FD00142A

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