Controllable Preparation of SERS-Active Ag-FeS Substrates by a Cosputtering Technique.

Ning Ma,Yongjun Zhang,Young Jung,Sila Jin,Yang Liu,Xin-Yuan Zhang,Wenyue Fan,Jinghai Yang,Lei Chen,Bingbing Han,Yeonju Park

doi:10.3390/molecules24030551

Ning Ma, Yongjun Zhang + Show 9 more

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https://doi.org/10.3390/molecules24030551

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Abstract

In this work, we introduced an ordered metal-semiconductor molecular system and studied the resulting surface-enhanced Raman scattering (SERS) effect. Ag-FeS nanocaps with sputtered films of different thicknesses were obtained by changing the sputtering power of FeS while the sputtering power of Ag and the deposition time remained constant. When metallic Ag and the semiconductor FeS are cosputtered, the Ag film separates into Ag islands partially covered by FeS and strong coupling occurs among the Ag islands isolated by FeS, which contributes to the SERS phenomenon. We also investigated the SERS enhancement mechanism by decorating the nanocap arrays produced with different FeS sputtering powers with methylene blue (MB) probe molecules. As the FeS sputtering power increased, the SERS signal first increased and then decreased. The experimental results show that the SERS enhancement can mainly be attributed to the surface plasmon resonance (SPR) of the Ag nanoparticles. The coupling between FeS and Ag and the SPR displacement of Ag vary with different sputtering powers, resulting in changes in the intensity of the SERS spectra. These results demonstrate the high sensitivity of SERS substrates consisting of Ag-FeS nanocap arrays.

Highlights

In 1974, Fleischmann and his collaborators found for the first time that pyridine on the surface of a rough silver electrode generates a strong Raman signal [1]
The deposition rate is proportional to the rate at which atoms escape from the cathode target
The surface-enhanced Raman scattering (SERS) effect of the prepared Ag/FeS array substrate shows that the substrate has a good Raman enhancement effect, and the enhancement factor is as high as 1.8 × 106

Summary

Introduction

In 1974, Fleischmann and his collaborators found for the first time that pyridine on the surface of a rough silver electrode generates a strong Raman signal [1]. Studies of the nature of the SERS enhancement mechanism are based on the enhancement of the incident electric field, E and the change in the molecular polarizability, α, which correspond to an electromagnetic field enhancement mechanism (EM) [5,6] and a chemical enhancement mechanism (CM) [7,8]. Molecules 2019, 24, 551 oscillation of the surface of the metal nanoparticles (NPs), the amplitude of the oscillation is maximized. This phenomenon is called localized surface plasmon resonance (LSPR) [9]. When an applied electromagnetic field is coupled with surface charge density oscillations, LSPR is excited at the interface between the metal nanofilm and the medium. The position of the LSPR peak is affected by the real part (ε1 ) of the dielectric constant of the metal NP and the dielectric constant (εm ) [10]

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Conclusion