\u201cOptical and Surface Enhanced Raman Scattering properties of Ag modified silicon double nanocone array\u201d

L Mehrvar,M Sadeghipari,M Fathipour,S H Tavassoli,S Mohajerzadeh

doi:10.1038/s41598-017-12423-2

L Mehrvar, M Sadeghipari + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-12423-2

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Abstract

Surface enhanced Raman scattering (SERS) systems with large number of active sites exhibit superior capability in detection of low concentration analytes. In this paper, we present theoretical as well as experimental studies on the optical properties of a unique hybrid nanostructure, Ag NPs decorated silicon double nanocones (Si-DNCs) array, which provide high density of hot spots. The Si-DNC array is fabricated by employing electron beam lithography together with plasma etching process. Multipole analysis of the scattering spectra, based on the multipole expansion theory, confirms that the toroidal dipole moment dominates over other electric and magnetic multipole moments in the Si-DNCs array. This response occurs as a result of generating current densities flowing in opposite directions and consequently generating H-field vortexes inside the nanocones. Moreover, SERS applicability of this type of nanostructure is examined. For this purpose, the Si-DNCs array is decorated with Ag nanoparticles (NPs) by means of electroless deposition method. Simulation results indicate that combination of multiple resonances, including LSPR resonance of Ag NPs, longitudinal standing wave resonance of Ag layer and inter-particle interaction in the gap region, result in a significant SERS enhancement. Our experimental results demonstrate that Si-DNC/Ag NPs array substrate provides excellent reproducibility and ultrahigh sensitivity.

Highlights

Surface enhanced Raman spectroscopy (SERS) is a powerful analytical tool for detection and identification of chemical[1,2,3,4] and biological[5,6,7,8] materials
Multiple resonances exist in the spectra, two dips at 528 and 578 nm for X-polarized light and at 536 and 584 nm for Y-polarized light are demonstrated in Fig. 4a and b
We described fabrication of the silicon double nanocones (Si-DNCs) array, and explained its applicability as a Surface enhanced Raman scattering (SERS) substrate when it is decorated with Ag NPs

Summary

Introduction

Surface enhanced Raman spectroscopy (SERS) is a powerful analytical tool for detection and identification of chemical[1,2,3,4] and biological[5,6,7,8] materials. Metallic NPs decorated on the side walls of the dielectric nanostructures is one of the high performance SERS substrates[14,15] In such hybrid nanostructures, the strong near electric field enhancement originates from excitation of multiple resonances. There are no reports on the excitation of toroidal moments in the dielectric nanostructures In this manuscript, we report a new SERS substrate, Ag NPs decorated Si-DNCs array, which provide ultra-high electromagnetic field enhancement. We report a new SERS substrate, Ag NPs decorated Si-DNCs array, which provide ultra-high electromagnetic field enhancement This unique SERS substrate creates multiple types of hot spot sources simultaneously, including (I) interaction mode between nanocone pairs, (II) LSPR modes of AgNPs, and (III) LSPR mode in the vicinity of metallic tips (lightning rod effect), which result in high concentration of active sites and high amount of enhancement factor (EF). The optical characterization of this new nanostructure shows that the toroidal dipole (TD) moment dominates over other electric and magnetic multipole moments which can produce many interesting properties such as nonreciporocal refraction[24] and magnetoelectric effect[25]

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Conclusion