Grating-assisted coupling enhancing plasmonic tip nanofocusing illuminated via radial vector beam

Fanfan Lu,Lu Zhang,Ting Mei,Chao Meng,Jiachen Zhang,Feng Gao,Wending Zhang,Min Liu,Tianyang Xue,Jianlin Zhao

doi:10.1515/nanoph-2019-0329

Fanfan Lu, Lu Zhang + Show 8 more

Open Access

https://doi.org/10.1515/nanoph-2019-0329

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Abstract

Abstract Tip-enhanced Raman spectroscopy (TERS) is a very useful method to achieve label-free and super-resolution imaging, and the plasmonic tip nanofocusing plays a decisive role for TERS performance. Here, we present a method to enhance the nanofocusing characteristic of a plasmonic tip integrated in a grating near the tip apex. Simulation results show that the grating near the tip apex can significantly improve the electric field intensity of the nanofocusing field compared with a conventional bare tip, under axial excitation of a tightly focused radial vector beam. The electric field enhancement characteristic is quantified in relation with the groove number of grating, excitation wavelength, period of grating, and numerical aperture of the micro-objective (MO). These simulation results could be a good reference to fabricate a plasmonic tip for TERS applications, which is an effective way to promote the development of tip-enhanced near-field optical microscopy.

Highlights

In the past two decades, tip-enhanced Raman spectroscopy (TERS) has received extensive attention
Simulation results show that the grating near the tip apex can significantly improve the electric field intensity of the nanofocusing field compared with a conventional bare tip, under axial excitation of a tightly focused radial vector beam
These simulation results could be a good reference to fabricate a plasmonic tip for Tip-enhanced Raman spectroscopy (TERS) applications, which is an effective way to promote the development of tip-enhanced near-field optical microscopy

Summary

Introduction

In the past two decades, tip-enhanced Raman spectroscopy (TERS) has received extensive attention. As an effective means of analysis, TERS was widely adopted to investigate the biological systems [2], low-dimensional materials [3], single-molecule detection [4], catalysis [5], surface physics [6,7,8], and so on. In the application process of TERS technology, the nanofocusing characteristic of the plasmonic tip plays a crucial role. Under illumination of the external focused light, the field can be compressed to the nanoscale at the tip apex due to the localized surface plasmon resonance effect [9,10,11,12,13]. The enhanced electric field at the tip apex is used to excite and enhance Raman signal within nanoscale

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