SPR-based Tip-enhanced Fluorescence/Raman Spectroscopy Studies

The local electromagnetic field enhancement induced by surface plasmonon resonance is the key factors to the high detection sensitivity and nanoscale spatial resolution of tip-enhanced spectroscopy(TES).However,the ability of electromagnetic enhancement in metal nanostructures greatly limits the further improvement of TES sensitivity.The developed surface plasmon coupled emission(SPCE)technology shows excellent directional emission characteristics,which can realize the high efficiency of signal collection and thus improve the detection sensitivity of molecular signals to a certain extent.Therefore,the combination of TES and SPCE technology will provide a feasible and important experimental method for further improving the sensitivity of TES,and provide a good choice for the characterization of two-dimensional materials and other molecules.Most of the studies on two-dimensional black phosphorus are focused on the photoelectric properties of materials,while the TES enhancement mechanism and spatial resolution of black phosphorus still need to be further studied.At the same time,a systematic study of the radiative and non-radiative processes of two-dimensional black phosphorus can deepen the understanding of its fluorescence spectrum characteristics.At present,most TES studies did not consider the large enhancement effect caused by high-order nonlinear effects,so we design a system to quantitatively separate the surface and coherent enhancement effects on tip-enhanced coherent anti-Stokes Raman scattering(TECARS).It is of great scientific significance to further understand the enhancement factor and spatial resolution higher than that of linear TES.In order to solve these problems,we systematically studied the enhancement factors,spatial resolution and directional emission characteristics of tip enhanced fluorescence and Raman systems.This paper is divided into five chapters.The first chapter,mainly summarizes the basic principle and research status of TES technology,and puts forward the research purpose and assumption of this paper.In the second chapter,the theory and numerical method of surface plasmon are introduced.In the third chapter,the radiative and non-radiative processes of two-dimensional black phosphorus were quantitatively studied,with emphasis on the quantitative relationship between fluorescence enhancement factor,SPCE characteristics and spatial resolution and tip,substrate and other factors.In the fourth chapter,the contribution of surface and coherent enhancement effects to TECARS enhancement factors in TECARS system is studied quantitatively.The fifth chapter,according to the research work,has carried on the summary and the prospect.In the main research contents of this paper are as follows:1.The fluorescence and directional scattering properties of two-dimensional black phosphorus were systematically studied.With the help of 3D-FDTD method,by optimizing the tip and substrate,the calculated fluorescence enhancement factor can reach three orders of magnitude,and the spatial resolution can reach 7 nm.It is also shown that the tip tilt has an important effect on the fluorescence directional scattering angle of two-dimensional black phosphorus.The theoretical results can not only deepen the understanding of the fluorescence characteristics of two-dimensional black phosphorus,but also provide a theoretical reference for obtaining high-quality fluorescence spectra of two-dimensional black phosphorus in experiments.2.The specific contributions of surface and coherent enhancement effects to TECARS enhancement were quantitatively separated.In this paper,the characteristics of TECARS in ultraviolet light band are studied theoretically for the first time,and the quantitative relationship between the factors such as the radius of curvature and cone angle of the tip of TECARS system,the enhancement factor and the spatial resolution of TECARS are discussed quantitatively.The quantitative separation of the surface contribution and quantum coherent contribution in TECARS enhancement is realized.Under the optimal system,the surface and coherent enhancement factors in TECARS enhancement are up to 10¹⁸ and 10⁹,respectively,and the resolution of TECARS enhancement can reach 3.7 nm and 4.8 nm,respectively,which is greatly improved compared with linear Raman enhancement.The research results have important guiding significance for further understanding TECARS enhancement mechanism and building efficient TECARS platform.