Effect of electric field gradient on sub-nanometer spatial resolution of tip-enhanced Raman spectroscopy.

Lingyan Meng,Zhilin Yang,Mengtao Sun,Jianing Chen

doi:10.1038/srep09240

Abstract

Tip-enhanced Raman spectroscopy (TERS) with sub-nanometer spatial resolution has been recently demonstrated experimentally. However, the physical mechanism underlying is still under discussion. Here we theoretically investigate the electric field gradient of a coupled tip-substrate system. Our calculations suggest that the ultra-high spatial resolution of TERS can be partially attributed to the electric field gradient effect owning to its tighter spatial confinement and sensitivity to the infrared (IR)-active of molecules. Particularly, in the case of TERS of flat-lying H2TBPP molecules,we find the electric field gradient enhancement is the dominating factor for the high spatial resolution, which qualitatively coincides with previous experimental report. Our theoretical study offers a new paradigm for understanding the mechanisms of the ultra-high spatial resolution demonstrated in tip-enhanced spectroscopy which is of importance but neglected.

Highlights

Tip-enhanced Raman spectroscopy (TERS) with sub-nanometer spatial resolution has been recently demonstrated experimentally
In the case of TERS of flat-lying H2TBPP molecules,we find the electric field gradient enhancement is the dominating factor for the high spatial resolution, which qualitatively coincides with previous experimental report
We show by theoretical calculations that for flat-lying H2TBPP molecules and H2TBPP molecules with a small tilted angle, the electric field gradient has a larger effect than the electric field in terms of the spectral spatial resolution

Summary

Introduction

Tip-enhanced Raman spectroscopy (TERS) with sub-nanometer spatial resolution has been recently demonstrated experimentally. Our theoretical study offers a new paradigm for understanding the mechanisms of the ultra-high spatial resolution demonstrated in tip-enhanced spectroscopy which is of importance but neglected. Tip-enhanced Raman spectroscopy (TERS) is a important technique for molecule analysis on the nanometer scale because of its high detection sensitivity and spatial resolution[1,2,3,4,5,6,7]. Higher order nonlinear effects are considered to be related to such ultra-high resolution[16] These physical mechanisms are not sufficient to comprehensively interpret the sub-nanometer spatial resolution in TERS. The calculated spectral spatial resolution, Raman and infrared spectra coincide with the experimental results indicating the strong influence of electric field gradient on the tip-enhanced spectroscopy[1]

Methods

Results

Conclusion