Directional Enhanced Probe for Side-Illumination Tip Enhanced Spectroscopy

TL;DR

This paper introduces a novel corrugated, asymmetric metal tip for side-illumination tip-enhanced spectroscopy that significantly improves emission directionality, collection efficiency, and signal-to-noise ratio for single-molecule detection.

Contribution

The study presents a new asymmetric, corrugated probe design that enhances local excitation and emission directivity, advancing the capabilities of tip-enhanced spectroscopy.

Findings

Enhanced local excitation field with corrugated probe

Unidirectional emission achieved with asymmetric nanorods

Increased detection efficiency at single-molecule level

Abstract

We demonstrate a high-performance apertureless near-field probe made of a tapered metal tip with a set of periodic shallow grooves near the apex. The spontaneous emission from a single emitter near the tip is investigated systematically for the side-illumination tip enhanced spectroscopy (TES). In contrast with the bare tapered metal tip in conventional side-illumination TES, the corrugated probe not only enhances strongly local excitation field but also concentrates the emission directivity, which leads to high collection efficiency and signal-to-noise ratio. In particular, we propose an asymmetric TES tip based on two coupling nanorods with different length at the apex to realize unidirectional enhanced emission rate from a single emitter. Interestingly, we find that the radiation pattern is sensitive to the emission wavelength and the emitter positions respective to the apex, which can result in an increase of signal-to-noise ratio by suppressing undesired signal. The proposed asymmetrical corrugated probe opens up a broad range of practical applications, e.g. increasing the detection efficiency of tip enhanced spectroscopy at the single-molecule level.