Single-molecule-resolution ultrafast near-field optical microscopy via plasmon lifetime extension

TL;DR

This paper introduces a novel ultrafast near-field optical microscopy technique leveraging plasmon lifetime extension near quantum emitters, achieving single-molecule resolution by using defect centers in 2D materials on a metal-coated tip.

Contribution

It demonstrates a new approach for ultrahigh-resolution SNOM by utilizing stress-induced defect centers in 2D materials to position quantum emitters at the tip apex.

Findings

Achieves resolution limited by quantum emitter size

Utilizes defect centers in 2D materials for emitter placement

Enables background-noise-free nonlinear imaging

Abstract

A recent study shows that: when a long lifetime particle is positioned near a plasmonic metal nanoparticle, lifetime of plasmon oscillations extends, but, "only" near that long-life particle [PRB 101, 035416 (2020)]. Here, we show that this phenomenon can be utilized for ultrahigh (single-molecule) resolution ultrafast apertureless (scattering) SNOM applications. We use the exact solutions of 3D Maxwell equations. We illuminate a metal-coated silicon tip, a quantum emitter (QE) placed on the tip apex, with a femtosecond laser. The induced near-field in the apex decays rapidly except in the vicinity of the sub-nm-sized QE. Thus, the resolution becomes solely limited by the size of the QE. As positioning of a QE on the tip apex is challenging, we propose the use of a newly-discovered phenomenon; stress-induced defect formation in 2D materials. When a monolayer, e.g., transition metal dichalcogenide (TMD) is transferred to the AFM tip, the tip indentation of 2D TMD originates a defect-center located right at the sharpest point of the tip; that is exactly at its apex. Moreover, the resonance of the defect is tunable via a voltage applied to the tip. Our method can equally be used for background-noise-free nonlinear imaging and for facilitating single-molecule-size chemical manipulation.