Amplitude- and phase-resolved nano-imaging and nano-spectroscopy of polaritons in liquid environment

TL;DR

This paper introduces two liquid-environment nanoimaging setups for polaritons, enabling detailed mode analysis and field confinement studies crucial for chemical and biological sensing applications.

Contribution

It presents novel liquid-based nanoimaging and spectroscopy methods for polaritons, expanding capabilities for in-situ chemical and biological analysis.

Findings

Demonstrated antenna mapping with infrared s-SNOM in liquid environment.

Implemented TIR-based setup for launching and probing polaritons in h-BN.

Established foundation for in-liquid polariton interferometry with broad application potential.

Abstract

Localized and propagating polaritons allow for highly sensitive analysis of (bio)chemical substances and processes. Nanoimaging of the polaritons evanescent fields allows for critically important experimental mode identification and for studying field confinement. Here we describe two setups for polariton nanoimaging and spectroscopy in liquid, which is an indispensable environment for (bio)chemical samples. We first demonstrate antenna mapping with a transflection infrared scattering-type scanning near-field optical microscope (s-SNOM), where the tip acts as a near-field scattering probe. We then demonstrate a total internal reflection (TIR) based setup, where the tip is both launching and probing ultra-confined polaritons in van der Waals materials, here phonon polaritons in hexagonal boron nitride (h-BN) flakes. This work lays the foundation for s-SNOM based polariton interferometry in liquid, which has wide application potential for in-situ studies of chemical reactions at the bare or functionalized surface of polaritonic materials, including (bio)chemical recognition analogous to the classical surface plasmon resonance spectroscopy.