Nanoscopy of Excitons in Atomically Thin In-Plane Heterostructures with Nanointerfaces

TL;DR

This study employs near-field nano imaging and spectroscopy to directly correlate local dielectric properties with excitonic behavior across atomically sharp in-plane heterostructure interfaces in 2D materials, revealing composition-dependent optical phenomena.

Contribution

It introduces a multimodal near-field spectroscopy framework for nanoscale probing of dielectric and excitonic properties in 2D heterostructures, providing direct correlation at the heterointerface.

Findings

Reversal of dielectric contrast at excitonic resonances.

Continuous variation of neutral-exciton emission across the interface.

Modeling links dielectric response to composition and excitonic trends.

Abstract

Atomically sharp 2D in-plane heterostructures with nanoscale interfaces provide a powerful platform for tailoring optical and electrical properties at the nanoscale, enabling novel device engineering and the exploration of new physical phenomena. However, direct experimental correlation between local dielectric response and excitonic properties across such interfaces has remained elusive. Here, we probed the nanoscale complex dielectric function and the corresponding localized photoluminescence (PL) modulations in heterostructure domains of lateral monolayer MoxW1-xS2 - WxMo1-xS2, synthesized using a liquid-phase precursor-assisted approach. Near-field nano imaging across the visible-near-infrared range enables real space mapping of sharp amplitude and phase changes at the heterointerface, resolving the local complex dielectric function with nano-meter scale spatial resolution. Excitation energy-dependent nano spectroscopy reveals a reversal of dielectric contrast between Mo-rich and W-rich domains at their respective excitonic resonances, consistent with Lorentz-oscillator fits. Complementary hyperspectral nano-PL mapping resolves the evolution of excitonic emission across the lateral heterointerface, with neutral-exciton intensities varying continuously from W-rich to Mo-rich regions. Effective-medium theory modeling of the imaginary part of the effective dielectric function of the heterostructure as a function of photon energy and Mo filling fraction reproduces the observed excitonic trends, linking the PL evolution to a composition-dependent dielectric response. Together, these results provide direct nanoscale correlation between dielectric and excitonic boundaries in laterally stitched monolayer heterostructures and establish a multimodal near-field spectroscopy framework for probing excitonic phenomena at the nanoscale.