Near-Field Coupling with a Nanoimprinted Probe for Dark Exciton Nanoimaging in Monolayer WSe₂

Abstract

Tip-enhanced photoluminescence (TRPL) is a powerful technique for spatially and spectrally probing local optical properties of 2-dimensional (2D) materials that are modulated by the local heterogeneities, revealing inaccessible dark states due to bright state overlap in conventional far-field microscopy at room temperature. While scattering-type near-field probes have shown the potential to selectively enhance and reveal dark exciton emission, their technical complexity and sensitivity can pose challenges under certain experimental conditions. Here, we present a highly reproducible and easy-to-fabricate near-field probe based on nanoimprint lithography and fiber-optic excitation and collection. The novel near-field measurement configuration provides an ∼3 orders of magnitude out-of-plane Purcell enhancement, diffraction-limited excitation spot, and subdiffraction hyperspectral imaging resolution (below 50 nm) of dark exciton emission. The effectiveness of this high spatial XD mapping technique was then demonstrated through reproducible hyperspectral mapping of oxidized sites and bubble areas.

Sub‐Diffraction Correlation of Quantum Emitters and Local Strain Fields in Strain‐Engineered WSe2 Monolayers

“…[ 27 ] Super‐resolution near‐field microscopy has been used in combination with atomic force microscopy (AFM) to correlate the emission spectra with local strain induced by small nanobubbles with heights up to 20 nm, [ 28,29 ] but these techniques are practically limited to noncryogenic temperatures where SPEs are not visible. [ 30–33 ] Cryogenic studies, on the other hand, have not incorporated nanoscale strain correlations when analyzing SPE properties. [ 34 ]…”

Core/Shell-Like Localized Emission at Atomically Thin Semiconductor–Au Interface

“…While there have been reports of strain-induced bound state emission of TMDCs, , there remains a paucity of research on the interplay between optical and electrical properties of the nanobubbles. While most prior near-field optical investigations on TMDCs have been conducted on plasmonic Au substrates, the charge transfer effects associated with Au substrates have been relatively unexplored. ,, One strategy to avoid charge transfer is placing a nanometer-thin insulating layer between the TMDC and the metal substrates. , In terms of electronic properties, prior studies have demonstrated in-plane piezoelectricity of 2D materials such as hBN and TMDCs with an odd number of layers, and their nanobubbles . However, a comprehensive exploration of the electronic and optical modifications within the bubbles due to the TMDC–substrate interaction is notably lacking.…”

“…16,19,20 One strategy to avoid charge transfer is placing a nanometer-thin insulating layer between the TMDC and the metal substrates. 7,21 In terms of electronic properties, prior studies have demonstrated in-plane piezoelectricity of 2D materials such as hBN 22 and TMDCs 23 with an odd number of layers, and their nanobubbles. 24 However, a comprehensive exploration of the electronic and optical modifications within the bubbles due to the TMDC−substrate interaction is notably lacking.…”