Nano-optical Visualization of Interlayer Interactions in WSe₂/WS₂ Heterostructures

Abstract

The interplay between excitons and phonons governs the optical and electronic properties of transition metal dichalcogenides (TMDs). Even though a number of linear and nonlinear optical-, electron-, and photoelectron-based approaches have been developed and/or adopted to characterize excitons and phonons in single/ few-layer TMDs and their heterostructures, no existing method is capable of directly probing ultralow-frequency and interlayer phonons on the nanoscale. To this end, we developed ultralow-frequency tip-enhanced Raman spectroscopy, which allows spectrally and spatially resolved chemical and structural nanoimaging of WSe 2 /WS 2 heterostructures. In this work, we apply this method to analyze phonons in nanobubbles that are sustained in these heterobilayers. Our method is capable of directly probing interlayer (de)coupling using our novel structurally sensitive nano-optical probe and the interplay between excitons and interlayer/intralayer phonons through correlation analysis of the recorded spectral images.

Hyperspectral imaging of exciton confinement within a moiré unit cell with a subnanometer electron probe

“…Nanoscale modulation or confinement of the center of mass of interlayer excitons has been recently probed in momentum space by using ultrafast angle-resolved photoemission electron spectroscopy (ARPES) ( 12 ). Similarly, the coupling and decoupling of interlayer excitons and phonons was probed by means of ultralow-frequency tip-enhanced Raman spectroscopy ( 13 ). A clear understanding of the degree of confinement of intralayer excitons as well as a measurement of the stacking at which the localization occurs has remained out of reach because of the diffraction limit of optical probes or the loss of phase information in ARPES.…”

Tip-enhanced nanoscopy of two-dimensional transition metal dichalcogenides: progress and perspectives

“…The decoupling of WS 2 and WSe 2 layers marked by the disappearance of the low frequency interlayer phonon mode was also observed by TERS. 76…”

“…The decoupling of WS 2 and WSe 2 layers marked by the disappearance of the low frequency interlayer phonon mode was also observed by TERS. 76 A TERS probe can also be used as an intermedium to load controllable strain onto TMD thin layers. As shown in Fig.…”

Plasmonic Gradient and Plexcitonic Effects in Single-Molecule Tip-Enhanced (Resonance) Raman Spectroscopy

“…Tip-enhanced Raman spectroscopy (TERS) integrates high-sensitivity vibrational fingerprinting of Raman spectroscopy and sub-nanometer resolution of scanning probe microscopy (SPM) and benefits from the excellent electromagnetic field and its gradient enhancements in TERS configuration. − ...…”

“…These eminent TERS platforms can significantly enhance molecular Raman signals, even at the level of a single molecule, 7,12,19,34,37,48,50,57,58,65,72,78,91,115,118,122 and at a single bond level, 78,90 TERS resolution can reach up to atomic scale, 8,19,29,48 benefiting from the enormous electromagnetic field in the nano-cavity (hotspot region) between the tip and the substrate. TERS has been widely applied to the fields of signal enhancement on Raman spectroscopy, 1−104 molecular images, 1 9 , 4 8 , 5 2 , 6 1 , 8 3 , 9 4 , 1 0 3 surface catalytic reactions, 13,40,50,60,76,81,117 inter-molecular interaction, 31,35,97 multiple-Raman scattering, 16,21,23,24,27,68,103,105 time-resolved TERS, 13,15 ultrafast TERS, 108,109 and so forth. More detailed information can refer to the review papers.…”