Probing the local nature of excitons and plasmons in few-layer MoS2

Abstract

Excitons and plasmons are the two most fundamental types of collective electronic excitations occurring in solids. Traditionally, they have been studied separately using bulk techniques that probe their average energetic structure over large spatial regions. However, as the dimensions of materials and devices continue to shrink, it becomes crucial to understand how these excitations depend on local variations in the crystal- and chemical structure on the atomic scale. Here we use monochromated low-loss scanning-transmission-electron-microscopy electron-energy-loss (LL-STEM-EEL) spectroscopy, providing the best simultaneous energy and spatial resolution achieved to-date to unravel the full set of electronic excitations in few-layer MoS2 nanosheets over a wide energy range. Using first-principles many-body calculations we confirm the excitonic nature of the peaks at ~2eV and ~3eV in the experimental EEL spectrum and the plasmonic nature of higher energy-loss peaks. We also rationalise the non-trivial dependence of the EEL spectrum on beam and sample geometry such as the number of atomic layers and distance to steps and edges. Moreover, we show that the excitonic features are dominated by the long wavelength (q=0) components of the probing field, while the plasmonic features are sensitive to a much broader range of q-vectors, indicating a qualitative difference in the spatial character of the two types of collective excitations. Our work provides a template protocol for mapping the local nature of electronic excitations that open new possibilities for studying photo-absorption and energy transfer processes on a nanometer scale.

arXiv commentMain paper: 19 pages, 5 figures Accepted for publication, Manuscript number: NPJ2DMATERIALS-00006, ISSN 2397-7132

References in corpus (13)

• Atomically thin MoS2: A new direct-gap semiconductor
• Graphene: Status and Prospects
• Two Dimensional Atomic Crystals
• High yield production of graphene by liquid phase exfoliation of graphite
• Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides
• Low-temperature photocarrier dynamics in monolayer MoS2
• Effect of spin-orbit interaction on the excitonic effects in single-layer, double-layer, and bulk MoS2
• The dielectric genome of van der Waals heterostructures
• Linear density response function in the projector-augmented wave method: Applications to solids, surfaces, and interfaces
• Exciton mapping at subwavelength scales in two-dimensional materials
• Layer-dependent anisotropic electronic structure of freestanding quasi-two-dimensional MoS${}_2$
• Dimensional cross-over of the bandgap transition in quasi-two-dimensional MoS2
• Investigation of the dispersion and the effective masses of excitons in bulk 2H-MoS2 using transition electron energy-loss spectroscopy

Cited by in corpus (13)

• Nanoscale modification of WS${}_2$ trion emission by its local electromagnetic environment
• Strongly coupled magnon-plasmon polaritons in graphene- 2D ferromagnet heterostructures
• Plasmons in MoS2 Studied via Experimental and Theoretical Correlation of Energy Loss Spectra
• Substrate influence on transition metal dichalcogenide monolayer exciton absorption linewidth broadening
• Flat-band plasmons in twisted bilayer transition metal dichalcogenides
• Fractional angular momentum and anyon statistics of impurities in Laughlin liquids
• Plasmon modes of bilayer molybdenum disulfide: A density functional study
• Correlating the Electronic Structures of Metallic/Semiconductor MoTe2 Interface to its Atomic Structures
• Electron energy-loss spectrum and exciton band structure of ${\mathrm{WSe}}_2$ monolayer studied by ab initio Bethe-Salpeter equation calculations
• Intrinsic edge excitons in two-dimensional MoS${}_2$
• Contamination of TEM Holders Quantified and Mitigated with Open-Hardware, High-Vacuum Bakeout System
• Excitons in epitaxially grown WS2 on Graphene: a nanometer-resolved EELS and DFT study
• Berry Curvature of Low-Energy Excitons in Rhombohedral Graphene