Figure 13.

(a) Top: Schematic illustration of electron–hole pairs forming 1s and 2s excitonic states in a 2D dielectric slab. Adapted with permission from ref (151). Copyright 2014 American Physical Society. Bottom: Theoretically calculated energies of the bandgap and exciton states in a WS₂ ML as a function of inverse squared external dielectric constant. Shaded areas indicate fluctuations from variations of the external screening. Adapted with permission from ref (202). Copyright 2019 Springer Nature. (b) Schematic of a device heterostructure to demonstrate the sensing capabilities of excitons in ML WSe₂. (c) Reflectance contrast of the 1s (left) and 2s and 3s (middle) excitonic transitions in the WSe₂ sensor, and the 1s exciton in the WS₂ sample as a function of the applied gate voltage (i.e., the electron concentration in WS₂). (b) and (c) Adapted with permission from ref (199). Copyright 2020 Springer Nature. (d) Left: Reflective magneto-circular dichroism as a function of magnetic field (bottom) measured in a monolayer WSe₂ and trilayer CrI₃ heterostructure, depicted above schematically. Orange and green curves represent magnetic field sweeping up (increase) and down (decrease), respectively. Right: Schematic of a ML WSe₂ and bilayer CrI₃ heterostructure (top). The layered AF spatial domains that are indistinguishable by reflective magneto-circular dichroism can be resolved by circular polarization-resolved PL from WSe₂ (bottom). Adapted with permission from ref (203). Copyright 2020 Springer Nature. (e) Measurement of the CrBr₃ magnetization hysteresis using the MOKE (bottom) in a device like schematically shown on top. Adapted with permission under a Creative Commons CC BY 4.0 license from ref (204). Copyright 2020 American Physical Society.