Monolayer-to-Mesoscale Modulation of the Optical Properties in 2D CrI3 Mapped by Hyperspectral Microscopy

M. Galbiati; F. Ramiro-Manzano; J. J. Pérez Grau; F. Cantos-Prieto; J. Meseguer-Sánchez; I. Kosic; F. Mione; A. Pallarés Vilar; A. Cantarero; D. Soriano; E. Navarro-Moratalla

doi:10.1103/PhysRevLett.130.176901

Research · Publication & note

April 27, 2023 September 9, 2026

Monolayer-to-Mesoscale Modulation of the Optical Properties in 2D CrI3 Mapped by Hyperspectral Microscopy - Notes

Research article

M. Galbiati, F. Ramiro-Manzano, J. J. Pérez Grau, F. Cantos-Prieto, J. Meseguer-Sánchez, I. Kosic, F. Mione, A. Pallarés Vilar, A. Cantarero, D. Soriano and E. Navarro-Moratalla

Physical Review Letters 130, 176901 (2023) · Published 27 April 2023

Published abstract

Magnetic 2D materials hold promise to change the miniaturization paradigm of unidirectional photonic components. However, the integration of these materials in devices hinges on the accurate determination of the optical properties down to the monolayer limit, which is still missing. By using hyperspectral wide-field imaging at room temperature, we reveal a nonmonotonic thickness dependence of the complex optical dielectric function in the archetypal magnetic 2D material CrI₃ extending across different length scales: onsetting at the mesoscale, peaking at the nanoscale, and decreasing again down to the single layer. These results portray a modification of the electronic properties of the material and align with the layer-dependent magnetism in CrI₃, shedding light on the long-standing structural conundrum in this material. The unique modulation of the complex dielectric function from the monolayer up to more than 100 layers will be instrumental for understanding mesoscopic effects in layered materials and tuning light-matter interactions in magnetic 2D materials.

Figures

Complete Figure 1 composition from the CrI3 hyperspectral microscopy article — **Figure 1. Summary.** Spectroscopic characterization of CrI3. (a) Visible range transmittance spectra of CrI3 crystals with a different number of layers.

Complete Figure 2 composition from the CrI3 hyperspectral microscopy article — **Figure 2. Summary.** Evolution of the dielectric functions in CrI3 as a function of the layer number. The calculated real (ε1) and imaginary (ε2) parts of ε̃ are represented by color maps [(a),(b)] and line plots [(c),(d)], respectively.

Complete Figure 3 composition from the CrI3 hyperspectral microscopy article — **Figure 3. Summary.** Identification of different thickness regimes in CrI3. The few-layer, multilayer, and bulk thickness regimes are depicted according to (a) the layer dependence of ε1 and ε2 at 2.66 eV from the fitting process to the dataset shown in Fig.

Complete Figure 4 composition from the CrI3 hyperspectral microscopy article — **Figure 4. Summary.** Theory calculations of the layer-dependent electronic and optical properties of CrI3. (a),(b) Evolution of ε1 and ε2 of CrI3 with an increasing number of layers calculated in the z direction perpendicular to the layers.

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Research fields

Simulations & fits

A multilayer Fabry-Pérot model and a two-oscillator dielectric function are fitted simultaneously to hyperspectral transmittance data from different CrI₃ thicknesses. First-principles calculations then relate the observed dielectric evolution to changes in the layer-dependent electronic structure.

Characterization

Hyperspectral microscopy maps transmittance from the monolayer to mesoscale thicknesses on the same exfoliated CrI₃ flake. The spatially registered spectra separate few-layer, multilayer and bulk-like regimes and show that the monolayer optical response is not a simple thin limit of the bulk material.

RESEARCH TOPICS

MagnetismCrI3 changes its magnetic ordering with thickness: few-layer samples are layered antiferromagnets, whereas the bulk is ferromagnetic, with the crossover occurring in the tens-of-nanometres range. The hyperspectral measurements reveal an optical crossover at a comparable mesoscale thickness.

MaterialsThe complex dielectric function is tracked continuously from a monolayer to flakes containing more than 100 layers. AFM and Raman checks confirm that the exfoliated flakes are atomically flat and chemically pristine, reducing thickness errors and degradation as alternative explanations.

QuantumThe optical trend is interpreted as a modification of CrI3's electronic structure, not merely as a classical interference artefact. This makes the thickness-dependent optical response relevant to quantum and spin-photonic devices in which magnetic order and light-matter interaction must be controlled together.

SetupsWide-field hyperspectral microscopy records transmission over many pixels and wavelengths at room temperature, allowing dielectric properties to be mapped on mechanically exfoliated flakes too small for conventional ellipsometry. Figure 3 provides an internal cross-check: parameters extracted from the fit reproduce the independent evolution of the transmittance minima, while AFM supplies the layer thickness and Raman spectroscopy identifies the structural phase.