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<p>The lateral dimensions of mechanically exfoliated flakes of emerging van der Waals (vdW) materials rarely exceed a few tens of micrometers. This limits the experimental determination of their complex dielectric function (<i>ϵ</i>(<i>ω</i>)) at mid-infrared (IR) frequencies, as the IR beam in conventional angle-resolved spectroscopic ellipsometry is typically larger than a flake. To overcome this, previous methods mapped the dispersion of surface phonon polaritons using near-field probes, but these require costly instrumentation, are sensitive to external factors, demand extensive numerical fitting, and become cumbersome for anisotropic or dispersive materials. Here, we introduce a simple empirical method to extract the in-plane dielectric tensor components of small flakes using conventional Fourier Transform Infrared (FTIR) micro-spectrometry. By identifying reflectance minima near phonon resonances, we determine <i>ϵ</i> per frequency without model fitting. Applying this approach to flakes of varying thicknesses enables reconstruction of <i>ϵ</i>(<i>ω</i>) over a broad spectral range.</p>

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Far-field extraction of the dielectric function of exfoliated flakes near phonon resonances

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年2月21日

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  • Mitradeep Sarkar,
  • Michael T. Enders,
  • Mehrdad Shokooh-Saremi,
  • Evgenia Klironomou,
  • Gonzalo Álvarez-Pérez,
  • Kenji Watanabe,
  • Takashi Taniguchi,
  • Hanan H. Sheinfux,
  • Frank H. L. Koppens,
  • Georgia T. Papadakis

摘要

The lateral dimensions of mechanically exfoliated flakes of emerging van der Waals (vdW) materials rarely exceed a few tens of micrometers. This limits the experimental determination of their complex dielectric function (ϵ(ω)) at mid-infrared (IR) frequencies, as the IR beam in conventional angle-resolved spectroscopic ellipsometry is typically larger than a flake. To overcome this, previous methods mapped the dispersion of surface phonon polaritons using near-field probes, but these require costly instrumentation, are sensitive to external factors, demand extensive numerical fitting, and become cumbersome for anisotropic or dispersive materials. Here, we introduce a simple empirical method to extract the in-plane dielectric tensor components of small flakes using conventional Fourier Transform Infrared (FTIR) micro-spectrometry. By identifying reflectance minima near phonon resonances, we determine ϵ per frequency without model fitting. Applying this approach to flakes of varying thicknesses enables reconstruction of ϵ(ω) over a broad spectral range.