Quantitative Nanoinfrared Spectroscopy of Anisotropic van der Waals Materials

Francesco L. Ruta, Aaron J. Sternbach, Adji B. Dieng, Alexander S. McLeod, D. N. Basov

Research output: Contribution to journalArticlepeer-review

Abstract

Anisotropic dielectric tensors of uniaxial van der Waals (vdW) materials are difficult to investigate at infrared frequencies. The small dimensions of high-quality exfoliated crystals prevent the use of diffraction-limited spectroscopies. Near-field microscopes coupled to broadband lasers can function as Fourier transform infrared spectrometers with nanometric spatial resolution (nano-FTIR). Although dielectric functions of isotropic materials can be readily extracted from nano-FTIR spectra, the in-and out-of-plane permittivities of anisotropic vdW crystals cannot be easily distinguished. For thin vdW crystals residing on a substrate, nano-FTIR spectroscopy probes a combination of sample and substrate responses. We exploit the information in the screening of substrate resonances by vdW crystals to demonstrate that both the in-and out-of-plane dielectric permittivities are identifiable for realistic spectra. This novel method for the quantitative nanoresolved characterization of optical anisotropy was used to determine the dielectric tensor of a bulk 2H-WSe2microcrystal in the mid-infrared.

Original languageEnglish (US)
Pages (from-to)7933-7940
Number of pages8
JournalNano letters
Volume20
Issue number11
DOIs
StatePublished - Nov 11 2020
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported as part of the Center for Novel Pathways to Quantum Coherence in Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. D.N.B. is the Vannevar Bush Faculty Fellow ONR-VB: N00014-19-1-2630 and Moore Investigator in Quantum Materials #9455.

Publisher Copyright:
© 2020 American Chemical Society. All rights reserved.

Keywords

  • dielectric
  • identifiability
  • optics
  • SNOM
  • van der Waals
  • WSe

PubMed: MeSH publication types

  • Journal Article

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