Full Crystallographic Imaging of Hexagonal Boron Nitride Monolayers with Phonon‐Enhanced Sum‐Frequency Microscopy

Hexagonal boron nitride (hBN) is an important 2D material for van der Waals heterostructures, single photon emitters, and infrared nanophotonics. The optical characterization of mono- and few-layer samples of hBN however, remains a challenge as the material is almost invisible optically. Here, phase-resolved sum-frequency microscopy is introduced as a technique for imaging monolayers of hBN grown by chemical vapor deposition (CVD) and visualizing their crystal orientation. Femtosecond mid-infrared (IR) and visible laser pulses are used for sum-frequency generation (SFG), which is imaged in a wide-field optical microscope. The IR laser resonantly excites a phonon of hBN that leads to an ≈800-fold enhancement of the SFG intensity, making it possible to image large 100 × 100 µm<sup>2</sup> sample areas in less than 1 s. Heterodyne detection combined with azimuthal sample rotation further provides full crystallographic information. Combined knowledge of topography and crystal orientation reveals that triangular domains of CVD-grown monolayer hBN have nitrogen-terminated zigzag edges. Overall, SFG microscopy is an ultra-sensitive tool with the potential to image crystal structure, strain, stacking sequences, and twist angles in a wide range of van der Waals structures, where locating and identifying monolayer regions and interfaces with broken inversion symmetry is of paramount importance.

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Publication Details

Journal
Advanced Materials
Published
2025-11-20
DOI
https://doi.org/10.1002/adma.202510124
Citations
1
Primary Topic
2D Materials and Applications
Type
article
Field-Weighted Citation Impact
0.52

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article

Full Crystallographic Imaging of Hexagonal Boron Nitride Monolayers with Phonon‐Enhanced Sum‐Frequency Microscopy

Andrew E. Naclerio, Christoph Scheurer, Martin Thämer, Niclas S. Mueller et al.
1 citations
Advanced Materials
2D Materials and Applications
0.52
article

Full Crystallographic Imaging of Hexagonal Boron Nitride Monolayers with Phonon‐Enhanced Sum‐Frequency Microscopy

Andrew E. Naclerio, Christoph Scheurer, Martin Thämer, Niclas S. Mueller, Piran R. Kidambi, Karsten Reuter, Hendrik H. Heenen, K. Gharagozloo-Hubmann, Ryan A. Kowalski, Christian Carbogno, Alexander Paarmann, Alexander P. Fellows, Ben John, Joshua D. Caldwell, Martin Wolf, Damián Baláž
article en
1 citations

Abstract

Hexagonal boron nitride (hBN) is an important 2D material for van der Waals heterostructures, single photon emitters, and infrared nanophotonics. The optical characterization of mono- and few-layer samples of hBN however, remains a challenge as the material is almost invisible optically. Here, phase-resolved sum-frequency microscopy is introduced as a technique for imaging monolayers of hBN grown by chemical vapor deposition (CVD) and visualizing their crystal orientation. Femtosecond mid-infrared (IR) and visible laser pulses are used for sum-frequency generation (SFG), which is imaged in a wide-field optical microscope. The IR laser resonantly excites a phonon of hBN that leads to an ≈800-fold enhancement of the SFG intensity, making it possible to image large 100 × 100 µm<sup>2</sup> sample areas in less than 1 s. Heterodyne detection combined with azimuthal sample rotation further provides full crystallographic information. Combined knowledge of topography and crystal orientation reveals that triangular domains of CVD-grown monolayer hBN have nitrogen-terminated zigzag edges. Overall, SFG microscopy is an ultra-sensitive tool with the potential to image crystal structure, strain, stacking sequences, and twist angles in a wide range of van der Waals structures, where locating and identifying monolayer regions and interfaces with broken inversion symmetry is of paramount importance.

Advanced MaterialsVol. 38(7)
Vanderbilt University (US), Fritz Haber Institute of the Max Planck Society (DE), University of Florida (US), Freie Universität Berlin (DE)
National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, European Commission, Deutsche Forschungsgemeinschaft, Multidisciplinary University Research Initiative, Office of Naval Research
Openalex Percentile: Top 30%
2D Materials and Applications
0.52
DOIOpen Access PDFOpenAlex
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