Full Crystallographic Imaging of Hexagonal Boron Nitride Monolayers with Phonon‐Enhanced Sum‐Frequency Microscopy
Abstract
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 2 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.
Article Details
Authors (16)
Niclas S. Mueller
Fritz‐Haber‐Institut der Max‐Planck‐Gesellschaft Berlin Germany
Alexander P. Fellows
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
Ben John
Department of Physical Chemistry Fritz‐Haber‐Institute of the Max‐Planck‐Society 14195 Berlin Germany
Andrew E. Naclerio
Chemical and Biomolecular Engineering Department Vanderbilt University Nashville TN 37212 USA
Christian Carbogno
Fritz‐Haber‐Institut der Max‐Planck‐Gesellschaft Berlin Germany
Katayoun Gharagozloo‐Hubmann
Department of Physics Freie Universität Berlin 14195 Berlin Germany
Damián Baláž
Theory Department Fritz‐Haber‐Institute of the Max‐Planck‐Society 14195 Berlin Germany
Ryan A. Kowalski
Vanderbilt University Nashville TN USA
Hendrik H. Heenen
Fritz-Haber-Institute of the Max-Planck-Society 23 , Berlin,
Christoph Scheurer
Fritz-Haber Institute of the Max Planck Society 1 , Berlin (DE),
Karsten Reuter
Theory Department, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
Joshua D. Caldwell
Department of Mechanical Engineering Vanderbilt University Nashville Tennessee USA
Martin Wolf
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
Piran R. Kidambi
Mechanical and Aerospace Engineering Department University of Florida Gainesville FL 32611 USA
Martin Thämer
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, Berlin 14195, Germany
Alexander Paarmann
Department of Physcial Chemistry Fritz Haber Institute of the Max Planck Society Berlin Germany