Researchers from the University of Iowa, McMaster University, and Vanderbilt University have demonstrated an accurate and precise way to determine the crystal orientation of ultrathin layered materials. When these materials, known as van der Waals (vdW) materials, are stacked with one layer rotated relative to another, the electronic and optical behavior of the resulting heterostructure can change dramatically.

In the study, published in open-access journal ACS Nanoscience Au, the team adapted electron backscatter diffraction (EBSD), a scanning electron microscope technique, to identify the crystal orientation of several low symmetry vdW materials. They showed EBSD gives excellent accuracy and a precision of ~0.2^o with molybdenum trioxide, an orthorhombic crystal. They further demonstrated that it worked for even lower symmetry vdW crystals, such as arsenic telluride, gallium telluride and rhenium diselenide, whose edges often do not reliably reveal their crystal orientation.

To demonstrate its practical value, the researchers used EBSD measurements to stack two flakes of molybdenum trioxide at a targeted twist angle and then directly verified the final angle after assembly. The resulting structure guided hybrid nanoscale light–matter waves in the infrared, known as phonon polaritons, along a narrow and highly directional path. The findings from this work, led by Ramachandra Bangari and Prof. Thomas Folland of Quantum Nanophotonic Materials Lab, provide scientists with a more reliable way to fabricate and verify precisely twisted vdW heterostructures for emerging nanophotonics and quantum technologies.