PSHG vs 4D STEM imaging of twist angle in 2D transition metal dichalcogenide bilayers
ORAL
Abstract
Atomically thin two-dimensional materials can be vertically stacked with van der Waals bonds that enable interlayer coupling. In the particular case of transition metal dichalcogenide (TMD) bilayers, the relative orientation between the two monolayers, i.e., the twist-angle, modifies the crystal symmetry and creates a superlattice with exciting properties. In this work, we demonstrate an all-optical, high resolution method for pixel-by-pixel mapping of the twist-angle, via polarization-resolved second harmonic generation (PSHG) microscopy and compare it with four-dimensional scanning transmission electron microscopy (4D STEM). It is found that the twist-angle imaging of WS2 bilayers, using the PSHG technique is in excellent agreement with that obtained using electron diffraction. The main advantages of the nonlinear optical method are that the characterization is performed on the same substrate that the bilayer is created on and that it is three orders of magnitude faster than the 4D STEM.
*This research has been co-financed by the European Union and Greek national funds through the Joint Calls for Proposals of European Networks ERA NETS (National project code: GRAPH-EYE T8ΕΡΑ2-00009 and European code: 26632, FLAGERA). L.M., G.Ko. and G.Ki. acknowledge funding by the Hellenic Foundation for Research and Innovation (H.F.R.I.). J.V acknowledges funding from FWO G093417N from the Flanders Research Fund, EU. J.V. and N.G. acknowledge funding from the European Union under the Horizon 2020 programme within a contract for Integrating Activities for Advanced Communities No 823717—ESTEEM3. J.V. N.G. and A.O. acknowledge funding through a GOA project "Solarpaint" of the University of Antwerp.
