B. Schuler, K. Cochrane, J.-H. Lee, C. Kastl, S. Refaely-Abramson, D. Qiu, S. Barja, C. Chen, N. Borys, F. Ogletree, S. Aloni, A. Schwartzberg, S. Louie, J. Neaton, and A. Weber-Bargioni
Lawrence Berkeley National Laboratory,
Keywords: TMD, defect, scanning probe microscopy, WS2
Summary:Point defects in transition metal dichalcogenide (TMD) monolayers have a tremendous impact on material properties owing to their intrinsic confinement. Particularly the creation of in-gap defect states is decisive for any defect functionality. Here we present a comprehensive study of defects in CVD-grown monolayer WS2 using high-resolution scanning probe microscopy with CO functionalized tips. We identified the intrinsic substitutional defects O_S (oxygen replacing sulfur), Cr_W (chromium replacing tungsten) and Mo_W (molybdenum replacing tungsten) as well as annealing-induced chalcogen vacancies (V_S) based on their characteristic electronic fingerprint. The in-gap defect states formed by Cr_W and V_S were found to be split due to spin-orbit coupling by direct orbital imaging, corroborated by density functional theory calculations. Moreover, we observed electron-induced luminescence at individual point defects. Spectrally integrated luminescence maps with sub-nanometer resolution will be shown that resemble the in-gap defect orbitals. Tunneling bias-dependent luminescence spectra further shine light on the electron-induced photon emission mechanism. The atomic-scale characterization of atomic, electronic and optical defect properties allows an unprecedentedly detailed picture on the structure and functionality of point defects in 2D-TMDs.