Polarized X-ray diffraction anomalous near-edge structure study on the orbital physics of thin WSe₂ layers

The electronic structures at band edges play an important role in the physical properties of few-layer and monolayer WSe 2 . In this study, polarization-dependent diffraction anomalous near-edge structure (DANES) is applied to measure and analyse the electronic orbitals of few-layer WSe 2 . By selecting diffraction geometries with the electric field perpendicular or parallel to the c axis of few-layer WSe 2 , this method can separately probe the in-plane and out-of-plane orbital components involved at the band edges. The WSe 2 (00.8) surface normal was aligned and the preferred orientation of few-layer WSe 2 grown on an Al 2 O 3 (00.1) substrate was identified. DANES was then performed for Se K -edge WSe 2 00.8 and 11.0 reflections to examine the W 5 d orbitals hybridized with the Se 4 p orbitals: these two DANES spectra exhibit fairly anisotropic valence orbital characteristics in few-layer WSe 2 . Coupled with first-principles calculations, these results allow the identification of the in-plane and out-of-plane orbital distribution and hybridization in WSe 2 . At the conduction band edge, the contributions of p x and p y orbitals are predominant over p z and the splitting of the p -orbital energy levels has been confirmed. Hence DANES is shown to be a useful synchrotron X-ray technique that can help identify the valence orbital structure of various 2D transition metal dichalcogenides.