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 WSe2. In this study, polarization‐dependent diffraction anomalous near‐edge structure (DANES) is applied to measure and analyse the electronic orbitals of few‐layer WSe2. By selecting diffraction geometries with the electric field perpendicular or parallel to the c axis of few‐layer WSe2, this method can separately probe the in‐plane and out‐of‐plane orbital components involved at the band edges. The WSe2 (00.8) surface normal was aligned and the preferred orientation of few‐layer WSe2 grown on an Al2O3 (00.1) substrate was identified. DANES was then performed for Se K‐edge WSe2 00.8 and 11.0 reflections to examine the W 5d orbitals hybridized with the Se 4p orbitals: these two DANES spectra exhibit fairly anisotropic valence orbital characteristics in few‐layer WSe2. Coupled with first‐principles calculations, these results allow the identification of the in‐plane and out‐of‐plane orbital distribution and hybridization in WSe2. At the conduction band edge, the contributions of px and py orbitals are predominant over pz 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. This work demonstrates the capability of polarization‐dependent diffraction anomalous near‐edge structure to differentiate and analyse the valence orbital structure of few‐layer WSe2 around the band edge.