Visualization of native defects in PdSe2 using scanning tunneling microscope*

Palladium diselenide (PdSe₂), a newly discovered 2D layered transition-metal dichalcogenide (TMD), have attracted great research interest recently due to its extraordinary high carrier mobility and interesting anisotropic properties. In contrast to most other TMDs with isotropic planar hexagonal structure, PdSe₂ has a unique buckled pentagonal structure in the 2D layer. Here we report our recent study on PdSe₂ bulk crystals cleaved in situ under ultra-high vacuum (UHV) using Scanning Tunneling Microscopy (STM). Atomic resolution images and scanning tunneling spectroscopy are acquired to reveal structural and electronic properties of the material. Interestingly, native defects in PdSe₂ appear as a ringlike feature in STM differential conductance (dI/dV) maps. The observation is explained by the reversibly switched charge states of the defects controlled by the tip-induced band bending. The defect structure and defect states are resolved experimentally and corroborated by first-principle calculations.