Exploring the Structural Stability of 1T-PdO and the Interface Properties of the 1T-PdO/Graphene Heterojunction.

Motivated by a recent study on the air stability of PdSe, which also reports the metastability of the PdO monolayer [Hoffman A. N.. npj 2D Mater. Appl.2019, 3( (1), ), 50.], in this work, we use density functional theory (DFT) to further explore the thermal, dynamic, and mechanical stability of monolayer PdO and study its structural and electronic properties. We further studied its vertical heterojunction composed of 1T-PdO and graphene monolayers. We show that both the monolayer and the heterojunction are energetically and dynamically stable with no negative frequencies in the phonon spectrum and belong to the vdW-type. 1T-PdO is an indirect-band-gap semiconductor with band-gap values of 0.5 eV (GGA) and 1.54 eV (HSE06). The interface properties of the heterojunction show that the n-type Schottky barrier height (SBH) becomes negative at the vertical interface in the PdO/graphene contact, forming an Ohmic contact and mainly suggesting the potential of graphene for efficient electrical contact with the PdO monolayer. However, at the same time, a negative band bending occurs at the lateral interface based on the current-in-plane model. Moreover, the optical absorption of the PdO/graphene heterojunction under visible-light irradiation is significantly enhanced compared to the situation in their free-standing monolayers.