Exploring the Structural Stability of 1T-PdO2 and the Interface Properties of the 1T-PdO2/Graphene Heterojunction

Motivated by a recent study on the air stability of PdSe₂, which also reports the metastability of the PdO₂ 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 PdO₂ and study its structural and electronic properties. We further studied its vertical heterojunction composed of 1T-PdO₂ 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-PdO₂ 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 PdO₂/graphene contact, forming an Ohmic contact and mainly suggesting the potential of graphene for efficient electrical contact with the PdO₂ 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 PdO₂/graphene heterojunction under visible-light irradiation is significantly enhanced compared to the situation in their free-standing monolayers.