Layer-dependent band engineering of Pd dichalcogenides: a first-principles study

Abstract

Among the families of transition metal dichalcogenides (TMDs), Pd-based TMDs have been one of the less explored materials. In this study, we investigate the electronic properties of PdX _2 (X = S, Se, or Te) bulk and thin films. The analysis of structural stability shows that the bulk and thin film (1 to 5 layers) structures of PdS _2 exhibit pyrite, while PdTe _2 exhibits 1T. Furthermore, PdSe _2 exhibits pyrite in bulk and thin films down to the bilayer. Most surprisingly, PdSe _2 monolayer transits to 1T phase. For the electronic properties of the stable bulk configurations, pyrite PdS _2 and PdSe _2 , and 1T PdTe _2 , demonstrate semi-metallic features. For monolayer, on the other hand, the stable pyrite PdS _2 and 1T PdSe _2 monolayers are insulating with band gaps of 1.399 eV and 0.778 eV, respectively, while 1T PdTe _2 monolayer remains to be semi-metallic. The band structures of all the materials demonstrate a decreasing or closing of indirect band gap with increasing thickness. Moreover, the stable monolayer band structures of PdS _2 and PdSe _2 exhibit flat bands and diverging density of states near the Fermi level, indicating the presence of van Hove singularity. Our results show the sensitivity and tunability of the electronic properties of PdX _2 for various potential applications.

Keywords

• palladium
• transition metal dichalcogenides
• thickness dependence
• density functional theory
• 2D materials
• thin films