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.