First-Principles Study of Thickness Dependence of Pt Dichalcogenides -- PtX₂ (X = S, Se, and Te)
Rovi Angelo B. Villaos1*, Christian P. Crisostomo1, Zhi-Quan Huang1, Hsin Lin2, Feng-Chuan Chuang1,3
1Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
2Institute of Physics, Academia Sinica, Taipei, Taiwan
3Multidisciplinary and Data Science Research Center, National Sun Yat-Sen University, Kaohsiung, Taiwan
* Presenter:Rovi Angelo B. Villaos
Using first-principles calculation, we explore the tunability of the electronic properties of PtX₂ (X = S, Se, and Te) with respect to the film thickness. We examine different known structures, including 1T, 2H, and 3R. For bulk and thin film (1 to 10 layers), octahedral 1T is the most stable. Surprisingly, we also find that 3R structure has comparable stability relative to 1T, implying synthesis of 3R. For bulk 1T, PtS₂ is semiconducting and the other two are semimetallic, while all their corresponding monolayer exhibit an indirect semiconducting phase. All structures manifest decreasing/closing of indirect bandgap with increasing thickness. Furthermore, we observe that the electronic properties of different chalcogens have varying sensitivity with respect to thickness change. 1T-PtTe₂ is the most sensitive based from its fast transition from semiconducting (only in monolayer with 0.40 eV bandgap) to semimetallic to metallic while increasing up to 10 layers. 1T-PtSe₂ exhibits a drastic decrease in bandgap from monolayer (1.18 eV) to bilayer (0.21 eV), with change from semiconducting to semimetallic phase occurring from bilayer to trilayer. However, scrutinizing the semimetallic layers of 1T-PtSe₂ reveal that the system bandgap substantially decreases until 6 layers, then slowly progress to bulk limit. 1T-PtS₂ (semiconducting from monolayer to bulk) possesses the most resilient band properties among the three materials because changes in the bandgap already start to approach the bulk bandgap (0.25 eV) as early as 4-layer thickness. Still, a significant decrease in bandgap occur from monolayer (1.68 eV) to bilayer (0.82 eV). These observed phenomena are due to the interplay between geometric confinement and interlayer interactions. Our results show that the sensitivity and tunability of electronic properties of PtX₂ pave a new path for future potential applications.

Keywords: Density-functional theory, Transition Metal Dichalcogenides, Thin Films