Flexible ferroelasticity in monolayer PdS2: a DFT study

Layer-dependent electronic structures and optical properties of two-dimensional PdSSe

Two-dimensional (2D) layered palladium dichalcogenides PdX₂ (X = S and Se) have attracted increasing interest due to their tunable electronic structure and abundant physicochemical properties. Recently, as the sister material of PdX₂, PdSSe has received increasing attention and shows great promise for technological applications and fundamental research. In the present study, we focus on the layer-dependent geometry, electronic structure, and optical properties of PdSSe using first-principles calculations. The lattice shrinkage effect present in the 2D structure is suppressed with increasing number of layers. Attributed to the strong interlayer coupling interactions, the band gap decreases from 2.30 to 0.83 eV with increased thickness. Particularly, the dispersion of the band edges on the high symmetry path changes considerably from the monolayer to bilayer PdSSe, resulting in shifts of the conduction band minimum and valence band maximum. The multilayer PdSSe shows band convergence feature with multi-valley for the conduction band, which are maintained with reduced effective mass. Furthermore, the increasing number of layers drives a wider absorption range in the visible light region, and the light absorption capability increases from ∼10% to ∼30%. Meanwhile, the band edge positions of the multilayer PdSSe are more appropriate for photocatalytic water splitting. Our theoretical study reveals the enhanced valley convergence, conductivity and optical absorption performance of the few-layer PdSSe, which suggests its promising application in thermoelectric conversion, solar harvesting and photocatalysis.

Centimeter-Scale PdS2 Ultrathin Films with High Mobility and Broadband Photoresponse

2D materials with mixed crystal phase will lead to the nonuniformity of performance and go against the practical application. Therefore, it is of great significance to develop a valid method to synthesize 2D materials with typical stoichiometry. Here, 2D palladium sulfides with centimeter scale and uniform stoichiometric ratio are synthesized via controlling the sulfurization temperature of palladium thin films. The relationship between sulfurization temperature and products is investigated in depth. Besides, the high-quality 2D PdS₂ films are synthesized via sulfurization at the temperature of 450-550 °C, which would be compatible with back-end-of-line processes in semiconductor industry with considering of process temperature. The PdS₂ films show an n-type semiconducting behavior with high mobility of 10.4 cm² V^-1 s^-1 . The PdS₂ photodetector presents a broadband photoresponse from 450 to 1550 nm. These findings provide a reliable way to synthesizing high-quality and large-area 2D materials with uniform crystal phase. The result suggests that 2D PdS₂ has significant potential in future nanoelectronics and optoelectronic applications.