Strong interlayer coupling and layer-dependent bandgap in 2D layered PdSe₂ synthesized by chemical vapor deposition

Two-dimensional (2D) noble metal dichalcogenides, such as PtS₂ or PdSe₂, have attracted much attention due to their remarkable layer-dependent electronic structures and superior electrical properties for device applications. However, most of the demonstrated experiments thus far are based on mechanical exfoliations from bulk crystals. Here, we demonstrate that highly crystalline and air stable PdSe₂, from bilayer up to few layers, can be synthesized by chemical vapor deposition. The atomic ratio and the lattice structure of PdSe₂ have been confirmed by x-ray photoemission and polarization-resolved Raman spectra. Low-frequency Raman measurements of breathing vibration modes reveal the strong interlayer coupling, which can also be used for identifying the layer numbers [1]. Based on absorption measurements, we observed a strongly layer-dependent bandgap, which shows a gap shrinkage up to 0.5 eV with the increasing layer number from bilayer to 7 layers. The dramatically layer-dependent bandgap shrinkage is also consistent with the calculated energy gap based on density functional theory.[2]

[1] Puretzky A.A., et al., 2D Materials, 5(3), p. 035016, 2018.
[2] Oyedele A.D., et al., J Am Chem Soc, 139(40), p. 14090-14097, 2017.