Excitation-Dependent Anisotropic Raman Response of Atomically Thin Pentagonal PdSe 2 .

The group-10 noble-metal dichalcogenides have recently emerged as a promising group of two-dimensional materials due to their unique crystal structures and fascinating physical properties. In this work, the resonance enhancement of the interlayer breathing mode (B1) and intralayer A g 1 and A g 3 modes in atomically thin pentagonal PdSe 2 were studied using angle-resolved polarized Raman spectroscopy with 13 excitation wavelengths. Under the excitation energies of 2.33, 2.38, and 2.41 eV, the Raman intensities of both the low-frequency breathing mode B1 and high-frequency mode A g 1 of all the thicknesses are the strongest when the incident polarization is parallel to the a axis of PdSe 2 , serving as a fast identification of the crystal orientation of few-layer PdSe 2 . We demonstrated that the intensities of B1, A g 1 , and A g 3 modes are the strongest with the excitation energies between 2.18 and 2.38 eV when the incident polarization is parallel to PdSe 2 a axis, which arises from the resonance enhancement caused by the absorption. Our investigation reveals the underlying interplay of the anisotropic electron-phonon and electron-photon interactions in the Raman scattering process of atomically thin PdSe 2 . It paves the way for future applications on PdSe 2 -based optoelectronics.