Anisotropic Phonon Response of Few-Layer PdSe2under Uniaxial Strain

PdSe2, an emerging 2D material with a novel anisotropic puckered pentagonal structure, has attracted growing interest due to its layer-dependent electronic bandgap, high carrier mobility, and good air stability. Herein, a detailed Raman spectroscopic study of few-layer PdSe2(two to five layers) under the in-plane uniaxial tensile strain up to 3.33% is performed. Two of the prominent PdSe(2)Raman peaks are influenced differently depending on the direction of strain application. TheAg1mode redshifts more than theAg3mode when the strain is applied along thea-axis of the crystal, while theAg3mode redshifts more than theAg1mode when the strain is applied along theb-axis. Such an anisotropic phonon response to strain indicates directionally dependent mechanical and thermal properties of PdSe(2)and also allows the identification of the crystal axes. The results are further supported using first-principles density-functional theory. Interestingly, the near-zero Poisson's ratios for few-layer PdSe(2)are found, suggesting that the uniaxial tensile strain can easily be applied to few-layer PdSe(2)without significantly altering their dimensions at the perpendicular directions, which is a major contributing factor to the observed distinct phonon behavior. The findings pave the way for further development of 2D PdSe2-based flexible electronics.