Anisotropic Phonon Response of Few‐Layer PdSe2 under 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 PdSe₂ Raman peaks are influenced differently depending on the direction of strain application. The $A_g^1$ mode redshifts more than the $A_g^3$ mode when the strain is applied along the a‐axis of the crystal, while the $A_g^3$ mode redshifts more than the $A_g^1$ mode when the strain is applied along the b‐axis. Such an anisotropic phonon response to strain indicates directionally dependent mechanical and thermal properties of PdSe₂ 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 PdSe₂ are found, suggesting that the uniaxial tensile strain can easily be applied to few‐layer PdSe₂ 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.