Anisotropic Phonon Response of Few‐Layer PdSe₂ under Uniaxial Strain

Abstract

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 Ag1 mode redshifts more than the Ag3 mode when the strain is applied along the a‐axis of the crystal, while the Ag3 mode redshifts more than the Ag1 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.

Review of Anisotropic 2D Materials: Controlled Growth, Optical Anisotropy Modulation, and Photonic Applications

“…[ 193 ] The intrinsic fourfold‐symmetry of the E 2g 1 mode in angle‐dependent Raman spectra is tuned to a twofold‐symmetry (Figure 8e). A redshift of Raman frequency was also observed in strain engineered tellurium, [ 17a ] PdSe 2 , [ 194 ] and WTe 2 . [ 195 ]…”

Giant anisotropic in-plane thermal conduction induced by Anomalous phonons in pentagonal PdSe2

“…Anisotropy of PdSe2 has also been reported, such as electrical [19,20], optical [15,19], and thermoelectric properties [16,21]. Much work has focused on the theoretical lattice dynamics calculations, but less was confirmed by measurements [22][23][24]. PdSe2 takes a puckered pentagonal structure with an orthorhombic lattice (a=5.75 Å, b=5.87 Å, c=7.69 Å, a/b=0.98) (Figure 1a) [25], in which four Se atoms covalently bond the Pd atom with a nearlyequal Pd-Se bond length (2.44 Å / 2.44 Å ≈ 1), bond strength (2.51 eV /2.50 eV ≈ 1), and bond force constant (4.18 eV Å -2 / 4.15 eV Å -2 ≈ 1) [26], showing a nearly-isotropic structure in the basal plane (Figure 1b).…”

Strongly Anisotropic Strain‐Tunability of Excitons in Exfoliated ZrSe3

“…Despite the recent interest on these families of anisotropic 2D materials, [19][20][21][22][23][24][25][26] the number of reported research works focused on studying the effect of strain along different crystal directions is still very scarce and primarily focused on the investigation of strain tunable Raman modes in black phosphorus, PdSe 2 , or tellurium. [27][28][29][30][31] The group IV-V transition metal trichalcogenides (TMTCs) are a less-explored family of materials with quasi-1D electrical and optical properties stemming from a reduced in-plane structural symmetry. [24,[32][33][34] These materials have a general formula of MX 3 being M a transition metal atomThe effect of uniaxial strain on the band structure of ZrSe 3 , a semiconducting material with a marked in-plane structural anisotropy, is studied.…”