Strain-induced variations in the Raman and infrared spectra of monolayer InSe: A first-principles study

Monolayer indium selenide (InSe), a two-dimensional material, exhibits exceptional electronic and optical properties that can be significantly modulated via strain engineering. This study employed density functional theory to examine the structural and vibrational properties of monolayer InSe under varying biaxial strains. Phonon dispersion analysis confirmed the stability of monolayer InSe, as indicated by the absence of imaginary frequencies. The study extensively detailed how Raman and infrared spectra adjust under strain, showing shifts in peak positions and variations in intensity that reflect changes in lattice symmetry and electronic structures. Specific findings include the stiffening of the A '(1) mode and the increased intensity of E '' and E ' modes under strain, suggesting enhanced polarizability and asymmetric vibrations. Moreover, the Raman intensity for the E ' mode at 167.3 cm(-1) increased under both tensile and compressive strain due to enhanced polarizability and symmetry disruption, while the IR intensity for the A ''(2) mode at 192.1 cm(-1) decreased, likely from diminished dipole moment changes. In contrast, the low-frequency modes, such as E '' at 36.8 cm(-1), demonstrated insensitivity to strain, implying a minimal impact on heavier atoms within these modes. Overall, this study highlights the sensitivity of vibrational modes to strain-induced changes, providing valuable insights into the behavior of monolayer InSe under mechanical stress.