Vibration modes of phonons in few-layer NbOCl2 modulated by uniaxial strain

Strain engineering is an important strategy to modulate the optical and electronic properties of two-dimensional materials. Phonon is one of the most significant elementary excitations of solids and plays a key role in heat conduction, phonon-photon interaction and phonon-electron interaction. NbOCl is abundant in phonon modes, demonstrates considerable monolayer-like exciton effects, possesses excellent second-order nonlinear optical response, and displays emerging physical properties attributed to its weak interlayer coupling. In this work, the phonon vibrational modes of NbOCl were modulated by uniaxial strain. The phonon vibrational modes P1 and P5 exhibited strain-dependent phonon displacements, with the strain coefficients of P1 under uniaxial tensile strain reaching 3.45 cm/% and that of P5 as high as 6.61 cm/%. Furthermore, the full width at half maximum (FWHM) of P5 tended to decrease during the tensile strain loading process. In addition, the sensitivity of the phonon vibrational modes of NbOCl to strain was also investigated for different layers, and it was found that the thin layers of NbOCl were highly sensitive to strain. This work broadens the application in flexible optoelectronic devices. It also has great potential application value in future fields such as quantum communication, design of lasers and solar cells.