Size-dependent localized acoustic vibrations in MoS2 thin film with patterned nanohole arrays

The study of coherent acoustic vibrations in nanostructured materials, particularly in two-dimensional (2D) semiconductors, has gained significant interest due to their potential applications in sensing, energy conversion, and nanoscale acoustic devices. While much of the research has focused on 2D transition metal dichalcogenides (TMDs), the effect of nanoscale patterning on the vibrational properties of TMDs remains less explored. Here, we investigate the coherent acoustic vibrations in MoS2 thin films with patterned nanohole arrays, excited by femtosecond laser pulses. Using pump–probe spectroscopy and finite element simulations, we explore the size-dependent vibrational frequencies of the nanohole arrays. The experimental results reveal two distinct vibrational modes: a thickness-dependent out-of-plane breathing mode of the MoS2 thin films, and a low-frequency mode corresponding to the in-plane periodic deformation of the nanoholes. The study highlights the size-dependent vibrational frequencies of the nanoholes, showing excellent agreement between experiments and simulations. These findings provide valuable insights into phonon engineering in 2D materials, enabling control over both in-plane and out-of-plane vibrational properties. This work paves the way for designing nanomechanical resonators and acoustic sensors based on 2D semiconductors.