Sputter-grown two-dimensional α-MoO3 thin films: Microstructure dependence on growth conditions

Van der Waals epitaxy is an emerging technology for transferring freestanding films grown at high temperatures onto arbitrary substrates using two-dimensional epitaxial layers. This study investigates the microstructure and growth of α-MoO ₃ thin films prepared via sputtering. Under a narrow deposition temperature range, epitaxial α-MoO ₃ thin films were successfully grown on SrTiO ₃ substrates. The films were characterized by a flat surface morphology, corresponding to (0k0) planes, without undergoing reaction with the substrates. To examine the growth behavior and surface morphological variation of the α-MoO ₃ thin films under various process parameters, we modified the Ar:O ₂ ratio, working pressure, sputtering power, and crystal structure of the substrates. Transmittance electron microscopy confirmed the epitaxial growth of the α-MoO ₃ thin films on (001)-oriented SrTiO ₃ substrates with a two-dimensional layer structure. Finally, we demonstrate the morphological evolution of the α-MoO ₃ thin films etched in heated water as a function of soaking time. The etching results suggest that the α-MoO ₃ thin films are promising sacrificial layers for the transfer of large-scale epitaxial thin films onto flexible substrates. External control of the strain states of transferred freestanding thin films by bending or stretching provides new perspectives for the design of flexible or wearable electronic devices.