Van Der Waals Epitaxy and Thin Film Transfer using Sputter-Grown Two-Dimensional α-MoO₃

The manipulation of electronic, optoelectronic, and magnetic properties of oxide thin films by applying strain provides powerful functionality for future electronic devices. Strain originated from lattice or thermal expansion mismatches changes the physical properties of epitaxial thin films. But external strain by mechanical deformation of rigid substrates has been prohibited due to the low mechanical stability of single crystalline substrates, which limited the application of the epitaxial layers to flexible electronics. The low thermal stability of polymer-based flexible substates has been motivated the development of advanced lift-off technique of van der Waals or remote epitaxy using two dimensional layers.<br/>We present the epitaxial growth of α-MoO₃ layers using sputtering for low cost and large area devices. The films grown at lower temperature and oxygen-free atmosphere showed randomly oriented growth while, they grew epitaxially on SrTiO₃ (001) substrates due to the coherent lattice constant along the in-plane at optimized deposition conditions. We detailed microstructure was investigated using an electron backscatter diffraction mapping and high-resolution transmission electron microscopy.<br/>We also report the transfer of high temperature grown thin films using sputter-grown α-MoO₃ layers consisting of MoO6 sheets with normal along the [010] direction bonded by weak van der Waals forces while the bonds within each layer are covalent and ionic. The metallic Au films on α-MoO₃ layer can be easily transferred to flexible supports by cracking the weak interface between the sheets using tapes or by dissolving the α-MoO₃ layer in heated water. We demonstrate that spinel-structured CoFe₂O₄ thin films with high crystallinity can be grown on α-MoO₃ layers and can be separated from substrates via mechanical exfoliation, which allows for the modulation of magnetic anisotropy of freestanding CoFe₂O₄ films by bending.