Conventional epitaxy of NiO thin films on muscovite mica and c-Al2O3 substrates

Fiber-textured and epitaxial NiO thin films were deposited on Si(100), c-Al₂O₃, and muscovite mica(001) substrates using reactive magnetron sputtering at substrate temperatures of 300 °C and 400 °C, to investigate the effect of film thickness and substrate temperature on epitaxial growth of NiO films. The as-deposited films exhibited a face-centered cubic structure with a larger lattice constant, attributed to strain induced during the sputtering process. With an increase in substrate temperature to 400 °C, the d-spacing decreased due to strain release, approaching the NiO bulk value for the thickest film. The NiO film grown on Si(100) displayed fiber texture. On c-plane sapphire, NiO thin films exhibited twin domains and three-fold symmetry, consistent with expected crystallographic orientation relationship for NaCl-structured materials on sapphire:${\left(111\right)}_{NiO}\parallel {\left(0001\right)}_{A{l}_2{O}_3}\text{and}{\left[0\overline{1}1\right]}_{NiO}\parallel {\left[\overline{1}010\right]}_{Al2O3}$, ${\left[01\overline{1}\right]}_{NiO}\parallel {\left[10\overline{1}0\right]}_{Al2O3}$. On muscovite mica(001) substrates, the observed epitaxial shows that the mechanism is conventional epitaxy, rather than van der Waals epitaxy, consistent with the epitaxial growth of the non-layered non-van-der-Waals compound NiO. The epitaxial relationship was identified as of ${\left(111\right)}_{NiO}\parallel {\left(001\right)}_{Mica}$ and ${\left[0\overline{1}1\right]}_{NiO}\parallel {\left[010\right]}_{Mica}$, ${\left[01\overline{1}\right]}_{NiO}\parallel {\left[0\overline{1}0\right]}_{Mica}$.