Initial phases in sputter deposited HfO2–Al2O3 nanolaminate films

Abstract

Nanolaminate films of crystalline HfO2 and amorphous Al2O3 were grown by reactive sputter deposition on unheated fused SiO2 and the surface oxide of ⟨111⟩ Si. X-ray diffraction showed the amount of monoclinic (m) HfO2 decreased with decreasing HfO2 layer thickness, consistent with a finite crystal size effect. High resolution transmission electron microscopy of individual crystallites detected tetragonal (t) and orthorhombic (o) HfO2 as the initial phases formed. Whereas the t→m transition is accomplished by a shear mechanism, we demonstrate the important role of polysynthetic twinning for the o→m transition.