Layer-by-layer epitaxial growth of polar MgO(111) thin films

We have observed layer-by-layer epitaxial growth mode of MgO (111) films on yttrium stabilized zirconia (111) substrates with NiO buffer layers by pulsed laser deposition despite a strong electrostatic instability of the [111] polar growth direction. Layer-by-layer growth has been realized up to ~10 MgO layers. For thicker films with 10--500 MgO layers, although clear step and terrace structures disappear, the root mean square surface roughness remains as small as ~0.2 nm with high crystalline quality comparable to single-crystals. MgO (111) films with the atomically flat surface thus obtained can be a platform to study polar surfaces and interfaces of simple binary oxides.