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 similar 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 similar to 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.