Ultra-thin MgO films grown reactively on the Fe(0 0 1) surface by evaporation of magnesium in an atmosphere of molecular oxygen have been investigated by low energy electron diffraction and non-contact atomic force microscopy. Preparation of structurally stable crystalline films requires a protocol that prevents an excessive interfacial reaction between oxygen and the Fe(0 0 1) surface, but at the same time provides a sufficient amount of oxygen in order to grow a stoichiometric MgO film. The proper ratio between the magnesium deposition rate and the oxygen pressure has been determined, as well as measures to prevent initial interfacial oxidation of the substrate. The effect of both post-annealing and an increased substrate temperature during the growth has been studied. We demonstrate that the reactive deposition method, which gives full control over the gaseous species that reach the surface, can produce terraces that have an average size of 10 nm (on an 8 monolayer thick film), which is a significant improvement compared to other preparation methods, such as thermal or electron beam evaporation of MgO. (C) 2013 Elsevier B.V. All rights reserved.