Improving MgO/Fe Insulator-Metal Interface Structure Through Oxygen-Precoating of Fe(0 0 1)

•* Controlled p(1 × 1) oxygen pre-coating of Fe(001) drastically improves MgO film growth.•* Upon oxygen pre-coating, the MgO island size is increased by a factor of 10.•* Atomically-flat high-quality insulating MgO islands contain only few atomic defects.•* MgO islands also work as an electronic decoupling layer from the metal substrate.