Atomic steps on the MgO(100) surface

Defects on insulating surfaces have been studied much less compared to conductors due to experimental difficulties. Here we report quantitative structure analysis of atomic steps on the MgO(100) surface combining aberration-corrected high resolution transmission electron microscopy and density function theory calculations. While the broad faces show little relaxation or rumpling, the atoms at the step sites have significant displacements, depending on the atomic coordination. The general trend is to smooth the steps and lower their formation energy. The angles at the upper and lower corners of the mono-atomic step increase from unrelaxed 90 to 94 and 101, respectively. The experimentally measured positions of the atoms at the step sites match the density function theory results within several picometers.