MgO remains a subject of intense research as one of the most technologically essential surfaces due to its importance in catalysis, and recently as a substrate in nanocatalysis. Oxygen vacancies (F-centers) on the surface have been proposed to play an important role as nucleating centres for catalytic nanoparticles. Scanning force microscopy (SFM) has the potential to image both the surface and any defects or adsorbates in atomic resolution, providing unprecedented details into surface processes. In this work we compare low temperature atomic resolution dynamic SFM imaging and force spectroscopy of the MgO (001) surface in UHV with first principles simulations of the tip-surface interaction. The experimentally obtained site-specific force spectroscopy can be directly compared to computational predictions of the short range interaction with different tip models, therefore leading to unambiguous characterization of surface species and point defects.
Tips are nanofabricated from silicon, but during SFM imaging, material is exchanged with the surface as well as with the ambient. Hence, we construct a set of probable tip models including adsorbates such as hydroxyl groups, hydrogen, magnesium and oxygen, as well as clean silicon tips. After testing the imaging of a perfect area of the MgO(001) surface with two dozen most probable tip models and different tip elasticity, we show characterization of the tip apex and surface species with unprecedented accuracy, and further simulate imaging of the most likely defects to characterize the defect seen on the surface in experiments. |