Atomistic study of comblike structure on the MoO ₂ /Mo(110) surface by scanning tunneling microscopy and density functional theory calculations

The origin of comblike step formation, which was previously observed in the initial oxidation stage of the Mo(110) surface, was investigated by comparing between scanning tunneling microscopy (STM) observations and ab initio density functional theory (DFT) calculations. The comblike steps were obtained by the formation and evaporation of cluster arrays during oxidation and thermal treatment. On the terraces surrounding the comblike steps formed by the evaporation of clusters, a characteristic “overstripe” pattern was found. On the basis of this pattern, it is assumed that a reliable unit cell with MoO 2 (010) placed on Mo(110) with in-plane rotation can be constructed and ab initio structural relaxations can be performed. The calculations included “small” model calculations for investigating stable interfacial oxygen sites and “large” model calculations for simulating STM images, and calculation results were compared with experimental results. The simulated STM images show good agreement with the experimental observations, indicating the relevance of the large model. From these analyses, it is pointed out that the local stresses on molybdenum in the oxide layer were important for the comblike step formation.