Recently, the oxygen-reconstructed tantalum surface $\mathrm{Ta}\left(001\right)\text{−}\mathrm{p}(3\times 3)\text{−}\mathrm{O}$ has experienced considerable attention due its use as a potential platform for studying spin chains on superconductors. Experimental studies using scanning tunneling microscopy and spectroscopy found rich atomic and electronic structures already for the clean Ta(001)-O surface, which we combine here with ab initio methods. We found a significant reconstruction of the surface into a 2D polymorph oxide with two distinct patterns of 1-nm scale. One of the patterns represents an unusual defect structural state. This state appears only in the simulations with the effective presence of oxygen vacancies, which we also discuss in the context of the oxide formation. A specific combination of structural and electronic properties was established behind the diverse shapes detected in topographic maps. We also observed the energy-dependent partial-charge localization effect under applied bias voltages, which includes a contrast reversal. These effects originate solely in miscellaneous ionic and metallic properties of the electronic system. The charge distribution and polarization properties of this atomically thin oxide layer is shown to vary significantly between normal and defective superstructures, possibly contributing to the rich phenomena related to topological superconductivity recently discussed for Fe adsorbates.

• Received 8 November 2018
• Revised 2 April 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.094801