Senior Staff Researcher, Principal Investigator (PI), International Iberian Nanotechnology Laboratory (INL), Portugal.

Speech Title: Atomic and Electronic Structure of Grain Boundaries in Titanium Dioxide
Abstract: Polycrystalline TiO₂ finds numerous technological applications where its grain boundaries (GBs) are known to influence its functionality. Light sensitive photovoltaics, oxygen transfer catalysts and host for semiconductor spintronics are just a few important examples. Grain boundaries in these systems can be either beneficial or detrimental to applications and have been a subject of intensive researches. Here, we fabricate the pristine (112)[1 0] symmetric tilt model GBs of TiO₂ using the bicrystal technique. We combine advanced electron microscopy, spectroscopy, and first-principles calculations to probe individual TiO₂ GB subject to treatment at different atmosphere, and demonstrate that stimulated structural defects can self-assemble at GB, forming an ordered superstructure, which results in GB nonstoichiometry and reconstruction at the atomic scale. Such structural transformation is accompanied with electronic transition at GB. In addition, we also fabricate the other pristine (221)[1 0] symmetric tilt model GB of TiO₂, and offer direct evidence that there occurs a periodic GB superstructure with a couple of Ti and Ti-O columns exactly on the mirror plane. We also identify coupled bright columns, which show a broader image contrast than its Ti-O mixed counterparts in the bulk. Such an interesting aggregation of oxygen atoms at GB shall give rise to electronic structure shift of the Σ13 GB by showing an electronic transformation at GB from rutile-like to anatase-like structure.