P10: Electromigration in materials with extended defects

Supervision:Bálint Aradi, Gabriele Penazzi

Motivation and state of the art: The migration of charged ions and impurities due to the electric field plays animportant role in many electronic materials – among others, in titanium dioxide, the key material for dye-sensitized solar cells and a promising candidate for new generation of memory devices based on the memristor principle. Extended structural disorders—grain boundaries, oxygen vacancy aggregates—and ionmigration in those disorders are crucial for understanding and designing such devices. In carbon nanostructures electro-migration can be exploited as a mechanism to control the morphology of nanogaps, edges or adsorbates. In a similar spirit, stable single atom electro-mechanical switches have been realized in gold break junctions. Therefore, understanding the structural changes of the extended disorders due to the electric field within the material is an important step in designing future devices.

Own work: We have studied various defects and interfaces in titanium dioxide using a wide range of simulation methods. We have investigated equilibrium and non-equilibrium charge transport phenomena in low dimensionality carbon systems and inorganic semiconductors.

Aims and work plan: We will study, how internal electric fields affect the migration of charged defects in extended disordered structures. In order to have a realistic potential profile within the material, we will apply an explicit bias to the material, using the non-equilibrium Greens function framework, which have been recently implemented in the DFTB+ simulation package. We will investigate the role of current forces in adiabatic approximation through coupling with molecular dynamics and development of a coupled NudgedElastic Band – NEGF simulation scheme. At a more ambitious level, energy dissipation and self-heating can be taken into account via electron-phonon interaction. Collaborations with P11 on method development and P6 on understanding materials properties are planned.