A Study of Atomic Diffusion from First Principles Theory

Abstract: In this work Density Functional Theory and the Nudged Elastic Band method are used to calculate energy barriers to study atomic diffusion. Diffusion is one of the processes that leads to non ideal experimental conditions such as defects or not sharp enough interfaces. In collaboration with Seagate Technology, vacancy-driven diffusion across an Au/X interface is studied in the first part of this thesis. This is done in the pursuit of the best X material that provides hardness to the Au/X heterostructure under high temperatures and still has good plasmonic properties. Itis found that a layered heterostructure of 10 monolayers of Au and 6 monolayers of TiN is the best of the combinations tested and it is attributed to TiN high packaging compared to Au. It is also seen that the density of the X material is more relevant than a high melting temperature or a good lattice match with the Au lattice, as it was suggested before. In a second project, the diffusion of an adatom on a surface of the same material is investigated to find out the infuence of the magnetic phase of the surface on the diffusion barriers. With this aim, ferromagnetic and non magnetic (001) fcc Ni surfaces and bcc Fe are simulated. Additionally, a paramagnetic (001) Fe surface has been simulated with the distribution of moments determined by a Special Quasirandom Structure approach to the Disordered Local Moment method. It is found that energy barriers relevant for diffusion along the surface are lower for the magnetic phases but that the infuence of the magnetic phase on diffusion is not trivial.