JENIFER JALOWITZKI SILVA

Abstract:

This master's work presents a study on the atomic structure of the SrTiO3 strontium titanate (STO) surface. This material has many interesting properties from the point of view of health. Depending on the type of surface reconstruction of the material, that is, the way it is organized, it is found that the surface can induce the growth of nanoparticles with very specific geometries. The SrTiO3 material used in this work was a monocrystal doped with 4.5% niobium (Nb), which was cut to the face (100). The STO used in this work was purchased commercially from the company SurfaceNet, with a purity of 99.99999%. Initially this crystal was cleaned in an ultra-high vacuum environment, with pressures of 1.3x10-10 mbar. The cleaning process consisted in heating the substrate in an oxygen environment with the sample heated at 700 °C for a few hours. This process was performed until all carbon was removed from the material surface occurred. To perform the experimental characterization of this material were used surface-sensitive techniques, available in the group of Surface Physics of Unicamp, such as: XPS (X-ray Excited Photoelectron Spectroscopy) and XPD (X-Ray Excited Photoelectron Diffraction), for the study of the atomic structure and composition of its surface. The Low Energy Electron Diffraction (LEED) technique was also used to verify the ordering of the crystal surface after heating. The experimental data were collected, to understand the atomic structure of the surface, the experimental diffraction patterns were simulated. For the theoretical modeling of the surface structures the MSCD computational package was used together with a genetic algorithm, that it is a computational search technique to find approximate solutions to optimization and search problems, to optimize the structural parameters of the proposed models. The simulations showed that the surface of the monocrystal could be composed of two types of termination, that is, SrO and TiO2.

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