Quantitative structure determination in transmission electron microscopy by means of the S-state model.

摘要

Quantitative high resolution transmission electron microscopy (HREM) has the unique ability to determine atomistic details on a local scale and this with high precision. This is necessary to understand the relation between the properties and structure of nano materials. The physical and chemical properties of nano materials are determined by their local structure. A better understanding of these relations will allow in the future designing new materials with interesting properties for industrial applications. In case of a quantitative treatment, HREM images are regarded as data planes and a model for the electron object interaction and the imaging in the electron microscope is needed. This model has parameters like atom column positions, which are unknown and has to be determined from the experiment. This can be done by model based fitting at the HREM images using a criterion. The research group EMAT (Electron Microscopy for Materials research) of the University of Antwerp has experience with modelling of the electron object interaction and the imaging in the electron microscope. Building on this experience a simple model for the electron object interaction, namely the S-state model is presented and optimised. This model allows determining the local structure with high precision. Besides that a simple and accurate method was developed to characterise the imaging in the electron microscope. Given these two new techniques, industrial interesting materials were studied like “colossal magneto resistance” La_0.9Sr_0.1 MnO₃-SrTiO₃ thin films grown on a substrate and Al₂CuMg precipitates in an Al matrix.