Atomic defects by ex-situ and in-situ (scanning) transmission electron microscopy will focus on the structural characterization of the grown layers and investigation of the resistive switching mechanism by means of transmission electron microscopy (TEM). The Project consists of the following tasks:
Task 1. Ex-situ TEM studies of intrinsic atomic defects. Ex-situ aberration corrected TEM and scanning TEM (STEM) is used to study intrinsic atomic defects (e.g. oxygen and metal vacancies) in Bulk crystal and epitaxial layers of SrTiO3 and In2O3 grown by MOCVD, PLD and MBE. We measure the distribution of atomic defects by the local distortion they induce into the crystal lattice. This is done either by high resolution TEM (HRTEM) or by STEM annular dark field imaging. In STEM mode, atomic defects can be visualized either due to their difference in atomic number compared to the matrix and/or because of their associated lattice distortion leading to diffuse scattering. HRTEM and STEM multi-slice image simulations based on structural models of atomic defects from state of the art ab-initio calculations are used to identify the nature of atomic defects and quantify their concentration and spatial distribution in the grown films.
Task 2. In-situ TEM investigation of intrinsic atomic defects. In order to obtain information on kinetics and thermodynamics of formation of intrinsic atomic defects, their diffusion and cluster processes, we carry out in-situ TEM investigations of SrTiO3 and Nb2O5 crystals under controlled annealing conditions. The in-situ investigation is performed with a dedicated in-situ holder (Protochips Inc.), which allows annealing of samples under oxidizing, inert or reducing atmospheres (using O2, Ar or forming gas) up to a pressure of 1 bar and at temperatures up to 1000 °C in the TEM, while maintaining the atomic resolution of the instrument. The results are used to develop quantitative thermodynamic models for formation, diffusion and clustering of atomic defects in these materials and to explain physical properties connected to those processes.
Task 3. In-situ TEM investigation of intrinsic defects under applied voltages. To examine diffusion of atomic defects under applied voltages we perform in-situ electrical TEM measurements of device structures. In contrast to studies presented in literature so far, we conduct these investigations under controlled atmospheres and temperatures using our environmental TEM holder. By this means, artificial generation of oxygen vacancies during the electrical measurements are avoided (which otherwise may occur under electron beam irradiation in vacuum during conventional in-situ electrical TEM experiments). Furthermore, we are able to tune the defect distribution in the device structure in a controllable manner. In-situ electrical biasing of device structures is achieved by connecting the TEM sample with contacts available on the sample carrier of the environmental TEM holder.
Major Accomplishments expected:
Collaboration with partners in the project:
Toni Markurt has been a PostDoc at Leibniz Institute for Crystal Growth (IKZ) in Berlin, since September 2015. His research interests are characterization of structural properties and atomic defects in semiconducting materials, mainly Oxide and III-Nitride crystals and quantitative transmission electron microscopy. His PhD thesis at IKZ “Transmission electron microscopy investigation of growth and strain relaxation mechanisms in GaN (0001) films grown on silicon (111) substrates” gained a summa cum laude.
If you have queries about the project, please contact the PI:
Martin Albrecht, Institut für Kristallzüchtung
Leibniz-Insitut im Forschungsverbund Berlin e.V.
10117 Berlin, Germany
The Leibniz ScienceCampus GraFOx is a network of two Leibniz institutes, two universities and one institute of the Max Planck Society. The Network is based in Berlin, Germany.