Focused Ion Beam Preparation and Transmission Electron Microscopy of Materials for Energy Applications

Throughout this thesis, samples of various materials with applications in energy converting devices have been prepared by focused ion beam machining and investigated by transmission electron microscopy. Energy converting devices can be solar cells or light emitting diodes, which turn light into electricity or vice versa. They can also be fuel cells or electrolyzer cells, which turn chemical energy into electricity or vice versa. To efficiently convert the energy, these devices require specialized materials. The results achieved by the characterization presented here include identifying twin and grain boundaries, the crystal structure and the chemical composition. The different transmission electron microscopy techniques and sample preparation methods used are explained and discussed. For example, the preparation of nanowires, which are used in solar cells and light emitting diodes, require additional steps to the standard in-situ lamella lift-out method. The nanowires have to be embedded in a polymer material by casting or spin coating and a frame lamella design is necessary to stabilize the thin region of interest.