Efficient harvesting of solar energy is the only technology that has the potential to eventually supply the entire population of the Earth with sufficient energy in a sustainable way as a stand-alone, long-term solution. The potential of harvesting is emphasized by the fact that covering 0.1% of the surface of the planet with a device that converts solar energy into a useable form at 10% efficiency would give more than the present worldwide consumption of fossil energy. Photocatalysts are of fundamental interest for sustainable energy research because they provide a viable route for converting solar energy into chemical bonds. By means of Transmission Electron Microscopy (TEM) it is possible to gain insight in the fundamentals of their reaction mechanisms, chemical behaviour, structure and morphology before, during and after reaction using in situ investigations. In particular, the environmental TEM (ETEM) is the instrument of choice employed in this thesis to perform such studies. Typically, photocatalysts work in gaseous or liquid atmosphere upon light illumination. We aim at reproducing their working conditions in situ. The ETEM allows exposing specimens to a controlled gas atmosphere, thus implementation of in situ sample illumination is needed. This Ph.D. project is divided in two phases. First, two novel specimen holders capable of shining light onto samples inside the TEM and to probe the sample using visible light spectroscopy techniques were designed and constructed. Secondly, the newly developed holders were used to characterize photocatalytic materials in a simulated working environment. Prototype design was followed by micromechanical manufacturing, implementation and test of the holders. These were then employed in the analysis of various photoreactive materials and structures with focus on photocatalysts. Novel information on the behaviour of such materials during reaction was acquired in a reproducible fashion and a new tool for investigation of photoactive materials was made available. In a wider perspective, the project aims at building a versatile experimental platform inside the microscope that allows electron microscopy under nonconventional TEM conditions and new kinds of in situ spectroscopy.
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Damsgaard, Christian Danvad, Hansen, Thomas Willum, Wagner, Jakob Birkedal