In situ visualization of the ammonothermal crystallization process using X-ray measurementtechniques

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Sub-project 5 of the research group ¿Chemistry and technology of ammonothermal synthesis of nitrides¿ addresses the crystallization process by the application of X-ray in situ visualization. During the ammonothermal synthesis in the closed high pressure autoclave only a limited visual access is given into the reaction chamber. Using 2D and 3D X-ray topography the crystallization process is visualized with a spatial resolution of ca. 100¿m and analyzed with respect to reaction kinetics and growth rate. Beside the crystal growth process, also the crystal dissolution is of particular interest because it facilitates the determination of nitride solubility in various mineralizer environments with high precision. The knowledge of reliable data that are so far missing in literature may pave a fundamental understanding of supersaturation and mass transport during ammonothermal crystal growth. In addition to topography, in situ X-ray diffraction enables the determination of initial crystallization on the ¿m length scale. The analysis of the shape and line width of the diffraction peaks is applied to evaluate the crystallinity.Three main scientific problems / issues are addressed within sub-project 5. Firstly, the solubility data base under ammonothermal growth conditions of GaN and other novel nitrides (Zn-IV-Nitride, Zn3N2, InN) shall be significantly extended. Secondly, it is intended to gain a deepened understanding of the faceting phenomena and in general the nucleation during crystallization. As a third point, fundamental materials data and in particular electro-optical semiconductor data of the new nitride materials shall be determined. For all three fields of research focus it is expected to gain significant new insight which is of particular interest for the scientific community.To accomplish the target work the close collaboration with the other sub-project in the field of chemical reaction engineering as well as high pressure autoclave technology is a key point.