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

研究小组“氮化物氨热合成化学与技术”的子项目5利用X射线原位可视化技术研究了氮化物的结晶过程。在密闭高压高压罐中进行氨热合成时，只允许有限的视觉通道进入反应室。利用二维和三维X射线形貌术对结晶过程进行了可视化，空间分辨率约为100？m，并从反应动力学和生长速率方面进行了分析。除了晶体生长过程外，晶体溶解也是特别重要的，因为它有助于高精度地测定氮化物在各种矿化剂环境中的溶解度。到目前为止，文献中缺乏的可靠数据的知识可能会为我们对非等温晶体生长过程中的过饱和和质量传输奠定基础。除了表面形貌外，原位X射线衍射法还可以测定长度为？m的初始结晶。通过对衍射峰的形状和线宽的分析来评估晶体的结晶性。在子项目5中涉及三个主要的科学问题/问题。首先，GaN和其他新型氮化物(锌-IV-氮化物、锌3N_2、InN)在氨热生长条件下的溶解度数据库将被显著地扩展。其次，它的目的是加深对刻面现象和结晶过程中的形核的理解。作为第三点，应确定新氮化物材料的基本材料数据，特别是电光半导体数据。对于所有这三个研究重点领域，都有望获得科学界特别感兴趣的重大新见解。为了完成目标工作，与化学反应工程领域的其他子项目以及高压蒸汽灭菌器技术领域的密切合作是关键。

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.