Microstructural investigations of SrTiO₃ single crystals and polysilicon using a powerful new X-ray diffraction surface mapping technique

In the research work described here, single-crystalline SrTiO₃ has been used as a model system to facilitate the development of a new qualitative characterization method for the nondestructive identification of small-angle boundaries in bulk single crystals. Subgrain misorientations with a lower limit in the range between 40 and 100'' were reliably identified. For scientists and engineers working in the field of single-crystal growth it is often indispensable to continuously check the structural quality of the grown bulk crystals, which is usually time consuming or challenging for large single crystals. This article presents in detail how a spatially resolved micro X-ray fluorescent device can be used for the identification of subgrains and merely a one-side-planarized sample of nearly arbitrary geometry is needed. The approach presented combines high-speed measurements and full sample area coverage with a high spatial resolution of 25 µm. The resolution is limited by the spot size of the focused X-ray beam. The Bremsstrahlung of the excitation source interacts with the crystals, and because of the instrument geometry it is possible to detect Bragg reflections. These reflections can be found at specific energies and can be displayed in two-dimensional diffraction intensity maps. These maps were used for the qualitative analysis of the crystal domains. The results obtained by this new approach were verified by rocking curve measurements and by defect-selective etching studies. Ultrafast large-area mappings on widely used polysilicon were additionally performed to demonstrate the potential of the developed method for use in industrial applications.