Application of synchrotron through-the-substrate microdiffraction to crystals in polished thin sections

Prior research has shown that synchrotron X-ray techniques are valuable for analyzing crystal structures at microscales. However, a gap remains in applying these methods to crystals embedded in polished thin sections of compact materials. Established methods often require isolated crystals or specific sample preparations. That uncertainty drove the need for a technique that could work with microvolumes in situ. No prior work had resolved how to handle randomly oriented crystals within substrates. It was already known that X-ray diffraction could determine crystal structures, but adapting this for thin sections remained unexplored. This gap motivated the development of a new approach using synchrotron radiation. The need for a simplified and versatile method became clear as researchers encountered limitations in traditional crystallographic techniques.

The aim of this study was to extend the synchrotron through-the-substrate X-ray microdiffraction (tts-μXRD) technique to analyze crystals in polished thin sections. The specific problem addressed was how to collect and refine structural data from microvolumes of crystals embedded in compact materials. The motivation stemmed from the limitations of conventional crystallographic methods in handling such samples. Researchers sought to develop a procedure that could handle randomly oriented crystal microvolumes. The study aimed to demonstrate the viability of this method for crystal structure solution and refinement. The goal was to provide a practical and versatile tool for various scientific disciplines. The approach was designed to simplify the experimental process while maintaining accuracy. The ultimate purpose was to enable structural studies in complex or in situ environments.

The tts-μXRD procedure involves collecting two-dimensional diffraction patterns from randomly oriented crystal microvolumes. These patterns are obtained from a limited number of consecutive frames. The next step is refining the metric using circularly averaged one-dimensional diffraction patterns. The reciprocal lattice orientation is determined for each crystal microvolume. This orientation allows assigning hkl indices to diffraction spots. Intensities from multiple frames are merged into a single-crystal dataset. Individual crystal datasets are then combined into an extended dataset. This merged dataset is used for structure refinement and solution via Patterson function direct methods.

The tts-μXRD method successfully produced extended datasets suitable for structure refinement. The viability of the method was demonstrated using examples from petrology. The technique enabled accurate single-crystal least-squares refinements. The crystal microvolume section size was comparable to the beam focus (15 × 15 µm). The method supported crystal structure solution via Patterson function direct methods. Frame merging and multicrystal merging were effective in producing usable datasets. The results showed that the method works with different glass substrate thicknesses. The technique proved versatile and experimentally simple for various applications.

The authors propose that tts-μXRD is a viable method for crystal structure analysis in polished thin sections. The method's viability was demonstrated through successful structure refinements and solutions. The technique is suitable for randomly oriented crystal microvolumes. The method allows merging of data from multiple frames and crystals. The crystal microvolume must be at least the size of the beam focus. The method supports accurate single-crystal refinements and structure solutions. The authors suggest the method is useful in petrology, materials science, and cultural heritage. The experimental simplicity and versatility of the method are key advantages.