Temperature and Strain Mapping with In Situ Transmission Kikuchi Diffraction in Scanning Electron Microscope

Transmission Kikuchi diffraction (TKD) is a powerful technique for high-resolution crystal orientation mapping in scanning electron microscopes (SEM). Combining the large collection angle from electron backscattered diffraction (EBSD) and the high spatial resolution from transmitted electrons, TKD excels in capturing detailed Kikuchi patterns. Such diffraction patterns with a large collection angle are crucial for reliable crystal phase and orientation mapping, despite some compromise in angular resolution. Historically, this limited angular resolution has impeded applying TKD to temperature and strain mapping. Given that the widths of Kikuchi bands and the angles between them are directly proportional to the lattice spacing and interplanar angle, high angular resolution is considered vital for precise lattice parameter measurements with TKD patterns. Although indirect temperature measurements have been done with the Debye-Waller effect, quantitative interpretation remains challenging. In this work, we introduce an expanded parameter space for cross-correlation indexing in TKD analysis, enabling picometer precision lattice parameter mapping even at low intrinsic angular resolutions. We demonstrate in situ temperature and strain mapping in graphite specimens with this enhanced analytical power of TKD, achieving thermal expansion detection at part-per-thousand level.