Combining ECCI and FIB milling techniques to prepare site-specific TEM samples for crystal defect analysis of deformed minerals at high pressure

Abstract Dislocation microstructures in experimentally deformed single-crystal pyrope-rich garnet, (Mg,Fe) 3 (Al,Cr) 3 Si 3 O 12 , and polycrystalline forsterite, Mg 2 SiO 4 , were investigated by using electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) combined with a focused ion beam (FIB)-microsampling. In the orientation-optimized ECCI method, we successfully observed individual dislocations across subgrain boundaries in a low-atomic-number mineral, pyrope-rich garnet (averaged Z -numbers, AZs ∼ 10). Dislocations in a deformed forsterite (iron-free olivine) were also visible in the ECCI. In the ECCI on the single-crystal garnet, deformation bands consisting of dislocations, unusual contrasts in stripes and inhomogeneous distributions of sub-micrometer-sized pores were found. Further site-specific TEM observation on the deformation band revealed a high density of partial dislocations and stacking fault ribbons. The site-specific characterizations from ECCI to TEM, with assistance of FIB, can provide a new approach to investigate dislocation microstructures of deformed materials at high pressure and high temperature.