Optimised Experimental Workflow to Monitor Recovery of Swift Heavy Ion Damage in Crystals

Abstract

In this study, the recrystallisation dynamics of swift heavy ion (SHI) tracks have been investigated in single crystal yttrium iron garnet (Y3Fe5O12-YIG). The material was irradiated at room temperature with 167 MeV Xe ions to a fluence of 2x10 11 cm-2. An optimised experimental protocol was developed to monitor the thermal recovery of ion tracks in real time with high temporal and spatial resolution. Plan-view TEM lamellae were prepared with the focused ion beam-scanning electron microscopy (FIB-SEM) and mounted onto the Si3N4 MEMS heating chips via FIB lift-out. In-situ TEM annealing was performed by synchronising frame capture from the high-speed camera and heating from the MEMS chip. This procedure was optimised by a custom graphical interface developed in Python to start and stop the camera and heating holder simultaneously, and select the appropriate parameters before the experiment could commence. The results obtained from in-situ BF TEM have been aligned and processed with automated threshold-based procedures that identified individual ion tracks. Other Python modules, such as Trackpy, were also introduced to monitor >150 tracks across the dataset from which measurements, such as equivalent track diameters, were extracted. The tracks are observed to be amorphous due to the uniform contrast and absence of lattice fringes. Large temperature steps have induced shifts and slight bending within the lamella; therefore, a two-stage heating strategy has been introduced to maintain high-contrast imaging, namely pre-heating to 773 K for final zone-axis alignment, then ramping to 823 K. This work demonstrates a streamlined approach to observe ion track recrystallisation on a nanoscale, which could help improve the development of radiation-resistant materials